The rs743572 common variant in the promoter of CYP17A1 is not associated with prostate cancer risk or circulating hormonal levels

OBJECTIVE

To use a large population-based case-control study to test the association between the common genetic variant rs743572 (-34 T to C), prostate cancer risk and circulating levels of several hormones.

SUBJECTS AND METHODS

A previous meta-analysis concluded that reported associations between rs743572 in the promoter of CYP17A1 and prostate cancer risk might reflect publication bias, but a few recent studies reported associations with prostate cancer risk and data suggesting that rs743572 is functional. We genotyped 824 prostate cancer cases and 737 population-based controls, and applied unconditional logistic regression to estimate the association between rs743572 and prostate cancer risk. We also used linear regression of transformed testosterone, androstanediol glucuronide, dehydroepiandrosterone sulphate, androstenedione, sex hormone-binding globulin and oestradiol (circulating levels) measured for controls, to estimate the association between these levels and rs743572. The linear models were adjusted for age and laboratory batch.

RESULTS

Men with different genotypes had similar circulating levels of all the hormones measured (all P < 0.05). In the case-control comparison using unconditional unadjusted logistic regression, the odds ratios (95% confidence interval) for prostate cancer were 1.07 (0.87-1.32) and 0.94 (0.71-1.25) for the dominant and recessive models, respectively, and for the co-dominant model, 1.10 (0.88-1.36) and 0.99 (0.73-1.35) for carriers of one or two copies of the C allele, respectively. There was no evidence of heterogeneity in the odds ratios by tumour stage (all P > 0.3) and grade (all P > 0.3).

CONCLUSION

The results of the present study are consistent with the conclusions of the previous meta-analysis, and suggest that rs743572 has no role in the risk of prostate cancer for men of Caucasian origin.

The effect of menopause on bone mineral density and bone-related biochemical variables in Indonesian women

OBJECTIVE

To determine the effects of menopause on bone-related variables in Indonesian women and to compare them with corresponding data in Caucasian Australian women.

DESIGN

A study of bone-related variables in women aged 45-55 years in Jakarta compared with corresponding historical data from Caucasian Australian women.

MEASUREMENTS

Dietary intakes, bone mineral density (BMD) and calcium-related variables in blood and urine.

RESULTS

Dietary calcium, phosphorus and protein intakes were significantly lower in the women from Jakarta than in those from Adelaide (all P < 0.001), probably because of lower milk consumption, but energy intake was similar in the two cities. Indonesian women were shorter and lighter than Australian women (P < 0.001) but had a comparable body mass index (BMI). The Indonesians also had a lower spinal BMD than the Australians but this was accounted for by the differences in height and weight between the two populations. The differences in serum and urinary calcium and phosphate and serum alkaline phosphatase across the menopause were comparable in Indonesian and Australian women but creatinine excretion was 25% lower in Jakarta than in Adelaide (P < 0.001) and this was probably sufficient to account for higher ratios of some urinary solutes to urinary creatinine in the Indonesians. Serum 25-hydroxyvitamin D (25OHD) levels were significantly lower (P < 0.001) and serum PTH levels significantly higher (P = 0.0045) in Jakarta than in Adelaide.

CONCLUSIONS

The differences in bone-related biochemical variables across the menopause were similar in the two populations, but calcium and protein intake and urine creatinine were lower in Indonesian than in Australian women. Serum 25OHD was lower and PTH higher in the Indonesian women, probably because of their darker skin, their practice of avoiding direct sunlight and the heavy atmospheric pollution in Jakarta.

Metabolism of vitamin D3 in human osteoblasts: evidence for autocrine and paracrine activities of 1 alpha,25-dihydroxyvitamin D3

Circulating 1 alpha,25-dihydroxyvitamin D(3) (1,25D) derives from renal conversion of 25-hydroxyvitamin D(3) (25D), by the 25D 1 alpha-hydroxylase (CYP27B1). Blood 25D levels, but not 1,25D levels, are the best indicator of vitamin D status and predict fracture risk in the elderly. We examined the extent to which osteoblasts can metabolize 25D. Well-characterized human primary osteoblasts and osteosarcoma (OS) cell lines were examined for the expression and regulation of genes associated with vitamin D metabolism, using real-time PCR. Primary osteoblasts and OS cell lines were found to express CYP27B1 mRNA and secreted detectable 1,25D in response to 25D. Of the OS cell lines tested, HOS expressed the most CYP27B1 mRNA and secreted the highest levels of 1,25D. All osteoblastic cells examined up-regulated expression of the catabolic regulator of 1,25D, the 25-hydroxyvitamin D-24-hydroxylase (CYP24), when incubated with either 1,25D or 25D. Exposure to physiological levels of 25D resulted in up-regulated transcription of the 1,25D responsive genes, osteocalcin (OCN), osteopontin (OPN) and RANKL. Specific knockdown of CYP27B1 in HOS cells using siRNA resulted in up to 80% reduction in both 1,25D secretion and the transcription of OCN and CYP24, strongly implying that the 25D effect in osteoblasts is preceded by conversion to 1,25D. Incubation with 25D, like 1,25D, inhibited primary osteoblast proliferation and promoted in vitro mineralization. Finally, we detected expression by osteoblasts of receptors for vitamin D binding protein (DBP), cubilin and megalin, suggesting that osteoblasts are able to internalize DBP-25D complexes in vivo. Together, our results suggest that autocrine, and perhaps paracrine, pathways of vitamin D(3) metabolism may regulate key osteoblast functions independently of circulating, kidney derived 1,25D. Our results are therefore consistent with the reported benefits of maintaining a healthy vitamin D status in the elderly to reduce the risk of fractures.

