Why is p53 protein stabilized in neoplasia? Some answers but many more questions?

The nuclear factor erythroid 2-related factor 2/p53 axis in breast cancer

One of the most important factors involved in the response to oxidative stress (OS) is the nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates the expression of components such as antioxidative stress proteins and enzymes. Under normal conditions, Kelch-like ECH-associated protein 1 (Keap1) keeps Nrf2 in the cytoplasm, thus preventing its translocation to the nucleus and inhibiting its role. It has been established that Nrf2 has a dual function; on the one hand, it promotes angiogenesis and cancer cell metastasis while causing resistance to drugs and chemotherapy. On the other hand, Nrf2 increases expression and proliferation of glutathione to protect cells against OS. p53 is a tumour suppressor that activates the apoptosis pathway in aging and cancer cells in addition to stimulating the glutaminolysis and antioxidant pathways. Cancer cells use the antioxidant ability of p53 against OS. Therefore, in the present study, we discussed function of Nrf2 and p53 in breast cancer (BC) cells to elucidate their role in protection or destruction of cancer cells as well as their drug resistance or antioxidant properties.

Analysis of Molecular Pretreated Tumor Profiles as Predictive Biomarkers of Therapeutic Response and Survival Outcomes after Neoadjuvant Therapy for Rectal Cancer in Moroccan Population

Pathologic features depending on tumor response to preoperative chemoradiotherapy are important to determine the outcomes in patients with rectal cancer. Evaluating the potential predictive roles of biomarker expression and their prognostic impact is a promising challenge. We reported here the immunohistochemical staining of a panel marker of mismatch repair protein (MMR), Ki67, HER-2, and p53. Additionally, identification of somatic mutations of KRAS, NRAS, and BRAF genes were performed by direct sequencing and pyrosequencing in pretreated biopsy tissues from 57 patients diagnosed for rectal cancer. Clinical features and pathological criteria for postneoadjuvant treatment surgical resection specimen's data were collected. Immunohistochemical expression and mutational status were correlated with therapeutic response, overall survival, and disease progression. The mean age of patients was 56 years. Seven (12.3%) out of 57 patients had a complete therapeutic response. Our analysis showed that when using complete therapeutic response (Dworak 4) and incomplete therapeutic response (Dworak 3, 2, and 1) as grouping factor, high p53 expression at the pretreatment biopsy was significantly associated to an incomplete response (p = 0.002). For 20 and 2 out of 57, KRAS and NRAS mutations were detected, respectively. The majority of these mutations affected codon 12. KRAS mutations detected at codon 146 (A146T, A146V) was associated with the appearance of recurrence and distant metastasis (p = 0.019). A high expression of HER-2 corresponding to score 3+ was observed in 3 pretreatment biopsy specimens. This class was significantly associated with a short relapse-free survival (p = 0.002). Furthermore, the high expression of Ki67 was moderately correlated with an older age (p = 0.016, r = 0.319). In addition, this shows that high p53 expression in the pretreatment biopsy was associated with an incomplete response in surgical resection specimens after neoadjuvant treatment, and a HER-2 score 3+ can be a predictive factor of distant metastasis and local recurrence. Larger, prospective, and more studies are needed.

Mutant p53 in breast cancer: potential as a therapeutic target and biomarker

OBJECTIVE

The aim of this article is to discuss mutant p53 as a possible therapeutic target and biomarker for breast cancer.

RESULTS

TP53 (p53) is the most frequently mutated gene in invasive breast cancer. Although mutated in 30-35% of all cases, p53 is mutated in approximately 80% of triple-negative (TN) tumors (i.e., tumors negative for ER, PR, and HER2). Because of this high prevalence, mutated p53 is both a potential biomarker and therapeutic target for patients with breast cancer, especially for those with the TN subtype. Although several retrospective studies have investigated a potential prognostic and therapy predictive role for mutant p53 in breast cancer, the results to date are mixed. Thus, at present, mutant p53 cannot be recommended as a prognostic or therapy predictive biomarker in breast cancer. In contrast to the multiple reports on a potential biomarker role, few studies had until recently, investigated mutant p53 as a potential target for breast cancer treatment. In the last decade, however, several compounds have become available which can reactivate mutant p53 protein and convert it to a conformation with wild-type properties. Some of these compounds, especially PRIMA-1, APR-246 PK11007, and COTI-2, have been found to exhibit anticancer activity in preclinical models of breast cancer.

