The programmed cell death plays a crucial role in the regulation of numerous physiological and pathological phenomena. In this study, we show that interleukin-1 beta (IL-1 beta) induces an early production of endogenous ceramides via N-sphingomyelinase (N-Smase) as well as an inhibition of adenylyl cyclase activity in pig thyroid cells. This effect is followed by a down-regulation of the extracellular signal-regulated protein kinase (ERK1/2) phosphorylation, an activation of caspase-3, and ends by setting up the programmed cell death. The permeable exogenous C-2-ceramide reproduces IL-1 beta effects on: (i) inhibition of adenylyl cyclase activity, (ii) down-regulation of ERK1/2 phosphorylation, (iii) activation of caspase-3, and (iv) apoptosis in pig thyroid cells. Cell treatment with a PKA inhibitor down-regulates ERK1/2 phosphorylation. Furthermore, inhibition of ERK1/2 signaling pathway by U-0126 enhances caspase-3 activity and sets up programmed cell death. Both IL-1 beta and exogenous C-2-ceramide effects are reproduced by U-0126 so illustrating the implication of ERK1/2 down-regulation in both caspase-3 activation and apoptosis induction. Our study shows for the first time that endogenous ceramides are important second messengers in IL-1 beta-induced apoptosis in pig thyroid cells through inhibition of adenylyl cyclase and ERK1/2 activities. (c) 2005 Elsevier Inc. All rights reserved.