Seasonal change in osteoid thickness and mineralization lag time in ambulant patients

Low vitamin D levels are common. Bone biopsies taken from 121 ambulant patients were therefore reviewed. Seasonal changes in mineralization correlated inversely with serum 25-hydroxyvitamin D but not the more active metabolite, 1,25-dihydroxyvitamin D. This implies that the latter is produced in bone.

INTRODUCTION

It has been 30 yr since a seasonal variation in osteoid surfaces and calcification fronts was noted in bone biopsies from hip fracture patients in Leeds and attributed to vitamin D status. It was suggested at that time that mild vitamin D deficiency might cause osteoporosis from malabsorption of calcium and more severe deficiency osteomalacia, but little has been published on this subject since.

MATERIALS AND METHODS

We examined bone biopsies, calcium absorption data, and serum vitamin D metabolites in 121 patients attending our osteoporosis clinics in Adelaide. Biopsies were collected from the anterior iliac crest with a Jamshidi needle after two stat oral doses of 1 g of tetracycline 10 days apart, processed into plastic without demineralization, and all parameters were measured by point counting using a Weibel II graticule. Calcium absorption was measured after an oral dose of 5 microCi of (45)Ca in 250 ml of water with 20 mg of calcium carrier. Serum 25-hydroxyvitamin D [25(OH)D] was measured by radioimmunoassay and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] by radioimmunoassay after high-performance liquid chromatography (HPLC).

RESULTS

25(OH)D levels were lower from late autumn to early spring (April to September) than from late spring to early autumn (October to March) (51 +/- 23 versus 61 +/- 27 [SD] nM; p=0.040). None of the biopsies yielded a diagnosis of osteomalacia, but osteoid thickness (O.Th.) was greater in the winter than the summer months (8.5 +/- 3.6 versus 7.1 +/- 2.8 microm; p=0.015) as was mineralization lag time (MLT; 11.9 +/- 5.2 versus 9.5 +/- 3.6; p=0.005). O.Th and log MLT were both inversely related to serum 25(OH)D (p=0.014 and 0.036) but not serum 1,25(OH)(2)D. Calcium absorption was related to serum 1,25(OH)(2)D but not serum 25(OH)D.

CONCLUSIONS

We conclude that circulating 25(OH)D affects the mineralization process, whereas circulating 1,25(OH)(2)D affects bone indirectly through its effect on calcium absorption.

Circulating Insulin-Like Growth Factor-I and Binding Protein-3 and the Risk of Breast Cancer

Four meta-analyses and literature reviews have concluded that a positive association exists between circulating levels of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) and breast cancer risk for premenopausal but not postmenopausal women. Recently, a large prospective study reported an association with IGF-I and IGFBP-3 concentration for breast cancer diagnosed after, but not before, the age of 50 years; and in a large cohort of primarily premenopausal women, IGF-I and IGFBP-3 were not associated with breast cancer risk. We did a case-cohort study within the Melbourne Collaborative Cohort Study, which included a random sample of 1,901 women (subcohort) and 423 breast cancer cases diagnosed during a mean of 9.1 years of follow-up. IGF-I and IGFBP-3 concentrations were measured in plasma collected at baseline. The association between quartiles of IGF concentration and breast cancer risk was tested using a Cox model adjusted for known and potential confounders. The hazard ratio (HR) for breast cancer comparing the fourth with the first quartiles was 1.20 [95% confidence interval (95% CI), 0.87-1.65] for IGF-I and 1.09 (95% CI, 0.78-1.53) for IGFBP-3. Both associations varied with age: for IGF-I, the HRs for breast cancer comparing the fourth with the first quartiles were 0.60 (95% CI, 0.25-1.45) before age 50 and 1.61 (95% CI, 1.04-2.51) after age 60 (test for the log-linear trend of HR according to age, P = 0.05); for IGFBP-3, the HRs were 0.79 (95% CI, 0.34-1.83) before age 50 and 1.62 (95% CI, 1.03-2.55) after age 60 (test for log-linear trend, P = 0.08). IGF-I and IGFBP-3 were positively associated with breast cancer risk in older women but not in younger women. More prospective studies are needed to clarify the age dependence of the association between IGF-I and IGFBP-3 and breast cancer.

