Misuzu Yamashita

Simvastatin antagonizes tumor necrosis factor-α inhibition of bone morphogenetic proteins-2-induced osteoblast differentiation by regulating Smad signaling and Ras/Rho-mitogen-activated protein kinase pathway

Recent studies have shown that the mevalonate pathway plays an important role in skeletal metabolism. Statins stimulate bone morphogenetic proteins-2 (BMP-2) production in osteoblasts, implicating a possible beneficial role for statins in promoting anabolic effects on bone. Here, we investigated the effects of a lipophilic simvastatin on osteoblast differentiation using mouse myoblast C2C12 cells, in the presence of tumor necrosis factor-alpha (TNF-alpha), an inflammatory cytokine that inhibits osteogenesis. The addition of TNF-alpha to C2C12 cells suppressed the BMP-2-induced expression of key osteoblastic markers including Runx2 and alkaline phosphatase (ALP) activity. Simvastatin had no independent effects on Runx2 and alkaline phosphatase activity; however, it reversed the suppressive effects of TNF-alpha. The ability of simvastatin to reverse TNF-alpha inhibition of BMP-induced Smad1,5,8 phosphorylation and Id-1 promoter activity suggests the involvement of Smad signaling pathway in simvastatin action. In addition, cDNA array analysis revealed that simvastatin increased expression levels of Smads in C2C12 cells exposed to TNF-alpha that also activated mitogen-activated protein kinase (MAPK) signaling pathways, including extracellular signal-regulated kinase 1/2 (ERK1/2), P38, and stress-activated protein kinase/c-Jun NH2-terminal kinase (SAPK/JNK). Simvastatin potently suppressed TNF-alpha-induced phosphorylation of ERK1/2 and SAPK/JNK by inhibiting TNF-alpha-induced membrane localization of Ras and RhoA. Farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) reversed the simvastatin effects on TNF-alpha-induced activation of Ras/Rho/MAPK pathways. FPP and GGPP also restored the simvastatin effects on TNF-alpha-induced suppression of Runx2 and ALP activity. In addition, simvastatin decreased the expression levels of TNF type-1 and -2 receptor mRNAs. Collectively, simvastatin supports BMP-induced osteoblast differentiation through antagonizing TNF-alpha-to-Ras/Rho/MAPK pathway and augmenting BMP-Smad signaling, suggesting a potential usage of statins to ameliorate inflammatory bone damage.

Bone morphogenetic protein 6 (BMP6) and BMP7 inhibit estrogen-induced proliferation of breast cancer cells by suppressing p38 mitogen-activated protein kinase activation

Estrogen is involved in the development and progression of breast cancer. Here, we investigated the effects of bone morphogenetic proteins (BMPs) on breast cancer cell proliferation caused by estrogen using human breast cancer MCF-7 cells. MCF-7 cells express estrogen receptors (ESR1 and ESR2), BMP receptors, and SMAD signaling molecules. Estradiol and membrane-impermeable estradiol stimulated MCF-7 cell proliferation. Estradiol also reduced mRNA levels of ESR1, aromatase, and steroid sulfatase. Treatment with BMPs and activin had no effects on MCF-7 cell proliferation. However, BMP2, BMP4, BMP6, BMP7, and activin suppressed estradiol-induced cell mitosis, with the effects of BMP6, BMP7, and activin being more prominent than those of BMP2 and BMP4. Activin decreased ESR1 mRNA expression, while BMP6 and BMP7 impaired steroid sulfatase expression in MCF-7 cells. Interestingly, SMAD1,5,8 activation elicited by BMP6 and BMP7, but not by BMP2 and BMP4, was preserved even under the exposure of a high concentration of estradiol. The difference of BMP responsiveness was likely due to the differential modulation of BMP receptor expression induced by estradiol. In this regard, estradiol decreased the expression levels of BMPR1A, BMPR1B, ACVR2A, and ACVR2B but did not affect ACVR1 and BMPRII, leading to the sustained effects of BMP6 and BMP7 in estrogen-treated MCF-7 cells. Estradiol rapidly activated MAPK phosphorylation including extracellular signal-regulated kinase 1/2, p38, and stress-activated protein kinase/c-Jun NH2-terminal kinase pathways and BMP6, BMP7, and activin preferentially inhibited estradiol-induced p38 phosphorylation. SB203580, a selective p38 MAPK inhibitor effectively suppressed estradiol-induced cell mitosis, suggesting that p38 MAPK plays a key role in estrogen-sensitive breast cancer cell proliferation. Thus, a novel interrelationship between estrogen and the breast cancer BMP system was uncovered, in which inhibitory effects of BMP6 and BMP7 on p38 signaling and steroid sulfatase expression were functionally involved in the suppression of estrogen-induced mitosis of breast cancer cells.

