Regulation of Lef-mediated Transcription and p53-dependent Pathway by Associating β-Catenin with CBP/p300

Abstract

CBP and its homologue p300 play significant roles in cell differentiation, cell cycle, and anti-oncogenesis. We demonstrated that ␤-catenin, recently known as a potent oncogene, and CBP/p300 are associated through its CH3 region, which is a primary target of adenoviral oncoprotein E1A and various nuclear proteins, such as p53, cyclin E, and AP-1, and both are colocalized in the nuclear bodies. CBP/p300 potentiated Lef-mediated transactivation of ␤-catenin, and E1A, a potent inhibitor of CBP/p300, repressed its transactivation. Furthermore, overexpression of stable ␤-catenin mutant competitively suppressed the p53-dependent pathway. These may be a key mechanism of ␤-catenin involved in oncogenic events underlying disruption of tumor suppressor function through CBP/p300.The coactivator CBP/p300 family is a central regulator of gene expression (1-5) and important in cell differentiation, cell cycle, and anti-oncogenesis (6 -9). The importance of CBP/p300 in such cellular functions is supported by their ability to potentiate the activity of a large number of nuclear factors such as adenoviral oncoprotein E1A, p53, cyclin E, and AP-1 (10 -14). In addition, CBP/p300 has been proposed as a bridging protein, bringing together proteins of the RNA polymerase II-dependent basal transcription complex with either specific transcription factors or other cofactors.Drosophila Armadillo and its vertebrate homologue ␤-catenin are scaffold proteins in cadherin-mediated cell-cell adhesion, and they function as signal transducers to the nucleus in Wnt/Wingless pathway (15-17). ␤-Catenin translocated to the nucleus regulates expression of various downstream genes by acting as a coactivator of Lef/TCF family. Furthermore, recent studies suggested that stable mutants of ␤-catenin leading to accumulation in the nucleus are implicated in the initiation of some forms of colon cancers and melanomas (18 -21).The involvement of ␤-catenin in its nuclear functions, including transcriptional activation and oncogenic events, addresses the existence of bridging nuclear factors for recruitment of RNA polymerase II. To test this hypothesis, in the present study, we explored the possible association of ␤-catenin with CBP/p300 and attempted to define the biological function of CBP/p300 and ␤-catenin interaction. EXPERIMENTAL PROCEDURESCell Culture and Transfections and Reporter Gene Assays-HeLa cells, L cells, and HEK293T cells were cultured in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum. HCT116 cells were maintained in McCoy 5A supplemented with 10% fetal bovine serum. Transfections were performed by the calcium phosphate method. Thirty ng of a RSV-Renilla luciferase control plasmid were included in each transfection experiment to control for the efficiency of transfection. To ensure equal DNA amounts, empty plasmids were added in each transfection. The luciferase activity was measured with AutoLumat (Berthold). The values were normalized to Renilla luciferase activity as an internal control.Antibodies-Anti-␤-catenin ...

TIS7 Regulation of the β-Catenin/Tcf-4 Target Gene Osteopontin (OPN) Is Histone Deacetylase-dependent

“…This finding suggests that TIS7 might regulate myogenesis by affecting the interaction between ␤-catenin and HDACs, mainly class II. Several groups have identified that ␤-catenin transcriptional activity is acetylation regulated by p300 (6,25,43,44). Our current data confirm these results, and furthermore we show that TIS7 has the capacity to inhibit ␤-catenin/Tcf-4 transcriptional activity even after strong p300 stimulation.…”

Differential roles for the coactivators CBP and p300 on TCF/β-catenin-mediated survivin gene expression

“…ICG-001-enhanced caspase-3 activation and DNA fragmentation was largely abolished by transfection with pCMV-hSurvivin wt ( Figure (Jiang et al, 1996). p53 transcriptional activation is enhanced by binding to CBP (Miyagishi et al, 2000). However, the synergistic effect of ICG-001 on STS-induced apoptosis in this study is likely independent of p53, as the p53 gene is mutated in SW480 cells (Abarzua et al, 1995).…”

Physical and functional cooperation between AP-1 and β-catenin for the regulation of TCF-dependent genes

“…The physical interaction between b-catenin and both c-Jun and c-Fos was demonstrated by co-immunoprecipitations in vivo and by glutathione S-transferase (GST) pull-down assays in vitro. The co-immunoprecipitation experiments do not directly prove that the b-catenin interaction with AP-1 proteins was direct, because b-catenin has been reported previously to bind other proteins that are also potential partners of c-Jun and c-Fos, such as CBP/p300 (Miyagishi et al, 2000;Takemaru and Moon, 2000;Harris and Peifer, 2005) or the LIM-only protein (Morlon and Sassone-Corsi, 2003). However, our in vitro pull-down assays clearly demonstrate a direct association between the armadillo repeats of b-catenin and the DNA-binding domain of c-Jun and the C-terminal domain of b-catenin with the N-terminal region of c-Fos.…”

“…Binding of b-catenin to LEF/TCF causes displacement of core-repressor complexes containing histone deacetylases (Billin et al, 2000), and heterodimerization that allows interaction with the C-terminal transactivation domain of b-catenin leading ultimately to the activation of transcription of Wntresponsive genes Moon et al, 2002). The coactivator function of b-catenin is induced by recruitment of the basal transcription machinery (Hecht et al, 1999) and is enhanced by synergistic cooperation with a number of other proteins such as coactivators, (Zhurinsky et al, 2000;Martin et al, 2002;Grueneberg et al, 2003;Wei et al, 2003) or proteins involved in chromatin remodeling and histone modification (Hecht et al, 2000;Miyagishi et al, 2000;Sun et al, 2000;Takemaru and Moon, 2000;Barker et al, 2001). Not surprisingly, mounting evidence indicate that b-catenin is able to cross-talk with a variety of signalling cascades, such as those involving Rac GTPase, forkhead box O transcription factors or transforming growth factor (TGF)b (Eger et al, 2004;Esufali and Bapat, 2004;Chakladar et al, 2005;Essers et al, 2005).…”