Biology subjects

Cadigan, K. M.

Publications and source records attributed to Cadigan, K. M..

4 recordsLinked to original sources

bioRxiv2024

Semaphorin Receptors Antagonize Wnt Signaling Through Beta-Catenin Degradation

Precise control of morphogen signaling levels is essential for proper development. An outstanding question is: what mechanisms ensure proper morphogen activity and correct cellular responses? Previous work has identified Semaphorin (SEMA) receptors, Neuropilins (NRPs) and Plexins (PLXNs), as positive regulators of the Hedgehog (HH) signaling pathway. Here, we provide evidence that NRPs and PLXNs antagonize Wnt signaling in both fibroblasts and epithelial cells. Further, Nrp1/2 deletion in fibroblasts results in elevated baseline Wnt pathway activity and increased maximal responses to Wnt stimulation. Notably, and in contrast to HH signaling, SEMA receptor-mediated Wnt antagonism is independent of primary cilia. Mechanistically, PLXNs and NRPs act downstream of Dishevelled (DVL) to destabilize {beta}-catenin (CTNNB1) in a proteosome-dependent manner. Further, NRPs, but not PLXNs, act in a GSK3b/CK1-dependent fashion to antagonize Wnt signaling, suggesting distinct repressive mechanisms for these SEMA receptors. Overall, this study identifies SEMA receptors as novel Wnt pathway antagonists that may also play larger roles integrating signals from multiple inputs.

developmental biology↗

bioRxiv2023

Beta-catenin-mediated activation of Wnt target genes utilizes a biomolecular condensate-dependent mechanism

The Wnt/{beta}-catenin signaling pathway plays numerous, essential roles in animal development and tissue/stem cell maintenance. The activation of genes regulated by Wnt/{beta}-catenin signaling requires the nuclear accumulation of {beta}-catenin, a transcriptional co-activator. {beta}-catenin is recruited to many Wnt-regulated enhancers through direct binding to T-cell factor/Lymphoid enhancer factor (TCF/LEF) family transcription factors. {beta}-catenin has previously been reported to form phase-separated biomolecular condensates (BMCs), which was implicated as a component of {beta}-catenins mechanism of action. This function required aromatic amino acid residues in the intrinsically disordered regions (IDRs) at the N- and C-termini of the protein. In this report, we further explore a role for {beta}-catenin BMCs in Wnt target gene regulation. We find that {beta}-catenin BMCs are miscible with LEF1 BMCs in vitro. We characterized a panel of {beta}-catenin mutants with different combinations of aromatic residue mutations in human cell culture and Drosophila melanogaster. Our data support a model in which aromatic residues across both IDRs contribute to BMC formation in vitro and signaling activity in vivo. Although different Wnt targets have different sensitivities to loss of {beta}-catenins aromatic residues, the activation of every target examined was compromised by aromatic substitution. These mutants are not defective in nuclear import, and residues in the N-terminal IDR with no previously known role in signaling are clearly required for the activation of various Wnt readouts. Consistent with this, deletion of the N-terminal IDR results in a loss of signaling activity, which can be rescued by the addition of heterologous IDRs enriched in aromatic residues. Overall, our work supports a model in which the ability of {beta}-catenin to form biomolecular condensates in the nucleus is tightly linked to its function as a transcriptional co-regulator.

molecular biology↗

bioRxiv2022

SOX9 binds TCFs to mediate Wnt/β catenin target gene activation

Activation of the Wnt/{beta}-catenin pathway regulates gene expression by promoting the formation of a {beta}-catenin-TCF complex on target gene chromatin. The transcription factor SOX9 antagonises Wnt signalling in many contexts through its ability to down-regulate {beta}-catenin protein levels. Here, we find that SOX9 promotes the proliferation of Wnt-driven colorectal cancer (CRC) cells. We identify multiple enhancers activated by SOX9 working in concert with the Wnt pathway. These enhancers are co-occupied by TCFs and SOX9 and contain TCF and SOX9 binding sites that are necessary for transcriptional activation. In addition, we identify a physical interaction between the DNA-binding domains of TCFs and SOX9 and show that TCF-SOX9 interactions are important for target gene regulation and CRC cell growth. Our work demonstrates a highly context-dependent effect of SOX9 on Wnt targets, with activation or repression being dependent on the presence or absence of SOX9 binding sites on Wnt-regulated enhancers respectively.

cancer biology↗

bioRxiv2021

Wnt-responsive enhancer regulation in mammals by a CDX/TCF transcription factor collective and a novel DNA sequence motif

Transcriptional regulation by Wnt signalling is primarily thought to be accomplished by a complex of {beta}-catenin and TCF family transcription factors (TFs). Although numerous studies have suggested that additional TFs play roles in regulating Wnt target genes, their mechanisms of action have not been investigated in detail. We characterised a Wnt-responsive element (WRE) downstream of the Wnt target gene Axin2 and found that TCFs and Caudal-related homeodomain (CDX) proteins were required for its activation. Using a new separation-of-function TCF mutant, we found that WRE activity requires the formation of a TCF/CDX complex. Our systematic mutagenesis of this enhancer identified other sequences essential for activation by Wnt signalling, including several copies of a novel CAG DNA motif. Computational and experimental evidence indicates that the TCF/CDX/CAG mode of regulation is prevalent in multiple WREs. Put together, our results demonstrate the complex nature of cis- and trans- interactions required for signal-dependent enhancer activity.

genetics↗