p53-independent induction of WAF1/Cip1 is correlated with osteoblastic differentiation by vitamin D3

Discovery of cancer-preventive juices reactivating RB functions

BACKGROUND

Recent advances have been achieved in the genetic diagnosis and therapies against malignancies due to a better understanding of the molecular mechanisms underlying carcinogenesis. Since active preventive methods are currently insufficient, the further development of appropriate preventive strategies is desired.

METHODS

We searched for drinks that reactivate the functions of tumor-suppressor retinoblastoma gene (RB) products and exert anti-inflammatory and antioxidant effects. We also examined whether lactic acid bacteria increased the production of the cancer-specific anti-tumor cytokine, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), in human, and examined whether the RB-reactivating drinks with lactic acid bacteria decreased azoxymethane-induced rat colon aberrant crypt foci (ACF) and aberrant crypts (ACs) in vivo.

RESULTS

Kakadu plum juice and pomegranate juice reactivated RB functions, which inhibited the growth of human colon cancer LIM1215 cells by G1 phase arrest. These juices also exerted anti-inflammatory and antioxidant effects. Lactiplantibacillus (L.) pentosus S-PT84 was administered to human volunteers and increased the production of TRAIL. In an in vivo study, Kakadu plum juice with or without pomegranate juice and S-PT84 significantly decreased azoxymethane-induced rat colon ACF and ACs.

CONCLUSIONS

RB is one of the most important molecules suppressing carcinogenesis, and to the best of our knowledge, this is the first study to demonstrate that natural drinks reactivated the functions of RB. As expected, Kakadu plum juice and pomegranate juice suppressed the growth of LIM1215 cells by reactivating the functions of RB, and Kakadu plum juice with or without pomegranate juice and S-PT84 inhibited rat colon ACF and ACs. Therefore, this mixed juice has potential as a novel candidate for cancer prevention.

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.

Association of bone loss with the upregulation of survival-related genes and concomitant downregulation of Mammalian target of rapamycin and osteoblast differentiation-related genes in the peripheral blood of late postmenopausal osteoporotic women

We aimed to identify bone related markers in the peripheral blood of osteoporotic (OP) patients that pointed toward molecular mechanisms underlying late postmenopausal bone loss. Whole blood from 22 late postmenopausal OP patients and 26 healthy subjects was examined. Bone mineral density (BMD) was measured by DXA. Protein levels of p70-S6K, p21, MMP-9, TGFβ1, and caspase-3 were quantified by ELISA. Gene expression was measured using real-time RT-PCR. OP registered by low BMD indices in late postmenopausal patients was associated with a significant upregulation of autophagy protein ULK1, cyclin-dependent kinase inhibitor p21, and metalloproteinase MMP-9 gene expression in the blood compared to the healthy controls and in a significant downregulation of mTOR (mammalian target of rapamycin), RUNX2, and ALPL gene expression, while expression of cathepsin K, caspase-3, transforming growth factor (TGF) β1, interleukin- (IL-) 1β, and tumor necrosis factor α (TNFα) was not significantly affected. We also observed a positive correlation between TGFβ1 and RUNX2 expression and BMD at femoral sites in these patients. Therefore, bone loss in late postmenopausal OP patients is associated with a significant upregulation of survival-related genes (ULK1 and p21) and MMP-9, as well as the downregulation of mTOR and osteoblast differentiation-related genes (RUNX2 and ALPL) in the peripheral blood compared to the healthy controls.

Role of cell cycle regulatory molecules in retinoic acid- and vitamin D3-induced differentiation of acute myeloid leukaemia cells

