Transforming growth factor beta-activated kinase 1 is a key mediator of ovine follicle-stimulating hormone beta-subunit expression

Transcriptional profiling and pathway analysis reveal differences in pituitary gland function, morphology, and vascularization in chickens genetically selected for high or low body weight

Background

Though intensive genetic selection has led to extraordinary advances in growth rate and feed efficiency in production of meat-type chickens, endocrine processes controlling these traits are still poorly understood. The anterior pituitary gland is a central component of the neuroendocrine system and plays a key role in regulating important physiological processes that directly impact broiler production efficiency, though how differences in pituitary gland function contribute to various growth and body composition phenotypes is not fully understood.

Results

Global anterior pituitary gene expression was evaluated on post-hatch weeks 1, 3, 5, and 7 in male broiler chickens selected for high (HG) or low (LG) growth. Differentially expressed genes (DEGs) were analyzed with gene ontology categorization, self-organizing maps, gene interaction network determination, and upstream regulator identification to uncover novel pituitary genes and pathways contributing to differences in growth and body composition. A total of 263 genes were differentially expressed between HG and LG anterior pituitary glands (P ≤ 0.05 for genetic line-by-age interaction or main effect of line; ≥1.6-fold difference between lines), including genes encoding four anterior pituitary hormones. Genes involved in signal transduction, transcriptional regulation, and vesicle-mediated transport were differentially expressed and are predicted to influence expression and secretion of pituitary hormones. DEGs involved in immune regulation provide evidence that inflammation and response to cellular stressors may compromise pituitary function in LG birds, affecting their ability to adequately produce pituitary hormones. Many DEGs were also predicted to function in processes that regulate organ morphology and angiogenesis, suggesting pituitary gland structure differs between the divergently selected lines.

Conclusions

The large number of DEGs within the anterior pituitary gland of birds selected for high or low body weight highlights the importance of this gland in regulating economically important traits such as growth and body composition in broiler chickens. Intracellular signaling, transcriptional regulation, and membrane trafficking are important cellular processes contributing to proper hormone production and secretion. The data also suggest that pituitary function is intimately tied to structure, and organization of the gland could influence hypothalamic and systemic metabolic inputs and delivery of hormones regulating growth and metabolism into peripheral circulation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5670-9) contains supplementary material, which is available to authorized users.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

Activin A stimulates migration of the fallopian tube epithelium, an origin of high-grade serous ovarian cancer, through non-canonical signaling

Factors that stimulate the migration of fallopian tube epithelial (FTE)-derived high-grade serous ovarian cancer (HGSOC) to the ovary are poorly elucidated. This study characterized the effect of the ovarian hormone, activin A, on normal FTE and HGSOC. Activin A and TGFβ1 induced an epithelial-to-mesenchymal transition in murine oviductal epithelial (MOE) cells, but only activin A increased migration. The migratory effect of activin A was independent of Smad2/3 and required phospho-AKT, phospho-ERK, and Rac1. Exogenous activin A stimulated migration of the HGSOC cell line OVCAR3 through a similar mechanism. Activin A signaling inhibitors, SB431542 and follistatin, reduced migration in OVCAR4 cells, which expressed activin A subunits (encoded by INHBA). Murine superovulation increased phospho-Smad2/3 immunostaining in the FTE. In Oncomine, transcripts for the activin A receptors (ACVR1B and ACVR2A) were higher in serous tumors relative to the normal ovary, while inhibitors of activin A signaling (INHA and TGFB3) were lower. High expression of both INHBA and ACVR2A, but not TGFβ receptors or co-receptors, was associated with shorter disease-free survival in serous cancer patients. These results suggest activin A stimulates migration of FTE-derived tumors to the ovary.

Normal gonadotropin production and fertility in gonadotrope-specific Bmpr1a knockout mice

Pituitary follicle-stimulating hormone (FSH) synthesis is regulated by transforming growth factorβsuperfamily ligands, most notably the activins and inhibins. Bone morphogenetic proteins (BMPs) also regulate FSHβ subunit (Fshb) expression in immortalized murine gonadotrope-like LβT2 cells and in primary murine or ovine primary pituitary cultures. BMP2 signals preferentially via the BMP type I receptor, BMPR1A, to stimulate murine Fshb transcription in vitro Here, we used a Cre-lox approach to assess BMPR1A's role in FSH synthesis in mice in vivo Gonadotrope-specific Bmpr1a knockout animals developed normally and had reproductive organ weights comparable with those of controls. Knockouts were fertile, with normal serum gonadotropins and pituitary gonadotropin subunit mRNA expression. Cre-mediated recombination of the floxed Bmpr1a allele was efficient and specific, as indicated by PCR analysis of diverse tissues and isolated gonadotrope cells. Furthermore, BMP2 stimulation of inhibitor of DNA binding 3 expression was impaired in gonadotropes isolated from Bmpr1a knockout mice, confirming the loss of functional receptor protein in these cells. Treatment of purified gonadotropes with small-molecule inhibitors of BMPR1A (and the related receptors BMPR1B and ACVR1) suppressed Fshb mRNA expression, suggesting that an autocrine BMP-like molecule might regulate FSH synthesis. However, deletion of Bmpr1a and Acvr1 in cultured pituitary cells did not alter Fshb expression, indicating that the inhibitors had off-target effects. In sum, BMPs or related ligands acting via BMPR1A or ACVR1 are unlikely to play direct physiological roles in FSH synthesis by murine gonadotrope cells.