Regulation of the CYP27B1 5'-flanking region by transforming growth factor-beta in ROS 17/2.8 osteoblast-like cells

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), regulates osteoblast proliferation and differentiation. Production of 1,25(OH)(2)D(3) is catalysed by the enzyme 25-hydroxyvitamin D(3)-1alpha-hydroxylase (CYP27B1). Though highly expressed in the kidney, the CYP27B1 gene is also expressed in non-renal tissues including bone. It is hypothesised that local production of 1,25(OH)(2)D(3) by osteoblasts plays an autocrine or paracrine role. The aim of this study was to investigate what factors regulate expression of the CYP27B1 gene in osteoblast cells. ROS 17/2.8 osteoblast cells were transiently transfected with plasmid constructs containing the 5'-flanking sequence of the human CYP27B1 gene fused to a luciferase reporter gene. Cells were treated with either parathyroid hormone (PTH), 1,25(OH)(2)D(3), transforming growth factor-beta (TGF-beta) or insulin-like growth factor-1 (IGF-1) and luciferase activity was measured 24h later. The results showed that 1,25(OH)(2)D(3) did not alter expression of the reporter construct, however treatment with PTH, IGF-1 and TGF-beta decreased expression by 18, 53 and 58% respectively. The repressive action of TGF-beta was isolated to the region between -531 and -305bp. These data suggest that expression of the 5'-flanking region for the CYP27B1 gene in osteoblast cells may be regulated differently to that previously described in kidney cells.

Role of oncoprotein growth factor independent-1 (GFI1) in repression of 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1): a comparative analysis in human prostate cancer and kidney cells

1,25-Dihydroxyvitamin D (1,25D) inhibits growth of prostate cancer cells and has been proposed to play a protective role in prostate cancer. However, 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1), the enzyme responsible for the cellular synthesis of 1,25D, is repressed in prostate cancer cells. Recently, we have identified a role for the transcription factor, Growth Factor Independent-1 (GFI1) in the repression of the CYP27B1 gene in human prostate cancer cell lines. GFI1 is known to form a large protein complex with co-repressors that recruit histone deacetylases. We have proposed a model for the molecular repression of CYP27B1 gene expression. The formation of such a repressive complex on the inhibitory domain of the CYP27B1 gene in prostate cancer cells could lead to the silencing of gene expression either by inactivating nearby enhancer or proximal promoter domains and lead to cancer progression by reducing local production of 1,25D. These studies demonstrate that GFI1 may play a significant role in the down regulation of endogenous production of 1,25D in prostate cancer cells and could provide a novel insight to future diagnosis and treatment.

25-Hydroxyvitamin D requirement for maintaining skeletal health utilising a Sprague-Dawley rat model

To study the role of vitamin D to optimise bone architecture, we have developed an animal model to investigate the effects of frank vitamin D-deficiency as well as graded depletion of circulating 25-hydroxyvitamin D(3) (25D) levels on the skeleton. Rats fed on dietary vitamin D levels from 0 to 500 ng/day achieved diet-dependent circulating levels of 25D ranging from 11 to 115 nmol/L. Levels of serum 1,25-dihydroxyvitamin D(3) (1,25D) increased as dietary vitamin D increased between 0 and 200 ng/day at which point a maximum level was achieved and retained with higher vitamin D intakes. The renal levels of 25-hydroxyvitamin D-1alpha-hydroxylase (CYP27B1) mRNA were highest in animal groups fed on vitamin D between 0 and 300 ng/day. In contrast, renal 25-hydroxyvitamin D 24-hydroxylase (CYP24) mRNA levels increased as dietary vitamin D increased achieving maximum levels in animals receiving 500 ng vitamin D/day. This animal model of vitamin D depletion is suitable to provide invaluable information on the serum levels of 25D and dietary calcium intake necessary for optimal bone structure. Such information is essential for developing nutritional recommendations to reduce the incidence of osteoporotic hip fractures.

RNAi-mediated silencing of CYP27B1 abolishes 1,25(OH)2D3 synthesis and reduces osteocalcin and CYP24 mRNA expression in human osteosarcoma (HOS) cells

Although local synthesis of 1,25D has been postulated to regulate parameters of cell growth and differentiation in non-renal cells, the physiological role of 1,25D production in bone cells remains unclear. We used the technique of RNA interference to inhibit the mRNA encoding the enzyme responsible for 1,25D synthesis, 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1). Human osteosarcoma (HOS) cells were transfected with siRNA for CYP27B1 or non-silencing RNA before being treated with 25D for 48h under normal growth conditions. De novo synthesis of 1,25D was measured in the media as well as mRNA levels for CYP27B1, osteocalcin (OCN) and 25-hydroxyvitamin D 24-hydroxylase (CYP24). We demonstrated that HOS cells express CYP27B1 mRNA, metabolize 25D and secrete detectable levels of de novo synthesized 1,25D. CYP27B1 mRNA silencing by RNAi, resulted in the suppression of 1,25D production and subsequent reduction of OCN and CYP24 mRNA expression. Our findings suggest that local 1,25D synthesis has paracrine effects in the bone microenvironment implying that vitamin D metabolism in human osteoblasts represents a physiologically important pathway, possibly regulating the maturation of osteoblasts.

