Impact of the Vitamin D3 receptor on growth-regulatory pathways in mammary gland and breast cancer

Ageing and vitamin D deficiency: effects on calcium homeostasis and considerations for vitamin D supplementation

Vitamin D is a fat-soluble, seco-steroid hormone. In man, the vitamin D receptor is expressed in almost all tissues, enabling effects in multiple systems of the human body. These effects can be endocrine, paracrine and autocrine. The present review summarises the effects of ageing on the vitamin D endocrine system and on Ca homeostasis. Furthermore, consequences for vitamin D supplementation are discussed.

Vitamin D's role in cell proliferation and differentiation

Vitamin D has pleiotropic effects that go beyond its traditional role in calcium homeostasis. Hundreds of genes with vitamin D receptor response elements directly or indirectly influence cell cycling and proliferation, differentiation, and apoptosis. Vitamin D compounds also have effects on cell function that are nongenomic. The noncalcemic actions of vitamin D influence normal and pathological cell growth, carcinogenesis, immune function, and cardiovascular physiology. This review examines many of the various mechanisms by which vitamin D alters cellular growth and differentiation and explores cell-specific factors that influence responsiveness to vitamin D.

Antiproliferative action of menadione and 1,25(OH)2D3 on breast cancer cells

Calcitriol or 1,25(OH)(2)D(3) is a negative growth regulator of MCF-7 breast cancer cells. The growth arrest is due to apoptosis activation, which involves mitochondrial disruption. This effect is blunted in vitamin D resistant cells (MCF-7(DRes) cells). Menadione (MEN), a glutathione (GSH)-depleting compound, may potentiate antitumoral effects of anticancer drugs. The aim of this study was to investigate whether MEN enhances cellular responsiveness of MCF-7 cells to 1,25(OH)(2)D(3). Cells were cultured and treated with different concentrations of 1,25(OH)(2)D(3)+/-MEN or vehicle for 96 h. GSH levels and the activity of antioxidant enzymes were determined by spectrophotometry and ROS production by flow cytometry. Both drugs decreased growth and enhanced ROS in MCF-7 cells, obtaining the maximal effects when 1,25(OH)(2)D(3) was combined with MEN (P<0.01 vs. Control and vs. each compound alone). MCF-7(DRes) cells were not responsive to 1,25(OH)(2)D(3), but the cell proliferation was slightly inhibited by the combined treatment. Calcitriol and MEN separately enhanced antioxidant enzyme activities, but when they were used in combination, the effect was more pronounced (P<0.05 vs. Control and vs. each compound alone). MEN, calcitriol and the combined treatment decreased GSH levels (P<0.05 vs. Control). The data indicate that MEN potentiates the effect of 1,25(OH)(2)D(3) on growth arrest in MCF-7 cells by oxidative stress and increases the activities of antioxidant enzymes, probably as a compensatory mechanism.

The vitamin D receptor in cancer

Over the last 25 years roles have been established for vitamin D receptor (VDR) in influencing cell proliferation and differentiation. For example, murine knock-out approaches have revealed a role for the VDR in controlling mammary gland growth and function. These actions appear widespread, as the enzymes responsible for 1alpha,25-dihydroxycholecalciferol generation and degradation, and the VDR itself, are all functionally present in a wide range of epithelial and haematopoietic cell types. These findings, combined with epidemiological and functional data, support the concept that local, autocrine and paracrine VDR signalling exerts control over cell-fate decisions in multiple cell types. Furthermore, the recent identification of bile acid lithocholic acid as a VDR ligand underscores the environmental sensing role for the VDR. In vitro and in vivo dissection of VDR signalling in cancers (e.g. breast, prostate and colon) supports a role for targeting the VDR in either chemoprevention or chemotherapy settings. As with other potential therapeutics, it has become clear that cancer cells display de novo and acquired genetic and epigenetic mechanisms of resistance to these actions. Consequently, a range of experimental and clinical options are being developed to bring about more targeted actions, overcome resistance and enhance the efficacy of VDR-centred therapeutics.

Intake of vitamin D and risk of breast cancer--a meta-analysis

Vitamin D insufficiency has been shown to be associated with a number of conditions including diabetes, multiple sclerosis and the overall risk of cancer. We aimed at studying the association between vitamin D intake and risk of breast cancer in a meta-analysis. We searched Pubmed, Embase, and Web of Science using the MESH terms "vitamin D" and "breast cancer". A total of 1731 studies were identified, but only 6 studies contained original data on the association between intake of vitamin D and risk of breast cancer. Overall there was no association between amount of vitamin D and risk of breast cancer (RR=0.98, 95% CI: 0.93-1.03, test for heterogeneity p<0.01). However, most studies reported on very low intakes of vitamin D (typically in the range 100-400 IU/day). Restricting the analyses to intakes > or =400 IU/day yielded a more homogenous result with a trend towards less breast cancer with > or =400 IU/day vs. the lowest intake (typically <50-150 IU/day), RR=0.92, 95% CI: 0.87-0.97, p for heterogeneity 0.14. In conclusion there may be a trend towards fewer cases of breast cancer with higher intakes of vitamin D (> or =400 IU/day). However, more research is needed, preferably in the form of randomized-controlled trials.

Vitamin D insufficiency in a multiethnic cohort of breast cancer survivors

BACKGROUND

Little is known about vitamin D status in breast cancer survivors. This issue is important because vitamin D influences pathways related to carcinogenesis.

OBJECTIVE

The objective of this report was to describe and understand vitamin D status in a breast cancer survivor cohort.

DESIGN

Data are from the Health, Eating, Activity, and Lifestyle study. With the use of a cross-sectional design, we examined serum concentrations of 25-hydroxyvitamin D [25(OH)D] in 790 breast cancer survivors from western Washington state, New Mexico, and Los Angeles County. Cancer treatment data were obtained from Surveillance, Epidemiology, and End Results registries and medical records. Fasting blood, anthropometry, and lifestyle habits were collected after diagnosis and treatment. We examined distributions of 25(OH)D by race-ethnicity, season, geography, and clinical characteristics. Multivariate regression tested associations between 25(OH)D and stage of disease.

RESULTS

Five hundred ninety-seven (75.6%) of the women had low serum 25(OH)D, suggesting vitamin D insufficiency or frank deficiency. The overall mean (+/-SD) was 24.8 +/- 10.4 ng/mL, but it was lower for African Americans (18.1 +/- 8.7 ng/mL) and Hispanics (22.1 +/- 9.2 ng/mL). Women with localized (n = 424) or regional (n = 182) breast cancer had lower serum 25(OH)D than did women with in situ disease (n = 184) (P = 0.05 and P = 0.03, respectively). Multivariate regression models controlled for age, body mass index (in kg/m(2)), race-ethnicity, geography, season, physical activity, diet, and cancer treatments showed that stage of disease independently predicted serum 25(OH)D (P = 0.02).

CONCLUSIONS

In these breast cancer survivors, the prevalence of vitamin D insufficiency was high. Clinicians might consider monitoring vitamin D status in breast cancer patients, together with appropriate treatments, if necessary.

