Protein kinase C delta (PKC?) affects proliferation of insulin-secreting cells by promoting nuclear extrusion of the cell cycle inhibitor p21Cip1/WAF1.

ABSTRACT:

Background

High fat diet-induced hyperglycemia and palmitate-stimulated apoptosis was prevented by specific inhibition of protein kinase C delta (PKC?) in ?-cells. To understand the role of PKC? in more detail the impact of changes in PKC? activity on proliferation and survival of insulin-secreting cells was analyzed under stress-free conditions.

Methodology and principal findings

Using genetic and pharmacological approaches, the effect of reduced and increased PKC? activity on proliferation, apoptosis and cell cycle regulation of insulin secreting cells was examined. Proteins were analyzed by Western blotting and by confocal laser scanning microscopy. Increased expression of wild type PKC? (PKC?WT) significantly stimulated proliferation of INS-1E cells with concomitant reduced expression and cytosolic retraction of the cell cycle inhibitor p21(Cip1/WAF1). This nuclear extrusion was mediated by PKC?-dependent phosphorylation of p21(Cip1/WAF1) at Ser146. In kinase dead PKC? (PKC?KN) overexpressing cells and after inhibition of endogenous PKC? activity by rottlerin or RNA interference phosphorylation of p21(Cip1/WAF1) was reduced, which favored its nuclear accumulation and apoptotic cell death of INS-1E cells. Human and mouse islet cells express p21(Cip1/WAF1) with strong nuclear accumulation, while in islet cells of PKC?WT transgenic mice the inhibitor resides cytosolic.

Conclusions and significance

These observations disclose PKC? as negative regulator of p21(Cip1/WAF1), which facilitates proliferation of insulin secreting cells under stress-free conditions and suggest that additional stress-induced changes push PKC? into its known pro-apoptotic role.

SUBMITTER: Ranta F 

PROVIDER: S-EPMC3246440 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature