Interleukin-1 beta-induced ceramide and diacylglycerol generation may lead to activation of the c-Jun NH2-terminal kinase and the transcription factor ATF2 in the insulin-producing cell line RINm5F

The aim of this investigation was to study the putative involvement of lipid second messengers, protein kinases, and transcription factors in interleukin-1 beta (IL-1 beta)-induced signal transduction in insulin-producing cells. For this purpose, insulin-producing RINm5F cells were exposed to IL-1 beta (25 units/ml), and the ceramide, ceramide 1-phosphate, sphingomyelin, diacylglycerol, and phosphatidic acid contents of the cells were subsequently determined, It was found that IL-1 beta induced a transient increase (2-5 min) in ceramide and diacylglycerol, which was not paralleled by an increase in ceramide 1-phosphate and phosphatidic acid. A rapid decrease in the sphingomyelin content of the cells was, however, observed. The cell-permeable ceramide analogue N-acetylsphingosine and the phorbol ester phorbol 12-myristate 13-acetate (PMA) both induced the phosphorylation and increased the activities of the protein kinase JNK1 and the transcription factor ATF2. These effects were, however, not as pronounced as those induced by IL-1 beta. The DNA binding activity of transcription factors in nuclear extracts was determined using the electrophoretic mobility shift assay method. Transcription factor binding to the ATF/cAMP-responsive element consensus sequence was increased 4-5-fold by acetylsphingosine, PMA, or IL-1 beta, whereas binding to the CCAAT/enhancer-binding protein and AP-1 elements was found to be only slightly stimulated by these three agents. Binding to the NF-kappa B element was strongly induced by IL-1 beta, but not by acetylsphingosine or PMA. Finally, acetylsphingosine and PMA did not mimic the nitric oxide-inducing effects of IL-1 beta. It is concluded that IL-1 beta-stimulated formation of ceramide and diacylglycerol may contribute to JNK1 and ATF2 transcription factor activation, which may be a necessary (but not sufficient) step in beta-cell nitric-oxide synthase induction.