TP53基因在特定血液病和淋巴瘤中的研究进展

TP53基因是重要的抑癌基因之一,其编码的蛋白——肿瘤抑制蛋白p53能够使许多基因保持其稳定性,并调节细胞的生长、分化、衰老,避免疾病产生,被称为“基因守护者”。当TP53基因缺失、突变和调节紊乱时,将直接影响p53蛋白的功能和活性,从而导致很多肿瘤的发生;除此之外TP53的基因状态也成为判断淋巴瘤和血液病预后的重要指标。本文通过综述TP53基因缺失和突变在不同血液病和淋巴瘤中的意义,使人们对TP53基因与血液肿瘤和淋巴瘤的关系有更清晰的认识。     

鼻咽癌中p73蛋白表达与细胞凋亡关系

p73基因是抑癌基因p53基因家族的一个新成员,一般认为它能以p53同样的方式激活p53的靶基因,抑制细胞生长,诱导凋亡[1].本文应用免疫组化方法和脱氧核糖核酸末端转移酶介导的缺口末端标记(TdT-mediated dUTP nick end labeling,TUNEL)技术检测鼻咽癌中p73蛋白表达和细胞凋亡的情况,旨在探讨p73基因在鼻咽癌发生发展中的作用以及p73蛋白表达与细胞凋亡的相互关系.     

p73基因与肿瘤

癌基因的激活和抑癌基因的失活是人类恶性肿瘤发生和发展的重要原因。p53基因是与人类肿瘤相关性最高的基因,近半数的恶性肿瘤与p53基因的突变有关,而p73基因是1997年发现的p53基因家族的一个成员,近年来对其结构、功能、分布和表达情况都有了深入的研究。我们就p73基因的研究现状以及其在人类肿瘤中的表达情况作一综述。p73基因定位于1p36.33,由13个外显子和12个内含子组成,表达相对分子质量为73×103的蛋白,在结构上与p53蛋白有同源性。p73过表达时能抑制细胞生长和诱导细胞凋亡,但是病毒原癌蛋白却与p73没有相互作用。C-Ab1激酶可以活化p73基因并参与凋亡反应。p73基因敲除的小鼠没有肿瘤易患现象发生,但却有严重的发育异常。p73基因在神经母细胞瘤中不常发生突变,在肺癌、食管癌、肝癌、卵巢癌、乳腺癌表达增高,在淋巴瘤和某些白血病表达降低。与p53基因有明显的不同,p73基因有自己独特的功能。对于野生型p73基因在多种人类肿瘤中过表达的一种解释是,p73基因的过表达可能是一种p53基因失活的代偿反应,虽然这种作用可能无法完全替代p53基因的作用。但是目前研究已经证实p73基因很少突变,而且在肿瘤组织中存在异常表达,增加其表达可能诱导肿瘤细胞的凋亡,并且在p53基因突变时起抑制肿瘤细胞增殖的作用。因此增强p73基因表达也许是恶性肿瘤治疗的一种新方法。     

p73基因与乳腺癌关系研究进展

p73基因是新近发现的p53基因家族成员之一,其编码的蛋白在结构和功能上与p53基因编码蛋白相似,因此人们认为它是一个候选的抑癌基因。     

p73基因与消化道肿瘤关系的研究进展

p73基因是肿瘤抑制基因p53家族的新成员,其在编码蛋白的结构、功能及表达特征方面与p53有很多相似之处,但在其他方面有非常显著的差异。为提高对p73基因研究的认识,以及为肿瘤冶疗提供新基因的靶点,现就p73基因与消化系统肿瘤的发生、发展、预后及表达作一综述。一、p73基因特征1997年Kaghad等[1]利用对用于胰岛素信号中介体(IRS-1)结构域的简并寡聚核苷酸探针对cos细胞cDNA文库进行杂交筛选时,意外地发现一个假阳性cDNA克隆。其编码序列与p53基因有高度同源性,编码分子量73×103的蛋白,被命名为p73基因,定位于1号染色体短臂(1P36)。其…     

p73基因与人类肿瘤的研究进展

p53基因家族新成员p73与其同源体p53在结构和功能上都具有高度相似性。p73基因过表达能够激活p53的靶基因从而诱导细胞凋亡,也能对异常的细胞增殖和一些DNA损伤事件产生反应性活化,同时因为p73在1p36的特殊定位,研究者认为p73基因或许像p53一样是一个肿瘤抑制基因。但是,p73基因敲除鼠并不发生自发性肿瘤,肿瘤中极少发现p73基因的突变,N末端转录活化区丢失的异构体ΔNp73具有与全长p73基因相反的功能,ΔTA p73更象一个癌基因起着促进肿瘤生长的作用。就p73及其异构体ΔTA p73在人类肿瘤中的矛盾表现及近期研究进展予以综述。     

