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miR-27b-Regulated TCTP as a Novel Plasma Biomarker for Oral Cancer: From Quantitative
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Proteomics to Post-Transcriptional Study
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Wan-Yu Lo1,2,3, Huang-Joe Wang4,5, Chih-Wei Chiu6, Sung-Fang Chen6*
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Department of life science, National Chung Hsing University, Taichung, Taiwan
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Department of Internal Medicine, School of Medicine, China Medical University, Taichung, Taiwan
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Division of Cardiology, Department of Medicine, China Medical University Hospital, Taichung, Taiwan
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Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan
Graduate Institute of Integrated Medicine, China Medical University, Taichung, Taiwan
Division of Surgery, Department of Medical Research, China Medical University Hospital, Taichung, Taiwan
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*Correspondence: Dr. Sung-Fang Chen, Depa rt m ent of C hem i st r y, National Taiwan Normal
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University, No. 88, Sec. 4, Ting-Chow Rd, Taipei, Taiwan, 11677 Taipei, Taiwan
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Phone: 886-2-77346210 Fax: 886-2-9324249
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Email: sfchen@ntnu.edu.tw
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Keywords: Quantitative proteomic analysis, iTRAQ, oral cancer, translationally controlled tumor
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protein, TCTP, miR-27b
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Abstract
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We combined an iTRAQ-based quantitative proteomic analysis and the miRNA determination to
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profile potentially novel biomarker from oral cancer. There are 757 and 674 unique proteins were
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identified from proteomic analysis, and 13 proteins displayed consistent underexpression (<0.67 fold)
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in normal tissues in comparison with the corresponding tumor tissues. After the preliminary screening,
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the EGFR, OAT, TPT1, ITGA6, G3BP1 and CB39L were the six genes validated in the 37 oral cancer
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patients (T1, n=10; T2, n=10; T3, n=10 and T4, n=7). The TPT1, ITGA6 and CAB39L genes were
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displayed the higher transcriptions level in the tumor tissues and the TPT1, ITGA6 and CAB39L
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proteins were also shown overexpression in the tumor tissues from the same patients. The miR-19a,
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19b, 27a, 27b, 186, 203 and 377 transcripts were predicted and the miRNA-27a and 27b level was
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shown significantly reduction in the tumor tissues and the plasma of OSCC patients. In the in vitro
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study, the overexpression of miR-27b significantly only decreased TCTP protein and gene levels in
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both of HSC-3 and Cal-27 cell lines. Our results demonstrate that human miR-27b regulates the
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expression of the TCTP tumor protein, and circulating miR-27b may be useful as a biomarker for oral
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cancer research.
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Introduction
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An estimated 263,900 new cases and 128,000 deaths from oral cavity cancer (including lip
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cancer) occur annually worldwide [1]. Smoking, betel-quid and areca-nut chewing, alcohol use,
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smokeless tobacco products and Human Papillomavirus (HPV) infection are the major risk factors for
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oral cancer. Various treatment options including surgery, radiotherapy and chemotherapy are available
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for oral cancer. However, the five-year survival rate of oral cancer is one of the lowest among common
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malignant neoplasms [2]. In Taiwan, an endemic betel quid chewing area, a significantly increasing
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trend in oral cancer has been observed in males [3]. In 2006, oral cancer became the 6th most common
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cancer in Taiwan and the 4th most common cause of cancer deaths in Taiwanese men. Therefore, the
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development of a reliable, accurate, cost-effective and noninvasive test for oral cancer is highly
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desirable [4,5]. The alteration of genes has been traditionally revealed by the use of cytogenetics,
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immunohistochemistry, or molecular approaches based on one or a few genes that change the
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expression of many genes, e.g., oncogenes and tumor suppressor genes, which have been associated
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with oral carcinogenesis [6-8]. Genomics has been incorporated in oncology research, and now, in the
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post-genomic era, there is a strong drive to additionally incorporate proteomic technologies[9,10].
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Proteomics can help us to better understand the changes in the levels of multiple proteins
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involved in oncogenesis and cancer progression and identify new diagnostic and prognostic biomarkers
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[11]. Quantitative proteomics is an important branch of proteomics that is applied to quantify and
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identify all the proteins expressed by a whole genome or in a complex mixture. The method of using
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isobaric tags for relative and absolute quantification (iTRAQ) was developed in 2004. This method
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uses global peptide labeling to preserve post-translational modification information and involves the
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simultaneous quantitative proteomic analysis of four samples under the same experimental conditions
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[12, 13]. This unique approach labels samples with four independent isobaric tags of the same mass that,
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after fragmentation in MS/MS, give rise to four unique reporter ions (with m/z values ranging from 114
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to 117) that provide quantitative information upon integration of the peak areas to quantify the four
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different samples [14, 15]. The advanced combination of proteomics and bioinformatics provides the
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opportunity to study changes in the global proteome and other molecular-level indicators of expression
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in cells at any time point or treatment. Unfortunately, only a few limited studies have been conducted
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in oral cancer research to date, and none have reported a miRNA-related approach.
