P53 Gene Alterations Research Articles

Carcinogenesis of gastric endocrine cell carcinoma: analysis of histopathology and p53 gene alteration.

Endocrine cell carcinoma of the stomach is characterized by endocrine differentiation and aggressive biological behavior, and is frequently accompanied by an adenocarcinoma component. Because the carcinogenic parthway and genetic alterations remain unclear, we investigated the histogenesis of the tumor by histopathological and p53 gene analysis. The materials were 68 gastric endocrine cell carcinomas and 30 carcinoid tumors, which were resected from 93 Japanese patients for histopathological and immunohistochemical investigation. We also analyzed the concordance of p53 mutational status between the associated adenocarcinoma and endocrine cell carcinoma components, using microdissection and direct sequencing techniques. An adenocarcinoma component was associated with 70.6% (48/68) of endocrine cell carcinomas, of which 42 (87.5%) were of well- to moderately differentiated type, while 36 of these 42 (85.7%) demonstrated histological continuity with the endocrine cell carcinoma components. Overexpression of p53 protein was observed in 58.8% (20/34) of cases. Common p53 mutational status between the two components was revealed in 73.3% (11/15) of cases analyzed. In contrast, carcinoid tumors did not exhibit p53 protein overexpression (0/15) or gene mutation (0/5). These data suggest that gastric endocrine cell carcinomas predominantly arise from endocrine precursor cell clones occurring in preceding adenocarcinoma components (particularly the differentiated type), transforming into endocrine cell carcinoma during rapid clonal expansion under the influence of p53 gene alteration. Endocrine cell carcinoma of the stomach is characterized by endocrine differentiation and aggressive biological behavior, and is frequently accompanied by an adenocarcinoma component. Because the carcinogenic pathway and genetic alterations remain unclear, we investigated the histogenesis of this tumor by histopathological and p53 gene analysis.

Investigation of c-myc and p53 Gene Alterations in the Tumor and Surgical Borderline Tissues of NSCLC and Effects on Clinicopathologic Behavior: By the FISH Technique

Genetic alterations on the primary tumoral tissues and surgical borderline tissues of 51 patients with NSCLC on which radiotherapy and chemotherapy had not been performed were analyzed by using the FISH method with locus-specific probes for p53 tumor suppressor gene and c-myc oncogene and centromere-specific probes for chromosome 17 and chromosome 8 on which these genes are located. P53 deletions were detected in 7 patients (13.7%), c-myc amplification in 4 patients (7.8%), monosomy 17 in 2 patients (3.9%) and trisomy 8 in 3 patients (5.8%), and a high level of polyploidy in tumoral tissues of 6 patients (11.7%). P53 deletion and c-myc amplification were found at surgical borderlines of 2 patients and 1 patient, respectively. Although both p53 deletion and c-myc amplification have low frequency at surgical border tissues, not only their detection is important for the follow-up of recurrency and metastasis, but it is also important for genetical and pathological staging. The results of this study show that c-myc amplification in NSCLC is related to the shortening of survival (p < 0.01). C-myc amplification and p53 deletion are also effective for the occurrence of metastasis (p < 0.05) and the effect of c-myc amplification in this matter is much higher than p53 deletion. The gain or loss of copy number of chromosome 8 and monosomy 17 show parallel effects with c-myc amplification and p53 deletion, respectively, on the clinicopathological behavior of tumors.

Trichostatin A, an inhibitor of histone deacetylases, strongly suppresses growth of pancreatic adenocarcinoma cells.

In cells with an altered p53 gene, the expression of p21(WAF1/CIP1), a potent inhibitor of cyclin-dependent kinases, can be induced by histone deacetylase (HDAC) inhibitors via a p53-independent pathway, which may play a critical role in arrest of cell growth. Accordingly, HDAC inhibitors such as trichostatin A (TSA) have potential utility in pancreatic cancer, as most of these tumors possess mutations in p53, which in fact is the main cause of chemoresistance to 5-fluorouracil. We have analyzed the effect of TSA on the proliferation of nine pancreatic adenocarcinoma cell lines, all containing a mutated p53 gene. TSA strongly inhibited the cellular growth of all these cell lines at submicromolar concentrations. The cellular mechanisms underlying this effect consisted of cell cycle arrest at the G2 phase and apoptotic cell death. The expression of p21(WAF1/CIP1) normally induced at the transcriptional level by p53 was also strongly activated by TSA. These findings suggest that inhibitors of HDAC may represent a novel therapeutic strategy for treatment of pancreatic cancer.