The important role of cell cycle regulatory molecules in all trans-retinoic acid (ATRA)- and vitamin D3-induced growth inhibition and differentiation induction has been intensively studied in both acute myeloid leukaemia primary cells and a variety of leukaemia cell lines. Cyclin-dependent kinases (CDK)-activating kinase has been demonstrated to interact with retinoic acid receptor (RAR)α in acute promyelocytic leukaemia cells, and inhibition of CDK-activating kinase by ATRA causes hypophosphorylation of PML-RARα, leading to myeloid differentiation. In many cases, downregulation of CDK activity by ATRA and vitamin D3 is a result of elevated p21- and p27-bound CDKs. Activation of p21 is regulated at the transcriptional level, whereas elevated p27 results from both (indirectly) transcriptional activation and post-translational modifications. CDK inhibitors (CKIs) of the INK family, such as p15, p16 and p18, are mainly involved in inhibition of cell proliferation, whereas CIP/KIP members, such as p21, regulate both growth arrest and induction of differentiation. ATRA and vitamin D3 can also downregulate expression of G1 CDKs, especially CDK2 and CDK6. Inhibition of cyclin E expression has only been observed in ATRA- but not in vitamin D3-treated leukaemic cells. In vitro, not only dephosphorylation of pRb but also elevation of total pRb is required for ATRA and vitamin D3 to suppress growth and trigger their differentiation. Finally, sharp reduction in c-Myc has been observed in several leukaemia cell lines treated with ATRA, which may regulate expression of CDKs and CKIs.

Plasma vitamin D levels, menopause, and risk of breast cancer: dose-response meta-analysis of prospective studies

Previous evidence suggests that higher circulating 25-hydroxyvitamin D (25[OH]D) levels are variably associated with lower breast cancer risk; however, prospective studies and clinical trials have been inconsistent, particularly between older and younger women of differing menopausal status. We conducted a quantitative nonlinear dose-response meta-analysis of prospective studies evaluating the association between circulating 25(OH)D and breast cancer risk, stratified by menopause. A systematic search of MEDLINE and EMBASE included studies published through May 2011. We reviewed references from retrieved articles and contacted relevant investigators for additional data from prospective studies on circulating 25(OH)D levels and incident breast cancers. Prospective studies of circulating vitamin D and breast cancer risk were reviewed, and no language restrictions were imposed. Information on study population, menopausal status, 25(OH)D levels, and relative risk (RR) estimates were extracted using a standardized protocol.A total of 9 prospective studies were included, comprising 5206 cases and 6450 controls. Data were pooled using dose-response random-effects meta-regression models. Identifying nonlinear effects, spline models were optimized for thresholds. The relationship between circulating 25(OH)D and breast cancer risk differed by menopausal status (p = 0.05 for effect modification). While no association was found in premenopausal women, dose-response modeling revealed a nonlinear inverse association among postmenopausal women. Notably, a flat association was observed in the lowest range of 25(OH)D levels <27 ng/mL (RR = 1.01 per 5 ng/mL; 95% confidence interval [CI], 0.98-1.04). In contrast, postmenopausal breast cancer risk decreased with 25(OH)D levels 27-<35 ng/mL (p = 0.02 for nonlinear risk change), where a 5 ng/mL increase in 25(OH)D was associated with a 12% lower risk of breast cancer (RR = 0.88 per 5 ng/mL; 95% CI, 0.79-0.97), with suggestive flattening at higher doses >35 ng/mL. The significant inverse association did not appear to vary across strata of invasive/in-situ cases, body mass index adjustment, region, postmenopausal hormone use, or assay method.In summary, this dose-response meta-analysis of prospective studies of plasma 25(OH)D suggested a breast cancer risk differential by menopause, whereby a step-wise inverse association was observed beyond a threshold of 27 ng/mL, but with flattening of effects above 35 ng/mL, in postmenopausal women. These findings help resolve prior inconsistent findings and may carry important clinical and public health implications.

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.

USP1 deubiquitinates ID proteins to preserve a mesenchymal stem cell program in osteosarcoma

Inhibitors of DNA binding (IDs) antagonize basic-helix-loop-helix (bHLH) transcription factors to inhibit differentiation and maintain stem cell fate. ID ubiquitination and proteasomal degradation occur in differentiated tissues, but IDs in many neoplasms appear to escape degradation. We show that the deubiquitinating enzyme USP1 promotes ID protein stability and stem cell-like characteristics in osteosarcoma. USP1 bound, deubiquitinated, and thereby stabilized ID1, ID2, and ID3. A subset of primary human osteosarcomas coordinately overexpressed USP1 and ID proteins. USP1 knockdown in osteosarcoma cells precipitated ID protein destabilization, cell-cycle arrest, and osteogenic differentiation. Conversely, ectopic USP1 expression in mesenchymal stem cells stabilized ID proteins, inhibited osteoblastic differentiation, and enhanced proliferation. Consistent with USP1 functioning in normal mesenchymal stem cells, USP1-deficient mice were osteopenic. Our observations implicate USP1 in preservation of the stem cell state that characterizes osteosarcoma and identify USP1 as a target for differentiation therapy.

