p53 mutations increase resistance to ionizing radiation.

Mouse and human tumors of diverse origin frequently have somatically acquired mutations or rearrangements of the p53 gene, or they have lost one or both copies of the gene. Although wild-type p53 protein is believed to function as a tumor-suppressor gene, it is as yet unclear how p53 mutations lead to neoplastic development. Wild-type p53 has been postulated to play a role in DNA repair, suggesting that expression of mutant forms of p53 might alter cellular resistance to the DNA damage caused by gamma radiation. Moreover, p53 is thought to function as a cell cycle checkpoint after irradiation, also suggesting that mutant p53 might change the cellular proliferative response to radiation. We have used transgenic mice expressing one of two mutant alleles of p53 to test this prediction. Our results show that expression of both mutant variants of the mouse p53 gene significantly increases the cellular resistance of a variety of hematopoietic cell lineages to gamma radiation. These observations provide direct evidence that p53 mutations affect the cellular response to DNA damage, either by increasing DNA repair processes or, possibly, by increasing cellular tolerance to DNA damage. The association of p53 mutations with increased radioresistance suggests possible mechanisms through which alterations in the p53 gene might lead to oncogenic transformation.     

Immune response to p53 is dependent upon p53/HSP70 complexes in breast cancers.

Overexpression of the p53 protein, resulting from gene mutations that increase protein stability, has been detected in greater than 25% of primary human breast cancers. In addition, approximately 10% of breast cancer patients have circulating antibodies to the p53 protein. In this study, the anti-p53 humoral response is correlated with the presence and type of mutant p53 protein expressed in the tumor. In a series of 60 breast cancer patients, 0 of 30 tumors with normal, low-level p53 expression induced anti-p53 antibodies, whereas 7 (23%) of 30 tumors with p53 overexpression elicited a specific anti-p53 antibody response. These 7 patients had anti-p53 antibodies that recognized wild-type p53 and a variety of mutant p53 proteins. A comparison of p53 mutations revealed that antibody-negative tumors had mutations exclusively in exons 7 and 8, whereas antibody-positive tumors had mutations primarily in exons 5 and 6. Moreover, all antibody-eliciting tumors contained complexes between p53 and a 70-kDa heat shock protein, whereas none of the antibody-negative tumors contained this complex. This study implicates a 70-kDa heat shock protein in the antigenic presentation of p53.     

p53 mutations in colorectal cancer.

Immunohistological staining of primary colorectal carcinomas with antibodies specific to p53 demonstrated gross overexpression of the protein in approximately 50% of the malignant tumors examined. Benign adenomas were all negative for p53 overexpression. To determine the molecular basis for this overexpression we examined p53 protein expression in 10 colorectal cancer cell lines. Six of the cell lines expressed high levels of p53 in ELISA, cell-staining, and immunoprecipitation studies. Direct sequencing and chemical-mismatch-cleavage analysis of p53 cDNA by using the polymerase chain reaction in these cell lines showed that all cell lines that expressed high levels of p53 were synthesizing mRNAs that encoded mutant p53 proteins. In two of those four cell lines where p53 expression was lower, point mutations were still detected. Thus, we conclude that overexpression of p53 is synonymous with mutation, but some mutations would not be detected by a simple immunohistochemical analysis. Mutation of the p53 gene is one of the commonest genetic changes in the development of human colorectal cancer.     

Genetic basis for p53 overexpression in human breast cancer.

Overexpression of an activated form of the p53 protein may be involved in neoplastic transformation. We found widespread overexpression of p53 by immunohistochemical staining in 11 (22%) of 49 primary invasive human breast cancers. Northern blot analysis showed that this overexpression was not due to an increase in the steady-state level of p53 mRNA. The p53 gene was directly sequenced in 7 of these tumors with elevated levels of the protein and, in each case, a mutation that altered the coding sequence for p53 was found in a highly conserved region of the gene. Whereas 4 of these tumors contained only a mutant p53 allele, the other 3 tumors exhibited coding sequences from both a mutant and a wild-type allele. p53 mutations have previously been correlated with allelic loss of part of chromosome 17p that contains the p53 locus. Examination of all 49 breast tumors revealed a 61% frequency of deletion at or near the p53 locus. However, the presence of allelic deletion did not correlate with overexpression of the protein. Six tumors that were deleted but did not express high levels of the protein were sequenced and all retained a wild-type p53 allele. In this series of human breast cancers, overexpression of the p53 protein, not allelic loss on chromosome 17p, was always associated with mutation of the p53 gene.     

