Papers by sylvia christakos
Cells
1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the hormonally active form of vitamin D, activates the nu... more 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the hormonally active form of vitamin D, activates the nuclear vitamin D receptor (VDR) to mediate the transcription of target genes involved in calcium homeostasis as well as in non-classical 1,25(OH)2D3 actions. In this study, CARM1, an arginine methyltransferase, was found to mediate coactivator synergy in the presence of GRIP1 (a primary coactivator) and to cooperate with G9a, a lysine methyltransferase, in 1,25(OH)2D3 induced transcription of Cyp24a1 (the gene involved in the metabolic inactivation of 1,25(OH)2D3). In mouse proximal renal tubule (MPCT) cells and in mouse kidney, chromatin immunoprecipitation analysis demonstrated that dimethylation of histone H3 at arginine 17, which is mediated by CARM1, occurs at Cyp24a1 vitamin D response elements in a 1,25(OH)2D3 dependent manner. Treatment with TBBD, an inhibitor of CARM1, repressed 1,25(OH)2D3 induced Cyp24a1 expression in MPCT cells, further suggesting that CARM1 is a significant c...
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Abstract: Non-classical actions of vitamin D were first suggested over 30 years ago when receptor... more Abstract: Non-classical actions of vitamin D were first suggested over 30 years ago when receptors for the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), were detected in various tissues and cells that are not associated with the regulation of calcium homeostasis, including activated human inflammatory cells. The question that remained was the biological significance of the presence of vitamin D receptors in the different tissues and cells and, with regard to the immune system, whether or not vitamin D plays a role in the normal immune response and in modifying immune mediated diseases. In this article findings indicating that vitamin D is a key factor regulating both innate and adaptive immunity are reviewed with a focus on the molecular mechanisms involved. In addition, the physiological significance of vitamin D action, as suggested by in vivo studies in mouse models is discussed. Together, the findings indicate the importance of 1,25(OH)2D3 as a regulator of k...
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JBMR Plus, 2021
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Journal of Biological Chemistry, 1990
Corticosterone was administered to normal and bilaterally adrenalectomized rats (250-300 g), and ... more Corticosterone was administered to normal and bilaterally adrenalectomized rats (250-300 g), and hormonal regulation of brain calbindin-D28k (CaBP28k) levels was investigated by radioimmunoassay for CaBP28k protein and by slot and Northern blot analyses for CaBP28k mRNA. The specificity of the changes observed in CaBP28k mRNA levels was tested by reprobing blots with calmodulin and B-actin cDNAs. Rats were either adrenalectomized, adrenalectomized treated with corticosterone, intact, or intact treated with corticosterone. Chronic corticosterone administration (subcutaneous injection for 7 days, 10 mg/day) to normal intact rats significantly increased levels of CaBP28k immunoreactivity (43%) and mRNA (125%) in the hippocampus. Adrenalectomy (animals were killed 7 days after adrenalectomy) produced a significant decrease in hippocampal CaBP28k immunoreactivity (85%) and mRNA (80%) compared with intact controls. Immunocytochemical analysis of tissue sections inducated a marked depletion of CaBP28k immunoreactivity in the dentate gyrus of the hippocampus 2 weeks after adrenalectomy. When adrenalectomized rats were treated with corticosterone (10 mg/day for 7 days), CaBP28k protein and mRNA levels in hippocampus were restored to levels observed in intact controls. No changes in CaBP28k protein and mRNA in kidney, cerebellum, striatum, or cerebral cortex were noted in adrenalectomized rats or in intact rats treated with corticosterone when compared with controls, indicating the specificity of the effect on CaBP28k for the hippocampus. These studies present the first evidence of a regulator of CaBP28k gene expression in the brain.
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Handbook of Experimental Pharmacology, 2019
Vitamin D is a principal factor required for mineral and skeletal homeostasis. Vitamin D deficien... more Vitamin D is a principal factor required for mineral and skeletal homeostasis. Vitamin D deficiency during development causes rickets and in adults can result in osteomalacia and increased risk of fracture. 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the hormonally active form of vitamin D, is responsible for the biological actions of vitamin D which are mediated by the vitamin D receptor (VDR). Mutations in the VDR result in early-onset rickets and low calcium and phosphate, indicating the essential role of 1,25(OH)2D3/VDR signaling in the regulation of mineral homeostasis and skeletal health. This chapter summarizes our current understanding of the production of the vitamin D endocrine hormone, 1,25(OH)2D3, and the actions of 1,25(OH)2D3 which result in the maintenance of skeletal homeostasis. The primary role of 1,25(OH)2D3 is to increase calcium absorption from the intestine and thus to increase the availability of calcium for bone mineralization. Specific actions of 1,25(OH)2D3 on the intestine, kidney, and bone needed to maintain calcium homeostasis are summarized, and the impact of vitamin D status on bone health is discussed.
