HIF-1α activation under glucose deprivation plays a central role in the acquisition of anti-apoptosis in human colon cancer cells

A poor vascular network development in a tumor mass leads to poor oxygen and nutrient supply. To adapt to a hypoxic microenvironment, it is well-known that cancer cells activate the transcription factor hypoxia-inducible factor-1 alpha (HIP-1 alpha). HIF-1 alpha plays a central role in hypoxia-induced metabolic switching, anti-apoptosis, angiogenesis and drug resistance. Glucose deprivation, another major stressful microenvironment, protects cancer cells from drug-induced apoptosis. However, the molecular mechanisms by which cancer cells adapt to poor nutrient conditions remain poorly understood. In this study, we focused on HIF-1 alpha, signal transducer and activator of transcription 3 (STAT3) and transcription factor 4 (TCF4), which are involved in cell survival, anti-apoptosis and drug resistance. We examined their activities and the relationships among these transcription factors under glucose deprivation. Our results showed that glucose deprivation increased HIF-1 alpha, STAT3 and TCF4 DNA-binding activity, as well as the expression levels of their target genes OCT4, BCL-2 and VEGF. HIF-1 alpha knockdown significantly increased poly(ADP-ribose) polymerase 1 (PARP-1) cleavage at higher levels than STAT3 knockdown under glucose deprivation. Furthermore, HIP-1 alpha knockdown led to a significant decrease in the expression levels of both STAT3 and TCF4, although STAT3 knockdown decreased only HIF-1 alpha expression level. Our data indicated that activation of the HIF-1 alpha signaling pathway under glucose deprivation leads to the acquisition of anti-apoptotic properties in human colon cancer cells, and targeting the HIP-1 alpha signaling pathway may provide an effective avenue for treating cancers resistant to conventional therapy.