Alteration of P53 protein expression and p53 gene in laryngeal carcinoma

To study the prevalence of P53 protein expression and p53 gene mutation in laryngeal carcinoma. Using immunohistochemistry P53 expression was detected in 31 patients with laryngeal carcinoma. In 11 P53 negative patients,microdissection-PCR-HA technique was used to determine mutation in p53 exon 5, 6, 7, 8. Among the 31 patients tested with immunostaining, the overall average positive rate was 64.5%. Positive rates for T3 and T4 tumors were 86.7% vs 43.8% in T1 and T2 tumors.The positive rate was 91.7% in those with cervical node metastasis compared with 47.4% in those without lymph node metastasis. The positive P53 immunostaining was more frequently found in poor differentiated carcinoma (87.5%) and moderate-differentiated carcinoma (66.7%),than in well differentiated carcinoma (45.5%). The abnormal exon 5 or 7 of p53 gene were detected in 2 out of 11 cases, in which P53 was negative. P53 gene mutation is related with TNM grading and cervical lymph node metastasis in laryngeal carcinoma. P53 mutation tents to be correlated to pathologic grading.

Human immunodeficiency virus (HIV)-associated polymorphic lymphoproliferative disorders.

The majority of AIDS-related non-Hodgkin's lymphomas are clinically aggressive monoclonal B-cell Burkitt's lymphomas, large cell lymphomas, or immunoblastic lymphomas. In contrast, the lymphoid proliferations arising in solid organ transplant recipients, collectively referred to as posttransplantation lymphoproliferative disorders (PT-LPDs), represent a clinically and histopathologically heterogeneous group of Epstein-Barr virus (EBV)-driven B-cell proliferations of variable clonal composition. During a retrospective histopathologic review of lymphoid proliferations associated with human immunodeficiency virus (HIV) infection we identified 10 cases that morphologically resemble the polymorphic PT-LPDs. They arose in lymph nodes (five), lungs (two), and the parotid gland, perineum, and skin (one each). They exhibit a diffuse growth pattern and are composed of a polymorphic lymphoid cell population exhibiting a variable degree of plasmacytic differentiation, cytologic atypia, and numbers of atypical immunoblasts. A clonal B-cell population was detected by immunoglobulin heavy and light chain gene rearrangement and/or EBV terminal repeat analysis in 8 of the 10 (80%) cases by Southern blotting. The nongermline hybridizing bands were usually faint, however, suggesting that the clonal B-cell population represented only a subpopulation within the polymorphic lesion. Strong clonal rearrangement bands were present in one case in which there was clear morphologic evidence of transformation to diffuse large cell lymphoma. This case exhibited C-MYC, BCL-6, and p53 gene mutations. One other case exhibited a p53 gene mutation. The remaining eight cases lacked C-MYC, BCL-6, RAS, and p53 gene alterations. Clonal EBV infection was detected in 4 of the 10 (40%) lesions. Like EBV-containing PT-LPDs, all four EBV-positive HIV-associated polymorphic lesions were associated with type A EBV. The Kaposi's sarcoma-associated herpesvirus was detectable in two cases by polymerase chain reaction analysis, but not by Southern blotting. In situ hybridization demonstrated Kaposi's sarcoma-associated herpesvirus in some of the cytologically malignant-appearing cells. In conclusion, polymorphic B-cell lymphoproliferative disorders comparable morphologically and molecularly to those arising after solid organ transplantation also occur in association with HIV infection. As in the case of their polymorphic PT-LPD counterparts, their malignant status, biologic significance, and relationship to monomorphic B-cell lymphomas remain to be elucidated.

TP53 and head and neck neoplasms.

