Telomerase adds new telomeric sequences to the end of chromosomal
DNA in order to overcome the end-replication problem. The upregulation of
telomerase activity in tumours has been reported in humans and some mammals and is considered to be a tumour marker; however, such activity has not been investigated in cows. Therefore, we investigated
telomerase activity in bovine leukaemia, the most common tumour in cows and its relationship with the bovine leukaemia virus (
BLV) infection, which is the major cause of leukaemia.
Telomerase activity was detected in 25 of 29 bovine leukaemia tissue samples. In peripheral blood lymphocytes (PBL) from BLV-infected cases that did not develop the tumour,
telomerase activity was detected in 11 of 71 cases (15.5%). When these cases were classified based on serological tests and the peripheral blood lymphocyte count, the
telomerase activity was observed to be the highest in the seropositive, non-lymphoproliferative (PBL<8000 microl(-1)) cases (three of seven cases, 42.9%), and not observed in the lymphoproliferative cases (PBL<16,000 microl(-1)) except in one case. Although the precise pathogenesis of BLV-related diseases remains obscure, persistent
lymphocytosis is considered as a pre-neoplastic state. In contrast, our results suggested that given the fact that
telomerase activity indicates tumour development, the aleukaemic stage could be defined as the 'pre-neoplastic state'. In conclusion, similar to many tumours in humans,
telomerase activity was detected in bovine leukaemia; further, this activity can be a potentially useful prediction marker for tumour development and/or a good therapeutic target.