Regulation of hypoxia-inducible factor 1 in enterocytic cells

Mucosal hypoxia due to intestinal hypoperfusion is characteristic of a number of clinical disorders. An early event in the adaptive response to cellular hypoxia is the binding of hypoxia-inducible factor 1 (HIF-1) to cis-acting regulatory sites in target genes.

We characterized the expression of HIF-1 in transformed (Caco-2(BBe) and T84) and nontransformed human (FHs 74 Int) and rat (IEC-6) intestinal epithelial cell lines.

The electrophoretic mobility shift assay detected increased HIF-1 DNA-binding activity in each cell line within 2 h of hypoxia (1% O2). HIF-1 binding was maximal within 4 h and remained stable for 24 h. HIF-1 DNA-binding activity was maximal in the established IEC-6 cell line below 2% oxygen, but HIF-1 DNA-binding activity was not detectable above 0.5% O2 in the primary human FHs 74 Int cell line. The nonspecific protein kinase inhibitor genistein (200 microM) inhibited HIF-1 binding at 4 h. Transfection of Caco-2 cells with a wild-type, but not a mutant, HIF-1-dependent luciferase expression vector resulted in a fourfold induction of reporter gene expression during hypoxia.

In conclusion, HIF-1 regulates gene expression in enterocytes and an undefined phosphorylation event is important for O2 sensing.