Sequential WT1 and CTNNB1 mutations and alterations of beta-catenin localisation in intralobar nephrogenic rests and associated Wilms tumours: two case studies

BACKGROUND: Intralobar nephrogenic rests (ILNRs) are precursor lesions for Wilms tumours and are associated with WT1 gene mutations. ILNR-associated Wilms tumours have a co-clustering of WT1 and beta-catenin (CTNNB1) mutations and unique histological features characterised by a stromal-predominant histology. AIM: To determine the order in which WT1 and CTNNB1 mutations occur to understand the ILNR-Wilms tumour sequence. METHODS: Of nine Wilms tumours with WT1 and CTNNB1 mutations, three ILNRs lesions in two Wilms tumours were available for analysis of WT1 and CTNNB1 mutations using microdissection. Immunohistochemistry was also performed to investigate how the mutations in beta-catenin alter the localisation in Wilms tumour development. RESULTS: WT1 mutations were present in the ILNRs, however CTNNB1 mutations were absent. Immunohistochemistry for WT1 confirmed inactivation of WT1 in both ILNRs and Wilms tumours. Both the ILNRs and the associated Wilms tumours had similar immunostaining patterns for beta-catenin in the blastemal and epithelial components. Although rhabdomyoblasts were not included in ILNRs, the associated Wilms tumours showed rhabdomyogenic differentiation with a positive beta-catenin nuclear staining. CONCLUSIONS: The results suggest that CTNNB1 mutation is a later event in Wilms tumourigenesis. CTNNB1 mutations might be associated with rhabdomyogenesis.     

Expression of mutant nuclear beta-catenin correlates with non-invasive hepatocellular carcinoma, absence of portal vein spread, and good prognosis

beta-catenin has functions both in the cadherin-mediated cell adhesion system and in the signalling pathway that mediates dorsal axis patterning in the embryo; it has been shown to be aberrantly expressed or mutated in diverse types of human tumour, but the biological significance of this remains to be clarified. To elucidate the clinical implications of aberrant beta-catenin expression and the potential differences between mutant and wild-type beta-catenin protein expression in hepatocellular carcinoma (HCC), the protein expression was analysed by immunohistochemical staining, supplemented by the analysis of gene mutation. Among 372 unifocal primary HCCs, beta-catenin was detected in the tumour cell membrane alone in 272 tumours (group A) and also in the nuclei in 100 (group B). In group A, 148 tumours had decreased beta-catenin expression, but the reduction did not correlate with invasion or prognosis. When compared with group A, however, group B had significantly lower frequencies of hepatitis B surface antigen carrier (p=0.015), and alpha-fetoprotein elevation (p=0.0003), but more often had non-invasive HCC (p<0.001) and better survival (p=0.01). Nuclear beta-catenin expression strongly correlated with mutation of the gene (p<0.00001). In group B, HCC with mutant nuclear beta-catenin correlated positively with non-invasive (stage 1) tumour and inversely with portal vein tumour thrombi (stage 3 HCC), and had significantly better 5-year survival, p<0.001 and p<0.0003, respectively. These results suggest that beta-catenin mutation plays an important role in the tumourigenesis of a subset of HCC of good prognosis, and that mutant and wild-type nuclear beta-catenin proteins are not functionally equivalent.     

The Wnt pathway, epithelial-stromal interactions, and malignant progression in phyllodes tumours