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American Journal of Physiology-Endocrinology and Metabolism, 2001
In this study, the interrelationship between signal transduction pathways and 1,25-dihydroxyvitam... more In this study, the interrelationship between signal transduction pathways and 1,25-dihydroxyvitamin D3[1,25(OH)2D3] action was examined in UMR106 osteoblastic cells. Treatment of these cells with 8-bromo-cAMP (1 mM) resulted in an upregulation of the vitamin D receptor (VDR) and an augmentation in the induction by 1,25(OH)2D3 of 25(OH)D3 24-hydroxylase [24(OH)ase] and osteopontin (OPN) mRNAs as well as gene transcription. Transfection with constructs containing the vitamin D response element devoid of other promoter regulatory elements did not alter the cAMP-mediated potentiation, suggesting that cAMP-enhanced transcription is due, at least in part, to upregulation of VDR. Treatment with phorbol ester [12- O-tetradecanoyl-phorbol-13-acetate (TPA) 100 nM], an activator of protein kinase C, significantly enhanced 1,25(OH)2D3-induced OPN mRNA and transcription but had no effect on VDR or on 24(OH)ase mRNA or transcription. Studies using OPN promoter constructs indicate that TPA-enhance...
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Journal of Biological Chemistry, 2017
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The Journal of Nutrition, 1992
Studies from our laboratory concerning regulation of calbindin include regulation by 1,25-dihydro... more Studies from our laboratory concerning regulation of calbindin include regulation by 1,25-dihydroxycholecalciferol [1,25(OH)2D3], receptor regulation as a possible mechanism for modulating calbindin's response to hormone, tissue specific regulation and regulation by factors other than 1,25(OH)2D3. With regard to receptor regulation, we found that the induction of calbindin mRNA in intestine and kidney by 1,25(OH)2D3 is not accompanied by a corresponding alteration in vitamin D receptor (VDR) mRNA in the vitamin D-deficient, low calcium rat. However, in the vitamin D-replete rat, administration of 1,25(OH)2D3 results in an induction of both calbindin and VDR mRNA in these tissues. These results suggest the presence of an inhibitor of 1,25(OH)2D3-mediated receptor up-regulation in the vitamin D-deficient, low calcium animal. Glucocorticoids can also regulate calbindin gene expression. Dexamethasone treatment (50 micrograms.100 g body weight-1.d-1 for 4 d) results in a 75% decrease in rat intestinal calbindin-D9k mRNA. This decrease may be related to the inhibition of intestinal calcium absorption previously observed after glucocorticoid administration. Kidney calbindin-D28k mRNA is unaffected by glucocorticoid treatment, indicating tissue specificity of the glucocorticoid response. To evaluate more precisely the means whereby 1,25(OH)2D3 and other modulators can influence calbindin gene expression, we isolated the chromosomal gene for calbindin-D28k by screening a mouse genomic library in cosmid. Ros 17/2.8 cells were transfected with recombinant plasmids in which the mouse calbindin promoter is fused to the reporter gene encoding chloramphenicol acetyltransferase. Deletion studies have enabled us to identify sequence elements in the mouse calbindin-D28k gene that confer basal activation and a hormone inducible response.
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Journal of Cellular Physiology, 2018
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Advances in experimental medicine and biology, 2017
The principal function of vitamin D in the maintenance of calcium homeostasis is to increase inte... more The principal function of vitamin D in the maintenance of calcium homeostasis is to increase intestinal calcium absorption. This conclusion was made from studies in vitamin D receptor (VDR) null mice which showed that rickets and osteomalacia were prevented when VDR null mice were fed a rescue diet that included high calcium, indicating that the skeletal abnormalities of the VDR null mice are primarily the result of impaired intestinal calcium absorption. Although vitamin D is critical for controlling intestinal calcium absorption, the mechanisms involved have remained incomplete. This chapter reviews studies, including studies in genetically modified mice, that have provided new insight and have challenged the traditional model of VDR-mediated calcium absorption.
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Endocrinology, 2017
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Bone Research, 2016
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Scientific Reports, 2016
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Proceedings of the National Academy of Sciences of the United States of America, 2008
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Journal of Bone and Mineral Research, 2014
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Biochemistry
ABSTRACT
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Journal of Bone and Mineral Research
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Methods in Enzymology, 1980
Publisher Summary This chapter discusses radioimmunoassay for chick intestinal calcium-binding pr... more Publisher Summary This chapter discusses radioimmunoassay for chick intestinal calcium-binding protein (CaBP). The most widely used methods for quantitating chick CaBP have been the relatively insensitive Chelex binding assay and the radial immunodiffusion assay, which uses antisera produced in the rabbit against highly purified chick intestinal CaBP. This chapter discusses about a radioimmunoassay that has been developed for chick intestinal CaBP. The assay system is based on the quantitative measurement of the displacement of radioactive antigen CaBP from its binding antibodies by the unlabeled antigen— that is, there is competitive binding of radioactive and unlabeled CaBP to the specific antiserum. Because there is a fixed, limited amount of labeled CaBP, antibody and varying amounts of unlabeled CaBP, the percentage of label that is bound is inversely related to the concentration of unlabeled CaBP. The chick intestinal CaBP radioimmunoassay utilizes the double-antibody technique, which reduces background to a minimum and maximizes sensitivity. Sensitivity, precision, and accuracy of the radioimmunoassay for chick intestinal CaBP is discussed in detail.
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Papers by sylvia christakos