Abstract 3781: Expression of ovarian cancer specific Drp1 splice variants regulate mitochondrial heterogeneity and cell plasticity during tumor progression
Authors: Javed Zaineb , Shin Dong-Hui , Pan Weihua , Elhaw Amal Taher , Tang Priscilla , Phaeton Rebecca , Trebak Mohamed , Walter Vonn , Hempel Nadine 
Published: June 2022

Abstract
Mitochondrial shape is integral for its proper function and is maintained by a dynamic balance between the events of fission and fusion. Hence, a disruption in the balance is detrimental and has been associated with multiple pathologies including tumorigenesis. We noticed significant heterogeneity in mitochondrial morphology and function in ovarian cancer, which remains the deadliest gynecologic malignancy to date. We discovered that heterogenous mitochondrial dynamics in ovarian cancer cells were associated with specific transcript variant signatures of the fission protein Drp1 (encoded by the gene DNM1L), the primary GTPase responsible for mitochondrial fission. While several Drp1 splice variants have been reported, few studies have linked expression and potential interplay of splice variants of Drp1 on mitochondrial dynamics and function with pathophysiology especially in ovarian cancer. We used 3’RACE, western blotting and LC-MS/MS proteomics analysis to establish the identity of the major Drp1 splice variants expressed in ovarian cancer. We found ovarian cancer cell lines as well as patient-ascites derived cells, predominantly express two Drp1 variants: a transcript including both exons 16 and 17 (16/17) and a transcript lacking exon 16 (-/17). We also validated our findings in TCGA ovarian cancer specimens by analyzing Drp1 splice variant transcripts following annotation of TCGA raw RNAseq data and Salmon expression analysis. Our TCGA analysis of these variants highlighted significant difference in overall survival of ovarian cancer patients. Samples with high Drp1(-/17) expression were associated with poorer overall survival compared to those predominantly expressing Drp1(16/17). Furthermore, carrying out gene set enrichment analysis (GSEA) on TCGA specimens split by high expression of these two variants showed enrichment of distinct gene expression signatures. Overexpression and splice variant specific siRNA knockdown studies demonstrated that Drp1 variants have unique localization and effects on mitochondrial morphology and function. Furthermore, metabolic profiling and 13C metabolic flux analysis highlighted variant specific alterations in mitochondrial metabolic pathways and the TCA cycle. Drp1(-/17) expression enhanced mitochondrial respiratory function and as previously shown, Drp1(-/17) associated with both mitochondria and microtubules, potentially implying a more regulated fission activity as a consequence of controlled subcellular localization. Additionally, Drp1(-/17) was enriched and associated with quiescent phenotype compared to more proliferative phenotype of Drp1(16/17). Hence, expression of distinct Drp1 splice variants may be a novel mechanism to regulate mitochondrial fission, and integral to ovarian cancer cell plasticity under different selection pressures during tumor progression.
Citation Format: Zaineb Javed, Dong-Hui Shin, Weihua Pan, Amal Taher Elhaw, Priscilla Tang, Rebecca Phaeton, Mohamed Trebak, Vonn Walter, Nadine Hempel. Expression of ovarian cancer specific Drp1 splice variants regulate mitochondrial heterogeneity and cell plasticity during tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3781.