p53 mutagenesis in Klatskin tumors

p63 and p73 expression in extrahepatic bile duct carcinoma and their clinical significance

p53 plays a pivotal role in the prevention of human tumor formation. p73 and p63 are new members of the p53 tumor suppressor family, which are becoming increasingly recognized as important players in human tumorigenesis. However, the roles of these proteins are not well elucidated in extrahepatic bile duct (EBD) carcinoma. We examined expressions of the p63 and p73 genes and proteins in normal biliary epithelia, biliary dysplasias, and EBD carcinomas using immunohistochemistry and RT-PCR analysis. p63 and p73 proteins were overexpressed in 26.3 and 41.0% of EBD carcinomas, respectively. p63 protein expression was more frequent in tumors with vascular invasion (P = 0.002) and distal location (P = 0.04), while p73 expression was more common in cancers with deeper tumor invasion (P = 0.04). Patients with tumors co-expressing both p63 and p73 were found to have a significantly worse overall survival rate compared to those with either p63 or p73 expression (P < 0.05) as determined in univariate and multivariate analyses. Our results strongly imply that the p53 family members have different functions in EBD carcinomas. Our data also indicate that interactions between p63 and p73 play an important role in tumorigenesis of EBD carcinoma.

p53 Mutations in human cholangiocarcinoma: a review

The reported mortality from intrahepatic bile duct tumours is increasing markedly in industrialised countries, for reasons that remain unknown. Inactivation of the tumour suppressor gene p53, is the commonest genetic abnormality in human cancer and has been implicated in the genesis of cholangiocarcinoma in various immunohistochemical and molecular epidemiological investigations, including gene sequencing studies. The structure and function of p53 and its role in linking cancer to specific carcinogens by way of mutational signatures is reviewed. The findings of previous p53 studies and their relevance in human cholangiocarcinoma are summarised.

Regulators of Apoptosis in Cholangiocarcinoma

Context.—Dysregulation of mediators of apoptosis is associated with carcinogenesis. For biliary duct cancers, p53 gene mutation is an important contributor to carcinogenesis. Mutations in the p53 gene affect transcription of the Fas gene, resulting in lack of Fas expression on cell membrane. It has been previously shown that cloned Fas-negative but not Fas-positive human cholangiocarcinoma cells are resistant to anti–Fas-mediated apoptosis and develop tumors in nude mice. In addition, interferon gamma induces Fas expression in Fas-negative cholangiocarcinoma cells and makes them susceptible to apoptosis. Therefore, it becomes important to characterize immunophenotypic expression of p53 and Fas in normal and neoplastic human tissues of the biliary tract to further understand the pathogenesis of the disease. To date, human studies to characterize differences in immunophenotypic expression of the Fas protein between intrahepatic and extrahepatic biliary duct cancers and in their precursor lesions have not been performed.

Objective.—To report the immunophenotypic expression of p53 and Fas expression in various stages in the development of bile duct cancers (intrahepatic and extrahepatic tumor location) and their association with tumor differentiation.

Design.—Thirty bile duct cancer samples (13 intrahepatic and 17 extrahepatic) from 18 men and 12 women who ranged in age from 44 to 77 years (mean age, 65.6 years) were retrieved from the surgical pathology files. Hematoxylin-eosin–stained slides were evaluated for the type and grade of tumor and dysplastic changes in the biliary tract epithelium. Additional slides were immunohistochemically stained with p53 and anti–Fas mouse monoclonal antibody. The pattern of Fas distribution and percentage of cells positive for p53 and Fas expression were determined.

Results.—The percentage of Fas-expressing cells is significantly (P = .01) more frequently noted in extrahepatic tumors compared with intrahepatic tumors. Furthermore, Fas expression decreased from dysplastic epithelium to cholangiocarcinoma (P = .01), and this decreasing trend continued from well to poorly differentiated tumors. Nuclear p53 expression was not identified in normal and dysplastic epithelium but was noted in 30% of carcinomas (P = .02).

