Seminar of Food Science and Biotechnology National Chung Hsign University
Title: Acetylated STAT3 is crucial for methylation of tumor-suppressor gene promoters and
inhibition by resveratrol results in demethylation
Journal: Proc Natl Acad Sci U S A. 2012 May 15 (IF:9.737)
Authors: Lee H, Zhang P, Herrmann A, Yang C, Xin H, Wang Z, Hoon DS, Forman SJ, Jove R, Riggs AD, Yu
H. Source: Department of Cancer Immunotherapeutics and Tumor Immunology, Beckman Research
Institute, City of Hope Comprehensive Cancer Center, Duarte, CA 91010, USA
Speaker: Diana Wong 黃珊珊 (No.8)
Advisor：Dr Chiang En-Pei Isabel
Moderator: 侯慧卿
Date: 6 December, 2013
1. Introduction
Signal transducer and activator of transcription 3, also known as STAT3, is a transcription factor
responsible for the regulation and control of the flow of genetic information. This protein is
phosphorylated by receptor-associated kinases and then forms homo- or heterodimers that
translocate to the cell nucleus, where they act as transcription activators. It responses to various
cytokines and growth factors including interferons, epidermal growth factor, Interleukin 5,
Interleukin-6, and hepatocyte growth factor. However, STAT3 acetylation is elevated in tumors. This
study aim at the importance of acetylated STAT3 as a target for cancer therapy.
2. Materials and Methods
2.1 Cell lines
A2058 human melanoma, HCT116 Cell, and MDA-MB468 human breast cancer cell.
2.2 In Vivo xenograft tumor models:
 A2058 human melanoma models: A2058cells were subcutaneously implanted into
immune-deficient NSG mice. When the tumor was palpable, mice were given 50 mg/kg
resveratrol in 100 μ L Neobee oil (Spectrum Chemicals) by intratumoral injection twice a
week. For the control group, the solvent DMSO was used in Neobee oil as a control.
 MDA-MB468 triple-negative breast tumor models: Cells were implanted subcutaneously
into the fl ank of athymic nude mice. When tumor volume reached ∼ 150 mm³, mice were
given the solvent control (combination of acetone and ethanol, 0.001%), resveratrol (25
mg/kg), tamoxifen (1 mg/kg), or a combination of both in Neobee oil, three times a week
for the indicated time periods by intraperitoneal injection.
2.3 Real-Time RT-PCR
2.4 Cell proliferation assay
2.5 Western Blotting and Coimmunoprecipitation
3. Results
3.1 STAT3 Acetylation increased tumor growth, DNA methylation, and tumor suppressor gene
silencing.
3.2 Loss of endogenous STAT3 acetylation results in reactivation and demethylation of tumorv
suppressor genes.
3.3 Acetylated STAT3 colocalized well with DNMT1 in different types of human cancer cells.
3.4 STAT3 Acetylation inhibition reactivates the ERα gene and sensitizes TNBC cells to tamoxifen
therapy.
3.5 Acetylated STAT3 contribute to the ERα gene promoter hypermethylation and is thereby
related to melanoma tumor progression.
4. Discussion
4.1 The polypeptide chains undergo post-translational modification (such as methylation,
acetylation), then becoming the mature protein product.
4.2 Proteins are typically acetylated on lysine (K) residues.
4.3 Protein acetylation has generally been thought to be a crucial posttranslational modification to
turn proteins and genes on and off.
4.4 STAT3 acetylation can silence gene expression and enhance DNA methylation of several
important tumor-suppressor gene promoters.
4.5 Persistent acetylation of STAT3 is generally found in various human tumors. Although
resveratrol is regarded as an inhibitor.
4.6 Resveratrol, a STAT3 inhibitor. It reduces STAT3 acetylation and reactivates ER α gene
expression in tumors where the ER α gene-promoter region is methylated.
4.7 Histone deacetylases (HDACs) are enzymes that modify chromatin structure and contribute to
aberrant gene expression in cancer. HDAC inhibitors have been developing as anticancer
agents. HDAC inhibitors induce hyperacetylation of oncogenic transcription factors, including
STAT3.
4.8 Blocking STAT3 acetylation can impact CpG island methylation to boost the anticancer
therapeutic efficacy of HDAC inhibitors.
Conclusion:
Targeting acetylation of an oncogenic transcription factor can affect CpG island methylation to benefit
chemoprevention.
References
1) Yuan ZL, Guan YJ, Chatterjee D, Chin YE (2005) Stat3 dimerization regulated by reversible
acetylation of a single lysine residue. Science 307:269–273.
2) Robert MF, et al. (2003) DNMT1 is required to maintain CpG methylation and aberrant gene
silencing in human cancer cells. Nat Genet 33:61–65.
3) Zhang X, Sun Y, Pireddu R, Yang H, Urlam MK, Lawrence HR, Guida WC, Lawrence NJ, Sebti SM
(2013) A novel inhibitor of STAT3 homodimerization selectively suppresses STAT3 activity and
malignant transformation. Cancer Res 73(6):1922-33