Parathyroid hormone-responsive Smad3-related factor, Tmem119, promotes osteoblast differentiation and interacts with the bone morphogenetic protein-Runx2 pathway

The mechanisms whereby the parathyroid hormone (PTH) exerts its anabolic action on bone are incompletely understood. We previously showed that inhibition of ERK1/2 enhanced Smad3-induced bone anabolic action in osteoblasts. These findings suggested the hypothesis that changes in gene expression associated with the altered Smad3-induced signaling brought about by an ERK1/2 inhibitor would identify novel bone anabolic factors in osteoblasts. We therefore performed a comparative DNA microarray analysis between empty vector-transfected mouse osteoblastic MC3T3-E1 cells and PD98059-treated stable Smad3-overexpressing MC3T3-E1 cells. Among the novel factors, Tmem119 was selected on the basis of its rapid induction by PTH independent of later increases in endogenous TGF-β. The levels of Tmem119 increased with time in cultures of MC3T3-E1 cells and mouse mesenchymal ST-2 cells committed to the osteoblast lineage by BMP-2. PTH stimulated Tmem119 levels within 1 h as determined by Western blot analysis and immunocytochemistry in MC3T3-E1 cells. MC3T3-E1 cells stably overexpressing Tmem119 exhibited elevated levels of Runx2, osteocalcin, alkaline phosphatase, and β-catenin, whereas Tmem119 augmented BMP-2-induced Runx2 levels in mesenchymal cells. Tmem119 interacted with Runx2, Smad1, and Smad5 in C2C12 cells. In conclusion, we identified a Smad3-related factor, Tmem119, that is induced by PTH and promotes differentiation in mouse osteoblastic cells. Tmem119 is an important molecule in the pathway downstream of PTH and Smad3 signaling in osteoblasts.     

Star-like oligo-arginyl-maltotriosyl derivatives as novel cell-penetrating enhancers for the intracellular delivery of colloidal therapeutic systems

A novel nonpeptide, multiarmed oligo-arginyl derivative was engineered as a cell-penetration enhancer for the delivery of bioactive macromolecules and colloidal drug systems. Hepta-arginyl-maltotriosylamido-N-acetyl-dodecanoyl acid (Arg(7)-Malt-NAcC(12) acid) was synthesized through a carefully designed multistep chemical protocol, as follows: (1) maltotriose derivatization with 12-amino-dodecanoic acid and acetylation of the free amino group; (2) esterification of the maltotriosyl hydroxyl groups with 2-bromo-isobutyryl bromide; and (3) synthesis of star-like oligomer bearing multiple copies of arginine moieties under atom transfer radical polymerization (ATRP) conditions. The intermediates and final product were characterized by (1)H NMR, IR, mass spectrometry, colorimetric assays, and elemental analysis. Cytotoxicity studies on the final polymeric material showed that this novel cell-penetrating enhancer does not have significant toxic effects on MCF-7 and MC3T3-E1 cell lines. The IC(50) was greater than 100 μM with both cell lines, while the polyethylenimine with similar average molecular mass (M(n)) that was used as a reference showed an IC(50) of 30 and 40 μM, for MCF-7 and MC3T3-E1, respectively. The biological properties of the novel bioconjugate were investigated using a fluorescein-labeled bovine serum albumin (FITC-BSA) as a hydrophilic cargo model. MCF-7 and MC3T3-E1 cells were incubated for 60 min with the Arg(7)-Malt-NAcC(12)-conjugated FITC-BSA [(Arg(7)-Malt-NAcC(12))(2)-FITC-BSA] or FITC-BSA, and the intracellular fluorescence level was analyzed by spectrofluorimetric analysis of cell lysate, cytofluorimetry, and confocal microscopy. The fluorescence of the lysate of MCF-7 and MC3T3-E1 cells that were incubated with (Arg(7)-Malt-NAcC(12))(2)-FITC-BSA at 37 °C was approximately 4.5 times higher than the fluorescence obtained with cells incubated with FITC-BSA. At 4 °C, the cell uptake of (Arg(7)-Malt-NAcC(12))(2)-FITC-BSA was only 2 times higher than that of FITC-BSA. Cytofluorimetric studies showed that, after (Arg(7)-Malt-NAcC(12))(2)-FITC-BSA treatment, over 80% of MCF-7 cells and over 95% of MC3T3-E1 cells displayed enhanced fluorescence. Confocal investigations showed punctuated fluorescence within the cytosol in both cell lines, indicating that (Arg(7)-Malt-NAcC(12))(2)-FITC-BSA was confined to endosomes, with no fluorescence observed in the nucleus.     