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The miRNAs are regulatory, non-coding RNAs approximately 21–23 nucleotides long that are
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expressed at specific stages of tissue development or cell differentiation and have large-scale effects on
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the expression of a variety of genes at the post-transcriptional level. Through base pairing with target
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mRNAs, miRNA induces RNA degradation or translational suppression of the targeted transcripts [16,
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17]. Mature miRNAs result from the processing of pri-miRNAs in two sequential cleavage steps
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mediated by two RNase III enzymes, Drosha and Dicer [18]. Each mature 21- to 23-nt miRNA product
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contains a 2-nt 3′ overhang on each strand and acts as the functional intermediate of RNAi that direct
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mRNA cleavage and translational attenuation. Although their biological functions remain largely
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unknown, recent studies suggest that miRNAs contribute to the development of various cancers [19-23].
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An important aspect of cancer biomarker identification is the development of simple, noninvasive tests
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that indicate cancer risk, allow for early detection, and enable the classification of tumors to ensure that
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patients receive the most appropriate therapy while monitoring disease progression, regression, and
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recurrence [24]. Serological biomarkers can be analyzed relatively easily and economically and
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therefore have the potential to greatly enhance screening acceptance [25]. Determinations of serum
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miRNA are more convenient and less costly than serum protein marker determinations. Thus, serum
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miRNA biomarkers are more suitable for future clinical applications in parallel with cancer-related
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examination and have the potential to be the reliable biomarkers that can be utilized to develop an
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effective approach for the early diagnosis of oral cancer.
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Our previous study exploited a high-throughput technique that yields results complementary to
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the traditional gel-based proteomics approaches for oral cancer and colon cancer [26, 27]. In this study,
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we globally surveyed differential protein expression to identify potential diagnostic marker proteins
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from the paired tissues of patients with early stage oral cancer using a comprehensive iTRAQ analysis
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and then utilized bioinformatics to predict the associated target miRNAs and validated the correlations
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from the tissues and sera from patients at varying stages of disease. We determined that plasma
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miR-27b levels can provide such a biomarker for early cancer detection in clinical applications and
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provide new insight in cancer research.
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Materials and methods
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Patients and clinical samples for iTRAQ
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We collected pairs of surgically archived specimens of primary oral squamous cell carcinoma
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(OSCC) and their matched adjacent normal surrounding mucosa specimens from 20 patients at the
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China Medical University Hospital (Taichung, Taiwan), the collection methods as described in our
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previous study.26 The 20 patients were classified into two categories: T1 (n=10) and T2 (n=10)
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according to UICC TNM staging. The cancer stage was defined by the extent of the lesion as
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determined by physical examination, radiological studies and pathological examination. The histology
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for each patient was confirmed by two independent histopathologists following fixation, embedding,
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sectioning and H&E staining. Overall, the tumor specimens all contained 90% tumor cells. No tumor
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cells were detected in the surrounding mucosal tissue. Tissues were kept at −80 °C continuously until
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analysis. The collection protocols were approved by the Institutional Review Board of China Medical
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University Hospital (DMR98-IRB-77) and informed consent was obtained from each subject.
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Sample preparations for iTRAQ
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The extraction of total protein from oral cancer tissues (Tumor, n=20) and the corresponding
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normal tissues (Normal, n=20) were performed as previously described. Additionally, the protein
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supernatants were enriched using a 3-kDa centrifugal filter as described by the manufacturer (Millipore,
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Merck KGaA, Germany). This process was repeated twice using ddH2O for desalting and to remove
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the protease inhibitor cocktail. The protein concentrations of the resulting supernatants were measured
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using the Bio-Rad Protein Assay (Bio-Rad, Hercules, CA) according to the manufacturer’s instructions
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and stored at -20 °C for subsequent processing. A total of 2000 µg of protein was collected from the
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paired tumor and normal tissues in the 20 patients (100 µg protein from the normal and tumor tissue in
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each patient; Normal group, n=20; Tumor group, n=20) for iTRAQ analysis.
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Chemicals and reagents for iTRAQ
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The acetonitrile solvent was chromatography grade from Merck KGaA. Bradford protein assay
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kits were purchased from Bio-Rad. Modified porcine trypsin (sequencing grade) was obtained from
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Promega (Madison, WI). The iTRAQ 4-plex reagent kits were purchased from Applied Biosystems
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(Framingham, MA). Desalting spin columns were purchased from Pierce (Thermo Scientific, San Jose,
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CA). Centrifugal filters were purchased from Millipore (Merck KGaA). Column packing materials for
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analyte column were purchased from Macherey Nagel (Düren, Germany). Packing materials for the
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trap column were purchased from Michrom Bioresources (Auburn, CA). All other chemicals and
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reagents were analytical grade from Sigma-Aldrich (St. Louis, MO) unless otherwise stated.
