Ras Activation Is Necessary for Integrin-mediated Activation of Extracellular Signal-regulated Kinase 2 and Cytosolic Phospholipase A2 but Not for Cytoskeletal Organization

doi:10.1074/jbc.271.25.14814

Ras Activation Is Necessary for Integrin-mediated Activation of Extracellular Signal-regulated Kinase 2 and Cytosolic Phospholipase A₂ but Not for Cytoskeletal Organization*

From the Howard Hughes Medical Institute, Center for Cancer Research, and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

^§ Investigator of the Howard Hughes Medical Institute. To whom correspondence should be addressed. Tel.: 617-253-6422; Fax: 617-253-8357.

Abstract

Cell adhesion to the extracellular matrix triggers a cascade of intracellular biochemical signals regulated by the integrin family of receptors. Recent evidence suggests that integrin engagement may activate a mitogen-activated protein (MAP) kinase cascade that may cooperate with more clearly defined mitogenic signaling pathways to regulate cell proliferation, adhesion, and migration. Here we report that the adhesion-dependent activation of the MAP kinase Erk2 (extracellular signal-regulated kinase 2) occurs in serum-starved NIH3T3 cells, and that this activation of Erk2 is preceded by the activation of the small GTP-binding protein Ras in fibronectin-adherent cells. Inhibition of Ras signaling by expression of a dominant-inhibitory mutant of Ras (N17Ras) in NIH3T3 cells blocked adhesion-dependent activation of Erk2, although the focal adhesion kinase (FAK) was still activated in these cells. Furthermore, activation of this Ras-MAP kinase pathway activated cytosolic phospholipase A₂, leading to the release of arachidonic acid metabolites, and N17Ras also inhibited these events. However, N17Ras expression does not inhibit cell adhesion, spreading, or focal contact and stress fiber formation. These results suggest that, while integrin-dependent activation of this MAP kinase pathway is Ras-dependent, the integrin-dependent activation of FAK and several morphological events are Ras-independent. Thus, integrin-mediated signals involved in regulating cell morphology appear to diverge from those regulating MAP kinase activation at a level upstream of Ras activation.

Footnotes

↵^‡ Associate of the Howard Hughes Medical Institute.
↵* This work was supported in part by Grant RO1CA17007 from NCI, National Institutes of Health, and grants from the Howard Hughes Medical Institute. 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:

ECM

extracellular matrix

MAP

mitogen-activated protein

Erk2

extracellular signal-regulated kinase 2

FAK

focal adhesion kinase

cPLA₂

cytosolic phospholipase A₂

DMEM

Dulbecco's modified Eagle's medium

RIPA

radioimmunoprecipitation assay

PBS

phosphate-buffered saline

PDGF

platelet-derived growth factor.
- Received March 19, 1996.
- Revision received April 23, 1996.