Multimerization of the Cytoplasmic Domain of Syndecan-4 Is Required for Its Ability to Activate Protein Kinase C*
- From the Department of Cell Biology and the Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294
Abstract
The transmembrane proteoglycan syndecan-4, which is a coreceptor with integrins in cytoskeleton-matrix interactions, appears to be multimerized in vivo. Both purified and recombinant core proteins form sodium dodecyl sulfate-resistant oligomers, and we now report that a synthetic peptide corresponding to the central region of syndecan-4 cytoplasmic domain (4V) also oligomerizes. The degree of oligomerization correlates with the previously reported ability to bind protein kinase C (PKC) and regulate its activity. Only multimeric recombinant syndecan-4 core protein, but not the monomeric protein, potentiated the activity of PKCα, and only oligomeric syndecan-4 cytoplasmic peptides were active. Changes in peptide sequence caused parallel loss of stable oligomeric status and ability to regulate a mixture of PKCαβγ activity. A synthetic peptide encompassing the whole cytoplasmic domain of syndecan-4 (4L) containing a membrane-proximal basic sequence did not form higher order oligomers and could not regulate the activity of PKCαβγ unless induced to aggregate by phosphatidylinositol 4,5-bisphosphate. Oligomerization and PKC regulatory activity of the 4V peptide were both increased by addition of N-terminal cysteine and reduced by phosphorylation of the cysteine thiol group. Concentration of syndecan-4 at sites of focal adhesion formation may enhance multimerization and both localize PKC and potentiate its activity to induce stable complex formation.
Footnotes
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↵* This work was supported by National Institutes of Health Grant GM50194.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.
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↵‡ To whom correspondence should be addressed: Dept. of Cell Biology, Cell Adhesion and Matrix Research Center, Volker Hall 201C, University of Alabama at Birmingham, Birmingham, AL 35294-0019. Tel.: 205-934-2626; Fax: 205-975-9956; E-mail:jrcouchman{at}cellbio.bhs.uab.edu.
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↵1 The abbreviation used are: PKC, protein kinase C; GST, glutathione S-transferase; PL, phospholipid; PIP2, phosphatidylinositol 4,5-bisphosphate; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate; PAGE, polyacrylamide gel electrophoresis.
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↵2 The mass spectrometer was purchased (National Institutes of Health Grant S10RR06487) and operated by the Comprehensive Cancer Center Mass Spectrometry Shared Facility, University of Alabama at Birmingham (supported in part by National Cancer Institute Grant P30CA13148).
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↵3 J. R. Couchman, A. Woods, E.-S. Oh, A. Theibert, and G. Prestwich, unpublished data.
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↵4 E.-S. Oh, A. Woods, and J. R. Couchman, unpublished data.
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- Received February 14, 1997.