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Reduction, alkylation, digestion, and labeling with iTRAQ
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For our iTRAQ experiment, the two groups of proteins isolated from the 20 patients were polled.
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Protein samples were then reduced, alkylated, digested, and labeled with iTRAQ reagents according to
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the recommended protocol (Applied Biosystems, Framingham, MA). The protein pellets were
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resuspended in 0.5 M triethylammonium bicarbonate (TEAB), pH 8.5, and 2% sodium dodecyl sulfate
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(SDS), reduced with 5 mM Tris (2-carboxyethyl) phosphine (TCEP) for 1 h at 60 °C, and alkylated
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with 10 mM s-methyl methanethiosulfonate (MMTS) at room temperature for 10 min. A total of 60 µg
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of protein was digested overnight in tryptic solution (30/1, w/w) at 37 °C. Digested samples were
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labeled with the iTRAQ reagents, and ethanol and the corresponding iTRAQ reagent was added to each
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sample vial. The samples were labeled as follows: 114, Tumor-1; 115, Normal-1; 116, Tumor-2; and
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117, Normal-2. Duplicate sets of iTRAQ samples were labeled to monitor the consistency of the results.
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After 1 h of iTRAQ labeling; the samples were then mixed and dried by centrifugal evaporation.
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Strong cation exchange chromatography (SCX) and solution IEF
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The dried, labeled peptide mixture was reconstituted with buffer A (10 mM KH2PO4 in 25%
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ACN, pH 3). Peptide separation was performed using a Polysulfoethyl A Column (200 mm L× 2.1 mm
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i.d., 5 µm, 300 Å, PolyLC, Columbia, MD) on an Agilent 1100 binary HPLC (Agilent Technologies,
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Wilmington, DE) using a 90 min gradient. One-hundred twenty micrograms of iTRAQ-labeled
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peptides were eluted at a flow rate of 200 µL/min with a gradient of 2% buffer B (10 mM KH 2PO4 in
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25% ACN/ 350 mM KCl, pH 3) for 15 min, 2-40% buffer B for 38 min and 40-98% buffer B for 7 min
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and then maintained in 98% buffer B for 5 min before equilibrating with 2% buffer B for 20 min. A
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total of 24 fractions were collected, pooled and purified using C-18 Spin columns (Thermo Scientific,
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San Jose, CA) for further nano-LC-MS/MS analysis.
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One-hundred twenty micrograms of dried, iTRAQ-labeled peptide was dissolved in 0.72 mL
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ddH2O and 2.88 mL IPG stock buffer (pH 3-10). The IPG strips (pH 3-10, 24 cm) were assembled on
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the OGE trays and rehydrated for 30 min with a solution of 240 µL H2O and 0.96 mL IPG stock buffer.
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The samples were loaded into 24 off-gel wells. Peptide separation was performed over 48 h using the
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3100 OFFGEL fractionator (Agilent Technologies, Wilmington, DE) with a limiting current of 50 µA
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and a limit of 50 kV·h before holding the voltage at 500 V. The samples from the collected fractions
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were purified using C-18 Spin columns (Thermo Scientific, San Jose, CA) for further nano-LC-MS/MS
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analysis.
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LC-ESI-MS/MS analysis
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Each separated peptide fraction was reconstituted in buffer A (0.1% formic acid in 1% ACN),
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and 0.5 µg of the peptides from each fraction were loaded onto a lab-made 2 cm trap column (100 μm
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i.d., 5μm, 200 Å) at a flow rate of 10 µL/min in 2% buffer A. Separation was performed on a lab-made
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10 cm analytical column (75 µm i.d., 3 µm, 100Å). Peptides were eluted at a flow rate of 250 nL/min
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across the analytical column with a linear gradient of 2-40% buffer B (0.1% formic acid in 99% ACN)
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for 95 min and 40-80% buffer B for 5 min and then maintained in 80% buffer B for 5 min before
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equilibrating with 2% buffer B for 25 min. The LTQ-XL settings were as follows: spray voltage, 2.0 kV;
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capillary temperature, 200 °C; and full MS scan range, 350-2000 Da. Thermo Scientific LTQ-XL was
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operated in a data-dependent mode, i.e., using one MS1 scan for precursor ions followed by three
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data-dependent zoom scans for precursor ions above a threshold ion count of 200,000 followed by three
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data-dependent PQD-MS2 scans and CID-MS2 scans for precursor ions in zoom scan above a threshold
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ion count of 100, with collisional energies of 29% for PQD and 35% for CID.
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Database search and iTRAQ quantification
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Protein identification and quantification in the iTRAQ samples were performed using Protein
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Discoverer software (ThermoFisher, version 1.1) using MASCOT search algorithm. The search was
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performed against the SwissProt v.2011_02 database (525207 sequences) with the following search
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parameters: taxonomy, Homo sapiens; enzyme, trypsin; max. miss cleavages, 1; fixed modifications,
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methylthiolation, N-terminal iTRAQ 4plex, lysine iTRAQ 4plex; variable modifications, methionine
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oxidation, tyrosine iTRAQ 4plex; MS peptide tolerance, 1.5 Da; and MS/MS tolerance, 0.6 Da.