加载野生型p53基因鼠树突细胞的抗肿瘤作用

目的 观察加载了野生型p53基因的树突细胞(DC)对不同位点p53基因突变肿瘤得庖咧瘟谱饔?方法通过锥虫蓝染色、同种异体混合白细胞反应及流式细胞仪检测DC细胞表面分子,评估腺病毒(Ad)-p53感染DC是否影响DC的免疫功能.以Ad或转导了野生型p53基因的Ad分别感染骨髓De(Ad-DC和Ad-p53-DC)后,静脉注射免疫C57BL/6小鼠各5只,分离脾细胞,采用标准6 h51 Cr释放试验测定其诱导不同肿瘤细胞系(MethA、D459和P815)细胞毒性T淋巴细胞(CTL)的杀伤活性;效应细胞(Ad-p53-DC免疫后的小鼠脾细胞)和靶细胞(Ad-p53-P815和D459)孵育时分别加入抗CD4抗体或抗CD8抗体,观察CTL的活性变化.使用MethA和D459肿瘤细胞系得到不同的荷瘤鼠,于肿瘤形成前后分别使用Ad-p53-DC免疫,Ad-DC对照,当实体瘤三维直径之和＞20 cm时处死小鼠,用生存曲线评估Ad-p53-DC免疫的预防或治疗作用.结果 (1)Ad-p53-DC免疫诱导的抗Ad-p53-P815、D459和MethA的CTL反应(效应细胞:靶细胞=50:1)分别为(27.8±3.4)%、(23.5±2.7)%及(58.3±9.2)%,与Ad-DC免疫诱导的反应[(9.3±1.8)%、(4.6±1.0)%及(23.5 ±3.7)%]相比,差异有统计学意义(td值分别为5.79、3.68、5.02,均P＜0.05).Ad-p53-DC免疫小鼠T淋巴细胞与靶细胞Ad-p53-P815或D459的CTL活性,抗CD4组[(59.8 ±4.6)%、(18.9±2.4)%]与无抗体组[(64.4±6.3)%、(22.2±3.0)%]相比,差异无统计学意义(td值分别为0.84、0.91,均P＞0.05),而抗CD8组[(26.7±2.8)%、(6.1±1.2)%]差异有统计学意义(td值分别为9.03、7.67,均P＜0.05).抗CD8组与抗CD4组比较,差异有统计学意义(td值分别为8.79、9.18,均P＜0.05).(2)Ad-p53-DC和Ad-DC静脉注射2次免疫小鼠后,分别以D459细胞或MethA肉瘤细胞荷瘤20只小鼠.在Ad-p53-DC免疫组分别有14只和16只小鼠肿瘤的生长得到完全抑制,与Ad-DC免疫组比较差异有统计学意义(x2值分别为6.72、5.86,P＜0.05).皮下接种小鼠D459后,Ad-p53-DC免疫治疗组的小鼠肿瘤生长速度比Ad-DC组延缓2周左右,二组比较差异有统计学意义(x2 值为9.48,P＜0.05).结论 Ad-p53-DC可诱导抗MethA、P815和D459靶细胞的由CD8+T淋巴细胞介导的CTL反应,并抑制鼠体内肿瘤细胞的形成和生长.     

Germ-line mutations of the p53 tumor suppressor gene in patients with high risk for cancer inactivate the p53 protein.

