TRAF2 mediates Wnt-induced β-catenin nuclear translocation by associating with the nuclear pore complex

Colorectal cancer (CRC), driven by Wnt/β-catenin hyperactivation, relies on nuclear import of β-catenin, but the underlying mechanism is not fully clarified. Given that tumor necrosis factor receptor-associated factor 2 (TRAF2) is a positive regulator of Wnt signaling by directly interacting with β-catenin, we aim to demonstrate the role of TRAF2 in Wnt-induced β-catenin nuclear translocation.

Wild-type and TRAF2 knockout cells (generated via CRISPR-Cas9) were utilized to validate the role of TRAF2 in β-catenin nuclear translocation through immunofluorescence and nucleoplasm separation assay. Proteomic profiling of TRAF2 condensates and interactomes was performed to identify proteins linked to nucleocytoplasmic transport. The interactions among TRAF2, β-catenin, nucleoporins (Nups) and B-cell lymphoma 9 (BCL9), as well as the inhibitory effects of small molecule liquidambaric acid (LDA) on these interactions were confirmed using proximity ligation assay (PLA), fluorescence resonance energy transfer (FRET), and co-immunoprecipitation (Co-IP) in cellular models and small intestine of mice.

TRAF2 is required for Wnt-induced β-catenin nuclear translocation. TRAF2 interacts with numerous Nups within the nuclear pore complex (NPC), and is upregulated upon Wnt stimulation. In the small intestine of mice, TRAF2/Nups interaction is mainly detected in the crypts-regions known to harbor colorectal cancer stem cells, as well as in APC^min/+ intestinal organoids. Of note, TRAF2 is indispensable for β-catenin interaction with Nups and the known chaperone BCL9. Finally, LDA blocks TRAF2/Nups interaction, inhibiting β-catenin nuclear translocation.

This study unveils TRAF2-mediated nucleocytoplasmic transport as a druggable mechanism, advancing targeted therapies against Wnt-driven colorectal cancers.