Characterization of the human p53 gene

Dissemination of a Sjögren's syndrome-associated extranodal marginal-zone B cell lymphoma: circulating lymphoma cells and invariant mutation pattern of nodal Ig heavy- and light-chain variable-region gene rearrangements

OBJECTIVE

Both the genesis and outgrowth of extranodal marginal-zone B cell lymphomas (MZLs) of the mucosa-associated lymphoid tissue (MALT) type are generally thought to represent antigen-driven processes. We undertook this study to analyze lymphoma progression and dissemination outside of the MALT-type lesions.

METHODS

Histopathologic and Ig heavy- and light-chain variable-region gene (V(H/L)) analyses were performed in sequential tissue samples from a patient with primary Sjögren's syndrome (SS) with glandular (parotid) manifestations and subsequent nodal dissemination of a low-grade MZL.

RESULTS

This MZL expressed a CD20+,CD27+,sIgM/kappa+,IgD-,CD5-,CD10-,Bcl-6-,CD23-,p53-,p21-,MDM2- phenotype and mutated V(H)1-69/D2-21/J(H)4alpha-V(kappa)A27/J(kappa)2 Ig rearrangements. Notably, circulating lymphoma cells from the parotid glands occurred transiently in the patient's blood, as detected by single-cell polymerase chain reaction. In addition, 2 minor B cell clones (clones 2 and 3, with V(H)3-07/D3-22/J(H)3b-V(lambda)3L/J(lambda)2/3 and V(H)3-64/D3-03/J(H)2-V(kappa)A19/J(kappa)2 rearrangements, respectively) were also detected in the parotid glands and blood, and 1 of these (clone 2) was also detected in the lymph nodes. Ig V(H/L) analyses revealed ongoing (antigen-driven) mutations of the glandular lymphoma rearrangements, but an invariant mutation pattern of their nodal counterparts.

CONCLUSION

These data indicate coexpansion and transient (re)circulation of the lymphoma clone and 2 additional glandular B cell clones in a primary SS-associated extranodal MZL. Combined histologic and molecular features of the nodal lymphoma subclone reflect a process of "follicular colonization" that eventually froze the mutation machinery after accumulation of additional (antigen-driven) Ig V(H/L) mutations.

PRIMA-1 induces apoptosis in acute myeloid leukaemia cells with p53 gene deletion

The p53 tumour suppressor gene located on chromosome 17p13 is the most frequently mutated gene in human tumours. About 5-8% of cases with acute myeloid leukaemia (AML) carry the p53 mutation. Recently, the compound p53-dependent reactivation and induction of massive apoptosis (PRIMA-1) has been shown to induce cytotoxic effects and apoptosis in human tumour cells by restoration of the transcriptional activity of mutated p53. This is believed to be mediated by a change in the conformation of mutated p53 protein, restoring DNA binding and activation of p53 target genes. We studied the effects of PRIMA-1 and commonly used antileukaemic drugs on AML cells from 62 patients. Cells were obtained from peripheral blood or bone marrow and were exposed to PRIMA-1, cytarabine, daunorubicin, chlorodeoxyadenosine and fludarabine. This study showed that PRIMA-1 had cytotoxic effects on AML cells. Conventional AML drugs were less effective in cells with hemizygous p53 deletion. Interestingly, our data indicated that PRIMA-1 was more effective in this subgroup of patients compared with patients with normal chromosome 17. Our data suggest that the concept of restoration of p53 protein by PRIMA-1 or a PRIMA-1-based new drug may increase the efficacy of AML treatment in patients with p53 mutations.

P53 mutations in tissue from Danish ovarian cancer patients

OBJECTIVES

The p53 gene, a tumor suppressor gene located on the short arm of chromosome 17 (17p13), has been found mutated in 30-80% of epithelial ovarian cancers (OC), with the most frequently detected mutations in the conserved regions of the gene. A small number of studies investigated the survival of patients with p53 mutations in OC, but their conclusions are not in agreement.

METHODS

We analyzed the frequency of p53 mutations in 124 Danish women with OC, using Single-Stranded Conformation Polymorphism analysis in addition with DNA sequencing and evaluated if mutations correlated with clinicopathological parameters and with patient survival.

RESULTS

Thirty-five (28%) ovarian tumors were found to contain one or more p53 variations, two of which were considered polymorphisms. Twenty-seven (82%) mutations were single nucleotide substitutions of which 23 (85%) were missense mutations and therefore led to amino acid substitutions. Significantly shorter survival was found for stage III/IV patients with a p53 missense mutation compared to stage III/IV OC patients with wild type p53 (P = 0.0018). Multivariate Cox regression analysis restricted to 107 OC patients with a p53 missense mutation or p53 wild type in the tumor tissue and with information on radicality of primary surgery showed that missense p53 mutation (HR = 2.5, 95% CI: 1.21-4.98), radicality after primary surgery (HR = 1.7, 95% CI: 1.04-2.88), tetranectin (mg/l: HR = 0.78, 95% CI: 0.67-0.91) and stage (I vs. III: HR = 0.30, 95% CI: 0.10-0.92, II vs. III: HR = 0.24, 95% CI: 0.05-1.05, IV vs. III: HR = 2.70, 95% CI: 1.22-5.98) were independent prognostic factors.

CONCLUSION

Missense mutations in the conserved regions of p53 may be of prognostic value in Danish OC patients.

Therapy-related leukemia: clinical characteristics and analysis of new molecular risk factors in 96 adult patients

Therapy-related leukemia or myelodysplasia (t-leuk/MDS) is a serious problem that is increasing in frequency. We studied the clinical characteristics of 96 patients (pts) with a mean age of 48 years, and analyzed the molecular parameters that could predispose to t-leuk/MDS. Hematological malignancies were the most common primary (53%), followed by breast and ovarian cancer (30% combined). The mean latency until the development of t-AML was 45.5 months. Median survival was 10 months. Cytogenetics was abnormal in 89% of pts. FLT3 internal tandem duplications were found in six of 41 (14.6%) pts, of whom four had an abnormal karyotype. Analysis of drug metabolism and disposition genes showed a protective effect of the CYP3A4 1*B genotype against the development of t-leuk/MDS, whereas the CC genotype of MDR1 C3435T and the NAD(P)H:quinone oxidoreductase1 codon 187 polymorphism were both noncontributory. Microsatellite instability (MSI) analysis using fluoresceinated PCR with ABI sequence analyzer demonstrated that 41% of pts had high levels of MSI in four or more of 10 microsatellite loci. Immunohistochemistry demonstrated reduced expression of MSH2 and MLH1 in 6/10 pts with MSI as compared to 0/5 of pts without MSI. In conclusion, genetic predisposition as well as epigenetic events contribute to the etiology of t-AML/MDS.

No significant role for beta tubulin mutations and mismatch repair defects in ovarian cancer resistance to paclitaxel/cisplatin

Background

The mechanisms of chemoresistance in ovarian cancer patients remain largely to be elucidated. Paclitaxel/cisplatin combination is the standard chemotherapeutic treatment for this disease, although some patients do not respond to therapy. Our goals were to investigate whether TUBB mutations and mismatch repair defects underlie paclitaxel and cisplatin resistance.

Methods

Thirty-four patients with primary ovarian carcinomas (26 serous and eight clear cell carcinomas) treated with paclitaxel/cisplatin were analysed. TUBB exon 4 was analysed by nested PCR after a first round PCR using intronic primers. Microsatellite analysis was performed with the quasimonomorphic markers BAT 26 and BAT 34.

