NNMT Involvement in CD44v3 Regulation Induced by Hepatic Stellate Cells Contributes to the Metastasis of Hepatocarcinoma Cells

The crosstalk between hepatic stellate cells (HSCs) and hepatic carcinoma cells contributes to hepatocellular carcinoma (HCC) progression, although the underlying mechanism is largely unknown. We found that activated HSCs upregulated nicotinamide (NAM) N-methyltransferase (NNMT) expression in hepatoma cells. NNMT regulates multiple metabolic pathways in the liver, and aberrantly high levels of NNMT in the HCC tissues were positively correlated with vascular invasion, serum HBV levels and distant metastasis in our study. Functional assays showed that NNMT promoted cell migration, invasion and metastasis in vitro and in vivo. Mechanistically, NNMT regulated the intracellular methylation potential which in turn altered histone H3K27 methylation pattern, resulting in the transcriptional activation of CD44. NNMT-mediated m6A modification of the CD44 mRNA resulted in the formation of the CD44v3 splice variant, while its product 1-MNA stabilized CD44 protein by preventing ubiquitin-mediated degradation. Finally, NNMT was also a target of statins which inhibited the metastatic ability of hepatoma cells. Taken together, our study provides evidence for the first time on the potential role of the NNMT/CD44v3 axis in regulating HCC metastasis, and presents NNMT as a promising prognostic biomarker and therapeutic target for HCC. Funding Statement: This study was supported by the National Natural Science Foundation of China (No.81672418 and 81871961, to Zhenyu Yin. No. 81802344,to Jie Li. No. 81572335,to Wenxiu Zhao) and the Xiamen Science and Technology Project of People-benefit (No. 3502Z20174089, to J.L.). Declaration of Interests: All of the authors have declared that no competing interests exist. Ethics Approval Statement: Specimen collection was performed after obtaining informed consent from each patient, and the utilization of the tumor materials for research purposes was carried out in accordance with the approved guidelines and approved by the Ethics Committee (No: 20111008) of Zhong Shan Hospital Xiamen University