CK2 Controls the Recruitment of Wnt Regulators to Target Genes In Vivo

SummaryNuclear β-catenin is a transcriptional coactivator of LEF-1/TCF DNA-binding proteins in the Wnt/Wg signaling pathway [1]. Casein Kinase 2 (CK2), a positive regulator of Wnt signaling 2, 3 and 4, is present in β-catenin complexes 5 and 6 and activated in Wnt-signaling cells [7]. We show here that CK2 enhances β-catenin:LEF-1 transactivation in vivo and in vitro and that β-catenin and CK2 cycle on and off the DNA in an alternating manner with the TLE1 corepressor at Wnt target genes. Interestingly, CK2 phosphorylates hLEF-1 directly and stimulates binding and transactivation of β-catenin:LEF-1 complexes on chromatin templates in vitro. In vitro, CK2 phosphorylation of hLEF-1 strongly enhances its affinity for β-catenin and reduces its affinity for TLE1. MALDI-TOF mass spectrometry (MS) identified two CK2 phosphorylation sites (S42, S61) within the amino terminus of hLEF-1, and mutation of these sites reduced binding to β-catenin in vitro and transactivation in vivo. Remarkably, treatment of cells with TBB, a pharmaceutical inhibitor of CK2, blocked the recruitment and cycling of β-catenin and TLE1 at Wnt target genes in vivo. Taken together, these data indicate that CK2 is required for the assembly and cycling of Wnt-enhancer complexes in vivo.