Results

Twenty-two of the 34 ovarian cancers (64.7%) presented residual tumour after surgery, seven of which (7/22; 31.8%) were shown to be chemoresistant (five serous and two clear cell tumours). Sequence analysis did not find any mutation in TUBB exon 4. Microsatellite instability was not detected in any of the ovarian carcinomas.

Conclusion

We conclude that TUBB exon 4 mutations and mismatch repair defects do not play a significant role in paclitaxel/cisplatin resistance.

The tumor suppressor gene TP53: implications for cancer management and therapy

The p53 protein is an inducible transcription factor with multiple anti-proliferative roles in response to genotoxic damage; unprogrammed proliferative stimuli; and deprivation of oxygen, nutrients, or ribonucleotides. Inactivation of the TP53 gene by mutation or deletion is the most common event in human cancer. Loss of p53 function compromises genetic homeostasis in cells exposed to mutagens and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Genetic interventions aiming at expressing wild-type TP53 in cancer cells, either by retroviral or adenoviral transfer, have met limited clinical success. However, recently, the use of a defective adenovirus (ONYX-015) that selectively kills p53-incompetent cells has shown promising effects in pre-clinical and clinical studies. Pharmacological methods are under development to either stimulate wild-type p53 protein function or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3), or single-chain Fv antibody fragments corresponding to defined p53 domains. In addition, detection of mutant TP53 may also serve as a marker for early cancer detection, prediction, and prognosis. In this review, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

Effects of PRIMA-1 on chronic lymphocytic leukaemia cells with and without hemizygous p53 deletion

The tumour suppressor gene p53 is the most commonly mutated gene in solid tumours. Although less common in haematological malignancies, 10-15% of B-cell chronic lymphocytic leukaemia (B-CLL) cases carry a p53 mutation. Recently, the compound P53-dependent reactivation and induction of massive apoptosis (PRIMA-1) has been shown to induce cytotoxic effects and apoptosis in human tumour cells by restoration of the transcriptional activity of mutated p53. This is believed to be mediated by a change in the conformation of mutated p53 protein, restoring DNA binding and activation of p53 target genes. We studied the effects of PRIMA-1 and commonly used anti-leukaemic drugs on B-CLL cells from 14 patients with and without hemizygous p53 deletion. Cells obtained from peripheral blood or bone marrow were exposed to PRIMA-1 and fludarabine alone or in combination. PRIMA-1 showed cytotoxic effects on B-CLL cells from samples with and without hemizygous p53 deletion. Furthermore, conventional B-CLL drugs were less effective in cell samples with hemizygous p53 deletion and the response depended on the size of the p53 deleted clone. Finally, we found evidence for synergistic and additive effects of PRIMA-1 in combination with fludarabine.

HIV-1 integration sites are flanked by potential MARs that alone can act as promoters

Matrix attachment regions (MARs) are cis regulatory elements that modulate gene expression in a tissue and cell stage specific manner. Recent reports show that viral integration within the genome takes place at nonrandom active genes. We have checked for the presence of MARs in the vicinity of the reported 524 HIV-1 integration sites. Our studies show that in 92.5% cases, MARs flank the integration sites. Similarly, for adeno-associated virus, two potential MARs were present next to the integration site on the human chromosome. Earlier we have shown that short MAR sequences present upstream of HIV-1 LTR promote processive transcription at a distance. Here, using a well-studied IgH-MAR and another potential MAR from p53 promoter, we demonstrate that MARs alone can act as promoters. Thus, we propose that MAR elements near the HIV-1 integration sites can act as potential promoters, which may facilitate proviral integration and transcription.

The role of steroid contraceptive hormones in the pathogenesis of invasive cervical cancer: a review

Invasive cervical cancer remains a leading cause of morbidity and mortality, especially among women in the developing world where screening is either deficient or absent. Of all agents linked to the causation of this disease, high-risk human papillomavirus (HPV) appears to be the strongest factor. However, not all women with HPV develop cervical cancer. Steroid contraception has been postulated to be one mechanism whereby HPV exerts its tumorigenic effect on cervical tissue. Steroids are thought to bind to specific DNA sequences within transcriptional regulatory regions on the HPV DNA to either increase or suppress transcription of various genes. Although some earlier studies were reassuring as no increased incidence of cervical cancer was observed, subsequent research has shown a causative association, especially among long-term users. The role of steroids was further enhanced by the discovery of hormone receptors in cervical tissue. Some earlier studies of oral contraceptive steroids found no increased risk, even after controlling for other risk factors, including smoking and number of partners. However, prospective studies have shown a greater progression of dysplasia to carcinoma-in-situ with more than 6 years of oral steroid contraceptive use. Similar findings were also evident from other work, including the Royal College of General Practitioners Oral Contraception Study. The WHO Collaborative Study of Neoplasia and Steroid Contraceptives showed a relative risk of 1.2 for invasive cancer in users of the long-acting progestational contraceptive, depo-medroxyprogesterone acetate. However, in users of more than 5 years duration, an estimate of 2.4 was reported. The upstream regulatory region (URR) of the HPV type 16 viral genome, mediates transcriptional control of the HPV genome and is thought to contain enhancer elements that are activated by steroid hormones. It has been shown that steroid hormones bind to specific glucorticoid-response elements within HPV-DNA. Experimental evidence has revealed that high-risk type HPV 16 are able to stimulate the development of vaginal and cervical squamous cell carcinomas in transgenic mice exposed to slow-release pellets of 17 beta-estradiol in the presence of human keratin-14 promoter. Squamous cell carcinomas developed in a multi-stage pathway only in transgenic mice and not in nontransgenic mice. The E6 oncoprotein of HPV 16 has been shown to bind to the p53 tumor suppressor gene and stimulate its degradation by a ubiquitin-dependent protease system. Steroid hormones are thought to increase the expression of the E6 and E7 HPV 16 oncogenes, which in turn bind to and degrade the p53 gene product, leading to apoptotic failure and carcinogenesis. However, the molecular basis of this remains to be proven.

8-Cl-cAMP affects glioma cell-cycle kinetics and selectively induces apoptosis

8-Chloro-cyclic-adenosine-3',5'-monophosphate (8-Cl-cAMP), a site-selective synthetic cyclic adenosine 3',5'-monophosphate (cAMP) analog exhibits growth inhibition in a broad spectrum of human cancer lines. However, detailed studies on the effects exerted by cAMP analogs on cell-cycle kinetics have been lacking. We have examined and compared the effect of 8-Cl-cAMP on cell-cycle kinetics in two human glioma cell lines, U87MG (p53wt) and U251MG (p53mt). A flow cytometric analysis of cell-cycle distribution as well as apoptosis evaluation were performed by univariate DNA analysis after 24-72 hr of treatment with 10-50 M concentrations of 8-Cl-cAMP. Longer incubation with 8-Cl-cAMP induced dose related accumulation of cells in S phase and a subsequent decrease in the proportion of cells in G0/G1 phase of cell cycle in both cell lines. Time-dependent suppression of cyclin B1 was detected in both glioma cell lines and could be associated with observed G2 delay. However, 8-aCl-cAMP selectively induced apoptotic cell death only in U87MG, but not in U251MG cells. Induction of apoptosis was revealed both by flow cytometry and apoptotic cell morphology. These results provide an insight into the mechanism of 8-aCl-cAMP action, suggesting that the disturbance of cell-cycle kinetics and induction of apoptosis might contribute to its growth-inhibitory effect on cancer cells.

