The inducible isoform of CREM (inducible cAMP early repressor, ICER) is a repressor of CYP19 rat ovarian promoter

Abstract

The synthesis of estradiol by the granulosa cells is a prominent event in ovarian physiology and depends on the expression of P450 AROM . FSH induces the expression of P450 AROM in granulosa cells as a result of the presence in the ovarian promoter of a CRE (cAMP response element)-like sequence (CLS). In rodents, LH downregulates aromatase expression during luteinization by an as yet undescribed mechanism. In granulosa cells, LH increases the expression of the inducible cAMP early repressor (ICER), an isoform of CREM (cAMP-responsive element modulator) that represses cAMP-induced transcription. The possibility that ICER represses the activity of the aromatase ovarian promoter, thus being part of the mechanism underlying the effects of LH was investigated. We have found that: (1) nuclear proteins from forskolinstimulated granulosa cells were specifically bound to an oligonucleotide containing the CLS sequence of the CYP19 ovarian promoter and one out of the two protein-DNA complexes formed was supershifted by an anti-CREM antibody; (2) in granulosa cells, forskolin-induced increases in P450 AROM promoter luciferase reporter gene activity were prevented by the transient overexpression of ICER; (3) similar results were obtained in 8-Br-cAMPstimulated R2C cells, a Leydig tumor cell line routinely used for the study of P450 AROM promoter activity; (4) both ICER mRNA levels and P450 AROM promoterdriven luciferase activity were elevated 6 and 12 h after stimulation of R2C cells with 8-Br-cAMP and were decreased 24 and 48 h later; (5) in an R2C polyclonal line overexpressing ICER, the promoter activity at early stages of stimulation was completely attenuated, while 24 and 48 h downregulation was prevented in another R2C line stably transfected with an antisense ICER construct. These results suggest that ICER represses CYP19 ovarian promoter and that LH-induced expression of ICER may serve to downregulate P450 AROM transcription in granulosa cells during luteinization.

Novel Insights into the Downstream Pathways and Targets Controlled by Transcription Factors CREM in the Testis

“…The reason for this could be that aromatase is expressed not only in Leydig cells but also in Sertoli and germ cells [74] and is therefore regulated in a different manners. Aromatase was repressed by Icer in ovarian granulosa cells and induced by 8-Br-cAMP in the Leydig cell line R2C [75] implying that it could also be under CREM control in germ cells.…”

Aromatase expression in the ovary: Hormonal and molecular regulation

“…ICER has been shown to participate in the repression of the inhibin α-subunit gene that takes place after the surge of LH [81]. Overexpression of ICER decreases aromatase promoter activity induced by forskolin [82] and mediates the inhibition of aromatase expression by tumor necrosis factor-α (TNF-α) [83].…”

The role of transcription factors cyclic-AMP responsive element modulator (CREM) and inducible cyclic-AMP early repressor (ICER) in epileptogenesis

“…The CREB transcription factor family is composed of three family members (CREB, CREM and ATF-1) sharing a high degree of similarity and all bind to CRE sites in gene promoter regions (Shaywitz and Greenberg, 1999, Mayr and Montminy, 2001, Conkright et al, 2003. While CREB primarily increases gene transcription most of the CREM splice variants and the related gene transcript, ICER, inhibit CRE mediated transcription (Molina et al, 1993, Maronde et al, 1999, Kemp et al, 2002, Morales et al, 2003.…”