Association of PI-3 kinase with PAK1 leads to actin phosphorylation and cytoskeletal reorganization.
The family of p21-activated kinases (PAKs) have been implicated in the rearrangement of actin cytoskeleton by acting downstream of the small GTPases Rac and Cdc42. Here we report that even though Cdc42/Rac1 or Akt are not activated, phosphatidylinositol-3 (PI-3) kinase activation induces PAK1 kinase activity. Indeed, we demonstrate that PI-3 kinase associates with the N-terminal regulatory domain of PAK1 (amino acids 67-150) leading to PAK1 activation. The association of the PI-3 kinase with the Cdc42/Rac1 binding-deficient PAK1(H83,86L) confirms that the small GTPases are not involved in the PI-3 kinase-PAK1 interaction. Furthermore, PAK1 was activated in cells expressing the dominant-negative forms of Cdc42 or Rac1. Additionally, we show that PAK1 phosphorylates actin, resulting in the dissolution of stress fibers and redistribution of microfilaments. The phosphorylation of actin was inhibited by the kinase-dead PAK1(K299R) or the PAK1 autoinhibitory domain (PAK1(83-149)), indicating that PAK1 was responsible for actin phosphorylation. We conclude that the association of PI-3 kinase with PAK1 regulates PAK1 kinase activity through a Cdc42/Rac1-independent mechanism leading to actin phosphorylation and cytoskeletal reorganization.
Department of Biochemistry, School of Medicine, University of Crete, GR-71110 Heraklion, Greece.
Evangelia A
EA
Papakonstanti
Christos
C
Stournaras
D000199:Actins / Q000378:metabolism*; D000730:Androstadienes / Q000378:metabolism; D000818:Animals; D002364:Caseins / Q000494:pharmacology; D002458:Cell Fractionation; D002460:Cell Line; D003599:Cytoskeleton / Q000378:metabolism*; D004789:Enzyme Activation; D016314:Ethylketocyclazocine / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007150:Immunohistochemistry; D007668:Kidney / Q000166:cytology; D009294:Narcotics / Q000494:pharmacology; D009893:Opossums; D010446:Peptide Fragments / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D000077191:Wortmannin; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
D000199:Actins; D000730:Androstadienes; D002364:Caseins; D016314:Ethylketocyclazocine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009294:Narcotics; D010446:Peptide Fragments; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins; D014409:Tumor Necrosis Factor-alpha; D000077191:Wortmannin; D020764:cdc42 GTP-Binding Protein; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein; C102368:alpha(S1)-casomorphin