Hypoxia inhibits HUNK-mediated phosphorylation of GEF-H1 for epithelial-to-mesenchymal transition

Hypoxia regulates epithelial to mesenchymal transition (EMT) of cancer cells. However, the mechanism underlying hypoxia-mediated EMT remains largely unknow. Here, utilizing colorectal cell carcinoma (CRC) as a model, we find that HUNK inhibits EMT and suppresses metastasis of CRC cells via its substrate GEF-H1 in a kinase-dependent manner. Mechanistically, HUNK directly phosphorylates GEF-H1 at ser645 site, which activates RhoA and consequently leads to a cascade of phosphorylation of LIMK1/CFL-1, thereby stabilizing F-actin and inhibiting EMT. Moreover, hypoxia suppresses HUNK activity and dephosphorylates GEF-H1 to promote EMT. Clinically, the expression levels of both HUNK and phosphorylation of GEH-H1 ser645 are not only downregulated in CRC tissues with metastasis compared to that without metastasis, but also positively correlated among these tissues. Our findings highlight the importance of hypoxia-regulated HUNK kinase activity and phosphorylation of GEF-H1 in regulation of EMT and metastasis of CRC. We conducted total RNA sequencing after HUNK genes were knocked out in SW480 cell lines. Totally 6 samples were generated.