1alpha,25(OH)2-vitamin D3 inhibits HGF synthesis and secretion from MG-63 human osteosarcoma cells

Role of Basic Fibroblast Growth Factor in Cancer: Biological Activity, Targeted Therapies, and Prognostic Value

Cancer is the leading cause of death worldwide; thus, it is necessary to find successful strategies. Several growth factors, such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF, FGF2), and transforming growth factor beta (TGF-β), are involved in the main processes that fuel tumor growth, i.e., cell proliferation, angiogenesis, and metastasis, by activating important signaling pathways, including PLC-γ/PI3/Ca2+ signaling, leading to PKC activation. Here, we focused on bFGF, which, when secreted by tumor cells, mediates several signal transductions and plays an influential role in tumor cells and in the development of chemoresistance. The biological mechanism of bFGF is shown by its interaction with its four receptor subtypes: fibroblast growth factor receptor (FGFR) 1, FGFR2, FGFR3, and FGFR4. The bFGF–FGFR interaction stimulates tumor cell proliferation and invasion, resulting in an upregulation of pro-inflammatory and anti-apoptotic tumor cell proteins. Considering the involvement of the bFGF/FGFR axis in oncogenesis, preclinical and clinical studies have been conducted to develop new therapeutic strategies, alone and/or in combination, aimed at intervening on the bFGF/FGFR axis. Therefore, this review aimed to comprehensively examine the biological mechanisms underlying bFGF in the tumor microenvironment, the different anticancer therapies currently available that target the FGFRs, and the prognostic value of bFGF.

Changes in MCP-1, HGF, and IGF-1 expression in endometrial stromal cells, PBMCs, and PFMCs of endometriotic women following 1,25(OH)2D3 treatment

1,25(OH)2D3 has anti‐inflammatory and growth inhibitory effects. Our study explored the effect of 1,25(OH)2D3 treatment on the expression of monocyte chemotactic protein‐1 (MCP‐1), hepatocyte growth factor (HGF), and insulin‐like growth factor‐1 (IGF‐1) by peripheral blood mononuclear cells (PBMCs), peritoneal fluid mononuclear cells (PFMCs), endometrial stromal cells (ESCs), and its effect on the proliferation of PBMCs and PFMCs of patients with endometriosis compared with controls. PBMCs, PFMCs, and ESCs were obtained from 10 endometriosis patients and 10 non‐endometriotic individuals. After treating cells with 0.1 μM of 1,25(OH)2D3 for 6, 24, and 48 h, the gene and protein expression of mentioned factors were evaluated by real‐time PCR and ELISA methods, respectively. 1,25(OH)2D3 treatment significantly reduced the protein expression of MCP‐1, HGF, and IGF‐1 in PBMCs and PFMCs of endometriotic patients at 48 h (p < 0.05–<0.01). Also, this treatment significantly reduced MCP‐1, HGF, and IGF‐1 gene and/or protein expression in EESCs and EuESCs at 24 and 48 h (p < 0.05–<0.01). 1,25(OH)2D3 treatment also reduced the proliferation of PBMCs and PFMCs of endometriotic patients compared with controls (p < 0.01). 1,25(OH)2D3 can be considered as a potentially effective agent in the prevention and treatment of endometriosis along with other therapies.

Effects of 1,25(OH)2 D3 and vitamin D receptor on peripheral CD4+ /CD8+ double-positive T lymphocytes in a mouse model of systemic lupus erythematosus