In vivo binding to and functional repression of the VDR gene promoter by SLUG in human breast cells

The regulation of vitamin D receptor (VDR), a key mediator in the vitamin D pathway, in breast cancer etiology has long been of interest. We have shown here that the transcriptional repressor protein SLUG inhibits the expression of VDR in human breast cancer cells. To explore the possibility that SLUG regulates the VDR gene promoter, we cloned a 628bp fragment (-613 to +15) of the human VDR gene promoter. This region contains three E2-box sequences (CAGGTG/CACCTG), the classical binding site of SLUG. SLUG specifically inhibited VDR gene promoter activity. Chromatin-immunoprecipitation (ChIP) assays revealed that SLUG is recruited on the native VDR gene promoter along with the co-repressor protein CtBP1 and the effector protein HDAC1. These data suggests that SLUG binds to the E2-box sequences of the VDR gene promoter and recruits CtBP1 and HDAC1, which results in the inhibition of VDR gene expression by chromatin remodeling.

Transactivation of a growth hormone (GH) promoter-luciferase construct in canine mammary cells

The gene encoding growth hormone (GH) is expressed not only in the pituitary but also in a variety of non-pituitary tissues. In the female dog, progestins are known to stimulate GH expression in the mammary gland. In order to investigate the regulation of the GH gene expression in the mammary gland, we transfected the canine mammary tumor cell line CMT-U229 with 3 different canine GH promoter-luciferase constructs. The constructs, varying in length between 252 bp and 673 bp, were transfected followed by an incubation for 4 h, 24 h and 48 h with cAMP, all-trans-retinoic acid (RA), 3,3',5-triiodothyronine (T3), 1,25-dihydroxy-vitamin D (VitD), progesterone and EGF. Promoter activity was stimulated by cAMP, T3 and RA whereas VitD clearly inhibited gene expression. However, despite the presence of nuclear and membrane receptors for progesterone, no direct effects of progesterone on promoter activity could be demonstrated. It is concluded that progesterone alone has no direct stimulatory effect on GH transcription. This finding is discussed in relation to the slow onset of progesterone-stimulated GH release in vivo and the absence of Pit-1 in canine mammary tissue.

Minireview: nuclear receptors and breast cancer

Until recently, the study of nuclear receptor (NR) function in breast cancer biology has been largely limited to estrogen and progesterone receptors. The development of reliable gene expression arrays, real-time quantitative RT-PCR, and immunohistochemical techniques for studying NR superfamily members in primary human breast cancers has now revealed the presence and potential importance of several additional NRs in the biology of breast cancer. These include receptors for steroid hormones (including androgens and corticosteroids), fat-soluble vitamins A and D, fatty acids, and xenobiotic lipids derived from diet. It is now clear that after NR activation, both genomic and nongenomic NR pathways can coordinately activate growth factor signaling pathways. Advances in our understanding of both NR functional networks and epithelial cell growth factor signaling pathways have revealed a frequent interplay between NR and epithelial cell growth factor family signaling that is clinically relevant to breast cancer. Understanding how growth factor receptors and their downstream kinases are activated by NRs (and vice-versa) is a central goal for maximizing treatment opportunities in breast cancer. In addition to the estrogen receptor, it is predicted that modulating the activity of other NRs will soon provide novel prevention and treatment approaches for breast cancer patients.

Vitamin D receptor polymorphisms and breast cancer risk in a large population-based case-control study of Caucasian and African-American women

Introduction

The involvement of vitamin D receptor (VDR), which is a key mediator in the vitamin D pathway, in breast cancer etiology has long been of interest.

Methods

We examined the association between polymorphisms in the 3' end of the VDR gene, specifically BsmI and Poly(A), and breast cancer risk within a large, population-based, case-control study of breast cancer. Cases (n = 1,631) were Caucasian and African-American women, aged 35 to 64 years, who were diagnosed with incident, invasive breast cancer between July 1994 and April 1998. Control individuals (n = 1,435) were women without breast cancer ascertained through random digit dialing.

Results

Accounting for age, study site, and sampling weights, we observed a significantly increased risk for breast cancer among Caucasian, postmenopausal carriers of the bb genotype of BsmI (odds ratio = 1.53, 95% confidence interval = 1.04 to 2.27). However, no associations with the bb genotype were observed in African-American women. Overall, there were no significant associations between the Poly(A) genotype and breast cancer risk in either racial group. Smoking status (ever/never) modified the association between both the BsmI and Poly(A) genotypes and breast cancer risk. The respective associations between these genotypes and breast cancer risk did not significantly vary by oral contraceptive use, hormone replacement therapy, or body mass index.

Conclusion

Our results provide additional support for an increased risk for breast cancer in postmenopausal Caucasian women with the BsmI bb genotype and shed light on possible differential effects by menopausal status and race.

Prospective studies of dietary vitamin D and breast cancer: more questions raised than answered

Prospective studies suggest that dietary vitamin D may at least modestly reduce the risk of breast cancer. This review addresses issues raised by recent studies, including differences in findings related to dietary source of vitamin D, menopausal status, and tumor characteristics. It also discusses the optimal timing of vitamin D assessment.

Differential antiproliferative effects of calcitriol on tumor-derived and matrigel-derived endothelial cells

The most active metabolite of vitamin D, calcitriol, is growth inhibitory for various tumor types in vitro and in vivo and inhibits the growth of endothelial cells freshly isolated from tumors [tumor-derived endothelial cells (TDEC)]. We compared the effects of calcitriol on Matrigel-derived endothelial cells (MDEC) and TDEC isolated from Matrigel plugs and squamous cell carcinoma tumors, respectively. TDEC and MDEC expressed vitamin D receptor (VDR) and responded to calcitriol by increasing VDR protein expression. Although no mutations were found in VDR from either cell type, Scatchard plot analysis revealed a higher ligand-binding affinity in TDEC (K(d), 0.26 nmol/L) than MDEC (K(d), 0.65 nmol/L). The VDR signaling axis in both cells was intact as shown using nuclear translocation and 24-hydroxylase promoter-luciferase reporter assays. However, unlike TDEC, MDEC were resistant to calcitriol-induced growth inhibition. Calcitriol (10 nmol/L) resulted in a 12.3% growth inhibition of MDEC compared with 47% in TDEC. In TDEC, calcitriol resulted in induction of G(0)/G(1) arrest (10.75%) and reduction of S-phase cells (6.8%) with induction of p27 and down-regulation of p21 protein expression. Apoptotic effects, determined by Annexin V staining were also observed in calcitriol-treated TDEC (38.6%). Calcitriol caused reduced expression of p-Erk and p-Akt and an increase of poly(ADP-ribose) polymerase and caspase-3 cleavage in TDEC. By contrast, none of these effects on cell cycle or apoptosis were seen in calcitriol-treated MDEC. These results show that TDEC were more sensitive than MDEC to the antiproliferative effects of calcitriol despite apparently normal VDR content and structure of signaling axis in both cell types.

Vitamin D receptor-dependent inhibition of mammary tumor growth by EB1089 and ultraviolet radiation in vivo

1,25-Dihydroxyvitamin D(3) (1,25D), the biologically active form of vitamin D(3), exerts antiproliferative and proapoptotic effects in multiple transformed cell types, and thus, the vitamin D signaling pathway represents a potential anticancer target. Although chronic treatment with 1,25D induces hypercalcemia, synthetic vitamin D analogs have been developed that inhibit tumor growth in vivo with minimal elevation of serum calcium. Furthermore, vitamin D is synthesized in skin exposed to UV light, and this route of vitamin D elevation is not associated with hypercalcemia. In this study, we examined whether enhancement of vitamin D status via exogenous (EB1089, a 1,25D analog) or endogenous (UV exposure) approaches could exert antitumor effects without hypercalcemia. We used mammary xenografts with differential vitamin D receptor (VDR) expression to examine whether the antitumor effects of either therapy are receptor mediated. We present evidence that both EB1089 and UV exposure inhibit tumor growth via induction of growth arrest and apoptosis. These antitumor effects were observed only in xenografts containing VDR-positive tumor cells; heterogeneous tumors containing VDR-negative tumor cells and VDR-positive stromal and endothelial cells were unresponsive to both therapies. No evidence for antiangiogenic effects of EB1089 were detected in this model system. Neither EB1089 nor UV was associated with overt toxicity, but keratinocyte proliferation was increased in UV-exposed skin. These data provide proof of principle that UV exposure modulates tumor growth via elevation of vitamin D signaling and that therapeutic approaches designed to target the vitamin D pathway will be effective only if tumor cells express functional VDR.