P53 autoantibodies in sera from Danish ovarian cancer patients and their correlation with clinical data and prognosis

The p53 gene, a tumour suppressor gene located on the short arm of chromosome 17 (17p13), is frequently mutated in various human tumours. Accumulation of p53 protein in neoplastic cells and its release following tumour necrosis can lead to development of circulating autoantibodies (AAb) against p53. Earlier studies of ovarian cancer (OC) patients reported different frequencies of p53 AAb and conclusions regarding the clinical and prognostic value of these AAb have not been in agreement. We therefore analysed for the presence of p53 AAb in a total of 227 preoperative serum samples from 193 OC patients and 34 patients with ovarian borderline tumours, and, in addition, serum samples from 86 healthy controls. An enzyme-linked immunosorbent assay (ELISA) was used to measure serum IgG antibodies against p53. The p53 protein used in the assay was produced as a hexahistidine-tagged fusion protein by baculovirus-infected Spodoptera frugiperda cells. Cut-off values for p53 AAb were evaluated, and correlations of p53 AAb with clinical-, biochemical data and survival were examined. We found a low sensitivity for p53 AAb alone, and no major additional effect of the detection rate of CA125 was found. No significant associations were found between p53 AAb and clinical stage, age, histological subtype and radicality after primary surgery. In contrast, we found significantly elevated CA125 levels in p53 AAb-positive patients compared to lower CA125 levels in p53 AAb-negative patients (p=0.003). No significant differences were found between p53 AAb-positive and p53 AAb-negative patients in the univariate and multivariate survival analyses. In conclusion, in a screening study for OC serum p53 AAb levels are of no diagnostic value, even if combined with the tumour marker CA125. The presence of increased serum p53 AAb in patients with diagnosed OC could not be correlated with any clinical data and preoperative serum p53 AAb status had no evident value.

Relationship between p53 codon 72 polymorphism and susceptibility to sunburn and skin cancer

Upregulation of p53 protein induces either growth arrest or apoptosis in response to cellular injury This is signaled from a highly conserved p53 domain between codons 64 and 92, where a functional polymorphism results in either a proline (p53-72P) or an arginine (p53-72R) at codon 72. Preliminary studies suggest that p53-72R may be a risk factor for cervical cancer and, consistent with this, preferential mutation and retention of the p53-72R allele has also been demonstrated in other cancers of squamous cell origin. Here we examine the relationship between allelic forms of p53 and nonmelanoma skin cancer, by determining the correlation with susceptibility to sunburn, which is a known risk factor, and then by p53 sequence analysis of a large series of tumors. We found a significant positive association between p53-72R and susceptibility to sunburn, as assessed by skin phototype and minimal erythemal dose following solar-simulated radiation (p = 0.0001 for trend). We also found a significant association between p53-72R homozygosity and nonmelanoma skin cancer in renal transplant recipients (basal cell carcinoma, p < 0.01; squamous cell carcinoma, p < 0.05) but not in immunocompetent patients compared with skin type matched controls. p53 sequence data revealed mutations in 30 of 70 (42.9%) nonmelanoma skin cancers, 28 (93%) of which were in the p53-72R allele. Loss of heterozygosity occurred more frequently in p53-72RP than in p53-72RR tumors (p = 0.0001) with preferential loss of p53-72P in heterozygotes (p = 0.016), irrespective of the mutant status of the concomitant allele. Together these data infer functional differences between polymorphic forms of p53 that are likely to be relevant to skin carcinogenesis.

Molecular characterization of p53 mutations in primary and secondary liver tumors: diagnostic and therapeutic perspectives

p53 is one of the most mutated genes in human cancer. We have performed the molecular characterization of p53 and have searched for correlations with etiological factors and clinical parameters in primary and secondary liver tumors. A systematic study was carried out, innovative in many respects, to determine the mutational pattern of all 11 exons of p53 and analysis was extended also to exons 1-4 and 9-11 and the exon/intron junctions. Our analyses were performed on case histories of 114 patients from the European area and highlighted p53 mutation patterns different from those reported in the literature for the same tumors. In our case history, different tumors of the same organ showed a different frequency and distribution of mutations. In analyzed tumor types, gene status was a prognostic indicator of survival because patients undergoing liver resection without mutated p53 had a more favorable prognosis than mutated patients. This suggests p53 molecular diagnosis could become a further criterion in the decision for surgery and possible therapies. We describe the ideal conditions for polymerase chain reaction (PCR), single-strand conformation polymorphism (SSCP), and direct sequencing, which we have set in order to optimize yields, sensitivity, and time of what might become a massive molecular screening.

The diversity of p53 mutations among human brain tumors and their functional consequences

The p53 tumor suppressor is implicated in cell cycle control, DNA repair, replicative senescence and programmed cell death. Inactivation of the p53 contributes to the wide range of human tumors, including glial neoplasms. In this review, we describe the regulation and biochemical properties of p53 protein that may explain its ability to activate various genetic programs underlying cellular responses to stress conditions. The overall spectrum of p53 mutations is rather shared between tumor types indicating that these mutations are not tumor type-specific. However, there is one example of germ-line mutation of p53 gene (the deletion of the codon 236) that is associated with a familiar brain tumor syndrome. We compare the frequency and type of most common mutations among various brain tumours (focusing on glioblastomas) and their consequences on protein functions. Furthermore, we discuss the most promising approaches of potential brain tumor therapy, including an adenovirus-mediated p53 gene transfer. Human glioblastomas are highly sensitive to the effects of p53 activity when the wild-type p53 is introduced ectopically. It suggests that the genetic or pharmacological modulation of the p53 pathway is potentially important strategy in the treatment of human cancers.

Anaplastic ganglioglioma with sarcomatous component: an immunohistochemical study and molecular analysis of p53 tumor suppressor gene

The present case report describes a case of ganglioglioma with a distinct sarcomatous component in the left temporal lobe of a 59-year-old Japanese man. Neoplastic neuroglial tissue contained both benign and anaplastic glial components with a MIB-1 labeling index of 0.1% and 12.0%, respectively. Sarcomatous tissue adjacent to the anaplastic glial tissue was dominated by pleomorphic fibroblastic cells with a MIB-1 labeling index of 10.8%. They were immunoreactive for smooth muscle actin, type IV collagen, and alpha 1 antitrypsin, but not for desmin and CD34. Interestingly, some of the sarcomatous cells were double-positive for smooth muscle actin and GFAP. The p53 protein had accumulated in the anaplastic astrocytes and sarcomatous cells, but direct DNA sequencing of PCR products failed to detect any mutation in the p53 gene (from exon 4 to exon 10).

Detection of p53 gene mutations by single strand conformational polymorphism (SSCP) in human acute myeloid leukemia-derived cell lines

We have identified new mutations in the p53 gene in 3/11 growth factor-independent and in 2/8 growth factor-dependent human acute myeloid leukemia (AML)-derived cell lines by single-strand conformational polymorphism (SSCP) and sequencing analysis. MEG-01 had a triplet deletion at codon 304; F-36P, NB-4 and MV4-11 showed point mutations at codon 344. F-36P had a second point mutation at codon 270 and NB-4 additionally at codon 319. M-MOK had a nucleotide substitution at codon 191. The frequency of p53 mutations in the cytokine-independent cell lines was comparable to that in the cytokine-dependent lines. These results suggest that loss of Wild type (wt) p53 is not the decisive event causing tumor cells to proliferate in vitro without externally added growth factors.

