Proliferating cell nuclear antigen (
PCNA) or
cyclin (C), a major
nuclear protein, has been shown to be associated with human
leukemia and
malignancies.
PCNA protein was quantitated in this study, in lymphocytes from bovine leukemia virus (BLV) infected and non-infected sheep, using two-dimensional
polyacrylamide gel electrophoresis (2-D PAGE) and
silver staining. The
PCNA mean levels in lymphocytes of BLV-infected sheep (27 months post-
infection) was significantly (P < 0.001) higher than in the lymphocytes of the non-infected sheep. The mean of
PCNA levels in lymphocytes of sheep, 21 days after
BLV infection, showed a two-fold increase compared with the non-infected sheep.
Phytohemagglutinin (PHA) (3 days) treatment of lymphocytes from the non-infected and from the BLV-infected sheep resulted in a significant (P < 0.01) increase in the mean of
PCNA levels only in the non-infected sheep. The mean lymphocyte counts of the BLV-infected sheep were not significantly different from the mean counts of the non-infected sheep at the time of lymphocyte
protein analysis. Thus, these findings showed, similar to human
leukemia and
malignancies, that high levels of
PCNA were found in lymphocytes from BLV-infected sheep compared with those from the non-infected sheep, and this was independent of high cell count. Our results also suggest that
PCNA protein may play a role in the process of lymphoid transformation as a result of
BLV infection of sheep.