p53: at the crossroads of molecular carcinogenesis and risk assessment

p53 gene mutations in rectal cancer associated with schistosomiasis japonica in Chinese patients

Mutations in p53 tumor suppressor gene were examined in 44 Chinese patients with rectal cancer, including 22 cases with advanced schistosomiasis japonica and 22 cases without schistosomiasis. In schistosomal rectal cancer (SRC), 13 mutations were found in 10 cases, which included 11 base-pair substitutions and two deletions. Of 11 base substitutions, nine were transitions and two were transversions and seven of them were located at CpG dinucleotides. In non-schistosomal rectal cancer (NSRC), 13 mutations were found in nine cases, all of which were base-pair substitutions. Of 13 substitutions, 10 were transitions and three were transversions and three of them were located at CpG dinucleotides. The proportion of base-pair substitutions at CpG dinucleotides was higher in SRC patients than in NSRC patients, although this was not statistically significant (P = 0.054). Point mutation was frequent at codon 248 in SRC. A higher frequency of arginine missense mutations was observed in SRC than in NSRC. These observations suggest that the mutations in SRC are the result of genotoxic agents produced endogenously through the course of schistosomiasis japonica.

Pathogenesis of hepatitis B and C-induced hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is estimated to have an annual worldwide incidence of 0.25 to 1.2 million new cases per year. Both the prevalence and incidence of HCC vary markedly as a function of geography and the local prevalence of chronic viral hepatitis. Both chronic hepatitis B and chronic hepatitis C are recognized as risk factors for HCC. The prevalence of cirrhosis in individuals with HCC and chronic hepatitis B or C is reported to be 80.9% and 75.8%, respectively. HCC occurs at a lower rate in chronic viral hepatitis in the absence of cirrhosis. Moreover, hepatitis C virus (HCV) rather than hepatitis B virus (HBV) is associated with the majority of non-cirrhotic cases of HCC. It is probable that the ongoing process of hepatocyte necrosis and liver cell renewal coupled with inflammation, which is characteristic of chronic viral hepatitis, causes not only nodular regeneration and cirrhosis but also progressive genomic errors in hepatocytes as well as unregulated growth and repair mechanisms leading to hepatocyte dysplasia and, in some cases, hepatic carcinoma. Current concepts concerning virus-induced HCC are reported and discussed in the following review.

Current trends in biocompatibility testing

Biocompatibility remains the central theme for biomaterials applications in medicine. It is generally accepted that this term means not only absence of a cytotoxic effect but also positive effects in the sense of biofunctionality, i.e. promotion of biological processes which further the intended aim of the application of a biomaterial. The national and international standards for testing regimes represent a lowest common denominator for such applications and do not necessarily ensure that optimal function will be achieved. The authors' thesis is that biocompatibility testing has scope for extensive development with respect to biofunctionality. The present paper reviews current trends in the in vitro aspects of biocompatibility testing. As well as a critical appraisal of the recent literature, future trends are also stressed, which the authors regard as essential for a meaningful integration of a modern biological approach into new developments in the material sciences. These include the application of modern techniques of cell and molecular biology, the concepts of tissue remodelling, hybrid organ development and encapsulated cell technology.

pZ402, an improved SV40-based shuttle vector containing a T-antigen mutant unable to interact with wild-type p53

Shuttle vectors are useful tools for studying DNA replication and mutagenesis. SV40-based shuttle vectors are popular because of their ease of use and quick results. However, one complication with the use of SV40-based shuttle vectors is the interaction of cellular p53 protein with the T-antigen of SV40. Wild-type, but not mutant p53 has been shown to be involved in DNA replication and DNA repair. To address this concern, we have modified an SV40-based shuttle vector, pZ189, by exchanging the wt T-antigen for a mutant SV40 T-antigen, which is unable to bind with p53. This shuttle vector, pZ402, provides us with a tool to study DNA replication and genomic instability in cells with varying genetic backgrounds without interference from the interaction of T-antigen with p53.

Effects of perturbations of pools of deoxyribonucleoside triphosphates on expression of ribonucleotide reductase, a G1/S transition state enzyme, in p53-mutated cells

Effects of drug treatment with antimetabolites on a human colon cancer cell line, SW480, were studied. Cells were treated with 10 microM of 5-fluorouracil (5FU), an inhibitor of pyrimidine synthesis, or 1000 microM of hydroxyurea (HU), an inhibitor of both purine and pyrimidine syntheses, or the combination. Recombinant alpha-2a-interferon (IFN), 500 U/mL, also was employed, as this augments the effects of both antimetabolites in vitro and in vivo. The predominant effect of this combination was to block cells in early S phase as measured by 5-bromo-2'-deoxyuridine (BrdUrd) incorporation. By 24 hr, 86% of the cells had accumulated in S phase, but failed to progress to G2/M. This was accompanied by an early, rapid decline in all four deoxyribonucleoside triphosphates (dNTPs) by 38-86% at 4-24 hr. Despite these effects, expression of the G1/S transition state enzyme, ribonucleotide reductase (RR), increased at 24 hr as measured by a 3 to 5-fold increase in mRNA levels for the M2 subunit, in the absence of a measurable effect on protein levels. The rise in levels of RR mRNA and the continued progression of cells into S phase were associated with a synergistic inhibition of cell cycle proliferation resulting from treatment with the three-drug combination. This suggests that in the presence of antimetabolite-induced depletion of dNTPs, SW480 cells, which lack a normal p53 gene, will proceed into S phase, and that this is associated with a rise in expression of the G1/S transition state enzyme, RR. Cells arrested in S phase by a p53-independent mechanism will undergo a synergistic enhancement of cell death.

p21(WAF1/Cip1) retards the growth of human squamous cell carcinomas in vivo

The excessive proliferation exhibited by cancer cells is frequently a result of their failure to adequately regulate cell cycle progression. In the present study, we developed a xenograft model of oral cancer in athymic mice, using squamous carcinoma cell lines and examined the ability of the cyclin-dependent kinase inhibitor p21 (WAF1/Cip1) to retard tumour growth in vivo, using a retroviral delivery system. Human p21 cDNA was cloned by polymerase chain reaction, expressed, and the encoded protein shown to have biological activity in in vitro kinase assays. Amphotropic retrovirus cultures which expressed recombinant p21 were generated and used to treat established squamous cell carcinoma xenografts. Two weeks following onset of treatment tumours injected with p21 virus producer cells showed a reduction in size between 3- and 10-fold compared with tumours which received control cells which produced control virus alone. The data indicate that recombinant p21 may be of future use for therapeutic intervention in oral cancer.