Increased Expression of Corepressors in Aggressive Androgen-Independent Prostate Cancer Cells Results in Loss of 1α,25-Dihydroxyvitamin D3 Responsiveness

Vitamin D has antiproliferative activity in prostate cancer; however, resistance to vitamin D-mediated growth inhibition occurs. To investigate the mechanisms of vitamin D resistance, we screened two prostate cancer sublines of CWR22rv1, CWR22R-1, and CWR22R-2, with differential sensitivity to vitamin D. CWR22R-2 showed less response to the antiproliferative effect of vitamin D than CWR22R-1. The vitamin D receptor (VDR)-mediated transcriptional activity was also decreased in CWR22R-2. We further showed that the DNA-binding ability of VDR was decreased and the amount of NCoR in VDR response element was increased in CWR22R-2. Analysis of VDR-associated protein profiles found higher expression of the corepressors, NCoR1 and SMRT, in CWR22R-2 cells. Treatment with the histone deacetylase inhibitor, trichostatin A, increased vitamin D/VDR transcriptional activity and promoted the antiproliferative effect of vitamin D in CWR22R-2 cells. Targeted down-regulation of NCoR1 and SMRT by small interference RNA was able to restore CWR22R-2 response to vitamin D. Together, we showed that increased NCoR1 and SMRT expression in CWR22R-2 cells resulted in reduced VDR-mediated transcriptional activity and attenuated antiproliferative response to vitamin D. Our data suggest that the integrity of the vitamin D/VDR-mediated signaling pathway is crucial in predicting vitamin D responsiveness and thus provide a rational design to improve vitamin D-based treatment efficacy based on molecular profiles of patients.

Effects of 1,25-dihydroxyvitamin D3 on proliferation and differentiation of porcine preadipocyte in vitro

1,25-Dihydroxyvitamin D3, the physiologically active form of vitamin D3, exerts its functions through a receptor-mediated mechanism and plays an important role in the cell differentiation. This study investigated the effects of 1,25-dihydroxyvitamin D3 on the proliferation and differentiation of porcine preadipocyte. Stromal-vascular cells containing preadipocytes were prepared from dorsal subcutaneous adipose tissue of approximately 3-day-old Chinese male crossbred pigs. After confluence, the differentiation was induced by transferrin, dexamethasone and insulin for 2 days, and then subsequently cultured for 6 days. The cells were treated with 1,25-dihydroxyvitamin D3 during the induction of differentiation (the early phase of differentiation) or throughout the differentiation period. The terminal differentiation markers, such as glycerol-3-phosphate dehydrogenase activity and lipid accumulation were measured during the process of cultures. The treatment with 1,25-dihydroxyvitamin D3 severely affected the induction of all differentiation markers throughout the differentiation period. 1,25-Dihydroxyvitamin D3 suppressed the expression of peroxisome proliferator-activated receptor gamma mRNA and interfered with the induction of retinoid X receptor alpha mRNA. The mRNAs of the adipogenesis-related genes, lipoprotein lipase, stearoyl-CoA desaturase, phosphoenolpyruvate carboxykinase, glycerol-3-phosphate dehydrogenase and glucose transporter 4 were reduced when 1,25-dihydroxyvitamin D3 was added into differentiation medium. Also, 1,25-dihydroxyvitamin D3 inhibited preadipocyte differentiation in dose-dependent manner. These results suggested that 1,25-dihydroxyvitamin D3 inhibited porcine preadipocyte differentiation through suppressing PPAR gamma and RXR alpha mRNA expressions and then down regulating the expression of adipogenesis-related genes.

Polymorphisms of vitamin D receptor and survival in early-stage non-small cell lung cancer patients

Our previous analysis suggested that surgery season in the summer time and high vitamin D intake are associated with improved survival in early-stage non-small cell lung cancer (NSCLC) patients. Here, we investigated the associations of vitamin D receptor (VDR) polymorphisms of Cdx-2 G>A, FokI C>T, and BsmI C>T with overall survival (OS) and recurrence-free survival (RFS) in 373 early-stage NSCLC patients. The data were analyzed using log-rank test and Cox proportional hazards models. The median follow-up time was 71 months (range, 0.1-140 months), with 186 deaths and 127 recurrences. There was no association between VDR polymorphisms and survival, overall or among adenocarcinoma patients. Among squamous cell carcinoma (SCC) patients, the G/A+A/A genotype group of the Cdx-2 polymorphism was associated with better OS: the 5-year OS rates were 41% [95% confidence interval (95% CI), 28-53] for the G/G and 55% (95% CI, 39-71) for the G/A+A/A genotypes, respectively (P = 0.04, log-rank test), with the adjusted hazard ratio of 0.56 (95% CI, 0.33-0.95) for G/A+A/A versus G/G. For the joint effects of the three polymorphisms, subjects with two or more "protective" alleles have better OS among SCC patients, with the adjusted hazard ratios of 0.20 (95% CI, 0.09-0.48), 0.40 (95% CI, 0.19-0.87), and 0.43 (95% CI, 0.19-0.97), respectively, for subjects with two, three, and four or more "protective" alleles when compared with subjects with zero or one "protective" allele (P(trend) = 0.71). Similar associations were found in haplotype analysis and for RFS among SCC patients. In conclusion, VDR polymorphisms may be associated with improved survival among SCC patients of early-stage NSCLC.

Mammary gland involution as a multi-step process

Mammary gland involution is a highly complex multi-step process in which the lactating gland returns to a morphologically near pre-pregnant state. This developmental stage is characterized by a high degree of epithelial cell death, redevelopment of the mammary adipose tissue and tissue remodelling. Many factors involved have been described and these have been reviewed intensively in this journal (Furth, P. A., J. Mammary Gland Biol. Neoplasia, 4:123-127, 1999) and elsewhere. Microarray analysis technology has now not only allowed us to identify genes not previously associated with involution (Stein, T., Morris, J.S., Davis, C.R.,Weber-Hall, S.J., Duffy, M.A., Heath, V.J., et al., Breast Cancer Res., 6: R75-R91, 2004; Clarkson, R.W., Wayland, M.T., Lee, J., Freeman, T., Watson, C.J., Breast Cancer Res., 6: R92-R109, 2004; Clarkson, R.W., Watson, C.J., J. Mammary Gland Biol. Neoplasia, 8: 309-319, 2003), it has also enabled us to define multiple phases of the controlled regulatory response to forced weaning on the basis of their transcriptional profiles. This review provides a synthesis of published data, integrating the time course of transcriptional activity in the mouse mammary gland with a gene ontology approach to identify the pathways involved.