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Proteins identified with at least two distinct peptides matched with a probability of 0.95 or above are
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considered as correct identifications.
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Patients and clinical samples for quantitative analysis of gene, tissue miRNA, plasma miRNA and
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protein expression
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The 17 patients were classified into two categories: T3 (n=10) and T4 (n=7) according to UICC
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TNM stages, and samples were collected to evaluate the levels of gene, miRNA and protein expression
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in the 20 patients following the same IRB project. Total RNA, miRNA and protein extractions were
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isolated from pairs of surgically archived specimens and their matching adjacent normal surrounding
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mucosa specimens in the total 37 patients. Following our previous study, the tumor and corresponding
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normal tissues were dissected by laser pressure catapulting [27].
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Plasma was collected from the above 37 patients and 20 healthy volunteers from the same
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department during 2007–2008. Cell-free nucleic acids were isolated from the blood samples using a
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3-spin protocol (1500 r.p.m. for 30 min, 3000 r.p.m. for 5 min, and 4500 r.p.m. for 5 min) to
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prevent contamination by cellular nucleic acids. All samples were then stored at −80 °C until further
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processing.
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Quantitative analysis of candidate gene expression
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Total RNA was extracted from cells using the RNeasy Mini kit (QIAGEN), and the RNA was
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reverse-transcribed with the SuperScript III First Strand Synthesis System (Invitrogen) according to the
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manufacturer's instructions. Real-time quantitative PCR was run on a LightCycler 480 with
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LightCycler 480 SYBR Green I Master kit (Roche). The primers used for real-time quantitative PCR
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are listed in Supplemental data 1. A reaction mixture containing the following components at the
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indicated final concentrations was prepared according to the manufacturer's instructions: 0.2 μL of
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forward primer (20 μmol), 0.2 μL of reverse primer (20 μmol), 0.1 μL of UPL probe and 5 μL master
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mix. Fifty nanograms of reverse-transcribed total RNA in a volume of 4.4 μL was added as the PCR
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template. The GAPDH gene was selected for data normalization. A negative control without a cDNA
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template was included to assess overall amplification specificity. The PCR cycle conditions were as
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follows: an initial denaturation for 10 min at 95 °C was followed by 40 cycles of amplification at 95 °C
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for denaturation, 60 °C for annealing and 72 °C for extension. After amplification, the temperature was
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slowly elevated above the melting temperature of the PCR product to measure the fluorescence and
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thereby determine the melting curve. The real-time PCR data were calculated by the 2−ΔΔCt method for
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RNA quantification.
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Immunoblotting
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For the immunoblot assays, 40 µg of each protein extract from the in vivo (Tumor and normal
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tissues) and in vitro (transfected and control groups) studies were individually separated by 12%
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SDS-PAGE and treated as described in our pervious study. After blocking, the membranes were probed
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with one of the following monoclonal antibodies: anti-CAB39L (Santa Cruz Biotechnology Inc., Santa
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Cruz, CA), anti-TCTP or anti-ITGA6 (Cell Signaling Technology).
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Quantization of miRNA expression
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Total miRNA was isolated from tissues and plasma using the miRNeasy Mini Kit (Qiagen)
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according to the manufacturer's instructions. All aliquots of crude products were treated using the same
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procedure except for the use of 5U DNase. RNA was purified using the RNeasy MinElute Cleanup Kit
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(Qiagen) according to the manufacturer's instructions. The microRNA levels were determined by
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real-time quantitative PCR using the TaqMan MicroRNA Assays kit (Applied Biosystems, Foster City,
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CA) according to the manufacturer's instructions for the analysis of the human miR-19a (ID 000395),
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miR-19b (ID 000396), miR-27a (ID 000408), miR-27b (ID 000409), miR-186 (ID 000486),
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miR-203(ID 000507) and miR-377 (ID 000566). The relative expression levels of the mature miRNAs
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were calculated using the comparative CT (2−ΔΔCT) method with miRNA-U6 as an endogenous control
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for data normalization. All experiments were performed in triplicate wells on an Applied Biosystems
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7900 real-time PCR system. The significance of the differences between the plasma miR-27b levels of
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the control subjects and patients was determined using Student’s t-test.
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Transfection of miR-27b
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The human oral cancer cell lines HSC-3 and Cal-27 were gifts from Dr. Jing-Gung Chung
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(China Medical University) and grown in DME/F-12 medium (Gibco) supplemented with 10% FBS
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and 1% glutamine under humidified 5% CO2 at 37℃. HSC-3 and Cal-27 Cells were plated in six-well
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plates at a density of 1×105 cells/well. The next day, the cells were transfected with 100 nM of
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synthetic miR-27b (Ambion) using Oligofectamine (Invitrogen) following the manufacturer's
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instructions, a cohort transfected with miRNA-let7 as a negative control. The treatment was performed
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in triplicate, and cells treated with the transfection reagent only were used as a mock control.