Determination of Vitamin D-dependent calcium absorption by 45Ca gavage in the rat

Precise determination of Vitamin D-dependent intestinal calcium absorption in longitudinal studies is problematic. We have assessed Vitamin D-dependent intestinal calcium absorption by (45)Ca gavage. Rats were gavaged with a 1mL solution containing (45)Ca (CaCl(2), 9.3MBq/mL) maintained at 37 degrees C. Total Ca concentration of the gavage fluid was optimised by comparing the absorption curves for fluids made up to 0.025, 2.025, 4.025 and 40.025 mmol/L with (40)CaCl(2). The effect of varying dietary Ca on fractional Ca absorption was determined in rats fed semi-synthetic diets containing either 0.05%, 0.2%, 0.4% or 1.0% Ca for 50 days. Serum 1,25 dihydroxyvitamin D (1,25D) was determined by radioimmunoassay. Total gavage Ca of 0.025 mmol/L achieved the highest peak fractional absorption and was adopted for all future experiments. Fifty days after allocation to the diets both fractional Ca absorption and 1,25D were highest in rats fed 0.05% Ca and lowest in those fed 1.0% Ca (absorption, P<0.05 and 1,25D, P<0.05). There was a strong logarithmic relationship between 1,25D and fractional Ca absorption (R(2) 0.69, P<0.001). Weekly repetition of the procedure did not cause a fall in haematocrit over 7 weeks. Radiocalcium ((45)Ca) absorption by gavage provides a simple measure of Vitamin D-dependent Ca absorption for repetitive use in longitudinal studies.

Osteoblast deletion of exon 3 of the androgen receptor gene results in trabecular bone loss in adult male mice

The mechanism of androgen action on bone was studied in male mice with the AR deleted in mature osteoblasts. These mice had decreased trabecular bone volume associated with a decrease in trabecular number, suggesting that androgens may act directly on osteoblasts to maintain trabecular bone.

INTRODUCTION

Androgens modulate bone cell activity and are important for the maintenance of bone mass. However, the mechanisms by which they exert these actions on bone remain poorly defined. The aim of this study was to investigate the role of androgens acting through the classical androgen receptor (AR) signaling pathways (i.e., DNA-binding dependent pathways) in osteoblasts using male mice in which exon 3 of the AR gene was deleted specifically in mature osteoblasts.

MATERIALS AND METHODS

Mice with a floxed exon 3 of the AR gene were bred with Col 2.3-cre transgenic mice, in which Cre recombinase is expressed in mineralizing osteoblasts. The skeletal phenotype of mutant mice was assessed by histomorphometry and quantitative microCT at 6, 12, and 32 weeks of age (n=8 per group). Wildtype, hemizygous exon 3 floxed and hemizygous Col 2.3-cre male littermates were used as controls. Data were analyzed by one-way ANOVA and Tukey's posthoc test.

RESULTS

microCT analysis of the fifth lumbar vertebral body showed that these mice had reduced trabecular bone volume (p<0.05) at 32 weeks of age compared with controls. This was associated with a decrease in trabecular number (p<0.01) at 12 and 32 weeks of age, suggesting increased bone resorption. These effects were accompanied by a reduction in connectivity density (p<0.01) and an increase in trabecular separation (p<0.01). A similar pattern of trabecular bone loss was observed in the distal femoral metaphysis at 32 weeks of age.

CONCLUSIONS

These findings show that inactivation of the DNA binding-dependent functions of the AR, specifically in mature osteoblasts in male mice, results in increased bone resorption and decreased structural integrity of the bone, leading to a reduction in trabecular bone volume at 32 weeks of age. These data provide evidence of a role for androgens in the maintenance of trabecular bone volume directly through DNA binding-dependent actions of the AR in mature osteoblasts.

