TY - JOUR
T1 - Ubiquitination capabilities in response to neocarzinostatin and h2o2 stress in cell lines from patients with ataxia-telangiectasia
AU - Taylor, Allen
AU - Shang, Fu
AU - Nowell, Thomas
AU - Galanty, Yaron
AU - Shiloh, Yosef
N1 - Funding Information:
We thank Dr Luciana Chessa for A-T cell lines. This work was supported by NIH EY013250, USDA contract 5000-052, and Fulbright Foundation CIES (to A Taylor), and research grants from The A-T Medical Research Foundation and the A-T Children's Project (to Y Shiloh). Y Galanty is a Thomas Appeal Fellow.
PY - 2002
Y1 - 2002
N2 - The human genetic disorder ataxia-telangiectasia (A-T) is due to lack of functional ATM, a protein kinase which is involved in cellular responses to DNA double strand breaks (DSBs) and possibly other oxidative stresses, as well as in regulation of several fundamental cellular functions. Studies regarding responses in A-T cells to the induction of DSBs utilize ionizing radiation or radiomimetic chemicals, such as neocarzinostatin (NCS), which induce DNA DSBs. This critical DNA lesion activates many defense systems, such as the cell cycle checkpoints. The cell cycle is also regulated through a timed and coordinated degradation of regulatory proteins via the ubiquitin pathway. Our recent studies indicate that the ubiquitin pathway is influenced by the cellular redox status and that it is the major cellular pathway for removal of oxidized proteins. Accordingly, we hypothesized that the absence of a functional ATM protein might involve perturbations to the ubiquitin pathway as well. We show here that upon treatment with NCS, there was a transient 50-70% increase in endogenous ubiquitin conjugates in A-T and wt lymphoblastoid cells. Ubiquitin conjugation capabilities per se and levels of substrates for conjugation were also similarly enhanced in wt and A-T cells upon NCS treatment. We also compared the ubiquitination response in A-T and wt cells using H2O2 as the stress, in view of preexisting evidence of the effects of H2O2 on ubiquitination capabilities in other types of cells. As with NCS treatment, there was an ≈45% increase in endogenous ubiquitin conjugates by 2-4 h after exposure to H2O2. Both cell types showed a rapid 50-150% increase in de novo formed 125I-ubiquitin conjugates. As compared with wt cells, unexposed A-T cells had higher endogenous levels of conjugates and enhanced conjugation capability. However, A-T cells mounted a more muted ubiquitination response to the stress. The enhanced ubiquitin conjugation in unstressed A-T cells and attenuated ability of these cells to respond to stress are consistent with the A-T cells being under oxidative stress and with their having an 'aged' phenotype. The indication that ubiquitin conjugate levels and ubiquitin conjugation capabilities are enhanced upon oxidative stress without significant changes in GSSG/GSH ratios indicates that assays of ubiquitination provide a sensitive measure of cellular stress. The data also add support to the impression that potentiated ubiquitination response to mild oxidative stress is a generalizable phenomenon.
AB - The human genetic disorder ataxia-telangiectasia (A-T) is due to lack of functional ATM, a protein kinase which is involved in cellular responses to DNA double strand breaks (DSBs) and possibly other oxidative stresses, as well as in regulation of several fundamental cellular functions. Studies regarding responses in A-T cells to the induction of DSBs utilize ionizing radiation or radiomimetic chemicals, such as neocarzinostatin (NCS), which induce DNA DSBs. This critical DNA lesion activates many defense systems, such as the cell cycle checkpoints. The cell cycle is also regulated through a timed and coordinated degradation of regulatory proteins via the ubiquitin pathway. Our recent studies indicate that the ubiquitin pathway is influenced by the cellular redox status and that it is the major cellular pathway for removal of oxidized proteins. Accordingly, we hypothesized that the absence of a functional ATM protein might involve perturbations to the ubiquitin pathway as well. We show here that upon treatment with NCS, there was a transient 50-70% increase in endogenous ubiquitin conjugates in A-T and wt lymphoblastoid cells. Ubiquitin conjugation capabilities per se and levels of substrates for conjugation were also similarly enhanced in wt and A-T cells upon NCS treatment. We also compared the ubiquitination response in A-T and wt cells using H2O2 as the stress, in view of preexisting evidence of the effects of H2O2 on ubiquitination capabilities in other types of cells. As with NCS treatment, there was an ≈45% increase in endogenous ubiquitin conjugates by 2-4 h after exposure to H2O2. Both cell types showed a rapid 50-150% increase in de novo formed 125I-ubiquitin conjugates. As compared with wt cells, unexposed A-T cells had higher endogenous levels of conjugates and enhanced conjugation capability. However, A-T cells mounted a more muted ubiquitination response to the stress. The enhanced ubiquitin conjugation in unstressed A-T cells and attenuated ability of these cells to respond to stress are consistent with the A-T cells being under oxidative stress and with their having an 'aged' phenotype. The indication that ubiquitin conjugate levels and ubiquitin conjugation capabilities are enhanced upon oxidative stress without significant changes in GSSG/GSH ratios indicates that assays of ubiquitination provide a sensitive measure of cellular stress. The data also add support to the impression that potentiated ubiquitination response to mild oxidative stress is a generalizable phenomenon.
KW - ATM
KW - Aging
KW - Ataxia-telangiectasia
KW - Oxidative stress
KW - Ubiquitination
UR - http://www.scopus.com/inward/record.url?scp=0037182751&partnerID=8YFLogxK
U2 - 10.1038/sj.onc.1205557
DO - 10.1038/sj.onc.1205557
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AN - SCOPUS:0037182751
SN - 0950-9232
VL - 21
SP - 4363
EP - 4373
JO - Oncogene
JF - Oncogene
IS - 28
ER -