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Statistical analysis
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All experiments were repeated at least in triplicate. All results are expressed as the means ± SD.
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Student’s t-test was used to evaluate differences between two groups. The data were analyzed using the
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SPSS 12.0 software package. P-values <0.05 were considered to be significant.
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Results
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iTRAQ analysis of the paired tumor and normal tissues from oral cancer patients
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A schematic flowchart of the iTRAQ method is provided in Figure 1. Protein identifications
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were initially accepted when based on at least two peptide identifications with (Mascot scores of ≥ 34)
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and a false discovery rate of < 3%. The following parameters were used: precursor mass tolerance, 1.5
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Da; fragment mass tolerance, 0.6 Da; static modification, methylthio (C), iTRAQ 4-plex (K) and
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iTRAQ 4-plex (N); and dynamic modification, iTRAQ 4-plex (Y) and oxidation (M). This resulted in
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the identification of 1959 and 2402 unique peptides, respectively, from the first and second iTRAQ
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experiments. The relative quantitation was measured as two pairwise ratios: the Normal group against
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the Tumor group (iTRAQ 115/114 or iTRAQ 117/116). From the two iTRAQ experiments 14,199 and
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8,618 MS/MS spectra were identified, leading to identification of 2,402 and 1,959 unique peptides with
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≥ 34 ion score and identification of 674 and 757 proteins for the respective groups (Supplemental data
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2). A total of 512 and 473 proteins were quantified with at least 2 MS/MS spectra assigned. The
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following criteria were applied to obtain differentially expressed proteins that displayed consistent
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under-expression in the Normal group: (1) the proteins are identified by two biological replicates; (2)
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the proteins have at least 2 quantified MS/MS spectra; (3) the iTRAQ 115/114 or iTRAQ 117/116
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ratios must be both lower than 0.67; (3) the variation of coefficient of the iTRAQ ratio must be less
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than 20%. The overall quality of the quantitation, and subsequent normalization, is revealed by a
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careful consideration of the ratios for the duplicate analyses at the peptide level. Among the identified
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proteins, 13 proteins displayed consistent under-expression in the Normal group (Table 1). To gain a
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better understanding of the 13 proteins in this study, we performed a functional annotation analysis of
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these proteins. The grouping and naming of the identified proteins in the functional annotation analysis
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were performed according to the Gene Ontology convention [27].
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Quantification of the expression of the six candidate genes
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Excluding ribosomal protein and the variability of both the 115/114 and 117/116 samples in
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over 10% of the candidates, among the 13 proteins, we selected the epidermal growth factor receptor
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(EGFR, coding for receptor tyrosine-protein kinase ErbB-1, EGFR), ornithine aminotransferase (OAT,
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coding for Ornithine aminotransferase, OAT), tumor protein, translationally controlled 1 (TPT1,
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coding for translationally controlled tumor protein, TCTP), integrin alpha-6 (ITGA6, coding for
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Integrin alpha-6 precursor, ITGA6), Ras GTPase-activating protein-binding protein 1 (G3BP1, coding
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for Ras GTPase-activating protein-binding protein 1, G3BP1) and calcium-binding protein 39-like
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(CB39L, coding for Calcium-binding protein 39-like, CB39L). The transcript levels of these six genes
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were validated in the paired tumor and normal tissues from 37 OSCC patients (T1=10, T2=10, T3,
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n=10 and T4, n=7) by real-time quantitative PCR. The dynamic results suggested that all of the
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candidate genes were overexpressed in the tumor tissues across all stages. Comparing the tumor and
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corresponding normal tissues from the 37 oral cancer patients, the EGFR, OAT, TPT1, ITGA6, G3BP1
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and CB39L genes were overexpressed by an average of 2.74-fold (95% CI, 1.53-3.25), 1.07-fold (95%
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CI, 0.57-1.65), 3.42-fold (95% CI, 1.80-4.52), 5.65-fold (95% CI, 1.58-5.22), 1.33-fold (95% CI,
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0.13-3.74) and 3.72-fold (95% CI, 1.08-4.22) in the tumor tissues, respectively (Figure 2A). These
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results indicate that the overexpression phenomena differentiating the tumor and normal tissues in the
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oral cancer patients were not only manifested at the tissue protein levels but also at the mRNA level. In
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addition, three genes, TPT1, CAB39L and ITGA6, displayed stable and higher expression levels related
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to gene transcription in the tumor tissues (with a 3-fold greater mean overexpression level).
