title: Loss of membranous expression of beta-catenin is associated with tumor progression in cutaneous melanoma and rarely caused by exon 3 mutations.
abstract: beta-Catenin plays a fundamental role in the regulation of the E-cadherin-catenin cell adhesion complex. It also plays a role in the Wnt signaling pathway by activating T-cell factor- and lymphoid enhancer factor-regulated gene transcription. The level of beta-catenin in cells is tightly controlled in a multiprotein complex, and mutations in the glycogen synthase kinase 3beta (GSK-3beta) phosphorylation sites of the beta-catenin gene (CTNNB1) result in nuclear and/or cytoplasmic accumulation of beta-catenin and constitutive transactivation of T-cell factor and lymphoid enhancer factor target genes, a mechanism occurring in many cancers. Melanoma cell lines may harbor beta-catenin mutations; in vivo, however, cellular accumulation of beta-catenin is rarely caused by CTNNB1 mutations. In our study, 43 primary cutaneous melanoma and 30 metastases were screened for CTNNB1 exon 3 mutations by using a denaturing gradient gel electrophoresis technique and sequencing. beta-Catenin mutations were found in 2 primary melanomas and 1 metastatic melanoma and were not correlated with nuclear accumulation of beta-catenin in these cases. Cellular expression of beta-catenin was evaluated by immunohistochemistry and by reverse polymerase chain reaction (RT-PCR) in 80 and 70 cases, respectively. Immunohistochemistry revealed a significant loss of membranous beta-catenin staining between the primary and metastatic melanomas as well as between radial and vertical growth phase. RT-PCR showed a significant inverse correlation between the amount of RNA and the proportion of cells with membranous expression of beta-catenin (P =.0015); no correlation existed between the amount of RNA and the number of cells with nuclear or cytoplasmic expression of beta-catenin. In conclusion, nuclear expression of beta-catenin is seen in cutaneous melanoma but, in contrast to the case of many other cancers, does not correlate with tumor stage or mutation status. A combination of immunohistochemistry and RT-PCR showed that down-regulation of membranous beta-catenin was associated with an increased amount of beta-catenin RNA in primary or metastatic melanoma. Our results suggest that posttranslational events, rather than CTNNB1 mutations, are responsible for the altered distribution of beta-catenin in cutaneous melanoma.
authors.affiliation: Department of Pathology, Laboratory of Morphology and Molecular Pathology, University Hospitals, Katholieke Universiteit Leuven, Belgium. anouk.demunter@uz.kuleuven.ac.be
authors.forename: Anouk
authors.initials: A
authors.lastname: Demunter
authors.forename: Louis
authors.initials: L
authors.lastname: Libbrecht
authors.forename: Hugo
authors.initials: H
authors.lastname: Degreef
authors.forename: Chris
authors.initials: C
authors.lastname: De Wolf-Peeters
authors.forename: Joost J
authors.initials: JJ
authors.lastname: van den Oord
mesh_terms: D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000235:genetics* / Q000378:metabolism; D004252:DNA Mutational Analysis; D004273:DNA, Neoplasm / Q000737:chemistry / Q000235:genetics; D018450:Disease Progression; D005091:Exons / Q000235:genetics*; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D008545:Melanoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D009154:Mutation; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D015534:Trans-Activators; D051176:beta Catenin
chemical_list: C495270:CTNNB1 protein, human; D003598:Cytoskeletal Proteins; D004273:DNA, Neoplasm; D015534:Trans-Activators; D051176:beta Catenin