EXPRESSION OF THE CITRULLINE-NITRIC OXIDE CYCLE IN RODENT AND HUMAN PANCREATIC BETA-CELLS - INDUCTION OF ARGININOSUCCINATE SYNTHETASE BY CYTOKINES

Nitric oxide (NO) may be a mediator of beta-cell damage in insulin-dep endent diabetes mellitus, beta-Cells express the inducible form of NO synthase (iNOS) and produce large amounts of NO upon exposure to cytok ines. iNOS requires the amino acid arginine for NO formation. It has b een shown in other cell types that interferon-gamma (IFN gamma) and ba cterial lipopolysaccharide induce the enzyme argininosuccinate synthet ase (AS), enhancing the capacity of these cells to regenerate arginine from citrulline and maintain NO production in the presence of low arg inine concentrations. To characterize the messenger RNA (mRNA) express ion of AS in insulin-producing cells, RINm5F cells (RIN cells) were ex posed to interleukin-1 beta (IL-1 beta) or to tumor necrosis factor-al pha plus IFN gamma. After 4-6 h, there was a significant and parallel induction of AS and iNOS mRNA. IL-1 beta-induced AS and iNOS mRNA expr ession was prevented by an inhibitor of the activation factor NF-kappa B pyrrolidine diaminoguanidine, an inhibitor of gene transcription (a ctinomycin D), and a blocker of protein synthesis (cycloheximide), sug gesting coregulation of AS and iNOS by cytokines. RIN cells exposed to IL-1 beta in the presence of citrulline but the absence of arginine h ad increased AS enzyme activity and produced NO, demonstrating that cy tokine-induced AS mRNA expression is accompanied by increased AS activ ity. Both adult rat islets exposed to IL-1 beta and human pancreatic i slets cultured in the presence of IL-1 beta, tumor necrosis factor-alp ha, and IFN gamma were able to use citrulline to regenerate arginine a nd produce NO. Taken as a whole, the present data suggest that regulat ion of AS activity may play a role in modulation of NO production in b oth rodent and human insulin-producing cells.