Biology subjects

Sweasy, J.

Publications and source records attributed to Sweasy, J..

3 recordsLinked to original sources

bioRxiv2026

DNA Polymerase Beta Catalytic and Fidelity Mutations Drive Platinum Specific Drug Sensitivity

With the advent of genome sequencing and its widespread use in the clinic, there is a great need to identify mutational biomarkers that predict therapeutic responses. DNA polymerase Beta (Pol{beta}) and the base excision repair (BER) pathway have been previously implicated as modulators of response to platinum-based chemotherapies and are mutated in as high as 30% of cancers. Here, we show in a triple-negative breast cancer (TNBC) model that two classes of mutations in Pol{beta}, reduced catalytic activity (E295K and D256A mutation) and reduced fidelity (I260M), are sufficient to drive cisplatin and carboplatin-specific sensitivity. Cellular response to oxaliplatin in these Pol{beta} mutant models is minimal relative to cisplatin and carboplatin. Additionally, we show that sensitivity is associated with reduced repair of both platinum-induced DNA intrastrand adducts and interstrand crosslinks (ICLs). Downregulation of the upstream BER factor uracil DNA glycosylase (UNG) reverses drug sensitivity consistent with these Pol{beta} mutations negatively impacting ICL DNA repair to drive drug sensitivity. In addition, intrastrand adduct repair readout indicates these lesions also play a role in the sensitivity observed in Pol{beta} mutant models. In vivo studies demonstrate a significant effect on tumor growth delay with cisplatin treatment in tumor xenografts harboring Pol{beta} mutations. These results support the potential for using Pol{beta} mutations as predictive biomarkers for cisplatin and carboplatin therapies in the clinical setting.

Cancer Biology↗

bioRxiv2021

Mutational signature profiling classifies subtypes of clinically different mismatch repair deficient tumors with a differential immunogenic response potential

BackgroundMismatch repair (MMR) deficiency is the hallmark of tumors from Lynch syndrome (LS), sporadic MLH1 hypermethylated, and Lynch-like syndrome (LLS), but there is a lack of understanding of the variability in their mutational profiles based on clinical phenotypes. The aim of this study was to perform a molecular characterization to identify novel features that can impact tumor behavior and clinical management. MethodsWe tested 105 MMR-deficient colorectal cancer tumors (25 LS, 35 LLS, and 45 sporadic) for global exome microsatellite instability, cancer mutational signatures, mutational spectrum and neoepitope load. Results78% of tumors showed high contribution of MMR-deficient mutational signatures, high level of global exome microsatellite instability, loss of MLH1/PMS2 protein expression and included sporadic tumors. 22% of tumors showed weaker features of MMR deficiency, 73% lost MSH2/MSH6 expression and included half of LS and LLS tumors. Remarkably, 9% of all tumors lacked global exome microsatellite instability. Lastly, HLA-B07:02 could be triggering the neoantigen presentation in tumors that show the strongest contribution of MMR-deficient tumors. ConclusionsNext-generation sequencing approaches allow for a granular molecular characterization of MMR-deficient tumors, which can be essential to properly diagnose and treat patients with these tumors in the setting of personalized medicine.

genomics↗

bioRxiv2018

DNA polymerase β fingers movement revealed by single-molecule FRET suggests a partially closed conformation as a fidelity checkpoint

The eukaryotic DNA polymerase {beta} plays an important role in cellular DNA repair as it fills gaps in single nucleotide gapped DNA that result from removal of damaged bases. Since defects in DNA repair may lead to cancer and genetic instabilities, Pol {beta} has been extensively studied, especially substrate binding and a fidelity-related conformational change called \"fingers closing\". Here, we applied single-molecule Forster resonance energy transfer to study the conformational dynamics of Pol {beta}. Using an acceptor labelled polymerase and a donor labelled DNA substrate, we measured distance changes associated with DNA binding and fingers movement. Our findings suggest that Pol {beta} does not bend its gapped DNA substrate to the extent related crystal structures indicate: instead, bending seems to be significantly less profound. Furthermore, we visualized dynamic fingers closing in single Pol {beta}-DNA complexes upon addition of complementary nucleotides and derived rates of conformational changes. Additionally, we provide evidence that the fingers close only partially when an incorrect nucleotide is bound. This \"ajar\" conformation found in Pol {beta}, a polymerase of the X-family, suggests the existence of an additional fidelity checkpoint similar to what has been previously proposed for a member of the A-family, the bacterial DNA polymerase I.

biophysics↗