5Z-7-Oxozeanol Inhibits the Effects of TGFβ1 on Human Gingival Fibroblasts

Transforming growth factor (TGF)β acts on fibroblasts to promote the production and remodeling of extracellular matrix (ECM). In adult humans, excessive action of TGFβ is associated with fibrotic disease and fibroproliferative conditions, including gingival hyperplasia. Understanding how the TGFβ1 signals in fibroblasts is therefore likely to result in valuable insights into the fundamental mechanisms underlying fibroproliferative disorders. Previously, we used the TAK1 inhibitor (5Z)-7-Oxozeaenol to show that, in dermal fibroblasts, the non-canonical TAK1 pathway mediates the ability of TGFβ1 to induce genes promoting tissue remodeling and repair. However, the extent to which TAK1 mediates fibroproliferative responses in fibroblasts in response to TGFβ1 remains unclear. Herein, we show that, in gingival fibroblasts, (5Z)-7-Oxozeaenol blocks the ability of TGFβ1 to induce expression of the pro-fibrotic mediator CCN2 (connective tissue growth factor, CTGF) and type I collagen protein. Moreover, genome-wide expression profiling revealed that, in gingival fibroblasts, (5Z)-7-Oxozeaenol reduces the ability of TGFβ1 to induce mRNA expression of essentially all TGFβ1-responsive genes (139/147), including those involved with a hyperproliferative response. Results from microarray analysis were confirmed using real time polymerase chain reaction analysis and a functional cell proliferation assay. Our results are consistent with the hypothesis that TAK1 inhibitors might be useful in treating fibroproliferative disorders, including that in the oral cavity.

MiR-29a reduces TIMP-1 production by dermal fibroblasts via targeting TGF-β activated kinase 1 binding protein 1, implications for systemic sclerosis

Background

Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterised by skin and internal organs fibrosis due to accumulation of extra cellular matrix (ECM) proteins. Tissue inhibitor of metalloproteinases 1 (TIMP-1) plays a key role in ECM deposition.

Aim

To investigate the role of miR-29a in regulation of TAB1-mediated TIMP-1 production in dermal fibroblasts in systemic sclerosis.

Methods

Healthy control (HC) and SSc fibroblasts were cultured from skin biopsies. The expression of TIMP-1, MMP-1 and TGF-β activated kinase 1 binding protein 1 (TAB1) was measured following miR-29a transfection using ELISA, qRT-PCR, and Western Blotting. The functional effect of miR-29a on dermal fibroblasts was assessed in collagen gel assay. In addition, HeLa cells were transfected with 3′UTR of TAB1 plasmid cloned downstream of firefly luciferase gene to assess TAB1 activity. HC fibroblasts and HeLa cells were also transfected with Target protectors in order to block the endogenous miR-29a activity.

Results

We found that TAB1 is a novel target gene of miR-29a, also regulating downstream TIMP-1 production. TAB1 is involved in TGF-β signal transduction, a key cytokine triggering TIMP-1 production. To confirm that TAB1 is a bona fide target gene of miR-29a, we used a TAB1 3′UTR luciferase assay and Target protector system. We showed that miR-29a not only reduced TIMP-1 secretion via TAB1 repression, but also increased functional MMP-1 production resulting in collagen degradation. Blocking TAB1 activity by pharmacological inhibition or TAB1 knockdown resulted in TIMP-1 reduction, confirming TAB1-dependent TIMP-1 regulation. Enhanced expression of miR-29a was able to reverse the profibrotic phenotype of SSc fibroblasts via downregulation of collagen and TIMP-1.

Conclusions

miR-29a repressed TAB1-mediated TIMP-1 production in dermal fibroblasts, demonstrating that miR-29a may be a therapeutic target in SSc.

Molecular regulation of hypothalamus-pituitary-gonads axis in males

The hypothalamic-pituitary-gonadal axis (HPG) plays vital roles in reproduction and steroid hormone production in both sexes. The focus of this review is upon gene structures, receptor structures and the signaling pathways of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The hormones' functions in reproduction as well as consequences resulting from mutations are also summarized. Specific characteristics of hormones such as the pulsatile secretions of GnRH are also covered. The different regulators of the HPG axis are introduced including kisspeptin, activin, inhibin, follistatin, androgens and estrogen. This review includes not only their basic information, but also their unique function in the HPG axis. Here we view the HPG axis as a whole, so relations between ligands and receptors are well described crossing different levels of the HPG axis. Hormone interactions and transformations are also considered. The major information of this article is depicted in three figures summarizing the current discoveries on the HPG axis. This article systematically introduces the basic knowledge of the HPG axis and provides information of the current advances relating to reproductive hormones.

