Association of Nuclear Matrix Proteins with Granular and Threaded Nuclear Bodies in Cell Lines Undergoing Apoptosis (original) (raw)

1997, Experimental Cell Research

recognized morphological hallmark of the apoptotic process. ᭧ 1997 Academic Press The granules which appear in the nucleolar area in apoptotic HL-60 cells after camptothecin administration (Zweyer et al., Exp. Cell Res. 221, 27-40, 1995) were detected also in several other cell lines induced to un-INTRODUCTION dergo apoptosis by different stimuli, such as MOLT-4 treated with staurosporine, K-562 incubated with acti-Apoptosis is a form of programmed cell death in nomycin D, P-815 exposed to temperature causing heat which superflous or harmful cells are removed from shock, Jurkat cells treated with EGTA, U-937 growing an organism [1]. The term programmed cell death is in the presence of cycloheximide and tumor necrosis usually reserved for physiological conditions during factor-a, and HeLa cells treated with etoposide. Using which disposal of cells takes place, such as development immunoelectron microscopy techniques, we demonand morphogenesis, clonal selection of lymphocytes, strate that, besides the already described nuclear matrix proteins p125 and p160, these granules contain and cell renewal in epithelia [2-4]. On the contrary, other nucleoskeletal polypeptides such as proliferat-the term apoptosis indicates a form of active cell death ing cell nuclear antigen, a component of ribonucleotriggered by pathological conditions such as inflammaprotein particles, a 105-kDa constituent of nuclear tion, cancer, viral infections (including AIDS), or expospliceosomes, and the 240-kDa nuclear mitotic apparasure to a wide variety of chemical and physical stimuli tus-associated protein referred to as NuMA. Moreover, [5-7]. A well-known series of morphological modificawe also found in the granules SAF-A/hn-RNP-U and tions take place during the apoptotic process: chroma-SATB1 proteins, two polypeptides that have been retin margination and condensation, cell shrinkage, ported to bind scaffold-associated regions DNA semembrane blebbing, and finally disintegration of the quences in vitro, thus mediating the formation of cell into membrane-bound fragments called ''apoptotic looped DNA structures in vivo. Fibrillarin and coilin bodies'' [8]. are not present in these granules or the PML protein. Thus, the granules seen during the apoptotic process Several biochemical changes also occur: in most apparently are different from coiled bodies or other types of apoptosis there is internucleosomal DNA fragtypes of nuclear bodies. Furthermore, these granules mentation, mediated by an as yet unidentified Ca 2/do not contain chromatin components such as histones and Mg 2/-dependent endonuclease, producing 200-bp and DNA. Last, Western blotting analysis revealed that oligonucleotides that have long been considered a ''hallnuclear matrix proteins present in the granules are mark'' of the phenomenon [9]. However, several reports not proteolytically degraded except for the NuMA now indicate that some types of apoptotic stimuli do polypeptide. We propose that these granules might not induce this kind of fragmentation [10-13]. On the represent aggregates of nuclear matrix proteins formother hand, genome fragmentation into 300-and 50ing during the apoptotic process. Moreover, since the kb pieces (effected by a different endonuclease activity) granules are present in several cell lines undergoing seems to occur in all types of apoptosis, and precedes apoptosis, they could be considered a previously unendonucleosomal fragmentation [14-16]. Recently, attention has been drawn to the fact that during apoptosis proteins can be proteolysed by several types