NUCLEAR RESPONSE OF PANCREATIC-ISLETS TO INTERLEUKIN-1-BETA

The mechanisms by which interleukin-1 (IL-1) exerts destructive action on the pancreatic islet beta-cells remain elusive. Fragmentation of DNA leading to the activation of poly(ADP-ribose) synthetase was investigated in the present study, by assessing the nuclear response to cytokines in rat pancreatic islets. Nuclear fractions display Mg2+-dependent poly(ADP-ribose) synthetase activity catalyzing the incorporation of [adenine-U-C-14]NAD, with K-a and K-m for Mg2+ and NAD amounting to 0.86 mM and 0.43 mM, respectively. Exposure of the nuclear fraction to rIL-1 beta (10IU/ml) provoked DNA strand breaks and increased nuclear poly(ADP-ribose) synthetase activity (148.4%, P<0.01). In intact islets, this nuclear response was observed after 18 h culture in medium containing rIL-1 beta, with a concomitant decrease in NAD (88.5%). Brief periods of pre-incubation (90 min) with rIL-1 beta were unable to induce any nuclear activity. Under these conditions, the presence of IFN-alpha (24 U/ml) and TNF (120 U/ml) was necessary to induce a response to rIL-1 beta. Under the latter experimental conditions, a decrease in NAD content was also observed. The nuclear effects of IL-1 beta Were modified by nicotinamide (10 mM), an inhibitor of poly(ADP-ribose) synthetase. It is thus conceivable that an increase in poly(ADP-ribose) synthetase activity together with DNA break is implicated in the beta cytotoxic effect of interleukin-1 beta.