CONCLUSION

Since p53 is mutated in the vast majority of TN breast cancers, compounds such as APR-246, PK11007, and COTI-2 are potential treatments for patients with this subform of the disease. Further research is necessary to identify a potential biomarker role for mutant p53 in breast cancer.

TAp73 alpha increases p53 tumor suppressor activity in thyroid cancer cells via the inhibition of Mdm2-mediated degradation

p53 family proteins include p53 tumor suppressor, p63, and p73. Despite the high similarity in structure and function with p53, p63, and p73 function in tumor suppression is still controversial. Here, we show that TAp73alpha, a transcriptionally active p73 isoform, is able to synergize p53 tumor suppressor function in thyroid cancer cells. Indeed, depletion of p73 by small interfering RNA in thyroid cancer cells resulted in a reduced transcriptional activity of p53. Ectopic coexpression of both p53 and TAp73alpha in thyroid cancer cells resulted in increased transcription and tumor suppressor function compared with p53 or TAp73alpha alone, as well as in increased p53 protein levels. The enhancing effect of TAp73alpha on p53 activity is Mdm2 dependent because it is prevented by Mdm2 depletion by small interfering RNA. At least two mechanisms may explain the interference of TAp73alpha with p53 function. First, in thyroid cancer cells, TAp73alpha inhibits the effect of p53 on Mdm2 induction by antagonizing p53 at the Mdm2 promoter level. Second, a TAp73alpha mutant (G264W), which is devoid of DNA binding capability, is still able to increase p53 protein levels by competing with p53 for Mdm2 protein binding. Taken together, these results indicate that in thyroid cancer cells, TAp73alpha is able to increase p53 protein level and function by interfering with Mdm2-mediated p53 degradation. These results may be useful for designing gene therapies aimed at restoring a normal p53 function in thyroid cancer cells.

Assessing p53 in clinical contexts: unlearned lessons and new perspectives

There is compelling evidence for the central role of the p53 pathway in human neoplasia but, despite an enormous literature, the clinical utility of assessing this pathway remains ambiguous. Even simple questions about the assessment of p53 status in clinical samples remain unanswered and the literature is confusing and often contradictory. The p53 pathway is certainly complicated and the biochemical mechanisms for regulating the function of p53 and its downstream consequences are rabbinical in complexity. This perspective considers this complexity and the reasons why establishing the true utility of clinical assessment of p53 has proven to be so difficult. Indeed, recent observations regarding the existence of alternate splice variants of p53, the complexity of p53 regulation, and the existence of allelic variants of p53 and its regulators with distinct functionality makes the situation even more complex. Problems with the available assays are considered and the need to consider an array of methodological issues is emphasized. Newer strategies including analysis of the expression of downstream targets of p53 and the use of threshold strategies to measure p53 protein may provide more robust measures of the p53 pathway in clinical settings, perhaps coupled with cheap sequencing-based approaches for mutation (and polymorphism) detection. However, progress will only be made if these methodological issues are resolved and robust assays are performed in the context of appropriately powered studies in clinical trial settings.

A Strategy for Defining Biologically Relevant Levels of p53 Protein Expression in Clinical Samples with Reference to Endometrial Neoplasia

Numerous studies have investigated p53 immunohistochemistry as a diagnostic, prognostic or predictive marker in various neoplasms. However, the literature is confused and contradictory paying little attention to pivotal aspects of p53 biology nor basic immunohistochemical principles. Here we highlight the effect of varying antibody concentration on p53 immunohistochemical expression. Six uterine endometrioid carcinomas, one uterine serous carcinoma (USC) and a proliferative endometrium were stained with antip53 antibody D07 at varying dilutions. Cases were scored on a scale of 0-6 depending on the percentage of positive nuclei. Greater than 95% of epithelial cells in the USC were positive at all dilutions. The proliferative endometrium exhibited positive staining of >95% of epithelial cells at low dilutions but at high dilutions most epithelial cells were negative. The proportion of positive tumor nuclei in the endometrioid carcinomas varied markedly with antibody concentration. We illustrate that the signal obtained from p53 immunohistochemistry is dependent on antibody concentration. This has diverse implications. First, the p53 labeling index is unreliable without attention to such issues. Second, comparisons between studies are not valid since different antibody concentrations (and other variables) are used. Thirdly, standardization between laboratories is necessary if clinical utility is to be attached to markers including p53. We propose a strategy for determining the optimal p53 antibody concentration.