Head and neck cancer is an important health problem around the world, accounting for approximately 500,000 new cases each year of head and neck squamous cell carcinoma (HNSCC). Carcinogenesis of head and neck results from a dysregulation of cellular proliferation, differentiation, and cell death. The major etiologic agents are tobacco and alcohol consumption and for some cases, human papilloma virus (HPV) infection. All three factors are associated with the disruption of a cellular pathway essential for the maintenance of cellular integrity, the p53 pathway. The objective of this review is to point out the specificity of p53 gene (TP53) alterations in head and neck cancer in relation with chemocarcinogenesis and to discuss whether or not the determination of p53 alterations will be of clinical relevance in the management of head and neck cancer in terms of prognosis and response to treatments.

TP53 and ovarian cancer.

Ovarian cancer represents the fourth most frequent type of cancer among females and is the leading cause of death from gynecological cancer in the western world. This review describes gene alterations in ovarian cancer. Specific emphasis is placed on genetic alterations and the prevalence of TP53 (p53) gene alterations in the distinct biological ovarian tumors (benign, borderline, and malignant) and histological subtypes (serous, mucinous, endometrioid, clear cell), as well as in BRCA1-associated hereditary ovarian cancer. Although multi-modality treatment regimens, including cytoreductive surgery and cisplatin-containing combination chemotherapy, have usefully prolonged survival, the overall cure rate of the disease has not changed dramatically. Ovarian cancer is difficult to eradicate completely by surgery and many patients have only a partial response to postoperative chemotherapy and/or many will develop chemotherapy resistance. All these important factors contribute to the poor prognosis of ovarian cancer patients. In this review, the putative prognostic or predictive value of TP53 in ovarian cancer is addressed.

Absence of p53 alterations in nasopharyngeal carcinoma Spanish patients with Epstein-Barr virus infection.

The objective of this study was to analyse the relationships between the Epstein-Barr virus (EBV) infection and the molecular abnormalities of the p53 oncoprotein in the nasopharyngeal carcinoma (NPC). Fifty-five NPC paraffin samples from a group of Spanish patients with EBV demonstrated presence by nested-PCR and non-isotopic in situ hybridisation, were analysed for p53 expression using immunohistochemistry. The positive samples by immunohistochemistry were studied for p53 gene alterations in the exon 5 by single strand conformation polymorphism (SSCP). Among the 55 specimens, 14 (25.5%) showed expression of p53 protein. All these positive samples corresponded to the late stage of the tumour. Of the 14 samples, p53 gene alterations were found only in three cases using SSCP. These results indicate that the p53 mutations are an infrequent event in NPC in Spanish patients needing exogenous factors as the EBV infection for the development of this malignancy.

HPV 16 detection in cervical lesions, physical state of viral DNA and changes in p53 gene.

Persistent infection with high risk human papillomavirus (HPV) has been linked to cervical carcinoma. Integration of viral DNA into host cell DNA is essential for this cancer development, promoting disruption of the HPV E2 gene, thus leading to unregulated increases in E6 and E7 proteins and inactivating the products of p53 and Rb tumor suppressor genes. To investigate HPV 16 infection in cervical lesions, physical state of viral DNA and p53 gene alterations in a group of women attending a public health service. Prospective, non-controlled, transversal study. Gynecological clinic of the School of Medicine, Universidade Federal Fluminense. 43 consecutive patients with cervical lesions referred to our service. Cases were classified via cytology/histology as normal, HPV infection, condyloma, low-grade squamous intraepithelial lesion (LSIL), high-grade squamous intraepithelial lesion (HSIL) and carcinoma. HPV infection was studied via polymerase chain reaction (PCR) using two PCR primer sets, to determine DNA integration. p53 gene changes were investigated by single-strand conformation polymorphism (SSCP) analysis. One normal case, 7 HPV infections, 6 condylomas, 7 LSIL, 14 HSIL and 8 cancers were found, with 95% positive for HPV genome when tested using both L1 and E6 primers. HPV 16 was most prevalent (73.1%). HPV 16 DNA was integrated within the host genome in 3 LSIL. One LSIL progressed to HSIL by 13 months after first diagnosis. Among HPV 16-positive HSIL cases, 50% contained integrated viral DNA. HPV 16 E2 gene disruption was seen in 7 cancers (87.5%). Only smal-cell carcinoma showed intact HPV 16 E2 gene. Abnormal p53 bands detected by PCR/SSCP were observed in 4 cases: 2 squamous carcinoma with parametrium (exon 8) and two cervical intraepithelial neoplasia (CIN) III (exons 5 and 7). All cases presented HPV 16 E2 gene loss. The sample had a high rate of high-risk HPV detected in benign and malignant lesions; high cervical cancer burden; HPV 16 DNA integration in all except one case of cancer; p53 gene changes in CIN III and in invasive cancer cases associated with DNA integration.

