[Show abstract][Hide abstract] ABSTRACT: Reproduction is integrated by interaction of neural and hormonal signals converging on hypothalamic neurons for controlling gonadotropin-releasing hormone (GnRH). Kisspeptin, the peptide product of the kiss1 gene and the endogenous agonist for the GRP54 receptor, plays a key role in the regulation of GnRH secretion. In the present study, we investigated the interaction between kisspeptin, estrogen and BMPs in the regulation of GnRH production by using mouse hypothalamic GT1-7 cells. Treatment with kisspeptin increased GnRH mRNA expression and GnRH protein production in a concentration-dependent manner. The expression levels of kiss1 and GPR54 were not changed by kisspeptin stimulation. Kisspeptin induction of GnRH was suppressed by co-treatment with BMPs, with BMP-4 action being the most potent for suppressing the kisspeptin effect. The expression of kisspeptin receptor, GPR54, was suppressed by BMPs, and this effect was reversed in the presence of kisspeptin. It was also revealed that BMP-induced Smad1/5/8 phosphorylation and Id-1 expression were suppressed and inhibitory Smad6/7 was induced by kisspeptin. In addition, estrogen induced GPR54 expression, while kisspeptin increased the expression levels of ERα and ERβ, suggesting that the actions of estrogen and kisspeptin are mutually enhanced in GT1-7 cells. Moreover, kisspeptin stimulated MAPKs and AKT signaling, and ERK signaling was functionally involved in the kisspeptin-induced GnRH expression. BMP-4 was found to suppress kisspeptin-induced GnRH expression by reducing ERK signaling activity. Collectively, the results indicate that the axis of kisspeptin-induced GnRH production is bi-directionally controlled, being augmented by an interaction between ERα/β and GPR54 signaling and suppressed by BMP-4 action in GT1-7 neuron cells. (254 words).
[Show abstract][Hide abstract] ABSTRACT: The role of melatonin, a regulator of circadian rhythm, in adrenocorticotropin (ACTH) production by corticotrope cells has not been elucidated. In this study, we investigated the effect of melatonin on ACTH production in relation to the biological activity of bone morphogenetic protein (BMP)-4 using mouse corticotrope AtT20 cells that express melatonin type-1 (MT1R) but not type-2 (MT2R) receptors. We previously reported that BMP-4 inhibits corticotropin-releasing hormone (CRH)-induced ACTH production and proopiomelanocortin (POMC) transcription by inhibiting MAPK signaling. Both melatonin and an MT1R/MT2R agonist, ramelteon, suppressed CRH-induced ACTH production, POMC transcription and cAMP synthesis. The inhibitory effects of ramelteon on basal and CRH-induced POMC mRNA and ACTH levels were more potent than those of melatonin. Treatment with melatonin or ramelteon in combination with BMP-4 additively suppressed CRH-induced ACTH production. Of note, the level of MT1R expression was upregulated by BMP-4 stimulation. The suppressive effects of melatonin and ramelteon on POMC transcription and cAMP synthesis induced by CRH were not affected by an MT2R antagonist, luzindole. On the other hand, BMP-4-induced Smad1/5/8 phosphorylation and the expression of a BMP target gene, Id-1, were augmented in the presence of melatonin and ramelteon. Considering that the expression levels of BMP receptors, ALK-3/BMPRII, were increased by ramelteon, MT1R action may play an enhancing role in BMP-receptor signaling. Among the MT1R signaling pathways including AKT, ERK and JNK pathways, inhibition of AKT signaling functionally reversed the MT1R effects on both CRH-induced POMC transcription and BMP-4-induced Id-1 transcription. Collectively, MT1R signaling and BMP-4 actions were mutually augmented, leading to fine-tuning of ACTH production by corticotrope cells. (259 words).