This study aims to explore effects of 1,25(OH)₂D₃ and vitamin D receptor (VDR) on peripheral CD4⁺/CD8⁺ double‐positive (DP) T lymphocytes in systemic lupus erythematosus (SLE). MRL‐LPr/LPr mice with SLE (n = 20) and normal MRL mice (n = 20) were assigned into the control group (normal mice, without feeding with 1,25(OH)₂D₃), the 1,25(OH)₂D₃ group (SLE mice, feeding with 1,25(OH)₂D₃), the VDR‐knock‐in + 1,25(OH)₂D₃ group (SLE mice, VDR‐knock‐in, feeding with 1,25(OH)₂D₃) and the VDR‐knockout group (normal mice, VDR‐knockout, without feeding with 1,25(OH)₂D₃) (n = 10 per group). Levels of T lymphocytes were measured by flow cytometry. The mRNA and proteins expressions of inflammatory factors were measured by qRT‐PCR and ELISA. Extracellular signal‐regulated kinase‐1/2 (ERK1/2) expression was measured by Western blotting. Compared with normal mice, SLE mice showed reduced levels of CD4⁺, CD4⁺/CD8⁺ ratio, and DP lymphocytes. The levels of SLE‐related indicators all increased significantly, followed with severe skin ulcers and urinary system infection. With the increase in time, skin ulcers and urinary system infection were significantly improved, levels of CD4⁺, CD4⁺/CD8⁺ ratio, and DP lymphocytes increased, and levels of SLE‐related indicators all decreased in the 1,25(OH)₂D₃ group. There were no significant changes in bioindicators in the control and the VDR‐knock‐in + 1,25(OH)₂D₃ groups. The symptoms of SLE gradually occurred in the VDR‐knockout group. This study demonstrates that VDR and 1,25(OH)₂D₃ could elevate CD4⁺/CD8⁺ DP T lymphocytes and reduce expressions of inflammatory factors, thus inhibiting the development and progression of SLE.

Vitamin D regulates tyrosine hydroxylase expression: N-cadherin a possible mediator

Vitamin D is a neuroactive steroid. Its genomic actions are mediated via the active form of vitamin D, 1,25(OH)2D3, binding to the vitamin D receptor (VDR). The VDR emerges in the rat mesencephalon at embryonic day 12, representing the peak period of dopaminergic cell birth. Our prior studies reveal that developmental vitamin D (DVD)-deficiency alters the ontogeny of dopaminergic neurons in the developing mesencephalon. There is also consistent evidence from others that 1,25(OH)2D3 promotes the survival of dopaminergic neurons in models of dopaminergic toxicity. In both developmental and toxicological studies it has been proposed that 1,25(OH)2D3 may modulate the differentiation and maturation of dopaminergic neurons; however, to date there is lack of direct evidence. The aim of the current study is to investigate this both in vitro using a human SH-SY5Y cell line transfected with rodent VDR and in vivo using a DVD-deficient model. Here we show that in VDR-expressing SH-SY5Y cells, 1,25(OH)2D3 significantly increased production of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine synthesis. This effect was dose- and time-dependent, but was not due to an increase in TH-positive cell number, nor was it due to the production of trophic survival factors for dopamine neurons such as glial-derived neurotrophic factor (GDNF). In accordance with 1,25(OH)2D3's anti-proliferative actions in the brain, 1,25(OH)2D3 reduced the percentage of dividing cells from approximately 15-10%. Given the recently reported role of N-cadherin in the direct differentiation of dopaminergic neurons, we examined here whether it may be elevated by 1,25(OH)2D3. We confirmed this in vitro and more importantly, we showed DVD-deficiency decreases N-cadherin expression in the embryonic mesencephalon. In summary, in our in vitro model we have shown 1,25(OH)2D3 increases TH expression, decreases proliferation and elevates N-cadherin, a potential factor that mediates these processes. Accordingly all of these findings are reversed in the developing brain in our DVD-deficiency model. Remarkably our findings in the DVD-deficiency model phenocopy those found in a recent model where N-cadherin was regionally ablated from the mesencephalon. This study has, for the first time, shown that vitamin D directly modulates TH expression and strongly suggests N-cadherin may be a plausible mediator of this process both in vitro and in vivo. Our findings may help to explain epidemiological data linking DVD deficiency with schizophrenia.

Interaction of vitamin D with membrane-based signaling pathways

Many studies in different biological systems have revealed that 1α,25-dihydroxyvitamin D₃ (1α,25(OH)₂D₃) modulates signaling pathways triggered at the plasma membrane by agents such as Wnt, transforming growth factor (TGF)-β, epidermal growth factor (EGF), and others. In addition, 1α,25(OH)₂D₃ may affect gene expression by paracrine mechanisms that involve the regulation of cytokine or growth factor secretion by neighboring cells. Moreover, post-transcriptional and post-translational effects of 1α,25(OH)₂D₃ add to or overlap with its classical modulation of gene transcription rate. Together, these findings show that vitamin D receptor (VDR) cannot be considered only as a nuclear-acting, ligand-modulated transcription factor that binds to and controls the transcription of target genes. Instead, available data support the view that much of the complex biological activity of 1α,25(OH)₂D₃ resides in its capacity to interact with membrane-based signaling pathways and to modulate the expression and secretion of paracrine factors. Therefore, we propose that future research in the vitamin D field should focus on the interplay between 1α,25(OH)₂D₃ and agents that act at the plasma membrane, and on the analysis of intercellular communication. Global analyses such as RNA-Seq, transcriptomic arrays, and genome-wide ChIP are expected to dissect the interactions at the gene and molecular levels.