A strategy for controlling potential interactions between natural health products and chemotherapy: a review in pediatric oncology

The high prevalence of complementary and alternative medicine use including natural health products (NHPs) in the pediatric oncology population is well established. The potential for concurrent use of NHPs with conventional chemotherapy necessitates physician awareness regarding the potential risks and benefits that might come from this coadministration. Knowledge of interactions between NHPs and chemotherapy is poorly characterized; however, an understanding of potential mechanisms of interaction by researchers and clinicians is important. Concerns regarding the use of antioxidants during chemotherapy are controversial and evidence exists to support both adherents and detractors in this debate. Our review addresses issues regarding potential interactions between NHPs and chemotherapies used in pediatric oncology from a pharmacokinetic and pharmacodynamic perspective. Examples of combinations of NHP and chemotherapies are briefly presented in addition to a strategy to avoid (or induce) a possible interaction between a NHP and chemotherapy. In conclusion, more clinical research is needed to substantiate or preclude the use of NHPs in the treatment of cancer and especially in combination with chemotherapy.

Vitamin D regulates the phenotype of human breast cancer cells

1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the most active vitamin D metabolite, regulates proliferation, survival, and differentiation in many cell types. 1,25(OH)(2)D(3) and several less calcemic analogs are in clinical trials against various neoplasias. We studied the effects of 1,25(OH)(2)D(3) on a panel of human breast cancer cells, which show similar vitamin D receptor (VDR) content but variable transcriptional and anti-proliferative responsiveness. In MDA-MB-453 cells, one of the responsive lines, 1,25(OH)(2)D(3) increased cell and nuclear size and induced a change from a rounded to a flattened morphology. By phase contrast, laser confocal and electron microscopy, we found that 1,25(OH)(2)D(3) changed the cytoarchitecture of actin filaments and microtubules and nuclear shape, induced filopodia and lamellipodia, and promoted cell-to-cell contacts via large cytoplasmic extensions. However, although claudin-7 and occludin content in the cells increased upon exposure to 1,25(OH)(2)D(3), these proteins were not located at the plasma membrane probably due to the absence of E-cadherin expression. Additionally, 1,25(OH)(2)D(3) induced the accumulation of alpha(v)-integrin, beta(5)-integrin, focal adhesion kinase (FAK), and paxillin in focal adhesion plaques, concomitant with the increased phosphorylation of the FAK. 1,25(OH)(2)D(3) enhanced MDA-MB-453 and MDA-MB-468 cell adhesion to plastic but decreased adhesion to laminin. The expression of the mesenchymal marker N-cadherin and of the myoepithelial marker P-cadherin was down-regulated by 1,25(OH)(2)D(3) in several breast cancer cell lines. Other myoepithelial proteins such as alpha(6)-integrin, beta(4)-integrin, and smooth muscle alpha-actin (SMA) were also repressed by 1,25(OH)(2)D(3) in MDA-MB-453 and MDA-MB-468 cells. Accordingly, mice lacking VDR (Vdr(-/-)) showed abnormally high levels of SMA and P-cadherin in their mammary gland. These findings show that 1,25(OH)(2)D(3) profoundly affects the phenotype of breast cancer cells, and suggest that it reverts the myoepithelial features associated with more aggressive forms and poor prognosis in human breast cancer.

The vitamin D receptor as a therapeutic target

The vitamin D receptor (VDR) is a member of the large family of nuclear receptor transcription factors and specifically binds the micronutrient-derived hormone 1alpha,25(OH)2D3. A central endocrine role for this receptor in bone health was established at the beginning of the 20th century. Over the last 25 years, additional roles, perhaps through autocrine and paracrine mechanisms, have been established for VDR to regulate cell proliferation and differentiation, and more recently to exert immunomodulatory and antimicrobial functions. These findings, from in vitro and in vivo experiments, have generated considerable interest in targeting the VDR in multiple therapeutic settings. As with many potential therapeutics, it has also become clear that cells and tissues may also display de novo and acquired mechanisms of resistance to these actions. Consequently, a range of experimental and clinical options are being developed to bring about more targeted actions, overcome resistance and enhance efficacy of VDR-centred therapeutics.

25(OH)D3 and 1,25(OH)2D3 serum concentration and breast tissue expression of 1alpha-hydroxylase, 24-hydroxylase and Vitamin D receptor in women with and without breast cancer

1,25(OH)2D3 is an antiproliferative agent that may inhibit proliferation of breast cancer (BC) cells in vitro and BC development in animals. Epidemiological studies have shown a high incidence of BC in people less exposed to solar rays. To unravel the role of Vitamin D3 in BC patients, we have investigated serum levels of 25(OH)D3 and its active form 1,25(OH)2D3 as well as tissue expression of 1alpha-hydroxylase, 24-hydroxylase, and Vitamin D-receptor (VDR), determined by semiquantitative RT-PCR, in 88 Brazilian BC patients and 35 women without cancer (submitted to mammoplasties or resection of benign lesions). Median age of women with and without cancer was 51 and 46 years, respectively, and the majority of BC patients were classified as clinical stage II (67%). Although no differences in 25(OH)D3 serum concentration were found, 1,25(OH)2D3 (40+/-21 pg/ml) levels in BC patients were lower than in women without cancer (53+/-23). Our results indicate that 24-hydroxylase, VDR and 1alpha-hydroxylase mRNA tissue expression is similar in both groups and no correlation between 24-hydroxylase, 1alpha-hydroxylase, and VDR expression in breast tumors was found. A low 1,25(OH)2D3 serum concentration seems to be associated to breast cancer, however, the mechanism involved in this regulation is still unclear.

Vitamin D, Calcium, and Breast Cancer Risk: A Review

Vitamin D and calcium are metabolically interrelated and highly correlated dietary factors. Experimental studies have shown their anticarcinogenic effects due to their participation in regulating cell proliferation, differentiation, and apoptosis in normal and malignant breast cells. Given the emerging interest in their potential roles in the etiology of breast cancer, we review the current epidemiologic literature on dietary and/or supplemental intakes of vitamin D, endogenous circulating levels of vitamin D, and dietary and/or supplemental intakes of calcium in relation to breast cancer risk. To place these studies in context, we also provide a brief review of other supporting epidemiologic evidence. Despite inconsistent results from the epidemiologic studies, several lines of evidence suggest that vitamin D and calcium may be involved in the development of breast cancer. Specifically, (a) there is some epidemiologic evidence for inverse associations between vitamin D and calcium intakes and breast cancer; (b) serum, plasma, and/or blood levels of vitamin D metabolites have been inversely associated with breast cancer risk in some studies; (c) high sunlight exposure, presumably reflecting vitamin D synthesis in the skin, has been associated with a reduced risk of breast cancer; (d) vitamin D and calcium intakes have been inversely related to breast density, an intermediate end point for breast cancer; (e) calcium has been associated with a reduced risk of benign proliferative epithelial disorders of the breast, putative precursors of breast cancer; and (f) certain polymorphisms of the vitamin D receptor might modify breast cancer susceptibility. To further confirm the potential protective effects of calcium and vitamin D on breast cancer, well-designed cohort studies and clinical trials are warranted.

