CDX2-regulated expression of iron transport protein hephaestin in intestinal and colonic epithelium

Background & Aims: The homeobox transcription factor CDX2 has a key role in intestinal development and differentiation. Mice heterozygous for Cdx2 inactivation develop colonic polyps with epithelial cells showing gastric or squamous differentiation. Loss of CDX2 expression is seen in some poorly differentiated colon carcinomas in humans. Conversely, ectopic CDX2 expression in the stomach of transgenic mice promotes intestinal metaplasia, and CDX2 expression often is seen in intestinal metaplasia in stomach and esophagus. To enhance knowledge of CDX2 function, we sought to define CDX2-regulated genes. Methods: HT-29 and WiDr colorectal cancer (CRC) cells with low endogenous CDX2 expression were transduced with a CDX2 expression vector, and gene expression changes were assessed by microarrays. Results: The gene for ceruloplasmin- related iron transport protein hephaestin (HEPH) was induced by CDX2 in HT-29 and WiDr. In other CRC lines and human and mice tissues, endogenous HEPH expression was linked to CDX2 expression. Activation of CDX2 rapidly induced HEPH expression, and RNA interference-mediated inhibition of CDX2 led to lower HEPH expression. Studies with HEPH reporter gene constructs and chromatin-immunoprecipitation approaches suggested that CDX2 directly regulates HEPH transcription. In CRC cells, CDX2 induction suppressed intracellular iron levels, consistent with the view that HEPH regulates iron export. CDX2 expression was modulated in response to changes in intracellular iron levels, implying a regulatory pathway in which increased iron levels lead to increased expression of CDX2 and HEPH and enhanced iron export. Conclusions: CDX2 has a key role in regulating HEPH expression and iron levels in intestinal cells.