In a previous study of phyllodes tumours, it has been shown that both the stroma and the epithelium can exhibit distinct molecular changes, suggesting that both are part of the neoplastic process. In view of this finding, it was decided to study stromal-epithelial interactions in these tumours by examining the Wnt-APC-beta-catenin pathway. Beta-catenin and cyclin D1 immunohistochemistry was performed on 119 phyllodes tumours. Eighty-six (72%) showed stromal nuclear beta-catenin localization and in 57% the staining was moderate or strong; however, of the eight malignant tumours in the series, seven showed absent or weak nuclear staining (p<0.025). In no tumour was nuclear beta-catenin staining seen in the epithelial component. Moderate or strong stromal cyclin D1 staining correlated with nuclear stromal beta-catenin staining (p<0.05). Forty-five of the tumours, including two malignant lesions, were screened for beta-catenin exon 3 mutations using SSCP and sequencing, but none was found. Loss of heterozygosity (LOH) of the marker D5S346 was used to infer APC mutation, but only one (benign) tumour showed LOH. Wnt2 and Wnt5a mRNA was localized by in situ hybridization in 13 cases (three malignant) chosen to reflect the different beta-catenin staining patterns. There was an association between strong nuclear beta-catenin staining of stromal cells and epithelial Wnt5a expression (p<0.0015). These data suggest that stromal proliferation in benign phyllodes tumours relies on abnormalities in the Wnt pathway which result not from mutation, but from Wnt5a expression in the epithelium. In the progression to malignancy, the stromal proliferation appears to become independent of the Wnt pathway and, presumably, of the epithelial component of these tumours.     

Alterations of beta-catenin pathway in non-melanoma skin tumors: loss of alpha-ABC nuclear reactivity correlates with the presence of beta-catenin gene mutation

To determine the role of beta-catenin pathway in human skin carcinogenesis, 135 non-melanoma skin tumors were analyzed for beta-catenin expression and gene mutations. Intense nucleo-cytoplasmic immunoreactivity for C terminus beta-catenin antibodies was observed in all pilomatricomas and in single cases of trichoepithelioma and squamous cell carcinoma showing peculiar signs of matrical differentiation. Moderate increase of beta-catenin nuclear staining was detected in a significant proportion of basal cell carcinomas, Bowen disease, spiroadenomas, and occasionally also in squamous cell carcinomas, but in these neoplasms only a limited fraction of tumor cells accumulated beta-catenin. Molecular analysis revealed that beta-catenin gene mutations are a peculiar feature of skin tumors with matrical differentiation and correlate with a pattern of intense and diffuse beta-catenin nuclear expression. In contrast, adenomatous polyposis coli (APC) and AXIN2 mutations were not involved in skin tumorigenesis. Analysis of Wnt pathway revealed that TCF-1 and MITF-M were selectively induced in the tumor types harboring beta-catenin mutations, indicating that a Wnt/beta-catenin pathway involving TCF-1 and MITF-M is activated in these tumors. Interestingly, high expression levels of TCF-3 were found in basal cell carcinomas and spiroadenomas. TCF-3 is reported to act as a negative modulator of beta-catenin degradation pathway. Thus, the moderate increase of beta-catenin nuclear staining detected in these tumor types might, at least in part, be due to a TCF-3-dependent mechanism. Finally, we found that the presence of beta-catenin mutations significantly correlated with loss of nuclear immunoreactivity for an antibody raised against the N terminus of beta-catenin (alphaABC). Thus, a combined analysis with C terminus-beta-catenin antibodies and alphaABC Ab may represent a powerful investigative approach for the detection of beta-catenin structural alterations.     

PTEN mutations do not cause nuclear beta-catenin accumulation in endometrial carcinomas

PTEN: and beta-catenin mutations constitute the predominant genetic alterations in endometrioid carcinomas of the endometrium. PTEN encodes a dual-specificity phosphatase with lipid phosphatase and protein tyrosine phosphatase activities that regulate both apoptosis and interactions with the extracellular matrix. Recent studies have associated PTEN mutations with tumorigenesis of prostate carcinoma via the Wnt signaling pathway, leading to nuclear beta-catenin accumulation. To elucidate the potential interaction of PTEN and beta-catenin in endometrial cancer, we performed mutation analyses of the entire PTEN gene and of exon 3 of the beta-catenin gene that is most frequently targeted by mutations. A total of 82 endometrial carcinomas comprising 62 type I endometrioid carcinomas and 20 type II high-grade carcinomas were investigated. In addition in a subset of 22 carcinomas, the intracellular beta-catenin distribution was analyzed by immunohistochemistry. Overall, 20 (24.4%) of 82 tumors revealed mutations in the PTEN gene, and 16 (19.5%) of 82, in the beta-catenin gene. Six tumors (7.3%) showed mutations in both the PTEN and beta-catenin gene. Mutations were mainly detected in endometrioid carcinomas of the endometrium. As expected, a striking nuclear accumulation of beta-catenin could be shown in tumors with beta-catenin mutations. In the vast majority of tumors with PTEN mutations, a regular staining pattern of the cytoplasmic and membranous compartments was found. We therefore conclude that, in contrast to prostate cancer, mutations in the PTEN gene seem not to affect cellular distribution of the beta-catenin protein in endometrial carcinomas.     

Nuclear Accumulation of Mutated β-Catenin in Hepatocellular Carcinoma Is Associated with Increased Cell Proliferation

Inappropriate activation of the Wnt pathway resulting from beta-catenin gene alterations has recently been implicated in the development of hepatocellular carcinoma (HCC). To explore the in vivo effects of mutated beta-catenin, HCC specimens from 32 patients carrying one or several tumors were screened for somatic mutations in exon 3 of the beta-catenin gene, and the expression and subcellular localization of beta-catenin was studied by immunohistochemistry. Missense mutations or interstitial deletions in beta-catenin exon 3 were detected in 12 of 35 (34%) HCC samples. After immunostaining, most tumors exhibited increased membranous and/or cytoplasmic expression of beta-catenin compared with adjacent nontumoral liver. Strong nuclear accumulation of beta-catenin was observed either focally or uniformly in 15 of 35 (43%) tumor specimens, but not in cirrhotic nodules or dysplastic liver cells in adjacent liver. Aberrant nuclear expression of beta-catenin was significantly associated with the presence of mutations in the beta-catenin gene (P < 0.005). Moreover, nuclear beta-catenin staining correlated significantly with increased Ki-67 proliferative index in tumor (P < 0.001) and seemed to be associated with poor outcome in patients with HCC. In conclusion, our data indicate that activation of the Wnt/beta-catenin pathway in HCC results mainly from somatic mutations in the beta-catenin gene and may promote tumor progression by stimulating tumor cell proliferation.     

Possible linkage between specific histological structures and aberrant reactivation of the Wnt pathway in adamantinomatous craniopharyngioma

This study concerns the significance of nuclear/cytoplasmic expression of beta-catenin and mutation of the beta-catenin gene in craniopharyngiomas. Fourteen adamantinomatous type and one squamous papillary type craniopharyngiomas were studied. Histologically, 13 of 14 adamantinomatous type craniopharyngiomas showed typical features, ie mixtures of 'palisading cells', 'stellate cells', and 'ghost cells'. In addition, 'whorl-like arrays' of epithelial cells were frequently observed in the areas of stellate cells. On immunohistochemistry, all typical adamantinomatous type craniopharyngiomas showed nuclear/cytoplasmic expression of beta-catenin predominantly in cohesive cells within the whorl-like arrays and in cells transitional towards ghost cells, where immunoreactivity for Ki-67 was almost absent. The cohesive cells in the whorl-like arrays also demonstrated loss of cytokeratin isoform expression. Using direct sequencing of amplified nucleic acids, nine of the 13 typical adamantinomatous type craniopharyngiomas with nuclear beta-catenin accumulation showed heterozygous one-base substitution mutation of the beta-catenin gene. The other unusual adamantinomatous type and squamous papillary type craniopharyngiomas showed no obvious nuclear/cytoplasmic beta-catenin immunoreactivity and no mutation of the beta-catenin gene, suggesting molecular heterogeneity. These findings suggest that the pathogenesis of typical adamantinomatous type craniopharyngioma is associated with abnormalities of Wnt signalling that act as a morphogenetic signal towards whorl-like arrays and ghost cells rather than as simple proliferation stimuli.     

Expression of beta-catenin in gastroenteropancreatic endocrine tumours: a study of 229 cases

AIMS: To clarify the role of beta-catenin in digestive endocrine carcinogenesis, a large and representative series of gastroenteropancreatic endocrine tumours was analysed in order to determine the incidence and pattern of beta-catenin changes and to analyse the clinical and histological characteristics of the tumours presenting immunohistochemically detectable changes in beta-catenin expression. METHODS: 229 cases of gastroenteropancreatic endocrine tumours (stomach, 11; duodenum and ampulla, 29; jejunum and ileum, 51; appendix, 13; colon and rectum, 17; and pancreas, 108) were studied by immunohistochemistry to assess the pattern of distribution of beta-catenin (membranous, cytoplasmic or nuclear). DNA was analysed to detect mutations in exon 3 of the CTNNB1 gene. RESULTS: The distribution of immunoreactive beta-catenin protein was membranous in 164 cases, cytoplasmic in 58 cases and nuclear in seven cases. No mutation was detected in exon 3 of the CTNNB1 gene in any case. The seven cases with nuclear accumulation of beta-catenin were large tumours (mean size 44 (standard deviation (SD) 18.5) mm) with metastases, including liver metastases in five cases, high Ki-67 index (mean 34% (SD 16.5%)) and cyclin D1 overexpression; p53 accumulation was detected in six cases. Five patients died of disease; the mean (SD) survival was 13.6 (4.8) months. CONCLUSIONS: Immunohistochemically detectable nuclear accumulation of beta-catenin is infrequent in gastroenteropancreatic endocrine tumours and is usually not associated with mutations in CNNTB1 exon 3. Changes in beta-catenin expression are late events in digestive endocrine carcinogenesis, associated with tumour progression and dissemination.     

The ABC of APC

Familial adenomatous polyposis (FAP) is an autosomal dominant inherited disease characterized by the presence of adenomatous polyps in the colon and rectum, with inevitable development of colorectal cancer if left untreated. FAP is caused by germline mutations in the adenomatous polyposis coli (APC) gene. Somatic mutations in the APC gene are an early event in colorectal tumorigenesis, and can be detected in the majority of colorectal tumours. The APC gene encodes a large protein with multiple cellular functions and interactions, including roles in signal transduction in the wnt-signalling pathway, mediation of intercellular adhesion, stabilization of the cytoskeleton and possibly regulation of the cell cycle and apoptosis. The fact that APC is an integral part of so many different pathways makes it an ideal target for mutation in carcinogenesis. This review deals with our understanding to date of how mutations in the APC gene translate into changes at the protein level, which in turn contribute to the role of APC in tumorigenesis.     

Cribriform-morular variant of papillary thyroid carcinoma: a pathological and molecular genetic study with evidence of frequent somatic mutations in exon 3 of the beta-catenin gene