Malignant transformation of recurrent respiratory papillomatosis associated with integrated human papillomavirus type 11 DNA and mutation of p53

Recurrent respiratory papillomatosis (RRP), usually confined to the nasopharynx, trachea, and larynx, occasionally can progress to extensive bronchopulmonary disease. Most cases of bronchopulmonary and laryngeal papillomatosis are cytologically benign and do not undergo malignant transformation; however, squamous cell carcinoma (SCC) can arise in RRP in the absence of known risk factors such as radiation and smoking. In this study, the authors investigated molecular genetic alterations occurring in a case of metastasizing SCC that arose in long-standing bronchopulmonary papillomatosis. Genomic DNA from tracheal papillomata, tracheobronchial papillomata, SCC of the lung, and a lymph node metastasis was extracted. The physical state of the human papillomavirus type 11 (HPV-11) DNA was investigated by two-dimensional gel electrophoresis. Molecular genetic alterations of the host genome were studied by direct sequencing of polymerase chain reaction-amplified gene fragments and restriction fragment length polymorphism (RFLP) analysis. Episomal and integrated forms of HPV-11 sequences were detected in histologically benign tumors, but only the integrated form of the viral DNA could be found in malignant tissue samples. Molecular genetic studies revealed that an allelic loss of the interferon-beta gene (IFNbeta-1) and an endogenous type of mutation of the p53 antioncogene were found only in the malignant lesions. Mutations were not observed in the ras, neu, or multiple tumor suppressor (MTS1/p16) genes in any specimens. The authors' data indicated that the p53 genetic mutation was associated with integration of HPV-11 in histologically malignant lesions. This association may promote a progressive genetic instability that can lead to the development and clonal expansion of malignant lesions in RRP.

p53 gene mutation in the bone-marrow of a patient with diffuse mixed cell type lymphoma at diagnosis predicting eventual progression to large cell lymphoma

Mutations of the p53 tumor suppressor gene have been used as molecular genetic markers of disease and serve as a prognostic indicator in various malignancies including non-Hodgkin's lymphoma (NHL). Alterations in the p53 gene were investigated in a bone marrow sample from a NHL patient admitted for autologous bone marrow transplantation. Diffuse mixed small and large cell NHL, was initially diagnosed which eventually progressed to large cell lymphoma at relapse following poly-chemotherapy. A sequential technique of polymerase chain reaction-mediated single-strand conformational polymorphism (PCR-SSCP) of the p53 gene revealed a shift in one band of exon 6 in the bone marrow, collected at the time of initial diagnosis. No mutations were detected in exons 5, 7, 8 and 9. Direct sequencing of exon 6 detected a single base change from G to C resulting in an amino acid substitution from glycine to histidine. Results of this study and data reviewed from other publications suggest that the missense p53 mutation seen in this patient at the time of diagnosis may perhaps have been used to predict the eventual outcome of the disease. This could, therefore, serve as an important genetic disease marker particularly in bone marrow or peripheral blood samples initially collected and cryopreserved for future possible autologous transplantation.

Roles of epidemiology, pathology, molecular biology, and biomarkers in the investigation of occupational lung cancer

The pathology and molecular biology of lung cancer demonstrate that these tumors evolve through a series of mutations, molecular changes, and corresponding morphologic changes. To elucidate how occupational and environmental factors influence lung cancer histogenesis it is important not only to understand epidemiology and the interactions between etiologic agents but also to integrate information from pathology, biochemistry and molecular biology. This review focuses on the range of techniques currently available for characterizing lung cancer and how their prudent use can be beneficial in the identification of occupational carcinogens. Because many occupational and environmental lung cancers are caused by multiple etiologic agents, the integration of histology with cellular, biochemical and molecular biomarker techniques may provide new approaches for understanding the disease process.

Li-Fraumeni syndrome and the role of the p53 tumor suppressor gene in cancer susceptibility

Mutation of the tumor suppressor gene p53 is a molecular genetic event frequently observed in human cancer, and inactivating missense mutations usually are accompanied by the resultant overexpression of mutant p53 protein. In gynecologic cancers, p53 is also often altered; the frequency varies depending on types of cancers and where they develop. Further, human papillomavirus oncoproteins that inactivate p53 and Rb proteins play important roles in the development of several gynecologic cancers. Individuals who are heterozygous for germline mutations of the p53 gene are strongly predisposed to a variety of cancers. The identification of these individuals may have profound value in the future when therapies or chemopreventive agents specific for the p53 alteration are available. The role of p53 tumor suppressor gene in gynecologic cancers and heritable cancer susceptibility syndromes including Li-Fraumeni and Lynch II syndromes is an active and important area of study.

DNA-binding activity of wild-type p53 protein is mediated by the central part of the molecule and controlled by its C terminus

The DNA binding activity of wild type p53 is central to its activity. The "central" part of the molecule, where most mutations appear in primary human tumors, is the actual DNA binding domain. The C-terminal part was shown to exert a negative effect on the DNA binding activity. In the present study we show that while anti-p53 antibodies recognizing the C terminus of the wild type p53 facilitate DNA binding activity, blocking of the wild type specific epitope by specific anti-p53 antibodies, inhibited the DNA binding activity of the wild type p53 protein. An alternatively spliced p53 protein exhibits an augmented DNA binding activity. The fact that most p53 mutants have lost the wild type p53 conformation specific epitope, coupled with the observation that blocking of this site by binding specific antibodies, prevents the interaction of wild type p53 with DNA, suggests that maintaining the correct structural conformation of this site is central for DNA binding activity. Still, the internal structure of the p53 target and particularly the length of the sequence between the two tandem inverted repeats, is critical for protein-DNA interaction behavior.

Cell and molecular mechanisms of pathogenesis and treatment of cancer

Surgery remains the mainstay of treatment for most classes of human solid tumours, with the principal exception of lymphomas, but it is insufficient in many cases to guarantee cure. With few exceptions, recurrent and metastatic solid tumours continue to defy attempts to develop effective adjuvant therapies. Recent insights into tumour biology reveal an increasingly complex picture of cell and molecular processes which confer heterogeneity and resistance to treatment upon tumours. These insights may also yield new targets for more effective adjuvant therapies.

Prognostic significance of MIB-1, p53, and bcl-2 immunoreactivity in meningiomas

Sixty biopsy specimens of meningiomas, including 37 benign, 10 atypical, and 13 malignant meningiomas, were examined immunohistochemically using the monoclonal antibodies MIB-1 (a cell proliferation marker), p53, and bcl-2 (two apoptosis-associated markers). Benign meningiomas were subdivided into two groups: group 1, 29 tumors without recurrence; and group 2, eight tumors with recurrence after complete surgical resection. The mean MIB-1 labeling index (LI) values+/-SD were 1.3+/-3.2% for the benign, 9.3+/-6.9% for the atypical, and 15.0+/-16.9% for the anaplastic meningiomas. The mean MIB-1 LI+/-SD in group 1 tumors (n = 29) was 1.06+/-1.15%, and in group 2 tumors (n = 8), 2.3+/-4.76% (P = .028). p53 protein expression was found in 10.8% of the benign (10.34% of group 1 and 12.5% of group 2), 50% of the atypical, and 77% of the anaplastic meningiomas. bcl-2 protein expression was observed in 21.6% of the benign, 20% of the atypical, and 46.1% of the anaplastic meningiomas. Among the benign meningiomas, group 2 tumors expressed significantly more often bcl-2 protein (62.5%) than group 1 neoplasms (10.3%). Our results indicate that (1) in meningiomas, a good correlation exists between histological grading, MIB-1 and p53 protein expression, and (2) in benign meningiomas, the presence of bcl-2 protein expression together with high MIB-1 LI are associated with unfavorable prognosis of the disease.

