Correlation of p53 mutations with epidermal growth factor receptor overexpression and absence of mdm2 amplification in human esophageal carcinomas

p53, MDM2, eIF4E and EGFR expression in nasopharyngeal carcinoma and their correlation with clinicopathological characteristics and prognosis: A retrospective study

In the present study, the expression of p53, mouse double minute 2 homolog (MDM2), eukaryotic translation initiation factor 4E (eIF4E), and epidermal growth factor receptor (EGFR) were investigated in nasopharyngeal carcinoma (NPC), and the correlation between their expression and clinicopathological characteristics and prognosis was analyzed. The medical records of 96 NPC patients who had undergone biopsy prior to radical radiotherapy and chemotherapy between 2005 and 2009 were reviewed, retrospectively. All patients received intensity-modulated radiotherapy with concurrent platinum-based chemotherapy. Patients were followed-up for three years. Streptavidin-peroxidase immunohistochemistry was used to evaluate the expression of p53, MDM2, eIF4E and EGFR in NPC biopsy specimens, and the association between their expression and clinical parameters and survival was analyzed. The p53, MDM2, eIF4E and EGFR expression rates were 65.6% (63/96), 79.16% (76/96), 77.08% (74/96) and 89.5% (86/96), respectively. p53 (χ²,20.322; P=0.001) and EGFR (χ²,8.337; P=0.005) expression were found to correlate with T stage, whereas MDM2 (χ²,16.361; P=0.001) expression was found to correlate with lymph node metastasis. p53 expression was found to inversely correlate with MDM2 expression (r, −3.24; P<0.05). Three-year survival rates were lower in p53-positive (76.2%) patients when compared with p53-negative (93.9%) patients. In addition, three-year survival rates were lower in EGFR-positive (75.8%) patients than in EGFR-negative patients (91.2%). The Cox proportional-hazards regression model revealed that p53 (β,−0.455; χ²,5.491; P=0.019) and EGFR (β, 3.93; χ², 11.95; P=0.001) expression were independent prognostic factors. Thus, it was hypothesized that p53 and EGFR expression present potential unfavorable prognostic markers for patients with NPC.

Diphenylpyrroles: Novel p53 activators

Cellular tumor antigen p53 is crucial for cancer prevention via different mechanisms. E3 ubiquitin-protein ligase HDM2 binds to p53, blocks its ability to activate transcription, and therefore acts as a negative regulator. Blocking p53 binding site on HDM2 was believed to generate efficient antitumor agents. So far, limited scaffolds were reported with HDM2 antagonist activity. Herein, diphenylpyrroles were introduced and evaluated as a novel scaffold in the field of p53 activators. An efficient synthesis of novel 3-heteroaryl-pyrroles is described via reactions of E-3-(dimethylamino)-1-(2-methyl-4,5-diphenyl-1H-pyrrol-3-yl)prop-2-en-1-one or E-1-(2-methyl-4,5-diphenyl-1H-pyrrol-3-yl)-3-morpholinoprop-2-en-1-one with hydrazine hydrate, phenyl hydrazine, hydroxylamine, various heterocyclic amines and active methylene compounds.

Trp53 haploinsufficiency modifies EGFR-driven peripheral nerve sheath tumorigenesis

Malignant peripheral nerve sheath tumors (MPNSTs) are genetically diverse, aggressive sarcomas that occur sporadically or in association with neurofibromatosis type 1 syndrome. Reduced TP53 gene expression and amplification/overexpression of the epidermal growth factor receptor (EGFR) gene occur in MPNST formation. We focused on determining the cooperativity between reduced TP53 expression and EGFR overexpression for Schwann cell transformation in vitro (immortalized human Schwann cells) and MPNST formation in vivo (transgenic mice). Human gene copy number alteration data, microarray expression data, and TMA analysis indicate that TP53 haploinsufficiency and increased EGFR expression co-occur in human MPNST samples. Concurrent modulation of EGFR and TP53 expression in HSC1λ cells significantly increased proliferation and anchorage-independent growth in vitro. Transgenic mice heterozygous for a Trp53-null allele and overexpressing EGFR in Schwann cells had a significant increase in neurofibroma and grade 3 PNST (MPNST) formation compared with single transgenic controls. Histological analysis of tumors identified a significant increase in pAkt expression in grade 3 PNSTs compared with neurofibromas. Array comparative genome hybridization analysis of grade 3 PNSTs identified recurrent focal regions of chromosomal gains with significant enrichment in genes involved in extracellular signal-regulated kinase 5 signaling. Collectively, altered p53 expression cooperates with overexpression of EGFR in Schwann cells to enhance in vitro oncogenic properties and tumorigenesis and progression in vivo.

Enhanced MDM2 Oncoprotein Expression in Soft Tissue Sarcoma: Several Possible Regulatory Mechanisms

Purpose. MDM2 is an oncogene whose protein product may promote tumorigenesis by blocking wild-type p53 tumor suppressor mediated G ₀/G₁ cell cycle arrest, thereby inhibiting repair of damaged DNA prior to cell division. While MDM2 DNA amplification is frequently observed in human sarcoma, the mechanisms linking this amplification to MDM2 oncoprotein over-production as well as its functional significance have not been well characterized in patients with soft tissue sarcoma.

