Abstract 4818: GCN2 eIF2 kinase and p53 coordinate amino acid homeostasis and metabolism in prostate cancer
Authors: Cordova Ricardo A. , Sommers Noah R. , Klunk Angela J. , Mohiuddin Haroon M. , Pili Roberto , Wek Ronald C. , Staschke Kirk A. 
Published: April 2023

Abstract
Activation of the integrated stress response (ISR) contributes to the progression of many cancers, including prostate cancer (PCa). The ISR features a family of protein kinases that phosphorylate the eukaryotic translation initiation factor 2 (eIF2) during different stress conditions, resulting in repression of global protein synthesis. In parallel, eIF2 phosphorylation also enhances the translation of select gene transcripts, such as ATF4, which directs the transcription of ISR-target genes that are critical for cancer stress adaptation. We recently reported (Cordova et al., 2022 eLife) that the eIF2 kinase GCN2 is a driver of the ISR in PCa and is critical for the maintenance of essential amino acid (EAA) homeostasis. GCN2 is activated in PCa due to EAA limitations, resulting in increased expression of key amino acid transporters which provide for nutrient import to facilitate protein synthesis and metabolism that drive PCa proliferation. Genetic loss or pharmacological inhibition of GCN2 results in lowered expression of amino acid transporters, leading to severe depletion of intracellular essential amino acids and reduced proliferation in PCa cell lines and xenograft models. These results support the therapeutic potential of targeting GCN2 in PCa.We recently determined that loss of GCN2 in PCa triggers a G1 nutrient-sensitive cell cycle checkpoint that is dependent on p53 and its target gene CDKN1A, encoding p21 inhibitor of cell cycle. Induced G1 arrest and p53/p21 signaling by GCN2 inhibition is reversed by supplementation with EAAs, suggesting amino acid limitation is critical for activation of p53. Metabolic stresses, such as amino acid starvation, have been suggested to activate p53 in different cancers and p53 regulates metabolic pathways that are critical for cancer cells adaptation to stresses. We also showed that depletion of specific amino acids activates GCN2 and p53 in cultured PCa cells. