Identification of APC2, a homologue of the adenomatous polyposis coli tumour suppressor.
(1/796)
The adenomatous polyposis coli (APC) tumour-suppressor protein controls the Wnt signalling pathway by forming a complex with glycogen synthase kinase 3beta (GSK-3beta), axin/conductin and betacatenin. Complex formation induces the rapid degradation of betacatenin. In colon carcinoma cells, loss of APC leads to the accumulation of betacatenin in the nucleus, where it binds to and activates the Tcf-4 transcription factor (reviewed in [1] [2]). Here, we report the identification and genomic structure of APC homologues. Mammalian APC2, which closely resembles APC in overall domain structure, was functionally analyzed and shown to contain two SAMP domains, both of which are required for binding to conductin. Like APC, APC2 regulates the formation of active betacatenin-Tcf complexes, as demonstrated using transient transcriptional activation assays in APC -/- colon carcinoma cells. Human APC2 maps to chromosome 19p13.3. APC and APC2 may therefore have comparable functions in development and cancer. (+info)
Expression of CD44 in Apc and Tcf mutant mice implies regulation by the WNT pathway.
(2/796)
Overexpression of cell surface glycoproteins of the CD44 family is an early event in the colorectal adenoma-carcinoma sequence. This suggests a link with disruption of APC tumor suppressor protein-mediated regulation of beta-catenin/Tcf-4 signaling, which is crucial in initiating tumorigenesis. To explore this hypothesis, we analyzed CD44 expression in the intestinal mucosa of mice and humans with genetic defects in either APC or Tcf-4, leading to constitutive activation or blockade of the beta-catenin/Tcf-4 pathway, respectively. We show that CD44 expression in the non-neoplastic intestinal mucosa of Apc mutant mice is confined to the crypt epithelium but that CD44 is strongly overexpressed in adenomas as well as in invasive carcinomas. This overexpression includes the standard part of the CD44 (CD44s) as well as variant exons (CD44v). Interestingly, deregulated CD44 expression is already present in aberrant crypt foci with dysplasia (ACFs), the earliest detectable lesions of colorectal neoplasia. Like ACFs of Apc-mutant mice, ACFs of familial adenomatous polyposis (FAP) patients also overexpress CD44. In sharp contrast, Tcf-4 mutant mice show a complete absence of CD44 in the epithelium of the small intestine. This loss of CD44 concurs with loss of stem cell characteristics, shared with adenoma cells. Our results indicate that CD44 expression is part of a genetic program controlled by the beta-catenin/Tcf-4 signaling pathway and suggest a role for CD44 in the generation and turnover of epithelial cells. (+info)
Analysis of masked mutations in familial adenomatous polyposis.
(3/796)
Familial adenomatous polyposis (FAP) is an autosomal-dominant disease characterized by the development of hundreds of adenomatous polyps of the colorectum. Approximately 80% of FAP patients can be shown to have truncating mutations of the APC gene. To determine the cause of FAP in the other 20% of patients, MAMA (monoallelic mutation analysis) was used to independently examine the status of each of the two APC alleles. Seven of nine patients analyzed were found to have significantly reduced expression from one of their two alleles whereas two patients were found to have full-length expression from both alleles. We conclude that more than 95% of patients with FAP have inactivating mutations in APC and that a combination of MAMA and standard genetic tests will identify APC abnormalities in the vast majority of such patients. That no APC expression from the mutant allele is found in some FAP patients argues strongly against the requirement for dominant negative effects of APC mutations. The results also suggest that there may be at least one additional gene, besides APC, that can give rise to FAP. (+info)
Administration of an unconjugated bile acid increases duodenal tumors in a murine model of familial adenomatous polyposis.
(4/796)
Intestinal carcinogenesis involves the successive accumulation of multiple genetic defects until cellular transformation to an invasive phenotype occurs. This process is modulated by many epigenetic factors. Unconjugated bile acids are tumor promoters whose presence in intestinal tissues is regulated by dietary factors. We studied the role of the unconjugated bile acid, chenodeoxycholate, in an animal model of familial adenomatous polyposis. Mice susceptible to intestinal tumors as a result of a germline mutation in Apc (Min/+ mice) were given a 10 week dietary treatment with 0.5% chenodeoxycholate. Following this, the mice were examined to determine tumor number, enterocyte proliferation, apoptosis and beta-catenin expression. Intestinal tissue prostaglandin E2 (PGE2) levels were also assessed. Administration of chenodeoxycholate in the diet increased duodenal tumor number in Min/+ mice. Promotion of duodenal tumor formation was accompanied by increased beta-catenin expression in duodenal cells, as well as increased PGE2 in duodenal tissue. These data suggest that unconjugated bile acids contribute to periampullary tumor formation in the setting of an Apc mutation. (+info)
Combined molecular and clinical approaches for the identification of families with familial adenomatous polyposis coli.
(5/796)
OBJECTIVE: Using an interdisciplinary clinical and molecular approach, the authors identified APC germline mutations in families with familial adenomatous polyposis (FAP). Correlation of mutation site with disease manifestation and the impact of molecular data on clinical proceedings were examined. SUMMARY BACKGROUND DATA: Germline mutations in the APC gene predispose to FAP. Established and proposed genotype-phenotype correlations as well as the influence of mutation site on surgical procedures have been reported. The predictive value of APC mutation analysis for disease manifestation and therapeutic decision making needs to be investigated further. METHODS: One hundred twenty-three kindreds of the local FAP registry were included in this study. CHRPE phenotype was defined as at least one large characteristic lesion or a total of four lesions in both eyes. APC mutations were identified by protein truncation test and automated DNA sequencing from patient lymphocyte DNA and RNA. RESULTS: APC germline mutations were identified in 85/123 families with FAP. They were located between codons 213 and 1581 of the APC gene and displayed distinct genotype-phenotype correlations. CHRPE status facilitated mutation analysis by discriminating regions of interest within the APC coding region. Severe manifestations of desmoids were restricted to mutations between codons 1444 through 1581. Whereas 91% (75/82) of at-risk persons were excluded as mutation carriers, APC germline mutations were detected before clinical examination in 9% (7/82) of at-risk persons. One patient agreed to endoscopy only after mutation detection. CONCLUSIONS: This study supports the feasibility of combined molecular and clinical screening of families with FAP and may provide a guideline for routine presymptomatic molecular diagnostics in a clinical laboratory. (+info)
Hereditary desmoid disease in a family with a germline Alu I repeat mutation of the APC gene.
(6/796)
Two families with autosomal dominantly inherited desmoid tumors have recently been shown to have germline mutations at the 3' end of the APC gene. We subsequently identified an Amish family with autosomal dominantly inherited desmoid tumors. Genetic analysis performed on one family member, a 47-year-old man with multiple desmoid tumors and no colon polyps, revealed a protein truncating mutation in the middle of the APC gene. The truncating mutation is the result of a 337-bp insertion of an Alu I sequence into codon 1526 of the APC gene. The presence of a poly(A) tail at the 3' end of the insertion suggests that the Alu I sequence was inserted by a retrotranspositional event. Germline insertions of Alu I sequences have occasionally been reported to cause other genetic diseases including type I neurofibromatosis, hereditary site-specific breast cancer (BRCA2), and hemophilia B. However, this is the first report of a germline mutation of the APC gene resulting from an Alu I insertion. (+info)
Cost comparison of predictive genetic testing versus conventional clinical screening for familial adenomatous polyposis.
(7/796)
BACKGROUND: Mutations of the APC gene cause familial adenomatous polyposis (FAP), a hereditary colorectal cancer predisposition syndrome. AIMS: To conduct a cost comparison analysis of predictive genetic testing versus conventional clinical screening for individuals at risk of inheriting FAP, using the perspective of a third party payer. METHODS: All direct health care costs for both screening strategies were measured according to time and motion, and the expected costs evaluated using a decision analysis model. RESULTS: The baseline analysis predicted that screening a prototype FAP family would cost $4975/ pound3109 by molecular testing and $8031/ pound5019 by clinical screening strategy, when family members were monitored with the same frequency of clinical surveillance (every two to three years). Sensitivity analyses revealed that the genetic testing approach is cost saving for key variables including the kindred size, the age of screening onset, and the cost of mutation identification in a proband. However, if the APC mutation carriers were monitored at an increased (annual) frequency, the cost of the genetic screening strategy increased to $7483/ pound4677 and was especially sensitive to variability in age of onset of screening, family size, and cost of genetic testing of at risk relatives. CONCLUSIONS: In FAP kindreds, a predictive genetic testing strategy costs less than conventional clinical screening, provided that the frequency of surveillance is identical using either strategy. An additional significant benefit is the elimination of unnecessary colonic examinations for those family members found to be non-carriers. (+info)
Dominant negative effect of the APC1309 mutation: a possible explanation for genotype-phenotype correlations in familial adenomatous polyposis.
(8/796)
Inactivation of the adenomatous polyposis coli (APC) gene product initiates colorectal tumorigenesis. Patients with familial APC (FAP) carry germ-line mutations in the APC gene and develop multiple colorectal adenomas and subsequent carcinomas early in life. The severity of the disease correlates with the position of the inherited APC mutation (genotype-phenotype correlation). Together with the fact that both germ-line and sporadic APC mutations cluster in the central region of the APC gene, this points to a dominant negative effect of certain APC mutants. Loss of APC function was recently shown to result in enhanced beta-catenin-/Tcf-mediated transcription in colon epithelial cells. Here, we provide experimental evidence for a dominant negative effect of APC gene products associated with severe polyposis. Wild-type APC activity in beta-catenin-/Tcf-mediated transcription was strongly inhibited by a mutant APC that is truncated at codon 1309. In contrast, mutant APC gene products that are associated with attenuated polyposis (codon 386 or 1465) interfered only weakly with wild-type APC activity. These results suggest a molecular explanation for the genotype-phenotype correlation in FAP patients and support the idea that colorectal tumor growth might be, in part, driven by selection for a mutation in the mutation cluster region. (+info)