TNFα and IFNγ potentiate IL-1β induced mitogen activated protein kinase activity in rat pancreatic islets of Langerhans

Aims/hypothesis. Interleukin-l beta (IL-I beta) in synergy with tumour necrosis 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 pathways. The aim of this study was to investigate if TNF alpha and IFN gamma signal through mitogen-activated protein kinases in isolated rat islets of Langerhans and if they potentiate mitogen-activated protein kinase activity induced by IL-I beta. Methods. Islets of Langerhans were isolated from 5- to 7-day-old Wistar rats and precultured for 7 days before stimulation with IL-1 beta, TNF alpha and/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 extracellular-signal-regulated kinase activity. Further, TNF alpha and IFN gamma 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 induction of cell death in pancreatic beta cells is signalled through a synergistic activation of mitogen-activated protein kinase activity.