Differential p53 phosphorylation and activation of apoptosis-promoting genes Bax and Fas/APO-1 by irradiation and ara-C treatment

Abstract

In this study, we examined the effects of radiation and ara-C on induction of apoptosis and on the apoptosis-promoting genes p53, Bax and Fas/APO-1, in BV173 human leukemia cells, which harbor the wild-type p53 gene. It has been reported that p53 upregulates Fas/APO-1 and Bax expression. Both irradiation and ara-C treatment resulted in apoptosis and induction of p53 proteins within hours. The Bax gene was activated in irradiated and ara-C-treated BV173 cells, but Fas/APO-1 was induced only in irradiated BV173 cells. Radiation and ara-C treatment did not induce Bax or Fas/APO-1 protein expression in p53-null HL60 cells. Radiation weakly induced Fas/APO-1 expression in KBM-7 cells, which harbor a partially defective p53 gene. Both HL60 and KBM-7 cells are more resistant to radiation-and ara-Cinduced apoptosis than BV173 cells. These results suggest that functional p53 is necessary for the activation of Bax and Fas/APO-1 expression. However, elevated p53 protein is not sufficient to activate Fas/APO-1 gene expression in ara-Ctreated cells. Using two-dimensional gel electrophoresis, we found that the p53 proteins in irradiated and ara-C-treated BV173 cells have different isoelectric points; they converged to a single isoelectric point after in vitro treatment with phosphatase. These results suggest that different genotoxic treatments cause different phosphorylations of p53, which may account for the different levels of activation of Fas/APO-1 expression.

Possible role of NF-κB and p53 in the glutamate-induced pro-apoptotic neuronal pathway

“…76 Moreover, different genotoxic treatments may cause distinct phosphorylation of p53, which may account for the activation of unique pro-apoptotic pathways. 77 In all, these data support the view that different intracellular programs leading to neuronal apoptosis may exist. It could be inferred that the apoptosis that occurs physiologically (i.e.…”

Tissue and cell-specific expression of the p53-target genes: bax, fas, mdm2 and waf1/p21, before and following ionising irradiation in mice

“…In an other cell type, a leukemia cell line, fas was shown to be up-regulated in a p53 dependent manner, and induced apoptosis following exposure to g-rays. In contrast, following treatment with Ara-C a chemotherapeuthic drug, fas was not up-regulated in these cells while bax gene was induced after both treatments (Kobayashi et al, 1998). This data reporting, in vitro, a discrepancy between fas and bax p53-dependent regulation, is supported by our in vivo results, showing that up-regulation of fas and bax are not superimposable.…”

“…The involvement of Fas in antigen-speci®c apoptosis during immune response is well documented (Nagata and Golstein, 1995;Van Parijs and Abbas, 1996;Walker et al, 1997). Interestingly, its expression was recently shown to be increased on normal lymphocytes exposed to ionising radiation (Kobayashi et al, 1998;Reap et al, 1997) leading to the hypothesis that Fas might also be involved in p53-dependent apoptosis following genotoxic stress. The implication of these p53-responsive genes in the cellular response to genotoxic stress in vivo is however still to be demonstrated.…”

Mechanisms of apoptosis induction by nucleoside analogs

“…The transcriptional activity of p53 is known to increase the expression of various proapoptotic genes including the Fas death receptor (Miyashita and Reed, 1995;Owen-Schaub et al, 1995;Muller et al, 1997;Kobayashi et al, 1998;Muller et al, 1998;Fukazawa et al, 1999). Increased levels of Fas and Fas ligand transcripts and accumulation of the proteins have been observed following DNA repair inhibition by fludarabine (Rao and Plunkett, 2002).…”