Author ORCID Identifier

https://orcid.org/0009-0007-9573-745X

Date Available

10-1-2025

Year of Publication

2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Medicine

Department/School/Program

Toxicology and Cancer Biology

Faculty

Dr. Eva Goellner

Faculty

Dr. Isabel Mellon

Abstract

The DNA mismatch repair (MMR) pathway identifies and corrects misincorporations that arise during DNA replication. MMR is a pathway that is critical for maintaining genomic stability. Mutations within the MMR pathway, both germline and somatic, lead to the development of cancer. There are a variety of mechanisms that regulate the MMR pathway including protein-protein interactions, DNA damage response, and post-translational modifications. In this study, we aim to dive deeper into each of these mechanisms to obtain novel information regarding the mechanisms and regulation of human DNA MMR. In this study we generated hExo1 constructs mutating Exo1’s interactions with MSH2 and MLH1 to analyze the effect of protein-protein interactions on MMR ability. We found that alteration of the Exo1-MSH2 interaction sites leads to a developed survival resistance following alkylation damage, causes alterations in the DNA damage response pathway, and hinders cGAS-STING pathway activation. We also uncovered that hExo1 has an additional binding site compared to the two binding sites previously uncovered in S. cerevisiae Exo1. It is known that Exo1 excision leads to activation of PARP to allow for downstream DNA damage response activation. To take a closer look into how this is occurring, we investigated how PARP inhibition paired with alkylation exposure affected cellular metabolomics. We found that PARP inhibition led to a decrease in oxidative respiration, but only when MSH2 was present within the cells suggesting that MSH2 is playing a key role in the DDR pathway and metabolic switching. In the final portion of this study, we found that ABL1 is responsible for phosphorylation of MLH1, allowing for enhanced protein stability. Treatment of cells with tyrosine kinase inhibitors (TKIs) caused a decrease in MLH1 protein expression that was significant enough to disrupt overall MMR ability. We found that this disruption of MMR stimulated an induced microsatellite instability which we proposed could be used to induce more favorable outcomes in metastatic melanoma patients who have become immunotherapy resistant by making these tumors immune hot. At the conclusion of this study, we have gained multiple valuable insights into the MMR pathway and its mechanisms of regulation. We have displayed the importance of gaining a deeper understanding of these mechanisms and how slight alterations within the pathway can have numerous downstream effects. Our hope is that these findings can be applied to improve outcomes in patients of various cancer types.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.08

Funding Information

  • NIEHS R00ES026653

  • COBRE P20GM121327

  • P30 UK CARES Career Development

  • Markey Women Strong Distinguished Researcher Award

  • Phi Beta Psi – Cancer Research Grant

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Available for download on Wednesday, October 01, 2025

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