1. ¹Department of Pathology, Laboratory of Morphology and Molecular Pathology, University Hospitals, Katholieke Universiteit Leuven, Leuven, Belgium
2. ²Department of Dermatology, University Hospitals, Katholieke Universiteit Leuven, Leuven, Belgium

Correspondence: A. Demunter, M.D., Dept. Pathology, Laboratory of Morphology and Molecular Pathology, University Hospital St. Rafael, Minderbroederstraat 12, B-3000 Leuven, Belgium. e-mail: anouk.demunter@uz.kuleuven.ac.be; fax: 00-32-16-33-65-48.

Accepted 12 December 2001.

Abstract

-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 -catenin in cells is tightly controlled in a multiprotein complex, and mutations in the glycogen synthase kinase 3 (GSK-3) phosphorylation sites of the -catenin gene (CTNNB1) result in nuclear and/or cytoplasmic accumulation of -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 -catenin mutations; in vivo, however, cellular accumulation of -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. -Catenin mutations were found in 2 primary melanomas and 1 metastatic melanoma and were not correlated with nuclear accumulation of -catenin in these cases. Cellular expression of -catenin was evaluated by immun-ohistochemistry and by reverse polymerase chain reaction (RT-PCR) in 80 and 70 cases, respectively. Immunohistochemistry revealed a significant loss of membranous -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 -catenin (P = .0015); no correlation existed between the amount of RNA and the number of cells with nuclear or cytoplasmic expression of -catenin. In conclusion, nuclear expression of -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 -catenin was associated with an increased amount of -catenin RNA in primary or metastatic melanoma. Our results suggest that posttranslational events, rather than CTNNB1 mutations, are responsible for the altered distribution of -catenin in cutaneous melanoma.