title: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Mineral Bioavailability Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA. rwood@hnrc.tufts.edu
authors.forename: R J
authors.initials: RJ
authors.lastname: Wood
authors.forename: L
authors.initials: L
authors.lastname: Tchack
authors.forename: S
authors.initials: S
authors.lastname: Taparia
mesh_terms: D018938:Caco-2 Cells; D064026:Calbindins; D002117:Calcitriol / Q000494:pharmacology*; D015220:Calcium Channels / Q000096:biosynthesis* / Q000235:genetics; D020895:Enterocytes / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007700:Kinetics; D012333:RNA, Messenger / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000096:biosynthesis / Q000235:genetics; D050916:TRPV Cation Channels; D015854:Up-Regulation
chemical_list: D064026:Calbindins; D015220:Calcium Channels; D012333:RNA, Messenger; D064030:S100 Calcium Binding Protein G; C576506:S100G protein, human; D050916:TRPV Cation Channels; C120776:TRPV6 channel; D002117:Calcitriol