Transcriptional activation of p21 by vitamin D(3) or vitamin K(2) leads to differentiation of p53-deficient MG-63 osteosarcoma cells

Vitamin K: New insights related to senescence and cancer metastasis

Several clinical trials and experimental studies have recently shown that vitamin K (VK) supplementation benefits the human body. Specifically, VK participates in coagulation and is associated with cellular senescence and cancer. VK has a potential anticancer effect in various cancers, such as pancreatic and prostate cancers. Through anti-inflammatory and antioxidant effects, VK can prevent senescence and inhibit cancer metastasis. Therefore, cancer prognosis can be improved by preventing cellular senescence. In addition, VK can inhibit the proliferation, growth, and differentiation of cancer cells through various mechanisms, including induction of c-myc and c-fos genes, regulation of B-cell lymphoma-2 (Bcl-2) and p21 genes, and angiogenesis inhibition. This review aims to discuss the relationship among VK, cellular senescence, and cancer metastasis and thus may improve comprehension of the specific functions of VK in human health. The potential application of VK as an adjuvant therapy for cancer (or in combination with traditional chemotherapy drugs or other vitamins) has also been highlighted.

Endocrine disruption of vitamin D activity by perfluoro-octanoic acid (PFOA)

Perfluoroalkyl substances (PFAS) are a class of compounds used in industry and consumer products. Perfluorooctanoic acid (PFOA) is the predominant form in human samples and has been shown to induce severe health consequences, such as neonatal mortality, neurotoxicity, and immunotoxicity. Toxicological studies indicate that PFAS accumulate in bone tissues and cause altered bone development. Epidemiological studies have reported an inverse relationship between PFAS and bone health, however the associated mechanisms are still unexplored. Here, we present computational, in silico and in vitro evidence supporting the interference of PFOA on vitamin D (VD). First, PFOA competes with calcitriol on the same binding site of the VD receptor, leading to an alteration of the structural flexibility and a 10% reduction by surface plasmon resonance analysis. Second, this interference leads to an altered response of VD-responsive genes in two cellular targets of this hormone, osteoblasts and epithelial cells of the colorectal tract. Third, mineralization in human osteoblasts is reduced upon coincubation of PFOA with VD. Finally, in a small cohort of young healthy men, PTH levels were higher in the exposed group, but VD levels were comparable. Altogether these results provide the first evidence of endocrine disruption by PFOA on VD pathway by competition on its receptor and subsequent inhibition of VD-responsive genes in target cells.

PLK2 modulation of enriched TAp73 affects osteogenic differentiation and prognosis in human osteosarcoma

There are three subtypes of undifferentiated human conventional osteosarcoma (HCOS): osteoblastic osteosarcoma (OOS), chondroblastic osteosarcoma (COS), and fibroblastic osteosarcoma (FOS). HCOS also exhibits heterogeneous pathological maldifferentiation in individual patients. Currently, the mechanism regulating HCOS differentiation remains unclear, and therapies are ineffective. Osteopontin (OPN) and osteocalcin (OCN) are markers of osteoblast maturation, and their expression is inhibited in HCOS. A previous study found that PLK2 inhibited TAp73 phosphorylation and consequent anti-OS function of TAp73 in OS cells with enriched TAp73. TAp73 was also reported to regulate bone cell calcification. Here, OOS was found to have higher TAp73 levels and PLK2 expression than those in COS, which is correlated with HCOS maldifferentiation according to Spearman analysis and affects patient prognosis according to Kaplan-Meier survival analysis. In the conventional OS cell-line Saos2 and in patient-derived xenograft OS (PDX-OS) cells, increased PLK2 expression owing to abundant TAp73 levels affected OPN and OCN content as measured by RT-PCR and Western blotting, and alizarin red staining showed that PLK2 affected calcium deposition in OS cells. In addition, PLK2 inhibition in PDX-OS cells prohibited clone formation, as indicated by a clonogenic assay, and sensitized OS cells to cisplatin (CDDP) (which consequently limited proliferation), as shown by the CCK-8 assay. In an established PDX animal model with abundant TAp73 levels, PLK2 inhibition or CDDP treatment prevented tumor growth and prolonged median survival. The combined therapeutic effect of PLK2 inhibition with CDDP treatment was better than that of either monotherapy. These results indicate that increased PLK2 levels due to enriched TAp73 affect osteogenic differentiation and maturation and OS prognosis. In conclusion, PLK2 is a potential target for differentiation therapy of OS with enriched TAp73.