Epstein-Barr virus-associated gastric lymphomas are distinct from mucosa-associated lymphoid tissue-type lymphomas: genetic abnormalities of p53 gene

The authors studied 46 primary gastric lymphomas for expression of the p53 gene by immunohistochemistry and screened for mutations in p53 exon 5-8 by polymerase chain reaction-single strand conformation polymorphism. Twenty-five specimens cases were also analyzed for loss of heterozygosity (LOH) of chromosomal region 17p12-13.1. In 36 lymphomas negative for Epstein-Barr virus (EBV) infection, of which 29 were of mucosa-associated lymphoid tissue (MALT) type, p53 genetic changes were found in 47.2% but correlated poorly with overexpression. Only 20% of the mutations involved exon 7. There were recurrent mutations of intron 7, intron 6, and exon 6. In contrast, the 10 EBV-positive cases, none of MALT type, had a much higher rate of mutation, and all showed both p53 overexpression and p53 mutation and/or LOH, and 87.5% had mutations involving exon 7. Four of these involved codon 242, not seen in the EBV-negative group. Splicing mutations of intron 8 were seen in three specimens, two involving the same nucleotide position. In four of five specimens, LOH analysis identified microsatellite instability, allelic loss, or both. The Helicobacter pylori infection rate in the EBV-positive group (20%) was much lower than in the EBV-negative group (91.7%). These differences between the two groups suggest involvement of different carcinogens. Mutation of codon 242 has not been specifically associated with other tumors and may represent a mutational hot spot in the EBV-positive lymphomas.

Characterization of nuclear factors binding to AT-rich element in the rat p53 promoter

In this study, we identified AT-rich element located at positions -504 to -516 in the rat p53 promoter by DNase I foot printing assay. This region was previously identified as a positive regulatory element in the murine p53 promoter and designated as PBF1 (p53 binding factor 1) binding site. However, the proteins binding to this AT-rich element have not been identified yet. Therefore, we characterized the binding protein by various biochemical methods. First, we confirmed that by the oligonucleotide competition assay, nuclear factors bound to the AT-rich element in a sequence-specific manner. Two binding proteins were identified in southwestern blotting analysis and the molecular masses of the proteins were 60 and 40 kDa, respectively. The proteins were stable to denaturants or ionic strength. Treatment of chelators showed that the binding proteins did not require divalent cation for DNA-binding activity. In addition, the binding proteins were labile to protease treatment. This study showed that 60 and 40 kDa proteins bound to AT-rich element and the physico-chemical properties provided new insights into the binding proteins.

Identification of a transcription factor, an 80-kDa protein that interacts with the HLH recognition motif of the rat p53 promoter

The p53 promoter has been shown to contain a number of potential regulatory motifs. It was previously reported that the upstream stimulating factor (USF) played a central role in regulating the p53 expression. The USF binding site, E-box, is located around 40 bp upstream of the major transcription start site. In this study, it was confirmed that the E-box binds to proteins by DNase I footprinting assay. In the electrophoretic mobility shift assay (EMSA), two retarded bands were detected. One band was abolished by the competition of USF consensus oligonucleotide, but the other band was not. This result indicated that a factor, other than USF, was bound to the E-box. The molecular masses of the binding proteins were determined by a Southwestern-blotting assay. As a result, 46- and 80-kDa proteins were detected. The 46-kDa protein was eliminated by the competition of USF consensus oligonucleotide. Also, the Southwestern-blotting assay with 32P-labeled USF consensus oligonucleotide showed only a 46-kDa protein. Therefore, the 46-kDa protein was USF. These results showed that USF and the 80-kDa protein were bound to the E-box. In addition, it was proved by in vitro transcription assay that this 80-kDa protein had a basal transcriptional activity.Key words: E-box, HLH, rat p53 promoter, transcription factor, upstream stimulating factor (USF).

Lack of ultraviolet-light inducibility of the medakafish (Oryzias latipes) tumor suppressor gene p53

P53 is by far the most frequently altered gene in mammalian tumors. However, so far not a single p53 lesion has been reported in malignancies of cancer model systems in lower vertebrates. For analyzing the function of p53 in lower vertebrates, the gene was cloned from the medakafish (Oryzias latipes). Despite some differences in the genomic organization, the fish p53 amino acid sequence is highly conserved. Contrary to higher vertebrates, the level of p53 mRNA in medaka embryos gradually increases during embryogenesis. High expression of the p53 mRNA was detected in melanoma cells compared to undetectable expression of the gene in embryonic stem cells and fibroblasts. No effect of ultraviolet (UV) irradiation on the expression of p53 in cell cultures as well as in medaka fry was observed, indicating a possible difference in the function of p53 in lower vertebrates.

Characterization of a nuclear factor that binds to AP1-like element in the rat p53 promoter during liver regeneration

The transcription level of the rat p53 gene increases at 5-12 h in the regenerating liver after partial hepatectomy. It was previously reported that an activator protein 1 (AP1)-like element (-264--284) mediated the induced transcription of the rat p53 gene during liver regeneration. In this study, we characterize the protein binding to the AP1-like element by various methods. Oligonucleotide competition assays showed that the binding protein did not require AP1 consensus sequence. Therefore, the binding protein is not an AP1 family protein. Zn(2+) was required for maximum DNA-binding activity of the protein, suggesting that the binding protein contains zinc fingers. The binding protein was highly resistant to denaturant. Even 1.8 M urea did not eliminate the protein-DNA complexes. In addition, the binding protein was stable up to 55 degrees C. The protein-DNA complexes were abolished in the presence of 0.6 M NaCl and higher. Protease clipping assay showed that the protein had a protease-resistant core DNA binding domain. These results provided new insights into the structure of the protein that binds to the AP1-like element of the p53 promoter during liver regeneration.

Alterations of P53 and RB genes and the evolution of the accelerated phase of chronic myeloid leukemia

Using the single-strand conformation polymorphism and heteroduplex analyses, the P53 and RB genes were analyzed in cell samples from twenty-eight patients with chronic myeloid leukemia (CML) both at diagnosis and at the onset of accelerated phase (AP) of the disease. No alterations of the P53 or RB genes were found in any of the chronic phase (CP) samples. Structural abnormalities of the P53 gene were observed in ten of twenty-eight AP samples within exons 4, 5, 7 and 9. Of the ten cases of AP disease with altered P53 genes, five patients also suffered from the deletion of the other allele. Alterations of the RB gene could be detected in six AP samples, and aberrant band patterns were found in the analysis of exons 2, 3, 4, 6, 7, 13, 14, 17, 21 and 26. Among the six AP samples with structural abnormalities of the RB gene, two showed the loss of the other allele. It is of note that alterations of both P53 and RB genes were observed in two AP samples. Our data strongly suggest that abnormalities of the P53 and RB genes and acceleration of CML are linked events in some cases of AP.

Single-step DGGE-based mutation scanning of the p53 gene: application to genetic diagnosis of colorectal cancer

We present a simple nonradioactive assay based on polymerase chain reaction (PCR) in combination with denaturing gradient gel electrophoresis (DGGE), which allows comprehensive mutation scanning of the entire coding sequence and splice junctions of the p53 gene in one analytical step. The key features of the present method are (1) all fragments can be amplified using one common PCR protocol; (2) all fragments can be scanned for mutations on a single "broad-range" denaturing gradient gel; and (3) all fragments were tailored by the attachment of appropriate GC clamps and otherwise manipulated to consist of only two melting domains in order to maximize resolution of mutations by DGGE. The entire procedure starting with a sample of genomic DNA can be completed within 6 hr and has the potential to detect any sequence variation, irrespective of its location in the p53 gene. The mutation detection sensitivity was demonstrated by the analysis of 26 constructed control mutations distributed over the whole of the p53 gene. We have applied the method to genetic diagnosis in 43 cases of colorectal cancer. Overall, a point mutation, microdeletion, or microinsertion was found in 26 (61%) of the tumors. In addition to missense and frameshift mutations within exons 4-8, a 20-bp insertion in exon 11 was found in one sample, illustrating the importance of comprehensive gene scanning for reliable diagnosis.