Gene expression profiling changes induced by a novel Gemini Vitamin D derivative during the progression of breast cancer

We investigated gene expression changes induced by a novel Gemini Vitamin D(3) analog, RO-438-3582 (1alpha,25-dihydroxy-20S-21(3-hydroxy-3-methyl-butyl)-23-yne-26,27-hexafluoro-cholecalciferol, Ro3582), in a unique human breast MCF10 model. We used two breast epithelial cell lines from this model, namely MCF10AT1 (Ha-ras oncogene transfected MCF10A, early premalignant) and MCF10CA1a (fully malignant and metastatic derived from the MCF10AT1 line). We analyzed gene expression changes induced by Ro3582 using GeneChip technology, quantitative RT-PCR, Western blot analysis, or a gene transcription assay. Interestingly, we found distinct gene expression profile differences between Ro3582-induced response of the early premalignant MCF10AT1 and the malignant and metastatic MCF10CA1a cell lines. Moreover, while the Gemini Vitamin D(3) analog Ro3582 modulated the expression of several Vitamin D target genes such as the 24-hydroxylase, CD14, osteocalcin, and osteopontin in both cell lines, Ro3582 regulated many genes involved in cell proliferation and apoptosis, cell adhesion, invasion, angiogenesis as well as cell signaling pathways, such as the BMP and TGF-beta systems, differently in the two cell lines. The Gemini Vitamin D(3) analog Ro3582 induced more significant gene changes in the early premalignant MCF10AT1 cells than in the malignant metastatic MCF10CA1a cells, suggesting that Gemini Vitamin D(3) analogs may be more effective in preventing the progression of an early stage of breast carcinogenesis than in treating late stage breast cancer.

Haplotype Analysis of Common Vitamin D Receptor Variants and Colon and Rectal Cancers

Inherited variants of the vitamin D receptor (VDR) gene may influence cancer risk by altering the effect of vitamin D on cell growth and homeostasis. Studies have examined genotypes for common VDR polymorphisms, including a single nucleotide polymorphism (SNP) detected by Bsm1, a polyadenosine [poly(A)] repeat polymorphism, and a SNP detected by Fok1, as candidates for susceptibility to cancer, but most have not evaluated haplotypes for these markers. We investigated haplotypes for these polymorphisms in case-control studies of colon cancer (1,811 cases and 1,451 controls) and rectal cancer (905 cases and 679 controls). We used the expectation-maximization algorithm to estimate haplotypes for White, Hispanic, African-American, and Asian subjects, tested for differences in VDR haplotype distribution, and calculated odds ratios (OR) for association between haplotype and cancer. The distribution of haplotypes differed by race or ethnic group, but four common haplotypes accounted for the majority of alleles in all groups. VDR haplotype distributions differed between colon cancer cases and controls (P = 0.0004). The common haplotype bLF, containing Bsm1 b (Bsm1 restriction site present), poly(A) long (18-22 repeats), and Fok1 F (restriction site absent) was associated with increased risk of colon cancer, OR 1.15 (95% confidence interval, 1.03-1.28), as was the rare haplotype BLF, containing Bsm1 B (restriction site absent), poly(A) long, and Fok1 F (OR, 2.40; 95% confidence interval, 1.43-4.02). No case-control differences were detected for rectal cancer. In this analysis, haplotypes of the VDR influenced risk of colon cancer, but haplotype variables had only slightly better ability to explain case-control differences than genotype variables.

Vitamin D and cancer

The impact of dietary intake upon cell and tissue physiology, as well as pathophysiology, has emerged as being highly significant to the etiology of a number of high-profile malignancies. The vitamin D receptor (VDR) is a member of a large transcription factor family of nuclear receptors and responds specifically to a hormonal micronutrient (1α25(OH)₂D₃). A central endocrine role for this receptor in bone health was established at the beginning of the 20th century. An alternative role has been established over the last 25 years for the VDR to regulate cell growth and division, and promote differentiation through autocrine and paracrine mechanisms. These findings from in vitro and in vivo experiments have generated considerable interest in the potential to target the VDR in either chemoprevention or chemotherapy cancer settings. As with many potential cancer therapeutics, it has become equally clear that cancer cells display de novo and acquired mechanisms of resistance to these actions. Consequently, researchers are developing a range of experimental and clinical options to bring about more targeted actions, overcome resistance and enhance the efficacy of VDR-centered therapeutics.

Influence of Insulin-like Growth Factors on the Strength of the Relation of Vitamin D and Calcium Intakes to Mammographic Breast Density

Diets with higher vitamin D and calcium contents were found associated with lower mammographic breast density and breast cancer risk in premenopausal women. Because laboratory studies suggest that the actions of vitamin D, calcium, insulin-like growth factor (IGF)-I, and IGF-binding protein-3 (IGFBP-3) on human breast cancer cells are interrelated, we examined whether IGF-I and IGFBP-3 levels could affect the strength of the association of vitamin D and calcium intakes with breast density. Among 771 premenopausal women, breast density was measured by a computer-assisted method, vitamin D and calcium intakes by a food frequency questionnaire, and levels of plasma IGF-I and IGFBP-3 by ELISA methods. Multivariate linear regression models were used to examine the associations and the interactions. The negative associations of vitamin D or calcium intakes with breast density were stronger among women with IGF-I levels above the median (beta = -2.8, P = 0.002 and beta = -2.5, P = 0.002, respectively) compared with those with IGF-I levels below or equal to the median (beta = -0.8, P = 0.38 and beta = -1.1, P = 0.21; P(interaction) = 0.09 and 0.16, respectively). Similar results were observed within levels of IGFBP-3 (P(interaction) = 0.06 and 0.03, respectively). This is the first study to report that the negative relation of vitamin D and calcium intakes with breast density may be seen primarily among women with high IGF-I or high IGFBP-3 levels. Our findings suggest that the IGF axis should be taken into account when the effects of vitamin D and calcium on breast density (and perhaps breast cancer risk) are examined at least among premenopausal women.

The vitamin D receptor represses transcription of the pituitary transcription factor Pit-1 gene without involvement of the retinoid X receptor

Pituitary transcription factor-1 (Pit-1) plays a key role in cell differentiation during organogenesis of the anterior pituitary, and as a transcriptional activator for the pituitary GH and prolactin genes. However, Pit-1 is also expressed in nonpituitary cell types and tissues. In breast tumors, Pit-1 mRNA and protein levels are increased with respect to normal breast, and in MCF-7 human breast adenocarcinoma cells, Pit-1 increases GH secretion and cell proliferation. We report here that 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] administration to MCF-7 cells induces a significant decrease in Pit-1 mRNA and protein levels. By deletion analyses, we mapped a region (located between -147 and -171 bp from the transcription start site of the Pit-1 gene) that is sufficient for the repressive response to 1,25-(OH)2D3. Gel mobility shift and chromatin immunoprecipitation assays confirmed the direct interaction between the vitamin D receptor (VDR) as homodimer (without the retinoid X receptor), and the Pit-1 promoter, supporting the view that Pit-1 is a direct transcriptional target of VDR. Our data also indicate that recruitment of histone deacetylase 1 is involved in this repressive effect. This ligand-dependent Pit-1 gene inhibition by VDR in the absence of the retinoid X receptor seems to indicate a new mechanism of transcriptional repression by 1,25-(OH)2D3.

Dairy, Calcium, and Vitamin D Intake and Postmenopausal Breast Cancer Risk in the Cancer Prevention Study II Nutrition Cohort

BACKGROUND

Calcium, vitamin D, and dairy products are highly correlated factors, each with potential roles in breast carcinogenesis. Few prospective studies have examined these relationships in postmenopausal women.

METHODS

Participants in the Cancer Prevention Study II Nutrition Cohort completed a detailed questionnaire on diet, vitamin and mineral supplement use, medical history, and lifestyle in 1992 to 1993. After exclusion of women with a history of cancer and incomplete dietary data, 68,567 postmenopausal women remained for analysis. During follow-up through August 31, 2001, we identified 2,855 incident cases of breast cancer. Multivariate-adjusted rate ratios (RR) were calculated using Cox proportional hazards models.