Follicle-stimulating hormone synthesis and fertility are intact in mice lacking SMAD3 DNA binding activity and SMAD2 in gonadotrope cells

The activin/inhibin system regulates follicle-stimulating hormone (FSH) synthesis and release by pituitary gonadotrope cells in mammals. In vitro cell line data suggest that activins stimulate FSH β-subunit (Fshb) transcription via complexes containing the receptor-regulated SMAD proteins SMAD2 and SMAD3. Here, we used a Cre-loxP approach to determine the necessity for SMAD2 and/or SMAD3 in FSH synthesis in vivo. Surprisingly, mice with conditional mutations in both Smad2 and Smad3 specifically in gonadotrope cells are fertile and produce FSH at quantitatively normal levels. Notably, however, we discovered that the recombined Smad3 allele produces a transcript that encodes the entirety of the SMAD3 C-terminal Mad homology 2 (MH2) domain. This protein behaves similarly to full-length SMAD3 in Fshb transcriptional assays. As the truncated protein lacks the N-terminal Mad homology 1 (MH1) domain, these results show that SMAD3 DNA-binding activity as well as SMAD2 are dispensable for normal FSH synthesis in vivo. Furthermore, the observation that deletion of proximal exons does not remove all SMAD3 function may facilitate interpretation of divergent phenotypes previously described in different Smad3 knockout mouse lines.

Mechanisms of activin-stimulated FSH synthesis: the story of a pig and a FOX

Activins were discovered and, in fact, named more than a quarter century ago based on their abilities to stimulate pituitary follicle-stimulating hormone (FSH) synthesis and secretion. However, it is only in the last decade that we have finally come to understand their underlying mechanisms of action in gonadotroph cells. In this minireview, we chronicle the research that led to the recent discovery of forkhead box L2 (FOXL2) as an essential mediator of activin-regulated FSH beta subunit (Fshb) transcription in vitro and in vivo.

Cycloheximide inhibits follicle-stimulating hormone β subunit transcription by blocking de novo synthesis of the labile activin type II receptor in gonadotrope cells

The pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), play essential roles in the regulation of vertebrate reproduction. Activins and inhibins have opposing actions on FSH (but not LH) synthesis, either inducing or inhibiting transcription of the FSHβ subunit gene (Fshb). The translational inhibitor cycloheximide (CHX) produces inhibin-like effects in cultured pituitary cells, selectively suppressing FSH production. Using the murine gonadotrope-like cell line, LβT2, as a model, we tested the hypothesis that a component of the activin pathway is highly labile in gonadotrope cells and that its rapid loss following CHX treatment impairs activin-stimulated Fshb transcription. Treatment of cells with CHX for 6h, but not 1h, blocked activin A-stimulated Fshb transcription. Pre-treatment of LβT2 cells with CHX for as few as 2-3h inhibited activin A-stimulated SMAD2/3 phosphorylation without altering total SMAD2/3 protein levels. These data indicated that CHX affects activin signalling upstream of SMAD proteins, most likely at the receptor level. Indeed, CHX rapidly reduced activin A binding to LβT2 cells. We went on to show that activin A signals via the type II receptor ACVR2, rather than ACVR2B, to regulate Fshb transcription and that the receptor has a half life of ~2h in LβT2 cells. The mechanism of ACVR2 turnover remains undefined, but appears to be ligand-, proteasome-, and lysosome-independent. Collectively, these data indicate that CHX produces inhibin-like effects in gonadotropes by preventing de novo synthesis of the highly labile ACVR2, thereby blocking activin signaling to the Fshb promoter.

Activin A induction of murine and ovine follicle-stimulating hormone β transcription is SMAD-dependent and TAK1 (MAP3K7)/p38 MAPK-independent in gonadotrope-like cells

