Characterization and regulation of upstream transcripts of the murine proopiomelanocortin gene

Upstream transcription start sites in the murine POMC gene were detected at -48, -113, and -134 by primer extension analysis of RNA derived from a murine pituitary (AtT20) cell line. By RNase protection assay, dexamethasone treatment of AtT20 cells was found to reduce levels of transcripts initiated from the major-transcription start site, but had a less prominent effect on levels of transcripts initiated upstream. Conversely, treatment with 8-bromo-cAMP was found to induce levels of POMC gene transcripts from the major start site and from upstream start sites at -113 and -134, but reduced transcript levels initiated at a start site at -48. Treatment with the phorbol ester PDBU had no significant effects on levels of transcripts originating from any of the transcription start sites. Chronic treatments with these agents did not alter the proportion of upstream transcripts to the total level of POMC mRNA.