IN-VITRO HEAT EXPOSURE INDUCES A REDISTRIBUTION OF NUCLEAR MATRIX PROTEINS IN HUMAN K562 ERYTHROLEUKEMIA-CELLS

By using both conventional and confocal laser scanning microscopy with three monoclonal antibodies recognizing nuclear matrix proteins we ha ve investigated by means of indirect fluorescence whether an incubatio n of isolated nuclei at the physiological temperature of 37 degrees C induces a redistribution of nuclear components in human K562 erythrole ukemia cells. Upon incubation of isolated nuclei for 45 min at 37 degr ees C, we have found that two of the antibodies, directed against prot eins of the inner matrix network (M(r) 125 and 160 kDa), gave a fluore scent pattern different from that observed in permeabilized cells. By contrast, the fluorescent pattern did not change if nuclei were kept a t 0 degrees C. The difference was more marked in case of the 160-kDa p olypeptide. The fluorescent pattern detected by the third antibody, wh ich recognizes the 180-kDa nucleolar isoform of DNA topoisomerase II, was unaffected by heat exposure of isolated nuclei. When isolated nucl ear matrices prepared from heat-stabilized nuclei were stained by mean s of the same three antibodies, it was possible to see that the distri bution of the 160-kDa matrix protein no longer corresponded to that ob servable in permeabilized cells, whereas the fluorescent pattern given by the antibody to the 125-kDa polypeptide resembled that detectable in permeabilized cells. The 180-kDa isoform of topoisomerase II was st ill present in the matrix nucleolar remnants. We conclude that a 37 de grees C incubation of isolated nuclei induces a redistribution of some nuclear matrix antigens and cannot prevent the rearrangement in the s patial organization of one of these antigens that takes place during m atrix isolation in human erythroleukemia cells. The practical relevanc e of these findings is discussed. (C) 1994 Academic Press, Inc.