Activins stimulate follicle-stimulating hormone (FSH) β subunit (Fshb) gene transcription in pituitary gonadotrope cells. Previous studies suggest that activins signal via homolog of Drosophila mothers against decapentaplegic (SMAD) proteins to stimulate murine or porcine Fshb promoter activity in the gonadotrope-like cell line, LβT2. In contrast, activins were suggested to regulate the ovine Fshb promoter via a SMAD-independent pathway involving TGFβ associated kinase 1 (TAK1, MAP3K7) and p38 mitogen activated protein kinase (MAPK). Here, we examined roles for TAK1 and p38 in activin A-stimulated murine and ovine Fshb transcription. The TAK1 inhibitor 5Z-7-Oxozeanol (Oxo) significantly impaired fold activin A induction of murine and ovine Fshb promoter-reporters (Fshb-luc) in LβT2 cells, but only at concentrations 50-100 fold greater than its IC(50) for TAK1. Moreover, Oxo failed to inhibit activin A induction of endogenous Fshb mRNA levels or fold induction of Fshb-luc activity by a constitutively active form of the activin type I receptor (ALK4). Oxo, at a concentration 5-10 fold greater than its IC(50) for TAK1, attenuated TAK1/TAB2 stimulation of a p38-dependent reporter in the same cells. A Map3k7 siRNA impaired TAK1/TAB2-stimulated p38-dependent reporter activity, but failed to antagonize activin A-stimulated Fshb-luc. Though TAK1 was previously suggested to act via p38 to stimulate the ovine Fshb promoter, activin A failed to stimulate p38 phosphorylation in LβT2 cells. In apparent contrast, however, the p38 inhibitors SB203580 and SB202190 concentration-dependently attenuated activin A-induced Fshb-luc activity. Given the lack of p38 activation, we postulated that the inhibitors might non-selectively antagonize ALK4 activity. Indeed, both attenuated activin A-stimulated SMAD2 phosphorylation, consistent with direct antagonism of ALK4 kinase activity. Finally, we observed that RNA-mediated suppression of Smad4, and to a lesser extent Smad3, attenuated activin A induction of both murine and ovine Fshb promoter-reporters. Collectively, these data suggest that activin A signals via SMAD proteins, but not TAK1 or p38, to regulate murine and ovine Fshb transcription in gonadotrope-like cells.

FOXL2 is involved in the synergy between activin and progestins on the follicle-stimulating hormone β-subunit promoter

Differential regulation of gonadotropin hormone production in the pituitary is critical for fertility. Activin and progesterone signaling in gonadotrope cells is important for Fshb gene expression. Previously, we reported that synergy between activin and progestins required the binding of SMAD proteins and the progesterone receptor (PR) to the murine Fshb promoter. In this study, we demonstrate that the FOXL2 transcription factor is also necessary for the full synergistic response between activin and progestins. We show that this synergy occurs in a species-specific manner and that multiple elements in the Fshb promoter that bind forkhead box L2 (FOXL2), SMA/mothers against decapentaplegic homologs (SMAD), and PR are required. Furthermore, we demonstrate that FOXL2 can physically interact with PR and SMAD3. Thus, it is likely that protein-protein interactions among FOXL2, SMAD, and PR recruited to the Fshb promoter play a key role in facilitating Fshb transcription before the secondary FSH surge in rodents.

SMADs and FOXL2 synergistically regulate murine FSHbeta transcription via a conserved proximal promoter element

Pituitary FSH regulates ovarian and testicular function. Activins stimulate FSHβ subunit (Fshb) gene transcription in gonadotrope cells, the rate-limiting step in mature FSH synthesis. Activin A-induced murine Fshb gene transcription in immortalized gonadotropes is dependent on homolog of Drosophila mothers against decapentaplegic (SMAD) proteins as well as the forkhead transcription factor FOXL2 (FOXL2). Here, we demonstrate that FOXL2 synergizes with SMAD2, SMAD3, and SMAD4 to stimulate murine Fshb promoter-reporter activity in heterologous cells. Moreover, SMAD3-induction of Fshb promoter activity or endogenous mRNA expression is dependent upon endogenous FOXL2 in homologous cells. FOXL2/SMAD synergy requires binding of both FOXL2 and SMAD3 or SMAD4 to DNA. Of three putative forkhead-binding elements identified in the murine Fshb promoter, only the most proximal is absolutely required for activin A induction of reporter activity in homologous cells. Additionally, mutations to the minimal SMAD-binding element adjacent to the proximal forkhead-binding element abrogate activin A or FOXL2/SMAD3 induction of reporter activity. In contrast, a mutation that impairs an adjacent PBX1/PREP1 (pre-B cell leukemia transcription factor 1-PBX/knotted-1 homeobox-1) binding site does not alter activin A-stimulated promoter activity in homologous cells. Collectively, these and previous data suggest a model in which activins stimulate formation of FOXL2-SMAD2/3/4 complexes, which bind to the proximal murine Fshb promoter to stimulate its transcription. Within these complexes, FOXL2 and SMAD3 or SMAD4 bind to adjacent cis-elements, with SMAD3 brokering the physical interaction with FOXL2. Because this composite response element is highly conserved, this suggests a general mechanism whereby activins may regulate and/or modulate Fshb transcription in mammals.

Activin A regulates porcine follicle-stimulating hormone beta-subunit transcription via cooperative actions of SMADs and FOXL2

