Vitamin D:Cancer and Differentiation

I. INTRODUCTIONThe seco-steroid hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is the most potent natural metabolite of vitamin D3 and is an important regulator of calcium homeostasis and bone metabolism via actions in intestine, bone, kidney, and parathyroid glands. 1,25-(OH)2D3 exerts its effects via an intracellular receptor that is a member of the steroid hormone receptor family (see Chapters 11–20 and 22 in this book). Throughout the last decades, it has become evident that the vitamin D receptor (VDR) is not limited to cells and tissues involved in regulation of calcium and bone metabolism but is also present in a wide variety of other cells and tissues including cancer cells of various origins. This led to a vast series of studies on the role of vitamin D in tumor cell growth regulation, treatment of cancer, and development of potent synthetic vitamin D analogs. Various specialized chapters will discuss in detail the effect of vitamin D on specific cancers (Chapters 89–97) and development and actions of vitamin D analogs (Chapters 80–88). In this chapter we aim to give an overview of the history and current stage and developments on vitamin D and cancer, regulation of tumor cells, possible mechanisms, and clinical applications

Vitamin D:Cancer and Differentiation

I. INTRODUCTIONThe seco-steroid hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is the most potent natural metabolite of vitamin D3 and is an important regulator of calcium homeostasis and bone metabolism via actions in intestine, bone, kidney, and parathyroid glands. 1,25-(OH)2D3 exerts its effects via an intracellular receptor that is a member of the steroid hormone receptor family (see Chapters 11–20 and 22 in this book). Throughout the last decades, it has become evident that the vitamin D receptor (VDR) is not limited to cells and tissues involved in regulation of calcium and bone metabolism but is also present in a wide variety of other cells and tissues including cancer cells of various origins. This led to a vast series of studies on the role of vitamin D in tumor cell growth regulation, treatment of cancer, and development of potent synthetic vitamin D analogs. Various specialized chapters will discuss in detail the effect of vitamin D on specific cancers (Chapters 89–97) and development and actions of vitamin D analogs (Chapters 80–88). In this chapter we aim to give an overview of the history and current stage and developments on vitamin D and cancer, regulation of tumor cells, possible mechanisms, and clinical applications

Genetic Vitamin D Receptor Polymorphisms and Risk of Disease

[...] Below, we present a more detailed description of the genomic organization of the VDR gene, including discussion on polymorphisms, linkage disequilibrium, and haplotypes. We then describe association studies of VDR polymorphisms in relation to different diseases. Historically speaking, studies of VDR polymorphisms in relation to bone endpoints, including osteoporosis in particular, have received most attention while the analysis of VDR polymorphisms in relation to other diseases, including breast and prostate cancer and immune-related disorders, has reached the literature somewhat later on. This allows studies on associations with bone endpoints to be compared to a certain extent and to illustrate some of the difficulties in interpreting the results. [...

Population analysis of the collagen type IIα1 3' variable number of tandem repeat polymorphism by heteroduplex genotyping

The AT-rich variable number of tandem repeat (VNTR) marker at the 3' end of the collagen type IIα1 (COL2A1) gene has been shown to have a complex structure with extensive sequence variations among repeat units. We analyzed this VNTR polymorphism in a large population of 972 Caucasian individuals with a genotyping procedure involving heteroduplex analysis of PCR products using polyacrylamide gel electrophoresis. Seven size alleles were identified, combining to 19 different homoduplex genotypes (heterozygosity = 0.64). These could be further dissected by analysis of heteroduplexes into 85 different heteroduplex genotypes (heterozygosity = 0.84). By systematically heteroduplexing homozygous and heterozygous individuals in vitro, characteristic heteroduplex doublet bands were generated of known allelic composition. A comparison of these doublets with heteroduplex patterns observed in the population allowed us to identify 29 alleles. The degree of correspondence with a different COL2A1 VNTR genotyping system, based on size separation of single-strand VNTR alleles, was investigated by the analysis of samples typed with both methods, including samples from reference CEPH pedigrees. This revealed improved genetic resolution by the heteroduplex method including discrimination of frequent alleles considered identical by the single-strand analysis. Our findings demonstrate heteroduplex analysis of the COL2A1 VNTR to be a robust and highly informative genetic marker system. The documented increased genetic variability has important implications in forensic and paternity testing, as well as in linkage and association studies relating genetic variation at this locus to disease endpoints

Tea flavonoids may protect against atherosclerosis : The Rotterdam Study

Background: Epidemiological studies have indicated a protective role of dietary flavonoids in cardiovascular disease, but evidence is still conflicting. Tea is the major dietary source for flavonoids in Western populations. We studied the association of tea intake with aortic atherosclerosis in a general population. Methods: The present analysis formed part of the Rotterdam Study, a prospective study of men and women 55 years and older. Dietary intakes were assessed at baseline by a trained dietician who used a semiquantitative food frequency questionnaire. Calcified plaques in the abdominal aorta were radiographically detected after 2 to 3 years of follow-up. Aortic atherosclerosis was classified as 'mild,' 'moderate,' or 'severe,' according to the length of the calcified area (5 cm, respectively). The association of tea intake with severity of aortic atherosclerosis was studied in 3454 subjects who were free of cardiovascular disease at baseline. Data were analyzed by logistic regression, adjusting for age, sex, body mass index (calculated as weight in kilograms divided by the square of height in meters), smoking, education, and intake of alcohol, coffee, vitamin antioxidants total fat, and total energy. Results: Multivariable analyses showed a significant, inverse association of tea intake with severe aortic atherosclerosis. Odds ratios decreased from 0.54 (95% confidence interval [CI], 0.32-0.92) for drinking 125 to 250 mL (1-2 cups) of tea to 0.31 (CI, 0.16-0.59) for drinking more than 500 mL/d (4 cups per day). The associations were stronger in women than in men. The association of tea intake with mild and moderate atherosclerosis was not statistically significant. Conclusion: This study indicates a protective effect of tea drinking against ischemic heart disease

