Differential regulation of p21 by p53 and Rb in cellular response to oxidative stress

Oxidative stress to mammalian cells causes cellular damage and triggers inducible cellular responses leading to cell death by apoptosis. In this paper, we report that p53 was required for programmed cell death induced by oxidative stress in both mouse and human cells and that p53 transactivation was involved in induction of oxidative cell death. Furthermore, we show that p21 was highly responsive to oxidative stress in a p53-dependent manner and that ectopic expression of p21 could increase cellular susceptibility to oxidative stress in the absence of p53. However, p21 was not required for p53-directed oxidative cell death because mouse embryo fibroblasts MEFs lacking p21(p21-/- MEFs) were still susceptible to oxidative cell death. Interestingly, bax, a cell-death mediator regulated by p53, was overexpressed in p21-/- MEFs that underwent cell death by oxidative stress, suggesting a compensation for loss of p21 that may be responsible for the existence of cell-death responses in p21-knockout mouse fibroblasts. Finally, we provide evidence that the retinoblastoma gene product (Rb) is a negative regulator of p21 and a repressor of the cellular apoptotic process. Because p21 is regulated by p53 positively and by Rb negatively, p21 may be a link between p53 and Rb in determining cell fate after oxidative damage.     

p53 polymorphism influences response in cancer chemotherapy via modulation of p73-dependent apoptosis

Intact p73 function is shown to be an important determinant of cellular sensitivity to anticancer agents. Inhibition of p73 function by dominant-negative proteins or by mutant p53 abrogates apoptosis and cytotoxicity induced by these agents. A polymorphism encoding either arginine (72R) or proline (72P) at codon 72 of p53 influences inhibition of p73 by a range of p53 mutants identified in squamous cancers. Clinical response following cisplatin-based chemo-radiotherapy for advanced head and neck cancer is influenced by this polymorphism, cancers expressing 72R mutants having lower response rates than those expressing 72P mutants. Polymorphism in p53 may influence individual responsiveness to cancer therapy.     

p53与化疗敏感性

本文归纳了p53涉及化疗敏感性的功能,汇总了近年来p53与化疗敏感性有关的基础和临床研究资料,阐述了p53调节化疗敏感性的可能机制,展望了对基因预测化疗敏感性的研究和应用前景.     

When p53 needs p73 to be functional - forced p73 expression induces nuclear accumulation of endogenous p53 protein

In human neuroblastoma (NB), wild type p53 protein does not elicit its archetypal human tumor suppressive activity so far described. To elucidate this alteration, substantial investigations using NB cell lines have underscored p53 protein nuclear localization defect and/or inappropriate conformation, but no definitive evidence has been provided so far. p73, the first homologue of the p53 gene, locates at the 1p36.3 locus, which is known to be deleted in various human tumors including NB. Unlike p53 mRNA, which specifies a single protein, p73alpha mRNAs encode two types of isoform (TAp73alpha and DeltaNp73alpha) resulting from the use of two different promoters, and eliciting or lacking NH(2)-terminal transactivation domain, respectively. DeltaNp73alpha inhibits p53 pro-apoptotic function in murine developing neurons and is abundantly expressed in human undifferentiated NB tumors. However, critical issues have been raised regarding p73alpha isoform roles, and their possible link to p53 are yet to be clarified in human NB using adenoviral infection approach.     

Subcellular distribution of p53 and p73 are differentially regulated by MDM2

The binding of MDM2 targets p53, but not p73, for degradation, whereas it suppresses the transactivation function of both proteins. MDM2 also mediates p53 nuclear export, but its role in the regulation of p73 distribution is unknown at the present time. We show here that, in sharp contrast to p53, MDM2 induces p73 to form nuclear aggregates that colocalize with MDM2 but are distinct from the promyelocytic leukemia dots. The MDM2 ring-domain that is necessary for mediating p53 nuclear export is not required for the induction of the p73 nuclear aggregates. Using a domain-swapping approach, we demonstrate that the inability of p73 to nuclear-export is attributable to its nonfunctional nuclear-export sequence.     

p53基因家族的新成员 p73和 p63

p53作为广泛存在的肿瘤抑制基因,最近发现了其家族成员：p73和p63。它们在结构和功能上具有相似性,均能触发细胞周期停滞,诱导凋亡,但它们在肿瘤抑制和组织发育中起着截然不同的作用,深入了解它们彼此之间的相似性和差异将对理解肿瘤发生的机制产生重要的影响。本文总结了最近几年来此领域内的最新进展。另外,p73和p63在C端的SAM结构说明它们可能参与组织的发育过程。     

Induction of p53-dependent and p53-independent cellular responses by topoisomerase 1 inhibitors.