Effect of 25-hydroxyvitamin D3 and 1 α,25 dihydroxyvitamin D3 on differentiation and apoptosis of human osteosarcoma cell lines

Osteosarcoma (OS) is a malignant bone tumor predominantly affecting children and adolescents. OS has a 60% survival rate with current treatments; hence, there is a need to identify novel adjuncts to chemotherapeutic regimens. In this pilot study, we investigated the dose-response to 1α,25-dihdroxyvitamin D(3) (1,α 25(OH)(2) D(3)) and 25-hydroxyvitamin D(3) (25(OH)D(3)) by human OS cell lines, SaOS-2, and 143B. We hypothesized that 1,α 25(OH)(2) D(3) and 25(OH)D(3) would stimulate differentiation and induce apoptosis in OS cells in a dose-dependent manner. Human OS cell lines, SaOS-2, and 143B, were treated with 1,α 25(OH)(2)D(3) or 25(OH)D(3) or an ethanol control, respectively, at concentrations ranging from 1 to 1,000 nM. Ki67 (a marker of cellular proliferation) immunocytochemistry revealed no significant changes in the expression of Ki-67 or MIB-1 in 1α,25(OH)(2)D(3) or 25(OH)D(3) treated SaOS-2 or 143B cells. Both control and 1α,25(OH)(2) D(3) treated SaOS-2 and 143B cells expressed vitamin D receptor (VDR). Markers of osteoblastic differentiation in 143B cells and SaOS-2 cells were induced by both 25(OH)D(3) and 1α,25(OH)(2) D, and evident by increases in alkaline phosphatase (ALP) activity, osteocalcin (OCN) mRNA expression, and mineralization of extra-cellular matrix (ECM) by alizarin red staining. An increasing trend in apoptosis in response to 25(OH)D(3), in both SaOS-2 and 143B cells was detected by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) staining. With 1α,25(OH)(2)D(3) treatment, apoptosis was evident at higher concentrations only. These preliminary findings suggest that OS cells express VDR and respond to 25(OH)D(3) and 1α,25(OH)(2)D(3) by undergoing differentiation and apoptosis.

Human bone marrow-derived stem cell proliferation is inhibited by hepatocyte growth factor via increasing the cell cycle inhibitors p53, p21 and p27

Human bone marrow-derived stem cells (hMSCs) are a major source of osteoprogenitors. Hepatocyte growth factor (HGF), a glycoprotein constitutively produced by hMSCs, is reported to act on differentiated osteoblasts and also osteoclasts. Moreover, HGF has been shown by us and others to enhance osteoblastic differentiation from hMSCs. Typically, the pro-differentiation effects of HGF have required cooperative action with regulatory factors such as vitamin D or bone matrix material. Here, we have pursued the molecular mechanisms underlying the osteogenic effect of HGF on hMSCs, the principal precursors to bone forming cells. HGF treatment of hMSCs reduced the cell number over time and increased G1/S cell-cycle arrest compared to control (non-treated) cells. RT-qPCR showed treatment with HGF increased gene expression of the cell-cycle inhibitors p53, p21, and p27, possibly explaining the cell growth inhibition and G1 arrest, a step critical to phenotypic differentiation. Transfection of siRNA specific for cMet, the HGF receptor, eliminated the HGF anti-proliferation effect on hMSCs and the HGF-mediated increase in p53, p21, and p27, strongly supporting a role for these cell-cycle inhibitors in HGF's regulation of hMSCs. HGF in combination with a known inducer of osteogenic differentiation, 1,25-dihydroxyvitamin D, significantly increased cell maturation/differentiation as indicated by an increase in several osteoblast markers. Taken together these results demonstrate that HGF significantly enhances hMSC osteoblast differentiation by 1,25-dihydroxyvitamin D.

