TY - JOUR

T1 - Role of topoisomerase II in the structural and functional evolution of mitogen-stimulated lymphocyte nuclei

AU - Daev, E.

AU - Chaly, N.

AU - Brown, D. L.

AU - Valentine, B.

AU - Little, J. E.

AU - Chen, X.

AU - Walker, P. R.

PY - 1994/1/1

Y1 - 1994/1/1

N2 - To examine the role of DNA topoisomerase II (Topo II) in the mitogenic activation of mouse lymphocytes, we applied the Topo II inhibitor VM26 throughout the stimulation period and monitored morphological and functional parameters of lymphocyte activation. Cell viability and the usual increase in cell size were little affected at doses between 0.05 and 0.5 μM. DNA synthesis, however, was already significantly inhibited at 0.05 μM, with RNA synthesis inhibited to a lesser extent. Light microscope autoradiography showed that a smaller proportion of cells entered S phase, with each S phase cell incorporating less [ 3 H]thymidine. In immunofluorescence studies, the nucleolar antigen fibrillarin was reduced, although only minor effects on the snRNP Sm antigen and the internal component labeled by antibody PI1 were observed. At the electron microscope level, nucleoli were remodeled and chromatin became aggregated. At a high dose of VM26 (5 μM), cells showed the expected high levels of apoptosis and strong inhibition in all activation parameters assayed. The results support the hypothesis that the Topo IIβ isoform is involved in the very early phases of lymphocyte activation, with function of the Topo IIα isoform, which is more sensitive to VM26, being required for progression through S phase.

AB - To examine the role of DNA topoisomerase II (Topo II) in the mitogenic activation of mouse lymphocytes, we applied the Topo II inhibitor VM26 throughout the stimulation period and monitored morphological and functional parameters of lymphocyte activation. Cell viability and the usual increase in cell size were little affected at doses between 0.05 and 0.5 μM. DNA synthesis, however, was already significantly inhibited at 0.05 μM, with RNA synthesis inhibited to a lesser extent. Light microscope autoradiography showed that a smaller proportion of cells entered S phase, with each S phase cell incorporating less [ 3 H]thymidine. In immunofluorescence studies, the nucleolar antigen fibrillarin was reduced, although only minor effects on the snRNP Sm antigen and the internal component labeled by antibody PI1 were observed. At the electron microscope level, nucleoli were remodeled and chromatin became aggregated. At a high dose of VM26 (5 μM), cells showed the expected high levels of apoptosis and strong inhibition in all activation parameters assayed. The results support the hypothesis that the Topo IIβ isoform is involved in the very early phases of lymphocyte activation, with function of the Topo IIα isoform, which is more sensitive to VM26, being required for progression through S phase.

UR - http://www.scopus.com/inward/record.url?scp=0027931668&partnerID=8YFLogxK

U2 - 10.1006/excr.1994.1265

DO - 10.1006/excr.1994.1265

M3 - Article

AN - SCOPUS:0027931668

VL - 214

SP - 331

EP - 342

JO - Experimental Cell Research

JF - Experimental Cell Research

SN - 0014-4827

IS - 1

ER -