Detection of p53 gene mutations in oral squamous cell carcinomas of a black African population sample

Mutations in the p53 gene have been reported in head and neck carcinomas. We determined the p53 mutation profile in 55 oral squamous cell carcinomas (OSCCs) from a black African population sample. DNA from all the patients were investigated using PCR amplification of the p53 gene (exons 5-9), followed by heteroduplex single-stranded conformational polymorphism (HEX-SSCP) analysis on the PCR products. Direct sequencing was performed on cases where mutations were identified. The results showed mutations in 13 of 55 (23.6%) tumours. Eleven of 13 (85%) were single base pair substitutions (9 transitions and 2 transversions), and 2 were deletions. Two novel mutations were identified: a large 63-base pair deletion, and a single base pair substitution. The mutations in our study occurred outside the head and neck tumour hot spot region (codons 238-248).

MDM2 mRNA expression is a favorable prognostic factor in non-small-cell lung cancer

MDM2 is one of the downstream target genes for transcriptional activation by the product of the p53 tumor-suppressor gene. Transactivation of MDM2 gene expression is represented by the presence of a functional p53 protein. We hypothesized that MDM2 mRNA expression may be a more suitable prognostic factor than p53 or MDM2 protein expression and p53 gene mutations. In this study, expression of MDM2 mRNA, p53 protein, and MDM2 protein and mutations of the p53 gene were assessed in 81 lung tumor tissue specimens using RT-PCR, immunohistochemistry, and direct sequencing among exons 5-8, respectively. By immunohistochemistry, 33 and 42 of 81 patients with p53 (40.7%) and MDM2 (51.5%) protein expression were found in lung tumor specimens, respectively. The p53 direct sequencing data indicated that 13 of 81 patients (16.0%) had p53 mutations. However, Kaplan-Meier analysis showed that p53 protein and MDM2 protein expression and p53 mutation were not useful as prognostic factors. Interestingly, the survival of patients with MDM2 mRNA expression was longer than that of patients without MDM2 mRNA expression, though MDM2 mRNA expression was not associated with clinicopathological parameters, including tumor grade, tumor stage, tumor type, and TNM values. Moreover, Cox regression analysis showed that MDM2 mRNA expression was a significantly independent favorable prognostic factor in non-small-cell lung cancer (NSCLC) patients. Thus, measuring MDM2 mRNA expression using RT-PCR may be a simple, useful approach for predicting the survival of NSCLC patients.

Biochemical characterization of a nuclear factor that binds to NF1-like elements in the rat p53 promoter

We previously reported that two nuclear factor 1-like elements mediated the transcription of the rat p53 gene. A 40-kDa protein was shown to bind to these elements, which was different from common NF1 family proteins. In this study, the biochemical properties of the 40-kDa binding protein were investigated. The metal ion dependency of the protein was examined with various chelators; the protein was proved to require Mg(2+) for maximum DNA-binding activity. The binding protein was highly resistant to ionic strength and denaturant. The protein-DNA complex was reduced at high NaCl concentration, but residual DNA-binding activity remained. Even 2 M urea did not completely eliminate the formation of protein-DNA complex. DNA-binding activity of the protein was also stable at high temperature. Treatment of the protein-DNA complex with increasing concentrations of proteinase K or trypsin demonstrated the existence of a protease-resistant DNA-bound core. These biochemical properties provide new insight into the 40-kDa NF1-like nuclear factor.

Gene response of human skin fibroblasts to urokinase- and tissue-type plasminogen activators

In a previous work we have reported evidences on the mitogenic activity of urokinase-type and tissue-type plasminogen activator (u-PA, t-PA) on serum-deprived human dermal fibroblasts. In this work we have studied the transcription-dependent changes of some cell-cycle related genes associated with the biological activity of PAs, as well as the possible involvement of protein tyr kinases (PTK) and/or protein kinase C (PKC) in the mitogenic signal transduction. The data obtained demonstrate that the growth factor activity of PAs is associated with: - a rapid transient activation of early response genes, c-fos, c-jun and c-myc; - the subsequent coordinated down-regulation of p53 and p21CIP1; - the constant expression of the MEK1 mRNA in every phase of the cell cycle. Quiescent (G0) cells did not express c-fos, c-jun, c-myc and cyclin A, but upon stimulation with mitogens (fetal calf serum (FCS), u-PA, t-PA) the cyclin A mRNA expression was observed in concomitance with the activation of DNA synthesis. Therefore u-PA, t-PA and FCS similarly modulate the expression of c-fos, c-jun, c-myc, p53, p21CIP1 and cyclin A with only slight differences likely related to the time required for activation of DNA synthesis. The PAs mitogenic stimulation of serum-starved cells was associated with the internalization of their molecules, as revealed by immunostaining. The biological activity of u-PA, t-PA, as well as that of limiting concentration of FCS (1%), was mediated by PTK and PKC. Conversely, PTK, but not PKC, was involved in the activation of the proliferative response of basic fibroblast growth factor in the same experimental conditions. In conclusion, u-PA and t-PA can utilize two different pathways, one depending on PTK and the other on PKC in a way similar to the mitogenic activity induced by low concentration of FCS (1%).

Adenovirus-mediated p53 gene therapy for human gliomas

OBJECTIVE

The rationale and current evidence for using p53 gene replacement as a potential treatment for human gliomas are reviewed. The possible benefits of and obstacles to this approach are delineated.

METHODS

One approach to overcoming the poor outcomes associated with conventional glioma therapies involves the replacement of tumor suppressor genes that are fundamental to glioma development. The p53 gene is one of the most frequently mutated genes in human gliomas, and loss of p53 function is critical to the development of glial neoplasms. Consequently, replacement of the p53 gene using viral vectors may be a potential treatment for human gliomas.

RESULTS

In vitro studies demonstrate that adenovirus-mediated p53 gene transfer into gliomas with mutant p53 results in massive apoptosis. Similarly, transfer of p53 inhibits tumor growth in vivo. In contrast to mutant p53 gliomas, wild-type p53 glioma cells are resistant to the apoptotic effects of p53 transfer, but this resistance can be overcome by the addition of deoxyribonucleic acid-damaging agents such as ionizing radiation or chemotherapy. The main obstacle to p53 gene therapy involves the limitations associated with current modes of delivery.

CONCLUSION

Preclinical data strongly support the use of p53 gene transfer as a potential treatment for human gliomas.

Mutation of the p53 Gene Is Not a Typical Feature of Hodgkin and Reed-Sternberg Cells in Hodgkin’s Disease

Point mutations of the p53 tumor suppressor gene are a frequent finding in human carcinomas and are thought to be an important oncogenic event. In non-Hodgkin lymphomas, p53 mutations occur in a minor fraction of cases. However, conclusive data are still lacking for Hodgkin’s disease (HD) where the analysis meets technical problems. The neoplastic tumor cell clone in HD is represented by the large Hodgkin and Reed-Sternberg (HRS) cells, which account for only a minority of all cells in the tumor tissue (often <1%). To identify putative HRS cell-specific mutations, single HRS cells were micromanipulated from frozen tissue sections of HD biopsy specimens. Exons 4 to 8 of the p53 gene (in which more than 90% of p53 mutations associated with human neoplasms occur) were amplified from these single cells and sequenced. Mutations of p53 were not found in HRS cells of any of 8 cases of HD analyzed. We conclude that mutation of the p53 gene is only rarely, if at all, involved in the pathogenesis of HD.

Mutation of the p53 Gene Is Not a Typical Feature of Hodgkin and Reed-Sternberg Cells in Hodgkin’s Disease

Point mutations of the p53 tumor suppressor gene are a frequent finding in human carcinomas and are thought to be an important oncogenic event. In non-Hodgkin lymphomas, p53 mutations occur in a minor fraction of cases. However, conclusive data are still lacking for Hodgkin’s disease (HD) where the analysis meets technical problems. The neoplastic tumor cell clone in HD is represented by the large Hodgkin and Reed-Sternberg (HRS) cells, which account for only a minority of all cells in the tumor tissue (often &lt;1%). To identify putative HRS cell-specific mutations, single HRS cells were micromanipulated from frozen tissue sections of HD biopsy specimens. Exons 4 to 8 of the p53 gene (in which more than 90% of p53 mutations associated with human neoplasms occur) were amplified from these single cells and sequenced. Mutations of p53 were not found in HRS cells of any of 8 cases of HD analyzed. We conclude that mutation of the p53 gene is only rarely, if at all, involved in the pathogenesis of HD.

Expression of p53 and retinoblastoma gene in high-grade nodal peripheral T-cell lymphomas: immunohistochemical and molecular findings suggesting different pathogenetic pathways and possible clinical implications

The expression of p53 and the retinoblastoma gene has been investigated by immunohistochemical and molecular analysis in 45 cases of nodal peripheral T-cell lymphoma with high-grade histology. Most cases (73.3 per cent) were primary nodal lymphomas without any extra-nodal site involvement. Most of them (75.6 per cent) were histologically classified as pleomorphic, small, medium, and large cell type. Immunohistochemistry detected p53 in nine cases (20 per cent). In each of these cases, the polymerase chain reaction (PCR)/heteroduplex analysis did not show the presence of mutations, this finding being consistent with an alteration of the p53 functional pathway, in the presence of a wild-type protein. The retinoblastoma gene product was detected by immunohistochemistry in 35 cases (77.8 per cent) and not detected in ten cases (22.2 per cent). In the latter cases, the reverse transcription (RT)-PCR analysis showed the presence of a specific retinoblastoma gene transcript in six cases and was negative in the remaining four cases. The immunohistochemical and molecular findings seem to be consistent with abnormalities of retinoblastoma gene expression at either the transcriptional or the post-transcriptional level. Since all nine p53-positive cases by immunohistochemical analysis were also retinoblastoma gene product-positive, and all ten retinoblastoma gene product-negative cases were also p53-negative, two different and mutually exclusive pathways of possible pathogenetic significance may be suggested, the former involving abnormalities of the functional pathway of p53 in the absence of mutations and the latter abnormalities of retinoblastoma gene expression at the transcriptional and/or post-transcriptional level. Finally, the clinico-pathological correlations showed that p53 immunohistochemical expression is significantly associated with a poorer response to intensive chemotherapy.

Lymphoma development in Sjögren's syndrome: novel p53 mutations

OBJECTIVE

Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by lymphocytic infiltrations of the exocrine glands. Disease progression may lead to uncontrolled clonal proliferation of B lymphocytes and development of lymphoma. This study was undertaken to examine the possible involvement of the cell cycle checkpoint genes p53 and p21 in the pathophysiology of the syndrome.

METHODS

Protein expression of p53 and p21 was studied, by immunohistochemistry and Western blot analysis, in minor salivary gland (MSG) biopsy specimens from 7 patients with SS and 5 control subjects. In addition, sequence analysis of the p53 gene was performed on DNA samples obtained from MSG biopsy samples of the same 7 patients with SS and from 4 patients with SS and in situ non-Hodgkin's lymphoma (NHL).

RESULTS

The study revealed increased protein expression of p53 and p21 in MSG biopsy specimens from patients as compared with controls, while sequence analysis showed that the p53 gene was of the wild type. Furthermore, sequence analysis of the p53 gene from patients with SS and in situ NHL revealed 2 novel mutations in exon 5 of the p53 gene. These mutations are single-base substitutions and appear to be functional since exon 5 is included in the coding region of the p53 gene.

CONCLUSION

This is the first report on wild-type p53 gene activation in SS. Our findings indicate a probable role for the DNA damage response genes in the pathogenesis of this syndrome. The novel mutations of the p53 gene implicate dysregulation of this tumor suppressor gene as a possible mechanism for lymphoma development in SS.

Mutations of p53 in thyroid carcinoma with an insular component

Thyroid carcinoma with an insular component (TCIC) is considered noteworthy in view of its peculiar histopathological features and clinicopathological behavior. The purpose of the present study was to clarify the rate of mutation in the p53 gene in TCIC as compared with rates in papillary and follicular carcinomas of the thyroid. Formalin-fixed and paraffin-embedded blocks of tissue from 46 cases of TCIC were analyzed. DNA was extracted from tissues and exons 5 through 8 of the p53 gene were amplified by the polymerase chain reaction. Mutations were detected by analysis of single-strand conformation polymorphism. Of the 46 cases of TCIC, 6 had a mutation in exon 5, 2 in exon 7, and 5 in exon 8, while 1 case had mutations in all exons examined. The mutation rate of the p53 gene in TCIC was 38%. Immunostaining revealed overexpression of p53 in nuclei that were mainly in areas of the insular component rather than in surrounding areas of well-differentiated carcinoma. The frequency of positive immunostaining in TCIC was 53%. Considering that TCIC is intermediate between papillary plus follicular carcinoma and anaplastic carcinoma in terms of survival and the rate of mutation of the p53 gene, we can speculate that mutation in the p53 gene might be associated with the insular component and might play an important role in the clinicopathological behavior of thyroid carcinoma.

Comprehensive TP53-denaturing gradient gel electrophoresis mutation detection assay also applicable to archival paraffin-embedded tissue

A comprehensive mutation detection assay is described for the entire coding region and all splice site junctions of TP53. The assay is based on denaturing gradient gel electrophoresis, which follows either multiplex polymerase chain reaction (PCR) applied to DNA extracted from fresh or frozen tissue samples or nested PCR applied to DNA extracted from paraffin-embedded tissue samples. In both instances, the analysis can be performed under a single set of conditions. When testing the assay on DNA from cultured lung cancer cell lines and from paraffin-embedded Dukes C colorectal carcinomas, significant TP53 mutations were observed at high frequencies in 15 of 16 lung cancer cell lines (94%) and in 21 of 30 paraffin-embedded tissue samples of Dukes C colorectal carcinomas (70%). A substantial proportion of these significant mutations occurred outside the evolutionary conserved region of TP53 in 4 of 16 lung cancer cell lines (25%) and in 11 of 30 paraffin-embedded colorectal carcinomas (37%). This underscores the importance of a comprehensive TP53 mutation analysis in those instances that TP53 mutation is taken into account for diagnostic and prognostic purposes.

Sources of bias in the detection and reporting of p53 mutations in human cancer: analysis of the IARC p53 mutation database

p53 gene encodes a transcription factor with tumor suppressive properties and to date, somatic mutation of this gene is the most common genetic event in human cancer. A relational database has been developed to facilitate the retrieval and analysis of these mutations at the International Agency for Research on Cancer (IARC) and it currently contains information on over 8000 individual tumors and cell lines. Many factors may influence the detection and reporting of mutations, including selection of tumor samples, study design, choice of methods, and quality control. There is also concern that several biases may affect the way data appear in the literature. Minimizing these biases is an essential methodological issue in the development of mutation data-bases. In this paper, we review and discuss these main sources of bias and make recommendations to authors in order to minimize bias in mutation detection and reporting.

p53 and the CNS: tumors and developmental abnormalities

This article reviews the recent molecular and clinical studies that characterize the role of p53 in pathologies of the central nervous system, p53 has many important biological functions, notably, maintenance of DNA stability and regulation of apoptosis. These features are essential to avoid cellular transformation and ensure normal brain development. Lack of p53 function in the brain results in tumor formation in the astrocytic and lymphoid lineages and in severe neurodevelopmental diseases, such as exencephaly.

