Human endogenous retroviruses env gene expression and long terminal repeat methylation in colorectal cancer patients

Human endogenous retroviruses (HERV) are remnants of exogenous retroviral infections, representing 8% of the human genome. Their regulation is based on the DNA methylation of promoters, the long terminal repeats (LTRs). Transcripts from HERV have been associated with cancers, but reports concerning HERV expression in colorectal cancer remain sporadic. Sixty-three patients with advanced stages of colorectal cancer were enrolled in this study. The expressions of HERV env gene, and HERV-H, -K, -R and -P LTRs and Alu, LINE-1 methylation levels, were investigated in the tumor, normal adjacent tissues, and, where possible, blood and plasmatic extracellular vesicles (EVs). Associations among HERV env expression, methylation status and clinical characteristics were evaluated. No differences were observed in HERV env gene expression levels among the clinical specimens, while Alu, LINE-1, HERV-H and -K LTRs were demethylated in the tumor compared to the normal adjacent tissues (p < 0.05).The HERV env gene was expressed in the EVs at of 54% (-H), 38% (-K), 31% (-R) patients. Association was not found between HERV env expression and LTR methylation, but significant higher expression of HERV-P and -R env was found in tumor tissues arising from the right colon. Our findings do not demonstrate significant overexpression of the studied HERV in colorectal cancer, but their association with tumor localization and specificity of the changes in DNA methylation of retroelements are shown. HERV sequences were packaged in the EVs and might be transferred from one cell to another.