A new method for the preparation of bioactive calcium phosphate films hybridized with 1alpha,25-dihydroxyvitamin D3

The primary goal of this investigation was to develop a calcium phosphate film hybridized with 1alpha,25-dihydroxyvitamin D(3) for the improvement of osteoconductivity of bone substitutes. The hybrid films (hCaP) were prepared at the different concentrations of 1 x 10(-10), 1 x 10(-8), and 1 x 10(-6) M designated as hCaPL, hCaPM, and hCaPH, respectively. The change of the hormone concentration during the preparation of the hybrid films did not cause significant variations on the physical properties of hCaPs, i.e. surface morphology and roughness. On the other hand, X-ray photon spectroscope (XPS) measurements revealed that the concentration change affected the chemical composition of the hybrid films. Recruitment of osteoblast-like MG-63 cells was considerably improved on hCaPs compared to tissue culture plate (TCP). However, cell proliferation on hCaPs was substantially suppressed and inversely proportional to the hormone concentration used. It was observed that bone-like nodules which consisted of bead-like components and well-developed matrix were rapidly formed on hCaPs. Masson's trichrome and safranin-O stainings elucidated that the bead-like components were MG-63 cells. Safranin-O staining showed that proteoglycan was produced actively. These results indicate that the cells cultured on hCaPs were strongly stimulated by the hormone to produce proteoglycan which can be considered as an induction of premature bone formation. The number of the nodules was increased with hormone concentration and most pronounced at the hCaPH. Gene expression patterns of alkaline phosphatase (ALP), transforming growth factor-beta (TGF-beta), and osteopontin (OPN) were strongly modulated by hybridized the hormone. For ALP and OPN, gene expressions were activated earlier on hCaPs than untreated calcium phosphate (CaP) confirming the effect of the hybridization was substantial. The TGF-beta gene expression was immediately activated after seeding but difference between samples was not significant suggesting that the gene expression was modulated not by the hormone hybridization but by CaP itself. As a result, hybridization of 1,25(OH)(2)D(3) with CaP can be a potentially strong candidate to promote osteoconductivity of implant materials.

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.

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.

Insulin-like growth factor binding protein-5 interacts with the vitamin D receptor and modulates the vitamin D response in osteoblasts

The 1,25 dihydroxyvitamin D3 [1,25(OH)2D3]-induced differentiation of osteoblasts comprises the sequential induction of cell cycle arrest at G0/G1 and the expression of bone matrix proteins. Reports differ on the effects of IGF binding protein (IGFBP)-5 on bone cell growth and osteoblastic function. IGFBP-5 can be growth stimulatory or inhibitory and can enhance or impair osteoblast function. In previous studies, we have shown that IGFBP-5 localizes to the nucleus and interacts with the retinoid receptors. We now show that IGFBP-5 interacts with nuclear vitamin D receptor (VDR) and blocks retinoid X receptor (RXR):VDR heterodimerization. VDR and IGFBP-5 were shown to colocalize to the nuclei of MG-63 and U2-OS cells and coimmunoprecipitate in nuclear extracts from these cells. Induction of osteocalcin promoter activity and alkaline phosphatase activity by 1,25(OH)2D3 were significantly enhanced when IGFBP-5 was down-regulated in U2-OS cells. Moreover, we found IGFBP-5 increased basal alkaline phosphatase activity and collagen alpha1 type 1 expression, and that 1,25(OH)2D3 was unable to further induce the expression of these bone differentiation markers in MG-63 cells. Expression of IGFBP-5 inhibited MG-63 cell growth and caused cell cycle arrest at G0/G1 and G2/M. Furthermore, IGFBP-5 reduced the effects of 1,25(OH)2D3 in blocking cell cycle progression at G0/G1 and decreased the expression of cyclin D1. These results demonstrate that IGFBP-5 can interact with VDR to prevent RXR:VDR heterodimerization and suggest that IGFBP-5 may attenuate the 1,25(OH)2D3-induced expression of bone differentiation markers while having a modest effect on the 1,25(OH)2D3-mediated inhibition of cell cycle progression in bone cells.

