Date of Award

January 2023

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Mustafa Khokha

Abstract

Wnt signaling is essential for embryonic development and adult tissue homeostasis; mutations in Wnt pathway components are major drivers of multiple diseases especially cancer. β-catenin is a key effector in this pathway that translocates into the nucleus and activates Wnt responsive genes. However, due to our lack of understanding of β-catenin nuclear transport, therapeutic modulation of Wnt signaling has been challenging. Here, we took an unconventional approach to address this long-standing question by exploiting a heterologous model system, the budding yeast Saccharomyces cerevisiae, which contains a conserved nuclear transport machinery. In contrast to prior work, we demonstrate that β-catenin accumulates in the nucleus in a Ran dependent manner, suggesting the use of a nuclear transport receptor (NTR). Indeed, a systematic and conditional inhibition of NTRs revealed that only Kap104, the orthologue of Kap-β2/Transportin-1 (TNPO1), was required for β-catenin nuclear import. We further demonstrate direct binding between TNPO1 and β-catenin that is mediated by a conserved amino acid sequence that resembles a PY NLS. Finally, using Xenopus secondary axis and TCF/LEF reporter assays, we demonstrate that our results in yeast can be directly translated to vertebrates. By elucidating the NLS in β-catenin and its cognate NTR, our study provides new therapeutic targets for a host of human diseases caused by excessive Wnt signaling. Indeed, we demonstrate that a small chimeric peptide designed to target TNPO1 can reduce Wnt signaling as a first step towards therapeutics.

Comments

This is an Open Access Thesis.

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