5α-Reductase type 2 gene variant associations with prostate cancer risk, circulating hormone levels and androgenetic alopecia

Controversy exists over the significance of associations between the SRD5A2 (5alpha-reductase type 2) polymorphisms, A49T and V89L, and risk of prostate cancer. These potentially functional polymorphisms may alter life-long exposure to androgens with subsequent effects on male health and aging. The aim of this study was to examine the association of these variants with prostate cancer risk, plasma hormone levels and androgenetic alopecia. Subjects include 827 cases and 736 controls from an Australian population-based case-control study of prostate cancer. Information on prostate cancer risk factors and patterns of balding were collected. Plasma levels of testosterone, 3alpha-diol glucuronide (3alpha-diolG), dehydroepiandrosterone sulfate, androstenedione, sex hormone-binding globulin and estradiol were measured for controls. No associations with the V89L polymorphism were found. Carriers of the rarer A49T A allele were at a 60% higher risk of prostate cancer (OR = 1.60; 95% CI 1.09-2.36; p = 0.02) and 50% lower risk of vertex and frontal balding (p = 0.03) compared with men homozygous for the more common G allele. Although we found little evidence of association between this variant and plasma levels of 5 measured androgens, circulating 3alpha-diolG levels were 34% lower in A49T A allele carriers (p < 0.0001). Our study provides evidence that the SRD5A2 A49T A variant is associated with an increased risk of prostate cancer, lower levels of circulating 3alpha-diolG and decreased risk of baldness. These findings raise important questions with respect to previous assumptions concerning hormonal influences on prostate cancer risk in ageing males.

Circulating insulin-like growth factor-I and binding protein-3 and risk of prostate cancer

Some recent epidemiologic studies have failed to confirm positive associations between insulin-like growth factor-I (IGF-I) and the risk of prostate cancer observed in earlier studies but have reported suggestive evidence for a positive association between IGF-binding protein-3 (IGFBP-3) and prostate cancer risk, a result contradicting the earlier assumption that high levels of IGFBP-3 would be protective against prostate cancer. We tested the association between IGF-I and IGFBP-3 and prostate cancer risk by measuring the two peptides in plasma samples collected at baseline in a prospective cohort study of 17,049 men. We used a case-cohort design, including 524 cases diagnosed during a mean of 8.7 years follow-up and a randomly sampled subcohort of 1,826 men. The association between each peptide level and prostate cancer risk was tested using Cox models adjusted for country of birth and alcohol consumption. The risk of prostate cancer was not associated with baseline levels of IGF-I or the molar ratio IGF-I/IGFBP-3 (all odds ratios are between 0.82 and 1.08; P(trend) > or = 0.2), whereas the risk increased with baseline levels of IGFBP-3 (P(trend) = 0.008), the hazard ratio (HR) associated with a doubling of the concentration of IGFBP-3 being 1.70 (95% confidence interval, 1.15-2.52). The HR for quartile 4 relative to quartile 1 of IGFBP-3 was 1.49 (95% confidence interval, 1.11-2.00). The HRs did not differ by tumor aggressiveness or age at onset (all Ps > or = 0.4). In our study, high levels of IGFBP-3 but not IGF-I were associated with an increased risk of prostate cancer.

ZNF652, A Novel Zinc Finger Protein, Interacts with the Putative Breast Tumor Suppressor CBFA2T3 to Repress Transcription

The transcriptional repressor CBFA2T3 is a putative breast tumor suppressor. To define the role of CBFA2T3, we used a segment of this protein as bait in a yeast two-hybrid screen and identified a novel uncharacterized protein, ZNF652. In general, primary tumors and cancer cell lines showed lower expression of ZNF652 than normal tissues. Together with the location of this gene on the long arm of chromosome 17q, a region of frequent loss of heterozygosity in cancer, these results suggest a possible role of ZNF652 in tumorigenesis. In silico analysis of this protein revealed that it contains multiple classic zinc finger domains that are predicted to bind DNA. Coimmunoprecipitation assays showed that ZNF652 strongly interacts with CBFA2T3 and this interaction occurs through the COOH-terminal 109 amino acids of ZNF652. In contrast, there was a weak interaction of ZNF652 with CBFA2T1 and CBFA2T2, the other two members of this ETO family. Transcriptional reporter assays further confirmed the strength and selectivity of the ZNF652-CBFA2T3 interaction. The transcriptional repression of growth factor independent-1 (GFI-1), a previously characterized ETO effector zinc finger protein, was shown to be enhanced by CBFA2T1, but to a lesser extent by CBFA2T2 and CBFA2T3. We therefore suggest that each of the various gene effector zinc finger proteins may specifically interact with one or more of the ETO proteins to generate a defined range of transcriptional repressor complexes.

Effects of amylin deficiency on trabecular bone in young mice are sex-dependent

Amylin deficiency in mice results in late-onset osteopenia. Sex differences have been identified in insulin secretion in Amylin-overexpressing transgenic mice, suggesting a possible interaction of sex steroids, growth factors, or cytokines and amylin. The aim of the current study was to compare the effects of amylin deficiency on bone in young and adult male and female mice. The metaphyses of the distal femora from male and female Amylin-deficient mice at 4, 6, and 26 weeks of age were assessed by bone histomorphometry. Femoral length was increased in Amylin-deficient male mice compared to wild-type (WT) mice at 26 weeks of age (P < 0.005) but not in females. This was associated with an increase in growth plate height in Amylin-deficient males at 4 (P < 0.01) and 6 (P < 0.05) weeks of age. Furthermore, young Amylin-deficient males had decreased trabecular number at 4 weeks of age (P < 0.05) and increased trabecular thickness at 4 and 6 weeks of age (P < 0.05) compared to WT mice, with no net change in trabecular bone volume. These effects of amylin deficiency were not observed in female mice. In conclusion, this study demonstrates that amylin deficiency exerts effects on bone during growth that are sex-dependent and suggest a possible interaction between amylin and testosterone, growth factors, or cytokines to regulate bone cell metabolism.