非小细胞肺癌组织p53基因家族成员的不同表达及意义

目的探讨p53基因家族成员p53、p63和p73在非小细胞肺癌(NSCLC)中的不同表达及其临床意义.方法利用免疫组化S-P法在60例NSCLC和7例正常肺组织中检测p53、p63和p73蛋白的表达.结果在NSCLC中,p53、p63和p73蛋白的阳性表达率分别为61.67%(37/60)、80.00%(48/60)和73.33%(44/60);与正常肺组织相比,p53、p63和p73蛋白阳性表达率的差异均有显著性(P＜0.05).p53蛋白表达与肺癌细胞分化程度有密切关系(P=0.023),而与组织学类型、淋巴结转移和临床分期均无明显关系(P＞0.05).p63蛋白表达与肺癌组织学类型(P=0.001)和淋巴结转移(P=0.028)有密切关系,而与细胞分化程度和临床分期无明显关系(P＞0.05).p73蛋白表达与肺癌的临床病理特征均无明显关系(P＞0.05).在NSCLC中,p63和p73蛋白表达之间呈显著正相关(P=0.000 1),p73与p53蛋白表达之间无显著相关性(P＞0.05).结论p53基因家族可能与NSCLC的发生发展有关.p63和p73蛋白有不同于p53蛋白的生物学功能,二者可能均起癌基因的作用.     

p73基因与人类肿瘤的研究进展

p53基因家族新成员p73与其同源体p53在结构和功能上都具有高度相似性。p73基因过表达能够激活p53的靶基因从而诱导细胞凋亡．也能对异常的细胞增殖和一些DNA损伤事件产生反应性活化，同时因为p73在1p36的特殊定位，研究者认为p73基因或许像p53一样是一个肿瘤抑制基因。但是．p73基因敲除鼠并不发生自发性肿瘤，肿瘤中极少发现p73基因的突变，N末端转录活化区丢失的异构体△Np73具有与全长p73基因相反的功能，△TA-p73更象一个癌基因起着促进肿瘤生长的作用。就p73及其异构体△TA-p73在人类肿瘤中的矛盾表现及近期研究进展予以综述。     

p53基因网络的研究进展

肿瘤抑制基因p53与其上、下游功能相关基因组成了一个复杂的基因网络。p53基因位于人染色体17q13．1区带,编码的野生型p53蛋白包含N—末端的转录激活结构域、DNA结合结构域、四聚体化结构域和C—末端调节域。p73、p5l、p63等基因由于在结构上与p53基因具有同源性,因而被归为p53基因家族。p53是联系不同遗传应急和细胞应答的中间环节,离子辐射、化疗药物及异常的细胞生长信号均能刺激p53基因表达。p53表达升高后,可通过p53-mdm2、p14^ARF—mdm2环路对p53表达水平进行精确调节,p53功能的发挥还同时需要p33^MG1b基因的协同作用。磷酸化和乙酰化是细胞内调节p53活性功能的主要途径。p53可以调控下游多种基因表达,其功能主要表现在阻滞细胞周期、促进细胞凋亡、维持基因组稳定性和抑制肿瘤血管生成四个方面。认识p53基因网络的功能将有助于理解p53及其相关基因间的具体作用机制。     

p73基因与乳腺癌关系的研究进展

p73基因是新近发现的基因,其结构和功能与抑癌基因p53有高度同源性,并定位于染色体上特殊区域,可能是新的抑癌基因.本文就p73基因特别是其表达两种功能不同而又密切相关的蛋白质即TAp73和DNp73的结构和功能以及p73基因与乳腺癌发生发展中的作用作一综述.     

TP53 mutations and molecular epidemiology

Tumor suppressor p53 protein is activated by a variety of cellular stresses through several pathways and transactivates its downstream genes, including regulators of cell cycle, apoptosis and DNA repair. The loss of p53 function by TP53 gene mutations therefore fails to activate these genes and is thought to be a critical cause of carcinogenesis and/or tumor progression. TP53 is one of the most frequently mutated genes in human cancer. TP53 mutations are found in about 50% of human cancers, although the frequency of TP53 mutations differs among tumor types. However, the degree of functional disorder of mutant p53 varies according to the type of TP53 mutation. And the effects of p53 on cancer formation and/or progression are influenced by the degree of p53 dysfunction. So it is important to analyze the effects of TP53 mutations carefully according to the oncogenicity of each mutation from the molecular epidemiological point of view. Here, together with some cautions needed for analyzing and interpreting the significance of TP53 gene mutations, we present some examples of the identified specific mutation spectrum and the correlation between the prognosis and TP53 mutation in some cancers.     