[Show abstract][Hide abstract] ABSTRACT: Imbalanced functions of osteoclasts and osteoblasts are involved in various types of bone damage including postmenopausal osteoporosis. In the present study, we investigated the cellular mechanism by which estrogen interacts in the process of osteoblastic differentiation regulated by BMP-4 using mouse MC3T3-E1 cells that express estrogen receptors (ER) and BMP-4. Estradiol enhanced BMP-4-induced Runx2, osterix, ALP and osteocalcin expression in MC3T3-E1 cells. BMP-4-induced mineralization shown by Alizarin red staining was also facilitated by estrogen treatment. It was revealed that estrogen upregulated BMP-4-induced Smad1/5/8 phosphorylation, BRE-Luc activity and Id-1 mRNA expression. The expression of BMPRII was increased by estrogen in MC3T3-E1 cells, and inhibition of BMPRII or ALK-2/3 signaling impaired the effect of estrogen on BMP-4 signaling. Of note, the enhanced expression of osterix, ALP and osteocalcin mRNAs induced by BMP-4 and estrogen was reversed in the presence of an ER antagonist. Given that membrane-impermeable estrogen also upregulated BMP-4-induced expression of osteoblastic markers and Id-1 mRNA, non-genomic ER activity is involved in the mechanism by which estrogen enhances BMP-4-induced osteoblast differentiation in MC3T3-E1 cells. On the other hand, the expression of ERα and endogenous BMP-4 was suppressed by BMP-4 treatment regardless of the presence of estrogen, implying the presence of a negative feedback loop for osteoblast differentiation. Thus, estrogen is functionally involved in the process of osteoblast differentiation regulated by BMP-4 through upregulating BMP sensitivity of MC3T3-E1 cells.
[Show abstract][Hide abstract] ABSTRACT: Somatostatin is expressed in the hypothalamus, pancreas and gastrointestinal tracts and it inhibits the secretion of various hormones in vivo.In the rodent ovary, somatostatin receptor (SSTR) subtypes 2 and 5 are expressed in granulosa cells and oocytes.Somatostatin analogs have been clinically used for treatment of endocrine tumors. For this purpose, relatively high-dose or long-term treatmentsof somatostatin analogs are necessary; however, the direct and continuous impact of somatostatin analogs on gonadal functions has yet to be elucidated. In the present study, we investigated the effects of somatostatin analogs(octreotide and pasireotide) on ovarian steroidogenesisby rat primary granulosa cell culture. The expression levels of SSTR2 and SSTR5 in granulosa cells were upregulated by FSH treatment.Treatment with somatostatin analogs decreased FSH-induced estradiol production with reduction in aromatase mRNA expression, while the treatment also suppressed FSH-induced progesterone production with reduction of mRNAs levels of StAR, P450scc and 3βHSD2 in granulosa cells. This trend was also observed in a granulosa/oocyte co-culture condition. The effect of pasireotide was more potent than that of octreotide. FSH-induced synthesis of steroids and cAMPwas also suppressed bysomatostatin analog treatment. Notably, pretreatment with a BMP-binding protein,noggin, reversed the suppressive effects of somatostatin analogs on progesterone and cAMPproduction, suggesting that the endogenous BMP system is functionally involved in the SSTR effects in granulosa cells. Treatment with BMP-2, -4, -6 and -7 decreased the mRNA expression of inhibitory Smads6 and 7, leading to enhancement of BMP actions detected by Id-1 transcription in granulosa cells. Collectively, the results revealed that SSTR activationmodulates ovarian steroidogenesis by upregulating endogenous BMP activity in growing follicles.
