BEHAVIOR OF NUCLEAR MATRIX PROTEINS DURING CAMPTOTHECIN-INDUCED APOPTOSIS IN HL-60 HUMAN LEUKEMIA-CELLS

In this study we focused our attention on the behavior of four nuclear matrix proteins during the various stages of apoptosis in the HL-60 c ell line exposed to the DNA topoisomerase I inhibitor, camptothecin. W e have examined the following antigens by immunocytochemical technique s: (i) the 18O-kDa nucleolar isoform of DNA topoisomerase II; (ii) a 1 26-kDa polypeptide of nuclear bodies; (iii) a 125-kDa protein; and (iv ) a 160-kDa polypeptide which are known to be components of the matrix inner network. Indirect immunofluorescence experiments were performed to follow these nuclear matrix antigens during apoptosis. Moreover, t he ultrastructural localization of both 125- and 160-kDa proteins was investigated by electron microscope immunocytochemistry with gold-conj ugated secondary antibodies. While the antibody to the nucleolar isofo rm of DNA topoisomerase II gave a fluorescent pattern that was well-ma intained until the late phases of apoptosis, the other three nuclear a ntigens showed marked modifications in their distribution. A common fe ature, particularly evident for 125- and 160-kDa proteins, was their a bsence from cap-shaped chromatin marginations, whereas they were prese nt in the areas of remaining decondensed chromatin. The 126-kDa polype ptide concentrated progressively in an irregular mass at the- opposite side of the crescentic caps and then broke up in fine spots. The 125- and 160-kDa proteins localized in the nucleolus and precisely within certain granules which are known to appear in the nucleolar area after camptothecin administration. These results show that, in addition to the well-known chromatin changes, nuclear organization undergoes other rearrangements during the apoptotic process. (C) 1995 Academic Press, Inc.