Expression of hepatocyte growth factor and the proto-oncogenic receptor c-Met in canine osteosarcoma

Hepatocyte growth factor (HGF) and the proto-oncogenic receptor c-Met are implicated in growth, invasion, and metastasis in human cancer. Little information is available on the expression and role of both gene products in canine osteosarcoma. We hypothesized that the expression of c-Met is associated with malignant histologic characteristics, a short survival time, and a reduced disease-free interval in canine osteosarcoma. Quantitative real-time polymerase chain reaction was used to analyze the messenger RNA (mRNA) expression of both HGF and c-Met in 59 canine osteosarcoma samples. The relationship between HGF and c-Met expression, patient outcome, and histologic characteristics of the tumor were studied. Western blot analysis was performed to investigate the presence of active HGF protein. The expression pattern of c-Met in 16 slides of canine osteosarcoma was identified by immunohistochemistry. Coexpression of HGF and c-Met mRNA in all canine osteosarcoma samples suggested autocrine or paracrine receptor activation. A significant, moderately positive correlation was found between c-Met and HGF mRNA expression. c-Met mRNA expression was not associated with survival time or disease-free interval. Expression of c-Met was significantly associated with metastasis via the lymphogenic route. Immunolabeling with c-Met revealed a cytoplasmic staining pattern in all osteosarcoma cell types. In this study, c-Met mRNA expression in canine osteosarcoma was found to be of no influence on survival time and disease-free interval. Further studies are necessary to confirm the involvement of the c-Met pathway in the lymphogenic route of metastasis.

Increased number of mesenchymal stem cell-like cells in peripheral blood of patients with bone sarcomas

BACKGROUND AND AIMS

The number of peripheral blood mesenchymal stem cells (PBMSCs) may increase under pathological conditions. We sought to compare the number of MSC-like cells in the peripheral blood of patients with bone sarcomas with healthy controls and to analyze related cytokines in the peripheral blood plasma.

METHODS

Peripheral blood mononuclear cells (PBMNs) of patients with bone sarcomas and control subjects were isolated for culture and analyzed by flow cytometry for MSC phenotype. Cytokines in the plasma obtained after cell separation were analyzed using enzyme-linked immunosorbent assay (ELISA). Annexin-V and beta-galactosidase staining were used to investigate whether the cells died from apoptosis or senescence.

RESULTS

Flow cytometric analysis demonstrated an >9-fold increase in the number of cells with MSC-like phenotypes (CD34(-), CD45(-), CD105(+)) in patients with bone sarcomas compared with control subjects (p<0.05). ELISA results showed that concentrations of hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) in patients with bone sarcomas were statistically higher than those in the control subjects (p<0.05), whereas there was no significant difference in plasma concentrations of leptin and stromal cell-derived factor 1 between the two groups. A significant, positive correlation between the percentages of PBMSC-like cells and concentrations of HGF in all samples (R=0.618; p=0.011). Annexin-V staining of MSC-like cells was positive, whereas beta-galactosidase staining was negative.

CONCLUSIONS

Peripheral blood of patients with bone sarcomas has more cells with MSC phenotypes than blood of healthy persons. The increased number is accompanied by increased HGF and VEGF in the plasma.

In vitro and in vivo evaluation of combined calcitriol and cisplatin in dogs with spontaneously occurring tumors

PURPOSE

Calcitriol potentiates cisplatin-mediated activity in a variety of tumor models. We examine here, the effect of calcitriol and cisplatin pre-clinically and clinically in canine spontaneous tumors through in vitro studies on tumor cells and through a phase I study of calcitriol and cisplatin to identify the maximum-tolerated dosage (MTD) of this combination in dogs with cancer and to characterize the pharmacokinetic disposition of calcitriol in dogs.

METHODS

Canine tumor cells were investigated for calcitriol/cisplatin interactions on proliferation using an MTT assay in a median-dose effect analysis; data were used to derive a combination index (CI). Cisplatin was given at a fixed dosage of 60 mg/m2. Calcitriol was given i.v. and the dosage was escalated in cohorts of three dogs until the MTD was defined. Serum calcitriol concentrations were quantified by radioimmunoassay.