Germ-line mutations in the p53 tumor suppressor gene have been observed in patients with Li-Fraumeni syndrome, brain tumors, second malignancies, and breast cancers. It is unclear whether all of these mutations have inactivated p53 and thereby provide an increased risk for cancer. Therefore, it is necessary to establish the biological significance of these germ-line mutations by the functional and structural analysis of the resulting mutant p53 proteins. We analyzed the ability of seven germ-line mutant proteins observed in patients with Li-Fraumeni syndrome, second primary neoplasms, or familial breast cancer to block the growth of malignant cells and compared the structural properties of the mutant proteins to that of the wild-type protein. Six of seven missense mutations disrupted the growth inhibitory properties and structure of the wild-type protein. One germ-line mutation retained the features of the wild-type p53. Genetic analysis of the breast cancer family in which this mutation was observed indicated that this germ-line mutation was not associated with the development of cancer. These results demonstrate that germ-line p53 mutations observed in patients with Li-Fraumeni syndrome and with second malignancies have inactivated the p53 tumor suppressor gene. The inability of the germ-line p53 mutants to block the growth of malignant cells can explain why patients with these germ-line mutations have an increased risk for cancer. The observation of a functionally silent germ-line mutation indicates that, before associating a germ-line tumor suppressor gene mutation with cancer risk, it is prudent to consider its functional significance.     

Conformational effects of environmentally induced, cancer-related mutations in the p53 protein.

The tumor suppressor gene p53 has been identified as the most frequent target of genetic alterations in human cancers. A considerable number of environmentally induced, cancer-related p53 mutations in human tumors have been found in a highly conserved proline-rich sequence of the p53 protein encompassed by amino acid residues 147-158. Using conformational energy analysis based on ECEPP (Empirical Conformational Energy for Peptides Program), we have determined the low-energy three-dimensional structures for this dodecapeptide sequence for the human wild-type p53 protein and three environmentally induced, cancer-related mutant p53 proteins with His-151, Ser-152, and Val-154, respectively. The results suggest that the wild-type sequence adopts a well-defined low-energy conformation and that the mutant peptides adopt well-defined conformations that are distinctly different from the conformation of the wild-type peptide. These results are consistent with experimental conformational studies demonstrating altered detectability of antigenic epitopes in wild-type and mutant p53 proteins. These results suggest that the oncogenic effects of these environmentally induced, cancer-related, mutant p53 proteins may be mediated by distinct local conformational changes in the protein.     

Cytotoxic effect of a non-peptidic small molecular inhibitor of the p53-HDM2 interaction on tumor cells

AIM: To investigate if non-peptidic small molecular inhibitors of the p53-HDM2 interaction could restore p53 function and kill tumor cells. METHODS: A series of non-peptidic small HDM2 inhibitors were designed by computer-aided model and synthesized by chemical method. Syl-155 was one of these inhibitors. Cytotoxic effect of syl-155 on three tumor cell lines with various states of p53, HT1080 (wild-type p53), KYSE510 (mutant p53), MG63 (p53 deficiency) was evaluated by MTT assay, Western blot and flow cytometry. RESULTS: Syl-155 stimulated the accumulation of p53 and p21 protein in HT1080 cells expressing wild-type p53, but not in KYSE510 and MG63 cells. Consequently, syl-155 induced cell cycle arrest and apoptosis in HT1080 cells. CONCLUSION: Non-peptidic small molecular inhibitors of the p53-HDM2 interaction show promise in treatment of tumors expressing wild-type p53.     

Role of AXL in invasion and drug resistance of colon and breast cancer cells and its association with p53 alterations

