Abstract A53: Energetic regulation of the Cyclin E oncoprotein in mitochondria-dependent ovarian tumor initiating cells
Authors: Mitra Kasturi , Spurlock Brian 
Published: September 2020

Study Purpose: Ovarian tumor-initiating (stem) cells (ovTICs) contribute to EOC chemoresistance. Thus, understanding their vulnerabilities may reveal novel therapeutic strategies. Overactivation of the cell cycle regulator Cyclin E is linked to chemoresistance of a subpopulation of epithelial ovarian carcinoma (EOC). However, role of Cyclin E in ovTIC maintenance is not clear. Energetics of TICs are rewired and Cyclin E function is uniquely linked to energetics and metabolism, which has not been tested in EOC. In nontumorigenic models, we reported that protein levels of Cyclin E (and certain stem cell markers) are elevated by boost in mitochondrial energetics caused by repression of the mitochondrial fission protein, Drp1. In EOC cells, Drp1 repression elevates the functional ovTIC marker Aldh, while active ovTICsAldh+ is dependent on mitochondrial energetics unlike the bulk tumor cells (BTCs Aldh-). Moreover, ovTICAldh+ potency is higher in cells with higher mitochondrial transmembrane potential. Therefore, we are investigating how mitochondrial energetics modulated by Drp1 regulates Cyclin E for ovTIC maintenance, which may reveal energetic vulnerabilities of ovTICs.

Experimental Procedures: We sort 4 cell populations based on Aldh activity and mitochondrial membrane potential and then study mitochondrial and Cyclin E properties. Here, we use biochemical and cell biologic techniques, including our unique high-resolution microscopy-based techniques. We isolate mitochondria by biochemical cell fractionation. We manipulate genes by shRNA mediated knockdown.

Unpublished Data: First, we confirmed the existence of the Aldh+ cell population with higher or lower mitochondrial membrane potential in mouse xenografts and patient EOC cells, and also confirmed a noncanonical mitochondrial pool of Cyclin E in EOC cells and xenografts as we reported for other cells. Interestingly, chemoresistance related ovTICAldh+ enrichment happens with increase in Cyclin E protein levels only when Drp1 is repressed to allow boost in mitochondrial energetics. Indeed, Cyclin E levels are higher in isolated quiescent ovTICsAldh+ than the ovBTCs Aldh-. More importantly, activation of TIC properties maintains the elevated Cyclin E levels in the more potent ovTICsAldh+ with higher mitochondrial potential, but not in the less potent ovTICsAldh+ with lower mitochondrial potential. This Cyclin E dependence on mitochondrial energetics in ovTICsAldh+ may be the underlying mechanism of the attenuation of chemoresistance with mitochondrial inhibitors, as we observed.

Conclusions: We propose the novel concept that ovTICsAldh+ “primed” by Drp1 regulated mitochondrial energetics maintain elevated Cyclin E levels, which may involve mitochondrial translocation and release of Cyclin E. We speculate that inclusion of specific mitochondrial inhibitors in the chemotherapeutic regime may eliminate mitochondria dependent ovTICAldh+ that are maintained by mitochondria regulated Cyclin E.

Citation Format: Kasturi Mitra, Brian Spurlock. Energetic regulation of the Cyclin E oncoprotein in mitochondria-dependent ovarian tumor initiating cells [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A53.