Vitamin K: Redox-modulation, prevention of mitochondrial dysfunction and anticancer effect

This review is directed to the redox-modulating properties and anticancer effect of vitamin K. The concept is focused on two aspects: (i) redox-cycle of vitamin K and its effect on the calcium homeostasis, “oncogenic” and “onco-suppressive” reactive oxygen species and the specific induction of oxidative stress in cancer; (ii) vitamin K plus C as a powerful redox-system, which forms a bypass between mitochondrial complexes II and III and thus prevents mitochondrial dysfunction, restores oxidative phosphorylation and aerobic glycolysis, modulates the redox-state of endogenous redox-pairs, eliminates the hypoxic environment of cancer cells and induces cell death. The analyzed data suggest that vitamin C&K can sensitize cancer cells to conventional chemotherapy, which allows achievement of a lower effective dose of the drug and minimizing the harmful side-effects. The review is intended for a wide audience of readers - from students to specialists in the field.

Hyperoside, a flavonoid compound, inhibits proliferation and stimulates osteogenic differentiation of human osteosarcoma cells

Osteosarcoma, one of the most common malignant bone tumours, is generally considered a differentiation disease caused by genetic and epigenetic disruptions in the terminal differentiation of osteoblasts. Novel therapies based on the non-cytotoxic induction of cell differentiation-responsive pathways could represent a significant advance in treating osteosarcoma; however, effective pharmaceuticals to induce differentiation are lacking. In the present study, we investigated the effect of hyperoside, a flavonoid compound, on the osteoblastic differentiation of U2OS and MG63 osteosarcoma cells in vitro. Our results demonstrated that hyperoside inhibits the proliferation of osteosarcoma cells by inducing G₀/G₁ arrest in the cell cycle, without causing obvious cell death. Cell migration assay further suggested that hyperoside could inhibit the invasion potential of osteosarcoma cells. Additionally, osteopontin and runt-related transcription factor 2 protein levels and osteocalcin activation were upregulated dramatically in hyperoside-treated osteosarcoma cells, suggesting that hyperoside may stimulates osteoblastic differentiation in osteosarcoma cells. This differentiation was accompanied by the activation of transforming growth factor (TGF)-β and bone morphogenetic protein-2, suggesting that the hyperoside-induced differentiation involves the TGF-β signalling pathway. To our knowledge, this study is the first to evaluate the differentiation effect of hyperoside in osteosarcoma cells and assess the possible potential for hyperoside treatment as a future therapeutic approach for osteosarcoma differentiation therapy.

The Current and Future Therapies for Human Osteosarcoma

Osteosarcoma (OS) is the most common non-hematologic malignant tumor of bone in adults and children. As sarcomas are more common in adolescents and young adults than most other forms of cancer, there are a significant number of years of life lost secondary to these malignancies. OS is associated with a poor prognosis secondary to a high grade at presentation, resistance to chemotherapy and a propensity to metastasize to the lungs. Current OS management involves both chemotherapy and surgery. The incorporation of cytotoxic chemotherapy into therapeutic regimens escalated cure rates from <20% to current levels of 65-75%. Furthermore, limb-salvage surgery is now offered to the majority of OS patients. Despite advances in chemotherapy and surgical techniques over the past three decades, there has been stagnation in patient survival outcome improvement, especially in patients with metastatic OS. Thus, there is a critical need to identify novel and directed therapy for OS. Several Phase I trials for sarcoma therapies currently ongoing or recently completed have shown objective responses in OS. Novel drug delivery mechanisms are currently under phase II and III clinical trials. Furthermore, there is an abundance of preclinical research which holds great promise in the development of future OS-directed therapeutics. Our continuously improving knowledge of the molecular and cell-signaling pathways involved in OS will translate into more effective therapies for OS and ultimately improved patient survival. The present review will provide an overview of current therapies, ongoing clinical trials and therapeutic targets under investigation for OS.