Results of p53 analysis in pediatric malignancies in Poland

BACKGROUND

Mutations of the p53 gene are thought to be causally associated with the development of various neoplasms. In tumors overexpressing the wild-form of p53, its functional inactivation has been suggested, and MDM2 seems to be important in this process. We analyzed p53 in childhood solid tumors, as data on pediatric malignancies are still limited.

PROCEDURE

The p53 gene was screened for mutations by the PCR-S SCP method and sequencing. p53, p21, and MDM2 proteins were analyzed by Western blotting.

RESULTS

Overall, p53 mutations were found at a low frequency, 7% (9/126); the frequency calculated for sarcomas was also low, 8.6%. Interestingly, three of the nine detected mutations were new ones. p53 protein was demonstrated in all tumor histotypes, overall, in 63% (43/68) of the tumors, with 18% showing marked overexpression. No p21 was found; and the 76 kDa MDM2 protein was demonstrated in 18% (6/33) of the sarcomas.

CONCLUSIONS

In the series of pediatric malignancies studied, the frequency of p53 mutations was very low, whereas p53 protein was present in a high fraction of the tumors. Thus, in total, p53 abnormalities were frequent.

Impact of genomic instability in risk assessment and chemoprevention of oral premalignancies

Head-and-neck cancer is a disfiguring disease with increasing incidence rates even in young people, whose exposure to known risk factors is limited. This emphasizes the importance of early identification, on an individual basis, of precursor lesions that will develop into carcinomas. The clinical value of identifying individuals at high risk of oral cancer is emphasized by the fact that these patients are likely to benefit from available chemopreventive measures, largely without adverse effects.

p53 expression, growth, and spontaneous metastasis of the human GI 101 breast carcinoma in athymic nude mice

The human GI 101 breast carcinoma cell lines produces spontaneous metastasis to the lungs when xenografted subcutaneously in female athymic nude mice. To establish the time-course of tumor growth and distant metastasis to the lungs and axillary lymph nodes, 5 mm3 of tumor tissue was implanted in the subaxial region of female athymic nude mice. Micrometastases in the lung were first detected 3 weeks after tumor implantation. The incidence of lung metastasis and the number of tumor emboli were correlated with the volume of the primary tumors. Ipsilateral axillary lymph node metastasis was observed within 17 weeks, indicating that metastasis to the lymph node is a later event. Unlike pulmonary micrometastases which were in the form of clusters of four to six tumor cells, metastasis to the lymph nodes were in nodules of poorly differentiated and larger tumor cells. Immunohistochemistry evaluation of p53 oncoprotein in the primary and metastatic tumor cells showed different patterns of subcellular accumulation. Cytoplasmic staining was mainly detected in the primary and secondary tumor cells disseminated to the lungs. In contrast, nuclear staining was only detected in tumor cells infiltrated to the axillary lymph nodes. There was no gain of loss of positivity of p53 accumulation (i.e., qualitative measurements) as the tumor grew in size. The data indicate that the GI 101 tumor cells could be used as a useful model for studying the malignant progression of hormone-independent breast cancer, antimetastatic drugs, and early events in tumor metastasis.

Mutation analysis of the p51 gene and correlation between p53, p73, and p51 expressions in prostatic carcinoma

BACKGROUND

p73 and p51 are genes possessing amino-acid similarities to p53. We previously found no mutation in p73 in prostatic carcinoma, but did find abnormal expression of the gene. Involvement of these genes in prostatic carcinogenesis is still poorly understood.

METHODS

Mutation analysis of the p51 gene and allelotyping of 3q28, on which p51 lies, were performed. Expression of p53, p73, and p51 was examined using reverse transcription-polymerase chain reaction, and expression levels were compared.

RESULTS

No mutation in p51 was found (0/55 cases). Loss of heterozygosity at 3q28 was detected in 6 of 28 cases (21.8%). By expression analysis we found that in p53, 4 of 38 cases (10.5%) showed downregulation. No cases showed upregulation of p53. In contrast, p73 and p51 were downregulated in 42.1 and 39.5% of cases, respectively, and upregulated in 31.5 and 34.2% of cases, respectively. Expression levels of p51 corresponded with those of p73 in 25 of 38 cases (65.8%).

