Hypoxia-inducible factor 3α1 increases epithelial-to-mesenchymal transition and iron uptake to drive colorectal cancer liver metastasis.

Abstract In the tumor hypoxic environment, three isoforms of hypoxia-inducible factor (HIF)-α activates transcription of genes critical in the adaptive response to low oxygen levels in mammals. Most studies have focused on HIF-1α and HIF-2α, but not HIF-3α. Using RNA-seq, we found that overexpression of HIF-3α1 in colorectal cancer cells resulted in a gene signature of epithelial-mesenchymal transition (EMT) with especially highlyupregulated zinc finger E-box binding homeobox 2 (ZEB2) gene expression. Importantly, the expression of HIF-3α and ZEB2 are highly increased and are positively correlated with each other in human liver metastases. Standard dual luciferase reporter assay showed that ZEB2 is a direct target gene of HIF-3α1. Scratch assay showed that overexpression of HIF-3α1 promoted cancer cell migration whereas ZEB2 knockdown resulted in decreased protein levels of mesenchymal markers and reduced cell migration. As expected, HIF-3α1 overexpression increased colon tumor growth and liver metastasis. Interestingly, HIF-3α1 overexpression increased the master iron importer transferrin receptor (TFRC) and cellular iron levels. Iron chelation reduced HIF-3α overexpression-mediated mesenchymal phenotype, the survival of tumor cells and tumor growth. Together, HIF-3α1 increases the expression of ZEB2 and TFRC to promote iron accumulation, EMT and colon tumor liver metastasis.