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 CCTα and Pcyt1b for CCTβ. In mouse tissues two different CCTβ variants named CCTβ2 and CCTβ3 have been identified. Although little is known about Pcyt1b gene expression, recent data from cell lines propose a distinct role for CCTβ2 in neuronal differentiation. Also, gonadal dysfunction in the CCTβ2 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 CCTβ 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 CCTβ2 promoter sequence suggested the transcription factor AP-1 as a potential regulator of CCTβ2 expression in neuronal cells. However, CCTβ3 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 CCTβ isoform expression.