Hepatitis B injury, male gender, aflatoxin, and p53 expression each contribute to hepatocarcinogenesis in transgenic mice

The major risk factors for human liver cancer: hepatitis B virus (HBV) related liver injury, male gender, aflatoxin exposure, and p53 expression, are evaluated and compared in experimental transgenic mouse models. Transgenic mice that express hepatitis B surface antigen (HBsAg) in their liver and develop liver tumors at 18 months of age (HBV+ mice) were bred to p53 null mice (p53-/-) to produce mice p53+/-, HBV+ mice. These mice and control littermates ([p53+/+, HBV+], [p53+/-, HBV-], and [p53+/+, HBV-) were divided into groups that did or did not receive an injection of aflatoxin at 1 week of age. At sacrifice at 13 months of age, 100% (7/7) of male mice with each of the three risk factors (p53+/-, HBV+, AFB1+) developed high-grade hepatocellular carcinomas (HCC). If any one of the risk factors was absent, the incidence drops: if both p53 alleles are present, 62% (10/16); if HBsAg is not expressed, 14% (1/7); if AFB1 is not given, 25% (2/8). If only one of the risk factors is present no tumors above grade I are found. Similar results were observed in female mice except that HCC incidence in each group is less than in male mice. Some of the tumors in mice with more than one risk factor are of unusual histological types, such as hepatocholangio-carcinomas, adenocarcinomas and undifferentiated carcinomas that are not usually seen in HBV transgenic C57BL/6 mice. No loss or mutation of the p53 gene is detected in any of the tumors. Possibilities of how the four major risk factors for HCC interact to produce malignant liver tumors in these transgenic mouse models of hepatocarcinogenesis are discussed.

Formation and repair of DNA lesions in the p53 gene: relation to cancer mutations?

The number and diversity of mutations in the p53 mutation data base provides indirect evidence that implicates environmental mutagens in human carcinogenesis. The p53 gene has a large mutational target size; more than 280 out of 393 amino acids are found mutated in tumors. We argue that there is possibly a limited involvement of selection for specific mutations in the central domain of the protein, and that the distribution of DNA damage along the p53 gene caused by environmental carcinogens can be correlated with the mutational spectra, i.e., hotspots and types of mutations, of certain cancers. This concept has been validated by experiments with sunlight and the cigarette smoke component benzo[a]pyrene representing the polycyclic aromatic hydrocarbon class of carcinogens. The damage/repair data obtained for these mutagens can predict certain parameters of the mutational spectra including the distribution of hotspots in human nonmelanoma skin cancers and lung cancers from smokers. Future studies with suspected mutagens may help to implicate causative agents involved in other cancers, such as colon and breast cancer, where the exact carcinogen has not yet been identified but an environmental factor is suspected.

Effects of endotoxin on expression of ras, p53 and bcl-2 oncoprotein in hepatocarcinogenesis induced by thioacetamide in rats

AIM

To evaluate the relationship between expression of ras, p53 and bcl-2 gene products and hepatocarcinogenesis since the endotoxemia produced from lipopolysaccharide administration and/or the hypophagocytic state of splenectomy significantly accelerated hepatocarcinogenesis induced by thioacetamide.

METHODS

The hepatocarcinoma model was induced by 6-mo oral intake of 0.03% thioacetamide. During the hepatocarcinoma modeling process, rats were additionally treated with splenectomy and/or lipopolysaccharide administration. The techniques of flow cytometry, immunohistochemistry and immunoelectronmicroscopy were applied for quantitative analysis of the expression of oncogene proteins.

RESULTS

In this model system, overexpression of ras p21 protein mainly occurred in the precancerous cell population or in cells in the early stage of hepatocyte transformation. The levels of ras p21 declined when nuclear DNA aneuploidy increased. Expression of bcl-2 protein slowly and steadily rose, with more hepatocytes staying in S + G2M phases, as the hepatocarcinoma became more malignant. p53 was moderately expressed during hepatocarcinogenesis. There was no statistical correlation between endotoxemia levels and the changes in levels of ras, p53 and bcl-2 gene products.

CONCLUSION

Overexpression of oncogene ras p21 was considered likely to be a precursor of premalignant hepatocytes and possibly as responsible for the initiation of hepatocarcinogenesis. Bcl-2 protein expression is proportional to the severity of malignancy in hepatocarcinogenesis. p53 may be involved in a key pathway underlying the transformation and development processes of hepatocarcinoma. This study confirmed the hypothesis that there are multiple genes and multiple steps involved in hepatocarcinogenesis. Expression of oncogene proteins reflects the properties of the premalignant and malignant cells, but is not directly related to endotoxemia statistically.

p53 mutations in childhood thyroid tumours from Belarus and in thyroid tumours without radiation history

Mutations in the p53 tumour-suppressor gene (exons 5-8) were investigated in 31 Belarussian childhood thyroid tumours (24 cases of papillary thyroid carcinoma, 3 benign tumours and 2 cases each of thyroiditis and goiter); 33 thyroid tumours from juveniles and adults without radiation exposures (25 carcinomas of various histological types, including 11 papillary carcinomas and 8 adenomas) and 6 tumours from adults (4 papillary carcinomas, 1 adenoma, 1 goiter) served as controls. The mutational spectrum of p53 differed greatly between the childhood thyroid carcinomas from Belarus and the control groups. In the control groups of 29 malignant thyroid tumours, 7 different mutations were detected on exons 5-8, none of which occurred among the 15 papillary carcinomas in this group. Five mutations were found in tissue samples of the 24 childhood papillary carcinomas, and they were all the same p53 point mutation (CGA --> CGG) on codon 213 of exon 6. To determine whether this mutation is simply a polymorphism or whether it is specific to the tumour cells, laser-assisted microdissection was applied to collect various areas of tumorous and non-tumorous cells (10-20 cells per sample) from each paraffin-embedded tissue section of 8 of the papillary thyroid carcinomas. Using PCR-SSCP and sequence analysis on these cells, the very same p53 mutation on codon 213 was detected in various microdissected tumour samples of 2 cases, but it was not found in any microdissected non-tumorous sample. The exclusive occurrence of this p53 mutation in selective microdissected samples of tumour cells, even as homozygous mutation in 1 case, reflects a distinct tumour heterogeneity within papillary childhood thyroid carcinomas.