The cribriform-morular variant (C-MV), an unusual and peculiar subtype of papillary thyroid carcinoma (PTC), has been observed frequently in familial adenomatous polyposis (FAP)-associated thyroid carcinoma and also in sporadic thyroid carcinoma. In this paper, five young women with the C-MV of PTC, aged 22-34 years at cancer diagnosis, are reported; two of them had attenuated FAP. Grossly, one FAP-associated tumour and one sporadic tumour were multicentric and the others were solitary. Histologically, the tumours were encapsulated and exhibited a combination of cribriform, follicular, trabecular, solid, and papillary patterns of growth, with morular areas. Immunohistochemically, the tumour cells showed cytoplasmic expression of thyroglobulin, neuron-specific enolase, epithelial membrane antigen, high- and low-molecular-weight cytokeratins, vimentin, and bcl-2 protein; nuclear expression of oestrogen and progesterone receptors, and retinoblastoma protein; and cytoplasmic and nuclear accumulation of beta-catenin. Germline mutations of the adenomatous polyposis coli (APC) gene were investigated using the protein truncation test in four subjects, including two FAP individuals. Germline APC mutation was identified in only one FAP patient with the multicentric C-MV of PTC, who had a thymidine deletion at codon 512, resulting in a frameshift leading to a premature stop codon. No loss of heterozygosity of loci close to the APC gene was detected in tumour tissues from these four patients. Somatic mutation analysis of exon 3 of the beta-catenin gene (CTNNB1) revealed alterations in seven tumours from all five individuals: one at a serine residue (codon 29), three at amino acids adjacent to serine or threonine residues (codons 22, 39, and 44), and three at other amino acids (codons 49, 54, and 56). Moreover, each of two different tumours examined from two patients with the multicentric C-MV of PTC, had different somatic mutations of the CTNNB1 gene. Taken together, these data suggest that accumulation of mutant beta-catenin contributes to the development of the C-MV of PTC.     

Cholestasis is a marker for hepatocellular carcinomas displaying beta-catenin mutations

The Wnt/beta-catenin signalling pathway is activated in many human hepatocellular carcinomas (HCC). Identification of beta-catenin mutation relies mostly on sequence analysis and/or immunohistochemistry. beta-catenin mutation may also be detected by analysing the expression of its target genes. The GLUL gene encoding glutamine synthetase (GS), for example, appears to be a pertinent marker. The aim of this study was to correlate GS immunostaining and beta-catenin mutations with clinicopathological features in HCC. We found that GS immunostaining had a sensitivity of 90% for the detection of beta-catenin mutations, with 98% specificity, whereas beta-catenin immunostaining had a sensitivity of 63% with 98% specificity. We used the sensitive GS marker to characterize 190 HCC cases. Sixty-eight (36%) cases displayed Wnt/beta-catenin activation. In addition to their well-differentiated pattern, these tumours exhibited significant features such as a homogeneous microtrabeculo-acinar pattern, low-grade cellular atypia, and cholestasis. As these tumours exhibited cholestasis, we hypothesized that beta-catenin acts on specific bile synthesis and/or transport pathways. In conclusion, we propose that GS immunostaining and a cholestatic pattern are relevant criteria for the identification of HCC with beta-catenin mutations.     

Fibromatosis of the breast and mutations involving the APC/beta-catenin pathway

Fibromatoses of the breast are nonmetastasizing tumors, but can be infiltrative and locally recurrent. Breast fibromatoses are rare, and their specific genetic alterations have not been elucidated. However, their occasional occurrence in patients with familial adenomatous polyposis (FAP) and their morphologic identification with other deep fibromatoses (desmoid tumors) suggest that alterations of the APC/beta-catenin pathway might be involved in the pathogenesis of sporadic and FAP-associated breast fibromatoses. We analyzed somatic beta-catenin and APC gene mutations in 33 breast fibromatoses (32 sporadic and 1 FAP-associated) using immunohistochemistry for beta-catenin, 5q allelic loss assays, and direct DNA sequencing for exon 3 of the beta-catenin gene and the mutation cluster region of the APC gene. Nuclear accumulation of beta-catenin was present in the stromal tumor cells in most (82%) cases but not in normal stroma or mammary epithelial cells. Somatic alterations of the APC/beta-catenin pathway were detected in 79% of breast fibromatoses, including activating beta-catenin gene mutations in 15 cases and somatic APC alterations (mutation or 5q allelic loss or both) in 11. These findings indicate that alterations of the APC/beta-catenin pathway with resultant nuclear translocation of beta-catenin are important in the pathogenesis of both sporadic and FAP-associated breast fibromatosis. The spectrum of beta-catenin and APC alterations is similar to that described for desmoid tumors of the abdomen, paraspinal region, and extremities.     

