Differentiation‐dependent Regulation of Intestinal Iron Absorption: Cell and Molecular Mechanisms

Abstract

Differentiation of intestinal epithelial cells is associated with up‐ and down‐regulation of a variety of genes, but little is known about the differentiation‐dependent regulation of genes encoding proteins involved in intestinal iron absorption. We have addressed this issue using human‐derived intestinal epithelial Caco‐2 cells and crypt/villus epithelial cells isolated from wild‐type mice as models. We examined expression of divalent metal‐ion transporter‐1 (DMT‐1; brush border iron importer), ferroportin (FPN; basolateral iron exporter) and hephaestin (HEPH; basolateral iron oxidase). Differentiation of Caco‐2 cells was associated with a significant up‐regulation of iron uptake. This up‐regulation was associated with a significant increase in the expression of DMT‐1 and HEPH mRNA and protein, as well as increased expression of FPN mRNA, but not FPN protein. Similarly, iron uptake and the expression of DMT‐1, HEPH, and FPN mRNAs was higher in mouse villous cells than crypt cells. Promoter‐reporter constructs were used to show that the activity of the promoters of DMT‐1 and HEPH increased with differentiation of Caco‐2 cells. These studies demonstrate that differentiation of intestinal epithelial cells is associated with up‐regulation of the iron uptake process and increased expression of DMT‐1, HEPH, and FPN. The expression of all these proteins of iron transport can be mediated at the post‐transcriptional level according to intracellular iron availability, but our results indicate that up‐regulation of DMT‐1 and HEPH during differentiation appears to be mediated at least in part via transcriptional regulatory mechanisms. (Supported by funds from the Department of Veterans Affairs.)