Induction of p53 protein expression by sodium arsenite

Arsenic is carcinogen for humans and has been shown to act as an enhancer in initiated animal models. In a previous work we found impairment of lymphocyte proliferation in arsenic-exposed individuals and in vitro we obtained dose-related inhibition of mitotic response and lymphocyte proliferation. Intrigued by these effects and based on the role of p53 on cell proliferation, we tested different concentrations of sodium arsenite for their ability to induce the expression of tumor suppressor gene p53 in different cell lines (HeLa, C-33A. Jurkat) and a lymphoblast cell line transformed with Epstein-Barr virus (LCL-EBV). We also evaluated changes in their viability after 24 h arsenic treatment; C-33A cells showed the higher sensitivity to arsenic treatment while HeLa, Jurkat and LCL-EBV cells showed similar cytotoxicity curves. Immunoblots showed an increased expression of p53 gene with 1 microM sodium arsenite in Jurkat cells and 10 microM sodium arsenite in HeLa and LCL-EBV cells. In addition, we transfected Jurkat cells and human lymphocytes with wild-type and mutated p53 genes; lymphocytes and Jurkat cells that received the mutated p53 showed increased sensitivity to arsenic cytotoxicity. Data obtained indicate that arsenic induces p53 expression and that cells with a functional p53 contend better with damage induced by this metalloid.

Comparison of the mutational specificity induced by environmental genotoxin nitrated polycyclic aromatic hydrocarbons in Salmonella typhimurium his genes

Mutagenicity of 15 nitrated polycyclic aromatic hydrocarbons (nitro PAHs), which were detected in ambient air particles and/or combustion source emissions, were examined using a set of six Salmonella typhimurium tester strains (TA7001 to TA7006), and the mutational specificity was characterized by the comparison of the mutagenic potencies of nitro-PAHs in the tester strains. Each strain carries a unique missense mutation in the histidine operon and is reverted by only one specific base-substitution out of six possible changes. All nitro-PAHs tested were mutagenic in multiple strains, and were classified into four categories based on the strains predominantly reverted. 1-Nitropyrene (1-NPy), 2,7-dinitrofluoren-9-one and 1,3-, 1,6- and 1,8-dinitropyrene isomers exerted the highest mutagenicity in strain TA7005 (C.G-->A.T transversion) followed by strain TA7006 (C.G-->G.C transversion). 2- And 3-nitrofluoren-9-one isomers, 2-NPy and 2,7-dinitrophenanthrene were also markedly mutagenic in strain TA7005 but not in strain TA7006. For 2-, 3- and 9-nitrophenanthrene isomers, 2-nitrofluoranthene (2-NFT) and 4-NPy, TA7004 (G.C-->A.T transition) was the most responsive strain. 3-NFT was unique, showing the highest mutagenicity in strain TA7002 (T.A-->A.T transversion). All nitro-PAHs tested induced C.G-->A.T transversion, which is observed as the most frequent base-substitution mutation of p53 tumor suppressor gene in human lung cancer.

Ki-ras oncogene and p53 tumour suppressor gene mutations in colorectal carcinomas from the European Saar-Luxembourg region are less frequent than predicted by the classic adenoma-carcinoma sequence model

Recent investigations of colorectal cancer (CRC) have suggested that the accumulation of specific alterations in cell-growth regulating genes trigger the stage-wise progression to malignancy and that at least some of them could be useful for prognosis. In this study, the frequency, location and type of mutations of the Ki-ras proto-oncogene exons 1-2 and p53 tumour-suppressor gene exons 5-9 were analysed in colorectal carcinomas of 72 patients from the European Saar-Luxembourg region using PCR-SSCP screening and direct sequencing. The incidences of Ki-ras activating and p53 inactivating point mutations in these European samples were much lower (Ki-ras: 5 (6.9%) and p53: 13 (18.1%)) than reported for both genes in American studies (40-50% at least) (P < 1 x 10(-3)). These results suggest that other genetic mechanisms than those proposed for the classic adenoma-carcinoma sequence model can frequently underlie CRC development and that Ki-ras and p53 mutations should not be considered as universal markers for CRC.

Cancer cells exhibit a mutator phenotype

This review analyzes the concept and evidence in support of a mutator phenotype in human cancer. The large number of mutations reported in tumor cells cannot be accounted for by the low mutation rates observed in normal somatic cells; rather, it must be a manifestation of a mutator phenotype present early during the tumorigenic process. The interaction between increased mutagenesis and clonal selection provides a mechanism for the selection of cells with increased proliferative advantage. The concept of a mutator phenotype in cancer has gained considerable support from the findings of enormous numbers of somatic mutations in repetitive sequences in human tumors. Moreover, cell lines exhibiting microsatellite instability demonstrate an increased mutation frequency in expressed genes. A knowledge of mechanisms that generate multiple mutations in cancer cells has important implications for prevention. For many tumors, a delay in the rate of accumulation of mutations by a factor of two could drastically reduce the death rates from these tumors.

Hydrophobic side-chain size is a determinant of the three-dimensional structure of the p53 oligomerization domain

The p53 tumor suppressor oligomerization domain, a dimer of two primary dimers, is an independently folding domain whose subunits consist of a beta-strand, a tight turn and an alpha-helix. To evaluate the effect of hydrophobic side-chains on three-dimensional structure, we substituted residues Phe341 and Leu344 in the alpha-helix with other hydrophobic amino acids. Substitutions that resulted in residue 341 having a smaller side-chain than residue 344 switched the stoichiometry of the domain from tetrameric to dimeric. The three-dimensional structure of one such dimer was determined by multidimensional NMR spectroscopy. When compared with the primary dimer of the wild-type p53 oligomerization domain, the mutant dimer showed a switch in alpha-helical packing from anti-parallel to parallel and rotation of the alpha-helices relative to the beta-strands. Hydrophobic side-chain size is therefore an important determinant of a protein fold.

The interplay of nitric oxide and peroxynitrite with signal transduction pathways: implications for disease

Since the discovery that at least one form of endothelium derived relaxing factor is nitric oxide (NO), numerous studies have uncovered diverse roles for this free radical in a variety of physiological and pathophysiological processes. NO production, a process mediated by a family of enzymes termed NO synthases, has been detected in most cell types. Many of the effects of NO are thought to be mediated through its direct interaction with specific and defined cell signaling pathways. The nature of such interactions are highly dependent on the concentration of NO and cell type. Furthermore, specific NO derived reaction products, such as peroxynitrite, also have the potential to effect cell signal transduction events. As with NO, this can occur through diverse mechanisms and depends on concentration and cell type. It is perhaps not surprising that the reported effects of NO in different disease states are often conflicting. In this brief overview, a framework for placing these apparently disparate properties of NO will be described and will focus on the effects of NO and peroxynitrite on signaling pathways.

