Abstract 5751: Detection of HMTV in breast and endometrium carcinomas

Retroviral sequences homologous to the betaretrovirus mouse mammary tumor virus (MMTV), the etiological agent of mammary tumor in mice, are present in 40% of American women's breast cancers. A 660 bp sequence homologous to MMTV env gene with no significant homology to any other viral or human sequence reported in the Gen Bank is found in breast cancer, but not in adjacent normal breast tissues, indicating its exogenous origin. A complete provirus structure with 95% homology to MMTV has been isolated from two human breast tumors and named human mammary tumor virus (HMTV). Betaretroviral particles from primary cultures of metastatic breast cancer cells (MSSM) have been isolated and characterized. HMTV virion RNA is more than 90% homologous to MMTV RNA and to the HMTV proviral DNA. HMTV is able to infect a variety of cells bringing about striking molecular changes, as seen by co-culture experiments between MSSM cells and normal human epithelial breast cells, B and T human lymphocytes and human dendritic cells. Protein expression was only observed in 10-15% of the infected cells by FACS analysis, suggesting the presence of innate resistance in human cells after HMTV infection, as well as in breast cancer cells. The human retroviral restriction factors APOBEC F and G and the TRIM proteins are all highly expressed in HMTV infected cells as well as in breast cancer cells as measured by quantitative RT-PCR. Disruption of the cytoskeleton, evidence for epithelial mesenchymal transition (EMT) and increase in invasiveness are additional molecular changes seen in HMTV infected cells. Analysis of the sequencing data showed that HMTV also contains hormone response elements (HRE) homologous to MMTV HRE. This result encouraged us to investigate if HMTV were present in hormonal responsive tissues other than breast. Endometrium is a classical example of such tissue. Endometrial cancers and normal endometrium were analyzed for HMTV env sequences. HMTV env sequences were present in 0% of 29 normal tissues and 23.2% of 56 tumors analyzed. Johal et al. recently reported that MMTV-like sequence was found in 10% of the endometrial cancers (J. Med. Virology; 82: 1044-50). We describe here the detection of HMTV proteins by immunohistochemistry (IHC) in formalin fixed paraffin embedded (FFPE) slides obtained from breast and endometrium carcinomas but not in their respective normal tissues. These results are compared with the results obtained by PCR. PCR is a very sensitive technique