Cytoskeletal reorganization by G protein-coupled receptors is dependent on phosphoinositide 3-kinase gamma, a Rac guanosine exchange factor, and Rac.
Reorganization of the actin cytoskeleton is an early cellular response to a variety of extracellular signals. Dissection of pathways leading to actin rearrangement has focused largely on those initiated by growth factor receptors or integrins, although stimulation of G protein-coupled receptors also leads to cytoskeletal changes. In transfected Cos-7SH cells, activation of the chemoattractant formyl peptide receptor induces cortical actin polymerization and a decrease in the number of central actin bundles. In this report, we show that cytoskeletal reorganization can be transduced by G protein betagamma heterodimers (Gbetagamma), phosphoinositide 3-kinase gamma (PI3-Kgamma), a guanosine exchange factor (GEF) for Rac, and Rac. Expression of inactive variants of either PI3-Kgamma, the Rac GEF Vav, or Rac blocked the actin rearrangement. Neither wortmannin nor LY294002, pharmacologic inhibitors of PI3-K, could inhibit the actin rearrangement induced by a constitutively active Rac. The inhibition of cytoskeletal reorganization by the dominant negative Vav variants could be rescued by coexpression of a constitutively active form of Rac. In contrast, a Vav variant with its pleckstrin homology (PH) domain missing constitutively induced JNK activation and led to cytoskeletal reorganization, even without stimulation by PI3-Kgamma. This suggests that the PH domain of Vav controls the guanosine exchange activity of Vav, perhaps by a mechanism regulated by D3 phosphoinositides generated by PI3-K. Taken together, these findings delineate a pathway leading from activation of a G protein-coupled receptor to actin reorganization which sequentially involves Gbetagamma, PI3-Kgamma, a Rac GEF, and Rac.
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Department of Medicine, University of Pennsylvania Medical School, Philadelphia, Pennsylvania 19104, USA.
Metjian
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Bagrodia
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Taylor
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Abrams
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D000199:Actins / Q000502:physiology*; D000818:Animals; D001426:Bacterial Proteins; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002630:Chemotactic Factors; D003599:Cytoskeleton / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006151:Guanosine; D018922:HL-60 Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins
D000199:Actins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002630:Chemotactic Factors; D019204:GTP-Binding Proteins; D006151:Guanosine; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D011956:Receptors, Cell Surface; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; C028640:fructose-induced HPr-like protein, bacteria