AIM To characterize AXL receptor tyrosine kinase(AXL)expression in relationship to tumor protein P53(TP53gene,p53 protein)and its role in tumor invasion and response to therapy.METHODS We used 14 cell lines,including 3 isogenic pairs carrying mutant/knockout p53,to gain insight into the relationship between AXL and TP53.These included HCT116,HCT116.p53 mutant,RKO,and RKO.p53-/-lines(all from colon cancers)as well as breast cancer cell lines MCF7 and 1001(MCF7-p53 mutant clone).He La cell line was used as a positive control for epithelial to mesenchymal transition(EMT).AXL expression was determined by Western blotting using rabbit monoclonal antibody clone C89E7.AXL si RNA silencing was performed and followed by collagen invasion assay.Cell viability analysis using the sulforhodamine B assay and the invasion assay were performed after exposure to chemotherapeutic agents(doxorubicin for breast cancer cells;5FU or irinotecan for colon cancer cells).RESULTS We showed that the introduction of p53 mutations or knockout increased expression levels of AXL in isogenic cells compared to the matching p53 wild-type parental cells.Overall,we found a trend for correlation between the potential EMT candidate AXL,p53 alterations,and EMT markers in colorectal and breast cancers.The expression of AXL in RKO cells,a rare colon cancer cell line with inactive Wnt signaling,suggests that the AXL oncogene might provide an alternative genetic pathway for colorectal carcinogenesis in the absence of Wnt signaling activation and TP53 mutation.AXL silencing in the TP53 mutant isogenic cell lines 1001,HCT116.p53 mutant and RKO.P53-/-was95%efficient and the silenced cells were less invasive compared to the parental TP53 wild-type cells.AXL silencing showed a subtle trend to restore colon cancer cell sensitivity to5FU or irinotecan.Importantly,AXL expressing cells developed more invasive potential after exposure to chemotherapy compared to the AXL-silenced cells.CONCLUSION AXL is influenced by p53 status and could cause the emergence of aggressive clones after exposure to chemotherapy.These findings could have applications in cancer management.     

Wild-type p53 can inhibit oncogene-mediated focus formation.

Mutant forms of the p53 cellular tumor antigen elicit neoplastic transformation in vitro. Recent evidence indicated that loss of normal p53 expression is a frequent event in certain types of tumors, raising the possibility that such loss provides transformed cells with a selective growth advantage. Thus, it was conceivable that the mutants might contribute to transformation by abrogating normal p53 function. We therefore studied the effect of plasmids encoding wild-type (wt) p53 on the ability of primary rat embryo fibroblasts to be transformed by a combination of mutant p53 and ras. It was found that wt p53 plasmids indeed caused a marked reduction in the number of transformed foci. Furthermore, wt p53 plasmids also suppressed the induction of transformed foci by combinations of bona fide oncogenes, such as myc plus ras or adenovirus E1A plus ras. On the other hand, plasmids carrying mutations in the p53 coding region totally failed to inhibit oncogene-mediated focus induction and often even slightly stimulated it. Hence, such mutations completely abolished the activity of wt p53 that is responsible for the "suppressor" effect. The latter fact is of special interest, since similar mutations in p53 are often observed in human and rodent tumors. The inhibitory effect of p53 was most pronounced when early-passage cells were used as targets, whereas established cell lines were less sensitive. These data support the notions that wt p53 expression may be restrictive to neoplastic progression and that p53 inactivation may play a crucial role in tumorigenesis.     

Regional analysis of p53 mutations in rheumatoid arthritis synovium

The p53 tumor suppressor protein plays a central role in cell cycle regulation, DNA repair, and apoptosis. Recent studies indicate that DNA damage and somatic mutations in the p53 gene can occur because of genotoxic stress in many tissues, including the skin, colon, and synovium. Although somatic mutations in the p53 gene have been demonstrated in rheumatoid arthritis (RA) synovial tissue and synoviocytes, no information is available on the location or extent of p53 mutations. Using microdissected RA synovial tissue sections, we observed abundant p53 transition mutations, which are characteristic DNA damage caused by oxidative stress. p53 mutations, as well as p53 mRNA expression, were located mainly in the synovial intimal lining rather than the sublining (P < 0.01). Clusters of p53 mutant subclones were observed in some microdissected regions, suggesting oligoclonal expansion. Because IL-6 gene expression is regulated by wild-type p53, IL-6 mRNA expression in microdissected tissues was quantified by using real-time PCR. The regions with high rates of p53 mutations contained significantly greater amounts of IL-6 mRNA compared with the low mutation samples (P < 0.02). The microdissection findings suggest that p53 mutations are induced in RA synovial tissues by inflammatory oxidative stress. This process, as in sun-exposed skin and inflamed colonic epithelium, provides some of the mutant clones with a selective growth advantage. A relatively low percentage of cells containing p53 mutations can potentially affect neighboring cells and enhance inflammation through the elaboration of proinflammatory cytokines.     

