title: Constitutive phosphorylation of a Rac GAP MgcRacGAP is implicated in v-Src-induced transformation of NIH3T3 cells.
abstract: MgcRacGAP plays critical roles in cell division through regulating Rho family small GTPases. As we previously reported, phosphorylation of MgcRacGAP on serine 387 (S387) is induced by Aurora B kinase at the midbody during cytokinesis, which is a critical step of cytokinesis. Phosphorylation of S387-MgcRacGAP converts it from RacGAP to RhoGAP, leading to completion of cytokinesis. Here we show that MgcRacGAP is prominently phosphorylated on S387 even in the interphase of v-Src-transformed NIH3T3 cells in the cytoplasm, but not in the interphase of parental NIH3T3 or H-RasV12-transformed NIH3T3 cells. Interestingly, levels of phosphorylation on S387 (pS387) correlated with soft agar colony-forming abilities of v-Src-transformed NIH3T3 cells. Expression of a phosphorylation-mimic mutant MgcRacGAP-S387D enhanced colony formation of v-Src-transformed NIH3T3 cells. Surprisingly, a Rac1 inhibitor but not kinase inhibitors including Aurora B kinase inhibitor specifically inhibited phosphorylation of S387-MgcRacGAP in v-Src-transformed NIH3T3 cells, suggesting the v-Src-induced pathological positive feedback mechanisms towards Rac1 activation using pS387-MgcRacGAP. These results indicated the difference in the mechanisms between v-Src- and H-RasV12-induced transformation, and should shed some light on pathological roles of disordered phosphorylation of MgcRacGAP at S387 in v-Src-induced cell transformation.
authors: Division of Cellular Therapy, The Institute of Medical Science, University of Tokyo, Minato-ku, Tokyo, Japan.
authors: Noriko
authors: N
authors: Doki
authors: Toshiyuki
authors: T
authors: Kawashima
authors: Yasushi
authors: Y
authors: Nomura
authors: Akiho
authors: A
authors: Tsuchiya
authors: Chitose
authors: C
authors: Oneyama
authors: Tsuyoshi
authors: T
authors: Akagi
authors: Yoshihisa
authors: Y
authors: Nojima
authors: Toshio
authors: T
authors: Kitamura
mesh_terms: D000634:Aminoquinolines / Q000494:pharmacology; D000818:Animals; D064107:Aurora Kinase B; D064127:Aurora Kinases; D015153:Blotting, Western; D002471:Cell Transformation, Neoplastic; D003114:Colony-Forming Units Assay; D020690:GTPase-Activating Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D015688:Oncogene Protein pp60(v-src) / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
chemical_list: D000634:Aminoquinolines; D020690:GTPase-Activating Proteins; C487513:NSC 23766; D011743:Pyrimidines; C115995:mgcRacGAP; D015688:Oncogene Protein pp60(v-src); C576924:Aurkb protein, mouse; D064107:Aurora Kinase B; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases; D020830:rac1 GTP-Binding Protein