Methods. A tissue bank of resected soft tissue sarcomas and autologous normal tissues was assembled; all specimens were snap frozen within 15 min of resection. DNA and RNA were extracted from tissues using isoamyl alcohol and phenol chloroform extraction methods, respectively; cell lysates were prepared using PBSTDS lysis buffer. DNA and mRNA were confirmed as being non-degraded and were then examined for MDM2 DNA amplification (Southern blots) and mRNA over-expression (Northern blots) using actin (DNA) and glyceraldehyde-3-phosphate dehydrogenase (mRNA) as loading controls. The MDM2 protein was examined on Western blots using the MDM2-specific monoclonal antibody IF2 (Oncogene Science, Inc). The presence of p53 DNA and expression of p53 mRNA was examined by rehybridizing the Southern and Northern filters using a p53-specific cDNA probe.

Results. Soft tissue sarcomas and autologous normal tissues were screened for MDM2 DNA amplification, which was detected in 10 of 30 tumors screened. After screening, there was sufficient biomaterials from six specimens for subsequent Northern and Western analysis to see whether MDM2 gene amplification correlated with over-expression of MDM2 mRNA and MDM2 protein. In addition, we examined whether other mechanisms may lead to over-expression of the MDM2 oncoprotein. Several possible mechanisms of MDM2 oncoprotein over-expression were identified. These most commonly included MDM2 DNA amplification, MDM2 mRNA over-expression and MDM2 oncoprotein over-expression. However, some soft tissue sarcoma patient specimens had no evidence of MDM2 mRNA over-expression yet had MDM2 oncoprotein over-production in the tumor relative to autologous normal tissue, implying possible post-transcriptional regulation. Of functional relevance, MDM2 oncoprotein over-production by tumors was associated with large decreases in the percentage of cells in the ₀/G₁ cell cycle interface compared with autologous normal tissue cells.

Discussion. It is likely that there are multiple mechanisms underlying human soft tissue sarcoma MDM2 oncoprotein over-production. Consequently, strategies that decrease MDM2 over-production, such as transcriptional repression to inhibit MDM2 promoter activity or RNA antisense approaches, may ultimately offer the best therapeutic efficacy.

MDM2 is overexpressed and regulated by the eukaryotic translation initiation factor 4E (eIF4E) in human squamous cell carcinoma of esophagus

BACKGROUND

We investigated the association between the increased eukaryotic translation initiation factor 4E (eIF4E) level and MDM2 overexpression in the esophageal cancer tissue and cells.

METHODS

This was a retrospective study of specimens from esophageal cancer patients treated over a 5-year period in a Taiwan university hospital. The predictor variable was eIF4E level in esophageal tumors and CE48T/VGH and TE6 esophageal carcinoma cell lines. The main outcome variable was MDM2 overexpression. Appropriate descriptive and univariate statistics were computed, and a P value of <0.05 was considered statistically significant.

RESULTS

There were two study sample groups. Immunohistochemistry analyses of the first sample group (51 esophageal tumors) revealed that 19 specimens demonstrated MDM2 elevation and 20 specimens had eIF4E overexpression. eIF4E elevation was evidenced by accumulation of the protein in the cytoplasm. There was a significant association between the eIF4E and MDM2 expression (P < 0.001). Western blot analysis and semiquantitative reverse transcriptase-polymerase chain reaction of the second specimen group (20 pairs of tumors and normal tissues) revealed the co-elevation of MDM2 and eIF4E (P = 0.008). There was no increased mdm2 transcript in most of the specimens. Without significant alterations in the mdm2 mRNA level and subcellular distribution, MDM2 protein was upregulated in CE48T/VGH cultured cells expressing ectopic eIF4E. Conversely, reduction of eIF4E by specific siRNA enabled TE6 cells synthesizing reduced amounts of MDM2.

CONCLUSIONS

Our findings indicate that MDM2 protein levels are strongly associated with and regulated by eIF4E in a posttranscriptional mechanism in esophageal cancer.

Insulin-like growth factor-binding protein-3 promotes transforming growth factor-{beta}1-mediated epithelial-to-mesenchymal transition and motility in transformed human esophageal cells

Insulin-like growth factor-binding protein (IGFBP)-3 is overexpressed frequently in esophageal squamous cell carcinoma. Yet, the role of IGFBP3 in esophageal tumor biology remains to be elucidated. We find that IGFBP3 facilitates transforming growth factor (TGF)-beta1-mediated epithelial-to-mesenchymal transition (EMT) in transformed human esophageal epithelial cells, EPC2-hTERT-EGFR-p53(R175H). In organotypic 3D culture, a form of human tissue engineering, laser-capture microdissection revealed concurrent upregulation of TGF-beta target genes, IGFBP3 and EMT-related genes in the cells invading into the stromal compartment. IGFBP3 enhanced TGF-beta1-mediated EMT as well as transcription factors essential in EMT by allowing persistent SMAD2 and SMAD3 phosphorylation. TGF-beta1-mediated EMT and cell invasion were enhanced by ectopically expressed IGFBP3 and suppressed by RNA interference directed against IGFBP3. The IGFBP3 knockdown effect was rescued by IGFBP3(I56G/L80G/L81G), a mutant IGFBP3 lacking an insulin-like growth factor (IGF)-binding capacity. Thus, IGFBP3 can regulate TGF-beta1-mediated EMT and cell invasion in an IGF or insulin-like growth factor 1 receptor-independent manner. IGFBP3(I56G/L80G/L81G) also promoted EMT in vivo in a Ras-transformed human esophageal cell line T-TeRas upon xenograft transplantation in nude mice. In aggregate, IGFBP3 may have a novel IGF-binding independent biological function in regulation of TGF-beta1-mediated EMT and cell invasion.