We have previously shown that loss of p53 function in A2780 human ovarian adenocarcinoma cells confers increased clonogenic resistance to several DNA-damaging agents, but not to taxol or camptothecin. We have now extended these studies, comparing wild-type p53-expressing A2780 cells with isogenic derivatives transfected with a dominant negative mutant (143; val to ala) p53. We show that, as well as retaining equivalent clonogenic sensitivity to camptothecin, mutant p53 transfectants of A2780 cells do not acquire significantly increased resistance to the camptothecin analogues topotecan and SN-38, the active metabolite of CPT-11. Compared with vector-alone transfectants they are, however, relatively (2.2-fold) resistant to GI 147211, a further camptothecin analogue undergoing clinical trial. Treatment of A2780 with camptothecin and each analogue produces an increase, maximal at 24-48 h after drug exposure, of cells in the G2/M phase of the cell cycle and a decrease in both G1 and S-phase cells. The G2 arrest is independent of p53 function for camptothecin and the three analogues. All four compounds can induce apoptosis in A2780, which is reduced in mutant p53 transfectants, as measured using the terminal DNA transferase-mediated b-d UTP nick end labelling (TUNEL) assay. Thus, although p53-dependent apoptosis is induced by camptothecin, topotecan and SN-38 in this human ovarian carcinoma cell line, these drugs induce p53-independent death, as measured by clonogenic assay.     

胃癌组织p53、p63、p73蛋白表达及细胞凋亡的研究

目的:探讨p53、p63、p73蛋白表达及细胞凋亡在胃癌发生发展中的可能机制。方法:选择57例手术切除的胃癌及胃癌旁组织,用免疫组化方法检测组织中的p53、p63、p73蛋白表达,同时用Tunel方法检测胃癌组织中的凋亡细胞。结果:胃癌组织p53、p63、p73蛋白表达率显著高于胃癌旁组织(P<0.05);低、未分化型腺癌表达率显著高于高、中分化型腺癌(P<0.05);有淋巴转移显著高于无转移组(P<0.05);p53、p63、p73高表达的癌组织,细胞凋亡指数减少,早期胃癌凋亡低于晚期胃癌(P<0.05)。结论:胃癌组织p53、p63、p73蛋白表达水平增高,可延缓细胞凋亡;细胞凋亡机制障碍可能是胃癌增生失控的基础。     

Analysis of p73 and p53 gene deletions in multiple myeloma.

Recently, p73, a protein with structural and functional similarities to p53, an extensively studied tumor suppressor gene, has been cloned. After being mapped to the chromosomal region 1p35-1p36, it has been postulated to act as a tumor suppressor gene, too, as this region is altered in several human malignancies. Deletions of the short arm of chromosome 1 have frequently been described in multiple myeloma (MM) whereas structural abnormalities of the 17p13 region including p53 are rare events in this disease. Since it has been proposed that especially neoplasias lacking p53 alterations might show a loss of heterozygosity at 1p35-1p36, we studied the frequency of p53 and p73 deletions in bone marrow mononuclear cells of 68 patients with MM, two patients with monoclonal gammopathy of undetermined significance and four patients with plasma cell leukemia. Dual-color fluorescence in situ hybridization (FISH) for p53 and p73 was performed using commercially available DNA probes for 17p13.3 and the microsatellite marker D1Z2, respectively. Centromeric DNA probes served to distinguish gene deletions from whole chromosome losses. In contrast to recently published FISH results, we only detected heterozygous p53 deletions in eight out of the 74 patients, three of them showing a monosomy 17. Heterozygous deletions of the D1Z2 region at 1p36 were found in six cases with one patient having a monosomy 1. Neither homozygous deletions of either chromosomal region nor nullisomies 1 or 17 could be detected. These results argue against a major role of p73 deletions in MM. As MM patients with 1p structural abnormalities have a significantly poorer survival rate than those with normal karyotypes, the role of other putative tumor suppressor genes located at the chromosomal region 1p36 in the pathogenesis of MM has to be determined.     

p73和p63蛋白在胰腺癌组织中过表达的意义

目的:探讨p53家族新成员p73和p63蛋白在胰腺癌组织中过表达的意义。方法:应用免疫组化LSAB法检测75例人胰腺癌组织中p73和p63蛋白的过表达。结果:p73和p63蛋白在人胰腺癌中的过表达率分别为46·7%(35/75)和42·7%(32/75),p73蛋白在胰腺囊腺癌中的过表达率88·9%(8/9)明显高于导管腺癌41·8%(23/55),P=0·009,且p73蛋白过表达与胰腺癌淋巴结转移、肿瘤大小、神经侵犯和p53表达呈显著负相关性,P<0·05;在腺鳞癌或腺癌伴鳞状上皮化生中p63蛋白的过表达率(100%,13/13)明显高于导管腺癌(40·0%,22/55),P=0·007,但p63蛋白过表达与胰腺癌临床病理学指标及p53和增殖细胞核抗原(pro-liferatingcellnuclearantigen,PCNA)表达间无明显相关性。结论:p73蛋白低表达可能在胰腺癌发生中起重要作用;p63蛋白过表达与腺鳞癌或腺癌鳞化有关。