Characterization of a hormonally induced reverse transcriptase (RT) from the human breast cancer cell line T47D: a possible involvement in human breast cancer

An RT transcript from T47D cells was isolated, using RT-PCR with primers based on the published T47D endogenous retroviral pol sequences. The PCR product encodes a 372-amino-acid long protein. The new T47D RT is almost identical to both previously described RTs from T47D cells, as well as to the enzymatically active RT from human bone marrow cells (95 and 97% identity, respectively). The DNA product was cloned into a bacterial expression system. A 42-kDa RT-related fragment was expressed, purified, and used to immunize rabbits. The antibodies recognize a 60-70 kDa hormonally induced protein specifically in T47D cells. Moreover, steroid hormones induce the apperance of RT protein foci in the cell cytoplasm, as demonstrated by confocal laser microscopy. A parallel hormonal induction of the RT activity in cell supernatants was observed. Expression of the RT-related protein was also detected in tumor cells of breast cancer biopsies sections. These results support the idea that retroviruses may be associated with human breast carcinoma.