α-Catenin overrides Src-dependent activation of β-catenin oncogenic signaling

Loss of α-catenin is one of the characteristics of prostate cancer. The catenins (α and β) associated with E-cadherin play a critical role in the regulation of cell-cell adhesion. Tyrosine phosphorylation of β-catenin dissociates it from E-cadherin and facilitates its entry into the nucleus, where β-catenin acts as a transcriptional activator inducing genes involved in cell proliferation. Thus, β-catenin regulates cell-cell adhesion and cell proliferation. Mechanisms controlling the balance between these functions of β-catenin invariably are altered in cancer. Although a wealth of information is available about β-catenin deregulation during oncogenesis, much less is known about how or whether α-catenin regulates β-catenin functions. In this study, we show that α-catenin acts as a switch regulating the cell-cell adhesion and proliferation functions of β-catenin. In α-catenin-null prostate cancer cells, reexpression of α-catenin increased cell-cell adhesion and decreased β-catenin transcriptional activity, cyclin D1 levels, and cell proliferation. Further, Src-mediated tyrosine phosphorylation of β-catenin is a major mechanism for decreased β-catenin interaction with E-cadherin in α-catenin-null cells. α-Catenin attenuated the effect of Src phosphorylation by increasing β-catenin association with E-cadherin. We also show that α-catenin increases the sensitivity of prostate cancer cells to a Src inhibitor in suppressing cell proliferation. This study reveals for the first time that α-catenin is a key regulator of β-catenin transcriptional activity and that the status of α-catenin expression in tumor tissues might have prognostic value for Src targeted therapy.