Bone Morphogenetic Protein 2 Stimulates Noncanonical SMAD2/3 Signaling via the BMP Type 1A Receptor in Gonadotrope-Like Cells: Implications for FSH Synthesis
Authors: Wang, Ying; Ho, Catherine C.; Bang, EunJin; Rejon, Carlis A.; Libasci, Vanessa; Pertchenko, Pavel; Hebert, Terence E.; Bernard, Daniel J.
FSH is an essential regulator of mammalian reproduction. Its synthesis by pituitary gonadotrope cells is regulated by multiple endocrine and paracrine factors, including TGF beta superfamily ligands, such as the activins and inhibins. Activins stimulate FSH synthesis via transcriptional regulation of its beta-subunit gene (Fshb). More recently, bone morphogenetic proteins (BMPs) were shown to stimulate murine Fshb transcription alone and in synergy with activins. BMP2 signals via its canonical type I receptor, BMPR1A (or activin receptor-like kinase 3 [ALK3]), and SMAD1 and SMAD5 to stimulate transcription of inhibitor of DNA binding proteins. Inhibitor of DNA binding proteins then potentiate the actions of activin-stimulated SMAD3 to regulate the Fshb gene in the gonadotrope- like L beta T2 cell line. Here, we report the unexpected observation that BMP2 also stimulates the SMAD2/3 pathway in these cells and that it does so directly via ALK3. Indeed, this novel, noncanonical ALK3 activity is completely independent of ALK4, ALK5, and ALK7, the type I receptors most often associated with SMAD2/3 pathway activation. Induction of the SMAD2/3 pathway by ALK3 is dependent upon its own previous activation by associated type II receptors, which phosphorylate conserved serine and threonine residues in the ALK3 juxtamembrane glycine-serine- rich domain. ALK3 signaling via SMAD3 is necessary for the receptor to stimulate Fshb transcription, whereas its activation of the SMAD1/5/8 pathway alone is insufficient. These data challenge current dogma that ALK3 and other BMP type I receptors signal via SMAD1, SMAD5, and SMAD8 and not SMAD2 or SMAD3. Moreover, they suggest that BMPs and activins may use similar intracellular signaling mechanisms to activate the murine Fshb promoter in immortalized gonadotrope- like cells.
Progestin increases the expression of gonadotropins in pituitaries of male zebrafish
JOURNAL OF ENDOCRINOLOGY
Authors: Wang, Cuili; Liu, Dongteng; Chen, Weiting; Ge, Wei; Hong, Wanshu; Zhu, Yong; Chen, Shi X.
Our previous study showed that the in vivo positive effects of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP), the major progestin in zebrafish, on early spermatogenesis was much stronger than the ex vivo ones, which may suggest an effect of DHP on the expression of gonadotropins. In our present study, we first observed that fshb and lhb mRNA levels in the pituitary of male adult zebrafish were greatly inhibited by 3 weeks exposure to 10 nM estradiol (E-2). However, an additional 24 h 100 nM DHP exposure not only reversed the E-2-induced inhibition, but also significantly increased the expression of fshb and lhb mRNA. These stimulatory effects were also observed in male adult fish without E-2 pretreatment, and a time course experiment showed that it took 24 h for fshb and 12 h for lhb to respond significantly. Because these stimulatory activities were partially antagonized by a nuclear progesterone receptor (Pgr) antagonist mifepristone, we generated a Pgr-knockout (pgr(-/-)) model using the TALEN technique. With and without DHP in vivo treatment, fshb and lhb mRNA levels of pgr(-/-) were significantly lower than those of pgr(+/+). Furthermore, ex vivo treatment of pituitary fragments of pgr(-/-) with DHP stimulated lhb, but not fshb mRNA expression. Results from double-colored fluorescent in situ hybridization showed that pgr mRNA was expressed only in fshb-expressing cells. Taken together, our results indicated that DHP participated in the regulation of neuroendocrine control of reproduction in male zebrafish, and exerted a Pgr-mediated direct stimulatory effect on fshb mRNA at pituitary level.