Submitted to: American Journal of Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/18/2001
Publication Date: 9/1/2002
Citation: Fleet, J.C., Eksir, F., Wood, R.J. 2002. Vitamin d-inducible net calcium transport and gene expression in three caco-2 cell lines. American Journal of Physiology. 283(3):G618-25. Interpretive Summary: Vitamin D status is an important determinant of intestinal calcium absorption. Low calcium absorption is a risk factor in elderly persons for future osteoporotic hip fracture. To understand the molecular determinants of calcium transport in the intestine we have studied in various cell culture models the effects of the active hormonal form of vitamin D, called 1,25-dihydroxyvitamin D, on the expression of genes that are important for calcium transport. We found that the level of a vitamin D-dependent calcium binding protein, called calbindin D, was not related to the rate of calcium transport in three different human intestinal cell lines. This information suggests that this protein may not be as important to intestinal calcium absorption as previously thought.
Technical Abstract: The parental cell line (P) of Caco-2 cells and two clones, BBe and TC7, were studied at 11 days postconfluence to test the facilitated diffusion model of vitamin D-mediated intestinal calcium absorption (CaTx). Nuclear vitamin D receptor (nVDR) and calbindin D9k (CaBP) were measured by Western blot; 1,25-hydroxyvitamin D3 24-hydroxylase (CYP24), CaBP, plasma membrane Ca-ATPase (PMCA), and Ca transport channel (CaT1) mRNA levels were examined by RT-PCR; and net apical-to-basolateral CaTx was examined after treating cells with vehicle or 10 nM calcitriol for 8 (mRNA levels) or 48 h (protein, CaBP mRNA, CaTx). nVDR level was lowest in BBe (38% P value) and directly related to CYP24 induction (TC7 = P, which were 1.56 times greater than BBe). nVDR was inversely related to the vitamin D-induced levels of CaT1 mRNA, CaBP mRNA, PMCA mRNA, and net CaTx, with the highest induction seen in BBe. Basal CaBP mRNA (86 times greater than P) and protein levels were highest in TC7 cells and were not associated with higher net CaTx, suggesting CaBP may not be rate limiting for CaTx in these cells.