RESULTS

Women with the highest intake of dietary calcium (>1,250 mg/d) were at a lower risk of breast cancer than those reporting < or =500 mg/d [RR, 0.80; 95% confidence interval (95% CI), 0.67-0.95; P(trend) = 0.02]; however, neither use of supplemental calcium nor vitamin D intake was associated with risk. Consumption starting at two or more servings of dairy products per day was likewise inversely associated with risk (RR, 0.81; 95% CI, 0.69-0.95; P(trend) = 0.002, compared with <0.5 servings/d). The associations were slightly stronger in women with estrogen receptor-positive tumors comparing highest to lowest intake: dietary calcium (RR, 0.67; 95% CI, 0.51-0.88; P(trend) = 0.004); dairy products (RR, 0.73; 95% CI, 0.57-0.93; P(trend) = 0.0003), and dietary vitamin D (RR, 0.74; 95% CI, 0.59-0.93; P(trend) = 0.006).

CONCLUSIONS

Our results support the hypothesis that dietary calcium and/or some other components in dairy products may modestly reduce risk of postmenopausal breast cancer. The stronger inverse associations among estrogen receptor-positive tumors deserve further study.

Cooperation between antioxidants and 1,25-dihydroxyvitamin D3 in induction of leukemia HL60 cell differentiation through the JNK/AP-1/Egr-1 pathway

Vitamin D derivatives have demonstrated anti-cancer activity, but their clinical use is precluded by hypercalcemia. Previously, we found that carnosic acid potentiates differentiation of human leukemia cells induced by low concentrations of 1alpha,25-dihydroxyvitamin D(3) (1,25D(3)). In this study, we investigated if this effect is a general property of antioxidants, and whether there is a common mechanism whereby antioxidants potentiate monocytic differentiation. We found that all antioxidants tested enhanced differentiation-related cell cycle arrest induced by a low (1 nM) concentration of 1,25D(3). Addition of antioxidants to 1,25D(3) activated the JNK pathway as indicated by increased phosphorylation of c-jun and ATF-2, although each compound alone had a minimal effect. Antioxidants also enhanced the 1,25D(3)-induced AP-1 DNA binding and transactivation ability. Expression of Egr-1 and c-fos was increased by combinations of antioxidants and 1,25D(3), in parallel with the activation of the JNK pathway. The potentiation of differentiation by antioxidants was inhibited by JNK inhibitor SP600125 and a dominant negative JNK 1/2 construct, and Egr-1 and c-fos expression was proportionally decreased, suggesting that JNK pathway regulates these transcription factors. While potentiating the prodifferentiation effect of 1,25D(3), antioxidants did not promote the elevation of basal levels of intracellular calcium by 1,25D(3). The results indicate that JNK-AP1 pathway has an important role in the potentiation of 1,25D(3)-induced differentiation by antioxidants, and regulates expression of Egr-1 and c-fos. Combinations of antioxidants with 1,25D(3) should be further evaluated for use in cancer chemoprevention and therapy.

Insulin-Like Growth Factor Pathway Polymorphisms Associated with Body Size in Hispanic and Non-Hispanic White Women

Polymorphisms affecting insulin-like growth factors (IGF), their binding proteins (IGFBP), insulin receptor substrates (IRS), and other IGF regulatory molecules may affect growth, obesity, and obesity-related diseases, including cancer. The objective of this study was to better describe the associations between several IGF pathway variants and body size. Hispanic (n = 462) and non-Hispanic White (n = 1,702) women were recruited as controls in collaborative population-based case-control studies in Arizona, New Mexico, Colorado, Utah, and California. Body size measurements were taken by trained interviewers; genotypes were determined for the IGF1 CA repeat, the IGFBP3 -202 C > A substitution, the IRS1 G972R and IRS2 G1057D substitutions, and the vitamin D receptor (VDR) BsmI and FokI polymorphisms. Two associations were observed that were consistent in both Hispanics and non-Hispanic Whites: IGF1 CA repeat alleles of length other than 19 were associated with higher mean waist-to-hip ratios (WHR), P = 0.01, and women who carried an IGFBP3 A allele, compared with women with the CC genotype, more often reported high birthweight (odds ratio, 1.9; 95% confidence interval, 1.1-3.2). We observed trends for associations between IGFBP3 A allele and taller height, IRS1R allele, and smaller WHR, and VDR FokI ff genotype and larger WHR; each of these trends was present in only one ethnic group, and heterogeneity of effect by ethnicity was detected. These results provide evidence that IGF pathway polymorphisms have functional effects on growth and central obesity and indicate that genotype-phenotype relationships are ethnic specific.

Vitamin D and Calcium Intakes from Food or Supplements and Mammographic Breast Density

BACKGROUND

A better understanding of factors that affect breast density, one of the strongest breast cancer risk indicators, may provide important clues about breast cancer etiology and prevention. This study evaluates the association of vitamin D and calcium, from food and/or supplements, to breast density in premenopausal and postmenopausal women separately.

METHODS

A total of 777 premenopausal and 783 post-menopausal women recruited at two radiology clinics in Quebec City, Canada, in 2001 to 2002, completed a food frequency questionnaire to assess vitamin D and calcium. Breast density from screening mammograms was assessed using a computer-assisted method. Associations between vitamin D or calcium and breast density were evaluated using linear regression models. Adjusted means in breast density were assessed according to the combined daily intakes of the two nutrients using generalized linear models.

RESULTS

In premenopausal women, total intakes of vitamin D and calcium were inversely related to breast density (beta = -1.4; P = 0.004 for vitamin D; beta = -0.8; P = 0.0004 for calcium). In multivariate linear regression, simultaneous increments in daily total intakes of 400 IU vitamin D and 1,000 mg calcium were associated with an 8.5% (95% confidence interval, 1.8-15.1) lower mean breast density. The negative association between dietary vitamin D intake and breast density tended to be stronger at higher levels of calcium intake and vice versa. Among postmenopausal women, intakes of vitamin D and calcium were not associated with breast density.

CONCLUSION

These findings show that higher intakes of vitamin D and calcium from food and supplements are related to lower levels of breast density among premenopausal women. They suggest that increasing intakes of vitamin D and calcium may represent a safe and inexpensive strategy for breast cancer prevention.

Regulation of the human vitamin D3 receptor promoter in breast cancer cells is mediated through Sp1 sites

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the active form of Vitamin D, mediates gene transcription through the Vitamin D receptor (VDR), a nuclear receptor expressed in multiple normal and transformed cell types. In mammary epithelial cells, including those derived from breast cancers, 1,25(OH)(2)D(3) induces growth arrest and/or apoptosis through VDR dependent mechanisms, and VDR agonists represent potential therapeutic agents for hyperproliferative diseases, including cancer. Since target cell sensitivity to 1,25(OH)(2)D(3) and its analogs reflects VDR expression, understanding the transcriptional regulation of the VDR gene is fundamental to development of VDR agonists as therapeutic agents. The studies reported here focused on molecular characterization of the promoter region upstream of exon 1c in the human VDR gene. In transient transfection assays, luciferase reporter constructs containing -800 to +31 of the VDR gene exhibit basal promoter activity in T47D breast cancer cells which is enhanced by 1,25(OH)(2)D(3), estrogen and the phytoestrogen resveratrol. Deletion constructs and site-directed mutagenesis were used to map three distinct GC-rich Sp1 consensus sites that independently mediate the effects of estrogen, resveratrol, and 1,25(OH)(2)D(3) on VDR promoter activity. Up-regulation of the VDR promoter by 1,25(OH)(2)D(3) was mapped to an Sp1 site 261bp upstream of exon 1c, estrogen responsiveness to a proximal Sp1 site beginning at -50, and resveratrol regulation to a distal Sp1 site beginning at -381. Studies with estrogen receptor (ER) subtype specific ligands suggest that the effect of estrogen on VDR promoter is dependent on both ERalpha and ERbeta, whereas the effect of resveratrol is dependent only on ERalpha. In summary, these studies demonstrate transcriptional regulation of the exon 1c VDR promoter in breast cancer cells, and identify three distinct GC-rich, Sp1 consensus sites that differentially confer responsiveness to estrogen, resveratrol and 1,25(OH)(2)D(3).

