In vivo effects of adrenocorticotrophin on the expression of the hamster steroidogenic acute regulatory protein.

In this study, we report the cDNA cloning of hamster adrenal steroidogenic acute regulatory (StAR) protein and the effect of adrenocorticotrophin (ACTH) on its expression in vivo. A hamster adrenal cDNA library was screened using an 852 bp fragment obtained by polymerase chain reaction; this fragment corresponds to the entire coding sequence (CDS) of the hamster adrenal StAR cDNA. Ten clones of different lengths were isolated and sequenced. The longest clone was 1564 bp and contained 34 bp in the 5'-untranslated region, 852 bp in the CDS, and 678 bp in the 3'-untranslated region (3'-UTR). Two polyadenylation signal sequences were found in the 3'-UTR. The CDS of the ten isolated clones was identical, but six of these lacked the last 132 nucleotides in the 3'-UTR, thus indicating that they had used the first polyadenylation signal. The hamster StAR protein contains 284 amino acid residues, and is 91.9% homologous to mouse, 90.5% to rat, 86.4% to human, 85% to porcine, and 82.5% to bovine StAR protein. Southern blot analysis indicated the presence of only one StAR gene in the hamster genome. Northern blotting analysis revealed the presence of the StAR mRNA in male and female steroidogenic tissues, namely adrenals and gonads, but not in the liver or in the kidneys of either sex. Three mRNA species of 1.7, 3.1 and 5.3 kb were found in whole hamster adrenals. Administration of ACTH to hamsters provoked increases (two- to threefold) in the adrenal content of the StAR mRNA within 1 h in vivo. Western blotting analysis on adrenal mitochondria showed that the level of StAR protein was also significantly elevated (1.5-fold) 1 h after ACTH treatment.