Sporadic Medulloblastomas Contain Oncogenic β-Catenin Mutations

Abstract

The β-catenin, glycogen synthase kinase 3β (GSK-3β), and adenomatous polyposis coli (APC) gene products interact to form a network that influences the rate of cell proliferation. Medulloblastoma occurs as part of Turcot's syndrome, and patients with Turcot's who develop medulloblastomas have been shown to harbor germ-line APC mutations. Although APC mutations have been investigated and not identified in sporadic medulloblastomas, the status of the β-catenin and GSK-3β genes has not been evaluated in this tumor. Here we show that 3 of 67 medulloblastomas harbor β-catenin mutations, each of which converts a GSK-3β phosphorylation site from serine to cysteine. The β-catenin mutation seen in the tumors was not present in matched constitutional DNA in the two cases where matched DNA was available. A loss of heterozygosity analysis of 32 medulloblastomas with paired normal DNA samples was performed with four microsatellite markers flanking the GSK-3β locus; loss of heterozygosity with at least one marker was identified in 7 tumors. Sequencing of the remaining GSK-3β allele in these cases failed to identify any mutations. Taken together, these data suggest that activating mutations in the β-catenin gene may be involved in the development of a subset of medulloblastomas. The GSK-3β gene does not appear to be a target for inactivation in this tumor.