Expression of the 170-kDa and 180-kDa isoforms of DNA topoisomerase II in resting and proliferating human lymphocytes

Abstract. The expression of the 170-kDa (α) and the 180-kDa ( β ) isoforms of DNA topoisomerase II (topo II) was investigated with two specific monoclonal antibodies (MoAbs) in human peripheral blood lymphocytes (PBL), before and after phyto-haemoagglutinin (PHA) stimulation. Binding of each MoAb was detected by indirect immunofluorescence labelling and quantified with flow cytometry. In resting PBL, the intensity of immunostaining was very low for both isozymes; however, topo II β -associated immunofluorescence was about 2.5 times significantly higher ( P< 0.001) than that associated with the a isoform. Between 48 and 72 h of PHA stimulation, when the highest percentage of cells in S and G₂+M phases was found, the levels of topo IIα and β increased up to about 30 and 10 times the value measured in resting PBL, respectively. Thus, the two isoforms reached comparable immunofluorescence values. At longer stimulation periods (96–120 h), topo IIα immunofluorescence was not significantly changed, while that relative to topo II β declined to about 50% of the peak value (P<0.02). At this time however, topo IIα-associated immunofluorescence was not significantly different from that related to the β isozyme. These results suggest that in resting PBL topo IIα is required at levels lower than topo II β , while in proliferating lymphocytes both isoforms are expressed to significantly higher levels.