Regulation of Hypoxia Inducible Factor in Intestinal Epithelial Cells in Inflammation

Abstract

Hypoxia and inflammation occur coincidentally in mucosal diseases. A number of studies have implicated the transcription factor hypoxia inducible factor (HIF) as a regulatory pathway under such conditions. Here, we hypothesized that inflammatory mediators may modulate HIF expression and/or function. Intestinal epithelial cells (Caco2 or T84 cells) were transfected with a luciferase reporter construct containing sequence corresponding to the erythropoietin hypoxia‐response element (HRE). Transfected cells were exposed to various concentrations of TNFα, IFNγ, IL‐4 or PGE2 in the presence and absence of hypoxia (p O2 20 torr) for 24 – 48h. HIF activity and expression were quantified by luciferase assay. Hypoxia (24h) induced HRE activity in intestinal epithelia by as much as 18±3‐fold (p<0.001). IFNγ selectively induced a concentration‐dependent repression of HIF activity under both normoxic (p<0.01) and hypoxic conditions (p<0.01). The level of inhibition by IFNγ (10ng/ml) was as much as 65±5% and 93±8% in normoxia and hypoxia, respectively, implicating a prominent and highly relevant repression by IFNγ. We conclude that HIF activity is prominently repressed by IFNγ, and since intestinal epithelial HIF has been implicated as a protective element in animal models of colitis, and the loss of HIF expression during inflammation may exacerbate inflammation.