The Journal of steroid biochemistry and molecular biology 11/2012; 134(1). DOI:10.1016/j.jsbmb.2012.10.018 · 4.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aldosterone is synthesized in the zona glomerulosa of the adrenal cortex. We previously reported the presence of a functional BMP system including BMP-6 in human adrenocortical cells. BMP-6 contributes to Ang II-induced aldosterone production by activating Smad signaling, in which endogenous BMP-6 action is negatively controlled by Ang II in vitro. In the present study, we examined the in vivo role of BMP-6 in regulation of aldosterone by neutralizing endogenous BMP-6 in rats treated with immunization against BMP-6. Three-week-old male rats were actively immunized with rat mature BMP-6 antigen conjugated with keyhole limpet hemocyanin (KLH). The immunization treatment had no effect on bilateral adrenal weight or its ratio to body weight. Urinary aldosterone excretion was time-dependently increased during the 8-week observation period in the control group. Of note, the level of urinary aldosterone excretion in BMP-6-KLH-immunized rats was significantly reduced compared to that in the control group, suggesting that endogenous BMP-6 contributes to the induction of aldosterone production in vivo. Moreover, the level of urinary aldosterone/creatinine after 8-week treatment was significantly lowered by treatment with BMP-6-KLH. In contrast, with chronic Ang II treatment, urinary aldosterone and creatinine-corrected values at 8 weeks were not significantly different between the two groups, suggesting that the effects of BMP-6-KLH were impaired under the condition of chronic treatment with Ang II. The mRNA levels of Cyp11b2, but not those of Star, P450scc and 3βhsd2, were significantly decreased in adrenal tissues isolated from BMP-6-KLH-immunized rats after 8-week treatment. Furthermore, the ratio of plasma aldosterone level to corticosterone was significantly decreased by immunization with BMP-6-KLH. Collectively, the results indicate that endogenous BMP-6 is functionally linked to aldosterone synthesis by the zona glomerulosa in the adrenal cortex in vivo.
The Journal of steroid biochemistry and molecular biology 04/2012; 132(1-2):8-14. DOI:10.1016/j.jsbmb.2012.04.004 · 4.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although kit ligand (KL)-c-kit interaction is known to be critical for oogenesis and folliculogenesis, its role in ovarian steroidogenesis has yet to be elucidated. We studied the impact of KL-c-kit interaction in regulation of steroidogenesis using rat oocyte/granulosa cell co-culture. In the presence of oocytes, soluble KL suppressed FSH-induced estradiol production and aromatase mRNA expression without affecting FSH-induced progesterone production. The KL effect on steroidogenesis was interrupted by an anti-c-kit neutralizing antibody, suggesting that KL-c-kit interaction is involved in suppression of estrogen by granulosa cells through oocyte c-kit action. The cAMP-PKA pathway activity was not directly involved in the estrogen regulation by KL-c-kit action. It was of note that KL treatment increased the expression levels of oocyte-derived FGF-8, GDF-9 and BMP-6, while it reduced the expression levels of oocyte-derived BMP-15 in the oocyte-granulosa cell co-culture. Given the findings that FGF-8, but not GDF-9, BMP-6 or -15, suppressed FSH-induced estrogen production by granulosa cells, oocyte-derived FGF-8 is linked to suppression of FSH-induced estrogen production through the KL-c-kit interaction. Furthermore, the suppression of FSH-induced estrogen production by KL in the co-culture was reversed by a FGF receptor kinase inhibitor and the effect of the inhibitor was enhanced in combination with extracellular-domain protein of BMPRII, which interferes with BMP-15 and GDF-9 activities. Thus, the actions of endogenous oocyte factors including FGF-8 and BMP-15/GDF-9 were involved in the KL activity that inhibited FSH-induced estradiol production. Collectively, the results indicate that KL-c-kit interaction plays a role in estrogenic regulation through oocyte-granulosa cell communication.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown that bone morphogenetic proteins (BMPs), particularly BMP-7, have an inhibitory role in the development of various renal diseases. We previously reported antagonistic effects of BMPs on renal mesangial cell proliferation induced by aldosterone (Aldo) in vitro. In the present study, we investigated in vivo roles of BMPs in Aldo-induced renal glomerular injury. BALB/c mice aged 6 weeks were treated with Aldo injection (5 μg per day, intraperitoneally) and/or oral administration of high-salt (2%) water for 9 weeks. Systemic blood pressure, body weight, kidney weight and daily proteinuria were not significantly changed by Aldo and/or high-salt treatment. However, renal histological examination revealed increases in glomerular cellularity and glomerular diameter in the groups treated with Aldo injection and high-salt administration. Immunohistochemistry demonstrated expression of BMP-4 and -7 in the glomerular mesangial region. Aldo causes renal glomerular damage by stimulating mesangial cell proliferation and increasing extracellular matrix via the mineralocorticoid receptor (MR). MR messenger RNA (mRNA) expression in the renal cortex was transiently increased by 3-week treatment with Aldo and high-salt intake, but was decreased by 9-week treatment. Furthermore, the expression levels of BMP-4 and -7 mRNA were enhanced in the renal cortex treated with Aldo and high-salt administration. These findings suggest that the renal BMP system is activated by Aldo under the condition of high-salt exposure, which may have a key role in antagonizing glomerular damage in vivo.
