MMTV-related sequences in feline breast carcinomas

Mouse mammary tumor virus (MMTV) has a proven role in breast cancer (BC) in susceptible murine lines. MMTV-related sequences were also found in significant proportion of human sporadic and familial BC patients (17-52%). MMTV-homologous sequences were found in liver, timus and spleen of wild commensal mice; in 63% animals analyzed the sequences were expressed [1–3]. However, the role and origin of MMTV-related infection in humans is unclear.

Earlier gag MMTV gene-related fragments were revealed in cats by other investigators [4]. We studied 9 female cats (7-15 years old) with BC treated at the Laboratory Animals Brunch to search MMTV-homologous sequences in tumor cells of BC animals. Specific PCRs with primers for gp52-coding area of the env MMTV and gag MMTV genes were used. PCR-products were sequenced and partially cloned in pGEM-T vector followed by sequencing. All experiments were isolated from ones with mice or infectious MMTV to avoid DNA contamination.

MMTV-related sequences were revealed in DNA samples from tumor and adjacent breast tissues in 3/9 (33.3%) of BC animals. The sequences analysis by BLAST and DNA Star was shown 92-97% homology of the gp52 env MMTV-related area with exogenous MMTV (C3H and HeJ strains), 93-97% - with Mus musculus cDNA and 93-98% homology with human MMTV-related betaretrovirus. Homology of the gag MMTV-related area with exogenous MMTV was 92-95%, with Mus musculus cDNA - 96-98% and with human MMTV-like betaretrovirus - 97-99%. Homology of the env and gag MMTV genes - homologous sequences between different animals was 92-93% and 97%, correspondingly; ORFs were found in sequenced PCR products.

Preliminary data show high similarity between feline and human MMTV-related sequences revealed in BC tissues. Feline might to be intermediate host for viral infection and transmission from mice to human.