RESULTS

In vitro, CIs < 1.0 were obtained for all combinations of calcitriol/cisplatin examined. The MTD was 3.75 microg/kg calcitriol in combination with cisplatin, and hypercalcemia was the dose-limiting toxicosis. The relationship between calcitriol dosage and either Cmax or AUC was linear. Calcitriol dosages >1.5 microg/kg achieved Cmax > or = 9.8 ng/mL and dosages >1.0 microg/kg achieved AUC > or = 45 h ng/mL.

CONCLUSIONS

Calcitriol and cisplatin have synergistic antiproliferative effects on multiple canine tumor cells and high-dosages of i.v. calcitriol in combination with cisplatin can be safely administered to dogs. Cmax and AUC at the MTD 3.75 microg/kg calcitriol exceed concentrations associated with antitumor activity in a murine model, indicating this combination might have significant clinical utility in dogs.

Calcitriol inhibits the growth of MHCC97 heptocellular cell lines by down-modulating c-met and ERK expressions

BACKGROUND

Previous studies have demonstrated that Calcitriol or its analogs has an anti-tumour activity. This study was designed to determine the effect and mechanism of Calcitriol on MHCC-97 heptocellular cell lines.

METHODS

MHCC97 cell lines were treated with Calcitriol of 10(-6) approximately 10(-9) M concentration and with Calcitriol in lipiodol ultra-fluid (LUF) respectively. The conditions of cell proliferation were analyzed by MTT method. The cell apoptosis and cycle were analyzed by using a flow cytometer. Hepatocyte growth factor (HGF) concentration in the cell supernatant was measured by using ELISA method. C-met and vitamin D receptor (VDR) mRNA in cells were determined by using RT-PCR method. VDR and ERK(1/2) proteins were determined by using Western Blotting method.

RESULTS

Calcitriol inhibited the proliferation of MHCC97 cell lines with an accumulation of cells in the G(0)/G(1) phase and reduction of cells in S phase. Calcitriol dissolved in LUF resulted in a better and longer inhibitive effect on the cell lines than Calcitriol alone. MHCC97 cell lines secreted HGF and expressed c-met mRNA and ERK(1/2) proteins abundantly. Calcitriol remarkably inhibited the expressions of c-met mRNA and ERK(1/2) proteins.

CONCLUSION

Calcitriol inhibits the growth of MHCC-97 heptocellular cell lines by down modulating c-met and ERK expressions.

A Hepatocyte Growth Factor (HGF)/receptor autocrine loop regulates constitutive self-renewal of human periodontal ligament cells but reduces sensitivity to exogenous HGF

BACKGROUND

In addition to its prominent role in liver regeneration, hepatocyte growth factor (HGF) is now generally thought to be produced by mesenchymal cells to promote the regeneration of epithelial tissue by a paracrine mechanism. However, it is not known how or if HGF could be involved in the regeneration of periodontal tissues. The purpose of this study was to characterize the ability of normal human periodontal ligament (PDL) cells to produce or respond to HGF.

METHODS

PDL cells derived from healthy young volunteers were used from passages four through 10. HGF receptors were detected both by immunocytochemical staining and Western-blotting analysis. Both DNA synthesis (by bromo-deoxyuridine [BrdU]-incorporation) and secreted HGF were quantified by enzyme-linked immunosorbent assays. Mitogen-activated protein kinase (MAPK) phosphorylation was also analyzed by Western blot.

RESULTS

Despite the immunocytochemical demonstration of HGF receptor protein in the cytoplasm and on the plasma membrane of PDL cells, exogenous recombinant human HGF did not exert the mitogenic effects expected. As reported for other mesenchymal cells, PDL cells were found to secrete HGF. Treatments with neutralizing anti-HGF antibody significantly suppressed constitutive PDL cell proliferation and sustained the receptor protein at higher levels than in non-treated cells. Under these conditions, exogenous HGF rapidly phosphorylated extracellular signal-regulated kinase (ERK), an action linked to the cell proliferation and downregulation of cell-surface receptors.

CONCLUSIONS

Unlike other known mesenchymal or epithelial cells, these findings suggest that normal PDL cells from young donors possess a constitutive HGF/receptor autocrine loop that normally regulates their replacement self-proliferation but reduces sensitivity to exogenously applied HGF by acute receptor downregulation.