Hypertension Research 11/2011; 35(3):312-7. DOI:10.1038/hr.2011.186 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: GH induces preantral follicle growth and differentiation with oocyte maturation. However, the effects of GH on ovarian steroidogenesis and the mechanisms underlying its effects have yet to be elucidated. In this study, we investigated the actions of GH on steroidogenesis by rat granulosa cells isolated from early antral follicles by focusing on the ovarian bone morphogenetic protein (BMP) system. We found that GH suppressed FSH-induced estradiol production with reduction in aromatase expression and, in contrast, GH increased FSH-induced progesterone level with induction of steroidogenic acute regulatory protein, side chain cleavage cytochrome P450, and 3β-hydroxysteroid dehydrogenase. The effects of GH on steroidogenesis by granulosa cells were enhanced in the presence of the BMP antagonist noggin. Coculture of GH with oocytes did not alter GH regulation of steroidogenesis. Steroid production induced by cAMP donors was not affected by GH treatment and the GH effects on FSH-induced steroid production were not accompanied by changes in cAMP synthesis, suggesting that GH actions were not directly mediated by the cAMP-protein kinase A pathway. GH exerted synergistic effects on MAPK activation elicited by FSH, which regulated FSH-induced steroidogenesis. In addition, GH-induced signal transducer and activator of transcription phosphorylation was involved in the induction of IGF-I expression. GH increased IGF-I, IGF-I receptor, and FSH receptor expression in granulosa cells, and inhibition of IGF-I signaling restored GH stimulation of FSH-induced progesterone production, suggesting that endogenous IGF-I is functionally involved in GH effects on progesterone induction. BMP inhibited IGF-I effects that increased FSH-induced estradiol production with suppression of expression of the GH/IGF-I system, whereas GH/IGF-I actions impaired BMP-Sma and Mad related protein 1/5/8 signaling through down-regulation of the expression of BMP receptors. Thus, GH acts to modulate estrogen and progesterone production differentially through endogenous IGF-I activity in granulosa cells, in which GH-IGF-I interaction leads to antagonization of BMP actions including suppression of FSH-induced progesterone production. Mutual balance between GH/IGF-I and BMP signal intensities may be a key for regulating gonadotropin-induced steroidogenesis in growing follicles.