CONCLUSIONS

Somatic mutations in p73 and p51 are not important in prostatic carcinogenesis. These genes may be associated with tumors by expression levels and may have roles in addition to tumor suppression.

Molecular predictors of survival after adjuvant chemotherapy for colon cancer

BACKGROUND

Adjuvant chemotherapy improves survival among patients with stage III colon cancer, but no reliable molecular predictors of outcome have been identified.

METHODS

We evaluated loss of chromosomal material (also called loss of heterozygosity or allelic loss) from chromosomes 18q, 17p, and 8p; cellular levels of p53 and p21(WAF1/CIP1) proteins; and microsatellite instability as molecular markers. We analyzed tumor tissue from 460 patients with stage III and high-risk stage II colon cancer who had been treated with various combinations of adjuvant fluorouracil, leucovorin, and levamisole to determine the ability of these markers to predict survival.

RESULTS

Loss of heterozygosity at 18q was present in 155 of 319 cancers (49 percent). High levels of microsatellite instability were found in 62 of 298 tumors (21 percent), and 38 of these 62 tumors (61 percent) had a mutation of the gene for the type II receptor for transforming growth factor beta1 (TGF-beta1). Among patients with microsatellite-stable stage III cancer, five-year overall survival after fluorouracil-based chemotherapy was 74 percent in those whose cancer retained 18q alleles and 50 percent in those with loss of 18q alleles (relative risk of death with loss at 18q, 2.75; 95 percent confidence interval, 1.34 to 5.65; P=0.006). The five-year survival rate among patients whose cancer had high levels of microsatellite instability was 74 percent in the presence of a mutated gene for the type II receptor for TGF-beta1 and 46 percent if the tumor did not have this mutation (relative risk of death, 2.90; 95 percent confidence interval, 1.14 to 7.35; P=0.03).

CONCLUSIONS

Retention of 18q alleles in microsatellite-stable cancers and mutation of the gene for the type II receptor for TGF-beta1 in cancers with high levels of microsatellite instability point to a favorable outcome after adjuvant chemotherapy with fluorouracil-based regimens for stage III colon cancer.

Quantitative p21(waf-1)/p53 immunohistochemical analysis defines groups of primary invasive breast carcinomas with different prognostic indicators

We used image cytometry to quantify the immunohistochemical expression of p21(waf-1) and p53 in primary breast carcinoma. Ratio analysis of the quantified p53/p21(waf-1) protein expression allowed us to define 3 groups of carcinomas, each characterized by specific pathological and biological profiles. The negative (NEG) group, characterized by negligible expression of both proteins, comprised small-sized, low-grade tumors associated with high contents of hormonal receptors and low growth fraction. In the NEG group, Ki-67 labelling index area (%LIa) was the only significant prognostic indicator. The P53H group, characterized by prevalence of p53 %LIa, was constituted by large-sized, high-grade tumors showing low hormonal receptor contents and high growth fraction. In the P53H group, both p53 and Ki-67 were inversely associated with both estrogen receptor (ER) and progesterone receptor (PGR), suggesting that extensive p53 immunostaining is related to poor differentiation and high proliferation. Only N status was prognostically significant in the P53H group. The P21H group, characterized by prevalence of p21(waf-1) %LIa, displayed intermediate pathological and biological features. A significant association between p53 and p21(waf-1) expression suggested functional stabilization of wtp53 and therefore possible DNA damage-dependent G1/S arrest (genetic instability) in the P21H group; P21(waf-1)expression was significantly associated with the presence of node metastasis. Patients in the P21H group had a higher recurrence rate and a shorter disease-free time interval from surgery with respect to the NEG group. Proportional hazard regression analysis disclosed Ki-67 %LIa and, to a lesser degree, PGR %LIa as significant relapse-free survival prognostic indicators.

Mdm2 and the p53 pathway in human pituitary adenomas

OBJECTIVE

Studies on pituitary tumours have failed to identify mutations in the tumour suppressor gene p53 suggesting that the protein identified is wild type. p21(WAF--1) is a downstream effector of p53 which promotes growth arrest. Mdm2 (mouse double minute) is a protein induced by wild type p53 and forms an autoregulatory feedback loop suppressing wild type p53 activity. The purpose of this study was to examine a group of pituitary tumours for expression of p53 and its two downstream effector proteins p21(WAF--1) and mdm2 and to compare this with their radiological invasive status and proliferative potential as assessed by Ki-67 expression.