Alterations in tumour suppressor gene p53 in human gliomas from Indian patients.

Alterations in tumour suppressor p53 gene are the most common defects seen in a variety of human cancers. In order to study the significance of the p53 gene in the genesis and development of human glioma from Indian patients, we checked 44 untreated primary gliomas for mutations in exons 5-9 of the p53 gene by PCR-SSCP and DNA sequencing. Sequencing analysis revealed six missense mutations. The incidence of p53 mutations was 13.6% (6 of 44). All the six mutations were found to be located in the central core domain of p53, which carries the sequence-specific DNA-binding domain. These results suggest a rather low incidence but a definite involvement of p53 mutations in the gliomas of Indian patients.

Interest of investigating p53 status in breast cancer by four different methods

Alterations in the p53 gene are among the most common molecular changes in breast cancer although its potential role as a prognostic and predictive factor of tumor response is controversial. All abnormalities of this tumor marker need to be detected with efficacy and practical technologies. In the present study, our aim was to compare four different analyses of p53 in order to determine how many and which techniques were necessary and sufficient to reflect the p53 status in breast cancer. We analyzed p53 at the molecular level with sequencing of total cDNA and allelic loss. Furthermore, we detected p53 protein accumulation by immunohistochemistry and presence of p53 antibodies by serological analysis. Nine patients (17%) had p53 gene alterations, 33% had allelic loss, 19% had positive p53 nuclear staining and p53 antibodies were detected in 12% of patients. We found p53 gene alterations associated with p53 nuclear protein expression (p=0.001). The single significant statistical correlation in this study suggested the need to define p53 status with more than one abnormality. The general view of a simultaneous multilevel analysis would make it possible to encompass the consequences of p53 abnormalities in breast cancer.

Genetic Imbalances in Progressed B-Cell Chronic Lymphocytic Leukemia and Transformed Large-Cell Lymphoma (Richter's Syndrome)

Chromosomal imbalances were examined by comparative genomic hybridization in 30 cases of B-cell chronic lymphocytic leukemia (CLL) at diagnosis, in sequential samples from 17 of these patients, and in 6 large B-cell lymphomas transformed from CLL [Richter's syndrome (RS)] with no available previous sample. The most common imbalances in CLL at diagnosis were gains in chromosome 12 (30%), and losses in chromosomes 13 (17%), 17p (17%), 8p (7%), 11q (7%), and 14q (7%). The analysis of sequential samples showed an increased number of chromosomal imbalances in 6 of 10 (60%) patients with clinical progression and in 2 patients with stable stage C disease. No karyotypic evolution was observed in four cases with stable stage A disease and in one RS clonally unrelated to the previous CLL. Gains of 2pter, and 7pter, and losses of 8p, 11q, and 17p were recurrent alterations associated with karyotype progression. RS showed a higher number of gains, losses, total alterations, and losses of 8p and chromosome 9 than CLL at diagnosis. 17p losses were associated with p53 gene mutations and with a significantly higher number of chromosomal imbalances than tumors with normal chromosome 17 profile. However, no relationship was observed between 9p deletions and p16(INK4a) gene alterations. Losses of 17p and an increased number of losses at diagnosis were significantly associated with a shorter survival. These findings indicate that CLL has frequent chromosomal imbalances, which may increase during the progression of the disease and transformation into large cell lymphoma. Genetic alterations detected by comparative genomic hybridization may also be of prognostic significance.

P16INK4A and p15INK4B gene alteration associated with oxidative stress in renal cell carcinomas after the chernobyl accident (pilot study).

Our study was undertaken to better understand the role of G1/S transition abnormalities in the malignant progression of renal cell carcinomas (RCCs), exposed to long-term low doses of ionizing radiation (IR), from patients living in radiocontaminated areas of the Ukraine after the Chernobyl accident. We studied p16 and p15 gene alteration in association with oxidative stress markers, including inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2). We analyzed 88 samples collected from 22 patients with RCCs and with different exposure to IR. Homozygous deletion of the p16 and p15 genes, as well as hypermethylation of the 5CpG island in the promoter region of the same genes, were analyzed by differential PCR and Methylation-Specific PCR respectively, in association with histopathology and immunohistochemical analysis of p16 and p15 proteins. COX2 and iNOS expression in the same tumors were likewise analyzed. Aberrant hypermethylation was observed in 7 (32%) and 5 (23%) cases accompanied, by immunohistochemical loss of expression for p16 and p15 genes respectively, in both high stage and grade tumors from patients living in radiocontaminated areas, this being especially outstanding for the p16 gene. An association with COX2 and less iNOS overexpression in the same tumors was observed. Our data suggest that inactivation of p16 gene, but not p15, induced by increased oxidative stress generated by persistent chronic exposure to IR, could be one of the major pathways responsible for RCCs malignant progression.

Alterations of the p16(INK4) locus in human malignant mesothelial tumors.

The INK4 locus has two promoters and encodes two unique proteins that share exons in different reading frames, p16(INK4a) and p14(ARF). The p16(INK4a) protein, by inhibiting cyclin-dependent kinase, down regulates Rb-E2F and leads to cell cycle arrest in the G1 phase. The p14(ARF) protein interacts with the MDM2 protein, neutralizing MDM2-mediated degradation of p53. Since p53/Rb genes are not altered in malignant mesothelioma, additional components of these pathways, such as p16(INK4a) and p14(ARF), are candidates for inactivation. In this study, we have examined p16(INK4a) and p14(ARF) alterations (gene deletion, mutation and promoter methylation) in 45 primary malignant mesothelioma specimens. Fourteen patients (31%) had altered p16; four tumors had a methylated promoter region (8.8%), 10 tumors showed p16 to be deleted (22.2%), and one tumor had a point mutation (2%). We did not find any instances of methylation in the p14(ARF) 5'-CpG island. Patients whose tumors had p16 deletion were significantly younger than those with methylation, and, in the patients whose lungs were studied for the prevalence of asbestos fibers, those with any p16 alteration had lower fiber counts than those with no p16 alteration. Hence, p16 gene alteration is relatively common in malignant mesothelioma, while p14(ARF) is rarely, if ever, methylated. Our data suggest that deletion of p16 occurs in a relatively susceptible subset of the population.

Hybrid Carcinomas of the Salivary Glands: Report of Nine Cases with a Clinicopathologic, Immunohistochemical, and p53 Gene Alteration Analysis

Hybrid carcinomas of the salivary gland are a recently defined and rare tumor entity, consisting of two histologically distinct types of carcinoma within the same topographic area. In this study, we examined nine such cases, which mainly arose in the parotid gland (seven cases), with an additional one each from submandibular and lacrimal glands, and analyzed their clinicopathologic profiles, including immunohistochemical features and p53 gene alterations. The prevalence of hybrid carcinomas was 0.4% among the 1863 cases of parotid gland tumors in our series. The nine patients comprised five men and four women, ranging in age from 40 to 81 years (mean, 62 y). Tumor size ranged from 2 to 10 cm (mean, 4.2 cm). Of the seven patients who were followed up, two were alive with disease and five were alive with no evidence of disease, although the follow-up period was short. Three cases had cervical lymph nodal metastases. The combinations of carcinoma components in our hybrid carcinomas were as follows: epithelial–myoepithelial carcinoma and basal cell adenocarcinoma in two cases, epithelial–myoepithelial carcinoma and squamous cell carcinoma in one case, salivary duct carcinoma and adenoid cystic carcinoma in two cases, myoepithelial carcinoma and salivary duct carcinoma in one, acinic cell carcinoma and salivary duct carcinoma in one, and squamous cell carcinoma and salivary duct carcinoma in two. Although the proportion of each carcinoma component in a tumor mass varied from case to case, the minor component always represented ≥ 10% of the area. Differences in cellular composition were studied by immunohistochemistry and electron microscopy. The Ki-67–labeling index apparently differed between the two carcinoma elements in five cases. Diffusely positive p53 immunoreactivity was observed in four cases, restricted to the more aggressive component in each pair. Furthermore, p53 gene alteration analysis of these p53-positive cases revealed that all and three cases demonstrated loss of heterozygosity at p53 microsatellite loci and p53 gene point mutations, respectively, which were detected only in the p53-immunoreactive carcinoma component. Therefore, there is the possibility that such molecular-genetic events take an integral part for inducing the transformation from histologically lower to higher grade tumor during the hybrid carcinoma genesis of the salivary glands.

