E. Prosperi et al., IMMUNOCYTOMETRIC DETERMINATION OF THE ALPHA-ISOFORM AND BETA-ISOFORM OF HUMAN DNA TOPOISOMERASE-II - INFLUENCE OF DIFFERENT FIXATIVES, Analytical cellular pathology, 10(2), 1996, pp. 137-148
The immunoreactivity of the alpha and beta isoforms (170 and 180 kDa,
respectively) of human DNA topoisomerase II (topo II) toward specific
monoclonal antibodies (MoAbs), was investigated in HeLa cells. The ext
ent of antigen preservation achieved with the dehydrating fixatives, e
thanol and acetone, was compared with that obtained with the cross-lin
king agent paraformaldehyde. Binding of each MoAb to the relative isoz
yme was detected by indirect immunofluorescence labelling and quantifi
ed by flow cytometry. The amount of antigen detectable was calculated
by normalizing the mean fluorescence intensity of samples incubated wi
th specific MoAbs, to the respective background fluorescence. For both
isozymes, acetone provided the highest immunofluorescence/background
ratio. A strong reduction in the immunoreactivity of the 180-kDa isofo
rm was observed after ethanol, and to a minor extent after paraformald
ehyde fixation, while reactivity of the 170-kDa isoform was not signif
icantly affected. Cell cycle distribution of each protein was assessed
by dual-parameter analysis of immunofluorescence vs, DNA content. No
evident difference in the cell cycle distribution of each isozyme was
found with each fixation protocol. At the morphological level, the pat
tern of immunofluorescence showed that the localization of each isozym
e was very similar for all these fixatives, These results confirm the
great sensitivity of the 180-kDa isoform to degradation, and indicate
that fixation has to be carefully chosen in order to determine the rel
ative amount of topo II isoforms with immunocytometric techniques.