Activin Regulates Estrogen Receptor Gene Expression in the Mouse Ovary

Abstract

Activin, a member of the transforming growth factor-␤ superfamily, is an important modulator of follicle-stimulating hormone synthesis and secretion in the pituitary and plays autocrine/paracrine roles in the regulation of ovarian follicle development. From a microarray study on mouse ovarian granulosa cells, we discovered that the estrogen receptor ␤ (ER␤) is inducible by activin. We previously demonstrated that estrogen suppresses activin gene expression, suggesting a feedback relationship between these two follicle-regulating hormones. The purpose of this study was to investigate fully activin A regulation of ER expression. Real time reverse transcription-PCR assays on cultured granulosa cells showed that both ER␣ and ER␤ mRNAs were induced by activin A at 4, 12, and 24 h in a dose-responsive manner. Western blots confirmed an increase in their protein levels. Consistent with increased ER␣ and ER␤ expression, activin A stimulated estradiol-induced estrogen response element promoter activity. Activin A stimulation of ER expression was a direct effect at the level of gene transcription, as it was not abolished by cycloheximide but was abolished by actinomycin D, and in transfected granulosa cells activin A stimulated ER␣ promoter activity. To investigate the effect of activin in vivo and, thus, its biological significance, we examined ER expression in inhibin transgenic mice that have decreased activin expression and discovered that these mice had decreased ER␣ and ER␤ expression in the ovary. We also found that ER mRNA levels were decreased in Mü llerian inhibiting substance promoter (MIS)-Smad2 dominant negative mice that have impaired activin signaling through Smad2, and small interfering RNAs targeting Smad2 or Smad3 suppressed ER␣ promoter activation, suggesting that Smad2 and Smad3 are involved in regulating ER levels. Therefore, this study reveals an important role for activin in inducing the expression of ERs in the mouse ovary and suggests important interplay between activin and estrogen signaling.Activin and its functional antagonist inhibin were originally isolated from gonadal sources as endocrine factors regulating the synthesis and secretion of follicle-stimulating hormone by the pituitary gland (1-8). More recent studies have indicated that activin acts predominantly as a local paracrine and autocrine factor (9, 10). Consistent with the fact that activin is a member of the transforming growth factor-␤ (TGF-␤) 2 superfamily, activin has a variety of functions and is involved in many physiological processes, including embryonic development, wound repair, inflammation, renal tubule morphogenesis, and neuroprotection. In the reproductive system, in addition to regulating gonadotropin release, activin and inhibin have been shown to play an important role in regulating the formation and development of ovarian follicles in the female (10 -15) and development and function of the testis in the male (16). Ovarian follicle formation and development is a dynamic process finely regulated by various intrinsic ...

Profiling neuroendocrine gene expression changes following fadrozole-induced estrogen decline in the female goldfish

“…These genes fall into two types of regulation of E2 actions: one is direct regulation of nER activity, which includes calmodulin (5), HSP90b (29), O-GlcNAc transferase (7), ubiquitin-conjugating enzyme E2 (UCE2) variant 1 (39), activin ␤A (11), and the dynein light chain (22,48). The second type is regulation of nER mRNA levels by such factors as PACAP (9) and activin-␤A (28). While speculative, observed changes in the expression of PACAP and activin-␤A following fadrozole treatment could potentially affect ER expression further modulating E2 actions in the brain.…”

“…Activin is a dimeric growth factor formed by two subunits and binds the membrane serine/threonine kinase receptors (33), which then induce the activation of downstream signaling pathways and affect activities of transcriptional factors such as Smad (50). Very recently, activin signaling was shown to regulate ER␣ activity in the human breast cancer cells (11) and induce expression of ER␤ in the mouse granulosa cells (28). Moreover, E2 has been shown to regulate the expression of the activin-␤ subunits in the mouse neonatal ovary (27) and type II activin receptor in rat Hyp (56).…”

Seasonal Changes in Immunoreactivity of Activin Signaling Component Proteins in Wild Ground Squirrel Testes

“…Recent studies have demonstrated the important interplay between SMAD-mediated TGF-β signaling and steroid hormone nuclear receptors in mammal target tissues or organs [25][26][27]. In some species, paracrine/autocrine systems appear to be important in modulating steroid hormone control of testicular function and spermatogenesis [28].…”

G protein-coupled receptor 48 upregulates estrogen receptor α expression via cAMP/PKA signaling in the male reproductive tract

“…We then identified a potential cAMP responsible element (TGACATCA) in the mouse ER variant C promoter. We further proved that this Cre motif was functional and essential for Gpr48 regulation of ER expression.Previous studies have reported that ER expression could be modulated by activin in the mouse ovary (Kipp et al, 2007) and also by prolactin in the rat corpus luteum via the Jak2-Stat5 pathway (Frasor et al, 2001;Frasor et al, 2003). In human, ER expression in osteoblast cells was upregulated by PKC/c-Src (Longo et al, 2006), and in breast carcinoma cells by ERF-1 (also known as TFAP2C), a member of the AP2 transcription factor family (McPherson et al, 1997).…”