Mutations in components of the Wnt signaling pathway in adenoid cystic carcinoma.

The Wnt signaling pathway is essential for normal development and organogenesis. However, inappropriate activation of Wnt signaling, which results in the nuclear translocation of beta-catenin, is associated with the development of various types of neoplasm. In this study, we investigated possible mutations in the genes for components of this pathway, namely, CTNNB1 (the gene for beta-catenin), AXIN1, and APC, in adenoid cystic carcinoma, by PCR, analysis of single-strand conformational polymorphism, and sequencing. Among a total of 20 cases of adenoid cystic carcinoma, seven cases (35%) were associated with mutations in one or more of these three components. A mutation in CTNNB1 was detected in one case. Five cases, including the case with a mutation in CTNNB1, were associated with missense mutations in AXIN1. An aberration in the mutation cluster region of APC was detected in two cases. Mutations trended to be detected more frequently in adenoid cystic carcinoma with solid growth pattern than that with tubular and cribriform growth pattern. In the cases in which we detected mutations, it is possible that the presence of the abnormal products of the mutated genes resulted in the inappropriate activation of the Wnt signaling pathway to tumorigenesis and the growth of adenoid cystic carcinoma.     

Beta-catenin mutations in pulmonary blastomas: association with morule formation

To elucidate the contribution of beta-catenin gene mutation to the development of pulmonary blastomas, we analysed mutations in three well-differentiated fetal adenocarcinomas (WDFAs) and six biphasic pulmonary blastomas (BPBs). For comparison, eight clear-cell adenocarcinomas with fetal lung features were also examined. beta-Catenin gene mutations were found in all three WDFAs, two BPBs, and none of the clear-cell adenocarcinomas with fetal lung features. All tumours with mutations had a common histological feature, namely morule formation, and showed a characteristic heterogeneous beta-catenin expression pattern that was revealed by immunohistochemistry. Strong nuclear/cytoplasmic expression of beta-catenin was seen in clustered cells in the morular areas and in single cells in glands, and was associated with neuroendocrine differentiation. As beta-catenin mutations are rare among lung tumours, this distinctive genetic feature, which is also immunohistochemically detectable as overexpression with a heterogeneous pattern, has diagnostic significance. The presence of this common genetic alteration found in both WDFA and BPB implies a histogenetic linkage between these tumours.     

Significance of aberrant (cytoplasmic/nuclear) expression of beta-catenin in pancreatoblastoma

This study concerns the significance of aberrant (nuclear/cytoplasmic) expression of beta-catenin in pancreatoblastoma (PBL). On immunohistochemistry, all seven PBLs examined showed nuclear/cytoplasmic expression of beta-catenin, predominantly in the squamoid corpuscles (SCs). In areas with acinar/ductular differentiation, few tumour cells displayed nuclear/cytoplasmic expression of beta-catenin and more than half of the tumour cells showed membranous expression. Two out of five (40%) tumours examined showed missense mutations in codons 33 and 37 of exon 3 of the beta-catenin gene. No mutation of the adenomatous polyposis coli (APC) gene was detected in two of the remaining three tumours. Amplifiable DNA for APC analysis was not obtained from the one other tumour. Immunoreactivity for cyclin D1, one of the nuclear targets of beta-catenin, was found predominantly in the SCs of the seven tumours. In contrast, the Ki-67 labelling index was 2-4% (median 3%) in the SCs and 8-18% (median 12%) in the other areas, indicating a negative correlation with nuclear cyclin D1 reactivity. These results imply that in PBLs, nuclear/cytoplasmic accumulation of beta-catenin and overexpression of its target gene cyclin D1 are not associated with the induction of tumour cell proliferation. Nuclear/cytoplasmic accumulation of beta-catenin may be related to the morphogenesis of the SCs that are considered most characteristic for PBL.