Epidermal growth factor receptor and mutant p53 expand an esophageal cellular subpopulation capable of epithelial-to-mesenchymal transition through ZEB transcription factors

Transforming growth factor-beta (TGF-beta) is a potent inducer of epithelial to mesenchymal transition (EMT). However, it remains elusive about which molecular mechanisms determine the cellular capacity to undergo EMT in response to TGF-beta. We have found that both epidermal growth factor receptor (EGFR) overexpression and mutant p53 tumor suppressor genes contribute to the enrichment of an EMT-competent cellular subpopulation among telomerase-immortalized human esophageal epithelial cells during malignant transformation. EGFR overexpression triggers oncogene-induced senescence, accompanied by the induction of cyclin-dependent kinase inhibitors p15(INK4B), p16(INK4A), and p21. Interestingly, a subpopulation of cells emerges by negating senescence without loss of EGFR overexpression. Such cell populations express increased levels of zinc finger E-box binding (ZEB) transcription factors ZEB1 and ZEB2, and undergo EMT on TGF-beta stimulation. Enrichment of EMT-competent cells was more evident in the presence of p53 mutation, which diminished EGFR-induced senescence. RNA interference directed against ZEB resulted in the induction of p15(INK4B) and p16(INK4A), reactivating the EGFR-dependent senescence program. Importantly, TGF-beta-mediated EMT did not take place when cellular senescence programs were activated by either ZEB knockdown or the activation of wild-type p53 function. Thus, senescence checkpoint functions activated by EGFR and p53 may be evaded through the induction of ZEB, thereby allowing the expansion of an EMT-competent unique cellular subpopulation, providing novel mechanistic insights into the role of ZEB in esophageal carcinogenesis.

p53 mutation profile of squamous cell carcinomas of the esophagus in Kashmir (India): a high-incidence area

Esophageal squamous cell carcinoma (ESCC) has been reported to show geographical variation in its incidence, even within areas of ethnic homogeneity. Kashmir valley, in north of India, has been described as a high-risk area for ESCC. Here, we make a preliminary attempt to study mutations in exons 5-8 (the DNA binding domain) of the tumor suppressor gene, p53, in 55 ESCC patients from Kashmir. Polymerase chain reaction followed by direct sequencing analysis revealed the presence of mutations in 36.36% (20/55) tumors, assessed for the extent of allelic instability. The 20 mutations, found in 20 patients, comprised of 17 single-base substitutions (11 transitions + 6 transversions) and 3 deletions. The 17 single-base variations represented 12 missense mutations, 2 nonsense mutations and 3 variations located in intron 6, 1 of which resulted in a splicing variant. The patients when compared for the incidence of p53 mutation with various demographic features revealed females to be at increased risk (p = 0.016; OR = 4.13; 95% CI = 1.26-13.46). Comparison of mutation profile with other high-risk areas reflected both differences and similarities indicating coexposure to a unique set of risk factors. This might be due to the special dietary and cultural practices of Kashmir that needs validation, as does the gender-based difference in the incidence of p53 mutation observed in this study.

Overexpression of Aurora-A contributes to malignant development of human esophageal squamous cell carcinoma

PURPOSE

Aurora-A/STK15/BTAK, a centrosome-associated oncogenic protein, is implicated in the control of mitosis. Overexpression of Aurora-A has been shown to result in chromosomal aberration and genomic instability. Multiple lines of evidence indicate that Aurora-A induces cell malignant transformation. In the current study, we are interested in investigating the expression of Aurora-A in human esophageal squamous cell carcinoma (ESCC) and characterizing the association of Aurora-A with ESCCmalignant progression.

EXPERIMENTAL DESIGN

Aurora-A protein expression was examined in 84 ESCC tissues and 81 paired normal adjacent tissues by either immunohistochemistry or Western blot analysis. In addition, a gene-knockdown small interfering RNA technique was used in ESCC cells to investigate whether Aurora-A contributes to the ability of a tumor to grow invasively.

RESULTS

The amount of Aurora-A protein in ESCC was considerably higher than that in normal adjacent tissues. Overexpression of Aurora-A was observed in 57 of 84 (67.5%) ESCC samples. In contrast, <2% of normal adjacent tissue displayed high expression of Aurora-A. Interestingly, overexpression of Aurora-A seemed to correlate with the invasive malignancy of ESCC. Disruption of endogenous Aurora-A using small interfering RNA technique substantially suppressed cell migrating ability.

CONCLUSION

The findings presented in this report show that Aurora-A expression is elevated in human esophageal squamous cell carcinoma and is possibly associated with tumor invasion, indicating that overexpression of Aurora-A may contribute to ESCC occurrence and progression.

Mutant p53 protein in the serum of patients with cervical carcinoma: correlation with the level of serum epidermal growth factor receptor and prognostic significance

We have previously reported that the serum level of epidermal growth factor receptor (EGFR) was significantly elevated in 38 cervical carcinoma patients. The levels of mutant p53 protein were determined in the serum of the same cohort (invasive or recurrent carcinoma: 26, carcinoma in situ (CIS): 12) and 18 controls using ELISA. The median serum level for mutant p53 in cervical carcinoma patients (0.11 ng/ml; range, 0-2.66 ng/ml) demonstrated no significant difference compared to that of controls (0.14 ng/ml; range, 0-0.34 ng/ml) (P=0.324). Serum mutant p53 showed positive elevation in 5 patients with invasive or recurrent carcinoma (19%) and 1 with CIS (8%). A significant correlation was found between EGFR and mutant p53 levels (r=0.668; P<0.0001). In invasive or recurrent cervical carcinoma, positive mutant p53 was significantly associated with poor overall survival in both univariate (P=0.035) and multivariate (P=0.046) analysis, while increased level of EGFR did not show prognostic significance (P=0.755). Serum mutant p53 could have potential usefulness as a biological marker of cervical carcinoma for prediction of prognosis and follow-up after treatment.

