Formation and phosphorylation of the PINCH-1-integrin linked kinase-alpha-parvin complex are important for regulation of renal glomerular podocyte adhesion, architecture, and survival.

Abstract

Alterations in the cellular architecture, adhesion, and/or loss of glomerular podocytes are causal factors in the development of proteinuria and the progression to end-stage renal failure. With the use of an inducible podocyte differentiation system, it was found that the cellular levels of PINCH-1, integrin linked kinase (ILK), and alpha-parvin, cytoplasmic components of cell-extracellular matrix adhesions, were significantly increased during podocyte differentiation. Concomitantly, an increased amount of the PINCH-1-ILK-alpha-parvin complex was detected in the differentiated, foot process-containing podocytes. Overexpression of the PINCH-1-binding ankyrin repeat domain of ILK but not that of a PINCH-1-binding defective mutant form of the ankyrin domain effectively inhibited the formation of the PINCH-1-ILK-alpha-parvin complex. Disruption of the PINCH-1-ILK-alpha-parvin complex significantly reduced the podocyte-matrix adhesion and foot process formation. Furthermore, a marked increase of apoptosis in the podocytes in which the assembly of the PINCH-1-ILK-alpha-parvin complex was compromised was detected. Inhibition of ILK with a small compound inhibitor also altered podocyte cytoskeleton and increased apoptosis. Finally, it is shown that alpha-parvin is phosphorylated in podocytes. Mutations at the alpha-parvin N-terminal proline-directed serine phosphorylation sites reduced its complex formation with ILK and resulted in defects in podocyte adhesion, architecture, and survival. These results provide important evidence for a crucial role of the PINCH-1-ILK-alpha-parvin complex in the control of podocyte adhesion, morphology, and survival.