SUBJECTS AND METHODS

Sixty-nine tumours removed at transsphenoidal surgery were examined by immunocytochemistry using antibodies against p53, p21(WAF--1), mdm2 and Ki-67 (MIB-1). The invasive status of the tumours was determined from the preoperative CT/MRI scans.

RESULTS

p53 was expressed in 42 of 69 (61%) pituitary adenomas but there was no relationship with either pituitary tumour invasive status (P = 0.71) or volume (P = 0.33). p53 expression correlated, however, with the proliferative state of the tumours as assessed by the MIB-1 labelling index (P = 0.0065). Invasive tumours had a higher growth fraction than non-invasive ones (P = 0.027). p21(WAF--1) was expressed in the nuclei of 58/69 (84%) pituitary adenomas and its expression correlated with that of p53 (r = 0.26, P = 0.03). Mdm2 was expressed in the cytoplasm of 46/69 (67%) tumours and this correlated with the nuclear staining for p53 (P = 0.022) while nuclear staining was seen in 32/69 (46%) tumours but this did not correlate significantly with nuclear p53 staining (P = 0.096).

CONCLUSIONS

These results suggest that p53, p21(WAF--1) and mdm2 are all expressed in pituitary tumours suggesting that the p53 protein detected by immunocytochemistry is wild type. Expression of p53 is associated with tumours which have a higher proliferative status. The p53 activity is probably the result of upstream signals of local stresses mediated through either genetic change, cytokines, hypoxia or hormonal factors. Our results suggest, however, that the downstream pathway mediated through the activities of p21(WAF--1) and mdm2 may be dysfunctional in these tumours.

Expression of p53 protein in T- and natural killer-cell lymphomas is associated with some clinicopathologic entities but rarely related to p53 mutations

To determine if p53 abnormalities could be involved in the pathogenesis of T- or natural killer (NK)-cell lymphomas, we investigated 51 cases of these lymphomas for the expression of p53 and its relationship with p53 gene mutations, the expression of the p21 protein as well as the proliferative and apoptotic indices. Overexpression of p53 was found in 19 cases (37%), whereas mutations of the p53 gene were observed in only 5 of 28 tested cases. The analysis of immunohistochemical data showed some entity-related phenotypic profiles. Anaplastic large cell lymphomas showed a frequent overexpression of p53 (7/8 cases) and p21 (6/8 cases) proteins and rare p53 mutations (1/7 cases), suggesting accumulation of a functional wild type p53 protein able to induce p21 expression. Nodal peripheral T-cell lymphomas unspecified showed relatively frequent overexpression of p53 protein (5/7 cases), infrequent p21 expression (2/7 cases), and rare p53 gene mutations (1/6 cases). In angioimmunoblastic lymphomas, the common phenotype was p53-/p21- (15/17 cases), with only a few scattered p53-positive cells, which, on the basis of double staining results, were mostly Epstein-Barr virus-infected B cells. A p53 gene mutation was only found in 1 case (1/8 cases) of angioimmunoblastic lymphoma, which showed cytologic tumor progression. Mycosis fungoides showed p53 overexpression in 2 of 4 cases, including 1 case with p53 gene mutation and features of cytologic tumor progression. Nasal NK/T lymphomas showed p53 overexpression in 2 of 5 cases, 1 of which had a p53 gene mutation. Finally, all lymphoblastic T-cell lymphomas (5 cases) and gammadelta hepatosplenic T-cell lymphomas (3 cases) were negative for expression of p53 and p21 proteins. We conclude that p53 protein overexpression is a common finding in some entities of T- and T/NK-cell lymphomas, whereas a p53 gene mutation is a rare, sporadic, and rather late event associated with tumor progression in some instances. The p53/p21 expression pattern appears to be variable in T- and T/NK-cell lymphoma entities, reinforcing the concept of distinct, entity-related mechanisms of pathogenesis in these tumors.

