Syndecan-4 Proteoglycan Regulates the Distribution and Activity of Protein Kinase C

doi:10.1074/jbc.272.13.8133

Syndecan-4 Proteoglycan Regulates the Distribution and Activity of Protein Kinase C*

From the Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294

^‡ To whom correspondence should be addressed:
Dept. of Cell Biology, Volker Hall 203A, University of Alabama at Birmingham, Birmingham, AL 35294-0019.
Tel.: 205-934-2626; Fax: 205-975-9956; E-mail: awoods{at}cellbio.bhs.uab.edu

Abstract

During cell-matrix adhesion, both tyrosine and serine/threonine kinases are activated. Integrin ligation correlates with tyrosine phosphorylation, whereas the later stages of spreading and focal adhesion and stress fiber formation in primary fibroblasts requires interactions of cell surface proteoglycan with heparin-binding moieties. This correlates with protein kinase C (PKC) activation, and PKCα can become localized to focal adhesions in normal, but not transformed, cells. PKC activation has been thought to be downstream of initial receptor-ligand interactions. We now show, however, that syndecan-4 transmembrane heparan sulfate proteoglycan and PKC co-immunoprecipitate and co-patch in vivo. The core protein of syndecan-4 can directly bind the catalytic domain of PKCα and potentiate its activation by phospholipid mediators. It can also directly activate PKCα in the absence of other mediators. This activity resides in the sequence LGKKPIYKK in the center of the short cytoplasmic domain, and other syndecans lack this sequence and PKC regulatory properties. Syndecan-4 is a focal adhesion component, and this interaction may both localize PKC and amplify its activity at sites of forming adhesions. This represents the first report of direct transmembrane signaling through cell surface proteoglycans.

Footnotes

↵* This work was supported in part by National Institutes of Health Grant GM50194 and the Cell Adhesion and Matrix Research Center at University of Alabama at Birmingham. 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:

PKC

protein kinase C

PKM

protein kinase M

DL

diolein

GST

glutathione S-transferase

PL

phospholipid

PMA

phorbol 12-myristate 13-acetate

PS

phosphatidylserine

REF

rat embryo fibroblasts; PAGE, polyacrylamide gel electrophoresis.
↵²A. Woods, R. L. Longley, A. Fleetwood, G. Cowling, J. T. Gallagher, and J. R. Couchman, manuscript in preparation.
- Received January 24, 1997.