The roles of two distinct regions of PINCH-1 in the regulation of cell attachment and spreading

Cells attach to the extracellular matrix (ECM) through integrins to form focal adhesion complexes, and this process is followed by the extension of lamellipodia to enable cell spreading. PINCH-1, an adaptor protein essential for the regulation of cell-ECM adhesion, consists of five tandem LIM domains and a small C-terminal region. PINCH-1 is known to interact with integrin-linked kinase (ILK) and Ras suppressor protein 1 (Rsu-1); however, the precise mechanism by which this complex regulates cell-ECM adhesion is not fully understood. We report here that the LIM1 domain of PINCH-1, which associates with ILK to stabilize the expression of this protein, is sufficient for cell attachment but not for cell spreading. In contrast, the C-terminal region of PINCH-1, which binds to Rsu-1, plays a pivotal role in cell spreading but not in cell attachment. We also show that PINCH-1 associates with Rsu-1 to activate Rac1 and that Rac1 activation is necessary for cell spreading. Thus, these data reveal how specific domains of PINCH-1 direct two independent pathways: one utilizing ILK to allow cell attachment, and the other recruiting Rsu-1 to activate Rac1 in order to promote cell spreading.