Cytokines activate genes of the endocytotic pathway in insulin-producing RINm5F cells

Abstract

Aims/hypothesis. Cytokines are important humoral mediators of beta cell destruction in autoimmune diabetes. The aim of this study was to identify novel cytokine-induced genes in insulin-producing RINm5F cells, which may contribute to beta cell death or survival. Methods. A global gene expression profile in cytokine-exposed insulin-producing RINm5F cells was achieved by automated restriction fragment differential display PCR. The expression of selected candidate genes was confirmed by real-time RT-PCR analysis. Results. Exposure of RINm5F cells to IL-1β or to a cytokine mixture (IL-1β, TNF-α, IFN-γ) for 6 h resulted in the differential expression of a functional gene cluster. Apart from the well-known up-regulation of the cytokine-responsive genes iNOS, NF-κB, MnSOD and Hsp70, several genes that belong to the functional cluster of the endocytotic pathway were identified. These endocytotic genes comprised: clathrin, megalin, synaptotagmin and calcineurin, which were up-regulated by IL-1β or the cytokine mixture. In contrast, the expression of the calcineurin inhibitor CAIN and of the GDP/GTP exchange protein Rab3 was down-regulated by cytokines. Other up-regulated cytokine-responsive genes were: agrin, murine adherent macrophage protein mRNA (MAMA) and transport-associated protein (TAP1/MTP), whereas the plasma membrane calcium ATPase (PMCA) 2 and PMCA 3 genes were down-regulated by cytokines. Conclusions/interpretation. Our results indicate that genes of the endocytotic pathway are regulated by pro-inflammatory cytokines. This might affect the density of cytokine receptors at the beta cell surface and concomitantly the sensitivity of the cells to cytokine toxicity. A better understanding of the functional cross-talk between endocytotic and cytokine signalling pathways could further the development of novel strategies to protect pancreatic beta cells against toxic effects of pro-inflammatory cytokines.