1,25-dihydroxyvitamin D inhibits renal interstitial myofibroblast activation by inducing hepatocyte growth factor expression

BACKGROUND

Vitamin D and its metabolites play an important role in calcium homeostasis, bone remodeling, hormone secretion, cell proliferation, and differentiation. Recent studies also suggest a beneficial role of vitamin D in slowing the progression of chronic renal glomerular diseases. This study investigated the effects and potential mechanism of 1,25-dihydroxyvitamin D(3)[1,25(OH)(2)D(3)] on the regulation of myofibroblast activation from interstitial fibroblast, a critical event in generating alpha-smooth muscle actin (alphaSMA)-positive, matrix-producing effector cells in renal interstitial fibrosis.

METHODS

Normal rat renal interstitial fibroblast cell line (NRK-49F) was used as a model system. Myofibroblast activation was initiated by incubation with transforming growth factor (TGF)-beta1. Expression of alpha-SMA, collagen I, thrombospondin-1, and hepatocyte growth factor (HGF) was assessed by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunostaining, respectively. HGF promoter activity was evaluated by using luciferase reporter assay.

RESULTS

Incubation of rat renal interstitial fibroblasts (NRK-49F) with 1,25(OH)(2)D(3) suppressed TGF-beta1-induced de novo alpha-SMA expression in a dose-dependent manner. 1,25(OH)(2)D(3) also suppressed type I collagen and thrombospondin-1 expression induced by TGF-beta1. Interestingly, 1,25(OH)(2)D(3) induced HGF mRNA expression and protein secretion in renal interstitial fibroblasts. Transfection studies revealed that 1,25(OH)(2)D(3) stimulated HGF gene promoter activity, which was dependent on the presence of vitamin D response element (VDRE). 1,25(OH)(2)D(3) induced the binding of vitamin D receptor to the VDRE in HGF promoter region. Furthermore, 1,25(OH)(2)D(3) was capable of stimulating HGF receptor phosphorylation in renal fibroblasts. Incubation with specific HGF neutralizing antibody largely abolished 1,25(OH)(2)D(3)-mediated suppression of myofibroblast activation.

CONCLUSION

These observations suggest that vitamin D analogue possesses renoprotective activity through suppression of the matrix-producing myofibroblast activation. This action of vitamin D is mediated, at least in part, by up-regulating antifibrotic HGF gene expression in renal interstitial fibroblasts.

The 1,25(OH)2D3-Regulated Transcription Factor MN1 Stimulates Vitamin D Receptor-Mediated Transcription and Inhibits Osteoblastic Cell Proliferation

The vitamin D endocrine system is essential for maintaining mineral ion homeostasis and preserving bone density. The most bioactive form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] elicits its effects by binding to the vitamin D receptor (VDR) and regulating the transcription of target genes. In osteoblasts, the bone-forming cells of the skeleton, 1,25-(OH)2D3 regulates cell proliferation, differentiation, and mineralization of the extracellular matrix. Despite these well-characterized biological functions, relatively few 1,25-(OH)2D3 target genes have been described in osteoblasts. In this study, we characterize the regulation and function of MN1, a novel 1,25-(OH)2D3-induced gene in osteoblastic cells. MN1 is a nuclear protein first identified as a gene disrupted in some meningiomas and leukemias. Our studies demonstrate that MN1 preferentially stimulates VDR-mediated transcription through its ligand-binding domain and synergizes with the steroid receptor coactivator family of coactivators. Furthermore, forced expression of MN1 in osteoblastic cells results in a profound decrease in cell proliferation by slowing S-phase entry, suggesting that MN1 is an antiproliferative factor that may mediate 1,25-(OH)2D3-dependent inhibition of cell growth. Collectively, these data indicate that MN1 is a 1,25-(OH)2D3-induced VDR coactivator that also may have critical roles in modulating osteoblast proliferation.