Vitamin D: metabolism, molecular mechanisms, and mutations to malignancies

The potential protective effects of vitamin D against cutaneous carcinogenesis are still poorly understood. The inhibition, by vitamin D, of various cancers in in vitro and in vivo models has triggered detailed investigation of vitamin D effects on neoplastic behavior. Recent studies highlight that such neoplastic features as the tumor microenvironment, angiogenesis, DNA mutagenesis, and apoptosis are all connected to vitamin D metabolic pathways. This review discusses these connections. Vitamin D modulation of the cell cycle, DNA repair and apoptosis via its receptors (VDRs) may have a suppressive effect on skin cancer as some studies suggest. The regulation of multiple tumor signaling pathways by vitamin D may have an implication in cutaneous carcinogenesis and tumor progression to malignancy.

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.

Defective osteogenic differentiation in the development of osteosarcoma

Osteosarcoma (OS) is associated with poor prognosis due to its high incidence of metastasis and chemoresistance. It often arises in areas of rapid bone growth in long bones during the adolescent growth spurt. Although certain genetic conditions and alterations increase the risk of developing OS, the molecular pathogenesis is poorly understood. Recently, defects in differentiation have been linked to cancers, as they are associated with high cell proliferation. Treatments overcoming these defects enable terminal differentiation and subsequent tumor inhibition. OS development may be associated with defects in osteogenic differentiation. While early regulators of osteogenesis are unable to bypass these defects, late osteogenic regulators, including Runx2 and Osterix, are able to overcome some of the defects and inhibit tumor propagation through promoting osteogenic differentiation. Further understanding of the relationship between defects in osteogenic differentiation and tumor development holds tremendous potential in treating OS.

p73 is essential for vitamin D-mediated osteoblastic differentiation

The secosteroid hormone vitamin D3 (VD3) exerts its biological actions through its cognate receptor, the vitamin D receptor (VDR). Vitamin D3 and VDR have a key function in bone formation and keratinocyte differentiation, exert antiproliferative actions in human cancer, and is widely used as a chemotherapeutic agent for cancer. In addition, VD3 promotes differentiation of human osteosarcoma cells by up-regulating genes involved in cell cycle arrest and osteoblastic differentiation. Although considerable work has been carried out in understanding the molecular mechanisms underlying the VD3-mediated differentiation of human osteosarcoma cells, the upstream regulation of VD3 signaling pathway is still unclear. In this study, we show that p73 acts as an upstream regulator of VD3-mediated osteoblastic differentiation. Transcription factor p73, a p53 homolog, has been shown to have a function in development and recently been termed as a tumor suppressor. Silencing p73 results in a significant reduction of VD3-mediated osteoblastic differentiation; although DNA damage induced p73 leads to an increase in VD3-mediated differentiation of osteosarcoma cells. Together, our data implicate a novel function for p73 in vitamin D-mediated differentiation of human osteosarcoma cells.

