Function and Sequence Analyses of Tumor Suppressor Gene p53 of CHO.K1 Cells

Tzang, Bor‐Show; Lai, Yi-Ting; Hsu, Mandy; Chang, Hsueh-Wei; Chang, Chia-Ching; Huang, P. C.; Liu, Yin Chang

doi:10.1089/104454999315376

Cited by 37 publications

(28 citation statements)

References 24 publications

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“…The presence of caffeine retards the entry of cells into the G2/M phase after UVc or ␥-ray radiations and perfectly mimics a G2/M override if the cell proliferation kinetics are ignored. 13 Similar experiments performed in our laboratory with the Chinese Hamster Ovary (CHO-K1) cell line which contains a missense mutation for p53 at codon 211 (Thr3 Lys) 14,15 led to identical conclusions (unpublished results).…”

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confidence: 57%

Caffeine and the G2/M block override: A concept resulting from a misleading cell kinetic delay, independent of functional p53

et al. 2001

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In the literature the sensitization of DNA to radiationinduced damage by caffeine has been attributed to an override of the G2/M block. This process was supposed to involve the tumor suppressor gene p53 as it was described that p53 negative cells were more sensitive to checkpoint inhibition by caffeine than the wildtype phenotype. We have recently shown that caffeine does not cause an override of the G2/M block induced by radiation in normal human fibroblasts. We demonstrate here that this also applies to a human transformed cell line, the thyroid carcinoma K1, when submitted to ␥-rays irradiation. Within 9 hr after irradiation over 70% of the cells accumulated in the G2/M phase. This block persisted at 16 hr. In caffeine containing cultures the percentage of cells attaining the G2/M phase was reduced by over 30% at 16 hr. This was reflected in an accumulation of the cells in G1 phase and an inhibition of the S phase traverse. Cell cycle analyses from further time points combined with cell proliferation measurements confirmed these data. These results were independent of p53 status as experiments performed with variant K1 cell lines having defective p53 functions, led to similar conclusions. In addition, caffeine restored a G1 delay after irradiation in the cell lines with abrogated p53 functions. The effects of caffeine undeniably cumulate with damages induced by irradiation but probably by inhibiting DNA repair mechanisms or by intervening with purine and pyrimidine metabolisms and not by causing a G2/M block override. © 2001 Wiley-Liss, Inc. Key words: K1; p53 status; ␥ radiation; cell cycle checkpoints; caffeine; G2/M overrideThe tumor suppressor gene p53 is mutated in over 50% of human tumors. 1 It has been defined as the "guardian of the genome" 2 and represents the keystone between the control of cell proliferation and the maintenance of genetic integrity. 3 Among a wide range of functions, 4 p53 intervenes in cell cycle control at checkpoints G1/S and possibly at the G2/M. 3,5 For several years, it has been emphasized that caffeine causes the override of the G2/M checkpoint, thus leaving the cells less time to repair drug and radiation induced damages. 6 -12 In addition, several authors have demonstrated that this property of caffeine was correlated with the p53 status of the cells i.e., p53 Ϫ/Ϫ cells were more sensitive to caffeine-induced radiosensitization than p53 ϩ/ϩ cells. 9 -11 By using normal human fibroblasts (NHFs), we have recently shown that the apparent override of the radiation induced G2 block in the presence of caffeine is in fact due to a slowing down of the cell cycle. The presence of caffeine retards the entry of cells into the G2/M phase after UVc or ␥-ray radiations and perfectly mimics a G2/M override if the cell proliferation kinetics are ignored. 13 Similar experiments performed in our laboratory with the Chinese Hamster Ovary (CHO-K1) cell line which contains a missense mutation for p53 at codon 211 (Thr3 Lys) 14,15 led to identical conclusions (unpublished results).To investi...

