Endocrine Abstracts

The murine ACTH receptor MC2-R is primarily expressed in the adrenal cortex and adipocytes where it binds ACTH leading to steroidogenesis and lipolysis, respectively. We have recently shown that the previously described 'adrenal' MC2-R promoter is transiently activated by PPAR gamma 2 early during differentiation of murine 3T3-L1 pre-adipocytes, declining to background levels from a peak of activity seen at day 4 following commencement of adipogenesis. This is mirrored by the transient up-regulation of exon 1-specific message. However, message from the coding exon of the gene remains elevated throughout a prolonged timecourse of differentiation. We have used 5' RACE to isolate the 5' ends of MC2-R-specific message from cells late in differentiation and show that they initiate from a position approximately 1.6kb downstream of the 'adrenal' promoter in the first intron of the gene. These transcripts are induced with delayed kinetics, with respect to those initiating from the upstream promoter, during differentiation and are only found in adipocytes, suggesting that the region upstream of the initiation site in the first intron contains an adipocyte-specific promoter which is activated later than the upstream promoter during adipogenesis. By producing 5' and 3' deletion series of the first intron sequences between the two promoters we are investigating the temporal regulation of these promoters during adipogenesis and the mechanisms controlling their distinct patterns of activation.