Genetics and biology of vitamin D receptor polymorphisms

The vitamin D endocrine system is involved in a wide variety of biological processes including bone metabolism, modulation of the immune response, and regulation of cell proliferation and differentiation. Variations in this endocrine system have, thus, been linked to several common diseases, including osteoarthritis (OA), diabetes, cancer, cardiovascular disease, and tuberculosis. Evidence to support this pleiotropic character of vitamin D has included epidemiological studies on circulating vitamin D hormone levels, but also genetic epidemiological studies. Genetic studies provide excellent opportunities to link molecular insights with epidemiological data and have therefore gained much interest. DNA sequence variations, which occur frequently in the population, are referred to as "polymorphisms" and can have modest and subtle but true biological effects. Their abundance in the human genome as well as their high frequencies in the human population have made them targets to explain variation in risk of common diseases. Recent studies have indicated many polymorphisms to exist in the vitamin D receptor (VDR) gene, but the influence of VDR gene polymorphisms on VDR protein function and signaling is largely unknown. So far, three adjacent restriction fragment length polymorphisms for BsmI, ApaI, and TaqI, respectively, at the 3′ end of the VDR gene have been the most frequently studied. Because these polymorphisms are probably nonfunctional, linkage disequilibrium with one or more truly functional polymorphisms elsewhere in the VDR gene is assumed to explain the associations observed. Research is therefore focussed on documenting additional polymorphisms across the VDR gene to verify this hypothesis and on trying to understand the functional consequences of the variations. Substantial progress has been made that will deepen our understanding of variability in the vitamin D endocrine system and might find applications in risk assessment of disease and in predicting response-to-treatment

Distinct effects on the conformation of estrogen receptor α and β by both the antiestrogens ICI 164,384 and ICI 182,780 leading to opposite effects on receptor stability

Tissue-specific effects of 17β-estradiol (E2) and synthetic estrogen receptor (ER) ligands on target gene regulation might, at least partly, be explained by a selective ligand-induced conformational change of their receptors (ERα and ERβ). In this study, the effects of E2 and the synthetic ER ligands tamoxifen (TAM), ICI 164,384, and ICI 182,780 on the conformation of ERα and ERβ were examined using limited proteolytic digestion analysis. We found that E2 induced a conformational change of ERα resulting in the protection of a 30-kDa product, whereas TAM protected a 28-kDa fragment. Strikingly, the ERα conformational change induced by both ICI 164,384 and ICI 182,780 did not result in protection but rather seems to induce a ligand concentration-dependent increase in proteolytic degradation of the 30- and 28-kDa products. Incubation of ERβ with E2 resulted in an increased protection of a 30-kDa fragment, whereas with TAM protection of a 29-kDa fragment was observed. In contrast to the situation with ERα, ICI 164,384 and ICI 182,780 incubation induced the protection in a manner similar to 30-kDa fragment E2. In addition, the ICI compounds also induced in a dose-dependent manner the preservation of a 32-kDa fragment. Our observations demonstrate that ICI 164,384 and ICI 182,780 have distinct effects on the conformation of ERα and ERβ, resulting in receptor subtype-selective opposite effects on receptor stability in vitro

Combined effects of 1,25-dihydroxyvitamin D3 and tamoxifen on the growth of MCF-7 and ZR-75-1 human breast cancer cells

In the present study we assessed the effect of combined treatment with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and tamoxifen (TAM) on the growth of estrogen-responsive (MCF-7) and estrogen-dependent (ZR-75-1) human breast cancer cells. Both basal and 17β-estradiol (17β-E2)-stimulated growth were studied. 1,25-(OH)2D3 (10-10 - 10-7 M) time- and dose-dependently inhibited basal growth of MCF-7 cells, with growth arrest at 10-7 M. Also, 17β-E2-stimulated growth of MCF-7 and ZR-75-1 cells was inhibited by 1,25-(OH)2D3 in a time- and dose-dependent manner. TAM inhibited 17β-E2-stimulated growth of both cell lines and at high concentration (10-6 M) it also inhibited basal growth of MCF-7 cells. 10-6 M TAM together with 1,25-(OH)2D3 resulted in a further inhibition of basal (MCF-7 cells) as well as 17β-E2-stimulated proliferation (MCF-7 and ZR-75-1 cells) compared to the inhibition by these agents alone. TAM in combination with 10-7 M 1,25-(OH)2D3 resulted in growth arrest of 17β-E2-stimulated growth of MCF-7 cells. The inhibition of basal and 17β-E2-stimulated growth of MCF-7 cells was additive at early time points (4 days), but less than additive at later time points (8-10 days). It was demonstrated that with co-treatment of MCF-7 cells an equipotent inhibition of basal growth could be reached with lower concentrations of 1,25-(OH)2D3, compared to treatment with 1,25-(OH)2D3 alone. Studies with low concentrations (< 10-7 M) of TAM revealed a partial estrogenic effect, i.e. stimulation of MCF-7 proliferation in the absence of 17β-E2. This effect, which may resemble TAM-induced tumor flare, was completely prevented by co-treatment with a low concentration of 1,25-(OH)2D3 (10-9 M). Together, these results demonstrate the potent inhibition of breast cancer cell proliferation by 1,25-(OH)2D3 combined with TAM and indicate a potential benefit of combining these agents for the treatment of breast cancer