-Catenin plays an important role in development and tumorigenesis. However, the effect of a key acetyltransferase p300/CBP-associated factor (PCAF) on -catenin signaling is largely unknown. In this study, we found PCAF could increase the -catenin transcriptional activity, induce its nuclear translocation, and up-regulate its protein level by inhibiting its ubiquitination and improving its stability. Further studies showed that PCAF directly binds to and acetylates -catenin. The key ubiquitination sites Lys-19 and Lys-49 of -catenin were shown as the critical residues for PCAF-induced acetylation and stabilization. Knockdown of PCAF in colon cancer cells markedly reduced the protein level, transcriptional activity, and acetylation level of -catenin; promoted cell differentiation; inhibited cell migration; and repressed xenografted tumorigenesis and tumor growth in nude mice. All these data demonstrate that PCAF acetylates -catenin and regulates its stability, and they raise the prospect that therapies targeting PCAF may be of clinical use in -catenin-driven diseases, such as colon cancer.
INTRODUCTIONThe Wnt signaling pathway has important roles in a variety of developmental processes (Logan and Nusse, 2004;Clevers, 2006). The key output of this pathway is the stabilization and nuclear translocation of -catenin, which determines the activation of -catenin-responsive genes. Aberrant activation of Wnt signaling is often associated with carcinogenesis. Colorectal tumors are among most common human neoplasms, and Ͼ90% of colorectal cancers have a mutation that activates Wnt signaling (Giles et al., 2003;Doucas et al., 2005). Inactivating adenomatous polyposis coli (APC) mutations has been demonstrated in ϳ85% of sporadic colorectal tumors. Among the 15% colon carcinomas without APC mutations, -catenin or the scaffolding protein Axin2 is mutant (Morin et al., 1997;Liu et al., 2000). Accumulating studies strongly suggest that disruption of Wnt signaling is a promising strategy for the prevention of colon cancers, and how to regulate the stability of -catenin is the key point (Clapper et al., 2004;Dihlmann and von Knebel Doeber, 2005; DvorySobol et al., 2006).It is well known that Wnt signaling is regulated by phosphorylation. Besides phosphorylation, ubiquitination and acetylation have also been reported to be involved in Wnt signaling (Aberle et al., 1997;Sun et al., 2000;Takemaru and Moon, 2000;Winer et al., 2006). Lys-19 and Lys-49 of -catenin were reported as important ubiquitination sites (Winer et al., 2006), and Lys-49 of -catenin was also reported to be acetylated by CBP (Wolf et al., 2002). Whether there is some cross-talk between the ubiquitination and acetylation of -catenin is yet to be elucidated. Some acetyltransferases such as CREB-binding protein (CBP)/p300 are related to colon cancer causation and progression (Muraoka et al., 1996;Ionov et al., 2004), and CBP/p300 can interact with -catenin and synergistically activate -catenin/T cell factor (TCF) transcription (Sun et al., 2000;Takema...