A radiation-induced acute apoptosis involving TP53 and BAX precedes the delayed apoptosis and neoplastic transformation of CGL1 human hybrid cells

Mendonca, M.S.; Mayhugh, B.M.; McDowell, B.; Chin-Sinex, H.; Smith, M.L.; Dynlacht, J.R.; Spandau, D.F.; Lewis, D.A.

Radiation Research 163(6): 614-622


ISSN/ISBN: 0033-7587
PMID: 15913393
DOI: 10.2307/3581404
Accession: 011704362

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Exposing CGL1 (HeLa X fibroblast) hybrid cells to 7 Gy of X rays results in the onset of a delayed apoptosis in the progeny of the cells 10 to 12 cell divisions postirradiation that correlates with the emergence of neoplastically transformed foci. The delayed apoptosis begins around day 8 postirradiation and lasts for 11 days. We now demonstrate that the delayed apoptosis is also characterized by the appearance of similar to 50-kb apoptotic DNA fragments and caspase 3 activation postirradiation. In addition, we confirm that stabilization of TP53 and transactivation of pro-apoptosis BAX also occurs during the delayed apoptosis and show that anti-apoptosis BCL-X-L is down-regulated. To test whether the delayed apoptosis was due to a nonfunctional acute TP53 damage response in CGL1 cells, studies of acute apoptosis were completed. After irradiation, CGL1 cells underwent an acute wave of apoptosis that involves TP53 stabilization, transactivation of BAX gene expression, and a rapid caspase activation that ends by 96 h postirradiation. In addition, the acute onset of apoptosis correlates with transactivation of a standard wildtype TP53-responsive reporter (pG13-CAT) in CGL1 cells after radiation exposure. We propose that the onset of the delayed apoptosis is not the result of a nonfunctional acute TP53 damage response pathway but rather is a consequence of Xray-induced genomic instability arising in the distant progeny of the irradiated cells. (c) 2005 by Radiation Research Society.