Regulation of cAMP responsive element binding modulator isoforms in cultured rat ovarian granulosa cells

A pituitary glycoprotein hormone FSH stimulates ovarian granulosa cells to induce ovarian follicular development. In this study we identified rat ovar ian genes that were rapidly induced by FSH in the cultured rat granulosa ce lls by means of subtraction cloning. Complementary DNA clones encoding cAMP responsive element binding modulator (CREM) were identified as one of the FSH inducible genes. Northern blotting and reverse transcription and polyme rase chain reaction (RT-PCR) analyses revealed that only the repressor type of CREM gene products, ICER (inducible cAMP early repressor) isoforms, wer e induced by FSH treatment in cultured rat granulosa cells. The induction o f ICER by FSH was mimicked by reagents known to increase intracellular cAMP levels, indicating that the induction is through cAMP and protein kinase A signal transduction system. Induction of ICER was also confirmed as the pr otein levels. Electrophoretic mobility shift assay of granulosa cell extrac ts with a radiolabeled double stranded oligonucleotide corresponding to som atostatin cAMP responsive element also revealed that only the ICER proteins were induced by FSH treatment, whereas levels of CREM proteins were nearly constant regardless of the FSH treatment. Our present study demonstrates t hat FSH-induced and cAMP-mediated induction and attenuation of transcriptio nal responses by CREM gene products may be a key mechanistic component for the granulosa cell differentiation and proliferation. (C) 1999 Elsevier Sci ence B.V. All rights reserved.