IL-1β released from immune cells induces beta cell pro-apoptotic signalling via mitogen-activated protein kinases (MAPKs) and nuclear factor-κB (NF-κB). In neurons, the neural cell adhesion molecule (NCAM) signals to several elements involved in IL-1β-induced pro-apoptotic signalling in beta cells. Pancreatic beta cells express NCAM, but its biological effects in these cells are unclear. The aim of this study was to investigate whether there is cross-talk between NCAM signalling and cytokine-induced pro-apoptotic signalling.Materials and methods
Western blotting was used to investigate levels of NCAM and inducible nitric oxide synthase, phosphorylation of Src and MAPKs, and cleavage of caspase-3. MAPK activity was investigated with an in vitro kinase assay. Apoptosis was detected by cleaved caspase-3 and a Cell Death Detection ELISAplus assay. NCAM-induced fibroblast growth factor receptor (FGFR) activation was investigated in NCAM−/− Trex293 cells where FGFR phosphorylation was measured by Western blotting after NCAM transfection.Results
Pre-exposure of INS-1E cells to the FGFR-inhibitor SU5402, but not to the Src-inhibitor PP2, dose-dependently inhibited IL-1β-mediated MAPK activity. A synthetic peptide, C3d, reported to bind NCAM, did not activate MAPK or Akt as reported in neurons but inhibited IL-1β-induced MAPK activity, thereby mimicking the effect of SU5402. Furthermore, C3d inhibited NCAM-induced FGFR phosphorylation and apoptosis induced by IL-1β plus IFN-γ, but did not affect IL-1β-induced NF-κB signalling.Conclusions/interpretation
We suggest that NCAM signalling through FGFR is required for efficient IL-1β pro-apoptotic signalling by facilitating IL-1β-induced MAPK activation downstream of the NF-κB-MAPK branching point. Further, these data identify a novel function of C3d as an inhibitor of NCAM-induced FGFR activity and of IL-1β-induced MAPK activation in beta cells.