Osteogenic BMPs promote tumor growth of human osteosarcomas that harbor differentiation defects

Osteosarcoma (OS) is the most common primary malignancy of bone. Here, we investigated a possible role of defective osteoblast differentiation in OS tumorigenesis. We found that basal levels of the early osteogenic marker alkaline phosphatase (ALP) activity were low in OS lines. Osteogenic regulators Runx2 and OSX, and the late marker osteopontin (OPN) expressed at low levels in most OS lines, indicating that most OS cells fail to undergo terminal differentiation. Furthermore, OS cells were refractory to osteogenic BMP-induced increases in ALP activity. Osteogenic BMPs were shown to upregulate early target genes, but not late osteogenic markers OPN and osteocalcin (OC). Furthermore, osteogenic BMPs failed to induce bone formation from human OS cells, rather effectively promoted OS tumor growth in an orthotopic OS model. Exogenous expression of early target genes enhanced BMP-stimulated OS tumor growth, whereas osteogenic BMP-promoted OS tumor growth was inhibited by exogenous Runx2 expression. These results suggest that alterations in osteoprogenitors may disrupt osteogenic differentiation pathway. Thus, identifying potential differentiation defects in OS tumors would allow us to reconstruct the tumorigenic events in osteoprogenitors and to develop rational differentiation therapies for clinical OS management.

Osteosarcoma development and stem cell differentiation

Osteosarcoma is the most common nonhematologic malignancy of bone in children and adults. The peak incidence occurs in the second decade of life, with a smaller peak after age 50. Osteosarcoma typically arises around the growth plate of long bones. Most osteosarcoma tumors are of high grade and tend to develop pulmonary metastases. Despite clinical improvements, patients with metastatic or recurrent diseases have a poor prognosis. Here, we reviewed the current understanding of human osteosarcoma, with an emphasis on potential links between defective osteogenic differentiation and bone tumorigenesis. Existing data indicate osteosarcoma tumors display a broad range of genetic and molecular alterations, including the gains, losses, or arrangements of chromosomal regions, inactivation of tumor suppressor genes, and the deregulation of major signaling pathways. However, except for p53 and/or RB mutations, most alterations are not constantly detected in the majority of osteosarcoma tumors. With a rapid expansion of our knowledge about stem cell biology, emerging evidence suggests osteosarcoma should be regarded as a differentiation disease caused by genetic and epigenetic changes that interrupt osteoblast differentiation from mesenchymal stem cells. Understanding the molecular pathogenesis of human osteosarcoma could ultimately lead to the development of diagnostic and prognostic markers, as well as targeted therapeutics for osteosarcoma patients.

Atorvastatin in patients with primary biliary cirrhosis and incomplete biochemical response to ursodeoxycholic acid

Statin therapy may target both hypercholesterolemia and cholestasis in primary biliary cirrhosis (PBC). However, little is known about the efficacy and safety of statins in PBC. The aim of this single-center study was therefore to prospectively examine the effects of atorvastatin on serum markers of cholestasis, aminotransferases, and lipid and bile acid metabolism as well as inflammatory and immunological markers in patients with PBC. Fifteen patients with early-stage PBC and an incomplete biochemical response to ursodeoxycholic acid (UDCA) therapy (defined as alkaline phosphatase 1.5-fold above the upper limit of normal after 1 year) were treated with atorvastatin 10 mg/day, 20 mg/day, and 40 mg/day for 4 weeks, respectively. Serum levels of alkaline phosphatase increased during atorvastatin 20 mg and 40 mg (P < 0.05), whereas leucine aminopeptidase and gamma-glutamyltransferase remained unchanged. No statistical differences in overall serum ALT, AST, bilirubin, and IgM levels were observed. However, atorvastatin was discontinued in 1 out of 15 patients because of ALT 2-fold above baseline, and 2 patients showed ALT elevations 3-fold above the upper limit of normal at the end of the atorvastatin treatment period. Serum total cholesterol and low-density lipoprotein cholesterol levels decreased by 35% and 49%, respectively (P < 0.001). Precursors of cholesterol biosynthesis (lanosterol, desmosterol, lathosterol) showed a similar pattern. No changes in serum bile acid levels and composition were observed during treatment.