Conclusion.—Fas expression is an early event in pathogenesis of bile duct cancers. Immunophenotypic expression of Fas is associated with well to moderately differentiated tumors but not with poor tumor differentiation.

Cellular and molecular biology of biliary tract cancers

Cancer of the biliary tract has been associated with point mutations of K-ras and beta-catenin proto-oncogenes; alterations of p53, p16, APC, and DPC4 tumor suppressor genes by a combination of chromosomal deletion, mutation, or methylation; and infrequently microsatellite instability. The frequencies of these alterations vary by location and race of the patient, tumor subsite, histology, and associated disease. Advances in the understanding of the genetics of this disease will help in diagnosing biliary tract cancer, screening at-risk patients, and developing therapies.

Inactivation of the INK4a/ARF locus and p53 in sporadic extrahepatic bile duct cancers and bile tract cancer cell lines

The tumor-suppressor genes p14(ARF), p16(INK4a) and Tp53 are commonly inactivated in many tumors. We investigated their role in the pathogenesis of 9 bile tract cancer cell lines and 21 primary sporadic extrahepatic bile duct carcinomas. p53 and p16 protein expression was examined by Western blot analysis and immunohistochemistry. Mutation screening of p53 was done by SSCP and direct sequencing. Inactivating mechanisms of p14 and p16 were addressed by screening for mutations, homozygous deletions, chromosomal loss of 9p21 (loss of heterozygosity [LOH] analysis) and promoter hypermethylation of the p14/p16 genes. p53 overexpression could be detected in 7 of 9 cell lines and 7 of 21 primary tumors, but mutations were found in 3 cell lines only. p16 expression was absent in all cell lines, due to homozygous deletion of the gene in 8 of 9 cell lines and hypermethylation of the p16 promoter in one cell line (CC-LP-1). p14 exon 1beta was homozygously deleted in 6 of 9 cell lines, while retained in CC-LP-1 and 2 additional lines. No p14 promoter hypermethylation could be detected. p16 expression was lost in 11 of 21 primary tumors. p16 promoter hypermethylation was present in 9 of 21 primary tumors, all with lost p16 expression. Allelic loss at 9p21 was detected in 13 of 21 primary tumors, 10 of 11 with lost p16 expression and 8 of 9 with methylated p16 promoter. No p14 promoter hypermethylation or p14/p16 mutations could be detected. Neither Tp53 nor p16 alterations showed obvious association with histopathologic or clinical characteristics. In conclusion, inactivation of the p16 gene is a frequent event in primary sporadic extrahepatic bile duct cancers, 9p21 LOH and promoter hypermethylation being the principal inactivating mechanisms. Therefore, p16, but not p14, seems to be the primary target of inactivation at the INK4a locus in bile duct cancers. Other mechanisms than Tp53 mutations seems to be predominantly responsible for stabilization of nuclear p53 protein in bile duct cancers.

New p53 mutations in hilar cholangiocarcinoma

BACKGROUND

Inactivation of the tumour suppressor gene, p53, is the commonest genetic abnormality in human cancer. The study of the type of p53 mutation in a given tumour may provide prognostic information, clues to aetiology and become useful for therapeutics.

MATERIALS AND METHODS

The molecular characterisation of p53 was performed by restriction analysis, denaturing gradient gel electrophoresis, and gene sequencing for exons 5-9.

RESULTS

We report, p53 mutational analysis in exons 5-9 in 29 European patients with hilar cholangiocarcinoma who underwent attempted resection. Four patients (14%) showed somatic single nucleotide substitutions with amino acid changes (146, 163, 175, 158, and 175) with one showing mutations in two different positions involving a loss of two CfoI sites. All the mutations occurred in exon 5. Three patients had a germline polymorphism (10%) with a silent substitution in codon 213 (exon 6).

CONCLUSIONS

The systematic screening for p53 mutations in European patients with hilar cholangiocarcinoma has shown that the type of mutation (except 175) is different and its incidence is much lower when compared to the pattern previously reported for intrahepatic cholangiocarcinoma in East Asian patients. A probable explanation is that the presence and type of p53 mutation is dependent on geographic and environmental factors which vary in different populations.