Author ORCID Identifier
https://orcid.org/0000-0002-2594-0459
Date of Award
Spring 4-22-2026
Document Type
Thesis (Ph.D.)
Department or Program
Molecular and Systems Biology
First Advisor
Yashi Ahmed
Second Advisor
Arminja Kettenbach
Abstract
Wnt/β-catenin signaling is a fundamental developmental pathway that regulates tissue patterning and stem cell maintenance, and its dysregulation is implicated in numerous cancers. Central to Wnt signaling is the dynamic control of protein function by post-translational modifications (PTMs), including phosphorylation and ubiquitination. Herein, we use mass spectrometry-based proteomics and phosphoproteomics, Drosophila genetics, and confocal microscopy to investigate how the serine/threonine phosphatase PP2A-B56 regulates Wnt signaling. We identify a highly conserved B56 short linear motif (SLiM) on Axin that mediates their interaction and enables localized phosphatase activity within Wnt pathway components. Using quantitative phosphoproteomics, we mapped B56-regulated phosphorylation sites on Axin and its interactors and show that PP2A-B56 functions as a regulator of signaling precision by priming the phosphorylation states of Axin and GSK3 in a basal manner. Further, we demonstrate that Axin-bound GSK3 exists in a distinct dephosphorylated state compared to its global cellular pool, supporting a model of proteoform-specific regulation within signaling complexes. Leveraging a competitive B56 inhibitor in Drosophila, we further demonstrate that the function and regulatory mechanisms of Drosophila B56 orthologs Well-rounded (Wrd) and Widerborst (Wdb) are evolutionarily conserved. In addition, the work herein also used proximity labeling approaches to identify interactors of the E3 ubiquitin ligase TRIP12 and the serine/threonine kinase STK38, expanding the network of PTM-mediated regulation in Wnt signaling. Together, this work highlights how PTMs, and in particular the phosphatase PP2A-B56, regulate Wnt signaling.
Recommended Citation
Bunnag, Nawat, "Uncovering post-translational regulatory mechanisms in Wnt signaling" (2026). Dartmouth College Ph.D Dissertations. 506.
https://digitalcommons.dartmouth.edu/dissertations/506
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