Activins stimulate FSH synthesis and secretion by pituitary gonadotrope cells. Activin A induction of porcine and murine FSHβ (Fshb) gene transcription in immortalized gonadotropes is dependent on homolog of Drosophila mothers against decapentaplegic (SMAD) proteins as well as the forkhead transcription factor L2 (FOXL2). Using both heterologous and homologous cell models, we demonstrate that FOXL2 functionally synergizes with SMAD3/4 to stimulate porcine Fshb promoter-reporter activity. We further show that endogenous FOXL2 and SMAD2/3 physically interact in homologous cells. We identify two composite cis-elements of adjacent FOXL2 and SMAD binding sites in the proximal porcine Fshb promoter that mediate activin A, FOXL2, and SMAD3 actions. FOXL2 can bind these elements independently of SMADs, whereas SMAD3/4 binding requires high-affinity FOXL2 binding. Conversely, FOXL2 alone is insufficient to regulate Fshb transcription and requires SMADs to induce promoter activity. Collectively, our data suggest a model in which activins stimulate formation and nuclear accumulation of SMAD3/4 complexes, which interact with FOXL2 bound to at least two proximal promoter elements. This association stabilizes SMAD3/4 binding to adjacent SMAD binding elements. SMAD-FOXL2 complexes then mediate activation of transcription through a currently unknown mechanism. Conservation of one of the two composite cis-elements suggests that this may form part of a general mechanism whereby activins regulate Fshb subunit transcription and FSH synthesis.

A FoxL in the Smad house: activin regulation of FSH

Follicle-stimulating hormone (FSH), produced by pituitary gonadotrope cells, is required for maturation of ovarian follicles. The FSHbeta subunit is the limiting factor for production of mature hormone and provides biological specificity. Activin dramatically induces FSHbeta transcription and the secondary rise in FSH, important for follicular development, is dependent on this induction. Thus, regulation of FSHbeta levels by activin is crucial for female reproductive fitness. This review discusses activin signaling pathways, transcription factors and FSHbeta promoter elements required for activin responsiveness. Because FoxL2, a forkhead transcription factor, was recently shown to be instrumental in relaying activin signaling to the FSHbeta promoter, we focus in this paper on its role and the inter-relatedness of several key players in activin responsiveness on the FSHbeta promoter.

Hormones in synergy: regulation of the pituitary gonadotropin genes

The precise interplay of hormonal influences that governs gonadotropin hormone production by the pituitary includes endocrine, paracrine and autocrine actions of hypothalamic gonadotropin-releasing hormone (GnRH), activin and steroids. However, most studies of hormonal regulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary gonadotrope have been limited to analyses of the isolated actions of individual hormones. LHbeta and FSHbeta subunits have distinct patterns of expression during the menstrual/estrous cycle as a result of the integration of activin, GnRH, and steroid hormone action. In this review, we focus on studies that delineate the interplay among these hormones in the regulation of LHbeta and FSHbeta gene expression in gonadotrope cells and discuss how signaling cross-talk contributes to differential expression. We also discuss how recent technological advances will help identify additional factors involved in the differential hormonal regulation of LH and FSH.

Hormonal signaling to follicle stimulating hormone beta-subunit gene expression

Expression of the hormone-specific beta-subunit of follicle stimulating hormone (FSHbeta) is regulated primarily by gonadotropin releasing hormone (GnRH) and activin, with additional feedback by various steroids. While the nature of this hormonal regulation appears conserved, the molecular mechanisms mediating these effects appear less so. This is apparent from the diverse cis-elements required for hormonal stimulation in different species, distinct transcription factors that seem to mediate the effects, as well as the lack of conservation of several reportedly functional cis-elements across species. Recent additional information on the molecular mechanisms through which these regulatory hormones exert their effects, supports the possibility of species-specific mechanisms of regulation, while some redundancy may exist in signaling by the activated transcription factors which allows preservation of the hormonal regulation in these different promoter contexts.

TAK1 is required for survival of mouse fibroblasts treated with TRAIL, and does so by NF-kappaB dependent induction of cFLIPL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is known as a “death ligand”—a member of the TNF superfamily that binds to receptors bearing death domains. As well as causing apoptosis of certain types of tumor cells, TRAIL can activate both NF-κB and JNK signalling pathways. To determine the role of TGF-β-Activated Kinase-1 (TAK1) in TRAIL signalling, we analyzed the effects of adding TRAIL to mouse embryonic fibroblasts (MEFs) derived from TAK1 conditional knockout mice. TAK1−/− MEFs were significantly more sensitive to killing by TRAIL than wild-type MEFs, and failed to activate NF-κB or JNK. Overexpression of IKK2-EE, a constitutive activator of NF-κB, protected TAK1−/− MEFs against TRAIL killing, suggesting that TAK1 activation of NF-κB is critical for the viability of cells treated with TRAIL. Consistent with this model, TRAIL failed to induce the survival genes cIAP2 and cFlipL in the absence of TAK1, whereas activation of NF-κB by IKK2-EE restored the levels of both proteins. Moreover, ectopic expression of cFlipL, but not cIAP2, in TAK1−/− MEFs strongly inhibited TRAIL-induced cell death. These results indicate that cells that survive TRAIL treatment may do so by activation of a TAK1–NF-κB pathway that drives expression of cFlipL, and suggest that TAK1 may be a good target for overcoming TRAIL resistance.