[Show abstract][Hide abstract] ABSTRACT: The existence of a functional bone morphogenetic protein (BMP) system in the pituitary has been recognized. Recent studies have provided evidence that BMPs elicit differential actions in the regulation of prolactin (PRL) and adrenocorticotropin (ACTH) release in lactotropinoma and corticotropinoma cells, respectively. BMPs play a key role in the modulation of somatostatin receptor (SSTR) sensitivity of lactosomatotrope cells in an autocrine/paracrine manner. In addition, SSTR action enhances BMP responsiveness in corticotrope cells. The functional link between BMP receptor signaling and SSTR actions may be crucial for individual tolerance to somatostatin analogs for controlling PRL and ACTH production. Adjustment of the endogenous SSTR sensitivity may be an effective strategy to inhibit the growth activity and hormonal productivity of intractable pituitary tumors.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have suggested possible adverse effects of thiazolidinediones on bone metabolism. However, the detailed mechanism by which the activity of PPAR affects bone formation has not been elucidated. Impaired osteoblastic function due to cytokines is critical for the progression of inflammatory bone diseases. In the present study, we investigated the cellular mechanism by which PPAR actions interact with osteoblast differentiation regulated by BMP and TNF-α using mouse myoblastic C2C12 cells. BMP-2 and -4 potently induced the expression of various bone differentiation markers including Runx2, osteocalcin, type-1 collagen and alkaline phosphatase (ALP) in C2C12 cells. When administered in combination with a PPARα agonist (fenofibric acid) but not with a PPARγ agonist (pioglitazone), BMP-4 enhanced osteoblast differentiation through the activity of PPARα. The osteoblastic changes induced by BMP-4 were readily suppressed by treatment with TNF-α. Interestingly, the activities of PPARα and PPARγ agonists reversed the suppression by TNF-α of osteoblast differentiation induced by BMP-4. Furthermore, TNF-α-induced phosphorylation of MAPKs, NFκB, IκB and Stat pathways was inhibited in the presence of PPARα and PPARγ agonists with reducing TNF-α receptor expression. In view of the finding that inhibition of SAPK/JNK, Stat and NFκB pathways reversed the TNF-α suppression of osteoblast differentiation, we conclude that these cascades are functionally involved in the actions of PPARs that antagonize TNF-α-induced suppression of osteoblast differentiation. It was further discovered that the PPARα agonist enhanced BMP-4-induced Smad1/5/8 signaling through downregulation of inhibitory Smad6/7 expression, whereas the PPARγ agonist impaired this activity by suppressing BMPRII expression. On the other hand, BMPs increased the expression levels of PPARα and PPARγ in the process of osteoblast differentiation. Thus, PPARα actions promote BMP-induced osteoblast differentiation, while both activities of PPARα and PPARγ suppress TNF-α actions. Collectively, our present data establishes that PPAR activities are functionally involved in modulating the interaction between the BMP system and TNF-α receptor signaling that is crucial for bone metabolism.
[Show abstract][Hide abstract] ABSTRACT: It is known that bone morphogenetic proteins (BMPs) regulate gonadotropin transcription and production by pituitary gonadotrope cells. However, the role of BMPs in gonadotropin-releasing hormone (GnRH)-induced FSH production remains uncertain. Here, we describe a functional link between BMP-6 and BMP-7 signals and FSH transcriptional activity induced by GnRH using mouse gonadotrope LβT2 cells. In LβT2 cells, BMP-6 and BMP-7 increased mouse FSHβ-promoter activity in a concentration-dependent manner. The induction by BMP-6 and BMP-7 was inhibited by treatment with extracellular domains of ActRII but not BMPRII. These findings suggest that the type II receptor ActRII participates in BMP-induced FSHβ transcription regulation. Notably, BMP-6, but not BMP-7, enhanced GnRH-induced FSHβ-promoter activity in LβT2 cells. Since GnRH stimulated MAPK phosphorylation in LβT2 cells, a functional link between MAPK and FSHβ transcription was examined. Inhibition of the ERK pathway, but not that of p38 or SAPK/JNK signaling, suppressed GnRH-induced FSHβ transcription, suggesting that ERK is functionally involved in GnRH-induced FSHβ transcription. Co-treatment with BMP-7, but not with BMP-6, suppressed GnRH-induced MAPK phosphorylation in LβT2 cells. Thus, the difference between BMP-6 and BMP-7 in enhancing GnRH-induced FSHβ transcription may be due to the differential effects of BMP ligands on GnRH-induced ERK signaling. On the other hand, GnRH reduced Smad1/5/8 phosphorylation but increased Smad6/7 expression. These findings imply the presence of a functional link between GnRH action, MAPK signaling and the BMP system in pituitary gonadotropes for fine-tuning of FSH gene expression.
