p120 GAP modulates Ras activation of Jun kinases and transformation.
Although recent evidence demonstrates that Ras causes transformation by activation of multiple downstream pathways, the specific role of non-Raf effector pathways is presently unknown. Although Ras causes activation of the Jun NH2-terminal kinases (JNKs) via a Raf-independent pathway, the contribution of JNK activation to Ras transformation and the effector that mediates JNK activation have not been established. We observed that a dominant negative mutant of SEK1/JNKK, an activator of JNKs, selectively inhibited oncogenic Ras activation of JNK and Ras transformation, but not Ras activation of the p42 mitogen-activated protein kinase. In contrast, overexpression of wild type SEK1 enhanced Ras activation of JNK and transforming activity. Thus, JNK activation promotes Ras transformation. Furthermore, a dominant negative mutant of p120 GAP (designated N-GAP), a candidate Ras effector, blocked Ras, but not Raf, transformation and blocked Ras, but not Rac, activation of JNK. Since N-GAP overexpression reduced the association of p190 Rac/Rho GAP with endogenous p120 GAP, N-GAP may form nonproductive complexes with components critical for p120 GAP function. In summary, p120 GAP may function as an effector for Ras activation of JNK and Ras transformation.
Clark
G J
GJ
Department of Pharmacology, University of North Carolina, and The Lineberger Comprehensive Cancer Center, Chapel Hill, North Carolina 27599, USA.
Westwick
J K
JK
Der
C J
CJ
D016475:3T3 Cells; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D004789:Enzyme Activation; D020690:GTPase-Activating Proteins; D048031:JNK Mitogen-Activated Protein Kinases; D051379:Mice; D020928:Mitogen-Activated Protein Kinases; D015689:Oncogene Protein p21(ras) / Q000037:antagonists & inhibitors; D011506:Proteins / Q000378:metabolism*; D020703:ras GTPase-Activating Proteins
D020690:GTPase-Activating Proteins; D011506:Proteins; D020703:ras GTPase-Activating Proteins; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D015689:Oncogene Protein p21(ras)