Tumor Suppressor 4.1N/ is Epigenetic Silenced by Promoter Methylation and MiR-454-3p in NSCLC

Non-small-cell lung cancer (NSCLC) is divided into three major histological types, namely, lung adenocarcinoma (LUAD), lung squamous cell carcinoma (LUSC), and large-cell lung carcinoma (LCLC). We previously identified that 4.1N/ acts as a tumor suppressor and is reduced in NSCLC patients. In the current study, we explored the underlying epigenetic mechanisms of 4.1N/ reduction in NSCLC. The 4.1N/ gene promoter region was highly methylated in LUAD and LUSC patients. LUAD patients with higher methylation level in the 4.1N/ gene promoter (TSS1500, cg13399773 or TSS200, cg20993403) had a shorter overall survival time (Log-rank = 0.02 HR = 1.509 or Log-rank = 0.016 HR = 1.509), whereas LUSC patients with higher methylation level in the 4.1N/ gene promoter (TSS1500 cg13399773, TSS1500 cg07030373 or TSS200 cg20993403) had a longer overall survival time (Log-rank = 0.045 HR = 0.5709, Log-rank = 0.018 HR = 0.68 or Log-rank = 0.014 HR = 0.639, respectively). High methylation of the 4.1N/ gene promoter appeared to be a relatively early event in LUAD and LUSC. DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine restored the 4.1N/ expression at both the mRNA and protein levels. MiR-454-3p was abnormally highly expressed in NSCLC and directly targeted 4.1N/ mRNA. MiR-454-3p expression was significantly correlated with 4.1N/ expression in NSCLC patients (r = -0.63, < 0.0001). Therefore, we concluded that promoter hypermethylation of the 4.1N/ gene and abnormally high expressed miR-454-3p work at different regulation levels but in concert to restrict 4.1N/ expression in NSCLC. Taken together, this work contributes to elucidate the underlying epigenetic disruptions of 4.1N/ deficiency in NSCLC.