Dishevelled-DEP domain interacting protein (DDIP) inhibits Wnt signaling by promoting TCF4 degradation and disrupting the TCF4/β-catenin complex

The TCF4/β-catenin complex, the executor of canonical Wnt/β-catenin signaling, is regulated by a variety of factors. Among these, Dishevelled (Dvl) is a critical regulator that releases β-catenin from degradation and stabilizes TCF4/β-catenin complex. Here, we report that DDIP (Dishevelled-DEP domain Interacting Protein, also named as Spats1, spermatogenesis associated, serine-rich 1), a novel protein that interacts with Dvl, regulates Wnt signaling. We provide evidence that DDIP suppresses Lef-1 luciferase reporter activity stimulated by Wnt1, Dvl2 or β-catenin, interacts with the TCF4/β-catenin complex, and disrupts the interaction of TCF4 and β-catenin by promoting TCF4 degradation through the proteasome pathway. Our results indicate that DDIP is a negative regulator of the canonical Wnt signaling.