Detection and analysis of beta-catenin mutations in prostate cancer

E-cadherin and alpha-catenin are components of adherens junctions which mediate calcium-dependent, cell-cell adhesion in a homotypic manner. Both these molecules have been defined as useful tumor markers as their altered expression correlates with increased tumor aggressiveness and dedifferentiation. More recently, alterations of a third component of adherens junctions, beta-catenin, have been observed to play a role in several human cancers. Dysregulation of beta-catenin, either by direct mutation or by defects in interacting pathways/regulators, can result in its cytoplasmic accumulation and nuclear translocation. In the nucleus, beta-catenin forms a transcriptional complex capable of upregulating target genes, many of which encode proliferative factors. Given its oncogenic activity and connection to human cancer, we examined the beta-catenin gene and its expression in prostate cancer.

By single-stranded conformational polymorphism (SSCP) and DNA sequencing analyses, we screened exon 3 of beta-catenin from a panel of 81 primary tumors obtained at radical prostatectomy, 22 lymph node metastases from untreated patients, and a unique set of 61 metastatic tissues from 19 patients who died of hormone-refractory disease.

We found putative activating mutations (missense and deletion) at a rate of 5% (7/138). One patient had the same 72 base pair deletion in each of nine separate metastases examined, indicating that this change was associated with a clonal population of metastatic cells.

Immunohistological staining of mutation-positive tumors demonstrated beta-catenin accumulation and nuclear localization in a heterogeneous fashion. Consistent with this in vivo finding, our in vitro analyses demonstrate that certain mutations can result in increased beta-catenin nuclear activity in prostate cancer cell lines. These data implicate the beta-catenin signaling pathway in the development of a subset of prostate cancers.