Biochemical and morphological changes in the nuclear matrix prepared from apoptotic HL-60 cells: Effect of different stabilizing procedures

Apoptotic cell death is characterized by deep morphological changes that la ke place in the nucleus. It is unclear whether modifications also occur in the nuclear matrix, a mainly proteinaceous structure that conceivably acts as a nuclear framework. We have investigated whether biochemical and morpho logical alterations of the nuclear matrix prepared from apoptotic HL-60 cel ls were dependent on the manipulations to which isolated nuclei were subjec ted before DNase I digestion and 2 M NaCl extraction. Our results showed th at the stabilizing procedures employed to preserve the inner fibrogranular network and nucleolar remnants of the matrix (i.e., a 37 degrees C incubati on; exposure to sodium tetrathionate at 4 degrees C; exposure to sodium tet rathionate at 37 degrees C) had no effect on the protein recovery of apopto tic nuclear matrices, which was always approximately two- to fivefold less than in control matrices. Moreover, one- and two-dimensional gel analysis o f nuclear matrix proteins showed that, in apoptotic samples, striking quant itative changes were present, as compared with controls. Once again, these changes were seen irrespective of the stabilizing procedures employed. Also , transmission electron microscope analysis showed similar morphological al terations in all types of apoptotic nuclear matrices. By contrast, the immu nofluorescent distribution of the 240-kDa NuMA protein seen in apoptotic sa mples was more sensitive to the stabilizing treatments. Our results indicat e that the biochemical and morphological changes of the apoptotic nuclear m atrix are largely independent of the isolation protocols and strengthen the contention that destruction of the nuclear matrix network is one of the ke y events leading to apoptotic nuclear destruction. I. Cell. Biochem. 74:99- 110, 1999. (C) 1999 Wiley-Liss, Inc.