p21-activated protein kinase gamma-PAK is translocated and activated in response to hyperosmolarity. Implication of Cdc42 and phosphoinositide 3-kinase in a two-step mechanism for gamma-PAK activation.
A member of the family of p21-activated protein kinases, gamma-PAK, has cytostatic properties and is activated during apoptosis and in response to DNA damage. To determine whether gamma-PAK is activated by other types of cell stress and to assess its mechanism of activation, the response of gamma-PAK to hyperosmotic stress was examined. In 3T3-L1 mouse fibroblasts, there are two pools of gamma-PAK: the majority of the protein kinase is soluble and has low specific activity, whereas gamma-PAK associated with the particulate fraction has significantly higher specific activity. Hyperosmolarity promotes translocation of gamma-PAK from the soluble to the particulate fraction; this parallels activation of the protein kinase. Activation but not translocation of gamma-PAK is wortmannin-sensitive, suggesting the involvement of a phosphoinositide 3-kinase-related activity. gamma-PAK translocation in response to hyperosmolarity parallels Cdc42 translocation to the particulate fraction in vivo and can be induced in vitro by guanosine 5'-3-O-(thio)triphosphate. Cotransfection of gamma-PAK with constitutively active Cdc42 induces gamma-PAK activation and translocation, whereas inactive Cdc42 inhibits both processes in response to hyperosmotic stress, suggesting that Cdc42 has a role in the translocation and activation of gamma-PAK. alpha-PAK is not activated in response to hyperosmolarity in 3T3-L1 cells. A two-step model of gamma-PAK activation is presented.
Roig
J
J
Department of Biochemistry and Biomedical Sciences, University of California, Riverside, California 92521, USA.
Huang
Z
Z
Lytle
C
C
Traugh
J A
JA
D016475:3T3 Cells; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D004789:Enzyme Activation; D006801:Humans; D051379:Mice; D015689:Oncogene Protein p21(ras) / Q000378:metabolism*; D009994:Osmolar Concentration; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D054462:p21-Activated Kinases
D015689:Oncogene Protein p21(ras); D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D020764:cdc42 GTP-Binding Protein; D054462:p21-Activated Kinases; C515907:PAK2 protein, human; C515909:Pak2 protein, mouse