Effects of exogenous p53 transduction in thyroid tumor cells with different p53 status

Recovery of p53 function in undifferentiated thyroid carcinoma cells carrying an altered p53 gene is able to modify cell tumorigenic properties. It is not known whether such an effect may also be achieved in thyroid cancer cells expressing wild-type p53, as in the majority of differentiated thyroid carcinomas. Effects of p53 transduction in a thyroid carcinoma cell line (FRO) exhibiting a wild-type endogenous p53 gene, in comparison to a cell line (WRO) exhibiting mutant p53, were investigated by using an inducible chimeric construct containing human p53 complementary DNA fused to the ligand binding domain of the estrogen receptor (p53ER). FRO cells were unaffected by exogenous p53 expression in terms of both proliferation and viability. On the contrary, p53 reexpression in WRO cells containing hemizygous mutated p53 allele caused a strong growth inhibition due to cell accumulation in the G1 phase of the cell cycle. In addition, exogenous p53 did not influence FRO cell behavior in response to TSH treatment or modify cell resistance to the chemotherapeutic agent, doxorubicin. Our results indicate that exogenous expression of wild-type p53 affects thyroid tumorigenic properties only in cells carrying an altered p53, whereas it is ineffective in cells expressing wild-type p53 activity. Therefore, the endogenous p53 status seems to be a major determinant for the effectiveness of a p53-based gene therapy for thyroid cancer.     

Induction of apoptosis by wild-type p53 in a human colon tumor-derived cell line.

A wild-type p53 gene under control of the metallothionein MT-1 promoter was stably transfected into human colon tumor-derived cell line EB. Repeated inductions of the metallothionein wild-type p53 gene with zinc chloride results in progressive detachment of wild-type p53 cells grown on culture dishes. Examination at both the light and electron microscopic level revealed that cells expressing wild-type p53 developed morphological features of apoptosis. DNA from both attached and detached cells was degraded into a ladder of nucleosomal-sized fragments. Expression of wild-type p53 inhibited colony formation in soft agar and tumor formation in nude mice. Furthermore, established tumors in nude mice underwent regression if wild-type p53 expression was subsequently induced. Regressing tumors showed histological features of apoptosis. Thus, regression of these tumors was the result of apoptosis occurring in vivo. Apoptosis may be a normal part of the terminal differentiation program of colonic epithelial cells. Our results suggest that wild-type p53 could play a critical role in this process.     

Adenovirus-mediated tumor suppressor p53 gene therapy for anaplastic thyroid carcinoma in vitro and in vivo

The present study was designed to evaluate the therapeutic efficacy of adenovirus-mediated wild-type (wt) tumor suppressor p53 expression in four human thyroid carcinoma cell lines harboring p53 mutations (ARO, FRO, NPA, and WRO) and normal human thyroid follicular cells with wt-p53 in vitro and in vivo. In vitro infection of replication-deficient recombinant adenovirus vector expressing wt-p53 led to a dose-dependent cell killing in both normal and carcinoma cells. In contrast, adenovirus expressing Escherichia coli beta-galactosidase showed little effect. The sensitivity to p53-mediated cell killing varied among the cells used. It was, at least partly, dependent on their adenovirus infectivity in carcinoma cells, whereas normal thyroid cells were relatively resistant to p53-mediated cell death despite its highest adenovirus infectivity. The mechanism of cell killing by wt-p53 was shown, by flow cytometric analysis, to be apoptosis. Furthermore, wt-p53 expression renders two out of four carcinoma cell lines (FRO and NPA) more sensitive to doxorubicin and one (FRO) to 5-fluorouracil, independent of treatment schedule. In vivo experiments, using FRO and NPA cells, showed that growth of sc tumors in nude mice was nearly completely inhibited by direct injection of adenovirus expressing wt-p53 [1 x 10(9) plaque-forming units/tumor]. This effect was augmented by its combination with doxorubicin treatment (4 mg/kg, thrice a week), which led to tumor regression. Our results therefore indicate that adenovirus-mediated wt-p53 gene introduction seems to be a potential clinical utility in gene therapy for anaplastic thyroid carcinomas, particularly when combined with chemotherapy.