Characterization of the vitamin D receptor from the Caco-2 human colon carcinoma cell line: effect of cellular differentiation.
The human colon carcinoma cell line, Caco-2, is the only intestinal cell line to spontaneously differentiate in culture to a population exhibiting structural and biochemical characteristics of mature enterocytes. We conducted studies to establish the presence of the vitamin D receptor (VDR), determine changes in VDR concentration and affinity with differentiation and determine whether 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) mediates a functional response in this cell line. We found that Caco-2 cells possess a specific 1,25(OH)2D3 binding protein similar to the mammalian VDR. It has an equilibrium dissociation constant (Kd) of 0.72 nM, binds vitamin D analogues in order of their biological activities in vivo (1,25(OH)2D3 greater than 25(OH)D3 greater than 24,25(OH)2D3), sediments as a single peak on sucrose density gradients at 3.7 S, and is eluted from a DNA-cellulose column by 0.16 M KCl. The maximum number of binding sites was 2.6-fold greater in the differentiated cell (Day 15) compared to the preconfluent, undifferentiated (Day 4) cell (23 fmol/mg protein vs 56 fmol/mg protein). Cell growth was reduced 59% when exposed to 10(-7) M 1,25(OH)2D3 for 8 days. Alkaline phosphatase activity significantly increased in cultures incubated with 10(-8) M 1,25(OH)2D3 for up to 4 days when treatment was started in both undifferentiated cells (Day 5) and differentiated cells (Day 11). These findings suggest that the VDR present in undifferentiated and differentiated Caco-2 cells is functional. Caco-2 cells provide a unique in vitro model to study vitamin D-regulated functions in differentiated mammalian enterocytes.
Giuliano
A R
AR
USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts 02111.
Franceschi
R T
RT
Wood
R J
RJ
D000469:Alkaline Phosphatase / Q000378:metabolism; D001667:Binding, Competitive; D002117:Calcitriol / Q000378:metabolism / Q000494:pharmacology; D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects; D002499:Centrifugation, Density Gradient; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D004247:DNA / Q000378:metabolism; D006801:Humans; D008871:Microvilli / Q000201:enzymology; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000502:physiology*; D013393:Sucrase / Q000378:metabolism; D014407:Tumor Cells, Cultured
D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D004247:DNA; D000469:Alkaline Phosphatase; D013393:Sucrase; D002117:Calcitriol