Abstract 3040: The eIF2 kinase GCN2 controls expression of key amino acid transporters and is critical for prostate cancer growth and progression
Authors: Cordova Ricardo , Misra Jagannath , Damayanti Nur P. , Amin Parth H. , Carlson Kenneth R. , Klunk Angela J. , Mirek Emily T. , Miller Marcus J. , Anthony Tracy G. , Pili Roberto , Wek Ronald C. , Staschke Kirk A. 
Published: June 2022

Abstract
The Integrated Stress Response (ISR) is central for adaptation and survival of tumor cells in response to exogenous and endogenous stresses. The ISR features a family of protein kinases that phosphorylate the eukaryotic translation initiation factor eIF2 in response to distinct stresses. While phosphoryation of eIF2 reduces global protein synthesis, there is paradoxical induced translation of select stress adapative gene transcripts, including ATF4, which is central for ISR-directed gene transcription. Therefore, the ISR directs translational and transcriptional control that is critical for cancer adaptation to stress. Recently, eIF2 phosphorylation and ATF4 were suggested to play a role in prostate cancer (PCa) growth and survival; however, the specific function of ISR kinase(s), its mode of activation, and mechanisms by which the ISR facilitate PCa progression are not known.We discovered that the eIF2 kinase GCN2 (EIF2AK4) is activated in a range of PCa cell lines, contributing to enhanced eIF2 phosphorylation and ATF4 expression. Genetic or pharmacological inhibition of GCN2 reduced growth in androgen-sensitive and castration-resistant PCa cell lines in culture and cell line-derived and patient-derived xenograft mouse models in vivo. Induction of GCN2 is accompanied by limitations of select amino acids and accumulation of cognate tRNAs that are reported to be activators of GCN2. A transcriptome analysis of PCa cells treated with a specific small molecular inhibitor of GCN2 indicates that this eIF2 kinase was critical for expression of multiple SLC genes, including amino acid transporters previously implicated in different cancers. We determined that GCN2 inhibition decreases intracellular amino acid levels, and reduced aminoacylation of select tRNAs, accounting for reduced growth in PCa cells. Using CRISPR-based phenotypic screens and genome-wide gene expression analyses of control and GCN2-depleted PCa cells, we confirmed the importance of the transporter genes in PCa fitness. One transporter, SLC3A2 (4F2), is a key SLC gene induced by GCN2 and is essential for PCa proliferation. SLC3A2 has been reported to associate with many SLC7 family transporters, allowing for the localization of these transporters to the plasma membrane for amino acid uptake. Of importance, expression of SLC3A2 partially restored amino acid levels and growth due to loss of GCN2. Our results indicate that select amino acid limitations activate GCN2 in PCa, resulting in the upregulation of key amino acid transporters, including SLC3A2, which provides for nutrient import to facilitate protein synthesis and metabolism required for PCa progression. We conclude that GCN2 and the ISR are promising new therapeutic targets for the treatment of PCa.
Citation Format: Ricardo Cordova, Jagannath Misra, Nur P. Damayanti, Parth H. Amin, Kenneth R. Carlson, Angela J. Klunk, Emily T. Mirek, Marcus J. Miller, Tracy G. Anthony, Roberto Pili, Ronald C. Wek, Kirk A. Staschke. The eIF2 kinase GCN2 controls expression of key amino acid transporters and is critical for prostate cancer growth and 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 3040.