Protein Kinase C δ Activates the MEK-ERK Pathway in a Manner Independent of Ras and Dependent on Raf

doi:10.1074/jbc.271.38.23512

Protein Kinase C δ Activates the MEK-ERK Pathway in a Manner Independent of Ras and Dependent on Raf*

From the Department of Molecular Biology, Yokohama City University School of Medicine, 3-9, Fuku-ura, Kanazawa-ku, Yokohama 236, Japan

^§ To whom correspondence should be addressed. Tel.: 81-45-787-2596; Fax: 81-45-785-4140; E-mail: ohnos{at}med.yokohama-cu.ac.jp

Abstract

Although the involvement of protein kinase C (PKC) in the activation of the mitogen-activated protein (MAP) kinase pathway has been implicated through experiments using 12-O-tetradecanoylphorbol-13-acetate (TPA), there has been no direct demonstration that PKC activates the MAP kinase pathway. A Raf-dependent intact cell assay system for monitoring the activation of MAPK/ERK kinase (MEK) and extracellular signal-related kinase (ERK) permitted us to evaluate the role of PKC isotypes in MAP kinase activation. Treatment of cells with TPA or epidermal growth factor resulted in the activation of MEK and ERK. The activation of the MAP kinase pathway triggered by epidermal growth factor was completely inhibited by dominant-negative Ras (RasN17), whereas the activation triggered by TPA was not, consistent with previous observations. The introduction of an activated point mutant of PKCδ, but not PKCα or PKCϵ, resulted in the activation of the MAP kinase pathway. The activation of MEK and ERK by an activated form of PKCδ requires the presence of c-Raf and is independent of RasN17. These results demonstrate that activation of PKCδ is sufficient for the activation of MEK and ERK and that the pathway operates in a manner dependent on c-Raf and independent of Ras.

Footnotes

↵^‡ Present address: Department of Cell Biology, Vanderbilt University School of Medicine, Nashville, TN 37232.
↵* This work was supported, in part, by research grants from the Ministry of Education, Science, Sports and Culture of Japan, The Cell Science Research Foundation, and the Uehara Memorial Foundation. 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:

MAP

mitogen-activated protein

ERK

extracellular signal-regulated kinase

MEK

MAPK/ERK kinase

EGF

epidermal growth factor

PKC

protein kinase C

TPA

12-O-tetradecanoylphorbol 13-acetate

MBP

myelin basic protein

DMEM

Dulbecco's modified Eagle's medium

GST

glutathione S-transferase

TRE

TPA response element

CAT

chloramphenicol acetyltransferase.
- Received May 6, 1996.
- Revision received June 25, 1996.