Protein Kinase Cδ Activation by Interleukin-1β Stabilizes Inducible Nitric-oxide Synthase mRNA in Pancreatic β-Cells

Exposure of pancreatic islets to cytokines such as interleukin (IL)-1β induces a variety of proinflammatory genes including type II nitric-oxide synthase (iNOS) which produces nitric oxide (NO). NO is thought to be a major cause of islet β-cell dysfunction and apoptotic β-cell death, which results in type I diabetes. Since protein kinase C (PKC) mediates some of the actions of cytokines in other cell types, our aim was to assess the role of PKC in IL-1β-induced iNOS expression in pancreatic β-cells. PKCδ, but not PKCα, was specifically activated in the rat INS-1 β-cell line by IL-1β as assessed by membrane translocation. Moreover, iNOS expression and NO production were significantly attenuated by the PKCδ specific inhibitor rottlerin and overexpression of a PKCδ kinase-dead mutant protein. Conversely, overexpression of PKCδ wild type protein significantly potentiated this response. These results were confirmed at the mRNA level by reverse transcriptase-polymerase chain reaction. However, a role at the level of transcriptional regulation appeared unlikely, since PKCδ was not required for the activation of NF-κB, activating protein 1, and activating transcription factor 2 signaling pathways in response to IL-1β. There was, however, a significant increase in iNOS mRNA stability mediated by PKCδ wild type, while PKCδ kinase-dead acted reciprocally, reducing iNOS mRNA stability. The results indicate that, in addition to transcriptional activation, mRNA stabilization is a key component of the mechanism by which IL-1β stimulates iNOS expression in β-cells and that PKCδ plays an essential role in this process. PKCδ activation may therefore have significant consequences with regard to cellular function and viability when β-cells are exposed to IL-1β and potentially other cytokines.