Syndecan-4 regulates localization, activity and stability of protein kinase C-alpha.
During cell-matrix adhesion, syndecan-4 transmembrane heparan sulphate proteoglycan plays a critical role in the formation of focal adhesions and stress fibres. We have shown previously that the syndecan-4 cytoplasmic domain directly binds to and activates PKC-alpha (protein kinase C-alpha) in vitro [Oh, Woods and Couchman (1997) J. Biol. Chem. 272, 8133-8136]. However, whether syndecan-4 has the same activity in vivo needs to be addressed. Using mammalian two-hybrid assays, we showed that syndecan-4 interacted with PKC-alpha in vivo and that this interaction was mediated through syndecan-4 cytoplasmic domain. Furthermore, the activation of PKC increased the extent of interaction between syndecan-4 and PKC-alpha. Overexpression of syndecan-4, but not a mutant lacking its cytoplasmic domain, specifically increased the level of endogenous PKC-alpha and enhanced the translocation of PKC-alpha into both detergent-insoluble and membrane fractions. In addition, rat embryo fibroblasts overexpressing syndecan-4 exhibited a slowed down-regulation of PKC-alpha in response either to a prolonged treatment with PMA or to maintaining cells in suspension culture. PKC-alpha immunocomplex kinase assays also showed that syndecan-4 overexpression increased the activity of membrane PKC-alpha. Taken together, these results suggest that syndecan-4 interacts with PKC-alpha in vivo and regulates its localization, activity and stability.
Keum
Eunyoung
E
Department of Life Sciences, Division of Molecular Life Sciences and Center for Cell Signaling Research, Ewha Womans University, Daehyun-dong, Seodaemoon-Gu, Seoul 120-750, South Korea.
Kim
Yeonhee
Y
Kim
Jungyean
J
Kwon
Soojin
S
Lim
Yangmi
Y
Han
Innoc
I
Oh
Eok-Soo
ES
D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000201:enzymology; D004795:Enzyme Stability; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D005347:Fibroblasts / Q000201:enzymology; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D011493:Protein Kinase C / Q000032:analysis* / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D011509:Proteoglycans / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D053671:Syndecan-4
D007527:Isoenzymes; D008562:Membrane Glycoproteins; D011509:Proteoglycans; C508304:SDC4 protein, human; C508307:Sdc4 protein, rat; D053671:Syndecan-4; D016222:Fibroblast Growth Factor 2; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha