PINCH-1 promotes tubular epithelial-to-mesenchymal transition by interacting with integrin-linked kinase.

PINCH-1 is an adaptor protein that binds to the integrin-linked kinase (ILK), an intracellular serine/threonine protein kinase that plays a critical role in mediating tubular epithelial-to-mesenchymal transition (EMT). To determine whether PINCH-1 is also involved in the EMT process, we investigated its regulation and function during TGF-beta1-stimulated EMT. TGF-beta1 induced PINCH-1 mRNA and protein expression in human proximal tubular epithelial cells in a time-dependent fashion, an effect that was largely dependent on intracellular Smad signaling. Overexpression of PINCH-1 suppressed epithelial markers E-cadherin and ZO-1 and increased fibronectin expression and extracellular assembly, whereas knockdown of PINCH-1 via small interfering RNA reduced TGF-beta1-mediated fibronectin expression and partially restored E-cadherin. PINCH-1 formed a ternary complex with ILK at the focal adhesion sites of tubular epithelial cells. Treatment with an ILK inhibitor or disruption of the ILK/PINCH-1 interaction by overexpressing a dominant-negative N-terminal ankyrin domain of ILK resulted in reduced fibronectin deposition, indicating that the ability of PINCH-1 to stimulate EMT is ILK-dependent. In a mouse model of obstructive nephropathy, PINCH-1 expression increased in a time-dependent manner, suggesting that it may play a role in EMT and renal fibrosis in vivo. We conclude that PINCH-1, through its interaction with ILK, plays an important role in regulating TGF-beta1-mediated EMT and could be a potential future therapeutic target to prevent progression of renal disease.