DNA Methylome Changes of Muscle- and Neuronal-Related Processes Precede Bladder Cancer Invasiveness

SIMPLE SUMMARY: Urinary bladder cancer can be therapeutically controlled until it becomes invasive, thus identifying critical molecular processes preceding and promoting the transition from pre-invasive to invasive tumors is of vital medical importance. Here, we tested epigenomic (DNA methylation) and gene expression profiles in non-invasive and invasive bladder cancers. We found methylation changes in the genes related to muscle and neuronal processes that discriminate between two cancer stages. Our results may open new avenues for early diagnosis of pre-invasive tumors by testing methylation profiles of tumor cells present in patients’ urine or biopsies leading to timely therapeutic measures. ABSTRACT: Bladder cancer (BC) is the ninth leading cause of cancer death with one of the highest recurrence rates among all cancers. One of the main risks for BC development is exposure to nitrosamines present in tobacco smoke or in other products. Aberrant epigenetic (DNA methylation) changes accompanied by deregulated gene expression are an important element of cancer pathogenesis. Therefore, we aimed to determine DNA methylation signatures and their impacts on gene expression in mice treated with N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN), a carcinogen similar to compounds found in tobacco smoke. Following BBN administration mice developed non-invasive or invasive bladder cancers. Surprisingly, muscle- and neuronal-related pathways emerged as the most affected in those tumors. Hypo- and hypermethylation changes were present within non-invasive BC, across CpGs mapping to the genes involved in muscle- and neuronal-related pathways, however, methylation differences were not sufficient to affect the expression of the majority of associated genes. Conversely, invasive tumors displayed hypermethylation changes that were linked with alterations in gene expression profiles. Together, these findings indicate that bladder cancer progression could be revealed through methylation profiling at the pre-invasive cancer stage that could assist monitoring of cancer patients and guide novel therapeutic approaches.