Abstract P015: Mechanisms of mitochondrial dysfunction in development of mismatch repair-deficient endometrial cancer
Authors: Moreno Diana L. , Borthwick Mikayla S. , Peralta Leah , Chan Wai Kin , Melendez Brenda , Zhang Qian , Gokul Nisha , Yates Melinda S. 
Published: January 2023

Abstract
Background: Lynch syndrome (LS) is a hereditary cancer syndrome carrying roughly 60% lifetime risk of endometrial cancer (EC) development. LS-EC is caused by mutations in mismatch repair genes (most commonly MSH2), which lead to DNA repair deficiency and hypermutability. Identifying mechanisms that impact cancer development could provide novel opportunities for EC prevention. Our recent studies in Msh2-deficient mice identified mitochondrial dysfunction in EC pathogenesis. The objective of this study is to define the impact of MSH2 loss on mitochondrial function and oxidative DNA damage to identify targets for EC prevention. We hypothesized that MSH2 loss disrupts mitochondrial function and increases oxidative DNA damage in EC cells. Methods: The effects of MSH2 loss on EC pathogenesis were evaluated using our novel mouse model for EC development (PR-Cre+Msh2flox/flox, abbreviated Msh2KO) and primary cell lines derived from this model. Mitochondrial stress tests (MSTs) compared mitochondrial function in murine and human MSH2-deficient and -intact EC cell lines. Western blots compared mitochondrial protein expression between cell lines. Transcriptomic data of human ECs from The Cancer Genome Atlas (TCGA) were probed using cBioPortal. To examine direct effects of MSH2 loss on oxidative stress and mitochondrial function, we performed lentiviral shRNA knockdown (KD) of MSH2 in two human EC cell lines (KLE, Hec1a) and MSH2 overexpression (MSH2++) in MFE280 cells. MSTs and Western blots were utilized as above. Immunofluorescent staining compared oxidative DNA damage in MSH2-KD, MSH2++, and control cell lines after pharmacologically induced oxidative stress via H2O2. RESULTS Transcriptomic signatures of histologically normal endometrium and EC from Msh2KO mice versus control mice reveal mitochondrial dysfunction as a key aberrant pathway. MSTs show reduced baseline and induced mitochondrial function in murine and human MSH2-deficient EC cells compared to MSH2-intact (p&lt;0.0001). Western blots show that MSH2-deficient EC cells exhibit loss of mitochondrial complex II compared to MSH2-intact cells (p&lt;0.05). TCGA data confirm MSH2-deficient human ECs have reduced complex II subunits (p&lt;0.05). Isogenic in vitro studies show MSH2-KD reduces complex II expression yet has variable effects on mitochondrial function. MSH2 overexpression increases complex II expression and mitochondrial function. Oxidative DNA damage did not differ at baseline, but H2O2-induced DNA damage increased after MSH2-KD in one of two cell lines. Conclusions: MSH2 and complex II loss are strongly associated in EC. Further studies on the downstream effects of complex II loss are necessary to determine the contribution to LS-EC development. Complex II loss could result in disruptions to oxidative phosphorylation, the citric acid cycle, metabolic reprogramming, and oncometabolite production. Defining direct effects of MSH2 loss on these potential cancer susceptibility mechanisms will open new avenues for LS-associated EC prevention.
Citation Format: Diana L. Moreno, Mikayla S. Borthwick, Leah Peralta, Wai Kin Chan, Brenda Melendez, Qian Zhang, Nisha Gokul, Melinda S. Yates. Mechanisms of mitochondrial dysfunction in development of mismatch repair-deficient endometrial cancer. [abstract]. In: Proceedings of the AACR Special Conference: Precision Prevention, Early Detection, and Interception of Cancer; 2022 Nov 17-19; Austin, TX. Philadelphia (PA): AACR; Can Prev Res 2023;16(1 Suppl): Abstract nr P015.