High calcium activates the EGF receptor potentially through the calcium-sensing receptor in Leydig cancer cells

Epidermal growth factor (EGF) plays an important role in the physiology and pathophysiology of the Leydig cell. In H-500 rat Leydig cancer cells, a model for humoral hypercalcemia of malignancy (HHM), we previously showed that the calcium-sensing receptor (CaR) stimulates PTHrP release and proliferation, both involving multiple mitogen-activated protein kinases. An emerging concept of signaling by G-protein coupled receptors (GPCR) is that it occurs via transactivation of receptor tyrosine kinases. Therefore, we investigated whether stimulation with calcium activates the EGFR in H-500 Leydig cancer cells. We show that treatment of H-500 cells with Ca(2+) results in EGFR phosphorylation. The CaR-induced activation of ERK1/2, induction of PTHrP release and stimulation of cellular proliferation in H-500 cells are likewise mediated, in large part, through the EGFR. In conclusion, the calcium activates the EGFR, possibly through the CaR, to regulate downstream signaling events and important biological functions in a model of HHM.

Expression of pituitary tumor transforming gene (PTTG) and its binding protein in human astrocytes and astrocytoma cells: function and regulation of PTTG in U87 astrocytoma cells

Human securin, pituitary tumor transforming gene (PTTG), is a protooncogene. Here we report expressions of PTTG and its interacting protein, PTTG-binding factor in human astrocytic cells. PTTG expression was higher in malignant cells than in primary astrocytes, whereas PTTG-binding factor was not. Using a xenotransplantable, glioma cell line (U87), we observed that knocking down PTTG mRNA by RNA silencing inhibited serum-induced proliferation by approximately 50%. Furthermore, in U87 cells PTTG expression was up-regulated by promalignant ligands epithelial growth factor (EGF) and TGFalpha, both at the protein and mRNA levels. PTTG induction by EGF receptor (EGFR) ligands could be blocked by the specific EGFR inhibitor, AG1478. Hepatocyte growth factor (HGF) also induced PTTG but to a lesser extent than EGF. Although EGF stimulates HGF secretion in U87 cells, the effect of EGF on PTTG mRNA expression is independent of HGF as neutralizing antibody against HGF failed to abolish EGF-induced up-regulation of PTTG mRNA. PTTG mRNA was unchanged by incubating U87 cells with the promalignant growth factor TGFbeta, apoptosis inducing TNFalpha and ligands for nuclear receptors, such as retinoic acid and retinoid X receptors and peroxisome proliferator-activated receptor-gamma, known for their growth-inhibitory and apoptosis-inducing effects on gliomas. In addition, 17beta-estradiol and Ca2+, known to activate PTTG expression, did not change PTTG mRNA levels in U87 cells. In summary, we show higher PTTG expression in astrocytoma than normal astrocytes and secondly, PTTG is involved in glioma cell growth. Finally, regulation of its expression has glioma-specific features and is selectively regulated by promalignant cytokines including EGFR ligands and HGF.

The functional consequences of cross-talk between the vitamin D receptor and ERK signaling pathways are cell-specific

The actions of the active metabolite of 1,25-(OH)2D3 (1,25-D) are mediated primarily by the vitamin D receptor (VDR), a member of the nuclear receptor family of ligand-activated transcription factors. Although their ligands cause transcriptional activation, many of the ligands also rapidly activate cellular signaling pathways through mechanisms that have not been fully elucidated. We find that 1,25-D causes a rapid, but sustained activation of ERK (extracellular signal-regulated kinase) in bone cell lines. However, the effect of ERK activation on VDR transcriptional activity was cell line-specific. Inhibition of ERK activation by the MEK inhibitor, U0126, stimulated VDR activity in MC3T3-E1 cells, but inhibited the activity in MG-63 cells as well as in HeLa cells. VDR is not a known target of ERK. We found that the ERK target responsible for reduced VDR activity in MC3T3-E1 cells is RXRalpha. MC3T3-E1 cells express lower levels of RXRbeta and RXRgamma than either HeLa or MG-63 cells. Although overexpression of RXRalpha in MC3T3-E1 cells increased VDR activity, U0126 further enhanced the activity. In contrast, overexpression of RXRgamma stimulated VDR activity but abrogated the stimulation by U0126. Thus, although 1,25-D treatment activates ERK in many cell types, subsequently inducing changes independent of VDR, the effects of treatment with 1,25-D on the transcriptional activity of VDR are RXR isoform-specific. In cells in which RXRalpha is the VDR partner, the transcriptional activation of VDR by 1,25-D is attenuated by the concomitant activation of ERK. In cells utilizing RXRgamma, ERK activation enhances VDR transcriptional activity.