A Selective Retinoid X Receptor Agonist Bexarotene (Targretin) Prevents and Overcomes Acquired Paclitaxel (Taxol) Resistance in Human Non–Small Cell Lung Cancer

PURPOSE

Paclitaxel is an important anticancer agent for the treatment of non-small cell lung cancer (NSCLC). However, its use in cancer therapy is limited by development of acquired drug resistance. The goal of this study was to determine the effect of bexarotene on development of acquired paclitaxel resistance in NSCLC.

EXPERIMENTAL DESIGN

Human NSCLC Calu3 cells were repeatedly treated in culture with intermittent paclitaxel alone or in combination with continuous bexarotene for 3 months. Thereafter, cells were isolated and characterized for their drug sensitivity in vitro and in vivo.

RESULTS

Repeat exposure to paclitaxel alone resulted in development of paclitaxel resistance with cross-resistance to multidrug resistance P-glycoprotein substrates, whereas the bexarotene/paclitaxel combination prevented the development of drug resistance and the cells remained chemosensitive. Furthermore, paclitaxel resistance could be overcome when the resistant cells were treated with the combination regimen. Fluctuation analysis showed that treatment with bexarotene decreased the rate of spontaneous development of paclitaxel resistance. In vivo, the bexarotene/paclitaxel combination regimen produced a statistically significant decrease in tumor growth in a Calu3 NSCLC xenograft model compared with the single agents (two-tailed, P < 0.05). In addition, paclitaxel-resistant Calu3 tumors treated with the bexarotene/paclitaxel combination showed greater delay in tumor growth compared with those treated with paclitaxel alone.

CONCLUSIONS

Our results suggest that bexarotene may offer a novel approach to prevent and overcome paclitaxel resistance in patients with NSCLC.

Vitamin D and breast cancer: insights from animal models

1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3[, the biologically active form of vitamin D that interacts with the vitamin D receptor (VDR), is a coordinate regulator of proliferation, differentiation, and survival of breast cancer cells. Therefore, vitamin D compounds that bind and activate VDRs offer promise as therapeutic agents for the treatment of established breast cancer. In addition, epidemiologic, clinical, and animal studies suggested that vitamin D status is important for protection against the development of breast cancer. To elucidate potential biological mechanisms through which vitamin D status might be associated with breast cancer risk, basic research studies focused on defining the molecular effects of vitamin D signaling in the normal mammary gland. Both VDR and vitamin D 1-hydroxylase, the enzyme that generates 1,25(OH)2D3, are expressed and dynamically regulated in the normal mammary gland. Furthermore, studies with mice lacking VDRs established that vitamin D participates in negative growth control of the normal mammary gland and that disruption of VDR signaling is associated with abnormal ductal morphologic features, increased incidence of preneoplastic lesions, and accelerated mammary tumor development. These studies support the concept that suboptimal generation of 1,25(OH)2D3 in the mammary gland might sufficiently deregulate VDR-mediated gene expression to sensitize mammary cells to transformation. In light of these observations, studies to define the most appropriate biomarkers of vitamin D status in relation to protection against breast cancer among human subjects are urgently needed.

Vitamin D receptor status alters mammary gland morphology and tumorigenesis in MMTV-neu mice

The vitamin D(3) receptor (VDR) is a ligand-dependent transcription factor implicated in regulation of cell cycle, differentiation and apoptosis of both normal and transformed cells derived from mammary gland. In these studies we examined whether VDR status altered mammary gland morphology or transformation in the well-characterized MMTV-neu transgenic model of breast cancer. We demonstrate that VDR protein is highly expressed in neu-positive epithelial cells of preneoplastic lesions, established tumors and lung metastases from MMTV-neu mice. Furthermore, MMTV-neu mice lacking VDR exhibit abnormal mammary ductal morphology characterized by dilated, distended ducts containing dysplastic epithelial cells. From 12 months of age on, MMTV-neu mice lacking VDR also experience body weight loss, atrophy of the mammary fat pad, estrogen deficiency and reduced survival. The limited survival of MMTV-neu mice lacking VDR precluded an accurate assessment of the impact of complete VDR ablation on tumor development. MMTV-neu mice heterozygous for VDR, however, did not exhibit body weight loss, mammary gland atrophy or compromised survival. Compared with MMTV-neu mice with two copies of the VDR gene, haploinsufficiency of VDR shortened the latency and increased the incidence of mammary tumor formation. Tumor histology and expression/subcellular localization of the neu transgene were not altered by VDR haploinsufficiency despite a significant decrease in tumor VDR expression. Collectively, these studies suggest that VDR gene dosage impacts on age-related changes in ductal morphology and oncogene-induced tumorigenesis of the mammary gland in vivo.

Stage-specific inhibition of mammary carcinogenesis by 1alpha-hydroxyvitamin D5

Active metabolites of vitamin D are well recognised as cancer chemopreventive and chemotherapeutic agents. However, they are toxic at effective concentrations. Earlier, we reported that a non-toxic analogue of vitamin D, 1alpha-hydroxyvitamin D5(1alpha(OH)D5), inhibited carcinogen-induced mammary lesion formation in mouse mammary organ cultures (MMOC) and in N-methyl-N-nitrosourea (MNU)-induced rat mammary carcinogenesis. In the present study, we determined if 1alpha (OH)D5 action is selective during the initiation or promotion phases in MMOC and in vivo. In MMOC, 1 microM 1alpha (OH)D5 suppressed both ovarian hormone-dependent and -independent mammary lesions by more than 60%. Inhibition of alveolar lesions was observed only during the promotion stage (p=0.0016). In a 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis experiment, 1alpha (OH)D5 (40 microg/kg diet) inhibited cancer incidence by 37.5% (p<0.05) if 1alpha (OH)D5 was present in food during the promotion phase (+1 to end). However, a D5-supplemented diet during the initiation phase (-2 to +1 week) did not provide any protection. These results clearly show, for the first time, that the effects of vitamin D may be mediated selectively during the promotion or progression phases of carcinogenesis.

