Gα12 Stimulates c-Jun NH2-terminal Kinase through the Small G Proteins Ras and Rac

doi:10.1074/jbc.271.29.17349

Gα₁₂ Stimulates c-Jun NH₂-terminal Kinase through the Small G Proteins Ras and Rac*

From the Department of Pharmacology, University of California at San Diego, La Jolla, California 92093-0636

^¶ To whom correspondence should be addressed:
Dept. of Pharmacology 9500 Gilman Dr., La Jolla, CA 92093-0636.

Abstract

The pertussis toxin (PTX) insensitive heterotrimeric G protein G₁₂ has been implicated in mitogenesis and transformation, but its direct effectors remain unknown. To define potential signaling pathways utilized by G₁₂, we expressed an activated mutant of its α subunit, Gα₁₂(Q229L), in HEK293 cells and examined its effects on Ras and mitogen-activated protein kinases (MAPKs). Transient expression of activated Gα₁₂ increased the percentage of Ras in the active, GTP-bound state, stimulated c-Jun NH₂-terminal kinase (JNK) activity, and enhanced the transcriptional activity of c-Jun. Dominant negative Ras (N17Ras) inhibited Gα₁₂-mediated JNK activation in NIH3T3 cells but failed to do so in HEK293 cells. In contrast, dominant negative Rac (N17Rac1) inhibited JNK activation by Gα₁₂ in HEK293 cells as well as three other cell lines. In 1321N1 cells, where thrombin stimulates G₁₂-dependent mitogenesis, coexpression of N17Rac1 or a dominant negative mutant of MEKK1 (MEKKΔ(K432M)) inhibits c-Jun/AP-1 sensitive reporter gene expression stimulated by thrombin or Gα₁₂. These data demonstrate that the α subunit of the heterotrimeric G protein G₁₂, like tyrosine kinase growth factor receptors, activates Ras and recruits a signal transduction pathway involving the small GTP-binding protein Rac that leads to JNK activation.

Footnotes

↵^‡ Supported by National Institutes of Health Predoctoral Fellowship GM17277. Work was in partial fulfillment of the Ph.D. degree in the Biomedical Sciences Graduate Program.
↵^§ Supported by National Institutes of Health Postdoctoral Fellowship F32CA65105.
↵* This work was supported in part by National Institutes of Health Grants GM36927 (to J. H. B.) and HL35018 (to M. K.). The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

JNK

c-Jun NH₂-terminal kinase

MAPK

mitogen-activated protein kinase

ERK

extracellular signal-regulated kinase

mAChR

muscarinic acetylcholine receptor

PTX

pertussis toxin

PAGE

polyacrylamide gel electrophoresis

HA

hemagglutinin

GST

glutathione S-transferase.
- Received March 27, 1996.
- Revision received May 3, 1996.