Epidermal growth factor receptor and p53 expression in T1-T2 glottic cancer involving the anterior or posterior commissure

OBJECTIVE

We surveyed retrospectively the expression of epidermal growth factor receptor (EGFR) and p53 in cases of T1-T2 glottis cancer involving the anterior (AC) or posterior commissure (PC) subsites to check for differences possibly explaining the different prognoses of cancer at these subsites.

MATERIAL AND METHODS

Between 1970 and 1995, 15 patients with T1-T2 primary glottis cancer involving the PC, either partly or entirely, were treated. Thirty more cases were selected among 184 patients treated during the same time period for AC glottis cancer, to match the former cases with regard to age, sex, tumor stage, smoking habits and alcohol consumption.

RESULTS

A significantly higher frequency of EGFR expression occurred in PC than in AC cancer.

CONCLUSION

These results, and the anatomy of the PC subsite, may explain the more frequent recurrence of T1-T2 PC compared to T1-T2 AC cancer and why radiotherapy achieves worse results in T1-T2 PC cancer than in AC cancer of comparable T grade.

Expression of matrix metalloproteinase 1, matrix metalloproteinase 2, and matrix metalloproteinase 9 in carcinoma of the head and neck

BACKGROUND

Numerous reports have documented a direct involvement of matrix metalloproteinase (MMP) overexpression in the development and progression of head and neck squamous cell carcinoma (HNSCC). In this study, the authors examined whether the expression of MMPs in HNSCC is correlated with other steps involved in tumor growth and metastasis, like angiogenesis, activation the nitric oxide (NO) pathway, and alteration of the p53 tumor suppressor gene.

METHODS

MMP-1, MMP-2, and MMP-9 expression levels were examined immunohistochemically in samples from 43 patients with HNSCC. Microvessel density (MVD) was determined by immunostaining of endothelial cells with anti-CD31 monoclonal antibody. Inducible nitric oxide synthase (iNOS) activity and cyclic guanosine monophosphatate (cGMP) levels were assessed in fresh tumor samples, whereas exons 5-9 of the p53 gene were analyzed by reverse transcriptase-polymerase chain reaction, single-strand conformation polymorphism analysis and were sequenced.

RESULTS

MMP-1 overexpression (>10% of tumor cells) was identified in 32 tumors (74.5%), whereas elevated levels of MMP-2 and MMP-9 were detected in 17 tumors (39.5%) each. Tumors with MMP-9 overexpression were characterized by significantly higher MVD (P = 0.05) and significantly higher iNOS activity and cGMP levels (P = 0.005 and P = 0.02, respectively). Moreover, p53 mutation was associated strongly with MMP-9 overexpression (P = 0.004). Conversely, no correlation was found between MMP-1 and MMP-2 expression, angiogenesis, iNOS activity, cGMP levels, and p53 mutation in this series.

CONCLUSIONS

This study documents the existence of a correlation between MMP-9 expression, activity of the iNOS pathway, p53 status, and angiogenesis in patients with HNSCC. This raises the possibility that p53 mutation, which frequently is present in HNSCC, may result in increased angiogenesis and invasiveness related to increased nitric oxide and MMP production by tumor cells, ultimately contributing to tumor progression.

The expression of murine double minute 2 is a favorable prognostic marker in esophageal squamous cell carcinoma without p53 protein accumulation

BACKGROUND

Murine double minute 2 (MDM2) is an oncoprotein that inhibits the function of p53 tumor-suppressor protein. Although there have been a few reports on MDM2 gene abnormalities, there has been no investigation into expression of the product of this gene in esophageal squamous cell carcinoma. Thus, the clinicopathological and prognostic significance of the product of the MDM2 gene is as yet unknown.

METHODS

MDM2 protein expression status was analyzed in surgically resected materials by immunohistochemical procedures.

RESULTS

The expression of MDM2 significantly correlated inversely with tumor size, depth of invasion, lymph node metastasis, lymphatic vessel invasion, and stage of disease. However, the expression of MDM2 correlated with neither p53 protein accumulation status nor Ki-67 labeling index. The prognosis with MDM2-positive status was significantly better than that with MDM2-negative status for patients with p53-negative tumors, but not in those with p53-positive tumors. Moreover, multivariate analysis showed that the expression of MDM2 was an independent prognostic factor in patients with p53-negative tumors.

CONCLUSIONS

These findings indicate that MDM2 immunohistochemical analysis may provide useful information concerning the prognosis in esophageal squamous cell carcinoma patients with p53-negative tumors.

