EXPRESSION OF STEROIDOGENIC ACUTE REGULATORY PROTEIN (STAR) IN THE HUMAN OVARY

Expression of steroidogenic acute regulatory protein (StAR) messenger ribonucleic acid (mRNA) in human ovary and cultured proliferating gran ulosa-lutein cells, theca interna cells, and luteinized granulosa cell s was examined. The StAR transcripts were restricted in situ to theca of preovulatory follicles and luteinized granulosa and thecal cells of the corpus luteum. The cyclic nucleotide analog, 8-bromo-cAMP (8-Br-c AMP), increased StAR mRNA in all cell types studied by a process requi ring on-going RNA and protein synthesis. Phorbol myristate acetate pre vented the stimulatory effects of 8-Br-cAMP. In proliferating granulos a-lutein cells, 8-Br-cAMP increased StAR gene transcription and did no t significantly affect StAR mRNA stability. Forskolin treatment was al so found to increase the expression of a human StAR proximal promoter- luciferase fusion gene transfected into the proliferating granulosa-lu tein cells. We conclude that 1) the StAR gene is expressed in the most steroidogenic compartments of the human ovary; 2) induction of StAR g ene transcription by cAMP, produced in response to the LH surge, accou nts for the appearance of StAR transcripts in luteinized granulosa cel ls; and 3) the effects of cAMP are antagonized by activators of protei n kinase C.