A recombinant cell-permeable p53 fusion protein is selectively stabilized under hypoxia and inhibits tumor cell growth

More than 50% of human tumors contain a mutation in p53. Over 90% of tumors are solid tumors. Solid tumors have low oxygenated regions, called hypoxic regions where the tumor cells are more resistant to radio- and chemo-therapy than their well-oxygenated counterparts. In this study, we constructed a cell-permeable p53 fusion protein with selective stability in the hypoxic region. The fusion protein contained the TAT peptide for transduction across membranes, the oxygen-dependent degradation domain of hypoxia-inducible factor-1alpha and wild-type p53. This protein was effectively delivered into tumor cells where it exerted anticancer activity leading to the inhibition of cancer cell growth in vitro and the reduction of tumor weight in vivo. Hence, the fusion protein can be a novel protein drug for antitumor therapies, especially for hypoxic tumor cells.     

Human p53-p51 (p53-related) fusion protein: a potent BAX transactivator.

We recently discovered human p51, a new gene structurally and functionally related to human p53. This gene encodes two major splicing variants, p51A and p51B, which differ in their carboxyl-terminal structure. However, p51A shows strong transactivation potential, while p51B has only weak potential. To clarify the reason for this difference, we made chimeric gene constructs expressing fusion proteins of p53-p51A and p53-p51B, having an N-terminus of p53 and a C-terminus of p51A or p51B, respectively. In a BAX promoter-luciferase assay using p53-deficient SAOS-2 cells, they exhibited up to 30-fold stronger transactivation potential than p53 and p51A themselves, suggesting that the C-terminus of p51B does not simply serve as a repressor. We obtained similar results with p21WAF1 promoter-reporter plasmids. These chimeras will be valuable tools for gene therapy.     

Characterization of a mutated p53 exhibiting a cell cycle-related nuclear translocation

We studied the p53 expression in the F4NW0 cell line. We found that this mutated p53 has a deletion of eight amino acids, between the conserved domains IV and V. Only one of the two alleles is expressed. It contains a single base mutation, which seems to promote the use of a cryptic splicing acceptor site, resulting in the observed deletion. The protein shows a cell cycle-dependent nuclear translocation: in G(1), it is exclusively cytoplasmic, and during the G(1)/S transition, it translocates into the nucleus. Nevertheless, different antibodies assayed revealed different patterns of localization.     

Detection of serum p53 protein in patients with different gastrointestinal cancers

Overexpression of p53 has been found in many types of human malignancy. The present study aimed to detect preoperative serum p53 among 158 patients with different gastrointestinal cancers using ELISA technique based on mouse anti-p53 DO-7 monoclonal antibody and anti-p53 rabbit polyclonal antibody. A single band of 53kDa was detected in nuclear protein tissue extracts of selected cancer patients and in 96% of the corresponding sera using Western blot assay. The ELISA technique revealed that the serum p53 was detected in 100% of patients with cholangiocarcinoma, 76% of pancreatic carcinoma, 75% of hepatocellular carcinoma, 70% of colon cancer, 60% of esophagus carcinoma, and 35% of gastric carcinoma. The serum p53 concentrations of the positive patients were highly elevated (P<0.001) compared with healthy individuals. These results suggest that immunodetection of serum p53 could be valuable for post-operative monitoring during follow up in preoperatively positive patients with gastrointestinal cancers.     

Isolation of DNAs that selectively bind a baculovirus produced mutant p53 (Ala 143) protein but not an RRL or WGL produced mutant p53 protein

A PCR-based technique was used to generate a large pool of random sequence double-stranded DNAs. Four DNA sequences that selectively bound in vitro to a mutant p53 143A protein, synthesized in baculovirus infected cells, were characterized. The four DNA sequences all approximated the known consensus sequence for wild-type p53. Wild-type p53 also bound the four DNA sequences. Two other mutant p53 proteins (His 175 or Trp 248) did not bind. The ability of mutant p53 143A protein to bind to DNA is totally dependent on the irt vitro system used to synthesize the p53 protein. Rabbit reticulocyte lysate (RRL) or wheat germ lysate (WGL) produced mutant p53 143A is unable to bind to DNA but does bind to a known protein partner, hdm2, thus these activities can be uncoupled.     

Antibody-mediated transduction of p53 selectively kills cancer cells

Some human cancers are caused by functional defects in p53 that are restored by gene therapy with wild-type p53. To circumvent the use of viral vectors, we reconstituted cancer cell lines with p53 by protein transduction. A fusion protein was produced from cDNA constructed from the Fv fragment of an antibody that penetrates living cells and wild-type p53 (Fv-p53). Fv-p53 penetrated and killed cancer cells that do not express p53. Additionally, Fv-p53 killed cancer cells that were malignant as a result of mutations within p53, nuclear exclusion of p53 and over-expression of MDM2. Non-specific toxicity was excluded by showing that Fv-p53 penetrated but did not kill primary cells and cancer cells unresponsive to p53. Fv fragments alone were not cytotoxic, indicating that killing was due to transduction of p53. Fv-p53 was shown to penetrate cancer cells engrafted in vivo. These results support continued efforts to evaluate the potential efficacy of Fv-p53 for the treatment of certain cancers in vivo.     

