ASSOCIATION OF NUCLEAR MATRIX PROTEINS WITH GRANULAR AND THREADED NUCLEAR-BODIES IN CELL-LINES UNDERGOING APOPTOSIS

The granules which appear in the nucleolar area in apoptotic HL-60 cel ls after camptothecin administration (Zweyer et al., Exp. Cell Res. 22 1, 27-40, 1995) were detected also in several other cell lines induced to undergo apoptosis by different stimuli, such as MOLT-4 treated wit h staurosporine, K-562 incubated with actinomycin D, P-815 exposed to temperature causing heat shock, Jurkat cells treated with EGTA, U-937 growing in the presence of cycloheximide and tumor necrosis factor-alp ha, and HeLa cells treated with etoposide. Using immunoelectron micros copy techniques, we demonstrate that, besides the already described nu clear matrix proteins p125 and p160, these granules contain other nucl eoskeletal polypeptides such as proliferating cell nuclear antigen, a component of ribonucleoprotein particles, a 105-kDa constituent of nuc lear spliceosomes, and the 240-kDa nuclear mitotic apparatus-associate d protein referred to as NuMA. Moreover, we also found in the granules SAF-A/hn-RNP-U and SATB1 proteins, two polypeptides that have been re ported to bind scaffold-associated regions DNA sequences in vitro, thu s mediating the formation of looped DNA structures in vivo. Fibrillari n and coilin are not present in these granules or the PML protein. Thu s, the granules seen during the apoptotic process apparently are diffe rent from coiled bodies or other types of nuclear bodies. Furthermore, these granules do not contain chromatin components such as histones a nd DNA. Last, Western blotting analysis revealed that nuclear matrix p roteins present in the granules are not proteolytically degraded excep t for the NuMA polypeptide. We propose that these granules might repre sent aggregates of nuclear matrix proteins forming during the apoptoti c process. Moreover, since the granules are present in several cell li nes undergoing apoptosis, they could be considered a previously unreco gnized morphological hallmark of the apoptotic process. (C) 1997 Acade mic Press.