Abstract
Colorectal cancer (CRC) is a leading cause of cancer-related deaths worldwide. Although epigenetic alterations are common in CRC, the epigenetic changes that occur during colorectal carcinogenesis remain unclear. Thus, we sought to elucidate the role of NOS1 methylation in colorectal carcinogenesis, which is essential for understanding disease pathology. We used the UCSC Xena database to comparatively analyze NOS1 expression and methylation status between tumour and adjacent normal tissues across 33 cancer types. Low expression and hypermethylation of NOS1 have been identified in 12 cancer types, with CRC demonstrating this characteristic epigenetic regulation. NOS1 promoter methylation status was examined using genomic DNA extraction and MassARRAY EpiTYPER methylation analysis. NOS1 hypermethylation was confirmed among CRCs in in-house dataset 1 (p < 0.001), and among CRCs and advanced adenomas in in-house dataset 2 (p < 0.001). An upward trend in methylation changes was identified from non-advanced adenoma to advanced adenoma to CRC (p for trend < 0.001). Quantitative real-time PCR was used to analyze NOS1 expression in in-house Dataset 3, and significantly low NOS1 expression was also identified in CRCs (p < 0.001). Kaplan-Meier estimator and Cox proportional hazard models were used to assess the prognostic and predictive roles of NOS1. NOS1 hypermethylation was significantly associated with better disease-specific survival (DSS) in CRC patients. NOS1 hypermethylation is an epigenetic driver of colorectal tumorigenesis and is associated with better survival.