The p53-positive phenotype of breast cancers

One hundred and eighty-one breast cancer specimens were analyzed for nuclear p53 staining by immunochemical methods. There were 123 fine-needle cytological specimens and 58 frozen tissue sections of surgical biopsies. The microscopic evaluation of the staining fitted with a 4 group classification. Ninety-one samples (50.6%) were devoid of any staining (-), while 42 (23.3%) showed only few stained nuclei (+/-), typically around 1%. Thirty-two (17.8%) samples presented with strong nuclear staining (++) which in practically all cases concerned more than 50% of the nuclei, but a few cases showed staining heterogeneity. A further 17 cases (9.4%) presented with nuclear staining which concerned 10-20% of the cancer cells (+). This four class system was used to compare p53 expression with other prognostic parameters. A strong inverse correlation was observed with steroid hormone receptor content and p53 positivity was highly significantly associated with higher S-phase. All but one of the highly positive cases were aneuploid. Twenty-five percent (29/120) of the aneuploid tumors were strongly stained and a further 10% were considered positive (+). On the other hand, only 5 out of 59 DNA-diploid tumors were considered as + and one ++. The DNA index distribution according to p53 positivity showed peaks of positivity for hypodiploid, triploid and hypertetraploid values. Negative tumors were in all regards similar to those with only few stained nuclei, in particular mean S-phases of 2.8 and 3.3% respectively. Altogether, the typical strong p53 phenotype concerned a DNA-aneuploid tumor with above median S-phase fraction (mean of 7.1%), negative steroid hormone receptors and cytoprognostic index III. The p53 positive cases (+), were frequently steroid hormone receptor positive and had on the average intermediate S-phase fractions (4.3%). The proportion of immunochemical positivity (27% in our series), is compatible with the published frequency of p53 mutations detected in breast cancers, but the differences in the phenotype according to the level of positivity should be further investigated.     

Prevalence of p53 mutations and protein expression in esophageal cancers in southern Thailand

To investigate p53 alterations in esophageal squamous-cell carcinomas of patients in the high-risk area of southern Thailand, 72 paraffin-embedded samples were analyzed immunohistochemically for p53 protein expression and 16 frozen samples for p53 mutational status. Forty-two of the 72 tumors (58.3%) showed p53 protein accumulation in the nuclei of tumor cells. Expression of p53 in tumors was not significantly correlated with gender, histological grading, depth of invasion, node involvement, smoking or alcohol consumption. Analysis of the p53 gene in a sub-set of 16 tumors showed mis-sense mutations in 7 out of 11 p53-positive and 1 out of 5 p53-negative tumors. The p53 mutational spectrum was 50% transitions (3 C-to-T and 1 G-to-A, all occurring at CpG dinucleotide sites) and 50% transversions (one each, C-to-G, G-to-T, T-to-G, and T-to-A). Our findings support the hypothesis that alterations of p53 are involved in the carcinogenesis of most squamous-cell carcinomas of the esophagus, irrespective of the population and the factors responsible for carcinogenesis. The mutation profile of the p53 gene might indicate etiologic contributions of different mutagen exposures in patients from high-risk areas of southern Thailand. Int. J. Cancer 72:23–26, 1997. © 1997 Wiley-Liss Inc.     

Targeted cytotoxic somatostatin analogue AN-238 inhibits somatostatin receptor-positive experimental colon cancers independently of their p53 status

The resistance of advanced colorectal cancers to therapy is often related to mutations in the p53 tumor suppressor gene. Because somatostatin (SRIF) receptors (ssts) are present in colorectal carcinomas, the treatment with targeted cytotoxic SRIF analogue AN-238, consisting of 2-pyrrolinodoxorubicin (AN-201) linked to octapeptide SRIF carrier RC-121, may overcome this resistance by producing a higher concentration of the cytotoxic agent in the tumors. Four colon cancer cell lines, HCT-116 and LoVo expressing wild-type p53, and HCT-15 and HT-29 with mutated p53, were investigated. HCT-116, HCT-15, and HT-29, but not LoVo possess functional ssts. We analyzed changes in p53, p21, and proliferating cell nuclear antigen (PCNA) concentrations in these cells in vitro by immunoblotting after exposure to AN-238, its radical AN-201, or doxorubicin (DOX). Equitoxic doses of AN-238, AN-201, or DOX affected p53, p21, and PCNA differently. Analysis of the p21:p53 ratios revealed that DOX increased p53 levels, but most of p53 was mutated and inactive, whereas AN-238 produced smaller changes in p53 concentrations but enhanced its activity. In HCT-15 cells, PCNA:p21 ratios, which are indicators of proliferation and repair processes, remained unchanged after exposure to AN-238 but were increased by DOX. In vivo studies in nude mice demonstrated that AN-238, AN-201, and DOX were equally effective on HCT-116 tumors that express wild-type p53. However, AN-238 also inhibited the growth of HCT-15 and HT-29 cancers that express mutant p53, whereas AN-201 and DOX showed no effect. None of the compounds could suppress the proliferation of LoVo tumors that lack functional ssts. In conclusion, cytotoxic SRIF analogue AN-238 inhibits the growth of experimental colon cancers that express ssts, regardless of their p53 status.     

Canarypox virus expressing wild type p53 for gene therapy in murine tumors mutated in p53

The antitumor activity of a recombinant canarypox virus expressing wild type murine p53 (ALVAC-p53) was investigated in two murine syngeneic tumors harboring an endogenous p53 mutation (CMS4 and TS/A). Direct intratumor injections of ALVAC-p53 in CMS4 pre-established subcutaneous tumors induced total tumor regression in 66% of mice. Furthermore, 100% of the cured mice was protected against a contralateral subsequent challenge with the parental tumor cells. The intravenous treatment of experimental lung metastasis by ALVAC-p53 also induced significant tumor growth inhibition in both models. The antitumor effect of ALVAC-p53 was only observed in immunocompetent animals and was associated with the generation of a specific antitumor immune response. ALVAC-p53 induced the expression of a functional p53 wild type protein as demonstrated by up-regulation of p21waf1 and induction of apoptosis. A vaccine strategy using intravenous or subcutaneous ALVAC-p53/NYVAC-p53 prime boost protocol failed to induce CTL against p53 wild type used as target tumor antigen, and failed to protect mice against challenge with the mutated tumor cells. The mechanism of the curative and protective effects observed after direct intratumor injections results from the induction of a specific antitumor response directed against other antigens than p53. Our results suggest that the local induction of tumor apoptosis, combined with the adjuvant effect of ALVAC vector, enhances the immunogenicity of the intratumor environment and allows induction of specific antitumor immune response.     

凋亡和p53突变对非小细胞肺癌预后的影响

目的:研究细胞凋亡及凋亡相关蛋白p53在肺癌组织中的表达水平,及其对预后的影响。方法:应用DNA缺口末端标记技术和免疫组化方法检测111例肺癌患者组织中细胞凋亡和突变型p53蛋白表达水平。结果:111例肺癌组织中,细胞凋亡数量≥1%的病例有47·7%(53/111),突变型p53蛋白阳性表达率为40·5%(45/111);单因素分析肺癌患者预后的影响因素有凋亡(χ2=6·77,P<0·01)、突变型p53(χ2=6·56,P<0·05)、淋巴结转移(χ2=16·31,P<0·01)和TNM分期(χ2=15·86,P<0·01);COX模型多因素分析显示,肿瘤大小(χ2=4·12,P<0·05)、淋巴结转移(χ2=12·94,P<0·01)和细胞凋亡(χ2=4·61,P<0·05)是肺癌患者的预后不良因素。结论:凋亡及凋亡相关蛋白p53影响肺癌患者的生物学行为及预后。     

Novel 1p tumour suppressor Dnmt1-associated protein 1 regulates MYCN/ataxia telangiectasia mutated/p53 pathway

Neuroblastoma (NB) is a paediatric solid tumour which originates from sympathetic nervous tissues. Deletions in chromosome 1p are frequently found in unfavourable NBs and are correlated with v-myc avian myelocytomatosis viral oncogene neuroblastoma derived homolog (MYCN) amplification; however, it remains to be elucidated how the 1p loss contributes to MYCN-related oncogenic processes in NB. In this study, we identified the role of Dnmt1-associated protein 1 (DMAP1), coded on chromosome 1p34, in the processes.We studied the expression and function of DMAP1 in NB and found that low-level expression of DMAP1 related to poor prognosis, unfavourable histology and 1p Loss of heterozygosity (LOH) of primary NB samples. Intriguingly, DMAP1 induced ataxia telangiectasia mutated (ATM) phosphorylation and focus formation in the presence of a DNA damage reagent, doxorubicin. By DMAP1 expression in NB and fibroblasts, p53 was activated in an ATM-dependent manner and p53-downstream pro-apoptotic Bcl-2 family molecules were induced at the mRNA level, resulting in p53-induced apoptotic death. BAX and p21^Cip1/Waf1 promoter activity dependent on p53 was clearly up-regulated by DMAP1. Further, MYCN transduction in MYCN single-copy NB cells accelerated doxorubicin (Doxo)-induced apoptotic cell death; MYCN is implicated in DMAP1 protein stabilisation and ATM phosphorylation in these situations. DMAP1 knockdown attenuated MYCN-dependent ATM phosphorylation and NB cell apoptosis. Together, DMAP1 appears to be a new candidate for a 1p tumour suppressor and its reduction contributes to NB tumourigenesis via inhibition of MYCN-related ATM/p53 pathway activation.     

Germline p53 mutation in a patient with multiple primary cancers

We report a case of multiple primary cancers having a germline missense mutation of the p53 gene. The patient was a Japanese female and had a history of five different types of cancers. PCR/direct sequencing analysis revealed the presence of a nucleotide substitution, AGC (Ser) to AGG (Arg), at codon 106 of the p53 gene in DNA from non-cancerous breast tissue. This is the first case of germline p53 mutation at codon 106, and could contribute to establishing correlations between the types and locations of germline p53 mutations and their phenotypical consequences.