Expression of p53 in oral squamous cell carcinoma is associated with the presence of IgG and IgA p53 autoantibodies in sera and saliva of the patients

Around 50% of head and neck cancers are known to have aberrations of the p53 gene. Overexpression of the mutant p53 protein can induce a specific humoral response in cancer patients. Matched saliva, serum, and tissue samples from 26 patients with histologically confirmed oral squamous and verrucous carcinoma were investigated. p53 protein expression was evaluated by immunohistochemistry and antibodies specific for 53 protein were analysed in sera and whole mouth saliva by ELISA, immunoprecipitation, and competition assays; 16/25 (64%) samples demonstrated the stabilized p53 protein in tissues and 7/26 (27%) had a high level of p53 antibody in serum. In samples where matching saliva was available, p53 antibody was also present in saliva. In some tumours, only IgA-type p53 antibody was detected. p53 antibodies were found only in the serum and saliva of patients who showed p53 overexpression in their tumour tissues. These results demonstrate that detection of p53 antibodies can offer a specific and non-invasive method for the detection of a subset of tumours with p53 aberrations.

Novel polymerase chain reaction approach for full-coding p53 mutation detection in microdissected archival tumors

Evidence suggests that up to 25% of p53 mutations are outside of exons 5-8 and that insertions, deletions, and polymorphic sites in the p53 gene may play a significant role in the process of carcinogenesis. A novel polymerase chain reaction (PCR) approach for the analysis of the entire p53 coding and splice site regions from microdissected, formalin-fixed, paraffin-embedded tumor tissues has been developed which allows multiple genetic analyses to be performed from one primary amplification reaction. The method was initially evaluated using well-characterized cell lines. In addition to confirming the published p53 mutations for HT29, Molt 4, A431, and HN5, a 16 base pair (bp) duplication within intron 3 was detected in both the A431 and HT29 cell lines. Analysis of archival samples of ovarian cancer identified the same 16-bp duplication and coding region variations. In all samples, using GenBank submission U94788 as a reference, a C-insertion was detected at nucleotide positions 11818 and 11874 within intron 2. At nucleotide position 14168, within intron 7, a T-to-G base change was found. This novel PCR approach has the potential to reduce the amount of clinical material required by up to 95%, thus facilitating retrospective studies on archival tumor collections. Furthermore, a wider analysis of the p53 gene, including splice sites and intronic regions, may yield additional information regarding cancer predisposition, response to therapy, and progression.

Lack of molecular markers to predict malignant potential of oral precancer

Studies on the natural history of oral squamous cell carcinoma suggest a clinically detectable phase which precedes the development of cancer. Among the precancerous states, leukoplakia is the most commonly encountered clinical lesion. Although epithelial dysplasia is the most important predictive factor, non-dysplastic lesions in the oral cavity may transform with time. Early reports describing p53 overexpression in oral leukoplakia has resulted in many authors misinterpreting this result by concluding that p53 is an early marker of oncogenesis. Using sequential biopsies, few reports have critically examined the clinical significance of p53 as a risk marker. These studies suggest that p53 protein stabilization, or indeed the spectrum of mutations of p53, has no major relationship to the biological characteristics and outcome of oral leukoplakia. When used as a single marker, p53 is unsuitable for the prediction of tumour development in high-risk subjects and no other maker has yet emerged as useful. Despite the impact of molecular diagnostics on the diagnosis of tumours, assessing a patient's risk for development of cancer of the oral cavity remains limited to 'H&E' pathology.

Microsatellite instability in hyperplastic and adenomatous polyps of the stomach

BACKGROUND

Few studies have focused on the presence and significance of microsatellite instability (MSI) in gastric polyps, and the results on record are conflicting. The aim of the current study was to address this issue, taking into consideration the 2 main types of gastric polyps, the coexistence of foci of malignant transformation, and the expression of p53 and ERBB-2.

METHODS

Six hyperplastic polyps, 10 adenomatous polyps, and 4 adenomatous polyps displaying foci of malignant transformation (intestinal-type carcinoma) were studied for MSI. The authors analyzed a mononucleotide repeat microsatellite (BAT-26) and 5 dinucleotide repeats in microdissected formalin fixed, paraffin embedded tissue sections that were representative of the lesions. Expression of p53 and ERBB-2 were evaluated by immunohistochemistry.

RESULTS

BAT-26 positivity was detected in 1 of 6 hyperplastic polyps (16.7%) and in 2 of 10 adenomas (20%) without malignant transformation. In the 4 adenomatous polyps with carcinomatous foci, BAT-26 positivity was detected in 2 cases (50%) in both (adenomatous and carcinomatous) components of the lesions. p53 immunoreactivity was observed in 6 adenomatous polyps, 2 of them with malignant transformation. Overexpression of the ERBB-2 protein was detected in 1 adenomatous polyp with malignant transformation.