Transcription of the rat p53 gene is mediated by factor binding to two recognition motifs of NF1-like protein

In this study we analyzed the ratp53 promoter by electrophoretic mobility shift assay (EMSA) and DNase I footprinting analysis. As a result we identified two protein binding elements (element 1: -296 to -312, element 2: -195 to -219) with sequence homology to each other. The two identified elements bind to the same kind of protein. To identify the protein binding to these elements, competition assays were carried out with double stranded oligonucleotides containing NF1, YY1, and CRE consensus motifs. Only the NF1 consensus motif competed with element 1 and 2. Element 2 is conserved between the rat, human, and mouse p53 promoters, and has an NF1 consensus motif. However, the sequences of element 1 are comparatively variable between the species. Only the element 1 region of the rat p53 promoter has partial homology to the NF1 consensus motif. This suggests that the element 1 is specific for the rat p53 gene. The molecular mass of the binding protein, determined by Southwestern blotting analysis, was 40 kDa, which is different from that of NF1. In EMSA with an anti-NF1 antibody, DNA-protein complexes were neither supershifted nor decreased. The 40 kDa protein was also detected in rat spleen and lung, but not in kidney. The binding protein was purified by sequence-specific DNA affinity chromatography and it was confirmed that the purified protein binds to the two regions. It was also proved that the identified two elements are required for basal level transcription of the rat p53 gene by in vitro transcription assay.

Epidemiological study of p53 tumor suppressor gene mutations in patients from Luxembourg and the German Saar region with an advanced colorectal cancer using PCR-SSCP analysis

Mutations in the p53 tumor suppressor gene are usually associated with an advanced development of colorectal cancer characterized by the transition from the adenoma to the carcinoma stage. We used the polymerase chain reaction (PCR) followed by single-strand conformation polymorphism (SSCP) analysis to screen for the presence of mutations in the p53 gene of patients from Luxembourg and the German Saar region with colorectal cancers at various developmental stages. While we detected no mutations in 16 colic polypi at an early to intermediate stage (adenoma), we revealed seven (13.7%) non-silent point mutations (transitions) in exons 5 to 9 of the p53 gene in 51 colorectal tumors at a late stage (carcinoma). In addition to confirming previous observations, these results show that PCR-SSCP analysis can provide both a sensitive and rapid method for the genetic determination of the histopathological stage of colorectal samples.

Genotypic analysis of tumor suppressor genes PTEN/MMAC1 and p53 in head and neck squamous cell carcinomas

OBJECTIVES

Tumor suppressor gene mutations in both p53 and PTEN/MMAC1 genomic DNA have been detected in many types of cancer. The purpose of this study was to investigate the presence and importance of PTEN/MMAC1 mutations in squamous cell carcinomas.

METHODS

Exons of each gene were amplified after polymerase chain reaction (PCR) using genomic DNA derived from cell lines of squamous cell carcinoma of the head and neck (SCCHN) and snap-frozen biopsy specimens from primary established head and neck tumors. The amplified and purified DNA was then sequenced directly.

RESULT

As anticipated, point mutations of the p53 gene were found in 80% of cell lines examined. A single base mutation in codon 151 was found in six of 10 cell lines studied. PTEN/MMAC1 gene mutations were found in neither the cell lines tested nor the tumor biopsy samples.

CONCLUSION

This study, as well as a large volume of data, confirms that mutations of the p53 gene are frequent events in head and neck cancer cell lines. Although PTEN/MMAC1 gene mutations have been found in a variety of carcinomas, this gene was not found to be mutated in SCCHN cell lines or in primary squamous cell carcinomas of the head and neck. This information is useful for further studies of mutations in these cell lines.

Establishment and characterization of a new HPV-negative squamous cell carcinoma cell line (Yumoto) from the human uterine cervix

A new cell line, Yumoto, derived from a squamous cell carcinoma of the uterine cervix, was established from serially transplanted tumor tissues in nude mice. Monolayer cultured cells were polygonal and formed pavement-like sheet. They showed a piling-up tendency and were devoid of contact inhibition. Electron micrographs demonstrated the presence of microvilli on the cell surface, abundant tonofilaments in the cytoplasm, and the connection with desmosomes. These electron micrographical characteristics of Yumoto cells were consistent with those of squamous cell origin. Yumoto cells were highly tumorigenic in BALB/c nude mice and produced a well-differentiated squamous cell carcinoma of keratinizing type which closely resembled to the original tumor tissues in nude mice. The presence of HPV DNA was examined using polymerase chain reaction and Southern blot analysis, but no known types of HPV DNA could be detected. Exons 2 through 11 of the p53 gene were analyzed by direct DNA sequencing, revealing a homozygous mutation at codon 281 in exon 8, GAC to CAC (Asp-->His). Furthermore, physical p53-gene deletion was demonstrated by dual-color fluorescence in situ hybridization. This cell line is useful for studying the carcinogenesis of cervical carcinoma and for investigating the biological characteristics of a HPV-negative and mutated p53 squamous cell carcinoma of the uterine cervix.

Effective treatment of early endobronchial cancer with regional administration of liposome-p53 complexes

BACKGROUND

Lung cancer originates in a diffusely damaged bronchial epithelium as a result of sequential and cumulative genetic alterations. We investigated the feasibility of in vivo gene replacement in endobronchial precancerous and cancerous cells by a regionally administered nonviral delivery system.

METHODS

After evaluating the in vitro transfection efficiency and cytotoxicity of a variety of cationic liposome-p53 formulations, a specific formulation, DP3-p53, was selected for further in vitro and in vivo evaluation. The ability of DP3-p53 to introduce the p53 gene in the normal bronchial epithelium was studied in transgenic mice that lack the p53 gene. The therapeutic effect of DP3-p53 administered intratracheally was studied in two nude mouse models of endobronchial human lung cancer by use of H358 (p53-null) and H322 (p53-mutant) cells.

RESULTS

DP3-p53 was able to effectively introduce and express the p53 gene and induce G1 arrest and apoptosis in H358 cells in vitro and to introduce and transcribe the p53 gene in the bronchial epithelium of transgenic mice that lack the p53 gene in vivo. In therapeutic experiments using groups of four or five mice each, administration of five intratracheal doses of DP3-p53 (2 microg or 8 microg DNA per dose) on days 4, 8, 12, 16, and 20 after intratracheal tumor inoculation significantly inhibited lung tumor formation and prolonged by approximately twofold the survival of mice bearing H358 or H322 endobronchial tumor cells in contrast to the survival among untreated mice and mice treated with the DP3-empty vector (P = .007 [two-sided logrank test] for mice bearing H358 cells and P = .008 [two-sided logrank test] for those bearing H322 cells).

CONCLUSIONS/IMPLICATIONS

Liposome-based p53 delivery through the airways is a potentially effective strategy for the treatment of early endobronchial cancer. These results have important implications for the gene therapy and prevention of human lung cancer.

