Cadmium induced apoptotic changes in chromatin structure and subphases of nuclear growth during the cell cycle in CHO cells

Abstract

CHO cells were grown in the presence of 1 mu M CdCl(2) and subjected to ATP-dependent replicative DNA synthesis after permeabilization. By decreasing the density of the cell culture replicative DNA synthesis was diminishing. At higher than 2 x 10(6) cell/ml concentration Cd had virtually no effect on the rate of DNA replication. Growth at higher cell concentrations could be suppressed by increasing Cd concentration. After Cd treatment cells were synchronized by counterflow centrifugal elutriation. Cadmium toxicity on cell growth in early and mid S phase led to the accumulation of enlarged cells in late S phase. Flow cytometry showed increased cellular and nuclear sizes after Cd treatment. As the cells progressed through the S phase, 11 subpopulations of nuclear sizes were distinguished. Apoptotic chromatin changes were visualized by fluorescent microscopy in a cell cycle dependent manner. In the control untreated cells the main transitory forms of chromatin corresponded to those we have published earlier (veil-like, supercoiled chromatin, fibrous, ribboned structures, chromatin strings, elongated prechromosomes, precondensed chromosomes). Cadmium treatment caused: (a) the absence of decondensed veil-like structures and premature chromatin condensation in the form of apoptotic bodies in early S phase (2.2-2.4 average C-value), (b) the absence of fibrous structures, the lack of supercoiled chromatin, the appearance of uncoiled ribboned chromatin and perichromatin semicircles, in early mid S phase (2.5-2.9 C), (c) the presence of perichromatin fibrils and chromatin bodies in mid S phase (2.9-3.2 C), (d) early intra-nuclear inclusions, elongated forms of premature chromosomes, the extrusion and rupture of nuclear membrane later in mid S phase (3.3-3.4 C), (e) the exclusion of chromatin bodies and the formation of clusters of large-sized perichromatin granules in late S phase (3.5-3.8 C) and (f) large extensive disruptions and holes in the nuclear membrane and the clumping of incompletely folded chromosomes (3.8-4. C).

Stage-dependency of apoptosis and the blood-testis barrier in the dogfish shark (Squalus acanthias): cadmium-induced changes as assessed by vital fluorescence techniques

“…Cadmium has a high affinity for nucleic acids and accumulates within the nuclear compartment, even when present in trace amounts (Snow 1992;Hamada et al 1994). Nuclear-associated cadmium may displace zinc in polymerases, other metalloenzymes or transcription factors, all of which are present in larger amounts in the nuclei of proliferating cells (Din and Frazier 1985) or it may directly induce chromatin changes (Banfalvi et al 2005). Interestingly, classic androgen and oestrogen receptors, both zinc-finger proteins, are concentrated in PrM regions of the shark testis (Callard et al 1985;Cuevas and Callard 1992) and cadmium can reduce liver vitellogenin expression through its direct binding to oestrogen receptor-α in the trout (Vetillard and Bailhache 2005).…”

Preapoptotic chromatin changes induced by ultraviolet B irradiation in human erythroleukemia K562 cells

“…The gradual change in shape of chromatin structures from 2.0 to 3.7 C-values is summarized in Fig. 3 (Elutriation fractions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Decondensed chromatin appears as a veil-like fibrillary structure (fraction 1-2), which becomes polarized with oval or elongated shapes (fraction 3-4).…”

“…The fibrillary structure changes to fibrous forms (fractions [7][8] showing the linear connection between early decondensed chromosomes (fractions 9-10). Supercoiled loops form chromatin bodies, which are regarded as the earliest visible forms of interphase chromosomes (fraction [11][12]. The continuity is maintained in precondensed bent chromosomal forms (fraction [13][14].…”

“…Abnormal chromosomal forms were found after cadmium treatment and gamma irradiation leading to apoptosis [12,13]. Cadmium treatment is known to cause disruptions and large holes on the nuclear membrane [12].…”

“…Abnormal chromosomal forms were found after cadmium treatment and gamma irradiation leading to apoptosis [12,13]. Cadmium treatment is known to cause disruptions and large holes on the nuclear membrane [12]. Experiments with gamma irradiated cells revealed that ionization generates apoptotic bodies the size of which depends on the cell cycle, with many small apoptotic bodies in early S phase.…”