Butyrate suppresses hypoxia-inducible factor-1 activity in intestinal epithelial cells under hypoxic conditions

Interaction between the products of intestinal bacteria and the intestinal epithelial cells is a key event in understanding the biological, physiological, and pathological functions of the intestinal epithelium. Here, we examined the effect of butyrate, one of the major intestinal bacterial products, on hypoxia-inducible factor-1 (HIF-1) activity under hypoxic conditions in intestinal epithelial cells. HIF-1 activity was assessed by luciferase assay using cytoplasmic extracts of intestinal epithelial cells, Caco-2, and IEC-6 cells. These cells were transiently transfected with hypoxia response element (HRE)-luciferase reporter plasmids and cultured under hypoxic conditions in the presence or absence of sodium butyrate (NaB). The effect of NaB on HIRE DNA binding activity in Caco-2 cells under hypoxic conditions was assessed by electrophoretic mobility shift assay. Expression of a hypoxia-responsive gene encoding intestinal trefoil factor (ITF) in Caco-2 cells after NaB treatment was assessed using reverse-transcription PCR. The barrier function of Caco-2 cells under hypoxic conditions was also evaluated by transepithelial electrical resistance measurement. NaB suppressed up-regulation of HIF-1 transcriptional activity under hypoxic conditions in Caco-2 and IEC-6 cells. In parallel, NaB reduced HRE DNA binding activity under the same conditions. Furthermore, NaB down-regulated enhanced transcription of ITF gene. Addition of NaB under hypoxic conditions delayed recovery of transepithelial electrical resistance of the monolayers after hypoxia-reoxygenation treatment. These findings indicate that NaB suppresses HIF-1 transcriptional activity on hypoxia-responsive genes by reducing the HRE DNA binding activity under hypoxic conditions in intestinal epithelial cells.