RAC GTPASE ACTIVITY IS ESSENTIAL FOR EGF-INDUCED MITOGENESIS

Rac, a member of the Rho family GTPases, has been implicated in the re gulation of a wide range of biological processes including actin remod eling, cell transformation, G1 cell cycle progression, and gene expres sion. To determine whether Rac GTPase activity is required for epiderm al growth factor-induced mitogenesis, Rat-2 stable cells expressing a dominant-negative Rac1 mutant, RacN17, were prepared, Exposure to EGF exhibited a significantly restricted growth response in Rat-2cRacN17 c ells compared to Rat-2 parental cells, suggesting an essential role of Rac in EGF-induced mitogenesis. In contrast, addition of lysophosphat idic acid exerted the same level of growth in Rat-2 and Rat-2-RacN17 c ells. To gain further evidence for the essential role of Rac in EGF-in duced mitogenesis, we performed the microinjection experiment. EGF-ind uced DNA synthesis was significantly blocked by microinjection of reco mbinant RacN17 protein, and not control IgG, Our further study to anal yze the downstream mediator of Rac in EGF-signaling to mitogenesis dem onstrated that Rac-activated phospholipase A, plays a critical role. T aken together, our results suggest that the ''Rac and Rac-activated PL A(2)'' cascade is one of the major mitogenic pathways induced by EGF.