Tumor necrosis factor type alpha (cachectin) stimulates mouse osteoblast-like cells (MC3T3-E1) to produce macrophage-colony stimulating activity and prostaglandin E2

To elucidate the mechanism of tumor necrosis factor alpha (TNF-alpha)-induced bone resorption, the effects of recombinant human TNF-alpha on mouse osteoblast-like cells (MC3T3-E1) were studied. TNF-alpha stimulated MC3T3-E1 cells to produce prostaglandin E2 (PGE2) and macrophage colony stimulating activity (M-CSA) in a dose-dependent manner. TNF decreased alkaline phosphatase (AL-P) activity of MC3T3-E1 cells. These TNF effects were observed at 1 ng/ml (approximately 6 X 10(-11)M). The inhibitory effect on AL-P activity was reversible and the cell growth of MC3T3-E1 cells was only slightly affected by TNF. These findings suggest that both PGE2 and M-CSA stimulated by TNF-alpha are possibly involved in osteoblast-mediated osteoclastic bone resorption, whereas inhibition of AL-P activity may lead to a decrease in bone formation.     

Recombinant human interleukin 1 alpha and beta stimulate mouse osteoblast-like cells (MC3T3-E1) to produce macrophage-colony stimulating activity and prostaglandin E2

The effects of interleukin 1 (IL-1) on MC3T3-E1 cells (clonal osteoblast-like cells established from mouse calvaria) were studied to elucidate the mechanism of IL-1-induced bone resorption. Recombinant human interleukin 1 alpha (rhIL-1 alpha) and beta (rhIL-1 beta) stimulated PGE2 production in MC3T3-E1 cells in a dose dependent manner. rhIL-1 alpha and 1 beta also stimulated MC3T3-E1 cells to produce macrophage-colony stimulating activity (M-CSA) in a dose-dependent manner. Indomethacin completely abolished PGE2 production but did not affect CSA. These results suggest that bone resorption induced by IL-1s is at least in part mediated by PGE2 produced by osteoblasts, and that M-CSA produced by osteoblasts may synergistically potentiate bone resorption by recruiting osteoclast precursors.     

Sonic hedgehog is involved in osteoblast differentiation by cooperating with BMP-2

The roles of Sonic hedgehog (Shh) and Bone morphogenetic protein-2 (Bmp-2) in osteoblast differentiation were investigated using in vitro cell systems. Recombinant amino-terminal portion of SHH (rSHH-N) dose dependently stimulated ALP activity in C3H10T1/2 and MC3T3-E1 cells. rSHH-N induced expression of Osteocalcin mRNA in C3H10T1/2 cells. A soluble form of the receptor for type IA BMP receptor antagonized rSHH-N-induced ALP activity in C3H10T1/2 and MC3T3-E1 cells, indicating that BMPs are involved in SHH-induced osteoblast differentiation. Simultaneous supplement with rSHH-N and BMP-2 synergistically induced ALP activity and expression of Osteocalcin mRNA in C3H10T1/2 cells. Pretreatment with rSHH-N for 6 h enhanced the response to BMP-2 by increasing ALP activity in C3H10T1/2 and MC3T3-E1 cells. Stimulatory effects of rSHH-N and additive effects with rSHH-N and BMP-2 on ALP activity were also observed in mouse primary osteoblastic cells. Transplantation of BMP-2 (1 microg) into muscle of mice induced formation of ectopic bone, whereas transplantation of r-SHH-N (1-5 microg) failed to generate it. These results indicate that Shh plays important roles in osteoblast differentiation by cooperating with BMP.     

