title: Analysis of small GTPase signaling pathways using p21-activated kinase mutants that selectively couple to Cdc42.
abstract: p21-activated kinase 1 (Pak1) is an effector for the small GTPases Cdc42 and Rac. Because Pak1 binds to and is activated by both these GTPases, it has been difficult to precisely delineate the signaling pathways that link extracellular stimuli to Pak1 activation. To separate activation of Pak1 by Cdc42 versus activation by Rac, we devised a genetic screen in yeast that enabled us to create and identify Pak1 mutants that selectively couple to Cdc42 but not Rac1. We recovered several such Pak1 mutants and found that the residues most often affected lie within the p21 binding domain, a region previously known to mediate Pak1 binding to GTPases, but that several mutations also map outside the borders of the p21 binding domain. Pak1 mutants that associate with Cdc42 but not Rac1 were also activated by Cdc42 but not Rac1. In rat 3Y1 cells expressing oncogenic Ha-Ras, the Pak1 mutants defective in Rac1 binding are not activated, suggesting that Ras signals through a GTPase other than Cdc42 to activate Pakl. Similar results were obtained when epidermal growth factor was used to activate Pak1. However, Pak1 mutants that are unable to bind Rac are nonetheless well activated by calf serum, implying that this stimulus may induce Pak activation independent of Rac.
authors.affiliation: Division of Basic Science, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Reeder
authors.forename: I G
authors.initials: IG
authors.lastname: Serebriiskii
authors.forename: E A
authors.initials: EA
authors.lastname: Golemis
authors.forename: J
authors.initials: J
authors.lastname: Chernoff
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D016296:Mutagenesis; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*; D054462:p21-Activated Kinases; D020830:rac1 GTP-Binding Protein / Q000378:metabolism
chemical_list: D017931:DNA Primers; C515906:Pak1 protein, rat; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020558:GTP Phosphohydrolases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein