Serum p53 antibodies as early markers of lung cancer.

The p53 alteration is the most common alteration found in human cancer. It usually involves missense mutations that stabilize the p53 protein, which in turn accumulates, reaching levels detectable by immunohistochemistry. We and others have demonstrated that this overexpression of mutant p53 protein can induce a specific humoral response in cancer patients. This result was assessed by the presence of p53 antibodies in sera of patients with various types of cancers, whereas normal populations do not exhibit such antibodies. In lung cancer, the prevalence of p53 antibodies is high (30%) and is correlated with a very high rate of p53 mutations in this cancer (60-70%). We show that these antibodies are always present at the time of diagnosis, but never appear during tumour development, an observation strengthened by the fact that these antibodies are mostly IgG, corresponding to a secondary immune response. These results suggest that the humoral response is an early event and that p53 antibodies can be used as a precocious marker of p53 alteration before clinical manifestation of the disease.

The immune response to p53 in breast cancer patients is directed against immunodominant epitopes unrelated to the mutational hot spot.

Alteration of the p53 gene is the most frequent genetic feature of human cancer and leads to overexpression of the altered protein in the tumor cell nucleus. Two diagnostic procedures are currently available to assess p53 mutations: (a) molecular analysis of the gene sequence; and (b) immunohistochemical analysis of p53 protein accumulation. We now report a third approach, serological analysis. Fifteen % of primary breast cancer patients were found to have circulating antibodies to p53 protein by immunoprecipitation or immunoblotting. We have found a close correlation between the presence of such antibodies and bad prognosis such as high histological grade and the absence of hormone receptors. Furthermore, we found that the B-cell response to p53 protein is induced by two immunodominant regions located at the carboxy and amino termini of the protein, outside the central mutational hot spot region. These findings suggest that serological analysis, combined with molecular and histochemical methods, may be suitable for assessing the state of the p53 gene in cancer patients.

Linear antigenic sites defined by the B-cell response to human p53 are localized predominantly in the amino and carboxy-termini of the protein.

Using a set of overlapping peptides of the human p53 protein, we analysed the epitopes recognized by 18 monoclonal antibodies specific for human p53. We showed that most of these epitopes correspond to linear antigenic determinants which lie predominantly in the amino- or carboxy-terminus of the p53 protein. Using either truncated p53 or the set of human p53 peptides, we directly analysed the sera of animals immunized with human p53. These sera contained antibodies which also recognized the regions corresponding to the extremity of the p53 protein. These p53 regions were similar to those recognized by p53-specific antibodies present in sera of patients with cancer. Preferential recognition of these regions by antibodies specific for non conformational epitopes suggested that these regions are localized at the surface of the p53 protein as unfolded structures.

Mutations in p53 produce a common conformational effect that can be detected with a panel of monoclonal antibodies directed toward the central part of the p53 protein.

Human p53 displays two immunodominant regions localized in the amino and carboxy termini of the protein. Using a truncated p53 (residues 66 to 361), we selected eight new monoclonal antibodies directed to the central part of the protein. We identified the epitopes recognized by seven out of eight antibodies with a set of overlapping peptides. One of these antibodies had an epitope similar to PAb240, whereas the others recognized novel and diverse antigenic determinants. Using a series of 19 p53 mutants, we show that the behavior of several of the new monoclonal antibodies is similar to that of PAb240 despite their various epitope localizations. This suggests that different mutations in the p53 protein induce an overall conformational change that can be detected by various monoclonal antibodies directed toward the central part of the protein.

Regulation of the specific DNA binding activity of Xenopus laevis p53: evidence for conserved regulation through the carboxy-terminus of the protein.

Recombinant human p53 isolated either from E. coli or from insect cells is poorly active for binding to DNA but it can be dramatically stimulated by phosphorylation, antibody binding to the carboxy-terminal negative regulatory domain, short peptides derived from this negative regulatory domain or short single strands of DNA. We report here that Xenopus p53 has a very similar behavior. Using a new set of monoclonal antibodies directed either to the amino- or the carboxy-terminus of Xenopus p53, we demonstrate that the frog protein can be activated by specific carboxy-terminus monoclonal antibodies in order to bind to human p53 DNA response element. In addition, we report that such activation of both humans and frogs protein can also be achieved by small peptides derived from the carboxy-terminus of both p53. Although, the sequence of this region is not conserved in the various p53 species, the presence of conserved basic residues indicates that such activation is charge-dependent. This is confirmed by the finding that small poly-lysine peptides can activate both human and Xenopus p53. In vivo expression of Xenopus p53 indicates that this protein is able to transactivate a wide variety of human p53 response elements as long as the experiments are performed at 32 degrees C since activity at 37 degrees C, a temperature well above the natural temperature of Xenopus, is lost. Finally, we demonstrate that human mdm2 is able to down regulate the transcriptional activity of Xenopus p53.

The cDNA cloning and immunological characterization of hamster p53.

We have cloned and sequenced the p53-encoding cDNA of Syrian hamster. The encoded product is 78% and 75% homologous to human and mouse p53, respectively. Immunoprecipitations of the cDNA-encoded protein by monoclonal antibodies specific for mammalian p53 confirmed the identity of the protein.

Production of human p53 specific monoclonal antibodies and their use in immunohistochemical studies of tumor cells.

We describe the production of 13 new monoclonal antibodies induced by the product of the human p53 tumor suppressor gene. All these monoclonal antibodies recognize human p53 irrespective of the detection technique: ELISA, immunoblot or immunoprecipitation. These antibodies can be divided into four groups according to such criteria as localization of the recognized epitopes and reactivity with p53 originating from other organisms. One monoclonal antibody was successfully used for immunohistochemistry detection of p53 accumulation in breast carcinoma. This novel panel of monoclonal antibodies represents a further tool for the study of the p53 protein.

Analysis of the most representative tumour-derived p53 mutants reveals that changes in protein conformation are not correlated with loss of transactivation or inhibition of cell proliferation.

In an effort to correlate the biological activity of the p53 protein with its conformation, we analysed 14 p53 mutants representative of the most frequently observed protein alterations in human cancers, at codons 175, 248 and 273 (22% of all mutations thus far reported), all three of which contained a CpG dinucleotide. Strikingly, most of the mutants at codons 248 and 273 did not display any change in their conformation, as probed by monoclonal antibodies PAb240 and PAb1620 or by binding to hsp70 protein. For all 14 mutants tested, we found a strict correlation between the transactivation properties of p53, tested either on RGC sequences or using the WAF-1 promoter, and inhibition of cell proliferation. All these mutants showed nuclear localization. Several mutants, present at a low incidence in human tumours, displayed wild-type activity in all our assays, suggesting that the presence of a mutation is not strictly correlated with p53 protein inactivation in tumours. Further analysis of nine thus far undescribed p53 mutants at codon 175 revealed a wild-type or mutant behaviour. All these results suggest that the occurrence of a mutation is dependent on two criteria: (i) the mutability of a given codon, such as those containing a CpG dinucleotide; (ii) the resulting amino acids, eventually leading to synthesis of a p53 conferring a growth advantage on the cell.

Human platelet antigen genotyping using a fluorescent SSCP technique with an automatic sequencer.

The typing of human platelet antigens (HPA) can be useful in many clinical situations such as neonatal alloimmune thrombocytopenia, post-transfusion purpura, and platelet transfusion refractoriness. The fluorescent-based single-strand conformation polymorphism (F-SSCP) technique is a fast and convenient way to perform HPA genotyping. Universal sequences from phage M13 were introduced at both ends of specific PCR-products by using 5'-tailed primers. A short second round of PCR with universal primers coupled to Cy-5 enabled the PCR-products to be fluorescently labelled. F-SSCP was performed by gel electrophoresis on an automated fluorescent DNA analyser. Genotyping of the three major HPA systems carried by the GP IIb-IIIa complex showed the F-SSCP technique to be accurate and reliable. A single gel procedure has been sufficient to detect HPA genetic polymorphisms tested to date. Neither restriction enzyme, radioactive material, nor any other hazardous chemicals such as ethidium bromide were required. This technique enabled us to genotype HPA-1, -3 and -4 alleles easily and to diagnose materno-fetal incompatibility in a rare alloantigenic system. F-SSCP is a promising technique for the detection of new mutations and/or DNA polymorphisms on a large scale.

