Malignant progression in cancer requires populations of tumor-initiating cells (TICs

SUMMARYNeural development requires crosstalk between signaling pathways and chromatin. In this study, we demonstrate that neurogenesis is promoted by an interplay between the TGF pathway and the H3K27me3 histone demethylase (HDM) JMJD3. Genome-wide analysis showed that JMJD3 is targeted to gene promoters by Smad3 in neural stem cells (NSCs) and is essential to activate TGF-responsive genes. In vivo experiments in chick spinal cord revealed that the generation of neurons promoted by Smad3 is dependent on JMJD3 HDM activity. Overall, these findings indicate that JMJD3 function is required for the TGF developmental program to proceed.

SUMMARY The Wnt3a/β-catenin and Activin/SMAD2,3 signaling pathways synergize to induce endodermal differentiation of human embryonic stem cells; however, the underlying mechanism is not well understood. Using ChIP-seq and GRO-seq analyses, we show here that Wnt3a-induced β-catenin:LEF-1 enhancers recruit cohesin to direct enhancer-promoter looping and activate mesendodermal (ME) lineage genes. Moreover, we find that LEF-1 and other hESC enhancers recruit RNAPII complexes (eRNAPII) that are highly phosphorylated at Ser5, but not Ser7. Wnt3a signaling further increases Ser5P-RNAPII at LEF-1 sites and ME gene promoters, indicating that elongation remains limiting. However, subsequent Activin/SMAD2,3 signaling selectively increases transcription elongation, P-TEFb occupancy, and Ser7P-RNAPII levels at these genes. Finally, we show that the Hippo regulator, YAP, functions with TEAD to regulate binding of the NELF negative elongation factor and block SMAD2,3 induction of ME genes. Thus, the Wnt3a/β-catenin and Activin/SMAD2,3 pathways act in concert to counteract YAP repression and upregulate ME genes during early hESC differentiation.

Mutation of the adenomatous polyposis coli (APC) tumor suppressor stabilizes b-catenin and aberrantly reactivates Wnt/b-catenin target genes in colon cancer. APC mutants in cancer frequently lack the conserved catenin inhibitory domain (CID), which is essential for b-catenin proteolysis. Here we show that the APC CID interacts with a-catenin, a Hippo signaling regulator and heterodimeric partner of b-catenin at cell:cell adherens junctions. Importantly, a-catenin promotes b-catenin ubiquitylation and proteolysis by stabilizing its association with APC and protecting the phosphodegron. Moreover, b-catenin ubiquitylation requires binding to a-catenin. Multidimensional protein identification technology (MudPIT) proteomics of multiple Wnt regulatory complexes reveals that a-catenin binds with b-catenin to LEF-1/TCF DNA-binding proteins in Wnt3a signaling cells and recruits APC in a complex with the CtBP:CoREST:LSD1 histone H3K4 demethylase to regulate transcription and b-catenin occupancy at Wnt target genes. Interestingly, tyrosine phosphorylation of a-catenin at Y177 disrupts binding to APC but not b-catenin and prevents repression of Wnt target genes in transformed cells. Chromatin immunoprecipitation studies further show that a-catenin and APC are recruited with b-catenin to Wnt response elements in human embryonic stem cells (hESCs). Knockdown of a-catenin in hESCs prevents the switch-off of Wnt/b-catenin transcription and promotes endodermal differentiation. Our findings indicate a role for a-catenin in the APC destruction complex and at Wnt target genes.