Characterization of the murine CTP:phosphocholine cytidylyltransferase beta gene promoter

CTP:phosphocholine cytidylyltransferase (CCT) is a key regulatory enzyme in phosphatidylcholine (PtdCho) biosynthesis by the Kennedy pathway. In mammals, there are two genes that encode the enzyme isoforms that catalyze this reaction: Pcyt1a for CCTalpha and Pcyt1b for CCTbeta. In mouse tissues two different CCTbeta variants named CCTbeta2 and CCTbeta3 have been identified. Although little is known about Pcyt1b gene expression, recent data from cell lines propose a distinct role for CCTbeta2 in neuronal differentiation. Also, gonadal dysfunction in the CCTbeta2 knockout mouse suggests a role for this protein in ovary maturation and the maintenance of sperm production. This work defines and characterizes two alternative promoters that drive the expression of the two murine CCTbeta isoforms. The promoter activities were measured in Neuro-2a (mouse neuroblastoma), TM4 (mouse Sertoli) and C3H10T1/2 (mouse embryo fibroblast) cell lines. The transcriptional start points of each transcript and the promoter regions essential for the expression of each isoform were determined. Analysis of the CCTbeta2 promoter sequence suggested the transcription factor AP-1 as a potential regulator of CCTbeta2 expression in neuronal cells. However, CCTbeta3 was not detected in this cell line suggesting a different role or regulation. The activities of alternative promoters provide for greater flexibility in the control of CCTbeta isoform expression.