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Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes
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Dual involvement of protein kinase C delta in apoptosis induced by syndecan-2 in osteoblasts

Armelle Orosco1, Olivia Fromigué, Eric Haÿ

  • 1Laboratory of Osteoblast Biology and Pathology, INSERM, Lariboisière Hospital, University Paris 7, Paris, France.

Journal of Cellular Biochemistry
|January 28, 2006
PubMed

Insights

Syndecan-2 (SYND2) regulates osteoblastic cell apoptosis by modulating protein kinase C delta (PKCdelta). SYND2 decreases PKCdelta activity, promoting osteoblast survival, but also increases PKCdelta levels, which can induce apoptosis.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Syndecans are proteoglycans involved in cell signaling.
  • Syndecan-2 (SYND2) has been previously linked to osteoblastic (OB) cell apoptosis.
  • The precise mechanisms by which SYND2 influences OB cell fate remain under investigation.

Purpose of the Study:

  • To elucidate the novel functional interaction between syndecan-2 (SYND2) and protein kinase C delta (PKCdelta) in osteoblasts.
  • To determine the role of PKCdelta in SYND2-mediated osteoblastic cell apoptosis.
  • To understand how SYND2 modulates PKCdelta activity and its downstream effects.

Main Methods:

  • Overexpression of SYND2 in MG63 OB cells.
  • Analysis of PKCdelta protein and mRNA levels.
  • Assessment of PKCdelta subcellular localization and phosphorylation status.
  • In vitro kinase assays using histone as a substrate.
  • Inhibition of PKCdelta using Rottlerin or dominant-negative constructs.
  • Rescue experiments with PKCdelta catalytic domain (CAT) construct.
  • siRNA-mediated knockdown of PKCdelta.

Main Results:

  • SYND2 overexpression increased cytosolic PKCdelta protein levels without altering mRNA.
  • SYND2 reduced PKCdelta activity by decreasing phosphorylation at threonine 505.
  • PKCdelta acts as a pro-survival kinase; its inhibition increased OB cell apoptosis.
  • SYND2-induced apoptosis was dependent on PKCdelta accumulation and required PKCdelta's pro-apoptotic function.
  • Overexpression of wild-type PKCdelta induced osteoblast apoptosis.

Conclusions:

  • SYND2 inhibits the anti-apoptotic function of PKCdelta through modulation of its activity.
  • SYND2 promotes osteoblast apoptosis by increasing PKCdelta protein levels, potentially activating a pro-apoptotic pathway.
  • A complex interplay exists where SYND2 can both inhibit PKCdelta activity and promote its pro-apoptotic role, depending on cellular context and protein levels.

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