Interaction of estrogen therapy with calcium and vitamin D supplementation on colorectal cancer risk: reanalysis of Women's Health Initiative randomized trial

Although calcium and vitamin-D intake were consistently shown to be inversely associated with colorectal cancer risk in several large prospective studies and protective against adenoma and cancer in multiple randomized trials, the Women's Health Initiative (WHI) of calcium and low-dose vitamin-D supplementation trial found no overall effects on colorectal cancer. However, the previous report did not recognize an important biologic interaction with estrogen therapy. We investigated the treatment interaction of estrogen with calcium and vitamin-D on risk of colorectal cancer via a reanalysis of primary data results from the WHI calcium and vitamin-D supplementation trial (1,000 mg elemental calcium, 400 IU of vitamin-D3, or placebo), reanalyzing results from women concurrently randomized to estrogen interventions and placebo. Results indicate that concurrent estrogen therapy was a strong effect modifier of calcium and vitamin-D supplementation on colorectal cancer risk. While calcium plus vitamin-D supplementation among women concurrently assigned to estrogen therapies suggested increased risk (Hazard Ratio = 1.50, 95% CI: 0.96-2.33), among women concurrently assigned to placebos arms of the estrogen trials, calcium plus vitamin-D indicated suggestive benefits (HR = 0.71, 95% CI: 0.46-1.09) (p-for-estrogen-interaction = 0.018). Consistent interaction was also found by reported estrogen use (p interaction = 0.037). Results indicate contrasting effects of calcium and vitamin-D by concurrent estrogen therapy on colorectal cancer risk. Although further clinical and mechanistic studies are warranted, the potential clinical implications of the apparent interaction of estrogen therapy with calcium and vitamin-D supplementation should be recognized. Important biological mechanisms related to the key membrane receptor megalin and estrogen-dependent protein calbindin are discussed.

Expression patterns of calretinin, calbindin and parvalbumin and their colocalization in neurons during development of Macaca monkey retina

The developmental expression of calbindin (CalB), calretinin (CaR) and parvalbumin (PV) was followed in Macaca monkey retina using single and double immunolabeling to identify which proteins provide distinctive labels for specific cell types and to clarify the role of these proteins during development. Ganglion cells (GC) expressed PV at fetal day (Fd)55 and CaR and CalB by Fd85. CaR was downregulated after birth. Separate subsets of amacrine (AM) cells expressed CaR and CalB at Fd65-70. After Fd115, many CaR+ AM coexpressed CalB. After Fd120 a few AM expressed PV and these added CaR and CalB after birth. A subset of horizontal cells (HZ) expressed CaR and CalB at Fd70. Slightly later all HZ express PV and CaR while the early subset is CalB+/PV+/CaR+. CaR downregulates in all HZ after birth. The DB3 cone bipolar cells (BP) under the HZ label for CalB by Fd90-110 while a probable OFF BP cell body just above the AM layer becomes CaR+ near birth with labeling increasing after birth. All cones outside of the fovea label for CalB by Fd125. Foveal cones, rods, most BP and Müller glia do not label for these proteins at any age. The complex patterns of up- and down-regulation found in Macaca retina are similar to previous reports of expression in human retina, but in many instances are quite different than earlier reports of CaR, CalB and PV expression patterns in monkey central visual centers. This makes it highly likely that each protein plays a specific but undetermined role(s) in each visual center, and that its expression is controlled at a given stage of retinal development by multiple intrinsic and extrinsic factors.

Glutathione depletion modulates gene expression in HepG2 cells via activation of protein kinase C alpha

Buthionine sulphoximine (BSO; 1mM) resulted in the depletion of glutathione (GSH) in HepG2 cells to 17+/-1.5% within 24h. This was not associated with apoptotic or necrotic cell death over this time period. Use of a human (Phase 1) cDNA custom toxicology-array and a larger scale (>10,000 gene) Affymetrix U95Av2 array identified a total of 48 and 104 genes, respectively, with a statistically significant (and >1.5-fold) change in expression. A total of 64 differentially expressed genes (6 of which were confirmed by real-time polymerase chain reaction) were suggestive of protein kinase C (PKC) activation. Activation of PKC-alpha (but not betaI or delta) was demonstrated at 24 h through activity measurements and through Western blot analysis of membrane-associated PKC-alpha protein. Activation did not occur in the presence of additional gamma-glutamylcysteine to prevent GSH depletion. Activation of PKC-alpha by GSH-depletion may, at least in part, be mediated by thiol oxidation and may contribute to a survival signal. If sustained, the activation may be important in non-genotoxic carcinogenesis.

