IL-4 enhances hypoxia induced HIF-1α protein levels in human transformed intestinal cells

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that mediates the adaptive response to hypoxia. Increasing evidence suggests a crucial role for HIF-1 in immune reactions. Here we investigated the effect of the Th2 type cytokines IL-4 and IL-10 on HIF-1α mediated response in normoxia (21% O2) and hypoxia (1% O2). Incubation of human transformed intestinal cells (HT-29) with IL-4 significantly increased HIF-1α protein levels during hypoxia but not during normoxia. Mechanisms involved are IL-4 induced up-regulation of HIF-1α gene transcription and the PI3K signaling pathway. The increase in hypoxia-induced accumulation of HIF-1α protein after IL-4 treatment did not result in up-regulation of HIF-1 DNA-binding activity or HIF-1 dependent gene expression. IL-10 did not affect HIF-1α protein levels.