Interaction of p53 with the human Rad51 protein

p53 is thought to function in the maintenance of genomic stability by modulating transcription and interacting with cellular proteins to influence the cell cycle, DNA repair and apoptosis. p53 mutations occur in >50% of human cancers, and cells which lack wild type p53 accumulate karyotypic abnormalities such as amplifications, deletions, inversions and translocations. We propose that p53 hinders these promiscuous recombinational events by interacting with cellular recombination and repair machinery. We recently reported that p53 can directly bind in vivo to human Rad51 (hRad51) protein and in vitro to its bacterial homologue RecA. We used GST-fusion and his-tagged protein systems to further investigate the physical interaction between p53 and hRad51, homologue of the yeast Rad51 protein that is involved in recombination and DNA double strand repair. The hRad51 binds to wild-type p53 and to a lesser extent, point mutants 135Y, 249S and 273H. This binding is not mediated by a DNA or RNA intermediate. Mapping studies using a panel of p53 deletion mutants indicate that hRad51 could bind to two regions of p53; one between amino acids 94 and 160 and a second between 264 and 315. Addition of anti-p53 antibody PAb421 (epitope 372-381 amino acids) inhibited the interaction with hRad51. In contrast, p53 interacts with the region between aa 125 and 220 of hRad51, which is highly conserved among Rad51 related proteins from bacteria to human. In Escherichia coli ecA protein, this region is required for homo-oligomerization, suggesting that p53 might disrupt the interaction between RecA and Rad51 subunits, thus inhibiting biochemical functions of Rad51 like proteins. These data are consistent with the hypothesis that p53 interaction with hRAD51 may influence DNA recombination and repair and that additional modifications of p53 by mutation and protein binding may affect this interaction.

Mutation analysis of p53 gene in childhood malignant solid tumors

Alterations of the p53 gene have been extensively investigated in a wide variety of human malignancies. However, data on childhood malignant solid tumors are still limited. Mutations of the p53 gene on exons 5 through 8 were examined in 82 childhood malignant solid tumors by the polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) method, and the nature of these mutations was confirmed by direct sequencing. The 82 tumors examined included neuroblastomas (n = 44), Wilms' tumors in = 13), hepatoblastomas (n = 11), rhabdomyosarcomas (n = 10), extraosseus Ewing sarcomas (n = 2), undifferentiated sarcoma of the liver (n = 1), and fibrosarcoma (n = 1). Two sarcoma samples were identified as having point mutations. One was a rhabdomyosarcoma with a missense mutation at codon 273, substituting histidine (His) for arginine (Arg). Another was an undifferentiated sarcoma of the liver with a missense mutation at codon 245, substituting serine (Ser) for glycine (Gly). No mutations were detected among neuroblastomas, Wilms' tumors, or hepatoblastomas. The two sarcomas with mutations were localized tumors. Both patients who had these tumors are disease free for 8 and 5 years after treatment, respectively. The overall incidence of p53 mutations was low (2.4%, 2 of 82). However, the incidence, when calculated for sarcomas, was higher at 14.3% (2 of 14). These data indicate that p53 mutations are generally uncommon in childhood malignant solid tumors examined. However, in some childhood sarcomas, p53 mutations appear to have a causative role in the development of these tumors.

An intronic deletion in TP53 gene causes exon 6 skipping in breast cancer

Six hundred and thirty primary breast cancer were screened for abnormalities in exons 5, 6, 7 and 8 of the TP53 tumour suppressor gene. Analysis of the structure of the TP53 gene exons was performed with the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method and with direct sequencing of amplified DNA. In a breast tumour case from a postmenopausal patient, we found a deletion of 36 bp in intron 5 and no immunohistochemical staining for p53. We amplified and sequenced the cDNA region between exons 4 and 7 and showed that the deletion causes the skipping of exon 6. The resulting mRNA sequence had a frameshift that yields an inactive protein with a truncated C terminus. These results show the first example of intronic deletion causing exon skipping at the TP53 gene level.

An unexpected spectrum of p53 mutations from squamous cell carcinomas in psoriasis patients treated with PUVA

Photochemotherapy employing 8-methoxypsoralen and long-wavelength ultraviolet radiation (UVA, 320-400 nm) is widely used in the treatment of psoriasis. The photoactivation of psoralens in skin cells leads to formation of DNA photoadducts which may be responsible, at least in part, for the efficacy of these photochemotherapies. However, mutations arising from these adducts may also lead to the well-characterized increased incidence of squamous cell carcinoma. Mutations in the p53 tumor suppressor gene have been detected in many human cancers. To determine whether p53 mutations occur in squamous cell carcinomas in PUVA patients, PCR was used to amplify the exons (5-9) in which other studies have found a high frequency of point mutations. Gel electrophoresis was used to detect single-strand conformational polymorphisms. Aberrantly migrating bands were excised, reamplified and sequenced. Thirty-four specimens from 10 patients were examined. Specimens from one patient who had received no phototherapy as well as from normal controls were also analyzed. Five of the 10 patients showed at least one p53 mutation. In contrast to previously reported psoralen-induced p53 mutations in mice, the expected psoralen type mutations at alternating AT sites were not detected. All but two of the altered sequences occurred at dipyrimidine sites which is typical of solar type mutations. Two C-->T mutations and two dipyrimidine mutations (CC-->TT) were found. Other mutations included: C-->G, G-->T, C-->A and an 18 bp deletion. A review of therapeutic history of these patients showed that some had also received UVB phototherapy. Furthermore, because sunlight is thought to be beneficial for psoriasis, nontherapeutic, casual UVB exposure cannot be excluded. Our observations suggest that the SCC may have arisen from the solar mutations and that PUVA may enhance tumor progression or immune suppression.

Induction of multiple PCR-SSCPE mobility shifts in p53 exons in cultures of normal human urothelium exposed to low-dose gamma-radiation

We have previously shown that primary explant cultures of human urothelium exposed to low doses of gamma-radiation subsequently accumulate a high level of stable p53 but it was not clear from those studies whether this protein stabilization occurred through an event in another gene involved in p53 protein control or possibly an epigenetic event. In these experiments, primary urothelial cultures from five different patients were exposed to either 0.5 or 5 Gy gamma-radiation from a 60 Cobalt source and allowed to grow for 7-10 division cycles to allow development of any radiation-induced, non-lethal changes in the cells. C-myc, Bcl-2 and stable p53 proteins were found to be elevated in cultures following both radiation doses. PCR-SSCPE analysis of the p53 gene was performed on cultures in order to determine whether genetic mutations could be the underlying basis for persistent increased stable p53 expression. Following 0.5 Gy exposure, the cultures also developed multiple distinct 'foci' of rapidly dividing cells which strongly overexpressed p53. These grew on a background of morphologically normal cells. When such foci were selectively analysed for their p53 mutation status by PCR-SSCPE, there was evidence that they contained cells which had developed changes to the p53 gene post-irradiation. These changes appeared to occur more frequently in focal cells than in cells of normal morphological appearance in the same culture. These results may have mechanistic importance given the controversy regarding low-dose radiation effects and p53-related genomic instability.

DNA bending is essential for the site-specific recognition of DNA response elements by the DNA binding domain of the tumor suppressor protein p53

We have used circular permutation assays to determine the extent and location of the DNA bend induced by the DNA binding domain of human wild type p53 (p53DBD) upon binding to several naturally occurring DNA response elements. We have found that p53DBD binding induces axial bending in all of the response elements investigated. In particular, response elements having a d(CATG) sequence at the junction of two consensus pentamers in each half-site favor highly bent complexes (bending angle is approximately 50 degrees ), whereas response elements having d(CTTG) bases at this position are less bent (bending angles from approximately 37 to approximately 25 degrees ). Quantitative electrophoretic mobility shift assays of different complexes show a direct correlation between the DNA bending angle and the binding affinity of the p53DBD with the response elements, i.e. the greater the stability of the complex, the more the DNA is bent by p53DBD binding. The study provides evidence that the energetics of DNA bending, as determined by the presence or absence of flexible sites in the response elements, may contribute significantly to the overall binding affinity of the p53DBD for different sequences. The results therefore suggest that both the structure and the stability of the p53-DNA complex may vary with different response elements. This variability may be correlated with variability in p53 function.

