NNMT Regulates Cancer Immunity and Is a Potential Prognostic Biomarker in Gastric and Colorectal Cancers

Background: Nicotinamide N-methyltransferase (NNMT), a cytosolic enzyme that catalyzes the N-methylation of nicotinamide, has been shown to be critical for promoting cancer progression, but little is known its role in gastric and colorectal cancers. Methods: We explored the role of NNMT in predicting prognosis and immune infiltration of gastric and colorectal cancers. Data was obtained from RNAseq Atlas, Oncomine, tumor Immune Estimation Resource (TIMER) databases, Kaplan-Meier plotter, PrognoScan database and Gene Expression Profiling Interactive Analysis (GEPIA). Findings: NNMT is overexpressed in gastric and colorectal cancers compared to adjacent normal tissues. High NNMT expression was significantly associated with worse outcome in gastric and colorectal cancer patients. However, high expression of NNMT was highly predictive of effectual 5-fluorouracil (5-FU) treatment in HER2 negative gastric cancer patients. Furthermore, there were significant positive correlations between NNMT expression and immune cells infiltration in gastric and colorectal cancers. Conversely, NNMT did not exert any significant effect on prognosis and immune infiltration in lung cancer. Interpretation: NNMT could be a prognostic factor for predicting clinical outcomes and immune infiltration, as well as a molecular target for the treatment of gastric and colorectal cancers. Funding: This work was supported in part by funding from the National Natural Science Foundation of China (No. 81502598). Declaration of Interest: The authors declare that they have no competing interests. Ethical Approval: Not required.