Infrequent p53 Gene Mutations and Lack of p53 Protein Expression in Clear Cell Sarcoma of the Kidney: Immunohistochemical Study and Mutation Analysis of p53 in Renal Tumors of Unfavorable Prognosis

A high prevalence of p53 gene mutation and protein expression has been found in the anaplastic variant of Wilms’ tumor (WT), known to be associated with poor outcome. However, there are very few studies of p53 alterations in the other two rare and highly malignant renal tumors in childhood, in other words, clear cell sarcoma of the kidney (CCSK) and malignant rhabdoid tumor of the kidney (MRTK). Overexpression of p53 protein has been detected in eight CCSKs in one study, and in two in another, yet no molecular correlation with p53 gene mutations has been carried out. Our study is the first molecular analysis concerning p53 in CCSK. We investigated eight cases of CCSK and one case of MRTK for p53 protein expression by immunohistochemical staining. All were analyzed for p53 mutations in the region of exons 4 to 8 by polymerase chain reaction–single-strand conformational polymorphism (PCR-SSCP) method and DNA sequencing analysis. By histological study, no CCSK showed anaplastic features. None expressed p53 protein, but two harbored p53 mutations. One was in exon 5, with a base pair insertion between codons 162 to 163 causing frameshift alteration in amino acid. Another was a silent CTC → CTT transversion in codon 289 of exon 8. The case of MRTK did not show any alterations of p53 protein or gene. Our result indicates that p53 alterations are infrequent in CCSK and do not seem to be primary genetic events in the pathogenesis of CCSK.

Ductal and acinar differentiation in pancreatic endocrine tumors.

Rare pancreatic endocrine tumors consisting of both exocrine and endocrine components have been reported sporadically. We investigated the ductal and acinar differentiation in pancreatic endocrine tumors. In immunohistochemical studies of 28 pancreatic endocrine tumors, staining with anti-carcinoembryonic antigen (CEA) or CA19-9 antibody indicated ductal differentiation, while staining with anti-amylase or anti-trypsin antibody indicated acinar differentiation. K-ras gene mutations and p53 gene alterations also were studied. Ten tumors were immunoreactive for CEA or CA19-9. Five tumors diffusely immunoreactive for CEA or CA19-9, in addition to endocrine markers, were diagnosed as duct-endocrine cell tumors of the pancreas. Two tumors diffusely immunoreactive for CEA or CA19-9 and also for pancreaticogut hormones as well as endocrine markers were diagnosed as duct-acinarendocrine cell tumors. These tumors showed uniform histologic features and synchronous ductal, acinar, and endocrine differentiation, distinct from the coexisting different cellular populations seen in collision tumors. All tumors were malignant. These duct-endocrine cell tumors or duct-acinar- endocrine cell tumors of the pancreas may be derived from a stem cell that retains the capability of expressing either an exocrine or endocrine phenotype. Only one K-ras gene mutation and no p53 gene alterations were detected in these tumors, which suggests that they constitute an entity with a different origin than ductal carcinomas.

Evaluation of relationship between chromosome 22 and p53 gene alterations and the subtype of meningiomas by the interphase-FISH technique.

