Abstract 2980: MIRO2/GCN1/ATF4 retrograde signaling modulates prostate cancer growth and invasion
Authors: Furnish Madison , Boulton Dillon , Genther Victoria , Grofova Denisa , Ellinwood Mitchell L. , Romero Lina , Lucia M. Scott , Cramer Scott D. , Caino M. Cecilia 
Published: June 2022

Abstract
Our understanding of the mechanisms that drive aggressiveness of metastatic prostate cancer (mPC) are limited. In this context, we aim to identify novel targets in mPC by focusing on key mitochondrial signaling pathways exploited by mPC. Here we identify a novel mitochondrial signaling pathway centered on mitochondrial Rho GTPase 2 (MIRO2). MIRO2 mRNA is upregulated in mPC compared to localized tumors, and higher MIRO2 levels are correlated with poor patient survival. Despite this association, the importance of MIRO2 in tumor cell biology has been overlooked. To address this, we examined MIRO2’s role in tumor cell-intrinsic phenotypes of relevance to metastatic potential. Using human cell lines that represent androgen-independent and -sensitive mPC, we showed that MIRO2 depletion impaired cell growth, colony formation, tumor cell invasion and migration, and tumor growth in mice. Next we reasoned that identifying MIRO2’s protein binding partners would shed light on the molecular function of MIRO2 in mPC. Network analysis of MIRO2’s binding partners identified metabolism, cell cycle, and cellular responses to extracellular stimuli amongst the top over-represented pathways. Interestingly, the top hit on our screen was General Control Non-derepressible 1 (GCN1). GCN1 was an essential gene for 90% of the cell lines in a large pan-cancer screen for gene essentiality. GCN1 is the upstream activator of the kinase GCN2, which senses amino acid availability, actin dynamics cues in cells, and regulates cell cycle progression. Our results showed that MIRO2 is necessary for efficient GCN2 signaling, activation of the integrated stress response, and downstream translation of the transcription factor ATF4 in culture and tumors in mice. Further, exogenous expression of ATF4 restored clonogenic growth of MIRO2 depleted cells. MIRO2 and GCN1 expression were positively correlated in mPC from patient cohorts, and GCN1 was overexpressed in mPC compared to primary PC. Further, MIRO2-GCN1 interacted in mPC cell lines and in primary PC cells. We showed activated GCN2 and HIF1α were positively correlated in tumors grown in mice. Together, the data suggest our pathway is important in nutrient limited regions of tumors. In conclusion, MIRO2 belongs to a novel protein network that controls mPC cellular responses and adaptation to extracellular stimuli. Overall, we propose a new mechanism by which a mitochondrial retrograde signal can drive prostate cancer cell growth.
Citation Format: Madison Furnish, Dillon Boulton, Victoria Genther, Denisa Grofova, Mitchell L. Ellinwood, Lina Romero, M. Scott Lucia, Scott D. Cramer, M. Cecilia Caino. MIRO2/GCN1/ATF4 retrograde signaling modulates prostate cancer growth and invasion [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 2980.