ADRENOCORTICOTROPIN REGULATES THE LEVEL OF THE STEROIDOGENIC ACUTE REGULATORY (STAR) PROTEIN MESSENGER-RNA IN HAMSTER ADRENALS

In this study, we report the cloning of a StAR cDNA from a hamster adr enal cDNA library. The library was screened using a PCR fragment speci fic for the hamster adrenal StAR cDNA. Several clones of different len gths were obtained and one of these was sequenced. Northern blotting a nalysis revealed the presence of the StAR mRNA in male and female adre nals, in testes and ovaries, but not in the liver or kidneys of either sex. Whole hamster adrenals revealed the presence of four mRNAs of 0. 65, 1.7, 3.1 and 5.25 kb, respectively. In addition, ACTH regulates th e expression of StAR mRNA in hamster adrenals. Indeed, when groups of hamsters were injected with ACTH and sacrificed at different times aft er treatment, only the 0.65 kb form of the StAR mRNA did not increase, whereas the other forms increased at varying levels. These results mi ght suggest that the expression of the StAR protein in hamster adrenal s depends upon different genes, different promoters, or different poly adenylation signal sites. In conclusion, these results indicate that i n vivo, StAR is regulated by ACTH, suggesting the participation of thi s protein in controlling the transformation of cholesterol to pregneno lone, a key regulatory step in corticosteroidogenesis.