p53 regulates a non-apoptotic death induced by ROS

DNA damage induced by reactive oxygen species and several chemotherapeutic agents promotes both p53 and poly (ADP-ribose) polymerase (PARP) activation. p53 activation is well known to regulate apoptotic cell death, whereas robust activation of PARP-1 has been shown to promote a necrotic cell death associated with energetic collapse. Here we identify a novel role for p53 in modulating PARP enzymatic activity to regulate necrotic cell death. In mouse embryonic fibroblasts, human colorectal and human breast cancer cell lines, loss of p53 function promotes resistance to necrotic, PARP-mediated cell death. We therefore demonstrate that p53 can regulate both necrotic and apoptotic cell death, mutations or deletions in this tumor-suppressor protein may be selected by cancer cells to provide not only their resistance to apoptosis but also to necrosis, and explain resistance to chemotherapy and radiation even when it kills via non-apoptotic mechanisms.     

p53 directly suppresses BNIP3 expression to protect against hypoxia-induced cell death

Hypoxia stabilizes the tumour suppressor p53, allowing it to function primarily as a transrepressor; however, the function of p53 during hypoxia remains unclear. In this study, we showed that p53 suppressed BNIP3 expression by directly binding to the p53-response element motif and recruiting corepressor mSin3a to the BNIP3 promoter. The DNA-binding site of p53 must remain intact for the protein to suppress the BNIP3 promoter. In addition, taking advantage of zebrafish as an in vivo model, we confirmed that zebrafish nip3a, a homologous gene of mammalian BNIP3, was indeed induced by hypoxia and p53 mutation/knockdown enhanced nip3a expression under hypoxia resulted in cell death enhancement in p53 mutant embryos. Furthermore, p53 protected against hypoxia-induced cell death mediated by p53 suppression of BNIP3 as illustrated by p53 knockdown/loss assays in both human cell lines and zebrafish model, which is in contrast to the traditional pro-apoptotic role of p53. Our results suggest a novel function of p53 in hypoxia-induced cell death, leading to the development of new treatments for ischaemic heart disease and cerebral stroke.     

p53-dependent neuronal cell death in a DJ-1-deficient zebrafish model of Parkinson's disease

Mutations in DJ-1 lead to early onset Parkinson's disease (PD). The aim of this study was to elucidate further the underlying mechanisms leading to neuronal cell death in DJ-1 deficiency in vivo and determine whether the observed cell loss could be prevented pharmacologically. Inactivation of DJ-1 in zebrafish, Danio rerio, resulted in loss of dopaminergic neurons after exposure to hydrogen peroxide and the proteasome inhibitor MG132. DJ-1 knockdown by itself already resulted in increased p53 and Bax expression levels prior to toxin exposure without marked neuronal cell death, suggesting subthreshold activation of cell death pathways in DJ-1 deficiency. Proteasome inhibition led to a further increase of p53 and Bax expression with widespread neuronal cell death. Pharmacological p53 inhibition either before or during MG132 exposure in vivo prevented dopaminergic neuronal cell death in both cases. Simultaneous knockdown of DJ-1 and the negative p53 regulator mdm2 led to dopaminergic neuronal cell death even without toxin exposure, further implicating involvement of p53 in DJ-1 deficiency-mediated neuronal cell loss. Our study demonstrates the utility of zebrafish as a new animal model to study PD gene defects and suggests that modulation of downstream mechanisms, such as p53 inhibition, may be of therapeutic benefit.     

Identification of NCF2/p67phox as a novel p53 target gene

Analysis of microarrays performed in p53-, TAp63α- and ΔNp63α-inducible SaOs-2 cell lines allowed the identification of NCF2 mRNA upregulation in response to p53 induction. NCF2 gene encodes for p67phox, the cytosolic subunit of the NADPH oxidase enzyme complex. The recruitment of p67phox to the cell membrane causes the activation of the NADPH oxidase complex followed by the generation of NADP+ and superoxide from molecular oxygen. The presence of three putative p53 binding sites on the NCF2 promoter was predicted, and the subsequent luciferase and chromatin immunoprecipitation assays showed the activation of NCF2 promoter by p53 and its direct binding in vivo to at least one of the sites, thus confirming the hypothesis. NCF2 upregulation was also confirmed by real-time PCR in several cell lines after p53 activation. NCF2 knockdown by siRNA results in a significant reduction of ROS production and stimulates cell death, suggesting a protective function of Nox2-generated ROS in cells against apoptosis. These results provide insight into the redox-sensitive signaling mechanism that mediates cell survival involving p53 and its novel target NCF2/p67phox.     

