GRP78 activates the Wnt/HOXB9 pathway to promote invasion and metastasis of hepatocellular carcinoma by chaperoning LRP6

Recent studies have shown that the expression levels of glucose-regulated protein 78 (GRP78) and homeobox B9 (HOXB9) are both upregulated in hepatocellular carcinoma (HCC) and are closely related to HCC invasion and metastasis. However, whether there is a regulatory relationship between GRP78 and HOXB9 is unclear. In this study, we examined the expression of GRP78 and HOXB9 in HCC tissues and adjacent nontumor tissues. Correlation analysis indicated that GRP78 and HOXB9 expression were positively correlated. High levels of GRP78 and HOXB9 expression are closely related to worse clinicopathological features. Knockdown of GRP78 in HCC cells decreased the mRNA and protein expression of HOXB9, but increase HOXB9 expression reversed the decrease in invasion and metastasis induced by knocking down GRP78. Further experiments showed that GRP78 regulates HOXB9 through the Wnt signaling pathway by chaperoning low-density lipoprotein receptor-related protein 6 (LRP6). Importantly, we found that GPR78 promoted maturation of LRP6, while knockdown of GRP78 led to LRP6 misfolding and endoplasmic reticulum-associated degradation (ERAD). Consequently, the levels of mature LRP6 were reduced, and Wnt/HOXB9 signaling was inhibited. Our data suggest that the GRP78-LRP6-HOXB9 axis regulates the invasion and metastasis of HCC and may represent a potential therapeutic target for the treatment of HCC. • GRP78 promotes the invasion and metastasis of HCC through HOXB9. • GRP78 interacts with LRP6 and regulates LRP6 protein levels, thereby actives Wnt/HOXB9 pathway. • GRP78 stabilizes the expression of LRP6 through promoting the maturation of LRP6 and protecting LRP6 from ERAD.