In this study, we investigated the relationship between genetic alterations such as chromosome 22 aneuploidy and p53 gene deletion, and the pathological types of meningioma of typical and aggressive forms. Thirty-four meningiomas (23 typical and 11 aggressive) were examined by application of fluorescence in situ hybridization (FISH) with chromosome 22 specific alpha satellite probe and a combination of p53 locus specific and chromosome 17 centromere specific alpha satellite probes, to evaluate the chromosome 22 aneuploidy and gain or loss of p53 gene along with chromosome 17. The results showed that, although chromosome 22 aneuploidy was seen in 7 out of 23 typical (30.4%) and 4 out of 11 aggressive meningiomas (36.3%), no p53 deletion was detected in typical meningiomas, and p53 deletion was detected in 3 out of 11 aggressive meningiomas (1 atypical and 2 malignant), which had recurrence. There were no simultaneous occurrences of p53 gene deletions between typical and aggressive meningiomas. The present findings indicate that the loss of chromosome 22 may be involved with tumorogenesis of typical and aggressive meningiomas, while p53 gene deletions may be involved with malignant progression and recurrence in the aggressive meningiomas.

A Phenotypic Shift from Gastric-Intestinal to Solely Intestinal Cell Types in Intestinal Metaplasia in Rat Stomach Following Treatment with X-rays.

Histological features and genetic changes induced by X-rays in intestinal metaplasia (IM) in rats were assessed by histochemistry and immunohistochemistry. A time course study and a PCR-SSCP analysis were performed. The IMs in rats were classified into two major types according to the cells forming the metaplastic glands. The first (the GI type) had both gastric and intestinal type cells forming the metaplastic glands. The second (the I-sol type) had solely intestinal cells forming the metaplastic glands. This characterization is similar to that used to define human IMs. The occurrence of IMs of the I-sol and GI types in rats gradually increased with time after X-ray irradiation. The number of IMs of the GI type was relatively high at 2 and 4 weeks after X-ray irradiation, and was low thereafter. On the other hand, the number of IMs of the I-sol type was extremely low at 2 weeks after treatment, then increased with time, and reached a maximum at 77 weeks after treatment. In the PCR-SSCP analysis, there were no alterations of the H-ras, K-ras, and p53 genes in the IM glands of rats treated with X-ray irradiation 8 weeks earlier. These observations suggest that the phenotypic change from IMs of the GI type to the I-sol type occurred without ras and p53 gene alterations.

Detection of genetic alterations in thep53 suppressor gene and the K-ras oncogene among different grades of dysplasia in patients with colorectal adenomas

Although it is believed that p53 suppressor gene mutations, compared with mutations in the K-ras oncogene, occur at a later stage of colorectal tumorigenesis, the distribution of these genetic alterations at an early stage remains poorly characterized. The authors analyzed the immunoreactivity for p53 protein (p53 protein expression), which reflects the functionally altered p53 gene, and K-ras mutations at codons 12 in 68 colorectal adenomas with both low-grade and high-grade dysplasia obtained from 62 patients. The prevalence of p53 positive immunostaining was significantly greater compared with the prevalence of K-ras mutations both in low-grade dysplasia and in high-grade dysplasia. Twenty-two adenomas (32.3%) showed positive immunostaining for p53 protein in high-grade dysplasia and also were positive for p53 in surrounding low-grade dysplastic tissues; 20 adenomas (29.4%) showed positive immunostaining for p53 protein in high-grade dysplasia and were negative for p53 in surrounding low-grade dysplastic tissues; 8 adenomas (11.7%) showed negative immunostaining for p53 protein in high-grade dysplasia and were positive for p53 in surrounding low-grade dysplastic tissues; and 18 adenomas (26.4%) showed negative immunostaining for p53 protein in both high-grade dysplasia and in surrounding low-grade dysplastic tissues. On the whole, a significant difference (P < 0.05) was seen in the frequency of p53 positive immunostaining between low-grade dysplasia and high-grade dysplasia (44.1% and 61.8%, respectively) but not in that of K-ras mutations (20.3% and 23.4%, respectively). The results of this study suggest that mutation of the p53 suppressor gene occurs earlier in the adenoma-carcinoma sequence than K-ras mutation, providing a clue for further understanding of the role of the p53 gene in the early stage of colorectal tumorigenesis.