β-catenin regulates FOXP2 transcriptional activity via multiple binding sites.

The transcription factor Forkhead-box-protein P2 (FOXP2) is a highly conserved key regulator of embryonal development. The molecular mechanisms of how FOXP2 regulates embryonal development, however, remain elusive. Using RNA sequencing we identified the Wnt signaling pathway as key target of FOXP2-dependent transcriptional regulation. Using cell-based assays we show that FOXP2 transcriptional activity is regulated by the Wnt co-regulator β-catenin, and that β-catenin contacts multiple regions within FOXP2. Using Nuclear Magnetic Resonance (NMR) Spectroscopy we uncovered the molecular details of these interactions. β-catenin contacts a disordered FOXP2 region with α-helical propensity via its folded armadillo domain, whereas the intrinsically disordered β-catenin N- and C-termini bind to the conserved FOXP2 DNA binding domain. Using RNA sequencing we confirmed that β-catenin indeed regulates transcriptional activity of FOXP2, and that the FOXP2 α-helical motif acts as a key regulatory element of FOXP2 transcriptional activity. Taken together, our findings provide first insight into novel regulatory interactions and help to understand the intricate mechanisms of FOXP2 function and (mis)-regulation in embryonal development and human diseases.