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)-1 beta induces a variety of proinflammatory genes including type II nitric-oxide synthase (MOS) which produces nitric oxide (NO). NO is thought to be a major cause of islet beta -cell dysfunction and apoptotic beta -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-1 beta -induced iNOS expression in pancreatic beta -cells. PKC delta, but not PKC alpha, was specifically activated in the rat INS-1 beta -cell line by IL-1 beta as assessed by membrane translocation. Moreover, MOS expression and NO production were significantly attenuated by the PKC delta specific inhibitor rottlerin and overexpression of a PKC delta kinase-dead mutant protein. Conversely, overexpression of PKC delta 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 PKC delta was not required for the activation of NF-kappaB, activating protein 1, and activating transcription factor 2 signaling pathways in response to IL-1 beta. There was, however, a significant increase in MOS mRNA stability mediated by PKC delta wild type, while PKC delta kinase-dead acted reciprocally, reducing MOS mRNA stability. The results indicate that, in addition to transcriptional activation, mRNA stabilization is a key component of the mechanism by which IL-1 beta stimulates MOS expression in beta -cells and that PKC delta plays an essential role in this process. PKC delta activation may therefore have significant consequences with regard to cellular function and viability when beta -cells are exposed to IL-1 beta and potentially other cytokines.