Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.20 (alpha-glucosidase)
 4,237 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The human colon carcinoma cell line HT-29 differentiates into functional enterocytes upon replacement of glucose by galactose in the culture medium. Since the differentiation of other types of cells is associated with the modulation of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) receptor concentrations and since enterocytes are classical target cells for 1,25(OH)2D3 we have examined the HT-29 cells to determine whether the differentiated and undifferentiated stages could be directly linked to the presence of 1,25(OH)2D3 receptors. HT-29 cells were grown in Dulbecco's modified medium containing 10% fetal calf serum (FCS) and glucose or galactose. Cell differentiation was assessed by measuring the brush border hydrolase, maltase. 1,25(OH)2D3 receptors were studied in the cells after 48 h without FCS. Nuclear uptake was measured in intact dispersed cells and the receptor protein was further characterized by vitamin D metabolite binding specificity, sucrose density gradient analysis and binding to DNA-cellulose. Maltase activity was 5-fold greater in differentiated HT-29 cells than in undifferentiated cells. Scatchard analysis showed a highly specific saturable (9500 sites per cell) high affinity (2 x 10(-10) M), binding of 1,25(OH)2D3 in undifferentiated cells. This receptor-like protein sedimented at 3.3S, bound to and eluted from DNA-cellulose and had all the characteristics of a 1,25(OH)2D3 receptor. No specific binding was detected in differentiated HT-29 cells. The presence of 1,25(OH)2D3 receptors in undifferentiated HT-29 cells implies that these cells are targets for vitamin D. The maltase activity increased significantly when undifferentiated cells were exposed to 1,25(OH)2D3 for 5-6 days, indicating that the hormone can promote differentiation of HT-29 cells. These results demonstrate that HT-29 cells can provide a new model for studying steroid receptor regulation and cell differentiation.
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PMID:Human colon cell line HT-29: characterisation of 1,25-dihydroxyvitamin D3 receptor and induction of differentiation by the hormone. 283 36

The effect of vitamin D status on the topography of intestinal cell membranes was studied in isolated brush borders, as well as their purified membranes, by limited proteolysis. Addition of papain to brush borders isolated from vitamin D3-treated and deficient chicks resulted in a differential solubilization of leucine aminopeptidase, maltase, and sucrase activities (114, 195, and 79%, respectively, of appropriate control levels) but not alkaline phosphatase activity. In comparison, proteolysis of purified membranes exhibited vitamin D3- and 1,25-dihydroxycholecalciferol [1,25(OH)2D3]-dependent differences in release of all four marker hydrolases monitored. Calcium uptake studies revealed that preincubation with papain yielded vesicles with a calcium content that was 125% of corresponding native vesicles, in preparations from vitamin D3-treated, as well as deficient birds. Membrane vesicles prepared from 1,25(OH)2D3-treated chicks initially accumulated calcium to a greater extent than those from rachitic birds, but thereafter exhibited a decline in calcium content to basal levels. Preincubation with papain, however, abolished this loss of calcium. The combined results indicate that vitamin D mediates alterations in brush border protein topography and raise the possibility that this action of the seco-steroid might be involved in calcium absorption. However, if vitamin D-stimulated calcium transport across the brush border is dependent on a protein carrier, the molecular entity is not sensitive to inactivation by papain.
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PMID:Vitamin D-mediated alterations in the topography of intestinal brush border proteins: effect of papain on hydrolase release and calcium uptake. 684 6