Variants in the Prostate-Specific Antigen (PSA) Gene and Prostate Cancer Risk, Survival, and Circulating PSA

An A to G substitution, rs925013, in the promoter of the prostate-specific antigen gene (PSA) was recently found to be associated with promoter activity and circulating PSA levels. The objective of this study was to test the associations between rs925013 and another A to G substitution, rs266882, in the PSA gene with prostate cancer risk using a population-based case-control study of 821 prostate cancer cases and 734 controls carried out in Perth and Melbourne, Australia. The study focused on young (i.e., < 70 years) and aggressive cases (i.e., well-differentiated tumors were excluded). Cases in the Melbourne arm of the study (N = 638) were followed up prospectively for an average period of 8.2 years and deaths from prostate cancer ascertained through record linkage to study the possible association between genetic variants and disease-specific survival. PSA-circulating levels were measured in controls to test the association with the genetic variants using a cross-sectional design. Linear regression of log PSA levels, unconditional logistic regression, Cox regression, and haplotype analyses were undertaken. For rs925013, the G allele was associated with an increased risk of prostate cancer [odds ratio, 1.4; 95% confidence interval (95% CI), 1.1-1.7; P = 0.001], and the hazard ratio for survival for cases homozygous for the G allele compared with cases homozygous for the A allele was increased but not statistically significant (hazard ratio, 2.3; 95% CI, 1-5.6; P = 0.06). For rs266882, there was no association with overall prostate cancer risk and survival (all P > 0.1). Men homozygous or heterozygous for the G/G (rs925013/rs266882) haplotype were at higher risk of prostate cancer than men homozygous for the A/A haplotype (odds ratio, 1.3; 95% CI, 1.1-1.7; P = 0.009). Adjusted geometric means of circulating PSA levels in controls were similar in men with zero, one, and two copies of the G allele in rs266882 (1.2, 1.1, and 1.3 ng/mL, respectively; all P > or = 0.2) and rs925013 (1.1, 1.2, and 1.5 ng/mL, respectively; all P > 0.1). For rs925013, our study provides good evidence of association with prostate cancer risk, marginal evidence of association with survival, and little evidence of detectable association with circulating PSA levels in controls. We found no evidence of an independent association between rs266882 and any of the outcomes. The genotypes and haplotypes studied might be associated with the PSA gene function or be in linkage disequilibrium with other unmeasured and functional variants in the PSA or other genes.

A comparison of estradiol levels between women with a hysterectomy and ovarian conservation and women with an intact uterus

OBJECTIVES

To compare the distribution of estradiol levels between women with a hysterectomy and ovarian conservation and women with an intact uterus.

METHODS

A large cross-sectional study of women aged between 40 and 69 years, residing in Melbourne, Australia. Estradiol levels were available for 152 women with a hysterectomy and ovarian conservation and 1423 women with an intact uterus. All of the women were 'never-users' of hormone replacement therapy.

RESULTS

For women under 55 years of age, we observed that those with a hysterectomy and ovarian conservation had slightly higher estradiol levels compared with those with an intact uterus after adjustment for age, body mass index, smoking status and alcohol intake (ratio of geometric means of estradiol levels = 1.24; 95% confidence interval = 1.00-1.53). For women who were 55 years or greater, the distribution of estradiol levels varied little by hysterectomy status.

CONCLUSIONS

Our data do not suggest that women with hysterectomy and ovarian conservation have markedly different estradiol levels compared to women with an intact uterus.

Circulating Steroid Hormones and the Risk of Prostate Cancer

Epidemiologic studies have failed to support the hypothesis that circulating androgens are positively associated with prostate cancer risk and some recent studies have even suggested that high testosterone levels might be protective particularly against aggressive cancer. We tested this hypothesis by measuring total testosterone, androstanediol glucuronide, androstenedione, DHEA sulfate, estradiol, and sex hormone-binding globulin in plasma collected at baseline in a prospective cohort study of 17,049 men. We used a case-cohort design, including 524 cases diagnosed during a mean 8.7 years follow-up and a randomly sampled sub-cohort of 1,859 men. The association between each hormone level and prostate cancer risk was tested using Cox models adjusted for country of birth. The risk of prostate cancer was approximately 30% lower for a doubling of the concentration of estradiol but the evidence was weak (P(trend)=0.07). None of the other hormones was associated with overall prostate cancer (P(trend) >or= 0.3). None of the hormones was associated with nonaggressive prostate cancer (all P(trend) >or= 0.2). The hazard ratio [HR; 95% confidence interval (95% CI)] for aggressive cancer almost halved for a doubling of the concentration of testosterone (HR, 0.55; 95% CI, 0.32-0.95) and androstenedione (HR, 0.51; 95% CI, 0.31-0.83), and was 37% lower for a doubling of the concentration of DHEA sulfate (HR, 0.63; 95% CI, 0.46-0.87). Similar negative but nonsignificant linear trends in risk for aggressive cancer were obtained for free testosterone, estradiol, and sex hormone-binding globulin (P(trend)=0.06, 0.2, and 0.1, respectively). High levels of testosterone and adrenal androgens are thus associated with reduced risk of aggressive prostate cancer but not with nonaggressive disease.

