The Proto-oncogene Product p120cbl Links c-Src and Phosphatidylinositol 3′-Kinase to the Integrin Signaling Pathway

doi:10.1074/jbc.272.6.3780

The Proto-oncogene Product p120^cbl Links c-Src and Phosphatidylinositol 3′-Kinase to the Integrin Signaling Pathway*

^‡ La Jolla Cancer Research Center, The Burnham Institute, La Jolla, California 92037 and the
^§ Division of Endocrinology and Metabolism, Department of Medicine, University of California at San Diego, La Jolla, California 92093

^| To whom correspondence should be addressed:
La Jolla Cancer Research Center, The Burnham Inst., 10901 N. Torrey Pines Rd., La Jolla, CA 92037.
Tel.: 619-646-3100; Fax: 619-646-3199; E-mail: kvuori{at}ljcrf.edu

Abstract

Integrin-mediated cell adhesion triggers intracellular signaling cascades, including tyrosine phosphorylation of intracellular proteins. We show in this report that p120^cbl (Cbl), the 120-kDa c-cbl proto-oncogene product, becomes tyrosine-phosphorylated during integrin-mediated macrophage cell adhesion to extracellular matrix substrata and anti-integrin antibodies. This tyrosine phosphorylation does not occur when cells attach to polylysine, to which cells adhere in a nonspecific fashion. It also does not take place when adhesion-induced reorganization of the cytoskeleton is inhibited with cytochalasin D. In contrast to the rapid and transient tyrosine phosphorylation of Cbl by CSF-1 stimulation, tyrosine phosphorylation of Cbl by cell attachment was gradual and persistent. Tyrosine-phosphorylated Cbl was found to form complexes with the SH2 domain-containing signaling proteins Src and phosphatidylinositol 3-kinase; in vitro kinase assays demonstrated that these kinases were active in the Cbl complexes following integrin ligand binding. Furthermore, Cbl was found to translocate to the plasma membrane in response to cell adhesion to fibronectin. These observations suggest that Cbl serves as a docking protein and may transduce signals to downstream signaling pathways following integrin-mediated cell adhesion in macrophages.

Footnotes

↵^¶ Recipient of a postdoctoral fellowship from the Associazione Italiana per la Ricerca sul Cancro.
↵* This work was supported in part by the Finnish Academy of Sciences and by National Institutes of Health Grants CA71560 (to K. V.) and DK33651 (to J. M. O). 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

FAK

focal adhesion kinase

PI

phosphatidylinositol

RIPA

radioimmune precipitation assay

GST

glutathione S-transferase

Pipes

1,4-piperazinediethanesulfonic acid

PAGE

polyacrylamide gel electrophoresis.
- Received July 22, 1996.
- Revision received October 11, 1996.