Distinct pattern of TP53 mutations in squamous cell carcinoma of the esophagus in Iran

Extremely high rates of squamous cell carcinoma of the esophagus (SCCE) are observed in Iran, reflecting unknown, genetic and/or epidemiological risk factors. Among genetic alterations in SCCE, TP53 mutations are the most frequent, vary among populations, and may provide clues on etiological mechanisms. We have analysed mutations in TP53 (exons 5-8) in 98 SCCE from Iran by temporal temperature gel electrophoresis and direct sequencing. We found 58 mutations in 49 patients (50%), with a high prevalence of C to T transitions at CpG dinucleotides (29.3%). The TP53 mutation pattern in Iran was significantly different from that observed in SCCEs from high incidence areas of China and Western Europe (P=0.007). Moreover, the prevalence of mutations at A : T base pairs (transitions and transversions) was higher in men than in women (38.7% vs 11.1%, P=0.033). COX-2 overexpression was detected in 69% of the cases evaluated (24/35), without significant association with TP53 mutation. Accumulation of nitrotyrosine, a marker of protein damage by excess levels of nitric oxide, was observed in tumor cells in six of 18 [corrected] cases analysed. These results are consistent with the hypothesis that several factors are involved in TP53 mutagenesis in Iran. These factors include a baseline of chronic inflammatory stress, which may have a multiplicative impact on the sensitivity of esophageal cells to exogenous factors of risk.

TP53 mutations, amplification of P63 and expression of cell cycle proteins in squamous cell carcinoma of the oesophagus from a low incidence area in Western Europe

In Europe, high incidence rates of oesophageal squamous cell carcinoma (SCCE) are observed in western France (Normandy and Brittany) and in north-eastern Italy. Analysis of TP53 mutations in tumours from these regions has shown a high prevalence of mutations at A:T basepairs that may result from DNA damage caused by specific mutagens. However, the spectrum of TP53 mutations in regions of low incidence is unknown. We report here TP53 mutation analysis in 33 SCCE collected in Lyon, an area of low incidence. These tumours were also examined for MDM2 and P63 amplification, and for expression of p16(INK4a/CDKN2a), cyclin E, p27(Kipl)and Cox2. TP53 mutations were detected in 36% of the cases (12/33). In contrast with regions of high incidence, the mutation spectrum did not show a high prevalence of mutations at A:T base pairs. P63 was amplified in 5/32 cases tested (15.5%). No amplification of MDM2 was found. Expression studies revealed frequent loss of p16(INK4a/CDKN2a)(46%) and p27(Kipl)(25%) expression, and frequent overexpression of Cyclin E (70%) and Cox2 (42%). Overall, these results indicate that in Europe, SCCE from areas of high and low incidence present a similar pattern of molecular alterations but differ by the type of TP53 mutations.

Telomerase activity of the Lugol-stained and -unstained squamous epithelia in the process of oesophageal carcinogenesis

Up-regulation of telomerase has been reported in many cancers. Our aim was to characterize telomerase activity in various states of the oesophagus to facilitate better understanding of carcinogenesis of oesophageal squamous cell carcinoma. During endoscopic examinations, we obtained 45 Lugol-stained normal epithelia, 31 Lugol-unstained epithelia (14 oesophagitis, 7 mild dysplasia, 5 severe dysplasia and 5 intramucosal cancer) and 9 advanced cancer. Telomerase activity was semi-quantified by a telomeric repeat amplification protocol using enzyme-linked immunosorbent assay, and expression of human telomerase reverse transcriptase mRNA was examined by in situ hybridization. In the Lugol-stained normal epithelia, telomerase activity increased in proportion to the increase of severity of the accompanying lesions, with a rank order of advanced cancer, intramucosal cancer, mild dysplasia and oesophagitis. In the Lugol-unstained lesions and advanced cancer, telomerase activity was highest in advanced cancer. Up-regulation of telomerase in normal squamous epithelium may be a marker of progression of oesophageal squamous cell carcinoma.

TP53 mutations and MDM2 gene amplification in squamous-cell carcinomas of the esophagus in south Thailand

Squamous-cell carcinoma of the esophagus (SCCE) shows geographic variations in incidence that are thought to reflect the etiological involvement of environmental or dietary risk factors. Mutations of TP53 are frequent in SCCE, and there is evidence that both the frequency and type of these mutations may differ from one geographic area to the other. Although SCCE is relatively rare in most parts of Thailand, the province of Songkhla (south Thailand) has been described as a high-risk area for SCCE. We have analyzed 56 SCCE cases from this area for TP53 mutations by denaturing gradient gel electrophoresis (DGGE, exons 5-8) and direct DNA sequencing. The same tumors were also analyzed for MDM2 gene amplification by differential PCR. TP53 mutations were detected in 23 cases (41%). In contrast, clear amplification of MDM2 was detected in only 2 cases (4%), both of which contained wild-type TP53. Comparison with published results from other geographic areas of high SCCE incidence revealed that the spectrum of TP53 mutations in south Thailand is similar to that observed in central China (Henan Province) but clearly differs from that of SCCE from western Europe (Normandy, France; northern Italy), with more G:T transversions and fewer mutations affecting A and T base pairs. These results suggest that SCCE from south Thailand and from central China may involve similar risk factors.

Retinoblastoma protein expression and prognosis in laryngeal cancer

Expression of retinoblastoma (Rb) protein was immunohistochemically examined in laryngeal squamous cell neoplasias from 72 patients. Staining patterns were considered with reference to such prognostic factors as patient's age, histologic grade, tumour size and lymph node status, and 5-year survival rate. Rb protein negativity, either partial or complete, was noted in 28.8% of cases and was associated with a significantly lower 5-year survival rate, as well as with a higher likelihood of lymph node metastasis. This suggests that Rb alteration may be a prognostic indicator in patients with laryngeal carcinoma.