Activin A induces ovine follicle stimulating hormone beta using -169/-58 bp of its promoter and a simple TATA box

BACKGROUND

Activin A increases production of follicle stimulating hormone (FSH) by inducing transcription of its beta subunit (FSHB). This induction has been studied here in LbetaT2 gonadotropes using transient expression of ovine FSHBLuc (-4741 bp of ovine FSHB promoter plus exon/intron 1 linked to Luc). Several sequences between -169/-58 bp of the ovine FSHB proximal promoter are necessary for induction by activin A in LbetaT2 cells, but deletions between -4741/-752 bp decrease induction > 70% suggesting the existence of other important 5' sequences. Induction disappears if a minimal T81 thymidine kinase promoter replaces the ovine FSHB TATA box and 3' exon/intron. The study reported here was designed to determine if sequences outside -169/-58 bp are important for induction of ovine FSHB by activin A.

METHODS

Progressively longer deletions of ovine FSHBLuc were created between -4741/-195 bp. Deletions internal to this region were created also, but replaced with substitute DNA. The ovine FSHB TATA box region (-40/+3 bp) was replaced by thymidine kinase and rat prolactin minimal promoters, and substitutions were made in 3' intron/exon sequences. All constructs were tested for basal and activin A-induced expression in LbetaT2 cells.

RESULTS

Successive 5' deletions progressively lowered fold-induction by activin A from 9.5 to zero, but progressively increased basal expression. Replacing deletions with substitute DNA showed no changes in basal expression or fold-induction. Induction by activin A was supported by the minimal rat prolactin promoter (TATA box) but not the thymidine kinase promoter (no TATA box). Replacement mutations in the 3' region did not decrease induction by activin A.

CONCLUSION

The data show that specific ovine FSHB sequences 5' to -175 bp or 3' of the transcription start site are not required for induction by activin A. A minimal TATA box promoter supports induction by activin A, but the sequence between the TATA box and transcription start site seems unimportant.

Paired-like homeodomain transcription factors 1 and 2 regulate follicle-stimulating hormone beta-subunit transcription through a conserved cis-element

Paired-like homeodomain transcription factors (PITX) regulate the activity of pituitary hormone-encoding genes. Here, we examined mechanisms through which the family of PITX proteins control murine FSH beta-subunit (Fshb) transcription. We observed that endogenous PITX1 and PITX2 isoforms from murine LbetaT2 gonadotrope cells could bind a highly conserved proximal cis-element. Transfection of PITX1 or PITX2C in heterologous cells stimulated both murine and human Fshb/FSHB promoter-reporter activities, and in both cases, mutation of the critical cis-element abrogated these effects. In homologous LbetaT2 cells, the same mutation decreased basal reporter activity and greatly reduced activin A-stimulated transcription from murine and human promoter-reporters. Transfecting dominant-negative forms of PITX1 or PITX2C or knocking down PITX1 or -2 expression by RNA interference in LbetaT2 cells inhibited murine Fshb transcription, confirming roles for endogenous PITX proteins. Both PITX1 and PITX2C interacted with Smad3 (an effector of the activin signaling cascade in these cells) in coprecipitation experiments, and the PITX binding site mutation greatly inhibited Smad2/3/4-stimulated Fshb transcription. In summary, both PITX1 and PITX2C regulate murine and human Fshb/FSHB transcription through a conserved cis-element in the proximal promoter. Furthermore, the data indicate both common and distinct mechanisms of PITX1 and PITX2C action.

Synergistic induction of follicle-stimulating hormone beta-subunit gene expression by gonadal steroid hormone receptors and Smad proteins

LH and FSH play crucial roles in mammalian reproduction by mediating steroidogenesis and gametogenesis. Gonadal steroid hormones influence gonadotropin production via feedback to the hypothalamus and pituitary. We previously demonstrated that progesterone and testosterone can stimulate expression of the FSH beta-subunit gene in immortalized gonadotrope-derived LbetaT2 cells. Herein, we investigate how these gonadal steroids modulate activin signaling in the gonadotrope. Cotreatment of LbetaT2 cells or mouse primary pituitary cells with steroids and activin results in a synergistic induction of FSHbeta gene expression. This synergy decreases when DNA-binding mutations are introduced into the steroid receptors or when mutations that reduce steroid hormone responsiveness are introduced into the FSHbeta promoter, indicating that synergy requires direct DNA binding of the steroid receptors. Furthermore, classical activin signaling via Smad proteins is necessary for this synergy. In addition, these steroid receptors physically interact with Smads and are sufficient for the synergism to occur on the FSHbeta promoter. Disruption of Smad binding to the promoter with a Smad protein lacking the DNA-binding domain or an FSHbeta promoter containing mutated activin-response elements prevents the synergistic enhancement of FSHbeta transcription. Collectively, our data demonstrate that the molecular mechanism for gonadal steroid hormone action on the FSHbeta promoter involves cross-talk between the steroid and activin signaling pathways. They also reveal that this synergism requires binding of both the steroid receptors and Smad proteins to their cognate DNA-binding elements and likely involves a direct protein-protein interaction between the two types of transcription factors.