The effect of calcitriol on fasting urine calcium loss and renal tubular reabsorption of calcium in patients with mild renal failure--actions of a permissive hormone

AIM

Renal production of 1,25-dihydroxycholecalciferol is attenuated in early renal failure. Renal tubular reabsorption of calcium is diminished in moderate renal failure and we wished to see if this were true in the early stages and whether supplementary calcitriol would bring about correction. We were interested in the idea of 1,25-dihydroxycholecalciferol being a permissive agent, operating indirectly.

METHODS

We measured calcium-related variables, including calculated ultrafiltrable serum calcium, before and after calcitriol 0.5 microg daily for six days in 34 subjects with stable mild renal failure.

RESULTS

The mean serum creatinine was 0.21 (+/- 0.08) mmol/l. The mean serum Ca++ was normal (1.18 mmol/l) but nine patients had values outside the normal range and in six cases, with low-normal serum Ca++ levels, there was a diminished tubular reabsorption. In five cases, basal serum Ca++ was mildly elevated. The coefficient of variation for serum Ca++ was 4.4%. PTH (1-84) levels were mildly elevated and 1,25-dihydroxycholecalciferol levels low-normal. The urine Ca/Cr, representing net bone resorption, was elevated in six cases. After calcitriol, the mean serum Ca++ level rose slightly and the coefficient of variation decreased to 3.6%. Changes in Ca++ whether upward or downward were accounted for by minor alterations in tubular reabsorption and a tendency to less net bone resorption. The initial Ca++ predicted (negatively) the magnitude of the correction. Neither the prevailing PTH nor the 1,25-dihydroxycholecalciferol levels explained any of the observed changes.

CONCLUSION

In early renal failure, there may be impaired regulation of serum Ca++. Despite elevated PTH, mild hypocalcemia may exist in the presence of increased net bone resorption relative to GFR. Hypocalcemia was accounted for by reduced renal tubular reabsorption of calcium which corrected after calcitriol. Net bone resorption tended to fall after calcitriol. Mild hypercalcemia, when present, was corrected by a reduction in tubular reabsorption. Calcitriol did not have a simple unidirectional effect but instead contributed to efficiency of the homeostatic mechanisms controlling the serum Ca++ set-point.

Identification of growth factor independent-1 (GFI1) as a repressor of 25-hydroxyvitamin D 1-alpha hydroxylase (CYP27B1) gene expression in human prostate cancer cells

The hormone 1,25-dihydroxyvitamin D (1,25D) may play a protective role in prostate cancer. 25-hydroxyvitamin D 1-alpha hydroxylase (CYP27B1) is the enzyme responsible for the regulation of cellular 1,25D levels. CYP27B1 is substantially repressed in prostate cancer cells. We have investigated the molecular basis for this inhibition. First, we identify a repressive region between -997 and -1200 in the human CYP27B1 promoter following transient transfection analysis in the prostate cancer cell lines DU145, PC3 and LNCaP. Next, we demonstrate a role for the transcription factor growth factor independent-1 (GFI1) in the repression of CYP27B1. Electrophoretic mobility assays with nuclear extracts from prostate cancer cell lines established binding of GFI1 to the sequence 5'-TGGTACAATCATAACTCACTGCAG-3' present at -997 to -1200 in the repressive region. Site directed mutagenesis of the core GFI1 binding sequence (5'-AATC-3') substantially increased while forced expression of GFI1 decreased the expression of the CYP27B1 reporter construct. Importantly, GFI1 repression is dependent on an intact GFI1 binding site in the -997 to -1200 region. GFI1 is an oncoprotein known to form a large protein complex with co-repressors that recruit histone deacetylases. We propose that the formation of such a repressive complex on the inhibitory domain of the CYP27B1 gene in prostate cancer cells could lead to silencing of either the nearby enhancer or proximal promoter domains and lead to cancer progression by reducing local production of 1,25D. These studies provide the basis for a more detailed understanding of CYP27B1 repression in prostate cancer cells and could provide a novel insight in future diagnosis and treatment.

