Abstract 2312: Mycoplasmal DNA methyltransferases induce aberrant global hypermethylation and activate cancer-specific genes in human cells
Authors: Chernov Andrei , Strongin Alex Y. 
Published: May 2015

Malignancies originate as a result of genetic/epigenetic abnormalities in the genome. These abnormalities, collectively, lend proliferative advantages to the affected cells. The high-throughput DNA sequencing data suggest that epigenetic aberrations may be a leading factor in cancer onset and progression. DNA methylation is one of a few major epigenetic mechanisms. In humans, DNA methylation results in the conversion of the cytosine in the context of CG-dinucleotides into 5-methylcytosine. This conversion is catalyzed by the DNMT1, DNMT3A and DNMT3B DNA methyltransferases (MTases). Aberrant DNA hypermethylation, both genome-wide and at the individual gene level, is frequently recorded in multiple cancer types. Somatic mutations in the genes, which are directly responsible for DNA methylation, however, are infrequent in human tumors. Therefore, non-mutagenic factors that promote aberrant methylation should be revealed.

A community of microbial species, the microbiome, existing in the human body, plays fundamental roles in health and disease. The microbiome contributes to cell metabolism, signaling and regulatory pathways, and inflammatory and immune responses. Mycoplasmas, the smallest self-replicating bacteria, frequently infect mucous surfaces in humans, including respiratory and urogenital tracts, mammary glands and joints, often without apparent pathologies. Mycoplasmas grow attached to the cell surfaces, but can spontaneously infiltrate the host cells and promote their transformation via yet unknown mechanisms. Although mycoplasmas are often found in prostate, renal, gastric, colon, lung, breast, ovarian and melanoma tumors, their role in carcinogenesis is a matter of debate.

Here, we demonstrate that the Mycoplasma hyorhinis CG- and GATC- specific MTases can promote aberrant hypermethylation in human cells. We expressed the M. hyorhinis MTases in human cancerous and non-cancerous cells and determined that both MTases are transported to the cell nucleus and methylate genomic DNA. Using bisulfite sequencing and MeDIP-seq we precisely mapped genomic locations of the de novo hypermethylation sites. We established that mycoplasmal MTases introduced global de novo hypermethylation and significantly altered the epigenetic landscape in human cells. Paradoxically, we discovered that promoters of active genes, including certain pro-tumorigenic genes, can escape the de novo hypermethylation. Strikingly, in non-cancerous trophoblast cells, GATC-specific hypermethylation activated the proliferation pathways via selective upregulation of the c-JUN and MYC oncogenes, and the ATF3, KLF6 and DKK1 transcription factors. Overall, our findings demonstrate, for the first time, that microbiome-derived factors directly impact the epigenetic control of cancer-specific pathways in human cells.

Note: This abstract was not presented at the meeting.

Citation Format: Andrei Chernov, Alex Y. Strongin. Mycoplasmal DNA methyltransferases induce aberrant global hypermethylation and activate cancer-specific genes in human cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2312. doi:10.1158/1538-7445.AM2014-2312