Mutation analysis of P73 and TP53 in Merkel cell carcinoma

The p73 gene has been mapped to 1p36.33, a region which is frequently deleted in a wide variety of neoplasms including tumours of neuroectodermal origin. The p73 protein shows structural and functional homology to p53. For these reasons, p73 was considered as a positional and functional candidate tumour suppressor gene. Thus far, mutation analysis has provided no evidence for involvement of p73 in oligodendrogliomas, lung carcinoma, oesophageal carcinoma, prostatic carcinoma and hepatocellular carcinoma. In neuroblastoma, two mutations have been observed in a series of 140 tumours. In view of the occurrence of 1p deletions in Merkel cell carcinoma (MCC) and the location of p73 we decided to search for mutations in the p73 gene in five MCC cell lines and ten MCC tumours to test potential tumour suppressor function for this gene in MCC. In view of the possible complementary functions of p73 and TP53 we also examined the status of the TP53 gene. Sequence analysis of the entire coding region of the p73 gene revealed previously reported polymorphisms in four MCCs. In one MCC tumour, a mis-sense mutation located in the NH2-terminal transactivation region of the p73 gene was found. These results show that p73, analogous to neuroblastoma, is infrequently mutated in MCC. This is also the first report in which the role of TP53 in MCC has been investigated by sequencing the entire coding region of TP53. TP53 mis-sense mutations and one non-sense mutation were detected in three of 15 examined MCCs, suggesting that TP53 mutations may play a role in the pathogenesis or progression of a subset of MCCs. Moreover, typical UVB induced C to T mutations were found in one MCC cell line thus providing further evidence for sun-exposure in the aetiology of this rare skin cancer.     

Inactivation of the INK4A/ARF locus frequently coexists with TP53 mutations in non-small cell lung cancer

Inactivation of the P16 (INK4A)/retinoblastoma (RB) or TP53 biochemical pathway is frequent event in most human cancers. Recent evidence has shown that P14ARF binds to MDM2 leading to an increased availability of wild type TP53 protein. Functional studies also support a putative tumor suppressor gene function for p14ARF suggesting that p14ARF or p53 inactivation may be functionally equivalent in tumorigenesis. To study the relative contribution of each pathway in tumorigenesis, we analysed and compared alterations of the p16, p14ARF and p53 genes in 38 primary non-small cell lung cancers (NSCLCs) (19 adenocarcinomas and 19 squamous carcinoma). The p16 tumor suppressor gene was inactivated in 22 of 38 (58%) tumors. Twelve of these samples (31%) had homozygous deletions by microsatellite analysis; eight of them (21%) had p16 promoter hypermethylation detected by Methylation Specific PCR (MSP) and the remaining two (5%) harbored a point mutation in exon 2 by sequence analysis. The absence of P16 protein in every case was confirmed by immunohistochemistry. Fourteen of the 22 tumors with p16 inactivation also inactivated the p14ARF gene (12 with homozygous deletions extending into INK4a/ARF and two with exon 2 mutations). Mutations of p53 were found in 18 (47%) of the tumors and nine of them (50%) harbored p14ARF inactivation. Thus, an inverse correlation was not found between p14ARF and p53 genetic alterations (P=0.18; Fisher Exact Test). Our data confirm that the p16 gene is frequently inactivated in NSCLC. Assuming that 9p deletion occurs first, the common occurrence of p53 and p14ARF alterations suggests that p14ARF inactivation is not functionally equivalent to abrogation of the TP53 pathway by p53 mutation.     

TP63 gene in stress response and carcinogenesis: a broader role than expected

The TP63 gene is a member of the TP53 gene family. In contrast with TP53, this gene is not frequently inactivated by mutation in cancer. Initial experiments with disrupted TP63 have allowed specifying p63 protein a role in the regulation of differentiation and morphogenesis in epithelial and mesenchymal tissues. Nevertheless, there is growing evidence that p63 is also involved in oncogenesis through several mechanisms. Indeed, amplification of TP63 is detected in about 25% of squamous cell carcinomas of lung, head and neck and oesophagus. This results in overexpression of a truncated form of p63 (DeltaNp63) that may counteract growth suppression induced by full length p63 (TAp63), as well as by the other family members, p53 and TAp73. Moreover, mice heterozygous for TP63 develop spontaneous tumours. Whereas p53 plays a major role in response to numerous DNA-damaging agents, the involvement of p63 in this process is not well documented. Nevertheless, several groups recently reported that TAp63 can induce cell cycle arrest and apoptosis in DNA-damaged cells, alone or in synergy with chemotherapeutic agents, and thus appears as a chemosensitivity factor. Overall, in addition to non-redundant, specific functions in differentiation and morphogenesis, p63 appears to exert biological functions similar to those of p53 and to take a growing place in oncogenesis and modulation of responses to anti-cancer therapy.