[Show abstract][Hide abstract] ABSTRACT: Mechanisms by which GHRP stimulates ACTH release in corticotrope cells were investigated using mouse corticotrope AtT20 cells by focusing on the biological activity of BMP-4. GHRP-2 increased ACTH and cAMP secretion by AtT20 cells; however, its effects were less potent than the effects of CRH. BMP-4 suppressed basal ACTH production and POMC transcription, and the inhibition of endogenous BMP receptor signaling led to an increase in ACTH production. Of note, BMP-4 suppressed ACTH production and POMC-promoter activity induced by CRH more efficaciously than that induced by GHRP-2. BMP-4 had no significant effect on cAMP synthesis induced by CRH or GHRP-2. Stimulation with CRH, but not GHRP-2, activated ERK1/2, p38, SAPK/JNK and Akt phosphorylation, in which CRH-induced phosphorylation of ERK and p38 was suppressed by BMP-4. GHRP-2-induced ACTH secretion was not affected by inhibitors of ERK, p38 and Akt pathways, which effectively suppressed CRH-induced ACTH release. Blockage of the cAMP-PKA pathway reversed CRH- as well as GHRP-2-induced ACTH secretion. Furthermore, the inhibition of ERK and p38 significantly reduced cAMP synthesis induced by CRH but not by GHRP-2. Thus, CRH activates ACTH production through ERK and p38 pathways in addition to the cAMP-PKA pathway, which is also activated downstream of MAPK. On the other hand, GHRP-2-induced ACTH production was predominantly linked to the cAMP-PKA pathway. Moreover, CRH and GHRP-2 upregulated BMP receptor signaling, while BMP-4, CRH and GHRP-2 had no significant effect on the expression level of GHSR. In addition, GHRP-2 suppressed the expression of Smad7, which is an inhibitor of the BMP-Smad1/5/8 pathway. Collectively, the results revealed a functional interaction between GHRP-2 and BMP signaling, in which endogenous BMP may act as an autoregulatory system in controlling ACTH production.
[Show abstract][Hide abstract] ABSTRACT: To investigate the mechanism by which prolactin (PRL) regulates follicular steroidogenesis in the ovary, we examined the functional roles of PRL in steroidogenesis using rat oocyte/granulosa cell coculture and focusing on the bone morphogenetic protein (BMP) system. The expression of long and short forms of PRL receptor (PRLR) were detected in both oocytes and granulosa cells, and PRL effectively up-regulated PRLR expression in granulosa cells in the presence of FSH. PRL suppressed FSH-induced estradiol production and increased FSH-induced progesterone production in granulosa cells. The PRL effects on FSH-induced progesterone were blocked by coculture with oocytes, implying roles of oocyte-derived factors in suppression of progesterone production in PRL-exposed granulosa cells. In accordance with the data for steroids, FSH-induced aromatase expression was suppressed by PRL, whereas FSH-induced steroidogenic acute regulatory protein, P450scc (P450 side-chain cleavage enzyme), and 3β-hydroxysteroid dehydrogenase type 2 levels were amplified by PRL. However, forskolin- and N(6),O(2)-dibutyryl cAMP-induced steroid levels and FSH- and forskolin-induced cAMP were not affected by PRL, suggesting that PRL action on FSH-induced steroidogenesis was not due to cAMP-protein kinase A regulation. Treatment with a BMP-binding protein, noggin, facilitated PRL-induced estradiol reduction, and noggin increased PRL-induced progesterone production in FSH-treated granulosa cells cocultured with oocytes, suggesting that endogenous BMPs reduce progesterone but increase estradiol when exposed to high concentrations of PRL. PRL increased the expression of BMP ligands in oocyte/granulosa cell coculture and augmented BMP-induced phosphorylated mothers against decapentaplegic 1/5/8 signaling by reducing inhibitory phosphorylated mothers against decapentaplegic 6 expression through the Janus kinase/signal transducer and activator of transcription (STAT) pathway. In addition to STAT activation, PRL enhanced FSH-induced MAPK phosphorylation in granulosa cells, in which ERK activation was preferentially involved in suppression of FSH-induced estradiol. Furthermore, noggin treatment enhanced PRLR signaling including MAPK and STAT. Considering that BMPs suppressed PRLR in granulosa cells, it is likely that the BMP system in growing follicles plays a key role in antagonizing PRLR signaling actions in the ovary exposed to high concentrations of PRL.