Simvastatin inhibits osteoclast differentiation induced by bone morphogenetic protein-2 and RANKL through regulating MAPK, AKT and Src signaling

The mevalonate pathway plays a crucial role in bone metabolism. Here we examined roles of simvastatin in osteoclast function and differentiation induced by RANKL and BMP-2 using mouse macrophage-like MLC-6 cells and human osteoclast precursor cells. MLC-6 cells expressed BMP type-I and -II receptors and Smads as well as osteoclast markers including TRAP, RANK, cathepsin-K, M-CSF receptor, MMP-9 and calcitonin receptor. Treatment with RANKL and BMP-2 acted synergistically to stimulate RANK, TRAP and cathepsin-K expression in MLC-6 cells. Simvastatin suppressed osteoclastic activity shown by increases in RANK, TRAP and cathepsin-K expression induced by RANKL and BMP-2. In contrast simvastatin alone had no effects on the osteoclastic markers in MLC-6 cells. Simvastatin activated ERK, SAPK/JNK and AKT pathways and inactivated Ras in MLC-6 cells. Simvastatin had no effect on BMP-induced Smad1/5/8 phosphorylation regardless of RANKL stimulation. Since chemical inhibition of ERK, SAPK/JNK and AKT increased TRAP and cathepsin-K expression induced by BMP-2 and RANKL, these pathways are functionally involved in inhibition of osteoclastic activity. In addition, Src phosphorylation induced by RANKL, which is involved in osteoclast differentiation, was suppressed by simvastatin. We further confirmed an inhibitory mechanism of simvastatin on osteoclast differentiation using human osteoclast precursor cells which express BMP receptor and Smad signaling machinery. Simvastatin also activated ERK pathways and inactivated Src phosphorylation in human osteoclasts differentiated by M-CSF and RANKL treatments. The inhibition of TRAP and RANK expression by simvastatin was reversed by ERK inhibition, whereas Src inhibitor enhanced simvastatin-induced suppression of osteoclast markers. Collectively, our data show that simvastatin inhibits osteoclastic differentiation through inhibiting Src as well as enhancing MAPK/AKT pathways.

p38-Mitogen-Activated Protein Kinase Stimulated Steroidogenesis in Granulosa Cell-Oocyte Cocultures: Role of Bone Morphogenetic Proteins 2 and 4

Roles of the p38-MAPK pathway in steroidogenesis were investigated using coculture of rat granulosa cells with oocytes. Activin and FSH readily phosphorylated p38 in granulosa cells. Activin effect on p38 phosphorylation was abolished by a selective activin receptor-like kinase-4, -5, and -7 inhibitor, SB431542. SB431542 decreased FSH-induced estradiol but had no effect on progesterone production with a marginal cAMP reduction, suggesting that endogenous activin is primarily involved in estradiol synthesis. FSH-induced p38 activation was not affected either by SB431542 or follistatin, suggesting that FSH activates p38 not through the endogenous activin. Bone morphogenetic protein (BMP)-2 and BMP-4 also enhanced FSH-induced p38 phosphorylation, which was augmented by oocyte action. A specific p38 inhibitor, SB203580, decreased FSH-induced estradiol production. However, FSH-induced cAMP accumulation was not changed by SB203580, suggesting that p38 activation is linked to estradiol synthesis independently of cAMP. BMP-2 and BMP-4 inhibited FSH- and forskolin (FSK)-induced progesterone and cAMP synthesis regardless of oocyte action. BMP-2, BMP-4, and activin increased FSH-induced estradiol production, which was enhanced in the presence of oocytes. In contrast to activin that enhanced FSK-induced estradiol, BMP-2 and BMP-4 had no effects on FSK-induced estradiol production, suggesting that BMP-2 and BMP-4 directly activate FSH-receptor signaling. Given that activin increased, but BMP-2 and BMP-4 decreased, FSH-induced cAMP, the effects of BMP-2 and BMP-4 on estradiol enhancement appeared to be diverged from the cAMP-protein kinase A pathway. Thus, BMP-2 and BMP-4 differentially regulate steroidogenesis by stimulating FSH-induced p38 and suppressing cAMP. The former is involved in estradiol production and enhanced by oocyte action, whereas the latter leads to reduction of progesterone synthesis.