Identification of NCF2/p67phox as a novel p53 target gene

Analysis of microarrays performed in p53-, TAp63α- and ΔNp63α-inducible SaOs-2 cell lines allowed the identification of NCF2 mRNA upregulation in response to p53 induction. NCF2 gene encodes for p67phox, the cytosolic subunit of the NADPH oxidase enzyme complex. The recruitment of p67phox to the cell membrane causes the activation of the NADPH oxidase complex followed by the generation of NADP+ and superoxide from molecular oxygen. The presence of three putative p53 binding sites on the NCF2 promoter was predicted, and the subsequent luciferase and chromatin immunoprecipitation assays showed the activation of NCF2 promoter by p53 and its direct binding in vivo to at least one of the sites, thus confirming the hypothesis. NCF2 upregulation was also confirmed by real-time PCR in several cell lines after p53 activation. NCF2 knockdown by siRNA results in a significant reduction of ROS production and stimulates cell death, suggesting a protective function of Nox2-generated ROS in cells against apoptosis. These results provide insight into the redox-sensitive signaling mechanism that mediates cell survival involving p53 and its novel target NCF2/p67phox.     

新的抑癌基因ASPP对p53作用的研究进展

p53是一个肿瘤抑制蛋白,它是通过调节相关基因表达,诱导细胞凋亡。p53诱导细胞凋亡的机制多年来一直不太清楚,而最近发现的ASPP(apoptosis stimulating protein of p53)蛋白家族对p53诱导细胞凋亡的机制研究有了新的进展。本文就此作一综述。     

Ad-P53癌基因治疗制剂质量分析研究

采用酶切图谱及ＰＣＲ法分析了Ａｄ－Ｐ５３癌基因治疗制剂中Ｐ５３基因的插入顺序;用ＰＣＲ及病变法检查产品中是否污染野生型腺病毒;用Ｗｅｓｔｅｒｎｂｌｏｔ验证Ｐ５３基因的表达。用分子生物学方法从几个主要方面对产品的安全性及有效性作出质量评价     

The p53 tumor suppressor: Critical regulator of life & death in cancer

p53 is the most commonly mutated or deleted known gene in human cancer. The consequences of its disruption are profound, either in the germlines of patients with Li-Fraumeni Syndrome, or in mice with targeted gene knockouts. Abundant evidence suggests that p53 exerts regulation of cell cycle progression as well as apoptotic cell death, both in response to identical environmental or metabolic stressors. The specific decision of cell cycle arrest vs. death may underlie p53's differential ability to trigger death in cancer cells and arrest with repair in non-cancer cells, thus producing a therapeutic index pertinent to cancer therapy. Indeed, p53 status is likely to correlate with prognosis in many human cancers and in multiple animal tumor models. The mechanistic basis for p53's functions are still emerging, and will hopefully yield new therapeutic strategies applicable to treatment of the many poor-prognosis, p53-deficient human malignancies.     

Palmdelphin,a novel target of p53 with Ser46 phosphorylation,controls cell death in response to DNA damage

The tumor suppressor gene p53 regulates apoptosis in response to DNA damage. Promoter selectivity of p53 depends on mainly its phosphorylation. Particularly, the phosphorylation at serine-46 of p53 is indispensable in promoting pro-apoptotic genes that are, however, poorly determined. In the current study, we identified palmdelphin as a pro-apoptotic gene induced by p53 in a phosphorylated serine-46-specific manner. Upregulation of palmdelphin was observed in wild-type p53-transfected cells, but not in serine-46-mutated cells. Expression of palmdelphin was induced by p53 in response to DNA damage. In turn, palmdelphin induced apoptosis. Intriguingly, downregulation of palmdelphin resulted in necroptosis-like cell death via ATP depletion. Upon DNA damage, palmdelphin dominantly accumulated in the nucleus to induce apoptosis. These findings define palmdelphin as a target of serine-46-phosphorylated p53 that controls cell death in response to DNA damage.     

New p53-based anti-cancer therapeutic strategies

Thep53 gene is frequently mutated in human tumours and therefore an important target for therapeutic intervention. Several p53-based strategies for treatment of cancer are currently under development.p53 gene therapy has resulted in tumour regression in patients with lung cancer. A mutant adenovirus can obliterate tumour cells carrying mutant p53 or lacking p53, but is unable to replicate in normal cells. Furthermore, current studies suggest that reactivation of mutant p53 proteins in tumours using small p53-activating molecules may initiate p53-dependent apoptosis and thus eliminate the tumour.     

Lactosylated polyethylenimine for gene transfer into airway epithelial cells: role of the sugar moiety in cell delivery and intracellular trafficking of the complexes

BACKGROUND: As we have previously shown that lactosylated polyethylenimine (PEI) is the most efficient glycosylated PEI for gene transfer into human airway epithelial cells in primary culture, we have studied here the role of the lactose residue in the enhancement of gene transfer efficiency observed with lactosylated PEI as compared with unsubstituted PEI in immortalized (Sigma CFTE29o- cells) and primary human airway epithelial cells. METHODS AND RESULTS: After three transfections of 1 h performed daily, 60% of Sigma CFTE29o- cells were transfected with lactosylated PEI, whereas 25% of cells were transfected with unsubstituted PEI (p < 0.05). Cell viability was 1.8-fold greater with lactosylated PEI as compared with unsubstituted PEI (p < 0.05). As assessed by flow cytometry, the cellular uptake of lactosylated complexes was greater than that of complexes made with unsubstituted PEI (p < 0.05) and involved mostly a receptor-mediated endocytosis. The study of the intracellular trafficking in airway epithelial cells of complexes showed an endosomal and lysosomal accumulation of lactosylated complexes. In the presence of a proton pump inhibitor, the level of lactosylated and unsubstituted PEI-mediated gene expression was reduced more than 20-fold, whereas the cell viability increased to almost 100%. For both complexes, a nuclear localization was observed for less than 5% of intracellular complexes. CONCLUSIONS: Our results show that the greater gene transfer efficiency observed for lactosylated complexes may be attributed to a higher amount of lactosylated complexes incorporated by airway epithelial cells and a lower cytotoxicity that might be related to reduced endosomolytic properties. However, the lactose residues substituting the PEI did not promote the entry of the plasmid into the nucleus.     