CONCLUSION

Atorvastatin does not improve cholestasis in PBC patients with an incomplete biochemical response to UDCA but effectively reduces serum cholesterol levels.

1alpha,25-Dihydroxyvitamin D(3) antiproliferative actions involve vitamin D receptor-mediated activation of MAPK pathways and AP-1/p21(waf1) upregulation in human osteosarcoma

The molecular mechanisms underlying antiproliferative actions of the steroid 1alpha,25-dihydroxy vitamin D(3) (1,25D) in human osteosarcoma cells are known only partially. To better understand the signaling involved in 1,25D anti-tumorigenic properties in bone, we stably silenced vitamin D receptor (VDR) expression in the human osteosarcoma SaOS-2 cell line. We found that 1,25D treatment reduced cell proliferation by approximately 25% after 3 days only in SaOS-2 cells expressing native levels of VDR protein, and involved activation of MAPK/AP-1/p21(waf1) pathways. Both sustained (3 days) and transient (15min) 1,25D treatment activated JNK and ERK1/2 MAPK signaling in a nongenomic VDR-dependent manner. However, only sustained exposure to hormone led to upregulation of p21 and subsequent genomic control of the cell cycle. Specific blockade of MEK1/MEK2 cascade upstream from ERK1/2 abrogated 1,25D activation of AP-1 and p21, and subsequent antiproliferative effects, even in the presence of a nuclear VDR. We conclude that 1,25D-induced inhibition of human osteosarcoma cell proliferation occurs via sustained activation of JNK and MEK1/MEK2 pathways downstream of nongenomic VDR signaling that leads to upregulation of a c-Jun/c-Fos (AP-1) complex, which in turn modulates p21(waf1) gene expression. Our results demonstrate a cross-talk between 1,25D/VDR nongenomic and genomic signaling at the level of MAP kinase activation that leads to reduction of cell proliferation in human osteosarcoma cells.

Vitamin K2 inhibits the proliferation of HepG2 cells by up-regulating the transcription of p21 gene

AIM

Vitamin K2 has been reported to inhibit the growth of human hepatocellular carcinoma (HCC) in vitro and suppress hepatocarcinogenesis in vivo. However, its inhibitory mechanism has not yet been clarified.

METHODS

Different concentrations of vitamin K2 (30, 10, 1, 0.1 and 0.01 muM) were added to the HCC cell line HepG2 to assess effects on cell growth. The effect of vitamin K2 on cell cycle progression was determined by flow-cytometric analysis. The expression of cell cycle regulatory proteins p21 and p27 was then examined by Western blot. Whether vitamin K2 regulates the gene expression through action on the p21 promoter region was investigated by luciferase assay.

RESULTS

Vitamin K2 inhibited the growth of HepG2 cells dose-dependently, and its inhibitory rate reached approximately 50% at the dose of 30 muM after 96 h treatment. After treatment with vitamin K2, the proportion of cells in G0-G1 phase increased, and in S phase decreased. Apoptotic cells were not detected. The expression of cell cycle regulatory protein p21 was induced by vitamin K2 treatment, but p27 was not. By the luciferase assay, vitamin K2 significantly activated the promoter of p21. Knock-down of p21 by siRNA reversed the growth inhibition of HepG2 cells by vitamin K2.

CONCLUSIONS

The findings suggest that vitamin K2 suppresses the proliferation of HCC cells by blocking the cell cycle G1/S progression through the transcriptional induction of p21.

High dose vitamin K3 infusion in advanced hepatocellular carcinoma

BACKGROUND AND AIM

The survival of patients with unresectable advanced hepatocellular carcinoma (HCC) with portal vein thrombosis is dismal. Current therapeutic options have limited efficacy. Vitamin K has been shown to have antitumor effect on HCC cells both in cell lines and patients with advanced HCC. The aim of this study was to assess the clinical efficacy of high dose vitamin K3 in the treatment of advanced HCC with portal vein thrombosis.

