Mesencephalic Astrocyte‐Derived Neurotrophic Factor Inhibits Liver Cancer Through Small Ubiquitin‐Related Modifier (SUMO)ylation‐Related Suppression of NF‐κB/Snail Signaling Pathway and Epithelial‐Mesenchymal Transition

BACKGROUND AND AIMS: Endoplasmic reticulum (ER) stress is associated with liver inflammation and hepatocellular carcinoma (HCC). However, how ER stress links inflammation and HCC remains obscure. Mesencephalic astrocyte‐derived neurotrophic factor (MANF) is an ER stress‐inducible secretion protein that inhibits inflammation by interacting with the key subunit of nuclear factor kappa light chain enhancer of activated B cells (NF‐κB) p65. We hypothesized that MANF may play a key role in linking ER stress and inflammation in HCC. APPROACH AND RESULTS: Here, we found that MANF mRNA and protein levels were lower in HCC tissues versus adjacent noncancer tissues. Patients with high levels of MANF had better relapse‐free survival and overall survival rates than those with low levels. MANF levels were also associated with the status of liver cirrhosis, advanced tumor‐node‐metastasis (TNM) stage, and tumor size. In vitro experiments revealed that MANF suppressed the migration and invasion of hepatoma cells. Hepatocyte‐specific deletion of MANF accelerated N‐nitrosodiethylamine (DEN)‐induced HCC by up‐regulating Snail1+2 levels and promoting epithelial‐mesenchymal transition (EMT). MANF appeared in the nuclei and was colocalized with p65 in HCC tissues and in tumor necrosis factor alpha (TNF‐α)‐treated hepatoma cells. The interaction of p65 and MANF was also confirmed by coimmunoprecipitation experiments. Consistently, knockdown of MANF up‐regulated NF‐κB downstream target genes TNF‐α, interleukin (IL)‐6 and IL‐1α expression in vitro and in vivo. Finally, small ubiquitin‐related modifier 1 (SUMO1) promoted MANF nuclear translocation and enhanced the interaction of MANF and p65. Mutation of p65 motifs for SUMOylation abolished the interaction of p65 and MANF. CONCLUSIONS: MANF plays an important role in linking ER stress and liver inflammation by inhibiting the NF‐κB/Snail signal pathway in EMT and HCC progression. Therefore, MANF may be a cancer suppressor and a potential therapeutic target for HCC.