Hypoxia inducible factor 3-alpha promotes a malignant phenotype in colorectal cancer cells.

Colorectal cancer (CRC) is the third most common cancer worldwide. Hypoxia is a hallmark of the tumor microenvironment, and cellular adaptation to it is primarily mediated by the family of Hypoxia-inducible factors (HIFs) HIF-1α, HIF-2α, and HIF-3α. However, in contrast to HIF-1α and HIF-2α, a specific role for HIF-3α in cancer biology has not yet been clearly established. This research was aimed to elucidate the role of HIF-3α in colon cancer. As reported previously for HIF-1α and HIF-2α, we found that HIF-3α is also overexpressed under normoxic conditions in all cancer cell lines examined and in patient-derived tumor tissue samples compared with non-malignant cells and normal tissue, but remarkably, pulse-chase experiments demonstrated that HIF-3α displays high stability in cells compared with HIF-1α and HIF-2α. Progno Scan data analysis showed that overexpression of HIF-3α correlated with a patient's lower survival rate and a poor prognosis in colon adenocarcinoma patients. Knockdown of HIF-3α expression was carried out to investigate the effects derived from its silencing on malignant phenotype. We found a significative decrease in the Hypoxia Response Element (HRE) reporter transcriptional activity mediated by HIF-3α and a reduction in cell viability under oxidative stress in colon cancer cells with HIF-3α knockdown compared with control HIF-3α expressing cells. In addition, HIF-3α silencing also produced an increase in apoptotic rate, decreased clonogenic capacity, altered autophagy flux, and modulated the canonical Wnt/β pathway in an isoform-dependent and cell context-dependent manner in colon cancer cells. Overall, these data show that transcriptional activity mediated by HI3-3α plays an essential role in promoting the malignant phenotype, cell survival, and resistance to cell death in CRC cells.