Architectural accommodation in the complex of four p53 DNA binding domain peptides with the p21/waf1/cip1 DNA response element

High resolution chemical footprinting and cross-linking experiments have provided a basis for elucidating the overall architecture of the complex between the core DNA binding domain of p53 (p53DBD, amino acids 98-309) and the p21/waf1/cip1 DNA response element implicated in the G1/S phase cell cycle checkpoint. These studies complement both a crystal structure and earlier biophysical studies and provide the first direct experimental evidence that four subunits of p53DBD bind to the response element in a regular staggered array having pseudodyad symmetry. The invariant guanosines in the highly conserved C(A/T)|(T/A)G parts of the consensus half-sites are critical to the p53DBD-DNA binding. Molecular modeling of the complex using the observed peptide-DNA contacts shows that when four subunits of p53DBD bind the response element, the DNA has to bend approximately 50 degrees to relieve steric clashes among different subunits, consistent with recent DNA cyclization studies. The overall lateral arrangement of the four p53 subunits with respect to the DNA loop comprises a novel nucleoprotein assembly that has not been reported previously in other complexes. We suggest that this kind of nucleoprotein superstructure may be important for p53 binding to response elements packed in chromatin and for subsequent transactivation of p53-mediated genes.

Noninvasive, real-time method for the examination of thymidine uptake events--application of the method to V-79 cell synchrony studies

[14C]Thymidine uptake into V-79 hamster lung fibroblasts has been successfully demonstrated using a noninvasive, real-time method utilizing Cytostar-T scintillating microplates. These plates are standard format, tissue culture-treated, 96-well microplates with an integral scintillating base. The microplates permit the culture and observation of adherent cell monolayers. Biological activities of the cells can be studied by the provision of specific radiolabeled compounds. The biological activities of the adherent monolayer bring the specific radiolabel into proximity with the scintillating base and a scintillation signal is thereby generated. [14C]Thymidine incorporation on the microplates can be used to examine cell proliferation and cell cycle events. Using a combined mitotic shake-off/aphidicolin treatment to achieve synchronization, the thymidine incorporation activities of V-79 cells have been examined on Cytostar-T plates and correlated to traditional methods of determining incorporation. The method was further used to examine the effects of colcemid and olomoucine, both chemical inhibitors of cell proliferation, on synchronous populations of cells. The homogeneous detection format and the microplate nature of the method suggest a role for scintillating microplates in cell biology research and drug discovery.

A review of the chronic toxicity, carcinogenicity, and possible mechanisms of action of inorganic acid mists in animals

Occupational exposure to inorganic acid mists containing sulfuric acid has been associated with increased laryngeal cancer. The primary objective of this review was to compile the literature regarding chronic toxicity and carcinogenicity of inorganic acid mists in laboratory animals. Several chronic toxicity studies had exposures of 1 year or longer. Whereas numbers of animals were limited, no evidence of neoplastic or preneoplastic lesions was reported. Two studies evaluated the carcinogenicity of inorganic acid mists in rats; however, one was limited by a short duration of exposure and the other did not achieve a maximum tolerated dose. A large lifetime study in hamsters evaluated the carcinogenicity of 100 mg/M3 sulfuric acid mist, as well as its ability to act as a promoter or co-carcinogen for benzo(a)pyrene. No evidence of carcinogenic potential was shown. Although an increase in papillomas was noted in the benzo(a)pyrene + H2SO4 group, the co-carcinogenic or promoting potential was considered equivocal. Thus, no evidence from experimental animals strongly supports or refutes the induction of cancer by inorganic acid mists. A possible mechanism that could be associated with inorganic acid mist carcinogenicity relates to the genetic consequences of lowering the pH. Reduced pH can induce chromosomal aberrations, enhance depurination, and deamination of cytidine in DNA. This mechanism has not been evaluated in tissues of the respiratory tract.

Expression of p53, Ki-67 and cytokeratin-4 (CK4) in oral papillomas

P53 is overexpressed in more than 50% of all human cancers. A previous study suggested that p53 was also overexpressed in oral papillomas. This study was carried out to investigate whether p53 expression was correlated with expression of the cellular proliferation marker Ki-67 and the epithelial differentiation marker cytokeratin-4 (CK4) in oral papillomas. Formalin-fixed paraffin-embedded sections of 30 oral papilloma specimens and 30 unmatched normal oral mucosal specimens were processed for immunohistochemistry, using an avidin-biotin-peroxidase procedure and monoclonal antibodies. A semiquantification analysis on p53 and Ki-67 labeling indices was performed. Twenty-eight of 30 (93%) papilloma specimens were positive for p53. The percentage of p53-positive cells in the basal layer was 60.4 +/- 14.8 (mean +/- SD, n = 28), and that of Ki-67-positive cells was 26.7 +/- 14.4. There was no correlation between expression of p53 and that of Ki-67. Expression of CK4 was inversely correlated with the expression of Ki-67 but not correlated with the expression of p53.

Differential induction of growth arrest inducible genes by selenium compounds

The effects of two types of selenium compounds on the expression levels of growth arrest and DNA damage-inducible (gadd) genes and on selected cell death genes were examined in mouse mammary MOD cells to test the hypothesis that the diversity of selenium-induced cellular responses to these compounds could be distinguished by unique gene expression patterns. Whereas the expression patterns of known cell death-related genes (bcl-2 and bax) were not informative with respect to the cellular response patterns upon exposure to selenium compounds, time-dependent and selenium species-specific induction patterns were observed for gadd34, gadd45 and gadd153 genes. It was also observed that the MOD cells expressed a truncated p53 transcript but no detectable immunoreactive P53 protein, indicating a null p53 phenotype. The fact that selenium compounds induced growth arrest and death of these cells and that these compounds induced specific patterns of expression of gadd genes indicates that these genes may mediate some selenium-induced cellular responses. The findings further imply that selenium compounds may be effective chemopreventive agents for human breast carcinogenesis, in which p53 mutations are frequent.

Meat, starch and non-starch polysaccharides, are epidemiological and experimental findings consistent with acquired genetic alterations in sporadic colorectal cancer?