TWEAK/Fn14 interaction regulates RANTES production, BMP-2-induced differentiation, and RANKL expression in mouse osteoblastic MC3T3-E1 cells

Tumour necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a member of the TNF family, is a multifunctional cytokine that regulates cell growth, migration, and survival principally through a TWEAK receptor, fibroblast growth factor-inducible 14 (Fn14). However, its physiological roles in bone are largely unknown. We herein report various effects of TWEAK on mouse osteoblastic MC3T3-E1 cells. MC3T3-E1 cells expressed Fn14 and produced RANTES (regulated upon activation, healthy T cell expressed and secreted) upon TWEAK stimulation through PI3K-Akt, but not nuclear factor-kappaB (NF-kappaB), pathway. In addition, TWEAK inhibited bone morphogenetic protein (BMP)-2-induced expression of osteoblast differentiation markers such as alkaline phosphatase through mitogen-activated protein kinase (MAPK) Erk pathway. Furthermore, TWEAK upregulated RANKL (receptor activation of NF-kappaB ligand) expression through MAPK Erk pathway in MC3T3-E1 cells. All these effects of TWEAK on MC3T3-E1 cells were abolished by mouse Fn14-Fc chimera. We also found significant TWEAK mRNA or protein expression in osteoblast- and osteoclast-lineage cell lines or the mouse bone tissue, respectively. Finally, we showed that human osteoblasts expressed Fn14 and induced RANTES and RANKL upon TWEAK stimulation. Collectively, TWEAK/Fn14 interaction regulates RANTES production, BMP-2-induced differentiation, and RANKL expression in MC3T3-E1 cells. TWEAK may thus be a novel cytokine that regulates several aspects of osteoblast function.     

Comparison of geno- and cytotoxicity of methylnitrosourea on MMR-proficient and MMR-deficient human tumor cell lines

Deficient mismatch repair (MMR) is identified as a mutation of one of four major MMR genes and(or) microsatellite instability. These genomic changes are used as markers of MMR status of the heredity nonpolyposis colorectal cancer (HNPCC) spectrum tumors--familial and sporadic tumors of colon and extracolonic cancers fulfilling Amsterdam clinical criteria II. MMR-deficiency results in mutator phenotype and resistance to geno- and cytotoxicity of alkylating agents. The main cytotoxic damage to DNA in response to chemical methylation is O6-methylguanine (O6-mG). The secondary DNA strand breaks, which are formed during the MMR functioning, are proposed to be required for methylation induced cytotoxicity. We have assumed that the secondary double stand breaks (DSB) upon DNA methylation are able to represent functional efficiency of MMR in cells. The purpose of the paper was to test this assumption on human tumor cells differing in MMR-status and pulse-treated with methylnitrosourea (MNU). We used 3 cell lines: HeLa (MMR-competent endometrial tumor cells), HCT116 (MMR-deficient colorectal carcinoma cells), and Colo320 (sigmoid intestine tumor cells with uncharacterized MMR status). DSBs were evaluated with neutral comet assay. Cytotoxicity/viability was evaluated with MTT-asay and apoptotic index (frequency of morphologically determined apoptotic cells). We show that 1) cytotoxic effect of MNU (250 microM) on HeLa cells was exhibited 3 days after pulse-treatment of cells with MNU; 2) DSBs occurred 48 h after the drug treatment but prior to the onset of apoptosis of HeLa cells; 3) MMR-deficient HCT116 cells were resistant to the drug: no decreased viability, DSBs and apoptosis were observed during 3 days after cell treatment. Both cell lines exhibited high sensitivity to etoposide, classical inductor of unrepairable DSBs and p53. Etoposide has been found to induce DSBs in 6-12 h, which was followed by apoptosis (in 24 h). Colo320 cells exhibited intermediate position between HeLa and HCT116 cell lines in regard to sensitivity to MNU according to MTT-assay and the number of secondary DSBs formed in MNU-treated cells. Nevertheless, in contrast to HeLa cells, these breaks did not induce apoptosis in Colo320 cells. Our data confirm the assumption about case/effect relationship between secondary DNA double strand breaks, induced by monofunctional methylating agent MNU, and functioning of MMR in human tumor cells.     

Serial passage of MC3T3-E1 cells down-regulates proliferation during osteogenesis in vitro

