Flow cytometric characterization of proliferation-associated nuclear antigen (p105) during the cell cycle in normal lymphocytes and promyelocytic leukemia cells (HL-60).

Bivariate flow cytometric analysis of p105 expression and DNA content was performed in human lymphocytes and promyelocytic leukemia cells (HL-60). We also employed a new method of detecting DNA strand breaks associated with apoptosis by labeling the 3'-OH termini in the breaks with biotinylated dUTP in a reaction employing exogenous terminal deoxynucleotidyl transferase (TdT). Phytohemagglutin-stimulated proliferating lymphocytes express p105 maximally after 48 hours, similar to HL-60 cells in exponential growth phase. Antigen expression in G1 was notably heterogeneous in G1 phase of both cell types and highest in M-phase cells treated for 6 hours with vinblastine. However, the p105-DNA ratio changed very little. Cycloheximide did not affect P105 expression. Methotrexate decreased p105 expression. Camptothecin and teniposide induced apoptosis, but apoptotic cells still expressed p105. Dual-parameter measurement also demonstrated that TdT-positive apoptotic cells expressed p105 at a higher level than apoptotic TdT negative cells. The data on drug treatment suggest that expression of p105 may be useful in monitoring chemotherapeutic effects but not as a marker of cell death from apoptosis.