Hormonal influences on cancer progression and prognosis

Cell differentiation, proliferation, apoptosis, and cell motility are induced and regulated by a host of growth factors, vitamins, and hormones. The mode of function of these modifiers of biological response, the signaling pathways that they activate, and the interacting pathways that can influence the biological outcome have been the focus of attention. Especially recognized and discussed in this review is the deregulation of their function, leading to abnormalities in cell proliferation, alteration of intercellular adhesive cohesion, remodeling of the extracellular matrix, and invasive behavior and metastatic deposition that are so characteristic of tumor development and progression, which strongly underscores the concept of molecular progression of cancer constructed on the basis of the relationship between genetic changes and the biological events associated with cancer progression. The molecular changes associated with hormone- and vitamin-driven responses and the deregulation of the expression and function of their target genes seem to correlate with specific biological events linked with cancer invasion and progression, and these findings could lead to the establishment of new markers of progression and to the development of new strategies for patient management. The scope of this work has been restricted by design and is dictated by the field of interest of the author's laboratory, but it is hoped that this field would be regarded adequately to reflect the wide genre of scientific interest in this field of human disease.

Platinum agents in the treatment of osteosarcoma: efficacy of cisplatin vs. carboplatin in human osteosarcoma cell lines

BACKGROUND

Cisplatin (cDDP), when used either alone or, more often, in combination with other agents, especially adriamycin, achieves a high response rate in osteosarcoma. Its use, however, is limited by severe nephro- and neuro-toxicity. Second generation platinum compounds, most notably carboplatin (CBDCA), have been developed in order to attempt to reduce these dose-limiting toxicities, and thus improve the therapeutic ratio. Studies evaluating the role of combination CT containing CBDCA vs. cDDP have demonstrated differing results depending on the tumor type tested and its role in the treatment of osteosarcoma has yet to be clarified.

PROCEDURE

In this study, we compared the in vitro anti-tumor activity of cDDP and CBDCA in a panel of three human osteosarcoma cell lines (HOS, MG63, and U2OS).

RESULTS

cDDP and CBDCA (0-20 micromol) showed marked variation in cytotoxicity among the three cell lines. EC(50) values for CBDCA in HOS and MG63 cells were approximately two-fold higher than for cDDP and the ratio of AUC(CBDCA) to AUC(cDDP) varied from 1.8 in the HOS cell line to 2.3 in the MG63 cell line. Exposure of MG63 and HOS cells to either cDDP or CBDCA (1.67 and 13.5 micromol) caused a G2/M cell cycle arrest by 24 hr. Also evident was a sub G1 peak indicative of cell death by apoptosis. U2OS cells were relatively resistant to the cytotoxic effects of both drugs, although a cell cycle arrest in response to DNA damage was observed. This suggests that unlike MG63 and HOS cells, U2OS cells have either a more efficient repair pathway for platinum-induced DNA damage or are able to evade apoptosis. Examination of apoptotic events and cellular recovery demonstrated that both an 8-16-fold higher concentration and longer treatment period for CBDCA compared with cDDP was required to produce equivalent cell death and a loss of the ability of single cell clones to form colonies in both the HOS and MG63, but not the U2OS cell line.

CONCLUSIONS

Our findings suggest that CBDCA at a two- to four-fold higher concentration than cDDP has potential therapeutic activity in platinum sensitive osteosarcomas, particularly when cDDP cytotoxicity compromises therapeutic efficacy.

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.