Characterization of calretinin I-II as an EF-hand, Ca2+, H+-sensing domain

Calretinin, a neuronal protein with well-defined calcium-binding properties, has a poorly defined function. The pH dependent properties of calretinin (CR), the N-terminal (CR I-II), and C-terminal (CR III-VI) domains were investigated. A drop in pH within the intracellular range (from pH 7.5 to pH 6.5) leads to an increased hydrophobicity of calcium-bound CR and its domains as reported by fluorescence spectroscopy with the hydrophobic probe 2-(p-toluidino)-6-naphthalenesulfonic acid (TNS). The TNS data for the N- and C-terminal domains of CR are additive, providing further support for their independence within the full-length protein. Our work concentrated on CR I-II, which was found to have hydrophobic properties similar to calmodulin at lower pH. The elution of CR I-II from a phenyl-Sepharose column was consistent with the TNS data. The pH-dependent structural changes were further localized to residues 13-28 and 44-51 using nuclear magnetic resonance spectroscopy chemical shift analysis, and there appear to be no large changes in secondary structure. Protonation of His 12 and/or His 27 side chains, coupled with calcium chelation, appears to lead to the organization of a hydrophobic pocket in the N-terminal domain. CR may sense and respond to calcium, proton, and other signals, contributing to conflicting data on the proteins role as a calcium sensor or calcium buffer.

Suppression of calbindin D28K in estrogen-induced hamster renal tumors

It has been hypothesized that generation of reactive estrogen-quinone species and oxidative stress, both of which result from the metabolic activation of estrogens, plays an important role in estrogen-induced carcinogenesis. In the present investigation, we used an estrogen-induced hamster renal tumor model to identify gene(s) associated with oxidative stress that may be differentially expressed in estrogen-induced tumors compared with untreated controls. Hamsters were implanted with 17beta-estradiol (E2) for 7 months. This treatment resulted in the development of target organ specific kidney tumors. Delta differential PCR technique on RNA isolated from estrogen-induced hamster renal tumors and untreated control kidneys identified a number of cDNA fragments that were differentially expressed in tumor RNA compared with untreated controls. We report the cloning of one of the differentially expressed cDNA fragments, the hamster calbindin-D28k (Cb28k) cDNA, and present a finding that both Cb28k mRNA and protein are suppressed in estrogen-induced hamster renal tumors compared with untreated controls. Cb28k is a Vitamin D3-dependent calcium binding protein that acts as a buffer to maintain intracellular calcium homeostasis, although its exact role is still not clear. Since Cb28k gene has been shown to be associated with providing cells resistance against oxidative stress, Cb28k may be an important biomarker in estrogen-mediated carcinogenesis and oxidative stress.

Prevention of glucocorticoid-induced apoptosis in osteocytes and osteoblasts by calbindin-D28k

This study show for the first time that calbindin-D28k can prevent glucocorticoid-induced bone cell death. The anti-apoptotic effect of calbindin-D28k involves inhibition of glucocorticoid induced caspase 3 activation as well as ERK activation.

INTRODUCTION

Recent studies have indicated that deleterious effects of glucocorticoids on bone involve increased apoptosis of osteocytes and osteoblasts. Because the calcium-binding protein calbindin-D28k has been reported to be anti-apoptotic in different cell types and in response to a variety of insults, we investigated whether calbindin-D28k could protect against glucocorticoid-induced cell death in bone cells.

MATERIALS AND METHODS

Apoptosis was induced by addition of dexamethasone (dex; 10-6 M) for 6 h to MLO-Y4 osteocytic cells as well as to osteoblastic cells. Apoptosis percentage was determined by examining the nuclear morphology of transfected cells. Caspase 3 activity was evaluated in bone cells and in vitro. SELDI mass spectrometry (MS) was used to examine calbindin-D28k-caspase 3 interaction. Phosphorylation of calbindin-D28k was examined by 32P incorporation as well as by MALDI-TOF MS. ERK activation was determined by Western blot.

RESULTS

The pro-apoptotic effect of dex in MLO-Y4 cells was completely inhibited in cells transfected with calbindin-D28k cDNA (5.6% apoptosis in calbindin-D28k transfected cells compared with 16.2% apoptosis in vector-transfected cells, p < 0.05). Similar results were observed in osteoblastic cells. We found that dex-induced apoptosis in bone cells was accompanied by an increase in caspase 3 activity. This increase in caspase 3 activity was inhibited in the presence of calbindin-D28k. In vitro assays indicated a concentration-dependent inhibition of caspase 3 by calbindin-D28k (Ki = 0.22 microM). Calbindin-D28k was found to inhibit caspase 3 specifically because the activity of other caspases was unaffected by calbindin-D28k. The anti-apoptotic effect of calbindin-D28k in response to dex was also reproducibly associated with an increase in the phosphorylation of ERK 1 and 2, suggesting that calbindin-D28k affects more than one signal in the glucocorticoid-induced apoptotic pathway.

CONCLUSION

Calbindin-D28k, a natural non-oncogenic protein, could be an important target in the therapeutic intervention of glucocorticoid-induced osteoporosis.