[Show abstract][Hide abstract] ABSTRACT: Involvement of the pituitary BMP system in the modulation of prolactin (PRL) secretion regulated by somatostatin analogs, including octreotide (OCT) and pasireotide (SOM230), and a dopamine agonist, bromocriptine (BRC), was examined in GH3 cells. GH3 cells are rat pituitary somato-lactotrope tumor cells that express somatostatin receptors (SSTRs) and BMP system molecules including BMP-4 and -6. Treatment with BMP-4 and -6 increased PRL and cAMP secretion by GH3 cells. The BMP-4 effects were neutralized by adding a BMP-binding protein Noggin. These findings suggest the activity of endogenous BMPs in augmenting PRL secretion by GH3 cells. BRC and SOM230 reduced PRL secretion, but OCT failed to reduce the PRL level. In GH3 cells activated by forskolin, BRC suppressed forskolin-induced PRL secretion with reduction in cAMP levels. OCT did not affect forskolin-induced PRL level, while SOM230 reduced PRL secretion and PRL mRNA expression induced by forskolin. BMP-4 treatment enhanced the reducing effect of SOM230 on forskolin-induced PRL level while BMP-4 did not affect the effects of OCT or BRC. Noggin treatment had no significant effect on the BRC actions reducing PRL levels by GH3 cells. However, in the presence of Noggin, OCT elicited an inhibitory effect on forskolin-induced PRL secretion and PRL mRNA expression, whereas the SOM230 effect on PRL reduction was in turn impaired. It was further found that BMP-4 and -6 suppressed SSTR-2 but increased SSTR-5 mRNA expression of GH3 cells. These findings indicate that Noggin rescues SSTR-2 but downregulates SSTR-5 by neutralizing endogenous BMP actions, leading to an increase in OCT sensitivity and a decrease in SOM230 sensitivity of GH3 cells. In addition, BMP signaling was facilitated in GH3 cells treated with forskolin. Collectively, these findings suggest that BMPs elicit differential actions in the regulation of PRL release dependent on cellular cAMP-PKA activity. BMPs may play a key role in the modulation of SSTR sensitivity of somato-lactotrope cells in an autocrine/paracrine manner.