Effects of bone morphogenetic protein (BMP) on adrenocorticotropin production by pituitary corticotrope cells: Involvement of up-regulation of bmp receptor signaling by somatostatin analogs

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.

Involvement of the bone morphogenetic protein system in endothelin-and aldosterone-induced cell proliferation of pulmonary arterial smooth muscle cells isolated from human patients with pulmonary arterial hypertension

Recent genetic studies have uncovered a link between familial and idiopathic pulmonary arterial hypertension (PAH) and germline mutations in the bone morphogenetic protein type-II receptor (BMPRII). The pathology of PAH is characterized by remodeling of the pulmonary arteries due to pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Although increased endothelial injury and impaired suppression of PASMC proliferation are both critical for the cellular pathogenesis of PAH, a detailed molecular mechanism underlying PAH has yet to be elucidated. In the present study, we investigated the roles of the BMP system and other vasoactive factors associated with PAH (including endothelin (ET), angiotensin II (Ang II) and aldosterone) in the mitotic actions of PASMCs isolated from idiopathic and secondary PAH lungs. ET1 and aldosterone stimulated PASMC proliferation of idiopathic PAH more effectively than secondary PAH, whereas Ang II and ET3 failed to activate mitosis in either of the PASMC cell type. The effects of ET1 and aldosterone were blocked by bosentan, an ET type-A/B receptor (ETA/BR) antagonist, and eplerenone, a selective mineralocorticoid receptor (MR) blocker, respectively. Among the BMP ligands examined, BMP-2 and BMP-7, but not BMP-4 or BMP-6, significantly increased cell mitosis in both PASMC cell types. Notably, ET1- and aldosterone-induced mitosis and mitogen-activated protein kinase phosphorylation were significantly increased in the presence of BMP-2 and BMP-7 in PASMCs isolated from idiopathic PAH, although additive effects were not observed in PASMCs isolated from secondary PAH. Inhibition of extracellular signal-regulated kinase 1 (ERK1)/ERK2 signaling suppressed basal-, ET1- and aldosterone-induced PASMC mitosis more potently than that of stress-activated protein kinase/c-Jun NH2-terminal kinase inhibition. Given the fact that BMP-2 and BMP-7 upregulated ETA/BR and MR expression and that BMP-2 decreased 11βHSD2 (11β-hydroxysteroid dehydrogenase type 2) levels in PASMCs isolated from idiopathic PAH, BMPR-Smad signaling may have a key role in amplifying the ETA/BR and/or MR-ERK signaling in PASMCs of the PAH lung. Collectively, the functional link between BMP and ET and/or the MR system may be involved in the progress of PASMC mitosis, ultimately leading to the development of clinical PAH.

Involvement of bone morphogenetic protein-4 in GH regulation by octreotide and bromocriptine in rat pituitary GH3 cells

Here we investigated roles of the pituitary bone morphogenetic protein (BMP) system in modulating GH production regulated by a somatostatin analog, octreotide (OCT) and a dopamine agonist, bromocriptine (BRC) in rat pituitary somatolactotrope tumor GH3 cells. The GH3 cells were found to express BMP ligands, including BMP-4 and BMP-6; BMP type-1 and type-2 receptors (except the type-1 receptor, activin receptor-like kinase (ALK)-6); and Smad signaling molecules. Forskolin stimulated GH production in accordance with cAMP synthesis. BRC, but not OCT, suppressed forskolin-induced cAMP synthesis by GH3 cells. Individual treatment with OCT and BRC reduced forskolin-induced GH secretion. A low concentration (0.1 microM) of OCT in combination with BRC (1-100 microM) exhibited additive effects on reducing GH and cAMP production induced by forskolin. However, a high concentration (10 microM) of OCT in combination with BRC failed to suppress GH and cAMP production. BMP-4 specifically enhanced GH secretion and cAMP production induced by forskolin in GH3 cells. BRC, but not OCT, inhibited BMP-4-induced activation of Smad1,5,8 phosphorylation and Id-1 transcription and decreased ALK-3 expression. Of note, in the presence of a high concentration of OCT, the BRC effects suppressing BMP-4-Smad1,5,8 signaling were significantly impaired. In the presence of BMP-4, a high concentration of OCT also attenuated the BRC effects suppressing forskolin-induced GH and cAMP production. Collectively, a high concentration of OCT interferes with BRC effects by reducing cAMP production and suppressing BMP-4 signaling in GH3 cells. These findings may explain the mechanism of resistance of GH reduction to a combination therapy with OCT and BRC for GH-producing pituitary adenomas.

