Integrins Enhance Platelet-derived Growth Factor (PDGF)-dependent Responses by Altering the Signal Relay Enzymes That Are Recruited to the PDGF β Receptor

doi:10.1074/jbc.274.28.19551

Integrins Enhance Platelet-derived Growth Factor (PDGF)-dependent Responses by Altering the Signal Relay Enzymes That Are Recruited to the PDGF β Receptor*

From the ^‡Schepens Eye Research Institute, Harvard Medical School, Boston, Massachusetts 02114 and ^§University of Colorado Health Sciences Center, Department of Pharmacology, Denver, Colorado 80262

Abstract

Since the extracellular matrix (ECM) can promote platelet-derived growth factor (PDGF)-dependent responses, we hypothesized that the ECM mediates this effect by preventing the PDGF β receptor (βPDGFR) from associating with the negative regulator, RasGAP (the GTPase-activating protein of Ras). We found that binding of RasGAP to the wild-type βPDGFR was decreased; the activation of Ras and Erk was enhanced, and [³H]thymidine uptake was better in cells cultured on fibronectin than in cells cultured on polylysine. To investigate the mechanism by which culturing cells on fibronectin diminished the recruitment of RasGAP to the βPDGFR, we focused on SHP-2 since it dephosphorylates the βPDGFR at the phosphotyrosine required for binding of RasGAP. Culturing cells on fibronectin increased the amount of SHP-2 that associated with the βPDGFR. Furthermore, cells expressing receptor mutants that failed to associate with SHP-2 were insensitive to fibronectin. The ECM enhances PDGF-dependent responses by increasing the association of SHP-2 with the βPDGFR, which in turn decreases the time that RasGAP interacts with the receptor. Thus, fibronectin changes PDGF-dependent signaling and biological responses by altering the signal relay enzymes that are recruited to the receptor.

Footnotes

↵* This work was supported by National Institutes of Health Grant GM48339.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.
↵¶ To whom correspondence should be addressed: Schepens Eye Research Institute, Harvard Medical School, 20 Staniford St., Boston, MA 02114. Tel.: 617-912-2517; Fax: 617-912-0128; E-mail: kazlauskas@vision.eri.harvard.edu.
↵2 Jones, S. M., Klinghoffer, R., Prestwich, G. D., Toker, A., and Kazlauskas, A. (1999) Curr. Biol. 9,512–521.
Abbreviations:

PDGF

platelet-derived growth factor

PDGFR

platelet-derived growth factor receptor

ECM

extracellular matrix

DME

Dulbecco’s modified Eagle’s

PI3K

phosphatidylinositol 3-kinase

RasGAP

GTPase-activating protein of Ras

PLCγ

phospholipase Cγ1

WT

wild type

GST

glutathione S-transferase

PAGE

polyacrylamide gel electrophoresis

BSA

bovine serum albumin

FBS

fetal bovine serum

PBS

phosphate-buffered saline
- Received February 8, 1999.
- Revision received March 25, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.