N6-methyladenosine demethylase FTO serves as an indicator for predicting prognosis and immunotherapy response in individuals with gastric cancer

Background N6-methyladenosine (m6A) RNA methylation is the most common chemical decoration in mammalian RNAs which exerts vital effects on numerous cellular processes. Recently, m6A regulators have been validated to participate in promoting immune evasion and act as prognostic factors in various cancers. Nevertheless, the predictive abilities of m6A regulators for the prognosis and immunotherapy response in gastric cancer (GC) remain indistinct. Methods Herein, The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx) database, The Human Protein Atlas (HPA), and a clinical GC cohort were applied for differential expression analysis, correlation analysis, survival analysis, and hazard model construction. Consensus clustering analysis was performed to authenticate the PD-L1 (CD274) expression, stemness features, immune cell infiltration, and tumor microenvironment (TME) in GC individuals. Furthermore, protein-protein interaction, immunotherapy response prediction, and drug susceptibility prediction were performed, respectively. Additionally, tissue microarray (TMA), immunohistochemical staining, western blot assay, Transwell assay, and flow cytometry assay were adopted to evaluate the protein expression, the prognostic value, and the influence of FTO on GC malignant phenotypes as well as the expression of PD-L1. Results In agreement with the majority of m6A regulators, FTO was overexpressed and predicted poor prognosis in GC. Based on consensus clustering analysis, two independent subgroups (G1/G2) were identified. Notably, FTO was upregulated in the G1 subgroup. Meanwhile, the infiltration level of CD8+ T cells was strikingly decreased while the stemness features were enhanced in the G1 subgroup. More importantly, FTO was negatively correlated with microsatellite instability (MSI) and tumor mutation burden (TMB). Furthermore, immune checkpoint blockade (ICB) response prediction indicated that patients with upregulated FTO showed high tumor immune dysfunction and exclusion (TIDE) scores. Subsequently, FTO was confirmed to be related to multiple immune checkpoints, particularly PD-L1. Specifically, FTO was dramatically upregulated in GC cell lines and clinical cancer samples. Functional experiments illustrated that FTO acted as an oncogene to facilitate malignant phenotypes. Notably, PD-L1 was remarkably downregulated after RNA interference-mediated knockdown of FTO. Conclusion FTO can aggravate GC malignant phenotypes. More importantly, it could be utilized to predict the long-term prognosis and the immunotherapy response in GC individuals. However, larger trials should be performed to verify the prediction accuracy.