Rearrangement of the p53 gene in human breast tumours

Rearrangement of the p53 gene is frequent in virus transformed cell lines and in chronic myelogenous leukemia. It is a rare event in solid tumours and has been reported only in osteosarcomas. In this study we have examined rearrangement of the p53 gene in human breast tumours. We found rearrangement in 35% of the patients (7 of 20 tumours examined). Normal tissue from these patients had an unrearranged gene, indicating that the genetic abnormality in the tumour is acquired during the natural process of tumorigenesis. No intronic rearrangement or allelic loss of the p53 gene was found in the breast tumour samples studied. Further, rearrangement of the p53 gene has been correlated with the p53 transcriptional status. Only two patients with rearranged p53 showed a high level of p53 RNA as well as protein expression. Thus, for the first time we report the rearrangement of the p53 gene in breast tumours, which may play a role in the process of tumorigenesis.

Mutant p53 may selectively suppress glial specific proteins in pluripotential human neuroectodermal tumor cells

The p53 gene is mutated in pluripotential human neuroectodermal tumor DAOY cells which express both glial and neuronal markers. In most cells, nuclear m-p53 immunostaining was intense while cytoplasmic glial specific proteins (GSPs) were present at low levels. Conversely, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS) were expressed in the few cells devoid of nuclear m-p53 immunoreactivity. The level of neuron specific enolase (NSE) staining was low and not different between p53 positive and p53 negative cells. Therefore, a selective, mutually exclusive expression relationship exists between cytoplasmic GSPs and nuclear m-p53. Upon treatment with epidermal growth factor (EGF) and dibutyrylcyclic AMP, overall cytoplasmic GFAP and GS levels were increased while nuclear p53 was suppressed but a mutually exclusive expression pattern between these proteins was maintained. In cells which also express NSE, GFAP was selectively stimulated suggesting that nuclear expression of m-p53 and cytoplasmic expression of GSPs may be functionally related.

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.

Genetic alterations in a patient with Turcot's syndrome

Turcot's syndrome (TS) is a rare disorder associated with the development of both brain and colon neoplasms. Because of the very low incidence of the disease, its molecular basis remains unclear. Presented is a TS case of a 30-year-old Japanese male with a histopathologically confirmed diagnosis of both brain tumor (glioblastoma multiforme) and colon tumor (well-differentiated adenocarcinoma). Germline mutations of the p53 gene, somatic mutations of the Ki-ras, p53 and APC genes, and microsatellite instability (MSI) was examined using polymerase chain reaction (PCR)-single strand conformation polymorphism analysis, followed by PCR-direct sequencing, and sequencing after subcloning. No germline mutations of the p53 gene were found. Somatic mutations of Ki-ras and APC genes were found in the colon adenocarcinoma but not in the brain tumor. No somatic mutation of the p53 gene was present in either colon or brain tumors. Microsatellite instability of both colon and brain tumors was positive in two of four loci. These results indicate that the colon tumor of the TS patient carries the Ki-ras and APC gene mutations. The finding of MSI in both the brain and the colon tumors may support the hypothesis that alterations of DNA repair genes are involved in the tumor development of the TS patient.

Determination of the replication error phenotype in human tumors without the requirement for matching normal DNA by analysis of mononucleotide repeat microsatellites

Microsatellite instability (MI) characterizing tumors with replication errors (RER+ tumors) was first described in colorectal tumors from hereditary non-polyposis colorectal cancer (HNPCC) patients as well as in sporadic cases. It has also been observed in subgroups of extracolonic sporadic tumors, but there is no consensus as to the number of microsatellite loci to examine, and the threshold percentage of unstable loci required to classify a tumor as RER+. We have recently shown that BAT-26, a mononucleotide repeat microsatellite, was quasi-monomorphic in DNA from normal individuals and from colorectal RER- samples, and showed important size variations in RER+ samples. In the present work, we analyzed BAT-26 allelic profiles in tumors of the breast (n = 107), brain (n = 78), stomach (n = 59), prostate (n = 49), esophagus (n = 36), thyroid (n = 31), endometrium (n = 12), and cervix (n = 10) whose RER status was already known, thus extending BAT-26 analysis to a total of 542 human solid tumors. BAT-26 alleles were quasi-monomorphic in RER- samples (475/481) and shortened in RER+ tumors (57/61), including four tumors shown to have been misclassified on the basis of dinucleotide repeat microsatellite analysis. In 3/481 RER- and 4/61 RER+ cases, BAT-26 size variation was important enough to attract attention, but not sufficient to establish the RER status of the corresponding tumors. In these cases, the analysis of BAT-25 and BAT-34C4, two other mononucleotide repeat microsatellites, was necessary to resolve the ambiguity. There were only 3 false positive cases. In conclusion, BAT-26 was able to identify the RER status of 539 out of 542 tumors from various origins (99.5% efficiency) in a single-step experiment without the requirement for matching normal DNA.

Role of p53 in UVB-induced apoptosis in human HaCaT keratinocytes

Apoptosis represents an active form of cell death that is involved in the control of tissue homeostasis and in the deletion of DNA-damaged cells. Because the product of the tumor suppressor gene p53 has been demonstrated to be crucial for the induction of apoptosis in certain cell types, the present study was aimed at elucidating its role in ultraviolet-induced apoptosis in HaCaT keratinocytes. After in vitro ultraviolet B irradiation, p53 protein levels were noted to increase prior to the induction of apoptosis in a time- and concentration-dependent fashion. This increase could not be inhibited by the protein synthesis inhibitor cycloheximide. Because HaCaT keratinocytes are known to bear two p53 point mutations and because it is unclear whether p53 in HaCaT cells is still functional regarding induction of apoptosis, HaCaT cells were stably transfected with wild-type p53 cDNA inserted into the expression vector pCMV-Neo-Bam in sense (pC53-SN3) and anti-sense (pC53-ASN) direction. After selection with geniticin, growing colonies were screened for the presence of the transfected cDNA constructs by polymerase chain reaction. Cell clones bearing the anti-sense product were further analyzed for p53 expression by western blotting. Clones showing reduced p53 protein levels were irradiated with ultraviolet B light, and there was a clear reduction of apoptosis in the pC53-ASN bearing cell clones compared with the parental HaCaT cells. These studies demonstrate that blocking mutated p53 can partially block apoptosis in HaCaT keratinocytes and furthermore can confirm the key role for p53 in ultraviolet-induced apoptosis in human keratinocytes. Moreover, HaCaT keratinocytes and their p53-transfectants provide a convenient model that allows for further detailed analyses of apoptosis-associated biochemical and molecular events in human keratinocytes.

Identification of a novel transcriptional regulatory element common to the p53 and interferon regulatory factor 1 genes

The promoter regions of both the interferon regulatory factor (IRF1) and p53 antioncogenes contain a previously unidentified sequence denoted IRF1 p53 common sequence (IPCS), which markedly increases the transcriptional activity of a reporter gene placed under the control of an heterologous promoter in transfected U937 cells. In contrast, transfection of U937 cells with reporter vectors containing p53 and IRF1 promoters with mutated IPCS sites resulted in a 4-fold reduction in the constitutive expression of those two genes. The transcriptional activity of IPCS is strictly correlated with the binding of a novel nuclear factor, IPCS-binding factor (IPCS-BF). IPCS-BF, which is composed of a single polypeptide of 26 kDa, is present constitutively in nuclear extracts of both U937 cells and peripheral blood mononuclear cells from healthy donors. The finding that the pattern of binding of IPCS-BF to the IPCS is unlike that of any known transcription factor and that the IPCS sequence does not exhibit any significant homology with any known binding site present in the data base, strongly suggest that IPCS-BF is a novel transcription factor which, by virtue of this ability to regulate the expression of the p53 and IRF1 genes, could play a central role in the control of cell proliferation and/or apoptosis.