International comparisons show strong inverse protective associations with starch, NSP (fibre, non-starch polysaccharides) and vegetable intakes, and positive associations with meat consumption in large bowel cancer. Estimates of relative risk from cohort investigations are in the same direction although generally weak, and red and processed meat, rather than white meat seem to be associated with elevated risk. A protective effect of starch and NSP probably arises from their marked effect on bacterial metabolism in the large bowel, which can be postulated to affect gene expression and DNA repair via increased butyrate production. Stool weight is also increased and pH reduced leading to alterations in secondary bile acid production, and mucosal cell proliferation. In rodent models, 'insoluble' sources of NSP are generally protective, although butyrate, resistant starch and soluble NSP may not reduce tumorigenesis. High levels of meat increase faecal ammonia and N-nitrosocompound (NOC) concentration. Some of the chromosomal mutations found in human colorectal cancer are consistent with effects of NOC and heterocyclic amines. More data are required from human experimental studies linking alterations in diet with known stages in carcinogenesis in the large bowel, and from large cohort studies which have collected biological samples in order that interaction between diet, biomarkers of diet, and different genotypes that may determine risk can be examined.

The human transcriptional adaptor genes TADA2L and GCN5L2 colocalize to chromosome 17q12-q21 and display a similar tissue expression pattern

The chromosomal locations and the tissue expression patterns of the human transcriptional adaptors TADA2L and GCN5L2 have been determined. Northern blot analysis across a range of human tissues revealed that both the TADA2L and the GCN5L2 mRNAs are expressed to varying degrees in all tissue types. Furthermore, in most tissue types, the genes are expressed at relatively similar levels, suggesting coordinated regulation of TADA2L and GCN5L2 transcription. Chromosomal mapping by fluorescence in situ hybridization indicated that these genes reside near each other on chromosome 17; TADA2L mapped within bands 17q12-q21, while GCN5L2 mapped distally within band 17q21.

Functional characterization in vivo of mutant p53 molecules derived from squamous cell carcinomas of the head and neck

Loss of wild-type p53, either through deletion or mutation, has been demonstrated in most squamous cell carcinomas of the head and neck (HNSCC). Whether these mutant molecules contribute to tumor progression purely through loss of wild-type functions or by growth-promoting mechanisms, however, remains unclear. To begin to address these issues, we isolated a series of p53 cDNAs from HNSCC cell lines that contain missense or nonsense point mutations, insertions, or deletions. The ability of each of these molecules to transform NIH/3T3 cells to a malignant phenotype was assessed by stable transfection and expression under the control of a strong heterologous promoter. NIH/3T3 cells transfected with pLTR6p53, which harbors an H179L missense mutation, formed large tumors rapidly (in less than 4 wk) when transplanted to athymic mice, as did cells expressing pLTR13p53, which had undergone a V173F missense mutation and an in-frame deletion of 48 bp between codons 208 and 223. Cells transfected with pLTR17p53, predicted from the nucleotide sequence to encode a severely truncated p53 corresponding to the N-terminal 56 amino acids, also formed tumors. Cells transfected with pLTR15p53, which was predicted to encode a less severely truncated molecule, formed much smaller tumors and at lower frequencies. NIH/3T3 cells transfected with pLTR12p53 (exon 7 splice donor mutant), pLTRwtp53 (wild-type p53), or vector alone failed to form tumors for up to 2 mo after transplantation. pLTR6p53-transfected cells exhibited a highly malignant phenotype with invasion of regional lymph nodes, mediastinal and lung metastases, invasion of the abdominal wall, and dissemination throughout the peritoneal cavity. Histological assessment of the tumors revealed intensely vascularized fibrosarcomas with numerous cellular atypia, including frequent and aberrant mitoses. Tumor explants were recultured, and northern blot analysis of cellular RNA confirmed that the expression of exogenous p53 was maintained in each case. These data indicate that different p53 mutants contribute to tumorigenesis by specific mechanisms. Furthermore, the results obtained by using the pLTR17p53 transfectants imply that some truncated molecules may overcome the effects of wild-type p53 to contribute to malignancy.

The natural somatic mutation frequency and human carcinogenesis

Much recent attention has been paid to the important role of the DNA mismatch repair system in controlling the accumulation of somatic mutations in human tissues and the association of mismatch repair deficiency with carcinogenesis. In the absence of an intact mismatch repair system, cells accumulate mutations at a rate some 1000 times faster than normal cells, and this mutator phenotype is easily measured by the detection of the formation of new variant alleles at microsatellite loci. However, the mismatch repair system is not 100% efficient, even when intact, and the pattern of microsatellite alterations in a wide variety of tumors is consistent with these being due to clonal amplification from tissues that are genetically heterogeneous at microsatellite loci rather than mismatch repair deficiency in the tumor itself. On this basis, it can be estimated that the mutation frequency of microsatellites in normal human tissues is approximately 10(-2) per locus per cell. Similarly, a frequency of mutation at minisatellite loci in normal tissues of around 10(-1) per locus per cell can be estimated. Such elevated levels of mutation are consistent with a recent study of the frequency of HPRT mutation in human kidneys that demonstrated these to be frequent (average 2.5 x 10(-4) in individuals of 70 years or more) and exponentially related to age. Taken as a whole, the data suggest that somatic mutation in human epithelial cells may be some 10-fold higher than in peripheral blood lymphocytes and that the underlying rate of spontaneous mutation is sufficient to account for a large proportion of human carcinogenesis without the need to evoke either stepwise alteration to a mutator phenotype of clonal expansion at all the mutation steps in carcinogenesis. The exponential increase in mutation frequency with age is predictable on the basis that the mutation rate is controlled at the level of repair and that mutation in genes that affect the efficiency of these processes will gradually increase the underlying rate. In addition, the age relatedness of mutation frequency strongly supports the concept that mutation is cell division dependent and that cellular proliferation per se is an important risk factor for cancer. Comparison of somatic mutations with those in the human germline mutation suggests common mechanistic origins and that the high levels of somatic mutation that occur are a direct reflection of the germline mutation rate selected over evolutionary time. Thus, the somatic accumulation of mutations can be seen as a natural process within the human body and cancer a normal part of the human life cycle. This point of view may explain why it has been so difficult to significantly reduce cancer incidence and suggests that, for this to be achieved, the means of altering the natural somatic mutation rate needs to be identified.

Barrett's esophagus. The significance of p53 in clinical practice

OBJECTIVE

The authors provide an updated review the molecular biology of the p53 tumor suppressor gene with reference to its role in the malignant degeneration of Barrett's esophagus.

SUMMARY BACKGROUND DATA

Appreciation of the function of the tumor suppressor gene p53 has given new insight into regulation of the cell cycle, and the gene appears to play an important role in many solid tumors. Esophageal adenocarcinoma is increasing in frequency in the western world at an alarming rate and is unique because there is a clear metaplasia (Barrett's mucosa)/ dysplasia/carcinoma sequence. p53 malfunction arises as an early event in this carcinogenic process and has been demonstrated in patients with nondysplastic Barrett's metaplasia. The possible causes of p53 malfunction in this setting are discussed. The most reliable method for the detection of p53 mutations is DNA sequencing. p53 immunohistochemistry appears too insensitive to act as a reliable marker for the presence of a mutation and cannot be used as a reliable marker for the future development of cancer.

CONCLUSIONS

High-grade dysplasia within Barrett's mucosa remains the best clinical predictor of adenocarcinoma. The mutational spectrum observed in these tumors should provide clues to their etiology.