CONCLUSIONS

Replication error (RER+) phenotype occurs in both hyperplastic and adenomatous polyps of the stomach. The highest frequency is observed in adenomatous polyps with carcinomatous foci, suggesting that MSI may play a role in the process of malignant transformation in this setting. No significant association was observed between RER+ phenotype and overexpression of p53 or ERBB-2 proteins.

p21(Waf1/Cip1) expression and the p53/MDM2 feedback loop in gastric carcinogenesis

Data are non-existent regarding coincidental alterations in the expression of p53 and its downstream target genes MDM2 and p21(Waf1/Cip1) in gastric carcinogenesis. An immunohistochemical study was therefore performed to examine the interrelationships of p53, MDM2, and p21(Waf1/Cip1) expression in a series of Caucasian early gastric carcinomas and precursor lesions. In normal gastric mucosa, chronic gastritis, and intestinal metaplasia, the surface cells expressed p21(Waf1/Cip1) in the absence of detectable nuclear p53 and MDM2 protein. Nuclear p53 protein accumulation was found in 60 per cent of the carcinomas, with significant differences in staining characteristics between the Lauren types in the absence of detectable MDM2 protein ( p< 0.005). Nearly 80 per cent of the carcinomas expressed p21(Waf1/Cip1), irrespective of Lauren type. Stratification of the carcinomas according to histological grade and growth pattern did not result in significant differences in p53 and p21(Waf1/Cip1) expression. Finally, no significant correlation was found between overall p53 and p21(Waf1/Cip1) expression in early gastric carcinomas. It is concluded that p21(Waf1/Cip1) expression in the non-neoplastic mucosa most likely relates to cell senescence and/or terminal differentiation, perhaps even in a p53-independent manner. In view of p53/MDM2 homeostasis, the differences in p53 staining characteristics between intestinal and diffuse-type carcinomas probably result, at least in part, from a difference in the prevalence of p53 gene mutations. Moreover, p53-independent induction of p21(Waf1/Cip1) expression apparently occurs in a considerable proportion of early carcinomas. Finally, in contrast to other carcinomas, p21(Waf1/Cip1) expression is not significantly correlated with histological grade in gastric carcinomas, suggesting possible defects downstream of p21(Waf1/Cip1) as an underlying cause for this apparent discrepancy.

The stabilization mechanism of mutant-type p53 by impaired ubiquitination: the loss of wild-type p53 function and the hsp90 association

Mutant-type p53 (mt p53) is largely accumulated in cancer cells due to its increased stability. To elucidate the mechanism of mt p53 stabilization, we analysed the turnover of p53 mutated at codon 248 whose alteration is most frequently found in human cancers. Proteasome inhibition induced the accumulation of ubiquitinated mt p53, indicating that the ubiquitinated forms were essentially unstable and degraded by the proteasome. The presence of a small amount of the ubiquitinated mt p53 relative to the abundant non-ubiquitinated form suggested that the mt p53 ubiquitination was a rate-limiting process in the slow turnover. Two phenomena destabilizing mt p53 via the ubiquitin-proteasome degradation were proved to be independent. First, the coexpression of wild-type p53 (wt p53) promoted mt p53 destabilization as feedback regulation. Second, geldanamycin also induced mt p53 destabilization through the dissociation of the protein from hsp90 but not through the restoration of wt p53 function. Neither the mutant-specific conformation nor the N-terminal phosphorylation seemed to contribute directly to the mt p53 stabilization. Further, a two-dimensional gel electrophoresis revealed that most of the post-translationally modified mt p53 was equally subjected to ubiquitination and subsequent proteasomal degradation. These findings are evidence that mt p53 stabilization depends on the impaired ubiquitination due to both the loss of wt p53 function and the hsp90 association.