Functional relationship between fibroblast growth factor-8 and bone morphogenetic proteins in regulating steroidogenesis by rat granulosa cells

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.

Enhancement of aldosterone-induced catecholamine production by bone morphogenetic protein-4 through activating Rho and SAPK/JNK pathway in adrenomedullar cells

Here we investigated the effects of mineralocorticoid in the regulation of catecholamine biosynthesis using rat pheochromocytoma PC12 cells. Expression of mineralocorticoid receptor (MR) was confirmed in undifferentiated PC12 cells. Aldosterone stimulated dopamine production by PC12 cells without any increase in cAMP activity. Aldosterone-induced dopamine accumulation was enhanced in accordance with the increase in the rate-limiting enzyme tyrosine hydroxylase (TH). Blocking MR with eplerenone suppressed aldosterone-induced increases of TH mRNA and dopamine production. A glucocorticoid receptor (GR) antagonist, RU-486, attenuated dexamethasone- but not aldosterone-induced TH expression. Cycloheximide reduced both aldosterone- and dexamethasone-induced TH mRNA. A SAPK/JNK inhibitor, SP600125, suppressed aldosterone-induced TH mRNA expression; however, the aldosterone-induced TH expression was not affected by inhibition of ERK1/2, p38-MAPK, Rho-kinase, PI 3-kinase, and PKC. It was of note that cotreatment with eplerenone and SP600125 restored aldosterone-induced TH mRNA expression to basal levels. To investigate the involvement of bone morphogenetic protein (BMP) actions in aldosterone-induced catecholamine production, we examined the effects of BMP-4 and BMP-7, which are expressed in the adrenal medulla, on catecholamine biosynthesis. BMP-4 preferentially enhanced aldosterone-induced TH mRNA and dopamine production, although BMP-4 alone did not affect TH expression. The BMP-4 enhancement of aldosterone-induced TH expression was not observed in cells treated with eplerenone. BMP-4 did not affect MR expression of PC12 cells; however, it did enhance aldosterone-induced SAPK/JNK phosphorylation. Inhibition of SAPK/JNK or Rho suppressed BMP-4 enhancement of aldosterone-induced TH expression. Collectively, our findings demonstrate that aldosterone stimulates catecholamine biosynthesis in adrenomedullar cells via MR through genomic action and partly through nongenomic action by Rho-SAPK/JNK signaling, the latter of which is facilitated by BMP-4. A functional link between MR actions and endogenous BMP may be involved in the catecholamine production.

Regulatory expression of bone morphogenetic protein-6 system in aldosterone production by human adrenocortical cells.

Bone morphogenetic protein-6 (BMP-6) enhances aldosterone production by upregulating angiotensin II (Ang II)-to-MAPK pathway. Here we investigated effects of Ang II and potassium on the BMP system in human adrenocortical H295R cells. BMP-6 transcription was transiently downregulated by treatments with Ang II and potassium. Aldosterone also decreased BMP-6 expression at a high concentration. Chemical inhibitions of transcription and translation abolished the transient reduction of BMP-6, suggesting that destabilization of BMP-6 mRNA was hardly involved while new protein synthesis was possibly mediated in this mechanism. However, BMP-6 protein was stably detected during the exposures of Ang II and potassium. Notably, Ang II, potassium and aldosterone decreased mRNA levels of follistatin that extracellularly neutralizes bioactivities of activins and BMPs although the BMP-6 receptor expression was unaffected. Given the maintenance of bioavailable BMP-6 protein and the receptor expression in adrenocortical cells, endogenous BMP-6 may be a key autocrine modulator for aldosterone production.