METHODS

Forty-two consecutive patients with advanced HCC (Stage C according to BCLC staging system) with portal vein thrombosis were randomized into two groups: (i) high dose vitamin K3 (n = 23); and (ii) placebo (n = 19). The vitamin K3 was administered by i.v. infusion of 50 mg/day with daily increase of dose by 50 mg for 6 days, followed by 20 mg i.m. twice daily for 2 weeks.

RESULTS

Of the 23 patients treated with vitamin K, one (4.3%) achieved complete response and three (13%) partial response, for a total of four (17.4%) objective responders overall. The overall mean survival was 8.9 +/- 8.8 months (median: 6; range 1-37 months) in the vitamin K group and 6.8 +/- 5.3 months (median: 5; range 1.5-21 months) in the placebo group (P = 0.552). The mean duration of survival was longer in patients in the vitamin K group who achieved objective response (22.5 +/- 12.2; median: 21; range 11-37 months) as compared to patients not achieving objective response (6.1 +/- 4.6; median: 5; range 1-16 months) (P = 0.0.002). Portal vein thrombosis resolved with complete patency in one (4.35%) patient.

CONCLUSIONS

Treatment with high dose vitamin K produces objective response in 17% patients with improved survival in patients achieving objective response; however, it does not affect the overall survival.

Molecular analysis of p53, MDM2 and H-ras genes in low-grade central osteosarcoma

Low-grade central osteosarcoma is an uncommon form that is characterized by a long premorbid history, and is compatible with prolonged survival after treatment. However, molecular abnormalities are rare in low-grade central osteosarcomas, whereas p53 mutations occur in approximately 20% of conventional high-grade osteosarcomas. In this study, 21 cases of low-grade central osteosarcoma were analyzed for mutations of the p53 gene, amplification of the MDM2 gene, and mutations of the H-ras gene using formalin-fixed, paraffin-embedded materials. We also examined the expression of p53, MDM2, and p21WAF1 protein immunohistochemically and assessed the proliferation activities using the monoclonal antibody MIB-1. One case (4.7%) showed strong p53 immunoreactivity, whereas p53 gene mutations were not detected at all. Seven cases (33.3%) showed immunoreactivity for MDM2 protein. As for gene alterations, MDM2 amplification was found in four cases (19.0%). p21WAF1 expression was detected in 12 cases (57.1%). MIB-1-LI showed very low levels in all the cases and no significant correlation with p53 or MDM2 immuno-reactivity. None of the tumors showed H-ras mutations. In conclusion, the number of p53 gene alterations in low-grade central osteosarcomas is lower than that in conventional high-grade osteosarcomas. MDM2 alterations and p21WAF1 expression might be involved in the tumorigenesis of low-grade central osteosarcomas.

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.

Molecular analysis of p21 promoter activity isolated from squamous carcinoma cell lines of the head and neck under the influence of 1,25(OH)2 vitamin D3 and its analogs

OBJECTIVE

The biologically active 1,25(OH)2 vitamin D3 and its analogs have been shown to have antiproliferative and differentiating effects in a variety of malignant and non-malignant cells. For squamous carcinoma cell lines of the head and neck (SCCHN) we could show that this antiproliferative activity of 1,25(OH)2 vitamin D3 is due to induced expression of the cell-cycle inhibitory proteins p21 and p27, causing an arrest in the G0/G1 cell-cycle phase.

MATERIAL AND METHODS

In this work we investigated the effects of three vitamin D3 analogs, EB1089, MC1288 and CB1093, on proliferation behavior and cell-cycle status in a laryngeal carcinoma cell line (JPPA) as well as in control human immortalized keratinocytes (HaCaT). To study the molecular mechanism the functional activity of the promoter region of p21, a potential target gene of vitamin D3 transcriptional regulation, was investigated. For this reason a 2.7-kb fragment of the p21 promoter was isolated by polymerase chain reaction from HaCaT, JPPA and SCC9 (tongue carcinoma) cells and directionally cloned into an enhanced green fluorescence protein (EGFP) reporter gene vector system. A construct was used to stably transfect HaCaT cells and to monitor the expression of the EGFP gene by confocal microscopy.