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Moreover, we organized the individual overexpression levels of TPT1, CAB39L and ITGA6 in
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the T1-4 groups. The overexpression of TPT1gene was observed not only in the early stage but also
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increased in the late stages from 4.51-fold (T1) and 4.3-fold (T2) to 4.62-fold (T3) and 5.74-fold (T4),
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although the overexpression was not significantly different between T1 + 2 and T3 + 4 (p= 0.078).
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Additionally, CAB39L and ITGA6 consistently displayed greater overexpression levels in the T1 and T2
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groups (with 6.9- and 6.6-fold increases on average for ITGA6 and 4.7- and 5.1-fold increases for
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CAB39L) in the tumor tissues (Figure 2B). However, lower transcription levels of these genes were
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observed in the tumor tissues of the T3 and T4 patients (with 3.8- and 3.1-fold increases for ITGA6 on
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average and 2.3- and 1.6-fold for CAB39L). These two genes displayed significant differences between
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their mean transcription levels in the T1+T2 and T3+T4 groups (P=0.02024 for ITGA6, and P=0.00038
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for CAB39L). These results indicated that tissue overexpression of CAB39L and ITGA6 were dominant
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in the early stage and not correlated with oral cancer progression, which are important for early
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diagnosis.
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Validation of the protein expressions in the tissues
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The protein expression levels of TPT1, ITGA6 and CAB39L were validated in the paired tumor
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and normal tissues from 37 OSCC patients (T1=10, T2=10, T3, n=10 and T4, n=7). The results
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suggested that all of the three proteins were overexpressed in the tumor tissues across all stages (Figure
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3A). Comparing the tumor and corresponding normal tissues from the 37 oral cancer patients, the TPT1,
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ITGA6 and CAB39L proteins were overexpressed by an average of 2.83-fold, 3.27-fold and 1.62-fold
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in the tumor tissues, respectively (Figure 3B).
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Predictions of the candidate miRNAs
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The candidate microRNA predictions were based on the 3′UTRs of the TPT1, CAB39L and
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ITGA6 genes using two bioinformatics tools, the mirSVR predicted target site scoring method [28] and
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the online tools at MicroRNA.org (http://www.mirbase.org). All the individual candidate miRNAs were
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reported (Table 2); we selected the seven overlapping miRNAs (miR-19a, miR-27a, miR-27b, miR-19b
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and miR-186 miR-203, miR-377) underlined in bold font as candidate targets for the subsequent
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miRNA determinations.
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Quantitative analysis of candidate miRNA expression
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In the tissue study comparing the paired normal and tumor tissues, the target miRNAs
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miR-19a, miR-19b, miR-186, miR-203 and miR-377 were detected by real-time Q-PCR and showed
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overexpression levels averaging 7.93-, 1.18-, 1.64-, 14.57- and 33.21-fold, respectively, in the tumor
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tissues from the 20 patients. However, only the has-miR-27a and has-miR-27b were underexpressed in
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the tumor tissues, by 0.57- and 0.32-fold on average, respectively (Figure 4A). Following the
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introduction, the overexpressions of miRNA will reduce the target protein expressions after
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transcriptions, thus we selected the has-miR-27a and has-miR-27b for advance detection.
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The plasma levels of miR-27a and miR-27b were determined and compared in 10 normal
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individuals and 20 oral cancer patients. Unlike the control, miR-16, which was found in all patients and
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normal individuals, plasma miR-27a was detected in only 11 % (4 of 37) of the OSCC patients and in
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only 25% (5 of 20) of the healthy volunteers under the same conditions. The data indicate that the
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major expression of miRNA-27a in tissues does not translated to higher plasma levels. However, the
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plasma miR-27b levels were detectable in 70 % (26 of 37) of the tumor patients and all the healthy
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volunteers; the levels tended to be significantly higher in the normal group than in the oral cancer
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group (P=0.00019; 95% confidence interval, 9.5-29.7; with a mean level 13.2-fold higher) (Figure 4B).
325
This result indicated that decreased plasma miR-27b levels are a significant indicator for oral cancer
326
and that the miR-27b suppression may involve the expression off the tumor-associated proteins TCTP,
327
CAB39L and ITGA6 in oral cancer. We also investigated possible correlations between plasma
328
miR-27b levels and sex, age and tumor size in the 37 patients; no significant associations were
329
observed.
330
Translational regulation of candidate proteins by miR-27b
16
331
To determine the effects of miRNA-27b on the expression of the TCTP, CAB39L and ITGA6
332
proteins, 100 nM of synthetic miR-27b was transfected into HSC-3 and Cal-27 cells. The
333
overexpression of miR-27b significantly decreased the expression of TCTP mRNA and protein in both
334
the HSC-3 and Cal-27 cell lines but did not significantly affect gene and protein expression in the
335
CAB39L and ITGA6, as determined by both Q-PCR and immunoblot assays (Figure 5A and B). These
336
results indicate that miRNA-27b expression is involved in the regulation of TCTP in oral cancer cells.
