Quantitative analysis of the HERV pol gene in human tissues

Human endogenous retroviruses (HERVs) have been associated with cancer pathogenesis due to their close homology to exogenous tumorigenic retroviruses. The expression pattern of HERVs could provide important insights into the pathogenic state between HERVs and various cancers. Using the RetroTector10 program, we identified four full-length HERV elements (HML4, HERV-T, HERV-F, and HERV-R) that contain pol genes with reverse transcriptase sub domains. Through a quantitative real-time RT-PCR approach, we investigated expression levels of their pol genes in various human tissues including tumor and adjacent normal tissue samples. The HML4 and HERV-T pol genes were ubiquitously expressed in all human tissues, whereas the HERV-F pol gene was only expressed in the human placenta. In further analysis, we compared expression levels of the HERV pol genes in normal tissues and their corresponding tumor tissues. Interestingly, the HERV-F pol gene showed high expression in lung tumors while its expression level was very low in normal lung tissues (p-value = 0.007). In addition, the HERV-R pol gene showed a higher expression in stomach tumors than in normal tissues (p-value = 0.044). Thus, we suggest that the expression profiling of HERV-F and HERV-R pol genes could be used as a molecular marker system to detect human stomach and lung cancers, respectively.