S14(Th)
PUROMYCIN AMINONUCLEOSIDE INDUCES NUCLEAR TRANSLOCATION OF
IQGAP1 PROTEIN WHILE DECREASING ITS INTERACTIONS WITH SLIT
DIAPHRAGM PROTEINS IN PODOCYTES.
Rigothier, C1,2, Saleem, M1, Ripoche, J2, Combe, C2,3, Welsh, G1.
1
Academic Renal Unit, University of Bristol, Bristol, United Kingdom, 2 INSERM U577,
Université de Bordeaux, Bordeaux, France; 3 Service de Néphrologie, CHU Bordeaux, Bordeaux,
France.
BACKGROUND: IQGAP1 is a scaffold protein that interacts with cytoskeletal proteins as well as
proteins of the glomerular slit diaphragm (SD). IQGAP1 is implicated in actin cytoskeleton
remodelling and in the regulation of cell migration, cell adhesion, cell division and gene expression.
We hypothesized that IQGAP1 is pivotal in maintaining glomerular barrier properties and podocyte
cytoskeleton remodelling as observed in glomerulonephropathies (GN). We report changes in
podocyte IQGAP1 subcellular localization and interaction with SD proteins upon exposure of
podocytes to puromycin aminonucleoside (PAN), an inducer of experimental nephrotic syndrome.
METHODS: In cultured human podocytes, a combination of Western blot (n=5) on cytoplasmic and
nuclear extracts, quantitative PCR (n=3), immunoprecipitation (n=5) and immunocytolocalization
(n=5) were performed to determine the subcellular localization, the transcription and interacting
protein partners of IQGAP1, upon exposure to PAN.
RESULTS: Upon exposure to PAN, IQGAP1 translocation from its usual localization on the plasma
membrane to the nucleus was observed by immunocytolocalization (cytoplasm/nuclei ratio, ctl:
10.8±1.3 vs PAN: 6.6±0.5 intensity/mm2, p=0.02) and confirmed by Western blot after selective
extraction (2.8±1.0 vs 1.4±0.4 intensity/mm2, p=0.03). qPCR experiments excluded an increase of
IQGAP1 transcription.
Interactions with proteins of the SD were also modified. We observed a reduction of IQGAP1
interactions with both nephrin and podocalyxin in response to PAN exposure.
CONCLUSION: The alteration of IQGAP1 in PAN-induced GN may be important in the loss of the
permeability of the glomerular barrier associated with this experimental model.
Also, the potential roles played by IQGAP1 in the nucleus in these conditions remain to be clarified,
particularly on account of IQGAP1 implication in gene regulation. The PAN model provides a useful
experimental tool to study the role of IQGAP1 in the alteration of podocyte cytoskeleton organization
and remodelling as observed in GN.