Genome-wide DNA methylation and RNA expression profiles identified RIPK3 as a differentially methylated gene in Chlamydia pneumoniae infection lung carcinoma patients in China

Aim: To explore the relationship between Chlamydia pneumonia (Cpn) infection and lung cancer using integrative methylome and transcriptome analyses. Methods: Twelve primary lung cancer patients who were positive for Cpn and twelve patients who were negative were selected for demographic, clinicopathological, and lifestyle matching. Genomic DNA and RNA were extracted and DNA methylation and mRNA levels were detected using the Infinium Human Methylation 450 Beadchip array and mRNA + lncRNA Human Gene Expression Microarray. We identified differentially expressed methylation and genes profiles. Results: Integrative analysis revealed an inverse correlation between differentially expressed genes and DNA methylation. Cpn-related lung cancer methylated genes (target genes) were introduced into the gene ontology and KEGG, PID, BioCarta, Reactome, BioCyc and PANTHER enrichment analyses using a q-value cutoff of 0.05 to identify potentially functional methylation of abnormal genes associated with Cpn infection. Gene sets enrichment analysis was evaluated according to MsigDB. Levels of differentially expressed methylated sites were quantitatively verified. The promoter methylation sites of 62 genes were inversely related to expression levels. According to the quantitative analysis of DNA methylation, the methylation level of the RIPK3 promoter region was significantly different between Cpn-positive cancerous and adjacent tissues, but not between Cpn-negative cancerous and adjacent tissues. Conclusion: Hypomethylation of the RIPK3 promoter region increases RIPK3 expression, leading to regulated programmed necrosis and activation of NF-κB transcription factors, which may contribute to the development and progression of Cpn-related lung cancer.