Modulation of CYP27B1 and CYP24 mRNA expression in bone is independent of circulating 1,25(OH)2D3 levels

Circulating levels of 1,25-dihydroxyvitamin D (1,25D) are determined by bioactivation catalyzed by the renal 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1) and degradation through the action of the renal 25-hydroxyvitamin D 24-hydroxylase (CYP24). CYP27B1 and CYP24 are also present in bone cells, but little is known of their physiological role. The purpose of this study was to determine the changes that occur with aging on the expression of CYP27B1 and CYP24 mRNA in whole kidney and femora of female Sprague-Dawley rats. Real-time RT-PCR was used to measure CYP27B1, CYP24 and vitamin D receptor (VDR) mRNA levels in the kidneys and bones of animals aged between 3 weeks and 2 years. Circulating 1,25D levels decreased exponentially with age which was correlated with both reduced kidney CYP27B1 mRNA (R(2) = 0.72) and increased CYP24 mRNA levels (R(2) = 0.71). In the bone, CYP27B1 mRNA levels were maintained at their highest level throughout the ages of 3 to 15 weeks before decreasing in adult animals (P < 0.05). Bone CYP24 mRNA levels were positively correlated with bone CYP27B1 mRNA and not circulating 1,25D levels (R(2) = 0.74). Levels of bone CYP27B1 mRNA were positively correlated with distal femoral epiphyseal trabecular number (Tb.N) (R(2) = 0.74) and negatively with the trabecular thickness (Tb.Th) (R(2) = 0.56) in animals aged between 12 weeks and 2 years. These findings indicate that the regulation of CYP27B1 and CYP24 mRNA expression in the bone is unique from that in the kidney. The synthesis of 1,25D in bone tissue regulates bone CYP24 expression and is associated with bone mineralization suggesting that vitamin D metabolism has an autocrine or paracrine function.

Response of the 5'-flanking region of the human 25-hydroxyvitamin D 1alpha-hydroxylase gene to physiological stimuli using a transgenic mouse model

The enzyme 25-hydroxyvitamin D 1alpha-hydroxylase, or CYP27B1, is the key enzyme in the two-step activation process of vitamin D to 1,25-dihydroxyvitamin D (1,25D). While a number of regulators of the renal CYP27B1 enzyme activity have been recognized for some years, their underlying molecular mechanisms remain largely unknown, and the DNA regions involved in the in vivo regulation of gene expression by these factors have not been delineated. We have generated a transgenic mouse line that expresses 1501 bp of 5' flanking region together with 44 bp of 5' untranslated region of the human CYP27B1 gene fused to the firefly luciferase reporter gene. Animals expressing the luciferase gene demonstrated that both luciferase protein and mRNA for CYP27B1 were localized to proximal convoluted tubule cells of the kidney. In 2-week-old animals, the expression of the transgene and the endogenous CYP27B1 mRNA levels in the kidney were highest and fell with increasing age. Both reporter gene expression and CYP27B1 mRNA levels were downregulated in response to increasing amounts of dietary calcium in a dose-dependent manner. Vitamin D deficiency resulted in an increase in both the reporter gene and CYP27B1 expression. Interestingly, the increase in CYP27B1 mRNA levels was substantially higher than the increase in reporter gene expression, suggesting either that there is a post-transcriptional mechanism that increases the amount of CYP27B1 mRNA or that other regulatory elements are required to maximize the effect of vitamin D deficiency. These findings demonstrate that the 1501 bp 5' flanking region of the CYP27B1 gene directs expression to the proximal convoluted tubules of the kidney and is responsible for increasing transcriptional activity when dietary calcium and vitamin D levels are depleted. It also responds in the kidney to the physiological regulators of development and ageing.

Vitamin D: a hormone for all seasons--how much is enough?

Further understanding of its endocrine mechanisms and increased evidence for autocrine/paracrine actions has recently enhanced our knowledge of the biological activities of the vitamin D metabolite 1,25-dihydroxyvitamin D (1,25(OH)2D). The recognition of the contribution of vitamin D depletion to increased risk of osteoporosis, and most importantly the risk of hip fracture in the elderly, has increased the clinical significance of clinical laboratory testing for vitamin D status. Research has revealed that at least three genes contribute to vitamin D activity within tissues. These are the vitamin D receptor as well as two major vitamin D metabolising enzymes, CYP27B1, responsible for synthesis of 1,25(OH)2D and CYP24, responsible for catabolism of vitamin D metabolites. Current research focuses on the contribution of vitamin D metabolism to increasing vitamin D activity. This is of particular interest in bone forming cells where increased 1,25(OH)2D activity has been proposed to contribute to strengthening the skeleton. As well, solid tumours such as prostate, breast and colon cancers are another increasing area of vitamin D research. The major issues for the clinical laboratory in vitamin D testing include defining clinical decision limits for the interpretation of serum 25-hydroxyvitamin D (25OHD) levels and improving the precision and accuracy of this assay.