Generally, fibroblast-like cells and other types of human cells have been used to demonstrate the principles of replicative senescence in vitro and in vivo. These cells go through three stages of proliferation, including vigorous proliferation, declining proliferation and quiescence or no proliferation. Any variation of this process occurring in osteoprogenitor cells may offer insight into the mechanism of age-related osteopaenia that predisposes individuals to osteoporosis and bone fractures. We selected MC3T3-E1 cells derived from mouse calvaria to study the mechanism of replicative senescence of pre-osteogenic cells because: (i) these cells constitute a well-known model for studying osteogenesis in vitro; (ii) they undergo a developmental sequence of proliferation and differentiation similar to primary cells in culture; and (iii) they show signs of replicative senescence. These cells were aged by multiple passaging before their use for studying growth kinetics and the effects of population density, effect of extracellular matrix (ECM), size and phases of the cell cycle. Our results show that (i) MC3T3-E1 cells go through the first two stages of proliferation in a manner similar to human cells, but escape the quiescent phase; (ii) the rate of proliferation is similar for low passage (LP) and high passage (HP) cells, but is decreased in very high passage cells (VHP); (iii) growth inhibition is observed using HP cells seeded at high density; (iv) HP ECM stimulates proliferation of both LP and HP cells; (v) a small increase in cell size is observed in HP cells, but no change is seen in the distribution analysis of their cell cycle; (vi) distribution analysis of the cell cycle of VHP cells reveals a decreased and an increased frequency of cells in S and G2 + M phases of their cell cycle, respectively. These results suggest that the mouse MC3T3-E1 cell line exhibits many of the cellular and molecular markers associated with replicative senescence in culture as defined by human cells, such as fibroblast-like cells. Alteration in the sensitivity of MC3T3-E1 cells to intercellular contact and increase in cell size are the primary factors contributing to decreased proliferation of HP cells.     

Apelin stimulates proliferation and suppresses apoptosis of mouse osteoblastic cell line MC3T3-E1 via JNK and PI3-K/Akt signaling pathways

The aim of this study was to investigate the effects of apelin on proliferation and apoptosis of mouse osteoblastic MC3T3-E1 cells. APJ was expressed in MC3T3-E1 cells. Apelin did not affect Runx2 expression, alkaline phosphatase (ALP) activity, osteocalcin and type I collagen secretion, suggesting that it has no effect on osteoblastic differentiation of MC3T3-E1 cells. However, apelin stimulated MC3T3-E1 cell proliferation and inhibited cell apoptosis induced by serum deprivation. Our study also shows that apelin decreased cytochrome c release and caspase-3, capase-8 and caspase-9 activation in serum-deprived MC3T3-E1 cells. Apelin activated c-Jun N-terminal kinase (JNK) and Akt (phosphatidylinositol 3-kinase downstream effector), and the JNK inhibitor SP600125, the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 or the Akt inhibitor 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate (HIMO) inhibited its effects on proliferation and serum deprivation-induced apoptosis. Furthermore, apelin protected against apoptosis induced by the glucocorticoid dexamethasone or TNF-alpha. Apelin stimulates proliferation and suppresses serum deprivation-induced apoptosis of MC3T3-E1 cells and these actions are mediated via JNK and PI3-K/Akt signaling pathways.     

Evidence for a direct effect of growth hormone on osteoblasts

In order to determine whether growth hormone (GH) exerts a direct effect on osteoblasts, in vitro and in vivo immunocytological studies were carried out on newborn rat calvaria and a clonal osteoblast-like cell line (MC3T3-E1) isolated from newborn mouse calvaria. After exposure to human growth hormone (hGH) or 1,25 dihydroxyvitamin D3 (1,25(OH)₂D₃), a significant increase in alkaline phosphatase activity was observed in MC3T3-E1 cells. Simultaneous exposure of MC3T3-E1 cells to hGH and 10 nM 1,25(OH)₂D₃ showed a synergistic effect of the two hormones on this activity. The optimal dose of hGH was 0.1 nM. An immunocytological procedure was performed on ultrathin frozen sections from 7-day-old rat calvaria and MC3T3-E1 cells cultured with hGH. GH-like immunoreactivity was observed in both cases. In calvaria, endogenous GH-like immunoreactivity was localized at the same ultrastructural level (plasma membrane, cytoplasmic and nuclear matrices) as exogenous GH-like immunoreactivity in MC3T3-E1 cells. Following the initial step of binding to the plasma membrane, GH may be internalized in the cytoplasmic matrix and nucleus. In situ hybridization revealed the presence of mRNA coding for GH receptor in calvaria cells. The density of these receptors seemed to be lower in osteoblasts than in hepatocytes. In MC3T3-E1 cells, hGH induced a dose-dependent secretion of insulin-like growth factor 1. In conclusion, these results indicate that GH may act directly on osteoblasts.     