17
337
Discussion
338
In tumorigenesis and cancer progression, dynamic protein expression is always a critical target
339
for initial investigation. Recently, functional proteomics combined with mass spectrometry (MS) has
340
offered great promise for unveiling the complex molecular events of tumorigenesis and transforming
341
the management of cancer by identifying new markers for screening, diagnosis, prognosis, and
342
monitoring responses to therapy [29-31]. Following previous reports, the rapid advances in quantitative
343
proteomic analysis based on isotope-dilution MS with mass-tagging reagents, such as iTRAQ, in
344
addition to multidimensional liquid chromatography−tandem mass spectrometry (LC−MS/MS) have
345
revolutionized the field of biomarker discovery and identification [32, 33]. Gel-free approaches
346
LC-MS/MS have been widely used for clinical tissue and cell line analysis. iTRAQ reagents contain
347
isobaric tags designed to bind specifically to the amine groups of peptides, enabling their quantitation
348
by the measurement of relative intensities of the reporter ions generated upon MS/MS fragmentation.
349
To avoid possible analytical and methodological biases, a technology different from the one used for
350
biomarker discovery is typically employed. Real-time Q-PCR and immunoblots are robust, powerful
351
techniques that are frequently selected for biomarker verification. These techniques permit not only the
352
identification and verification of biomarkers but also their quantification in various tissues and body
353
fluids [27]. Studies evaluating the prognostic utility of potential biomarkers identified using gel
354
free-proteomic techniques are not rare and are also needed to substantiate advances in clinical utility
355
and elucidate the potential mechanisms of new biomarkers.
356
The mature 20- to 23-nt miRNAs act as functional intermediates of RNAi that direct mRNA
357
cleavage and translational attenuation, and recent studies suggest that miRNAs contribute to the
358
development of hand and neck cancers [19, 34]. Generally, the miRNA can be easily and quickly
359
determined using real-time Q-PCR and is more suitable as a potential biomarker than protein
18
360
biomarkers for clinical applications. Generally, mRNA profiling with microarrays has been widely
361
used for miRNA target identification, but microarrays only detect the effects of miRNAs at the
362
transcriptional level and will miss targets repressed solely at the protein level. However, methods based
363
on the use of miRNA profiling techniques to predict proteins levels are difficult to implement in a
364
high-throughput fashion. Thus, we designed a new platform to demonstrate the potential for the
365
prognostic applications of candidate biomarkers identified using tissue proteomics by iTRAQ analysis
366
and attempted to identify biomarkers related to target miRNAs to replace proteins as useful biomarkers
367
for oral cancer.
368
In the iTRAQ analysis, we identified and quantified a total of 13 down-regulated and 6
369
up-regulated proteins with consistently different expression from the Normal tissue group. The 6
370
up-regulated proteins have been identified for future work in another study. In this study, we focus on
371
the 13 down-regulated proteins and the characterization of their mRNA- and miRNA-associated
372
expression levels in tissues and plasma. Moreover, we integrated in vivo and in vitro studies to
373
demonstrate that the expression of miR-27b significantly affects the downregulation of the TCTP
374
protein, one of the three candidate biomarkers. The developed platform represents the first combined
375
application of a differentially expressed tumor proteomic study to the identification of miRNA
376
biomarkers. Until now, there have been no reports of the identification of potential miRNA biomarkers
377
based on protein data from iTRAQ analysis in cancer research utilizing two types of quantitation. This
378
novel plateform can facilitate simultaneous screening for potentially correlated genes, miRNA and
379
downstream proteins.
380
Among of the 13 underexpressed proteins, we selected 6 proteins for subsequent study. The
381
expression of their coding genes, EGFR, OAT, TPT1, ITGA6, G3BP1 and CAB39L, were confirmed by
382
real-time quantitative PCR analysis. The TPT1, ITGA6 and CB39L genes were found to be the most
19
383
consistently over-expressed in the tumor tissues, and we suggest that detecting the these three genes
384
could contribute considerably to the early diagnosis of oral cancer (T1 or T2). Excluding TPT1, the
385
QPCR results for the ITGA6 and CB39L genes demonstrated that their over-expression appears more
386
significantly in the early stages of oral cancer (T1+T2) than in the late stages (T3+T4) (Figure 2). In
387
previous studies, the TPT1, ITGA6 and CB39L genes were reported to be implicated in tumor growth,
388
malignancy and poor survival rates in breast cancer and monocytic leukemia [35-37], but the studies
389
have not reported the protein levels and correlated miRNAs associated with cancer. The three
390
tumor-related proteins and genes were also demonstrated for the first time here to be useful as the
391
biomarkers for oral cancer based on a clinical global quantitative proteomic analysis. The correlation of
392
Q-PCR data with protein expression provides evidence that the iTRAQ labeling method for large-scale
393
protein quantification is powerful and reliable for advanced miRNA biomarker profiling.
