Exploration of bladder cancer-associated methylated miRNAs by methylated DNA immunoprecipitation sequencing

Background: The current study aimed to explore the association between two epigenomic components, miRNA and DNA methylation, in bladder cancer (BC). Methods: Eight paired samples of tumor tissue and matched adjacent normal tissues from BC patients were subjected to methylated DNA immunoprecipitation sequencing and sRNA-Seq for differentially methylated miRNA genes and differential miRNA analysis. The miRNAs regulated by DNA methylation were screened and their functions involved in BC were analyzed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) as well as a miRNA-mRNA interaction network. Results: The methylation levels of 212 genes were different between tumors and normal tissues with specific enrichment at transcription initiation and termination sites. Among these genes, 154 were hypermethylated and 58 were hypomethylated. GO and KEGG pathway enrichment analysis indicated that differentially methylated miRNA genes were mainly enriched in tumor-associated GO terms and signaling pathways. Pairwise statistical analysis of MeDIP-Seq and sRNA-Seq data showed that there are 154 and 165 candidate methylation-regulated genes in tumors and normal tissues, respectively. Notably, an interaction network indicated that the miRNAs regulated by methylation regulated a broad range of mRNAs associated with cancer development and progression. In particular, the most differentially expressed miRNAs were validated by qRT-PCR, such that miR-145-5p was down-regulated and miR-182-5p was upregulated in patients with bladder cancer. Conclusion: A large number of miRNA genes were modified by methylation in BC. Identification of changes in the expression of these miRNAs provides a great deal of important information for BC diagnosis.