G-protein -Subunits Activate Mitogen-activated Protein Kinase via a Novel Protein Kinase C-dependent Mechanism

doi:10.1074/jbc.271.3.1266

G-protein -Subunits Activate Mitogen-activated Protein Kinase via a Novel Protein Kinase C-dependent Mechanism (*)

From the (1)Howard Hughes Medical Institute, Departments of Medicine, Biochemistry, and
Surgery, Duke University Medical Center, Durham, North Carolina 27710 and
(2)Medical Service, Veterans Administration Medical Center, Durham, North Carolina 27710

^§§ To whom correspondence should be addressed:
Howard Hughes Medical Inst., Box 3821, Duke University Medical Center, Durham, NC 27710
.

Abstract

Mitogen-activated protein kinase (MAPK) is activated in response to both receptor tyrosine kinases and G-protein-coupled receptors. Recently, G-coupled receptors, such as the α adrenergic receptor, were shown to mediate Ras-dependent MAPK activation via a pathway requiring G-protein β subunits (G) and many of the same intermediates involved in receptor tyrosine kinase signaling. In contrast, G-coupled receptors, such as the M muscarinic acetylcholine receptor (MAChR), activate MAPK via a pathway that is Ras-independent but requires the activity of protein kinase C (PKC). Here we show that, in Chinese hamster ovary cells, the MAChR and platelet-activating factor receptor (PAFR) mediate MAPK activation via the α-subunit of the G protein. G-mediated MAPK activation was sensitive to treatment with pertussis toxin but insensitive to inhibition by a G-sequestering peptide (βARK1ct). MAChR and PAFR catalyzed G α-subunit GTP exchange, and MAPK activation could be partially rescued by a pertussis toxin-insensitive mutant of G but not by similar mutants of G. G-mediated MAPK activation was insensitive to inhibition by a dominant negative mutant of Ras (N17Ras) but was completely blocked by cellular depletion of PKC. Thus, MAChR and PAFR, which have previously been shown to couple to G, are also coupled to G to activate a novel PKC-dependent mitogenic signaling pathway.

Footnotes

↵^§ Recipient of a postdoctoral award from the Alberta Heritage Foundation for Medical Research.
↵^¶ Supported by a grant from the Department of Veterans Affairs and by United States Public Health Service Grant NS30927.
↵** Recipient of a National Institutes of Health clinical investigator development award.
↵* This work was supported in part by Grant HL16037 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

MAPK

mitogen-activated protein kinase

RTK

receptor tyrosine kinase

GPCR

G-protein-coupled receptor

αAR

α adrenergic receptor

PTX

pertussis toxin

MAChR

M muscarinic acetylcholine receptor

PAF

platelet-activating factor

PAFR

platelet-activating factor receptor

αAR

α adrenergic receptor

PKC

protein kinase C

CHO

Chinese hamster ovary

PMA

phorbol 12-myristate 13-acetate

MBP

myelin basic protein.
↵²T. van Biesen, B. E. Hawes, J. R. Raymond, L. M. Luttrell, W. J. Koch, and R. J. Lefkowitz, unpublished observations.
- Received September 18, 1995.
- Revision received November 13, 1995.