Pulsatile gonadotropin-releasing hormone stimulation of gonadotropin subunit transcription in rat pituitaries: evidence for the involvement of Jun N-terminal kinase but not p38

We investigated whether Jun N-terminal kinase (JNK) and p38 mediate gonadotropin subunit transcriptional responses to pulsatile GnRH in normal rat pituitaries. A single pulse of GnRH or vehicle was given to female rats in vivo, pituitaries collected, and phosphorylated JNK and p38 measured. GnRH stimulated an increase in JNK phosphorylation within 5 min, which peaked 15 min after GnRH (3-fold). GnRH also increased p38 phosphorylation 2.3-fold 15 min after stimulus. Rat pituitary cells were given 60-min pulses of GnRH or media plus the JNK inhibitor SP600125 (SP, 20 microM), p38 inhibitor SB203580 (20 microM), or vehicle. In vehicle-treated groups, GnRH pulses increased LHbeta and FSHbeta primary transcript (PT) levels 3-fold. SP suppressed both basal and GnRH-induced increases in FSHbeta PT by half, but the magnitude of responses to GnRH was unchanged. In contrast, SP had no effect on basal LHbeta PT but suppressed the stimulatory response to GnRH. SB203580 had no effect on the actions of GnRH on either LH or FSHbeta PTs. Lbeta-T2 cells were transfected with dominant/negative expression vectors for MAPK kinase (MKK)-4 and/or MKK-7 plus a rat LHbeta promoter-luciferase construct. GnRH stimulated a 50-fold increase in LHbeta promoter activity, and the combination of MKK-4 and -7 dominant/negatives suppressed the response by 80%. Thus, JNK (but not p38) regulates both LHbeta and FSHbeta transcription in a differential manner. For LHbeta, JNK is essential in mediating responses to pulsatile GnRH. JNK also regulates FSHbeta transcription (i.e. maintaining basal expression) but does not play a role in responses to GnRH.

p38 mitogen-activated protein kinase is critical for synergistic induction of the FSH(beta) gene by gonadotropin-releasing hormone and activin through augmentation of c-Fos induction and Smad phosphorylation

GnRH and activin independently and synergistically activate transcription of the FSH beta-subunit gene, the subunit that provides specificity and is the limiting factor in the synthesis of the mature hormone. This synergistic interaction, as determined by two-way ANOVA, is specific for FSHbeta and may, therefore, contribute to differential expression of the two gonadotropin hormones, which is critical for the reproductive cycle. We find that the cross-talk between the GnRH and activin signaling pathways occurs at the level of p38 MAPK, because the synergy is dependent on p38 MAPK activity, which is activated by GnRH, and activin cotreatment augments p38 activation by GnRH. Both the Smad and activator protein-1 binding sites on the FSHbeta promoter are necessary and sufficient for synergy. After cotreatment, Smad 3 proteins are more highly phosphorylated on the activin-receptor signaling-dependent residues on the C terminus than with activin treatment alone, and c-Fos is more highly expressed than with GnRH treatment alone. Inhibition of p38 by either of two different inhibitors or a dominant-negative p38 kinase abrogates synergy on FSHbeta expression, reduces c-Fos induction by GnRH, and prevents the further increase in c-Fos levels that occurs with cotreatment. Additionally, p38 is necessary for maximal Smad 3 C-terminal phosphorylation by activin treatment alone and for the further increase caused by cotreatment. Thus, p38 is the pivotal signaling molecule that integrates GnRH and activin interaction on the FSHbeta promoter through higher induction of c-Fos and elevated Smad phosphorylation.

Activin B can signal through both ALK4 and ALK7 in gonadotrope cells

BACKGROUND

Activins stimulate pituitary FSH synthesis via transcriptional regulation of the FSHbeta subunit gene (Fshb). Like other members of the TGFbeta superfamily, these ligands signal through complexes of type I and type II receptor serine/threonine kinases. The type I receptors, or activin receptor-like kinases (ALKs), propagate intracellular signals upon ligand binding and phosphorylation by associated type II receptors. ALK4 is generally regarded as the type I receptor for activins; however, recent data suggested that activin B and AB might also signal through ALK7. Here, we examined a role for ALK7 in activin B-regulated Fshb transcription.

METHODS

We analyzed ALK7 mRNA expression in immortalized gonadotrope cells, LbetaT2, and adult murine pituitary by RT-PCR. We next transfected LbetaT2 cells with wild-type and kinase-deficient (Lys to Arg, KR) forms of ALK4 and ALK7 and examined the effects of these receptors on activin A and B stimulated Fshb promoter-reporter activity. Cells were also transfected with constitutively active (Thr to Asp, TD) forms of the receptors and their effects on endogenous Fshb mRNA levels and phosphorylation of transfected Smad2/3 were measured by RT-PCR and Western blot, respectively. Finally, we measured ALK4(TD) and ALK7(TD) stimulation of Fshb transcription when endogenous Smad3 levels were depleted using short hairpin RNAs.