In vitro testing of the potential for orthopedic bone cements to cause apoptosis of osteoblast-like cells

The purpose of this study was to investigate in vitro the apoptosis- and/or necrosis-inducing potential of polymethylmethacrylate (PMMA)-based bone cements for prosthetic surgery. Four bone cements widely used in orthopedics were tested as extracts onto osteoblast-like MG-63 cells and for comparison, HL-60 cells, which are remarkably sensitive to apoptotic stimuli. Neutral red uptake (NRU) was used to measure cell viability while Hoechst 33258 staining was used to detect DNA content. Apoptosis was characterized using a BrdU-based ELISA assay for DNA fragmentation and examined by fluorescence microscopy using acridine orange and propidium iodide staining of nuclei. The generation of reactive oxygen species (ROS), which could mediate apoptosis, was verified using dichlorofluorescein-diacetate (DCFH-DA) oxidation to DCF. After 24 h of challenge of the cells with the four cement extracts, the viability of either MG-63 or HL-60 cells was found to be unaltered, as recorded by NRU. Apoptotic cell death was induced by three cements in HL-60, whereas MG-63 cells were significantly affected by the four cements tested: the finding of DNA fragments both in the cytoplasm and supernatants of MG-63 after 24 h demonstrated that these cells underwent late-apoptosis secondary necrosis. Fluorescent staining of the nuclei confirmed the results obtained with the ELISA test. Oxygen free radicals were elicited by two cements in HL-60 cells, while MG-63 did not generate ROS in response to cements. This study helps to gain more insight into the mechanism of cell death induced by PMMA-based cements and suggests apoptosis of osteoblasts as a part of the tissue reaction around cemented prostheses.

MCF-7/VD(R): a new vitamin D resistant cell line

Several in vitro and in vivo experiments have demonstrated potent cell regulatory effects of vitamin D compounds in cancer cells. Moreover, a promising phase I study with the vitamin D analogue Seocalcitol (EB 1089) in patients with advanced breast and colon cancer has already been carried out and more clinical trials evaluating the clinical effectiveness of EB 1089 in other cancer types are in progress (Mørk Hansen et al. [2000a]). However, only little is known about the mechanisms underlying the actions of vitamin D or about the possible development of drug resistance in the patients. Therefore, in an attempt to gain more insight into these aspects, we have developed the MCF-7/VD(R) cell line, a stable subclone of the human MCF-7 breast cancer cell line, which is resistant to the growth inhibitory and apoptosis inducing effects of 1alpha,25(OH)(2)D(3). Despite this characteristic, receptor studies on the VDR have clearly demonstrated that the MCF-7/VD(R) cells contain fully functional VDRs, although in a lower number than seen with the parental MCF-7 cells. The regulation of the 24-hydroxylase enzyme appeared to be intact in the MCF-7/VD(R) cells and no differences with regard to growth rate and morphological appearance between the MCF-7/VD(R) cells and the parental MCF-7 cells were observed. Interestingly, however, the sensitivity of the MCF-7/VD(R) cells to the pure anti-estrogen ICI 182,780 was found to be increased. The MCF-7/VD(R) cell line shows characteristics different from those of previously described vitamin D resistant breast cancer cell lines but also some similarities. Together such vitamin D resistant cell lines therefore serve as a useful tool for studying the exact mechanism of action of vitamin D and the development of vitamin D resistance.

EGR-1, a UV-inducible gene in p53(-/-) mouse cells

Changes in gene expression were examined in p53(-/-) and p53(+/+) mouse cells after ultraviolet (UV) irradiation. Differential display was used to identify differentially expressed gene(s) in UV-treated p53(-/-) and p53(+/+) cells. One of the differentially expressed genes was EGR-1 (early growth response gene-1), which was shown to be induced only in p53(-/-) cells. The induction of this gene by UV was detected as early as 0.5 h, peaked at 2 h, and returned to normal levels by 4 h. De novo protein synthesis was not required for UV-induced EGR-1 expression in p53(-/-) cells. Pretreatment of p53(-/-) cells with suramin, an inhibitor of growth factor receptors, completely suppressed UV-induced EGR-1 expression, suggesting that the induction may be mediated via the growth factor receptors. The presence of wild-type p53 suppressed the induction of EGR-1 after UV treatment. Overexpression of EGR-1 promoted the UV-induced transformation in p53(+/+) cells, but not in p53(-/-) cells. These data suggested that EGR-1 may be an important player in the UV responses of mammalian cells and may influence UV-induced transformation.

