Regulation of Cdc42 Gtpase by Proline-Rich Tyrosine Kinase 2 Interacting with Psgap, a Novel Pleckstrin Homology and Src Homology 3 Domain Containing Rhogap Protein

Abstract

Proline-rich tyrosine kinase 2 (PYK2), a tyrosine kinase structurally related to focal adhesion kinase (FAK), is implicated in regulating cytoskeletal organization. However, mechanisms by which PYK2 participates in and regulates cytoskeletal organization remain largely unknown. Here we report identification of PSGAP, a novel protein that interacts with PYK2 and FAK and contains multiple domains including a pleckstrin homology domain, a rhoGTPase-activating protein domain, and a Src homology 3 domain. PYK2 interacts with PSGAP Src homology 3 domain via the carboxyl-terminal proline-rich sequence. PSGAP is able to increase GTPase activity of CDC42 and RhoA in vitro and in vivo. Remarkably, PYK2, but not FAK, can activate CDC42 via inhibition of PSGAP-mediated GTP hydrolysis of CDC42. Moreover, PSGAP is localized at cell periphery in fibroblasts in a pleckstrin homology domain–dependent manner. Over expression of PSGAP in fibroblasts results in reorganization of cytoskeletal structures and changes of cellular morphology, which requires rhoGTPase-activating activity. Taken together, our results suggest that PSGAP is a signaling protein essential for PYK2 regulation of cytoskeletal organization via Rho family GTPases.

Focal Adhesion Kinase Regulation of N-WASP Subcellular Localization and Function

“…FAK has also been shown to bind Graf, a GAP for Rho and Cdc42 (49,50). More recently, FAK and the related kinase Pyk2 have been shown to associate with a novel protein PSGAP containing a rhoGAP domain (51). However, Pyk2, but not FAK, can activate Cdc42 by inactivating the GAP activity of PSGAP.…”

Thrombospondin Induces RhoA Inactivation through FAK-dependent Signaling to Stimulate Focal Adhesion Disassembly

“…Whereas FAK translocates to the newly formed adhesions on a similar time course as p190 RhoGAP, no direct correlation between FAK and p190 RhoGAP has been made to date (63). FAK can interact with RhoGAPs, including Graf and PSGAP, through its proline-rich regions suggesting that FAK can act directly on components of the RhoA inactivation pathway (35,36). Consistent with this, FAK knockout fibroblasts have increased levels of active RhoA, which is responsible for the increased levels of focal adhesions and stress fibers in these cells.…”

“…TSP1/hep I stimulated FAK phosphorylation mediates activation of ERK and PI 3-kinase, both of which are required for TSP1/hep I-induced RhoA inactivation and focal adhesion disassembly (41,42). Whereas little is currently known about PI 3-kinase or ERK regulation of RhoGAP activity, the FAK-associated RhoGAPs Graf and PSGAP both contain pleckstrin homology domains and consensus ERK phosphorylation sites (35,36). Pleckstrin homology domains can selectively regulate enzyme activity depending upon the phosphoinositide bound, suggesting that increased levels of phosphatidylinositol 3,4,5-P 3 production by PI 3-kinase may alter their RhoGAP activity (64).…”

“…However, focal adhesion turnover under these conditions is extensive, resulting in complete loss of cell adhesion. FAK signaling is proposed to inactivate RhoA, because RhoA activity is elevated in FAK knockout fibroblasts and FAK associates with several RhoGAPs (8,35,36). Furthermore, RhoA inactivation and inhibition of the RhoA effector ROCK are both sufficient to induce focal adhesion disassembly (5,6).…”

Calcium-dependent growth regulation of small cell lung cancer cells by neuropeptides

“…However, a function for Graf in Pyk2 signalling has not been described so far (Hildebrand et al 1996, Xiong et al 1998. It was suggested that PSGAP may be an essential protein for regulation of cytoskeletal organization by Pyk2 via RhoGTPases (Ren et al 2001). Furthermore, Pyk2 binds to an ArfGTPase-activating protein ASAP1, thereby regulating Arf1 activity by phosphorylation building another bridge to reorganization of the actin cytoskeleton (Kruljac-Letunic et al 2003).…”