Regulation of mutant p53 temperature-sensitive DNA binding.

We have examined in detail the DNA binding properties of several immunopurified tumor-derived mutant p53 proteins (Val-143 --> Ala, Arg-175 --> His, Arg-248 --> Trp, Arg-249 --> Ser, and Arg-273 --> His). While all mutants were defective for binding to DNA at 37 ;C, each bound specifically to several cognate p53 binding sites at sub-physiological temperatures (25-33 ;C), and several mutants activated transcription from a p53-responsive promoter at 26 degrees C in transfected H1299 cells. Heating mutant p53 proteins at 37 degrees C irreversibly destroyed their ability to subsequently bind at 25 degrees C. However, several different monoclonal antibodies that each share the ability to recognize an epitope encompassing amino acids 46-55 markedly stabilized binding by mutant p53 proteins at 37 degrees C. Both intact antibody and FAb fragments allowed mutant p53 to bind to DNA. By contrast, antibodies that recognize epitopes located elsewhere within p53 stabilized mutant p53 binding significantly less effectively. Our data show that the major hot-spot p53 mutants have the intrinsic ability to bind to DNA and that a unique region within the N terminus of p53 may be critical for rescuing them from loss of binding at physiological temperatures. This suggests the possibility of developing small molecules that can stabilize mutant p53 proteins under physiological conditions.

p53-mediated cellular response to DNA damage in cells with replicative hepatitis B virus.

Wild-type p53 acts as a tumor suppressor gene by protecting cells from deleterious effects of genotoxic agents through the induction of a G1/S arrest or apoptosis as a response to DNA damage. Transforming proteins of several oncogenic DNA viruses inactivate tumor suppressor activity of p53 by blocking this cellular response. To test whether hepatitis B virus displays a similar effect, we studied the p53-mediated cellular response to DNA damage in 2215 hepatoma cells with replicative hepatitis B virus. We demonstrate that hepatitis B virus replication does not interfere with known cellular functions of p53 protein.

p53 immunolabeling in archival paraffin-embedded tissues: optimal protocol based on microwave heating for eight antibodies on lung carcinomas.

The prognostic value of p53 gene mutations is dealt with by several recent reports. However, retrospective assessment of p53 tumor status on archived samples has been prevented by p53 epitope alteration during routine fixation and embedding procedures. This study aimed at establishing a reproducible low-cost protocol to retrieve not only N-terminal, but also midregion and C-terminal, epitopes, with special attention to possible artifacts induced by epitope retrieval procedures. Using microwave heating, we compared the epitope retrieval efficiency of five solutions with eight commercial antibodies on 21 lung carcinomas for which frozen tissue and samples fixed with formalin and Bouin's liquid were available. All eight epitopes were retrieved, citrate buffer proving efficient for seven. PAb 240 epitope was restored by target unmasking fluid only. No false positivity was observed. Fixation-induced loss of p53 immunoreactivity was minimal for formalin (two of 10 tumors for one antibody each), more significant for Bouin (six of 10 tumors for one to five antibodies). On the other hand, staining intensity was maintained or even improved, and nonspecific staining reduced, through fixation. We conclude that p53 stabilization can be detected on routinely processed archival tumor samples with a reliability similar to that of frozen tissue by means of a microwave-based procedure and a panel of at least three antibodies, with epitopes on the N-terminal, C-terminal, and midpart of the molecule.