Acceptors of poly(ADP-ribosylation) in differentiation inducer-treated and untreated Friend erythroleukemia cells

The apoptotic and nonapoptotic nature of the terminal differentiation of erythroid cells

The morphology of erythroid cells changes dramatically during the course of their terminal differentiation. According to calculations made with cytospin preparations obtained from Syrian hamster yolk-sac-derived erythroid cells, the area of nuclei at day 10 of gestation ranges from 25 to 85 micron 2 and is reduced to 15-25 micron 2 on day 13 [K. Morioka and R. Minamikawa-Tachino, Dev. Growth Differ. 35, 569-582, 1993]. The DNA and protein contents of each nucleus also decrease during this period. Nonspecific fragmentation of DNA was detected by agarose gel electrophoresis in all samples obtained from day 10 to day 13 of gestation, while distinct ladders of DNA fragments were not detected. DNA fragmentation was also detected by an in situ DNA-end labeling (TUNEL) assay. As the terminal differentiation proceeded, gradual decreases in levels of both histone H1 and most nonhistone proteins were observed by SDS-polyacrylamide gel electrophoresis, while levels of core histones appeared to be constant. In particular, lamin B2 was almost completely lost from the nuclear matrix fraction on day 11. These results suggest that the terminal differentiation of erythroid cells and apoptosis might have common mechanisms. However, expansion of the cytoplasm during the terminal differentiation distinguishes these processes. In addition, in the erythroid terminal differentiation, nuclei never form lobules or become fragmented; no apoptotic bodies are formed, occurrence of the apoptosis-like cellular change is not sporadic but rather synchronous, and the process is slow, with at least several days being required for cell death. These characteristics are different from those of typical apoptosis. Thus, the terminal differentiation of nucleated embryonic erythroid cells exhibits both apoptotic and nonapoptotic features.

Oxidant injury of cells. DNA strand-breaks activate polyadenosine diphosphate-ribose polymerase and lead to depletion of nicotinamide adenine dinucleotide

To determine the biochemical basis of the oxidant-induced injury of cells, we have studied early changes after exposure of P388D1 murine macrophages to hydrogen peroxide. Total intracellular NAD+ levels in P388D1 cells decreased with H2O2 concentrations of 40 microM or higher. Doses of H2O2 between 0.1 and 2.5 mM led to an 80% depletion of NAD within 20 min. With doses of H2O2 of 250 microM or lower, the fall in NAD and, as shown previously, ATP, was reversible. Higher doses of H2O2 that cause ultimate lysis of the cells, induced an irreversible depletion of NAD and ATP. Poly-ADP-ribose polymerase, a nuclear enzyme associated with DNA damage and repair, which catalyzes conversion of NAD to nicotinamide and protein-bound poly-ADP-ribose, was activated by exposure of the cells to concentrations of 40 microM H2O2 or higher. Activation of poly-ADP-ribose polymerase was also observed in peripheral lymphocytes incubated in the presence of phorbol myristate acetate-stimulated polymorphonuclear neutrophils. Examination of the possibility that DNA alteration was involved was performed by measurement of thymidine incorporation and determination of DNA single-strand breaks (SSB) in cells exposed to H2O2. H2O2 at 40 microM or higher inhibited DNA synthesis, and induced SSB within less than 30 s. These results suggest that DNA damage induced within seconds after addition of oxidant may lead to stimulation of poly-ADP-ribose polymerase, and a consequent fall in NAD. Excessive stimulation of poly-ADP-ribose polymerase leads to a fall in NAD sufficient to interfere with ATP synthesis.

Induction and modification of erythropoiesis in a suspension culture system derived from long-term bone marrow culture of Syrian hamster

Cells in a subculture system derived from long-term hamster bone marrow culture were induced to differentiate into hemoglobin-producing cells in response to added erythropoietin. Treatment of the subculture with dimethyl sulfoxide or other 'Friend inducers' but not 5-azacytidine effected no remarkable induction, though they enhanced the effect of externally added erythropoietin. 3-Aminobenzamide, a weak inducer of Friend cell differentiation [Morioka, K., K. Tanaka, M. Ishizawa and T. Ono: Dev. Growth Differ. 24, 507-512 (1982)], had a strong inhibitory effect on erythropoiesis in the subculture system. Phorbol esters and glucocorticoids (both are known to be strong inhibitors of Friend cell differentiation) acted as strong inhibitors of the differentiation in our system as well. The present system was shown to provide a useful in vitro model to compare the differentiation of normal erythroid progenitors with the previously established systems of neoplastic cells.