Beta-catenin/LEF-1 signalling in breast cancer--central players activated by a plethora of inputs.

Although the role of Wnt signalling in breast cancer is far from being fully understood, in the last years its importance has been reported frequently. Besides stimulation by canonical Wnt signalling, the downstream effectors beta-catenin and the transcriptional modulators of the T-cell factor/lymphoid enhancer-binding factor (TCF/LEF) family can also be activated by other inputs including the TGF-beta pathway. Wnt and TGF-beta signalling are both major signal transduction pathways, which provide important cues during development and tumor progression. However, particularly TGF-beta has a complicated influence on oncogenesis, which ranges from suppressive to promoting activity. Signalling pathways activated in parallel with TGF-beta might determine the oncogenic influence, and therefore place signals cooperating with TGF-beta into the limelight. During early development Wnt and TGF-beta signalling collaborate extensively. Here we provide an overview of the known interactions of Wnt with TGF-beta signalling in development and metastasis, particularly in breast cancer. We want to focus on the Wnt-activated transcription factor complex beta-catenin/LEF-1, its upstream activators, its downstream targets and consequences on the cellular level in response to beta-catenin/LEF-1 activation.