Differential and antagonistic effects of 9-cis-retinoic acid and vitamin D analogues on pancreatic cancer cells in vitro

Retinoids and vitamin D are known to exert important anti-tumour effects in a variety of cell types. In this study the effects of 9-cis-retinoic acid (9cRA) the vitamin D analogues EB1089 and CB1093 on three pancreatic adenocarcinoma cell lines were investigated. All compounds caused inhibition of in vitro growth but the vitamin D analogues were generally the more potent growth inhibitors. They were also more effective on their own than in combination with 9cRA. Growth arrest correlated with an increased proportion of cells in the G0/G1 phase. Apoptosis was induced in the three cell lines by 9cRA, whereas neither EB1089 nor CB1093 had this effect. Furthermore, addition of EB1089 or CB1093 together with 9cRA resulted in significantly reduced apoptosis. Our results show that retinoic acids as well as vitamin D analogues have inhibitory effects on pancreatic tumour cells but different and antagonistic mechanisms seem to be employed.

Overlapping and divergent actions of estrogen and the neurotrophins on cell fate and p53-dependent signal transduction in conditionally immortalized cerebral cortical neuroblasts

The developing cerebral cortex undergoes overlapping periods of neurogenesis, suicide, and differentiation to generate the mature cortical plate. The following experiments examined the role of the gonadal hormone estrogen in comparison to the neurotrophins, in the regulation of p53-dependent cortical cell fate. To synchronize choices between neurogenesis, apoptosis, and neural differentiation, embryonic rat cerebral cortical neuroblasts were conditionally immortalized with the SV40 large T antigen containing the tsA58/U19 temperature-sensitive mutations. At the nonpermissive temperature, cessation of large T antigen expression was accompanied by induction of p53, as well as the p53-dependent proteins, wild-type p53-activated fragment-1/Cdk (cyclin-dependent kinase)-interacting protein-1 (p21/Waf1), Bcl (B-cell lymphoma)-associated protein (Bax), and murine double minute 2 (MDM2), that lead to cell cycle-arrest, suicide, and p53 inhibition, respectively. Simultaneously, neuroblasts exit cell cycle and die apoptotically or differentiate primarily into astrocytes and immature postmitotic neuroblasts. At the nonpermissive temperature, estrogen specifically induced an antagonist-independent increase in phosphorylated p53 expression, while increasing p21/Waf1 and decreasing Bax. Coincidentally, estrogen rapidly increased and then decreased MDM2 relative to controls, suggesting temporal modulation of p53 function. Both estrogen and neurotrophins prevented DNA fragmentation, a marker for apoptosis. However, estrogen also induced a transient increase in released lactate dehydrogenase, suggesting that estrogen simultaneously induced rapid cell death in a subpopulation of cells. In contrast to the neurotrophins, estrogen also increased cell proliferation. Both estrogen and the neurotrophins supported neuronal differentiation. However, in contrast to the neurotrophins, estrogen only supported the expression of a subset of oligodendrocytic markers. These results suggest that estrogen and the neurotrophins support overlapping and distinct aspects of differentiation in the developing cerebral cortex.

Differentiation-related mechanisms which suppress DNA replication

Differentiation of mammalian cells implies cessation of DNA replication and cell proliferation; the potential controls of this coupling are examined here. It is clear that the known or proposed mechanisms of down-regulation of replicative cellular activities vary in different lineages of cell differentiation, and occur in all phases of the cell cycle. In G1 these regulators include p21/Cip1 or p27/Kip1, pRb, and p53; the novel, recently reported mechanisms of their action are summarized. In S phase the availability of nucleotide precursors, the origin recognition complex (ORC), and other replication proteins may be important in differentiation, and in G2 phase the cdc2/cyclin B complex and replication licensing factors determine normal G2 traverse versus an arrest or polyploidisation. Other replication-related mechanisms include transcription factors, e.g., Sp1, telomerase, and nuclear matrix changes. Thus, differentiation alters the activity not only of the various checkpoint proteins, but also of the components of the replicative machinery itself.