TNF alpha and IFN gamma potentiate IL-1 beta induced mitogen activated protein kinase activity in rat pancreatic islets of Langerhans

Aims/hypothesis. Interleukin-l beta (IL-I beta) in synergy with tumour necr osis factor alpha (TNF alpha) and interferon gamma (IFN gamma) is cytotoxic to pancreatic beta cells. Mitogen-activated protein kinase (MAPK) activity that is induced by interleukin-1 beta has been suggested to signal nitric oxide-dependent as well as nitric oxide-independent beta-cell destructive p athways. The aim of this study was to investigate if TNF alpha and IFN gamm a signal through mitogen-activated protein kinases in isolated rat islets o f Langerhans and if they potentiate mitogen-activated protein kinase activi ty induced by IL-I beta. Methods. Islets of Langerhans were isolated from 5- to 7-day-old Wistar rat s and precultured for 7 days before stimulation with IL-1 beta, TNF alpha a nd/or IFN gamma for 20 min followed by lysis. Kinase activity was measured with a whole cell lysate kinase assay and after immunoprecipitation of the kinase using immunocomplex kinase assay. Results. Exposure to IL-1 beta or TNF alpha significantly increased mitogen -activated protein kinase activity, whereas IFN gamma tended to decrease ex tracellular-signal-regulated kinase activity. Further, TNF alpha and IFN ga mma were found to synergistically increase mitogen-activated protein kinase activity induced by IL-1 beta. Conclusion/interpretation. We hypothesise that the synergistic effect of IL -1 beta, TNF alpha and IFN gamma, in the functional inhibition and inductio n of cell death in pancreatic beta cells is signalled through a synergistic activation of mitogen-activated protein kinase activity.