β-Catenin, a novel prognostic marker for breast cancer: Its roles in cyclin D1 expression and cancer progression

β-Catenin can function as an oncogene when it is translocated to the nucleus, binds to T cell factor or lymphoid enhancer factor family members, and transactivates its target genes. In this study, we demonstrate that cyclin D1 is one of the targets of β-catenin in breast cancer cells. Transactivation of β-catenin correlated significantly with cyclin D1 expression both in eight breast cell lines in vitro and in 123 patient samples. More importantly, we found that high β-catenin activity significantly correlated with poor prognosis of the patients and was a strong and independent prognostic factor in breast cancer. Our studies, therefore, indicated that β-catenin can be involved in breast cancer formation and/or progression and may serve as a target for breast cancer therapy.