Abstract 2723: Host response to HMTV

Abstract

Abstract Work from our laboratory demonstrated the presence of retroviral sequences homologous to the mouse mammary tumor virus (MMTV) in a large proportion of human breast cancers. These observations have been confirmed by others. A 660 bp sequence of the MMTV env gene, with no significant homology to any viral or human sequence reported in the GenBank, has been found in 40% of the U.S. human breast cancers studied. This sequence is expressed in most of the env positive tumors, and is not detected in the normal breast tissue of patients with env positive carcinomas, indicating its exogenous origin. A complete provirus structure with 95% homology to MMTV has been described and designated as human mammary tumor virus (HMTV). Betaretroviral particles from primary cultures of breast cancer cells (MSSM) have been isolated and characterized. Virion RNA is more than 90% homologous to MMTV RNA and to the HMTV proviral DNA previously identified. To find out if these particles were infectious, co-culture experiments between MSSM cells and normal human epithelial breast cells, B and T human lymphocytes and human dendritic cells were performed. The results demonstrated that the recipient human cells became infected with HMTV. However, protein expression was only observed in 10-15% of the infected cells by FACS analysis suggesting the presence of an innate resistance to HMTV in human cells. We have then investigated whether human APOBEC and TRIM proteins are implicated in resistance to HMTV expression. The results indicated that APOBEC G and F, TRIM 5, 21 and 25 are all highly expressed in HMTV cells as measured by quantitative RT-PCR. Additional molecular changes seen in infected cells are disruption of the cytoskeleton and evidence for epithelial-mesenchymal transition (EMT). Since expression of an endogenous retrovirus (HERV-K) env gene has been reported to be upregulated in human breast cancers we have also investigated its expression in HMTV-infected cells, primary MSSM cells and breast tumors by quantitative RT PCR. The results indicated that in all instances where HMTV was present, expression of HERV-K (HML-2) was less than the control counterpart. In conclusion, HMTV is able to infect a variety of cells bringing about striking molecular changes. Whether these changes play a role in tumorigenesis remains to be shown. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2723. doi:10.1158/1538-7445.AM2011-2723