TYROSINE KINASE INVOLVEMENT IN IL-1-BETA-INDUCED EXPRESSION OF INOS BY BETA-CELLS PURIFIED FROM ISLETS OF LANGERHANS

Nitric oxide is believed to mediate the inhibitory effects of cytokines on glucose-stimulated insulin secretion by both rat and human islets. The aims of this study were 1) to determine the cellular source of the cytokine-inducible isoform of nitric oxide synthase (iNOS) expressed in islets following cytokine stimulation and 2) to determine whether tyrosine kinase activity participates in cytokine-induced iNOS expression. In this report we demonstrate that the cytokine interleukin-1 beta (IL-1 beta) stimulates the expression of iNOS and the formation of nitric oxide (as determined by nitrite formation, a stable oxidative product of nitric oxide) by isolated intact rat islets and by primary beta-cells purified by fluorescence-activated cell sorting (FACS). Both the expression of iNOS and nitrite formation induced by IL-1 beta were prevented by the mRNA transcriptional inhibitor actinomycin D. IL-1 beta did not induce the expression of iNOS by FACS-purified alpha-cells the other major endocrine cell type of the islet. The tyrosine kinase inhibitors genistein and herbimycin A prevented IL-1 beta-induced expression of immunoprecipitable iNOS and nitrite release by islets, by insulinoma RINm5F cells, and by FACS-purified beta-cells. Herbimycin A and genistein also prevented IL-1 beta-induced iNOS mRNA accumulation as determined by Northern blot analysis of total RNA isolated from RINm5F cells. These findings indicate tyrosine kinase activation participates in IL-1 beta-induced expression of iNOS by the insulin-secreting beta-cell. Specific expression of iNOS by the insulin-secreting beta-cell raises interest in the possibility that nitric oxide may participate in selective destruction of beta-cells that occurs during the etiology of autoimmune diabetes.