The MDM2 gene amplification database

The p53 tumor suppressor gene is inactivated in human tumors by several distinct mechanisms. The best characterized inactivation mechanisms are: (i) gene mutation; (ii) p53 protein association with viral proteins; (iii) p53 protein association with the MDM2 cellular oncoprotein. The MDM2 gene has been shown to be abnormally up-regulated in human tumors and tumor cell lines by gene amplification, increased transcript levels and enhanced translation. This communication presents a brief review of the spectrum of MDM2 abnormalities in human tumors and compares the tissue distribution of MDM2 amplification and p53 mutation frequencies. In this study, 3889 samples from tumors or xenografts from 28 tumor types were examined for MDM2 amplification from previously published sources. The overall frequency of MDM2 amplification in these human tumors was 7%. Gene amplification was observed in 19 tumor types, with the highest frequency observed in soft tissue tumors (20%), osteosarcomas (16%) and esophageal carcinomas (13%). Tumors which showed a higher incidence of MDM2 amplification than p53 mutation were soft tissue tumors, testicular germ cell cancers and neuro-blastomas. Data from studies where both MDM2 amplification and p53 mutations were analyzed within the same samples showed that mutations in these two genes do not generally occur within the same tumor. In these studies, 29 out of a total of 33 MDM2 amplification-positive tumors had wild-type p53. We hypothesize that heretofore uncharacterized carcinogens favor MDM2 amplification over p53 mutations in certain tumor types. A database listing the MDM2 gene amplifications is available on the World Wide Web at http://www. infosci.coh.org/mdm2 . Charts of MDM2 amplification frequencies and comparisons with p53 genetic alterations are also available at this Web site.

Analysis of p53, p16MTS, p21WAF1 and H-ras in archived bladder tumours from workers exposed to aromatic amines

Exposure to aromatic amines is considered a major risk factor for the development of bladder cancer. In this study, we have analysed the pattern of point mutations in several tumour genes in 21 cases of bladder cancer arising among western European workers exposed to aromatic amines in an attempt to determine whether this exposure may be associated with a unique spectrum of mutations. Of the four genes analysed (p53, p16MTS1, p21WAF1 and H-ras), only p53 showed a high frequency of mutations (in 8 out of 21 cases, 38%). Two mutations were found in p16, one in H-ras and none in p21 exon 3. All mutations were at G:C base pairs, mostly at non-CpG residues. This spectrum of mutations, which is highly suggestive of an involvement of exogenous carcinogens, is however identical to the spectrum of p53 mutations detected in bladder cancers of the general population. In exposed workers, p53 mutations were associated with tumour grade and with high occupational and tobacco exposure. Taken together, our data suggest that the same carcinogens may be responsible for the development of bladder cancers in workers exposed to aromatic amines and in the general population.

p16/CDKN2 alterations and pRb expression in oesophageal squamous carcinoma

BACKGROUND

Upregulation of the cell cycle associated genes, p16/CDKN2 and the retinoblastoma susceptibility gene (Rb), is commonly seen during the proliferation of normal cells. An inverse relation between the expression of p16/CDKN2 and Rb has been noted in many tumours, but has not yet been determined in oesophageal squamous carcinoma.

AIMS

To investigate p16/CDKN2 genetic alterations and both the p16/CDKN2 and the Rb protein (pRb) immunophenotypes in oesophageal squamous carcinoma.

METHODS

Twenty primary oesophageal squamous carcinomas were examined for mutations in p16/CDKN2 by the polymerase chain reaction, single stranded conformational polymorphism, and DNA sequencing. Synthesis of p16/CDKN2 and pRb proteins was determined by immunohistochemistry in 19 specimens of formalin fixed, paraffin wax embedded tissues.

RESULTS

Mutations of p16/CDKN2 were not detected in exons 1 and 2. In only one case, G to C and C to T base changes were detected in a non-coding region of exon 3. Expression of p16/CDKN2 and Rb was observed in both normal and neoplastic areas of tissue sections, indicating neither consistent homozygous deletion nor consistent hypermethylation of the genes in tumours. Fourteen tumours showed an inverse expression of p16/CDKN2 and Rb. An increased percentage of cells that immunostained positively for p16/CDKN2 but not for pRb was observed in eight tumours, five of which had no detectable pRb, suggesting defective Rb expression in these oesophageal squamous carcinomas.

CONCLUSIONS

These results indicate that p16/CDKN2 mutations occur infrequently in oesophageal squamous carcinoma. The alteration of the Rb gene is suggested as an important step in the development of these tumours.

Prevalence and predictive value of p53 mutation in patients with oesophageal squamous cell carcinomas: a prospective clinico-pathological study and survival analysis of 70 patients

The tissues from 70 Chinese patients with oesophageal squamous cell carcinoma were prospectively collected to study for the pattern of p53 mutations and its relationship with clinico-pathological features and prognosis using immunohistochemistry, polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis and DNA sequencing. p53 over-expression and p53 mutations were detected in 73% and 44% of the patients. These p53 aberrations had no relationship with the patient age, sex, smoking/drinking habits and tumor site, size or stage. The p53 over-expression was more intense in moderately/poorly-differentiated squamous cell carcinomas. Thirty-three p53 mutations were noted in 31 patients; 18.2% in exon 5, 15.2% in exon 6, 33.3% in exon 7 and 33.3% in exon 8. Mutations were primarily point mutations and common in codons 248, 273 and 285. There were 46% transversions, 36% transitions and 18% frameshift. The survival of the patients depended mainly on the extent of resection. In patients with stage III oesophageal cancer, the median survival of those with p53 mutations was 6.8 months whereas those without was 12.5 months. The results were of clinical importance although the value did not reach statistical significance. Thus, there was a definite role of p53 mutations in the pathogenesis of oesophageal squamous cell carcinomas. p53 mutations were not synonymous with p53 over-expression. The distribution of p53 mutations in oesophageal cancers suggested that the etiologic contribution might be complex and probably involve different exogenous and endogenous exposures. p53 mutations also appear to play a role in predicting the survival of patients with stage III oesophageal squamous cell carcinomas.