394
It is known the miRNAs can control the expression levels of particular genes by binding to the
395
3′UTRs of mRNAs. Thus, the dysregulation of miRNAs is expected to be found in diseases such as
396
cancer that are attributed to deregulated gene expression, suggesting that miRNA alteration may initiate
397
carcinogenesis [38]. However, there is limited information on the aberrant expression of miRNAs in
398
oral cancer [39]. Among the 7 miRNAs that were predicted for the TPT1, CAB39L and ITGA6 genes in
399
a bioinformatic analysis, miR-27a and miR-27b demonstrated consistent under-expression in the laser
400
pressure catapulting dissected tumor tissues in comparison with the corresponding normal tissues;
401
unfortunately, the miR-27a was found in too few plasma samples in the oral cancer patients to be
402
statistically significant in this group. Specially, the tissue related determinations were carried out after
403
the laser pressure catapulting dissection that has been reported is the best tool to define the malignant
404
and benign sample in the translational medicine. Thus, we focused on miR-27b in this study. The
405
aberrant expression of miRNAs has been implicated in the carcinogenesis of various cancers. In
20
406
previous studies, an up-regulation of miR-27b was observed in OSCC and breast cancers as the tumors
407
suppress various factors in genomic experiments, but the effects of miR-27b on the regulation of
408
intercellular proteins in oral tumorigenesis remains unclear [40, 41].
409
As established in previous studies, TCTP is a highly conserved protein expressed abundantly
410
across a wide range of eukaryotes and is known to promote diverse cellular functions by interacting
411
with various proteins, with expression levels varying depending on the tissue type, growth, stress
412
factors and cytotoxic signals [42]. Knocking down TCTP protein expression in tumor cells inhibits
413
their growth, motility and invasive functions, and its expression levels have been demonstrated to be
414
downregulated by the activation of the tumor suppressor protein p53 [43, 44]. It also has been
415
suggested that several breast tumor cell lines, including MCF-7 and T47D, have high endogenous
416
levels of TCTP protein, and siRNA transfection promotes the downregulation of TCTP, resulting in
417
tumor reversion. However, the molecular mechanisms of tumor reversion remain to be defined.
418
Recently, TCTP was demonstrated to induce the chronic activation of Src, and EGFR and downstream
419
signaling molecules associated with cell transformation were significantly down-regulated by TCTP
420
siRNA [45]. It thus appears that the down-regulation of TCTP quenches the activation of
421
tumor-associated signals, causing tumor reversion [46, 47]. So far, it has not been investigated
422
whether the TCPT protein or the TPT1 gene can be regulated by miRNAs.
423
Thus, we performed transient transfection to overexpress the human miR-27b in oral cancer cell
424
lines to identify its regulatory role. This is the first report demonstrating that miR-27b is a negatively
425
regulator of the expression the of TPT1 gene and TCPT protein. We further demonstrated that miR-27b
426
overexpression not only reduced the level of TPT1 gene expressions and also downregulates cellular
427
TCPT expression in the oral cancer cells (Figure 4), but also that gene and protein levels of CAB39L
428
and ITGA6 are not significantly regulated by miR-27b overexpression, although the miR-27b sequence
21
429
was predicted from these three genes’ 3-UTR. These interesting and varied regulatory mechanisms
430
require further study to clarify their roles in cancer cells.
431
Our results indicate that miR-27b may function as a tumor-suppressor gene, whereas another
432
study suggested it may function as an oncogene in MDA-MB-231 cells [47]. They revealed that the
433
introduction of miR-27b into cells expressing the target gene, ST14, did not suppress cell growth,
434
suggesting that both miR-27b-dependent and independent functions of ST14 protein exist in breast
435
cancer. Furthermore, the miR-19a, miR-19b, miR-20a and miR-27b sequences were identified as the
436
major growth-sustaining micro-RNAs in the tumor cells in an assay of individual cell growth arrest
437
[48]. The complementary screening study unveiled only functional differences between homologous
438
mi-RNAs; miR-27b appears to be involved in an important novel mechanism in tumorigenesis. These
439
differences may occur due to differences in cancer types, patient organization, tumor status or
440
histologic tumor grade, etc.
441
Conclusion
442
Our study introduced the efficient use of an iTRAQ proteomics study to identify three protein
443
biomarkers for early stage oral cancer. We additionally discovered that tissue and plasma miR-27b
444
levels are better biomarkers than protein biomarkers due to their convenient determination by Q-PCR,
445
and that miR-27b overexpression in oral cancer cells significantly down-regulates the tumor associated
446
TCTP protein. The integrated study of quantitative proteomics and molecular biology will provide new
447
insights in both Proteomics and Translational medicine.
448
449
450
451
Acknowledgements
This study was supported by grants from the National Science Council (NSC 96-2320-B-039-024,
22
452
NSC 97-2320-B-039-016-MY3, and NSC 98-2113-M-003-007-MY2), the China Medical University
453
Hospital (DMR-98-100) and China Medical University (CMU100-S-04).
454
23
455
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