Ceramide synergizes with phorbol ester or okadaic acid to induce IκB degradation

Ceramide is a lipid second messenger which is generated in response to stimulation of a number of surface receptors, treatment with chemotherapeutic agents, or ionising radiation. Depending on the target cell, ceramide induces diverse biological responses including apoptosis, cell-cycle arrest, differentiation, and also proliferation. We studied the effect of ceramide on the degradation of I kappa B, the cytoplasmic inhibitor of the transcription factor NF-kappa B. We show that ceramide treatment results in reduced levels of phosphorylated I kappa B alpha and degradation of both I kappa B alpha and I kappa B beta. Ceramide synergised with okadaic acid (OA), a compound which interferes with the protein phosphatase 2A-controlled component of the NF-kappa B activation pathway, enhancing OA-induced I kappa B degradation. Ceramide also synergised with phorbol 12-myristate 13-acetate, which mimics protein kinase C activation. Finally, we show that the synergistic effect of ceramide with OA or phorbol ester can be observed in primary lymph node T-cells as well as in transformed T-cells. (C) 1999 Academic Press.