The ceramide pathway increases cholesterol mobilization and steroidogenic acute regulatory protein mRNA

Cytokines affect placental steroid production and may have an important role during labor. An important part of cytokine signal transduction appears to be the activation of sphingomyelinase (SMase), which hydrolyses membrane sphingomyelin (SM) and releases the lipid mediator ceramide (CER). During steroidogenesis, cholesterol is transported into the mitochondria by a process regulated by steroidogenic acute regulatory protein (StAR) and possibly sterol carrier protein 2 (SCP2). There, cholesterol is hydrolysed by side chain cleavage enzyme (CSCC). We previously showed that SMase increases steroid production in JEG-3 choriocarcinoma cells but the mechanism is unknown. In the present study, we examined the effects of SMase on cholesterol mobilization and the effects of SMase and CER on the mRNAs encoding the proteins which regulate steroid synthesis. Cells were labelled with [³H]-cholesterol and CE formation was determined by thin layer chromatography. SMase significantly increased CE formation (39 ± 1 vs 6 ± 0.2 fmol/mg protein, P<0.0005 compared to control). Polyadenylated RNA was isolated, reverse transcribed and amplified by the polymerase chain reaction. CER increased StAR mRNA (2.12 ± 0.39 vs 0.68 ± 0.1 in the control cells, P<0.05), but neither SMase nor CER had any effect on SCP2 or CSCC mRNA. These data suggest that together, SMase and CER regulate steroid biosynthesis at least in part by increased cholesterol mobilization and StAR formation. This could be an important part of the signaling system involving cytokines and the initiation of labor.