Non-canonical Wnt co-receptors ROR1/ROR2 are differentially regulated by hypoxia in colon cancer cells

ROR1 and ROR2 co-receptors are transducers of non-canonical Wnt responses that promote an aggressive phenotype in several cancer types, including colon cancer. It has been demonstrated that hypoxia promotes tumor progression through the action of Hypoxia Inducible Factors (HIFs). An in silico analysis revealed that ROR2 is overexpressed in the advanced clinical stages of colon cancer. In line with this, ROR1 and ROR2 were found to be only expressed in malignant colon cells compared to non-malignant ones. The blockade of either ROR1 or ROR2 impaired colon cancer cells' colony formation abilities and the migration capacity of them. Additionally, the silencing of the ROR2 co-receptor blocked the metastatic ability of colon cancer cells in a xenografted mice model. We found that while silencing HIF-1α did not significantly reduce ROR1 or ROR2 expression, inhibiting HIF-2α and HIF-3α expression greatly decreased the protein levels of both co-receptors in colon cancer cells. The HIF-1α subunit expression is induced in acute hypoxia, whereas HIF-2α and HIF-3α show higher activity in chronic hypoxia, which may be functionally relevant since hypoxia induced a decrease in the constitutive active β-catenin transcriptional activity in SW480 cells. While both ROR1 and ROR2 stimulate proliferation and migration under normoxic conditions, the exposure of cells to hypoxia increased the expression of ROR1 or ROR2, depending on the Wnt cellular context, Thus, our results indicate that hypoxia partially represses β-catenin transcriptional activity and activates non-canonical Wnt signaling by regulating ROR1/ROR2 expression to induce an aggressive migrating and metastatic phenotype in colon cancer cells.