Sp5 and Sp8 recruit β-catenin and Tcf1-Lef1 to select enhancers to activate Wnt target gene transcription

Abstract

The ancient, highly conserved, Wnt signaling pathway regulates cell fate in all metazoans. We have previously shown that combined null mutations of the specificity protein (Sp) 1/Klf-like zinc-finger transcription factors Sp5 and Sp8 (i.e., Sp5/8) result in an embryonic phenotype identical to that observed when core components of the Wnt/β-catenin pathway are mutated; however, their role in Wnt signal transduction is unknown. Here, we show in mouse embryos and differentiating embryonic stem cells that Sp5/8 are gene-specific transcriptional coactivators in the Wnt/β-catenin pathway. Sp5/8 bind directly to GC boxes in Wnt target gene enhancers and to adjacent, or distally positioned, chromatin-bound T-cell factor (Tcf) 1/lymphoid enhancer factor (Lef) 1 to facilitate recruitment of β-catenin to target gene enhancers. Because Sp5 is itself directly activated by Wnt signals, we propose that Sp5 is a Wnt/β-catenin pathway-specific transcripton factor that functions in a feed-forward loop to robustly activate select Wnt target genes.S ignaling pathways in multicellular organisms have evolved over millions of years to accommodate complex programs of tissue-specific gene expression. One such pathway, the Wnt/ β-catenin pathway, regulates gene expression by elevating the cytosolic levels of the transcription coactivator β-catenin (1). Stabilized β-catenin translocates to the nucleus, where it interacts with the DNA-bending, DNA-binding Tcf1 and Lef1 transcription factors (TFs), which subsequently replace Groucho/ Tcf3 repressor complexes on Wnt target gene enhancers (2). β-Catenin interacts with cell context-dependent cofactors (web. stanford.edu/group/nusselab/cgi-bin/wnt/) to associate with RNA polymerase II and the general transcription apparatus to activate transcription. However, the nature of the β-cateninTcf/Lef enhancer-binding protein complex and the mechanisms that facilitate its association with regulatory elements at Wnt target genes remain poorly understood.The formation of a Wnt signaling center during gastrulation is essential for animal development (3). Secreted Wnts emanating from the primitive streak regulate the fate of posterior progenitors, including the neuromesodermal progenitor (NMP), an embryonic cell that depends upon Wnt3a for self-renewal and mesodermal differentiation and that gives rise to the spinal cord, dermis, and musculoskeletal system of the trunk and tail (4-6). Embryos lacking Wnt3a, Ctnnb1 (β-catenin), T-cell factor (Tcf) 1 and lymphoid enhancer factor (Lef) 1, or specificity protein (Sp) 5 and Sp8 display similar severe posterior truncations caused by the loss of NMPs (7-10). These genes define a syn-phenotype group that, together with the genetic interactions observed between Sp5 and Wnt3a, suggests that Sp5/8 could be effectors of Wnt signaling. Sp5/8 are closely related to Sp1, which is one of the first identified eukaryotic TFs (11) and is frequently associated with the regulation of housekeeping genes. In contrast to the ubiquitously expressed Sp1, Sp5 expression is restricte...

Genome-Wide Temporal Profiling of Transcriptome and Open Chromatin of Early Cardiomyocyte Differentiation Derived From hiPSCs and hESCs

“…Multiple signaling pathways are involved in the EMT process, including WNT/β-catenin signaling, TGF-β signaling and Notch signaling. 70-73 One important feature of EMT is the down-regulation of Cadherin 1 (CDH1, also known as E-cadherin) by ZEB1 and ZEB2. In the present study, we observed that expression of CDH1 was down-regulated from day 4 to day 30 (Online Figure X A-B).…”

Wnt target genes and where to find them

“…Consistent with this, genome-wide surveys of TCF or β-cat binding in vertebrates reveal the presence of several TF binding site motifs besides the TCF site consensus 1, 30, 39, 77, 78 . Other TFs have been reported to co-localize with TCFs 36, 38, 39, 79, 80 , and in the cases of Cdx2 79 , Sp5/8 81 , and TEAD TFs 82 , a co-dependency with TCFs or β-cat for chromatin association has been reported. In addition, TCF binding to chromatin is highly cell type specific 36 and is dynamic over time in the same cell type 38, 39 .…”

Wnt regulates amino acid transporter Slc7a5 and so constrains the integrated stress response in mouse embryos

“…If this were the case, we would expect Slc7a5 to be lost in embryos in which the b-catenin downstream transcription factors Sp5 and Sp8 are mutated, as these embryos also fail to form paraxial mesoderm [69]. Indeed, available ChIP-seq data show that while Sp5 and Sp8 bind to early mesodermal genes, they do not target Slc7a5 in differentiating mouse ESCs [70]. This finding indicates that Slc7a5 expression in the neural tube does not depend on signals from the newly formed paraxial mesoderm and further that Slc7a5 is regulated by b-catenin downstream transcription factors other than Sp5 and Sp8.…”