Transcriptional repression of the CTP:phosphocholine cytidylyltransferase gene by sphingosine

We examined the effects of the bioactive lipid, sphingosine, on the expression of the rate-limiting enzyme involved in surfactant phosphatidylcholine synthesis, CCTα (CTP:phosphocholine cytidylyltransferase α). Sphingosine decreased phosphatidylcholine synthesis by inhibiting CCT activity in primary alveolar type II epithelia. Sphingosine decreased CCTα protein and mRNA levels by approx. 50% compared with control. The bioactive lipid did not alter CCTα mRNA stability, but significantly inhibited its transcriptional rate. In murine lung epithelia, sphingosine selectively reduced CCTα promoter-reporter activity when transfected with a 2 kb CCTα promoter/luciferase gene construct. Sphingosine also decreased transgene expression in murine type II epithelia isolated from CCTα promoter-reporter transgenic mice harbouring this 2 kb proximal 5′-flanking sequence. Deletional analysis revealed that sphingosine responsiveness was mapped to a negative regulatory element contained within 814 bp upstream of the coding region. The results indicate that bioactive sphingolipid metabolites suppress surfactant lipid synthesis by inhibiting gene transcription of a key surfactant biosynthetic enzyme.