RESULTS

Analysis of proliferation and cell-cycle status revealed decreased growth rates and G0/G1I cell-cycle arrest in cells treated with 1,25(OH)2 vitamin D3 and its analogs The EGFP reporter gene-transfected cells showed distinct fluorescence under the influence of 1,25(OH)2 vitamin D3 and its analogs compared to control cells.

CONCLUSION

These results demonstrate that the cell-cycle inhibitor protein p21 is a direct target gene of biologically active 1,25(OH)2 vitamin D3, inducing G0/G1 cell-cycle arrest. The ability of vitamin D analogs to act via the same molecular mechanism as the natural hormone but with less hypercalcemic activity may have therapeutic implications for patients with SCCHN malignancy.

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

Several mesenchymally derived cells, including osteoblasts, secrete hepatocyte growth factor (HGF). 1alpha,25(OH)(2)-vitamin D(3) [1,25(OH)(2)D(3)] inhibits proliferation and induces differentiation of MG-63 osteoblastic cells. Here we show that MG-63 cells secrete copious amounts of HGF and that 1,25(OH)(2)D(3) inhibits HGF production. MG-63 cells also express HGF receptor (c-Met) mRNA, suggesting an autocrine action of HGF. Indeed, although exogenous HGF failed to stimulate cellular proliferation, neutralizing endogenous HGF with a neutralizing antibody inhibited MG-63 cell proliferation; moreover, inhibiting HGF synthesis with 1,25(OH)(2)D(3) followed by addition of HGF rescued hormone-induced inhibition of proliferation. Nonneutralized cells displayed constitutive phosphorylation of c-Met and the mitogen-activated protein kinases mitogen/extracellular signal-regulated kinase (MEK) 1 and extracellular signal-regulated kinase (Erk) 1/2, which were inhibited by anti-HGF antibody. Constitutive phosphorylation of Erk1/2 was also abolished by 1,25(OH)(2)D(3). Addition of HGF to MG-63 cells treated with neutralizing HGF antibody induced rapid phosphorylation of c-Met, MEK1, and Erk1/2. Thus endogenous HGF induces a constitutively active, autocrine mitogenic loop in MG-63 cells. The known antiproliferative effect of 1,25(OH)(2)D(3) on MG-63 cells can be accounted for by the concomitant 1,25(OH)(2)D(3)-induced inhibition of HGF production.

1 alpha,25-dihydroxyvitamin D3 increases TGF beta 1 binding to human osteoblasts

1alpha,25-Dihydroxyvitamin D3 (1alpha,25(OH)2D3) increases the binding of transforming growth factor beta1(TGF beta1) via TGF beta receptors to the surface of human osteoblasts. The increase in TGF beta receptors induced by 1alpha,25(OH)2D3 is dependent on increases in TGF beta secretion induced by 1alpha,25(OH)2D3, since antibodies directed against TGF beta block the increase in TGF beta1 binding. The increase in TGF beta type I and II receptors on cell surfaces following 1alpha,25(OH)2D3 treatment is associated with increases in receptor mRNA concentrations. Increases in receptor mRNA concentrations following 1alpha,25(OH)2D3 treatment are not due to changes in receptor gene transcription. The role of TGF beta receptors, in mediating the growth responses to 1alpha,25(OH)2D3 is demonstrated by showing that osteoblasts which express dominant negative, kinase-deficient TGF beta type II receptors, fail to respond to the growth-inhibitory effects of 1alpha,25(OH)2D3. An increase in TGF beta receptor expression is important in mediating 1alpha,25(OH)2D3-associated changes in the growth rate of osteoblasts.