Deletion of the p53 gene in a patient with aggressive burn scar carcinoma

BACKGROUND

Aggressive squamous cell carcinoma (SCC) is known to occur in scars that develop after a burn injury, especially in the underdeveloped areas of the world where care is lacking. Because most SCC are associated with abnormalities in tumor suppressor genes, particularly p53, we postulated that similar mechanisms may underlie the development of burn-associated SCC.

METHODS

We analyzed tissue DNA from a patient who died from an aggressive SCC in a burn scar for evidence of p53 gene abnormalities by polymerase chain reaction and immunohistochemical staining for p53 protein.

RESULTS

Using polymerase chain reaction, the p53 gene could not be detected in DNA from the patient's cancer. The p53 protein was also undetectable by immunohistochemical staining.

CONCLUSION

These studies indicate that there was a homozygous deletion of the p53 gene in this burn-related carcinoma. Further studies of other patients may lead to new understanding of this cancer, explain in part the usual aggressive behavior, and lead to new methods of prevention and treatment.

A high-resolution analysis of chromatin structure along p53 sequences

A detailed investigation of how nucleosomes are formed and arranged on the DNA sequence is a prerequisite to understanding the molecular mechanisms of DNA-dependent processes such as transcription, replication, DNA repair, and mutagenesis. In this report we analyzed the chromatin structure of exons 5-8 of the p53 gene in human fibroblasts. We mapped at the nucleotide level the positions of DNase I and micrococcal nuclease cleavage sites in permeabilized cells. Areas of clear DNase I protection, which would be indicative of the binding of sequence-specific proteins, were not detected. Instead, the micrococcal nuclease and DNase digestion patterns suggested that this region was covered by nucleosomes and that two areas spanning exons 5 and 6 are occupied preferentially. These nucleosomes could influence DNA damage distribution, repair of certain lesions, and other aspects of the mutagenesis process in p53 sequences.

Mutations in the p53 gene in pulmonary blastomas: immunohistochemical and molecular studies

Well-differentiated fetal adenocarcinomas and biphasic blastomas are types of lung cancer that contain glands that mimic the appearance of fetal lung. Biphasic blastomas also show a primitive embryonic stroma. Despite histological similarities leading these two tumors to be classified as pulmonary blastomas, they have distinct clinical and prognostic features. Little information is available on genetic changes in these tumors because they are rare; therefore, the authors studied nine biphasic blastomas and 12 well-differentiated fetal adenocarcinomas for the presence of mutations in the p53 gene. Mutations in the p53 gene are common in other lung cancers, and the type of mutation in the p53 gene can provide information about the original or inciting mutagens. The authors found five biphasic blastomas (42%) had mutations in the p53 gene by immunohistochemical and molecular analysis, whereas none of the well-differentiated fetal adenocarcinomas contained mutations. These results provide molecular support for the significance of distinguishing between well-differentiated fetal adenocarcinoma and biphasic blastoma histologically and identify several types of p53 gene mutations that occur in these tumors.

The role of altered [Ca2+]i regulation in apoptosis, oncosis, and necrosis

Understanding the processes and events that occur when a cell undergoes a prelethal injury or that lead the cell to death following a lethal injury has been the aim of our research for a number of years. Throughout this period much has been learned, recently at rapid rates, not only by us but by many other investigators as well. Based on the data gathered, we proposed a working hypothesis over a decade ago and have since continually updated it as new experimentation is performed. Our laboratory has focused particularly on the role of cytoplasmic ionized calcium ([Ca2+]i) and the effects of its deregulation on prelethal events, including oncosis and apoptosis, and lethal events (necrosis) following cell death. [Ca2+]i appears to be a major link and signalling event. Understanding the mechanisms involved by using a variety of in vivo and in vitro models, coupled with state-of-the-art methodologies, should now allow us to prevent cell death by killing cells when necessary through gene therapy and cancer chemotherapy.

Functional interaction between DP-1 and p53

The cellular transcription factor DRTF1/E2F and the tumor suppressor protein p53 play important roles in controlling early cell cycle events. DRTF1/E2F is believed to coordinate and integrate the transcription of cell cycle-regulating genes, for example, those involved in DNA synthesis, with the activity of regulatory proteins, such as the retinoblastoma tumor suppressor gene product (pRb), which modulate its transcriptional activity. In contrast, p53 is thought to monitor the integrity of chromosomal DNA and when appropriate interfere with cell cycle progression, for example, in response to DNA damage. Generic DRTF1/E2F DNA binding activity and transcriptional activation arise when members of two distinct families of proteins, such as DP-1 and E2F-1, interact as DP/E2F heterodimers. In many cell types, DP-1 is a widespread component of DRTF1/E2F DNA binding activity which when expressed at high levels oncogenically transforms embryonic fibroblasts. Here, we document an association between DP-1 and p53 and demonstrate its presence in mammalian cell extracts. In vitro p53 interacts with an immunochemically distinct form of DP-1 and in vivo can regulate transcription driven by the DP-1/E2F-1 heterodimer. At the biochemical level, p53 competes with E2F-1 for DP-1, with a consequent reduction in DNA binding activity. Mutational analysis defines within DP-1 a C-terminal region required for the interaction with p53 and within p53 an N-terminal region distinct from that required to bind to MDM2. Our results establish DRTF1/E2F as a common cellular target in growth control mediated through the activities of pRb and p53 and suggest an alternative mechanism through which p53 may regulate cellular proliferation.

The flow cytometric analysis of total p53 protein content and proliferation indices in colorectal cancer, in relation to clinical outcome

This study was undertaken to assess the value of flow cytometric measurements of total p53 protein content and proliferation indices derived from in vivo halogenated pyrimidine labelling. Two series of colorectal cancer specimens were studied for which clinical outcome data were recorded. A series of 84 archival, ethanol-fixed, bromodeoxyuridine (BrdUrd) labelled colorectal tumours were analysed by flow cytometry for their total and cell cycle phase p53 protein content using the pAb1801 monoclonal antibody. A second series of 33 freshly obtained tumours was used for assay evaluation and for comparison with the archival material. In the archival series (n=84), the median p53-pAb1801 LI was 81.9% (range: 11.1-99.8%). In only three tumours could significant amounts of p53 protein not be detected. The median phase specific p53-pAb1801 LI in G0/G1 was 71.6%, in S was 95.5%, and in G2/M was 98.5%. In the series of fresh tumours (n=33), the median p53-pAb1801 labelling index (LI) was 94.6% (range: 17.9-99.9%). Only two tumours failed to express significant amounts of p53 protein. There was no significant difference in the generally high levels of p53 protein content between the fresh and archival series. Life-table analysis of the patients in the archival series failed to demonstrate a statistical difference in life expectancy in relation to Dukes' stage when tumours were stratified by the median total p53 labelling index. In this study, p53 content and proliferative indices measured by flow cytometry do not have independent predictive value over Dukes' grading in determining the outcome of colorectal cancer. Flow cytometry is confirmed as a practical tool for multi-parametric and cell cycle analysis of oncoprotein expression in human tumour biopsies.