Involved in signal transduction through the Wnt pathway. Interacts with BCL9 via The PHD-type zinc finger motiv, and thereby becomes part of the nuclear beta-catenin/TCF complex. Identified in a complex with BCL9L, CDC73, CTNNB1 and PYGO1. Interacts with histone H3 mono-, di- or tri-methylated at 'Lys4' (H3K4me1, H3K4me2, H3K4me3); the interaction is enhanced by the interaction with BCL9.