[Show abstract][Hide abstract] ABSTRACT: Bone morphogenetic proteins (BMPs) have been recognized as crucial molecules in regulating ovarian physiology, with different BMPs having differential actions in FSH-induced estradiol production. To identify the roles of oocyte factors that modulate steroidogenesis controlled by BMPs, we here investigated the effects of FGF-8 in rat granulosa/oocyte co-cultures. FGF-8 potently suppressed FSH-induced estradiol production, but did not affect cAMP-induced estradiol produced by rat granulosa cells. FGF-8 had no effects on progesterone and cAMP production induced by FSH and forskolin. The inhibitory effects of FGF-8 on FSH-induced estradiol production were not altered by BMP-2, -4, -6 or -7. In the presence of FGF-8, BMPs suppressed FSH-induced progesterone by reducing cAMP, suggesting that FGF-8 and BMP independently regulate FSH receptor signaling. Notably, FGF-8-induced ERK and SAPK/JNK phosphorylation in granulosa cells, in which ERK activation was further enhanced by FSH and oocytes. Inhibition of ERK and SAPK/JNK reduced FSH-induced progesterone and cAMP levels, suggesting that the activation of these pathways enhances FSH-induced cAMP signaling. In addition, ERK inhibition upregulated FSH-induced estradiol synthesis, indicating that ERK pathway is also involved in suppressing aromatase activity in granulosa cells. Interestingly, FGF-8 enhanced BMP-induced Smad1/5/8 and Id-1-promoter activities with decreased expression of Smad6/7. Since the SAPK/JNK inhibitor inhibited FGF-8 effects in upregulating Id-1 transcription, SAPK/JNK appears to be involved in the mechanism by which FGF-8 enhances BMP-Smad signaling. Furthermore, in the presence of oocytes, the inhibition of endogenous FGF receptor signaling suppressed FSH- and forskolin-induced progesterone and cAMP, showing that endogenous FGF system is involved in activation of FSH-induced cAMP-PKA signaling via ERK and SAPK/JNK. Thus, the oocyte factor, FGF-8, not only suppresses FSH-induced estradiol production by activating ERK, but also enhances BMP-Smad signaling in granulosa cells. This interaction between FGF-8 and BMPs may play a key role in regulating steroidogenesis through oocyte-granulosa cell communication.
[Show abstract][Hide abstract] ABSTRACT: The mechanism by which somatostatin analogs suppress ACTH production by corticotropinomas has yet to be fully elucidated. We here studied the effects of somatostatin analogs on ACTH secretion using mouse corticotrope AtT20 cells focusing on the biological activity of bone morphogenetic proteins (BMPs). BMP ligands, receptors and Smads, and somatostatin receptors (SSTRs)-2, -3, and -5 were expressed in AtT20 cells. BMP-2, -4, -6, and -7 decreased basal ACTH production with BMP-4 effects being the most prominent. BMP-4 also inhibited CRH-induced ACTH production and proopiomelanocortin (POMC) transcription. However, the decrease in CRH-induced cAMP accumulation caused by BMP-4 was not sufficient to completely account for BMP-4 actions, indicating that ACTH suppression by BMPs was not directly linked to cAMP inhibition. CRH-activated ERK1/ERK2, p38-MAPK, stress-activated protein kinase/c-Jun NH(2)-terminal kinase, protein kinase C, and Akt pathways and CRH-induced ACTH synthesis was significantly decreased in the presence of U0126 or SB203580. Because BMPs attenuated CRH-induced ERK and p38 phosphorylation, it was suggested that BMP-4 suppresses ACTH production by inhibiting CRH-induced ERK and p38 phosphorylation. Somatostatin analogs octreotide and pasireotide (SOM230) significantly suppressed CRH-induced ACTH and cAMP production in AtT20 cells and reduced ERK and p38 phosphorylation. Notably, CRH-induced ACTH production was enhanced in the presence of noggin, a BMP-binding protein. The inhibitory effects of octreotide and SOM230 on CRH-induced ACTH production were also attenuated by noggin, implying that the endogenous BMP system plays a key role in inhibiting CRH-induced ACTH production by AtT20 cells. The findings that OCT and SOM230 up-regulated BMP-Smad1/Smad5/Smad8 signaling and ALK-3 and BMPRII and down-regulated inhibitory Smad6/7 establish that the activation of endogenous BMP system is functionally involved in the mechanism by which somatostatin analogs suppress CRH-induced ACTH production.
[Show abstract][Hide abstract] ABSTRACT: We report a rare case of polycystic ovary syndrome (PCOS) complicated with acromegaly due to a growth hormone (GH)-producing pituitary adenoma. Complete removal of the pituitary adenoma successfully reduced circulating levels of GH and insulin-like growth factor (IGF)-1, which, in turn, resulted in the amelioration of gonadal dysfunction, hyperandrogenism, lutenizing hormone hypersecretion, and severe insulin resistance. This clinical complication suggests that activation of systemic GH-IGF-1 axis is potentially involved in the development of PCOS.