CYTOKINES INHIBIT PROLIFERATION AND INSULIN-SECRETION BY CLONAL RAT INSULINOMA CELLS (RINM5F) NON-SYNERGISTICALLY AND IN A PERTUSSIS TOXIN-INSENSITIVE MANNER

It has been proposed that certain cytokines secreted by islet-infiltrating leukocytes may be involved in the pathogenesis of insulin-dependent diabetes mellitus. Since the cytotoxic actions by the cytokines may reflect interactions with islet cell types other than the beta-cell, in this work I have investigated the effects of different combinations of various cytokines on the proliferation and hormone content and secretion by a pure insulin-producing cell population, i.e., the clonal rat insulinoma cell line RINm5F. For this purpose RINm5F cells were exposed in culture for 1-2 days to interleukin-1-beta (IL-1-beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and interferon-alpha (IFN-alpha) at different concentrations. It was found that IL-1-beta markedly decreased the cellular content of insulin and secretion of the hormone into the culture medium, while causing a very slight inhibition of RINm5F cell proliferation. On the other hand, IFN-gamma and IFN-alpha both elicited marked decreases in proliferation and insulin content and secretion by the insulinoma cells. IL-6 and TNF-alpha were found not to affect these parameters. No additive or synergistic effects were observed when the cytokines were added in various combinations. There was no protection against the cytotoxicity of IL-1-beta, IFN-gamma or IFN-alpha by pre-treatment with pertussis toxin. From these findings it is concluded that the cytokines IL-1-beta, IFN-gamma and IFN-alpha act in a non-synergistic fashion in suppressing RINm5F cell proliferation and hormone secretion. Furthermore, it is demonstrated that these effects by the cytokines result from events other than interaction with pertussis-toxin sensitive GTP-binding proteins.