Syndecan-4 regulates localization, activity and stability of protein kinase C-α

Eunyoung Keum, Yeonhee Kim, Jungyean Kim, Soojin Kwon, Yangmi Lim, Innoc Han, Eok Soo Oh

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72 Scopus citations


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-α (protein kinase C-α) 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-α 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-α. Overexpression of syndecan-4, but not a mutant lacking its cytoplasmic domain, specifically increased the level of endogenous PKC-α and enhanced the translocation of PKC-α into both detergent-insoluble and membrane fractions. In addition, rat embryo fibroblasts overexpressing syndecan-4 exhibited a slowed down-regulation of PKC-α in response either to a prolonged treatment with PMA or to maintaining cells in suspension culture. PKC-α immunocomplex kinase assays also showed that syndecan-4 overexpression increased the activity of membrane PKC-α. Taken together, these results suggest that syndecan-4 interacts with PKC-α in vivo and regulates its locali-zation, activity and stability.

Original languageEnglish
Pages (from-to)1007-1014
Number of pages8
JournalBiochemical Journal
Issue number3
StatePublished - 15 Mar 2004


  • Activation
  • Cytoplasmic domain
  • Fibroblast growth factor (FGF)
  • Membrane localization
  • Protein kinase C
  • Syndecan-4


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