Vitamin D, Calcium, and Mammographic Breast Densities

Vitamin D and calcium are being evaluated as potential breast cancer prevention agents. This study reports on the relation of dietary vitamin D and calcium to mammographic breast densities, one of the strongest breast cancer risk factors. Participants were women ages 40 to 60 years who had had a screening mammogram in Rhode Island and eastern Massachusetts (1989–1990). Diet was assessed by semiquantitative food frequency questionnaire, and the percentage of the breast showing densities was estimated visually by a single observer without information on subjects. Multivariate logistic regression was used to compare dietary intakes of vitamin D and calcium between women classified as having few densities (≤30% of the breast with density, n = 287) and extensive densities (≥70% of the breast with density, n = 256). For categories of increasing vitamin D intake (&lt;50, 50–99, 100–199, and ≥200 IU/d), adjusted odds ratios (OR) for extensive densities were 1.00 (reference), 0.51, 0.37, and 0.24, respectively (P for trend = 0.0005). For increasing calcium intake (&lt;500, 500–749, 750–999, and ≥1,000 mg/d), adjusted ORs were 1.00 (reference), 0.63, 0.25, and 0.24, respectively (P for trend = 0.0006). Combination of higher intakes of vitamin D and calcium (≥100 IU/d and ≥750 mg/d, respectively) were associated with a reduction of breast densities (OR, 0.28; 95% confidence interval, 0.15–0.54) compared with those consuming &lt;100 IU/d and &lt;750 mg/d. Increases in vitamin D and calcium intakes were associated with decreases in breast densities, suggesting that dietary vitamin D and calcium could reduce breast cancer risk possibly through influences on breast tissue morphology.

Growth and EGFR Regulation in Breast Cancer Cells by Vitamin D and Retinoid Compounds

The effect of 1,25-dihydroxyvitamin D(3), analog C (1,25-(OH)(2)-16-en-23-yn-26,27-F(6)-vitamin D(3)), 9-cis retinoic acid, and all-trans retinoic acid on the growth and expression of EGFR in MCF7, T47D, BT474, and BT549 breast cancer cells was examined. Significant growth inhibition was noted in MCF7, T47D, and BT474 cells by 8 days of treatment, while BT549 cells showed none. MCF7, T47D, and BT549 cells treated with 1,25-dihydroxyvitamin D(3) demonstrated a 50% decrease in EGFR mRNA within 2 h which was sustained to 72 h, while BT474 cells demonstrated a 200-500% increase. EGFR protein levels correlated with these mRNA changes in BT474 and BT549 cells. Measurement of mRNA stability in vitamin D treated BT474 cells indicated that there was no change in EGFR mRNA half-life. Transfection of an EGFR promoter containing reporter plasmid demonstrated vitamin D induced changes in reporter gene activity that paralleled the changes observed in EGFR mRNA and protein. Electrophoretic mobility shift assays using a putative vitamin D response element within this region of the EGFR promoter demonstrated specific VDR binding. These results indicate that the vitamin D effect on EGFR expression in breast cancer cells has a transcriptional component likely mediated through a vitamin D responsive promoter sequence. They also suggest that growth inhibition and EGFR down-regulation by vitamin D and retinoids may be related events in some breast cancer cells, but not in all.

Role of vitamins in the risk, prevention, and treatment of breast cancer

PURPOSE OF REVIEW

This article presents an overview of the role of vitamins in the risk, prevention, and treatment of breast cancer, with emphasis on current evidence from English-language articles published since 1 August 2002 and indexed in MEDLINE.

RECENT FINDINGS

Findings from epidemiologic studies that have evaluated vitamin A and carotenoids in relation to breast cancer risk have been inconclusive. The available data, especially from prospective studies, do not support an association between vitamins E and C and risk of breast cancer. Recent studies suggest that folate plays an important role in the prevention of breast cancer, particularly among women consuming alcohol. Limited data also support a potential role of vitamin D in the prevention of breast cancer.

SUMMARY

High intake of folate or adequate circulating levels of folate may reduce the risk of breast cancer. Adequate folate levels may be particularly important for women who are at higher risk of breast cancer because of high alcohol consumption. The inverse association between vitamin D and risk of breast cancer needs to be evaluated in more studies.

The highly conserved region of the co-repressor Sin3A functionally interacts with the co-repressor Alien

The Sin3 proteins are evolutionarily conserved co-repressors (CoR) that function as mediators of gene repression for a variety of transcriptional silencers. The paired amphipathic helices of Sin3A were identified and studied as protein-protein interacting domains. Previously we have shown the interaction of Sin3A with the CoR Alien in vivo and in vitro. Here, we show that Alien and Sin3A reside together in vivo with the vitamin D3 receptor on the human 24-hydroxylase (CYP24) promoter containing vitamin D3 response elements by chromatin immunoprecipitation. We delineated and characterized the interaction domains of Sin3A with Alien. Interestingly, the highly conserved region (HCR) of Sin3A, which has not yet been functionally characterized, interacts with Alien. The HCR encompasses only 134 amino acids, shares more than 80% identity with Sin3B and binds to the N-terminus of Alien, which harbours a transferable silencing function. Functionally, co-expression of Sin3A enhances Alien-mediated gene repression and overexpression of the HCR alone leads to the inhibition of Alien-mediated repression and to the induction of the endogenous CYP24 promoter. Our results therefore indicate a novel functional role of the Sin3 HCR and give novel insights into Alien-mediated gene repression.

Inhibition of serum-stimulated mitogen activated protein kinase by 1?,25(OH)2-vitamin D3 in MCF-7 breast cancer cells

1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D3, has been shown to be a potent negative growth regulator of breast cancer cells both in vitro and in vivo. 1alpha,25(OH)2D3 acts through two different mechanisms. In addition to regulating gene transcription via its specific intracellular receptor (vitamin D receptor, VDR), 1alpha,25(OH)2D3 induces rapid, non-transcriptional responses involving activation of transmembrane signal transduction pathways, like growth factors and peptide hormones. The mechanisms that mediate the antiproliferative effects of 1alpha,25(OH)2D3 in breast cancer cells are not fully understood. Particularly, there is no information about the early non-genomic signal transduction effectors modulated by the hormone. The present study shows that 1alpha,25(OH)2D3 rapidly inhibits serum induced activation of ERK-1 and ERK-2 MAP kinases. The tyrosine kinase Src is involved in the pathway leading to activation of ERK 1/2 by serum. Furthermore, 1alpha,25(OH)2D3 increases the tyrosine-phosphorylated state of Src and inhibits its kinase activity, while induces the association of the VDR with Src, either in the presence or absence of serum. In parallel, the hormone rapidly increases the amounts of VDR associated to plasma membranes (PM). Pretreatment with the tyrosine phosphatase inhibitors orthovanadate or bpV (phen) prevented mitogen-activated protein kinase (MAPK) inhibition by 1alpha,25(OH)2D3. These data altogether suggest that 1alpha,25(OH)2D3 inhibits the MAPK cascade by inactivating Src tyrosine kinase through a mechanism mediated by the VDR and tyrosine phosphatases.

Steroid hormone interactions with target cells: cross talk between membrane and nuclear pathways

The biological effects of steroid hormones are mediated by receptors associated with the plasma membrane as well as located inside of target cells. This perspective focuses on recent advances in our understanding of the integration that occurs between membrane-associated rapid signaling events and various changes in gene transcription that modulate the function and phenotype of steroid-responsive cells. Three frequently studied members of the steroid hormone receptor superfamily, the estrogen receptors, the thyroid hormone receptors, and the vitamin D receptors, are included to illustrate the emerging concepts. Each of these hormones has been conclusively shown to function at multiple subcellular sites leading to a continuum of signals intimately linked by intracellular cross talk. Understanding the molecular mechanisms by which these steroid hormones and their receptors transduce cellular signals will allow us to create new pharmacologic therapies aimed at treatment of a variety of human diseases affecting the cardiovascular system, the reproductive system, the skeletal system, the nervous system, the mammary gland, and many others.