IN-VIVO EFFECTS OF ADRENOCORTICOTROPIN ON THE EXPRESSION OF THE HAMSTER STEROIDOGENIC ACUTE REGULATORY PROTEIN

In this study, we report the cDNA cloning of hamster adrenal steroidog enic acute regulatory (StAR) protein and the effect of adrenocorticotr ophin (ACTH) on its expression in vivo. A hamster adrenal cDNA library was screened using an 852 bp fragment obtained by polymerase chain re action; 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 3 4 bp in the 5'-untranslated region, 852 bp in the CDS, and 678 bp in t he 3'-untranslated region (3'-UTR). Two polyadenylation signal sequenc es were found in the 3'-UTR. The CDS of the ten isolated clones was id entical, but six of these lacked the last 132 nucleotides in the 3'-UT R, 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 th e presence of only one StAR gene in the hamster genome. Northern blott ing analysis revealed the presence of the StAR mRNA:A in male and fema le steroidogenic tissues, namely adrenals and gonads, but not in the l iver or in the kidneys of either sex. Three mRNA species of 1.7, 3.1 a nd 5.3 kb were found in whole hamster adrenals. Administration of ACTH to hamsters provoked increases (two- to threefold) in the adrenal con tent of the StAR mRNA within 1 h in vivo. Western blotting analysis on adrenal mitochondria show-ed that the level of StAR protein was also significantly elevated (15-fold) 1 h after ACTH treatment.