Author ORCID Identifier
Date of Award
2026
Document Type
Thesis (Ph.D.)
Department or Program
Molecular and Systems Biology
First Advisor
Yashi Ahmed
Abstract
The Wnt/β-catenin signaling pathway is an evolutionarily conserved pathway that regulates embryonic development, tissue homeostasis, and regeneration. Dysregulation of Wnt signaling contributes to the initiation and progression of multiple human diseases, most notably colorectal cancer. Post-translational regulation, particularly ubiquitin-mediated protein modification, plays a critical role in controlling pathway activity. However, how distinct E3 ubiquitin ligases regulate Wnt signaling at multiple levels remain incompletely understood.
This thesis investigates the role of ubiquitin ligases in regulating Wnt/β-catenin signaling using biochemical, cellular, and in vivo approaches in human cell lines, zebrafish embryos, mouse intestinal organoids, and Drosophila melanogaster. The studies identify multiple ubiquitin ligase-dependent mechanisms that promote Wnt/Wingless pathway activity.
The first part of this thesis identifies the E3 ubiquitin ligase TRIP12 as a conserved positive regulator of Wnt signaling. TRIP12 is required for Wnt-dependent transcription downstream of the β-catenin destruction complex and does not affect β-catenin protein levels. TRIP12 interacts with and ubiquitinates the SWI/SNF chromatin remodeling complex catalytic subunit BRG1. TRIP12-mediated ubiquitination does not alter BRG1 stability but enhances the interaction between BRG1 and β-catenin in a Wnt-dependent manner, thereby promoting transcription of Wnt target genes.
In addition, TRIP12 may regulate the abundance of specific SWI/SNF components in vivo. Loss of TRIP12 increases PBRM1/Polybromo levels in the larval wing disc, while PBRM1/Polybromo depletion reduces expression of the Wingless target gene senseless, indicating that TRIP12 modulates Wnt signaling through multiple chromatin-associated mechanisms.
The second part of this thesis examines how Wnt/Wingless signaling regulates the CRL4CRBN ubiquitin ligase complex to control the stability of Casein Kinase 1 alpha (CK1α), a negative regulator of the β-catenin destruction complex. Although CK1α was previously identified as a neosubstrate of CRBN in the context of immunomodulatory drugs, studies demonstrate that CK1α also undergoes ubiquitin-dependent degradation under physiological Wnt signaling conditions. Loss-of-function analysis shows that CRL4 core components are required for Wnt/Wingless pathway activity and CRBN-dependent regulation of CK1α, supporting a model in which Wnt/Wingless signaling promotes destruction complex inhibition through regulated activation of CRL4CRBN E3 ligase complex.
Finally, this thesis identifies additional CRL4 substrate receptors involved in Wingless signaling. An in vivo loss-of-function screen targeting conserved DDB1-CUL4- associated factors (DCAFs) in Drosophila identifies multiple DCAFs required for pathway activity in distinct tissues, indicating that CRL4 complexes regulate Wingless signaling through multiple substrate receptors.
Together, these studies define multiple ubiquitin ligase-dependent mechanisms that positively regulate Wnt/β-catenin signaling and expand current understanding of ubiquitin-mediated control of Wnt pathway activity.
Recommended Citation
Yuan, Kai, "Ubiquitin Ligase-Mediated Regulation of Wnt/β-Catenin Signaling" (2026). Dartmouth College Ph.D Dissertations. 472.
https://digitalcommons.dartmouth.edu/dissertations/472