RESULTS

ALK7 mRNA was expressed in LbetaT2 cells and pituitary gland. Transfection of ALK4 cDNA potentiated the effects of both activin A and activin B on Fshb promoter-reporter activity in LbetaT2 cells. In contrast, ALK7 transfection selectively potentiated activin B's effects. Transfection of ALK4(KR) and ALK7(KR) partly inhibited basal and activin B-stimulated reporter activity, whereas ALK4(TD) and ALK7(TD) potently stimulated the Fshb promoter and endogenous mRNA levels. Transfection of both ALK4(TD) and ALK7(TD) stimulated Smad2/3 phosphorylation, and the effects of both receptors on Fshb promoter activity were inhibited by depletion of endogenous Smad3 protein levels.

CONCLUSION

These data suggest that immortalized gonadotropes express ALK7 and that activin B can signal through this receptor to stimulate Fshb transcription. The relative roles of endogenous ALK4 and ALK7 receptors in mediating activin B's effects in these cells have yet to be determined.

Activin inhibits the human Pit-1 gene promoter through the p38 kinase pathway in a Smad-independent manner

The pituitary transcription factor Pit-1 regulates hormonal production from the anterior pituitary gland. However, the mechanisms by which Pit-1 gene expression is regulated in humans are poorly understood. Activin, a member of the TGFbeta superfamily, acts as a negative regulator of cell growth and prolactin gene expression in lactotrope cells. In this study, we show that activin negatively regulates the human Pit-1 gene promoter. We defined a 117-bp element within the Pit-1 promoter that is sufficient to relay these inhibitory effects. We further investigated the signaling pathways that mediate activin-induced inhibition of Pit-1 gene promoter in pituitary lactotrope cells. We found that the activin effects on Pit-1 gene regulation are Smad independent and require the p38 MAPK pathway. Specifically, blocking p38 kinase activity reverses activin-mediated inhibition of the Pit-1 gene promoter. Together, our results highlight the p38 MAPK pathway as a key regulator of activin function in pituitary lactotrope cells and further emphasizes the critical role played by activin in regulating hormonal production in the pituitary gland.

Differential regulation of follicle stimulating hormone by activin A and TGFB1 in murine gonadotropes

BACKGROUND

Activins stimulate the synthesis of follicle stimulating hormone (FSH) in pituitary gonadotropes, at least in part, by inducing transcription of its beta subunit (Fshb). Evidence from several laboratories studying transformed murine LbetaT2 gonadotropes indicates that activins signal through Smad-dependent and/or Smad-independent pathways, similar to those used by transforming growth factor beta-1 (TGFB1) in other cell types. Therefore, given common intracellular signaling mechanisms of these two ligands, we examined whether TGFBs can also induce transcription of Fshb in LbetaT2 cells as well as in purified primary murine gonadotropes.

METHODS

Murine Fshb promoter-reporter (-1990/+1 mFshb-luc) activity was measured in LbetaT2 cells treated with activin A or TGFB1, and in cells transfected with either activin or TGFB receptors. The ability of the ligands to stimulate phosphorylation of Smads 2 and 3 in LbetaT2 cells was measured by western blot analysis, and expression of TGFB type I and II receptors was assessed by reverse transcriptase polymerase chain reaction in both LbetaT2 cells and primary gonadotropes purified from male mice of different ages. Finally, regulation of endogenous murine Fshb mRNA levels by activin A and TGFB1 in purified gonadotropes and whole pituitary cultures was measured using quantitative RT-PCR.

RESULTS

Activin A dose-dependently stimulated -1990/+1 mFshb-luc activity in LbetaT2 cells, but TGFB1 had no effect at doses up to 5 nM. Similarly, activin A, but not TGFB1, stimulated Smad 2 and 3 phosphorylation in these cells. Constitutively active forms of the activin (Acvr1b-T206D) and TGFB (TGFBR1-T204D) type I receptors strongly stimulated -1990/+1 mFshb-luc activity, showing that mechanisms down stream of Tgfbr1 seem to be intact in LbetaT2 cells. RT-PCR analysis of LbetaT2 cells and whole adult murine pituitaries indicated that both expressed Tgfbr1 mRNA, but that Tgfbr2 was not detected in LbetaT2 cells. When cells were transfected with a human TGFBR2 expression construct, TGFB1 acquired the ability to significantly stimulate -1990/+1 mFshb-luc activity. In contrast to LbetaT2 cells, primary murine gonadotropes from young mice (8-10 weeks) contained low, but detectable levels of Tgfbr2 mRNA and these levels increased in older mice (1 yr). A second surprise was the finding that treatment of purified primary gonadotropes with TGFB1 decreased murine Fshb mRNA expression by 95% whereas activin A stimulated expression by 31-fold.

CONCLUSION

These data indicate that TGFB1-insensitivity in LbetaT2 cells results from a deficiency in Tgfbr2 expression. In primary gonadotropes, however, expression of Tgfbr2 does occur, and its presence permits TGFB1 to inhibit Fshb transcription, whereas activin A stimulates it. These divergent actions of activin A and TGFB1 were unexpected and show that the two ligands may act through distinct pathways to cause opposing biological effects in primary murine gonadotropes.