Investigation of oesophageal adenocarcinoma for viral genomic sequences

Overexpression of the tumour suppressor gene product p53 is common in oesophageal adenocarcinoma. This may be due to gene mutation, but overexpression can also result from complexing between viral proteins and p53; a number of viruses are causally linked with malignancy. This study therefore investigated the prevalence in oesophageal adenocarcinoma of viruses whose gene products are capable of interacting with p53. Seventeen tumours and 17 normal oesophagi were screened for specific DNA sequences from human papilloma virus (HPV), Adenovirus type 12, Epstein-Barr Virus (EBV), and cytomegalovirus (CMV). Frozen sections were analysed by polymerase chain reaction, and results were confirmed by Southern blot hybridization. Overexpression of p53 was studied immunohistochemically. Overexpression of p53 was identified in 11 of 17 tumours. No viral sequences were detected for HPV, CMV, or Adenovirus in any tumour. EBV sequences were found in eight of 17 tumours, and eight of 17 negative controls. There is therefore no evidence of HPV 16, 18 and 33, Adenovirus 12 or CMV infection in oesophageal adenocarcinoma. EBV infection in the oesophagus is of doubtful significance, in view of the high incidence in the control population. Overexpression of p53 cannot be explained by complexing with common viral proteins, and must be related to other intracellular mechanisms.

A molecular and immunohistochemical study of the MDM2 protein isoforms and p53 gene product in bronchogenic carcinoma

Forty-one bronchogenic carcinomas were investigated for expression of MDM2 protein isoforms and their relationship to p53 protein levels and p53 gene alterations using molecular and immunohistochemical techniques. The findings were correlated with the pathological features of the carcinomas. MDM2 protein was overexpressed in 26 cases (63 percent). Western blot analysis with two monoclonal antibodies, 1B10 and IF2, revealed three MDM2 protein isoforms, p90, p57 and p76/74. p90 and p57 are capable of interacting with p53 protein, while p76/74 is not. Various patterns of MDM2 isoforms were seen. Although no correlation between the patterns and pathological features was observed, lymph node metastases were more frequent in the cases with MDM2 overexpression (P < 0.005). In 3 out of 17 specimens of normal lung tissue examined, there was a low level of expression of p90. Molecular analysis revealed that MDM2 overexpression was a consequence of increased transcription rather than MDM2 gene amplification. p53 protein was overexpressed in 21 cases (51 percent) and p53 gene alterations (mutations + allelic deletions) were detected in 23 patients (56 percent). A high degree of concordance (76 percent) between p53 mutations and p53 staining was noticed (P < 10(-5)). p53 gene alterations were significantly associated with lymph node disease (P < 0.01). MDM2 and p53 proteins were simultaneously detected in 21 cases (51 percent), of which 17 (42 percent) showed p53 and MDM2 overexpression. The latter group was positively correlated with p53 mutations (P < 0.05). A strong correlation between MDM2/p53 co-expression and lymph node metastases was observed (P < 0.001). The findings suggest that MDM2 overexpression is a common event in bronchogenic carcinoma. The selective expression of some MDM2 isoforms in neoplastic tissue and not in the surrounding normal areas underscores the pathological role of the various MDM2 products. Finally, the coexistence of MDM2 protein(s) and p53 aberrations (mutations and/or overexpression) in a subset of lung carcinomas may be indicative of a 'gain of function' phenotype, with more aggressive characteristics.

Genetic alterations in esophageal cancer and their relevance to etiology and pathogenesis: a review

Cancer of the esophagus exists in 2 main forms with different etiological and pathological characteristics-squamous cell carcinoma (SCC) and adenocarcinoma (ADC). This review focuses on the occurrence of genetic alterations in SSC and ADC of the esophagus and on their possible implications for the elucidation of the etiology and pathogenesis of these cancers. The most common alterations found in esophageal cancers include allelic losses at chromosomes 3p, 5q, 9p, 9q, 13q, 17p, 17q and 18q, as well as mutations of p53 (mostly missense), Rb (deletions), cyclin DI (amplifications) and c-myc (amplifications). The sequence of occurrence of these alterations with respect to histopathological tumor progression is discussed. Our findings underscore the different etiology and pathogenesis of SCC vs. ADC and suggest that the genetic alterations observed may represent molecular fingerprints of critical risk involved in the development of these 2 cancers.

Low frequency of p16/CDKN2 gene mutations in esophageal carcinomas

Mutational analysis of the p16/CDKN2 gene was conducted by direct sequencing of the whole coding sequence (exons 1-3 and flanking splicing sites) in 21 esophageal squamous-cell carcinomas and 3 adenocarcinomas from a high-incidence area of Italy. Two inactivating mutations were found in exon 1 of the gene (both in squamous-cell carcinoma), whereas no mutations were detected in exon 2, where most of the sequence changes reported so far have been located, or in exon 3. Southern blot analysis of exon 2 in this set of samples and in a complementary set of 12 tumor samples from France did not show homozygous deletions or detectable gene rearrangements. Thus, p16/CDKN2 gene alterations do not appear to play a major role in the group of patients examined.

