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1,25-Dihydroxyvitamin D3 increases the expression of the CaT1 epithelial calcium channel in the Caco-2 human intestinal cell line.

ABSTRACT: BACKGROUND:The active hormonal form of vitamin D (1,25-dihydroxyvitamin D) is the primary regulator of intestinal calcium absorption efficiency. In vitamin D deficiency, intestinal calcium absorption is low leading to an increased risk of developing negative calcium balance and bone loss. 1,25-dihydroxyvitamin D has been shown to stimulate calcium absorption in experimental animals and in human subjects. However, the molecular details of calcium transport across the enterocyte are not fully defined. Recently, two novel epithelial calcium channels (CaT1/ECaC2 and ECaC1/CaT2) have been cloned and suggested to be important in regulating intestinal calcium absorption. However, to date neither gene has been shown to be regulated by vitamin D status. We have previously shown that 1,25-dihydroxyvitamin stimulates transcellular calcium transport in Caco-2 cells, a human intestinal cell line. RESULTS:In the current study, we have demonstrated that Caco-2 cells express low but detectable levels of CaT1 mRNA in the absence of 1,25-dihydroxyvitamin D treatment. CaT1 mRNA expression is rapidly up regulated (4-fold increase at 4 h and 10-fold at 24 h) by treatment with 1,25-dihydroxyvitamin D (10(-7) moles/L). Moreover, the increase in CaT1 mRNA expression preceded by several hours the vitamin D induction of calbindin D9K, a putative cytosolic calcium transport protein. CONCLUSION:These observations are the first to demonstrate regulation of CaT1 expression by vitamin D and are consistent with a new model of intestinal calcium absorption wherein vitamin D-mediated changes in brush border membrane CaT1 levels could be the primary gatekeeper regulating homeostatic modulation of intestinal calcium absorption efficiency.

SUBMITTER: Wood RJ

PROVIDER: S-EPMC55338 | biostudies-literature | 2001

REPOSITORIES: biostudies-literature

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1,25-Dihydroxyvitamin D3 increases the expression of the CaT1 epithelial calcium channel in the Caco-2 human intestinal cell line.

Wood R J RJ Tchack L L Taparia S S

BMC physiology 20010817

<h4>Background</h4>The active hormonal form of vitamin D (1,25-dihydroxyvitamin D) is the primary regulator of intestinal calcium absorption efficiency. In vitamin D deficiency, intestinal calcium absorption is low leading to an increased risk of developing negative calcium balance and bone loss. 1,25-dihydroxyvitamin D has been shown to stimulate calcium absorption in experimental animals and in human subjects. However, the molecular details of calcium transport across the enterocyte are not fu ...[more]

PMID: 11545681

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Project description:The effect of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] on 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] metabolism was examined in rats fed on a low-calcium diet. These rats exhibit hypocalcaemia, high urinary cyclic AMP excretion, a markedly elevated serum 1,25(OH)2D concentration and low serum concentrations of both 24,25(OH)2D and 25(OH)D. When the rats are treated orally with 1, 5 or 10 micrograms of 24,25(OH)2D3/100 g every day, there is a dramatic decrease in serum 1,25(OH)2D concentration in a dose-dependent manner concomitant with an increase in serum 24,25(OH)2D concentration. Serum calcium concentration and urinary cyclic AMP excretion are not significantly affected by the 24,25(OH)2D3 treatment, which suggests that parathyroid function is not affected by the 24,25(OH)2D3 treatment. The 25(OH)D3 1 alpha-hydroxylase activity measured in kidney homogenates is markedly elevated in rats on a low-calcium diet but is not affected by any doses of 24,25(OH)2D3. In contrast, recovery of intravenously injected [3H]1,25(OH)2D3 in the serum is decreased in 24,25(OH)2D3-treated rats. Furthermore, when [3H]1,25(OH)2D3 is incubated in vitro with kidney or intestinal homogenates of 24,25(OH)2D3-treated rats there is a decrease in the recovery of radioactivity in the total lipid extract as well as in the 1,25(OH)2D3 fraction along with an increase in the recovery of radioactivity in the water-soluble phase. These results are consistent with the possibility that 24,25(OH)2D3 has an effect on 1,25(OH)2D3 metabolism, namely that of enhancing the degradation of 1,25(OH)2D3. However, because a considerable proportion of the injected 24,25(OH)2D3 is expected to be converted into 1,24,25(OH)3D3 by renal 1 alpha-hydroxylase in 24,25(OH)2D3-treated rats, at least a part of the decrease in serum 1,25(OH)2D concentration may be due to a competitive inhibition by 24,25(OH)2D3 of the synthesis of 1,25(OH)2D3 from 25(OH)D3. Thus the physiological importance of the role of 24,25(OH)2D3 in regulating the serum 1,25(OH)2D concentration as well as the mechanism and metabolic pathway of degradation of 1,25(OH)2D3 remain to be clarified.

Project description:BackgroundCalcium is a vital mineral and an indispensable component of milk for ruminants. The regulation of transcellular calcium transport by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3, the active form of vitamin D) has been confirmed in humans and rodents, and regulators, including vitamin D receptor (VDR), calcium binding protein D9k (calbindin-D9k), plasma membrane Ca(2+)-ATPase 1b (PMCA1b), PMAC2b and Orai1, are involved in this process. However, it is still unclear whether 1,25-(OH)2D3 could stimulate calcium transport in the ruminant mammary gland. The present trials were conducted to study the effect of 1,25-(OH)2D3 supplementation and energy availability on the expression of genes and proteins related to calcium secretion in goat mammary epithelial cells.MethodsAn in vitro culture method for goat secreting mammary epithelial cells was successfully established. The cells were treated with different doses of 1,25-(OH)2D3 (0, 0.1, 1.0, 10.0 and 100.0 nmol/L) for calcium transport research, followed by a 3-bromopyruvate (3-BrPA, an inhibitor of glucose metabolism) treatment to determine its dependence on glucose availability. Cell proliferation ratios, glucose consumption and enzyme activities were measured with commercial kits, and real-time quantitative polymerase chain reaction (RT-qPCR), and western blots were used to determine the expression of genes and proteins associated with mammary calcium transport in dairy goats, respectively.Results1,25-(OH)2D3 promoted cell proliferation and the expression of genes involved in calcium transport in a dose-dependent manner when the concentration did not exceed 10.0 nmol/L. In addition, 100.0 nmol/L 1,25-(OH)2D3 inhibited cell proliferation and the expression of associated genes compared with the 10.0 nmol/L treatment. The inhibition of hexokinase 2 (HK2), a rate-limiting enzyme in glucose metabolism, decreased the expression of PMCA1b and PMCA2b at the mRNA and protein levels as well as the transcription of Orai1, indicating that glucose availability was required for goat mammary calcium transport. The optimal concentration of 1,25-(OH)2D3 that facilitated calcium transport in this study was 10.0 nmol/L.ConclusionsSupplementation with 1,25-(OH)2D3 influenced cell proliferation and regulated the expression of calcium transport modulators in a dose- and energy-dependent manner, thereby highlighting the role of 1,25-(OH)2D3 as an efficacious regulatory agent that produces calcium-enriched milk in ruminants when a suitable energy status was guaranteed.

Dataset Information

1,25-Dihydroxyvitamin D3 increases the expression of the CaT1 epithelial calcium channel in the Caco-2 human intestinal cell line.

Publications

1,25-Dihydroxyvitamin D3 increases the expression of the CaT1 epithelial calcium channel in the Caco-2 human intestinal cell line.

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