Regulation of Extracellular Signal-regulated Kinase Activity by p120 RasGAP Does Not Involve Its Pleckstrin Homology or Calcium-dependent Lipid Binding Domains but Does Require These Domains to Regulate Cell Proliferation

The gene encoding for p120 RasGAP, has been disrupted in mice (M. Henkemeyer et al., Nature (Lond.), 377: 695–701, 1995).In this study, using fibroblasts derived from these mouse embryos (Gap / ; P. van der Geer et al., Mol. Cell Biol., 17: 1840 –1847, 1997), we demonstrate that mitogenactivated protein kinase (MAPK) activation is prolonged after epidermal growth factor (EGF), but not lysophosphatidic acid, stimulation as compared with wild-type cells. Furthermore, these cells exhibited a moderate increase in their proliferative rate and saturation density, as well as a limited ability to form colonies in soft agar. Stable cell lines expressing fulllength p120 GAP not only restored the ability to downregulate MAPK after EGF stimulation but also lowered their saturation densities. Similarly, expression of p120 GAP , missing either its pleckstrin homology (PH) or its calcium-dependent lipid binding (CaLB)/C2 domain, restored MAPK down-regulation and retained the ability to associate with p190 RhoGAP and to be phosphorylated by v-src but exhibited higher saturation densities similar to Gap / cells. Our results, therefore, suggest that p120 GAP functions not only by down