Abstract 1133: Mitochondria localized EGFRvIII promotes stemness through regulation of mitochondrial dynamics in glioblastoma stem cells
Authors: You Yeonhee , Hong Jun Hee , Yin Jinlong , Oh Young Taek , Kim Sung Soo , Park Jong Bae 
Published: August 2018

Purpose Changes in mitochondrial morphology have been linked with mitochondrial function and host cell homeostasis in many metabolic diseases. Cancer is increasingly perceived as metabolic disease, so understanding and regulating mitochondrial dynamics is of interest in cancer therapeutics. Recent studies indicate that distinct metabolic profile of cancer is dependent on genes that regulate the fusion and fission of mitochondria. Importantly, high levels of mitochondrial fission activity are common in cancer cell malignancy and in stem cell′s resistance to differentiation. Since these two phenotypes converge into cancer stem cells, investigating mitochondrial fission activity will provide hints to target cancer stem cell in therapeutics. Purpose of this study is to elucidate what regulates mitochondrial dynamics in cancer stem cells to sustain their stemness properties. In GBM, amplification of the oncogenic variant of EGFR, EGFRvIII, is associated with poor patient prognosis and has recently been known as the major contributor for stemness. Thus, we investigated the role of this oncogenic change in mitochondrial dynamics and stemness control in glioblastoma stem cells (GSCs). Methods Patient-derived GSCs were cultured and sorted by FACS based on tetramethylrhodamine ethyl ester (TMRE) dye emission level, which indicates mitochondrial membrane potential and functional activeness. The highest and the lowest TMRE groups each was collected and subject to further experiments. siRNA was used for loss-of-function study and lentivirus containing overexpression vector was used for gain-of-function study. In order to show the effect of EGFRvIII kinase activity inhibition, gefitinib and its derivative were used.

Results High TMRE GSCs showed stronger self-renewal ability in spheroid culture and higher levels of stemness marker Nestin, EGFRvIII, and mitochondrial fission regulator DRP1 expression than low TMRE GSCs. The high TMRE GSCs also showed more fragmented mitochondrial pattern, indicative of active mitochondrial fission. As underlying mechanism of EGFRvIII action on mitochondrial membrane potential, we figured out that EGFRvIII is localized at mitochondria. In order target mitochondria localized EGFRvIII, we used a gefitinib derivative which has mitochondria targeting moiety. This drug reduced mitochondrial membrane potential, self-renewal property, protein levels that regulate mitochondrial dynamics and less fragmented mitochondria, compared to gefitinib treated cells.

Conclusion EGFRvIII promotes self-renewal property of GSCs by translocating to mitochondria and upregulating mitochondrial membrane potential and fission-related protein levels. This finding highlights the role of mitochondrial dynamics as a mediator mechanism between tumor-specific oncogenic change and stem cell self-renewal ability.

Citation Format: Yeonhee You, Jun Hee Hong, Jinlong Yin, Young Taek Oh, Sung Soo Kim, Jong Bae Park. Mitochondria localized EGFRvIII promotes stemness through regulation of mitochondrial dynamics in glioblastoma stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1133.