Function of p53 and its target genes

1.新的P53靶基因：肿瘤抑制因子P53是一种转录因子，可在细胞应激反应中诱导生长停滞和/或细胞凋亡。为了寻找新的P53诱导基因，我们用cDNA代表性差异分析(RDA)比较了正常小鼠胚胎成纤维细胞和P53缺失细胞中的基因表达。我们已经证实，DNA损伤以p53依赖的方式上调了小鼠胚胎成纤维细胞内源性SCN3B(钠通道亚基β3)和OPN(骨桥蛋白)的表达。P53对OPN表达的调控提示了一种新的P53参与免疫监视的模式，涉及到与宿主免疫系统的相互作用，以防止受损细胞发生恶性转化。上述结果还表明，SCN3B介导了一条依赖于P53的细胞凋亡途径，并可能成为联合抗癌药物进行基因治疗的候选基因。P53家族成员基因P63和P73的生物学功能：Re…更多的人被确认为p53基因家族的成员。然而，与p53相反，p63和p73在人类癌症中很少发生突变。为了确定p63和p73如何参与肿瘤的发生和正常发育，我们试图确定受p63和/或p73特异性调控但不受p53调控的靶基因。我们鉴定了编码Notch受体配体的JAG1和JAG2基因，而PEDF基因是p63和p73的直接靶标。我们还发现，IL-4受体α被p73上调。这些发现显示了P53家族基因和Notch信号之间的关联，并提示了P53家族基因参与正常发育的潜在分子机制。我们的数据还表明，IL-4Rpha可能在一定程度上介导某些免疫反应和p73依赖的细胞死亡。腺病毒介导的p53家族基因、p73和p63基因转移可诱导人肿瘤细胞周期停滞和细胞凋亡：p53基因治疗正被临床用于治疗人类癌症，然而，一些肿瘤模型(体内和体外)对p53具有耐药性。为了探索P53同源物p73和P63在肿瘤基因治疗中的潜在应用，我们通过腺病毒载体将P53、P73和P63导入结直肠癌细胞系，并比较它们对细胞生长的影响。在被测试的10个细胞系中，6个细胞系在转导p53、p73β或p63伽马后表现出类似的反应；两个细胞系发生了细胞周期停滞，3个细胞系出现了凋亡，1个细胞系在转导后没有作用。在其他四种细胞系中，对细胞周期进程的影响是不同的。有趣的是，有三个细胞株对P53介导的细胞凋亡具有抵抗力，其中两个细胞株具有内源性野生型P53等位基因，但在p73β或p63伽马转导后发生了凋亡。转导p73β和p63伽马基因也降低了两种结直肠癌细胞的体内致瘤性。这些结果表明，腺病毒介导的p73β和p63伽马转移是治疗人类癌症的潜在新方法，特别是对于对p53基因治疗耐药的肿瘤。较少

1. Novel p53-target genes : Tumor suppressor p53 is a transcription factor that induces growth arrest and/or apoptosis in response to cellular stress. To identify novel p53-inducible genes, we compared the expression of genes in normal mouse embryo fibroblasts to p53-null cells by cDNA representational difference analysis (RDA). We have identified that expression of endogenous SCN3B (sodium channel subunit beta 3) and OPN (osteopontin) are upregulated in mouse embryonic fibroblasts by DNA damage in a p53-dependent manner. The p53-directed regulation of OPN expression suggests a novel model of p53 participation in immunosurveillance, involving interaction with the host immune system to prevent damaged cells from undergoing malignant transformation. The results presented above also suggest that SCN3B mediates a p53-dependent apoptotic pathway and may be a candidate for gene therapy combined with anticancer drugs.2. Biological functions of the p53 family member genes : p63 and p73 were re … More cently identified as members of the p53 gene family. In contrast to p53 however, p63 and p73 are rarely mutated in human cancers. To determine how p63 and p73 are involved in carcinogenesis and normal development, we attempted to identify target genes that are specifically regulated by p63 and/or p73 but not p53. We identified the JAG1 and JAG2 genes, encoding ligands for the Notch receptors, and the PEDF gene are direct target of p63 and p73. We also found that IL4 receptor alpha is upregulated by p73. These findings show an association between the p53 family genes and Notch signaling and suggest a potential molecular mechanism for the involvement of the p53 family genes in normal development. Our data also suggest that IL-4Ralpha could mediate, in part, certain immune responses and p73-dependent cell death.3. Adenovirus-mediated transfer of the p53 family genes, p73 and p63 induces cell cycle arrest and apoptosis in human cancer cell lines : p53 gene therapy is being tested clinically for the treatment of human cancer, however, some cancer models (in vivo and in vitro) are resistant to p53. To explore the potential use of two p53 homologues, p73 and p63, in cancer gene therapy, we introduced p53, p73 and p63 into colorectal cancer cell lines via adenoviral vectors, and compared their effects on cell growth. Among 10 cell lines tested, six cell lines displayed a similar response following transduction of p53, p73beta or p63gamma ; two lines underwent cell-cycle arrest, three lines exhibited apoptosis and one line showed no-effect following transduction. The effect on cell-cycle progression was variable in the other four cell lines. Interestingly, three cell lines were resistant to p53-mediated apoptosis, including two lines having endogenous wild-type p53 alleles, but underwent apoptosis after transduction of p73beta or p63gamma. Transduction of p73beta and p63gamma also reduced the tumorigenicity of two colorectal cancer cells in vivo. These results suggest that adenovirus-mediated p73beta and p63gamma transfer are potential novel approaches for the treatment of human cancers, particularly for tumors that are resistant to p53 gene therapy. Less