The WW domain containing oxidoreductase (WWOX) has recently been shown to inhibit of the Wnt/b-catenin pathway by preventing the nuclear import of disheveled 2 (DVL2) in human breast cancer cells. Here, it is revealed that WWOX also interacts with the BCL9-2, a cofactor of the Wnt/b-catenin pathway, to enhance the activity of the b-catenin-TCF/LEF (T-cell factor/ lymphoid enhancer factors family) transcription factor complexes. By using both a luciferase assay in MCF-7 cells and a Xenopus secondary axis induction assay, it was demonstrated that WWOX inhibits the BCL9-2 function in Wnt/b-catenin signaling. WWOX does not affect the BCL9-2-b-catenin association and colocalizes with BCL9-2 and b-catenin in the nucleus of the MCF-7 cells. Moreover, WWOX inhibits the b-catenin-TCF1 interaction. Further examination found that HDAC3 associates with BCL9-2, enhances the inhibitory effect of WWOX on BCL9-2 transcriptional activity, and promotes the WWOX-BCL9-2 interaction, independent of its deacetylase activity. However, WWOX does not influence the HDAC3-BCL9-2 interaction. Altogether, these results strongly indicate that nuclear WWOX interacts with BCL9-2 associated with b-catenin only when BCL9-2 is in complex with HDAC3 and inhibits its transcriptional activity, in part, by inhibiting the b-catenin-TCF1 interaction. The promotion of the WWOX-BCL9-2 interaction by HDAC3, independent of its deacetylase activity, represents a new mechanism by which this HDAC inhibits transcription.
Implications:The inhibition of the transcriptional activity of BCL9-2 by WWOX and HDAC3 constitutes a new molecular mechanism and provides new insight for a broad range of cancers.