Alterations in transforming growth factor-alpha and epidermal growth factor receptor expression during rat esophageal tumorigenesis

Transforming growth factor-alpha (TGF-alpha) stimulates cell proliferation through interaction with its receptor, the epidermal growth factor receptor (EGFR), by activating its tyrosine kinase activities. The simultaneous overexpression of TGF-alpha and EGFR by tumor cells is thought to trigger the autocrine growth pathway, leading to uncontrolled proliferation. To examine their roles in rat esophageal tumorigenesis induced by the chemical carcinogen N-nitrosomethylbenzylamine (NMBA), TGF-alpha, and EGFR expression was evaluated in normal rat esophageal epithelium, in NMBA-induced preneoplastic lesions, and in papillomas by quantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical analyses. Compared with the levels in normal epithelium, the TGF-alpha and EGFR mRNA levels in esophageal papillomas were 3.6 and 1.9 times higher, respectively. In the preneoplastic epithelium, although a trend of increased TGF-alpha and EGFR mRNA levels was observed, collectively there were no significant differences between preneoplastic and normal samples by RT-PCR analysis. In situ hybridization and immunohistochemical staining showed increased levels of TGF-alpha and EGFR mRNA and protein products in papillomas and in pronounced hyperplastic and dysplastic lesions. TGF-alpha and EGFR expression correlated with each other and with the expression of proliferating cell nuclear antigen, a marker for cell proliferation. These results suggest that disregulation of TGF-alpha and EGFR expression may contribute to autonomous cell growth and may play an important role in rat esophageal tumorigenesis induced by NMBA.

MDM2 overexpression is rare in ovarian carcinoma irrespective of TP53 mutation status

Somatic mutations in TP53 are seen in many human cancers. In addition, the protein product of the wild-type TP53 can be sequestered by the protein MDM2 (murine double minute 2). This protein is commonly overexpressed in human sarcomas and gliomas, usually as a result of gene amplification. In this study, 43 ovarian carcinomas (OCs) were analysed for aberrations in the TP53 gene by immunohistochemistry (IHC), loss of heterozygosity (LOH) or mutation analysis. The MDM2 gene and its product was studied by Southern blotting and IHC. Over 50% of the OCs studied showed mutations in TP53 by either direct sequencing (19/36, 53%), positive IHC (23,43, 53%) or both, whereas 0/32 had amplification of MDM2 and only 1/37 tumours had positive IHC using the anti-MDM2 antibody IF-2. The solitary example of positive IHC in this series was seen in a mixed müllerian tumour with sarcomatous differentiation and was not accompanied by MDM2 DNA amplification. These results support previous data showing that around 50% of OCs have mutations in TP53 and in addition, suggest that MDM2 is not amplified in OC, but the presence of sarcomatous features in mixed müllerian tumours may result in positive immunohistochemistry with IF-2.

p53 mutations in esophageal tumors from high-incidence areas of China

Carcinomas of the upper digestive tract (squamous-cell carcinoma of the esophagus, adenocarcinoma of the cardia) from 24 patients residing in Linxian (China) and near-by high-incidence areas were analyzed for mutations in exons 5-8 of the p53 tumor-suppressor gene. Mutations were identified by polymerase chain reaction amplification and direct sequencing in 50% of the specimens. Eleven tumors harbored a single base-pair substitution leading to either an amino-acid substitution (8 tumors) or a chain-termination signal (3 tumors), and one tumor revealed a 15-bp deletion in exon 7 with a silent base substitution adjacent to the deletion site. Mutations occurred in all 4 exons examined, with a preponderance in exon 5. Of the 6 mutations identified among the 14 adenocarcinomas examined, 3 were G to T transversions, a mutation that has thus far been absent from reported mutations in Barrett's esophageal adenocarcinomas and dysplasias from patients residing in Europe and North America.

Multiple patterns of MDM-2 deregulation in human leukemias: implications in leukemogenesis and prognosis

The human analogue of the mouse double minute-2 (MDM-2) protein binds to p53 protein and abrogates its tumor-suppressing activity. MDM-2 overexpression may represent an alternative mechanism to p53 mutation for escaping the p53-mediated growth control. Interestingly, multiple MDM-2 protein isoforms have been described and the possibility of functional differences between various isoforms has been raised. Previously, we demonstrated significant MDM-2 mRNA overexpression in human leukemias and suggested that MDM-2 overexpression may be a marker of aggressiveness of the disease. Polyclonal antibodies (Ab) have been generated to detect various isoforms of the MDM-2 protein. Using these Abs, we confirmed MDM-2 protein overexpression in leukemias. Furthermore, we observed heterogeneity in the isoforms expressed in various types of leukemias. In addition, we demonstrated that analysis by flow cytometry could be used as a diagnostic tool for detecting altered MDM-2 protein expression in leukemias. Here we review and expand our initial observations and confirm MDM-2 mRNA and protein overexpression by reverse transcription-polymerase chain reaction (RT-PCR), flow cytometry, and western blot analyses. Understanding the possible role of MDM-2 oncogene expression in leukemias may establish the scientific basis for new therapeutic approaches.