The use of histological and immunohistochemical markers to distinguish pleural malignant mesothelioma and in situ mesothelioma from reactive mesothelial hyperplasia and reactive pleural fibrosis

Distinguishing malignant mesothelioma from reactive mesothelial hyperplasia and reactive fibrosis can be a diagnostic problem in small pleural biopsies, made more difficult by the recent recognition of mesothelioma-in-situ. Antibodies to epithelial membrane antigen (EMA), p53, and bcl-2 have all been advocated for differentiating reactive from neoplastic conditions, but reports are inconsistent. These antibodies have therefore been applied to 31 cases of malignant mesothelioma, 34 cases of reactive pleural disease (20 reactive mesothelial hyperplasia and 14 reactive pleural fibrosis) and four small biopsies that were initially coded as suspicious, from patients who later developed frank mesothelioma. Thirty out of 31 (97 per cent) cases of mesothelioma showed positive nuclear staining for p53, with a higher incidence of positivity in epithelioid than in sarcomatoid elements and 30/31 (97 per cent) showed diffuse linear membrane staining for EMA, again more intense in the epithelioid elements. No mesothelioma was positive for bcl-2. In seven cases that contained both in situ and invasive mesothelioma, the in situ elements showed similar staining patterns to the invasive epithelioid elements. Thirteen out of 20 (65 per cent) cases of reactive mesothelial hyperplasia showed occasional nuclear positivity for p53 and 5/20 (25 per cent) cases showed focal weak membrane staining for EMA. Three out of 14 (21 per cent) cases of reactive pleural fibrosis showed positive nuclear staining for p53 and 6/14 (43 per cent) cases showed focal membrane staining with EMA. No reactive cases stained for bcl-2. All four suspicious cases showed diffuse linear staining with EMA and three showed focal staining for p53. It is concluded that strong diffuse linear staining for EMA is a good marker of malignancy when differentiating epithelioid malignant mesothelioma and mesothelioma-in-situ from reactive mesothelial hyperplasia, although weak focal staining may occur in reactive conditions. Nuclear staining for p53 is also suggestive of epithelioid mesothelioma, but should be regarded as no more than suspicious. The antibodies used in this investigation are less helpful in differentiating sarcomatoid mesothelioma from reactive pleural fibrosis.

Growth dysregulation and p53 accumulation in human primary colorectal cancer

p53 accumulation is common in colorectal cancer, but effects on growth homeostasis are unclear. In this study, DNA content, cell cycle phase fractions and DNA strand-breaks consistent with apoptosis were assessed by flow cytometry in 42 fresh primary colorectal tumours and matched normal mucosa. p53 accumulation was assessed in 37 fixed tumour sections, by immunohistochemistry. In normal mucosa, 10.3 +/- 6.6% (mean +/- s.d.) cells were in DNA synthesis phase while 28.7 +/- 17.9% showed apoptosis. A relationship suggestive of growth homeostasis, was observed between these parameters (r = 0.8; P < 0.05). In cancers, a greater number of cells were in DNA synthesis phase (15.6 +/- 12.9% tumour vs mucosa 10.3 +/- 6.6%; P < 0.02) while fewer showed apoptosis than normal mucosa (18.5 +/- 17.0% tumour vs mucosa 28.7 +/- 17.9%; P < 0.01). DNA synthesis and apoptosis fractions were unrelated in cancers, suggesting growth dysequilibrium. p53 accumulation was detected in 59% (22/37) tumours and was associated with reduced apoptosis compared to p53-negative tumours or mucosa (14.8 +/- 15% p53 accumulation vs 26.3 +/- 18% p53-negative; P < 0.05; vs 28.7 +/- 17.9% mucosa; P < 0.05). p53 accumulation was unrelated to DNA synthesis phase fractions. p53 accumulation is accompanied by reduced apoptosis which may accentuate growth dysequilibrium in colorectal cancer.

p53 overexpression in oral mucosa in relation to smoking

The tumour-suppressor protein p53 is mutated in many head and neck squamous cell carcinomas (HNSCCs). In this immunohistochemical study, similar numbers of p53-overexpressing cells were uniformly distributed throughout normal oral epithelium, irrespective of different smoking habits or the presence of an adjacent HNSCC. In a previous study, an increased number of proliferating cells were observed in normal oral mucosa from (ex)-smoking individuals and the present observations indicate that overexpression of p53 does not play a role in this increase. In contrast, focally overexpressed p53 occurred more frequently (p<0.05) in the tumour-adjacent normal mucosa (TAM) from smoking HNSCC patients (50 per cent) than in that from non-smoking HNSCC patients (20 per cent). This increase in focal p53 overexpression might represent an early alteration in the development of HNSCC, but it could not be detected in mucosa from healthy smokers. This indicates that besides the abuse of tobacco, other environmental and/or genetic factors must contribute to the presence of p53-positive clusters in TAM. Abuse of alcohol, an additional factor in these HNSCC patients, together with the abuse of tobacco, might play a role in the development of the p53-positive clusters.