DNA microarray analysis of vitamin D-induced gene expression in a human colon carcinoma cell line.

The full extent to which 1,25-dihydroxyvitamin D(3) affects gene expression in human intestinal epithelial cells is unknown. We used oligonucleotide arrays to catalog vitamin D-induced changes in gene expression in Caco-2 cells, a human colon carcinoma cell line. Five paired sets of Caco-2 cell cultures were subjected to either control conditions or 1,25-dihydroxyvitamin D (10(-7) mol/l x 24 h), and RNA was analyzed on an Affymetrix cDNA array containing 12,625 human sequences. Only 13 sequences representing 12 distinct genes exhibited statistically significant changes in expression of twofold or greater and were also called as "present" or "marginal" by the array-reading software in all five experiments. Genes regulated by 1,25-dihydroxyvitamin D included two previously known genes (25-hydroxyvitamin D-24-hydroxylase and amphiregulin) and 10 genes (sorcin, Gem, adaptin-gamma, TIG1, CEACAM6, carbonic anhydrase XII, junB, ceruloplasmin, and two unidentified sequences) that were novel. We tested and independently confirmed the effect of 1,25-dihydroxyvitamin D on 11 of these genes by RT-PCR. Increased protein expression was tested and confirmed in two of the novel 1,25-dihydroxyvitamin D-regulated genes, ceruloplasmin and sorcin. The known function of these genes suggests that many of them could be involved in the antiproliferative effects of 1,25-dihydroxyvitamin D3.

Iron treatment downregulates DMT1 and IREG1 mRNA expression in Caco-2 cells.

Iron deficiency is the most common nutritional disorder worldwide, whereas pathologic elevations of body iron stores can occur under certain circumstances due to genetic abnormalities or in association with other diseases. The intestine is the exclusive locus of homeostatic regulation of body iron stores, which is accomplished by changes in iron absorption efficiency by largely unknown molecular mechanisms in response to alterations in body iron stores. Recently, a number of novel genes involved in iron metabolism, such as the iron uptake transporter DMT1/DCT1/Nramp2 and the iron export transporter IREG1/ferroportin1/MTP1, have been identified, providing important insights about molecular aspects of intestinal iron absorption and its regulation. The aim of this study was to investigate the effects of iron treatment on DMT1 and IREG1 mRNA expression in Caco-2 cells, a human intestinal cell line. Exposure of the cells to iron (200 micromol/L ferric nitrilotriacetic acid for 72 h) significantly decreased transferrin receptor mRNA (80%), DMT1 mRNA (57%) and IREG1 mRNA (52%). These observations are consistent with the notion of parallel regulation of these iron-responsive genes in vivo to protect the enterocyte from iron toxicity and mediate a decreased efficiency of intestinal iron absorption to prevent iron overload.