It is widely accepted that the majority of
cancers result from multiple cellular events leading to
malignancy after a prolonged period of clinical latency, and that the
immune system plays a critical
role in the control of
cancer progression.
Bovine leukemia virus (
BLV) is an oncogenic member of the
Retroviridae family. Complete genomic sequences of
BLV strains isolated from
peripheral blood mononuclear cells (PBMC) from
cattle have been previously reported. However, a detailed characterization of the complete
genome of
BLV strains directly isolated from bovine
tumors is much needed in order to contribute to the
understanding of the mechanisms of leukemogenesis induced by
BLV in
cattle. In this study, we performed a molecular characterization of
BLV complete
genomes from bovine B-
cell lymphosarcoma isolates. A
nucleotide substitution was found in the
glucocorticoid response element (GRE) site of the 5'
long terminal repeat (5'LTR) of the
BLV isolates. All
amino acid substitutions in
Tax previously found to be related to stimulate high transcriptional activity of 5'LTR were not found in these studies.
Amino acid substitutions were found in the
nucleocapsid, gp51 and G4
proteins. Premature stop-
codons in R3 were observed. Few
mutations or
amino acid substitutions may be needed to allow
BLV provirus to achieve silencing. Substitutions that favor
suppression of viral expression in malignant B
cells might be a strategy to circumvent effective immune attack(AU)