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confidence: 57%

Caffeine and the G2/M block override: A concept resulting from a misleading cell kinetic delay, independent of functional p53

et al. 2001

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“…Previously, we have shown that p21 (waf1/cip1) mRNA was not detected in UV-irradiated CHO-K1 cells [Tzang et al, 1999a]. The absence of p21 expression was confirmed at the protein level by the Western analysis (Fig.…”

Section: Deregulation Of Cdk2 Activity Is Associated With Uv-induced supporting

confidence: 53%

“…We have previously reported that UVC irradiation (at 25 J/m 2 ) causes significant apoptosis in Chinese hamster ovary cells (CHO-K1) [Tzang et al, 1999b] and expression of the p21 (Waf1/Cip1) gene is absent despite the induction of p53 and gadd45 in the UV-irradiated cells [Tzang et al, 1999a]. p21 (Waf1/Cip1) is an universal inhibitor of cyclin-dependent kinases (Cdks), which is induced during DNA damage [Harper et al, 1993;Xiong et al, 1993;Dulic et al, 1994;Michieli et al, 1994].…”

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confidence: 99%

Deregulation of cyclin‐dependent kinase 2 activity correlates with UVC‐induced apoptosis in Chinese hamster ovary cells

Liao

Chang

Kao

et al. 2005

J of Cellular Biochemistry

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Progression through the cell cycle relies on the activities of cyclin-dependent kinases (Cdk), which in turn are modulated by inhibitory proteins such as p21(waf1/cip1) that are induced when genomic damage occurs. In this study, we show that exposure of normal mammalian cells, such as NIH3T3 fibroblasts, to UVC (25 J/m2, at 254 nm) induces the expression of p21 without causing significant apoptosis, whereas similar treatment of Chinese hamster ovary (CHO-K1) cells with UVC causes apoptosis without inducing p21. The absence of p21 in UV-irradiated CHO-K1 cells is accompanied by the deregulation of Cdk2 activity. The elevation of Cdk2 activity correlates with the increase of UV-induced apoptosis, which can be suppressed by small-molecule Cdk2 inhibitors such as roscovitine and pyrrolidine dithiocarbamate. The results of this study suggest that the deregulation of Cdk2 activity may be critical to UV-induced apoptosis in CHO-K1 cells.

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“…How valid are CHO cells as a model for studying the FA pathway? The Tp53 defect in CHO cells [Lee et al, 1997;Hu et al, 1999;Tzang et al, 1999] …”

Section: Resultsmentioning

confidence: 99%

How Fanconi anemia proteins promote the four Rs: Replication, recombination, repair, and recovery

Thompson

Hinz

Yamada

et al. 2005

Environ and Mol Mutagen

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The genetically complex disease Fanconi anemia (FA) comprises cancer predisposition, developmental defects, and bone marrow failure due to elevated apoptosis. The FA cellular phenotype includes universal sensitivity to DNA crosslinking damage, symptoms of oxidative stress, and reduced mutability at the X-linked HPRT gene. In this review article, we present a new heuristic molecular model that accommodates these varied features of FA cells. In our view, the FANCA, -C, and -G proteins, which are both cytoplasmic and nuclear, have an integrated dual role in which they sense and convey information about cytoplasmic oxidative stress to the nucleus, where they participate in the further assembly and functionality of the nuclear core complex (NCCFA= FANCA/B/C/E/F/G/L). In turn, NCCFA facilitates DNA replication at sites of base damage and strand breaks by performing the critical monoubiquitination of FANCD2, an event that somehow helps stabilize blocked and broken replication forks. This stabilization facilitates two kinds of processes: translesion synthesis at sites of blocking lesions (e.g., oxidative base damage), which produces point mutations by error-prone polymerases, and homologous recombination-mediated restart of broken forks, which arise spontaneously and when crosslinks are unhooked by the ERCC1-XPF endonuclease. In the absence of the critical FANCD2 monoubiquitination step, broken replication forks further lose chromatid continuity by collapsing into a configuration that is more difficult to restart through recombination and prone to aberrant repair through nonhomologous end joining. Thus, the FA regulatory pathway promotes chromosome integrity by monitoring oxidative stress and coping efficiently with the accompanying oxidative DNA damage during DNA replication.

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Function and Sequence Analyses of Tumor Suppressor Gene p53 of CHO.K1 Cells

Cited by 37 publications

References 24 publications

Caffeine and the G2/M block override: A concept resulting from a misleading cell kinetic delay, independent of functional p53

Caffeine and the G2/M block override: A concept resulting from a misleading cell kinetic delay, independent of functional p53

Deregulation of cyclin‐dependent kinase 2 activity correlates with UVC‐induced apoptosis in Chinese hamster ovary cells

How Fanconi anemia proteins promote the four Rs: Replication, recombination, repair, and recovery

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