VRK2 promotes HCC metastasis through stabilizing ATG5 to activate autophagy-mediated degradation of ZO-1

Vaccinia-related kinase 2 (VRK2) is involved in the process of multiple cancers, but its role in the metastasis of hepatocellular carcinoma (HCC) is largely unknown. Here, we have found that VRK2 was markedly overexpressed in HCC, high expression of VRK2 was positively correlated with poor prognosis. Functionally, silencing VRK2 caused a decrease of HCC cell’s invasion and metastasis in vitro and vivo, whereas VRK2 overexpression increased the invasion and metastasis abilities of HCC cells. What’s more, we revealed that the pro-metastatic function of VRK2 was mediated by tight junction protein ZO-1 (Zonula occluden-1), ZO-1 overexpression attenuated the increase of HCC cell’s invasion and metastasis abilities induced by VRK2 overexpression. Notably, we surprised to find that VRK2 promoted the degradation of ZO-1 protein through autophagic degradation pathway instead of known ubiquitin proteasome pathway. Mechanically, phosphorylation mass spectrometry identified ATG5, a E3 conjugating enzyme which catalyze the lipidation of LC3, as a new substrate of VRK2. VRK2 phosphorylates ATG5 at serine 106 and protects it from ubiquitin-dependent proteasomal degradation by enhancing the interaction of ATG5 with USP13, promote autophagy-mediated degradation of ZO-1. The regulatory axis involving VRK2, ATG5, autophagy and ZO-1 also existed in HCC tissue further proved that VRK2 might be a promising therapeutic target for HCC. In summary, our research shows that the crosslink between VRK2 and autophagy plays an important role in HCC metastasis, thus providing a new theoretical basis for treatment of HCC by targeting VRK2.