Abstract
BackgroundPINCH1, an adaptor protein containing five LIM domains, plays an important role in regulating the integrin-mediated cell adhesion, migration and epithelial-mesenchymal transition. PINCH1 is induced in the fibrotic kidney after injury, and it primarily localizes at the sites of focal adhesion. Whether it can translocate to the nucleus and directly participate in gene regulation is completely unknown.Methodology/Principal FindingsUsing cultured glomerular podocytes as a model system, we show that PINCH1 expression was induced by TGF-β1, a fibrogenic cytokine that promotes podocyte dysfunction. Interestingly, increased PINCH1 not only localized at the sites of focal adhesions, but also underwent nuclear translocation after TGF-β1 stimulation. This nuclear translocation of PINCH1 was apparently dependent on the putative nuclear export/localization signals (NES/NLS) at its C-terminus, as deletion or site-directed mutations abolished its nuclear shuttling. Co-immunoprecipitation and pull-down experiments revealed that PINCH1 interacted with Wilms tumor 1 protein (WT1), a nuclear transcription factor that is essential for regulating podocyte-specific gene expression in adult kidney. Interaction of PINCH1 and WT1 was mediated by the LIM1 domain of PINCH1 and C-terminal zinc-finger domain of WT1, which led to the suppression of the WT1-mediated podocalyxin expression in podocytes. PINCH1 also repressed podocalyxin gene transcription in a promoter-luciferase reporter assay.Conclusion/SignificanceThese results indicate that PINCH1 can shuttle into the nucleus from cytoplasm in podocytes, wherein it interacts with WT1 and suppresses podocyte-specific gene expression. Our studies reveal a previously unrecognized, novel function of PINCH1, in which it acts as a transcriptional regulator through controlling specific gene expression.
Highlights
Podocytes are highly differentiated glomerular visceral epithelial cells that play an essential role in the establishment of the glomerular filtration barrier, a structural apparatus that selectively restricts the filtration of different macromolecules in the blood stream on the basis of their sizes, shape and charge [1,2]
We found that PINCH1 could interact with Wilms tumor 1 protein (WT1), a transcription factor that is exclusively expressed in podocytes in adult kidney
We provide evidence demonstrating that PINCH1 functions as a transcriptional regulator by interacting with nuclear WT1, a podocyte-specific transcription factor that plays a pivotal role in the establishment and maintenance of the unique differentiated features of podocytes in adult kidney
Summary
Podocytes are highly differentiated glomerular visceral epithelial cells that play an essential role in the establishment of the glomerular filtration barrier, a structural apparatus that selectively restricts the filtration of different macromolecules in the blood stream on the basis of their sizes, shape and charge [1,2]. WT1, the product of Wilms tumor gene 1, is a key nuclear transcription factor that plays a fundamental role in controlling the expression of major podocyte-specific genes such as podocalyxin in adult kidney [8,9,10,11,12,13]. WT1 expression is exclusively restricted to glomerular podocytes [16]. Based on these findings, WT1 is often utilized as a molecular marker for evaluating podocyte number and density under different circumstances [17]. PINCH1, an adaptor protein containing five LIM domains, plays an important role in regulating the integrinmediated cell adhesion, migration and epithelial-mesenchymal transition. Whether it can translocate to the nucleus and directly participate in gene regulation is completely unknown
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