Prostate cancer cells and bone stromal cells mutually interact with each other through bone morphogenetic protein-mediated signals

Functional interactions between cancer cells and the bone microenvironment contribute to the development of bone metastasis. Although the bone metastasis of prostate cancer is characterized by increased ossification, the molecular mechanisms involved in this process are not fully understood. Here, the roles of bone morphogenetic proteins (BMPs) in the interactions between prostate cancer cells and bone stromal cells were investigated. In human prostate cancer LNCaP cells, BMP-4 induced the production of Sonic hedgehog (SHH) through a Smad-dependent pathway. In mouse stromal MC3T3-E1 cells, SHH up-regulated the expression of activin receptor IIB (ActR-IIB) and Smad1, which in turn enhanced BMP-responsive reporter activities in these cells. The combined stimulation with BMP-4 and SHH of MC3T3-E1 cells cooperatively induced the expression of osteoblastic markers, including alkaline phosphatase, bone sialoprotein, collagen type II α1, and osteocalcin. When MC3T3-E1 cells and LNCaP cells were co-cultured, the osteoblastic differentiation of MC3T3-E1 cells, which was induced by BMP-4, was accelerated by SHH from LNCaP cells. Furthermore, LNCaP cells and BMP-4 cooperatively induced the production of growth factors, including fibroblast growth factor (FGF)-2 and epidermal growth factor (EGF) in MC3T3-E1 cells, and these may promote the proliferation of LNCaP cells. Taken together, our findings suggest that BMPs provide favorable circumstances for the survival of prostate cancer cells and the differentiation of bone stromal cells in the bone microenvironment, possibly leading to the osteoblastic metastasis of prostate cancer.     

Growth stimulatory effect of pancreatic spasmolytic polypeptide on cultured colon and breast tumor cells

The effects of a novel polypeptide, pancreatic spasmolytic polypeptide (PSP) on a colon carcinoma cell line (HCT 116) were examined. PSP stimulated the incorporation of [3H]thymidine into HCT 116 cells as well as cell proliferation in a dose-dependent manner. Maximal increase in [3H]thymidine incorporation of 50-60% occurred at 3-300 microM PSP. The VIP-mediated-increase in cAMP levels was reduced by PSP at greater than 1 microM concentrations. PSP is highly homologous to the estrogen-induced pS2 protein in MCF-7 breast cancer cells. We find that PSP also enhanced [3H]thymidine incorporation in MCF-7 cells. These findings indicate for the first time that PSP has growth stimulatory properties.     

Vitamin K2 modulates proliferation and function of osteoblastic cells in vitro.

A human osteosarcoma cell line, HOS TE85 cells, and a mouse osteoblastic cell line, MC3T3-E1 cells, were cultured for 3 days in a medium containing various concentrations of menaquinone-4 (vitamin K2). As a result, the proliferation of HOS cells was suppressed by vitamin K2 in a dose dependent manner up to 56% of control by 10(-7)M of vitamin K2 and that of MC3T3-E1 cells was suppressed to 84% of control by 10(-6)M of vitamin K2. Vitamin K2 increased alkaline phosphatase activity in both kinds of cells. Warfarin counteracted the effect of vitamin K2 on osteoblastic cell proliferation. Our results show that vitamin K2 modulates proliferation and function of osteoblastic cells by some mechanisms including gamma-carboxylation system.     

A platform of high-efficiency nonviral gene transfer in mouse osteoblast cells in vitro

We have previously established mouse genetic models and identified the genetic components of quantitative trait loci (QTL) on mouse chromosomes that contribute to phenotypes such as bone size, bone density, and bone's anabolic response to mechanical loading. However, these regions contain dozens of unknown genes that are needed for functional testing. In this study, we provided a protocol of nucleoporation with high efficiency by using a commercial nucleofection buffer and Gene Pulser to deliver a test gene into bone cells for functional studies. We cloned an osteoblast differentiation-specific geneosterix (Osx) from a mouse bone cDNA library into a pHGCX expression vector and used nucleoporation to deliver pHGCX/Flag-Osx into the nuclei of MC3T3-E1 cells. We then examined the transfection efficiency transgene expression, and function. Our results have demonstrated that nucleoporation can deliver a transgene into MC3T3-E1 osteoblast cells with approx 94% transfection efficiency, and express a functional Flag-Osx fusion protein capable of inducing cell differentiation as measured by an incease in alkaline phosphatase (ALP) activity. Therefore, this experimental system provides a rapid, safe, and efficient cell-based model of high-throughput phenotypic screening to identify candidate genes from physically mapped regions that are important for osteoblast differentiation.