Identification and characterization of a novel peptide ligand of Tie2 for targeting gene therapy

Tyrosine kinase with immunoglobulin and epidermal growth factor homology domain-2 (Tie2) has been considered as a rational target for gene therapy in solid tumors. In order to identify a novel peptide ligand of Tie2 for targeted gene therapy, we screened a phage display peptide library and identified a candidate peptide ligand NSLSNASEFRAPY (designated GA5). Binding assays and Scatchard analysis revealed that GA5 could specifically bind to Tie2 with a dissociation constant of 2.1 × 10⁻⁸ M. In addition, we showed that GA5 was internalized into tumor cells highly expressing Tie2. In the biodistribution assay, ¹²⁵I-GA5 was mainly accumulated in SPC-A1 xenograft tumors that express Tie2. In gene delivery studies, GA5-conjugated polyethylenimine vector could achieve greater transgene transduction than non-targeted vectors both in vitro and in vivo . Tumor growth inhibition was observed in SPC-A1 xenograft-bearing mice that received eight intratumoral injections of GA5-polyethylenimine/ p53 complexes in 3 weeks. The difference in tumor volume between the experiment and control groups was significant ( P < 0.05). Our results showed that GA5 is a potentially efficient targeting element for cancer gene or moleculartherapy.     

Cell-mediated cytotoxicity can be regulated by p53 tumor suppressor gene activity in vitro

Summary— The wild-type human p53 tumor suppressor gene was tested for its ability to modulate cytotoxic activity of in vitro activated peripheral blood lymphocytes. Peripheral blood mononuclear cells (PBMCs) were stimulated by phytohemagglutinin (PHA), interferon α2b (IFNα2b), interleukin 2 (IL-2) or their combinations to induce cytotoxicity. This stimulation significantly increased the percentage of cells expressing p53, which was at its maximum when induced by IL-2 combined with IFNα2b. The role of p53 in the modulation of different aspects of cytotoxic activity of these cells was analyzed by studying the effects of p53 abrogation by antisense oligonucleotide (p53 AS) treatment in comparison with p53 sense or scrambled (missense) oligonucleotide (p53 S or p53 MS) treatment. We show that p53 plays a key role through induction of apoptosis in target cells (tumor necrosis factor pathway) rather than through osmolytic degeneration (perforin pathway) which is only slightly increased by p53 abrogation. Meanwhile, in vitro abrogation of p53 expression in PBL was found to be accompanied by an increase of CD8+ lymphocytes and an important increase of the CD56 ‘bright’ NK cell sub-population.     

促凋亡基因p53AIP1的研究进展

p53AIPl基因是近年发现的促凋亡基因,在p53依赖性的凋亡通路中起重要作用。p53AIPl介导线粒体凋亡途径,其表达依赖于p53蛋白的Ser^46的磷酸化。p53AIPl可直接促进凋亡,其促凋亡作用可能强于p53本身,并对p53抗性的肿瘤细胞也有作用。因此,对p53AIPl的深入研究可能会为对p53基因治疗有抗性的肿瘤患者带来新的希望。     

The p53-inducible E3 ubiquitin ligase p53RFP induces p53-dependent apoptosis

Recently, it has been shown that really interesting new gene (RING)-in between ring finger (IBR)-RING domain-containing proteins, such as Parkin and Parc, are E3 ubiquitin ligases and are involved in regulation of apoptosis. In this report, we show that p53-inducible RING-finger protein (p53RFP), a p53-inducible E3 ubiquitin ligase, induces p53-dependent but caspase-independent apoptosis. p53RFP contains an N-terminal RING-IBR-RING domain and an uncharacterized, evolutionally highly conserved C-terminal domain. p53RFP interacts with E2 ubiquitin-conjugating enzymes UbcH7 and UbcH8 but not with UbcH5, and this interaction is mediated through the RING-IBR-RING domain of p53RFP. Interestingly, the conserved C-terminal domain of p53RFP is required and sufficient for p53RFP-mediated apoptosis, suggesting p53RFP-mediated apoptosis does not require its E3 ubiquitin ligase activity. Together with a recent report showing that p53RFP is involved in ubiquitination and degradation of p21, a p53 downstream protein promoting growth arrest and antagonizing apoptosis, our findings suggest that p53RFP is involved in switching a cell from p53-mediated growth arrest to apoptosis.