Tcf4 can specifically recognize β-catenin using alternative conformations

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Abstract
Accumulation of the Wnt pathway effector β-catenin is a hallmark of a number of cancers, including colon cancer. As β-catenin accumulates in the cell, it forms a complex with Tcf family transcription factors and activates the transcription of several critical genes involved in cell proliferation. Because Tcf4 is the predominant Tcf factor present in colon cancer cells, drugs that specifically disrupt the β-catenin–Tcf4 complex could be useful in treating colon cancers. Earlier structural and biochemical studies demonstrated that the central region of the β-catenin binding domain of Tcf is essential for anchoring Tcf to β-catenin via two conserved lysines in β-catenin (called the charged 'buttons'). Here we report the crystal structure of a β-catenin–Tcf4 complex at 2.0 Å resolution. Our structural and mutagenesis studies show that Tcf4 docks specifically to β-catenin using several distinct conformations in its essential central region. These conformations allow different glutamate residues in the central region of Tcf4 to form a salt bridge with the same critical charged button, Lys 312 of β-catenin. We propose that this interaction may be the first event in β-catenin–Tcf4 recognition.

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