Involvement of the ceramide signaling pathway in modulating the differentiated state of porcine thyroid cells

Thrombospondin-1 C-terminal-derived peptide protects thyroid cells from ceramide-induced apoptosis through the adenylyl cyclase pathway

Thrombospondin-1, a multi-modular matrix protein is able to interact with a variety of matrix proteins and cell-surface receptors. Thus it is multifunctional. In this work, we examined the role of thrombospondin-1 in ceramide-induced thyroid apoptosis. We focused on the VVM containing sequence localized in the C-terminal domain of the molecule. Primary cultured thyroid cells synthesize thrombospondin-1 depending on their morphological organization. As it leads thyrocytes to organize into monolayers before inducing apoptosis ceramide can modulate this organization. Here, we established that C(2)-ceramide treatment decreased thrombospondin-1 expression by interfering with the adenylyl cyclase pathway, thus leading to apoptosis. Furthermore, we demonstrated that the thrombospondin-1-derived peptide 4N1 (RFYVVMWK) abolished ceramide-induced thyroid cell death by preventing intracellular cAMP levels from dropping. Finally, we reported that 4N1-mediated inhibition of ceramide-induced apoptosis was consistently associated with a down-regulation of the caspase-3 processing. Integrin-associated protein receptor (IAP or CD47) was identified as a molecular relay mediating the observed 4N1 effects. Taken together, our results shed light for the first time on anti-apoptotic activities of the thrombospondin-1-derived peptide 4N1 and provide new information on how thrombospondin-1 may control apoptosis of non-tumoral cells.

Interleukin-1beta-induced apoptosis through adenylyl cyclase and ERK1/2 inhibition in primary cultured thyroid cells

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-1beta) 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-1beta 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-1beta 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-1beta-induced apoptosis in pig thyroid cells through inhibition of adenylyl cyclase and ERK1/2 activities.

Interleukin-1beta (IL-1beta) induces a crosstalk between cAMP and ceramide signaling pathways in thyroid epithelial cells

Interleukin-1 beta (IL-1beta) is an important regulator of the thyroid cell function. This cytokine has been largely described to trigger an important biological signaling cascade: the sphingomyelin/ceramide pathway. In this report, we show that IL-1beta induces the transient activation of a neutral sphingomyelinase in porcine thyroid cells. Moreover, IL-1beta and ceramides are demonstrated to inhibit the TSH-induced cAMP production via the implication of alphaGi subunit of the adenylyl cyclase system. This crosstalk between cAMP and ceramide pathways constitutes a preponderant process in the TSH-controlled differentiation state of thyrocytes. All these results argue for the involvement of ceramides and IL-1beta in the thyroid function regulation, leading to a cell dedifferentiated state.

Ceramide mediates age-associated increase in macrophage cyclooxygenase-2 expression

Previously, we showed that macrophages (MØ) from old mice have significantly higher levels of lipopolysaccharide (LPS)-induced prostaglandin E(2) (PGE(2)) production than young mice, due to increased cyclooxygenase-2 (COX-2) mRNA levels. The aim of the current study was to determine the underlying mechanisms of age-associated increase in COX-2 gene expression. The results demonstrate that increased COX-2 mRNA expression in the old mice is due to a higher rate of transcription rather than increased stability of COX-2 mRNA. Furthermore, the results show that LPS-induced ceramide levels from the old mice are significantly higher than those of young mice, whereas there is no age-related difference in concentration of its down stream metabolite, sphingosine. The addition of ceramide in the presence or absence of LPS resulted in a significant increase in PGE(2) production in a dose- and time-dependent manner. Inhibition of ceramide conversion to sphingosine had no effect on this ceramide-induced effect. The ceramide-induced up-regulation in PGE(2) production was mediated through increase in COX activity and transcriptional up-regulation of COX-2 mRNA. Collectively, these data suggest that the age-associated increase in MØ COX-2 mRNA is due to transcriptional up-regulation. Furthermore, this increase in transcription is mediated by higher cellular ceramide concentration in old MØ compared with that of young MØ.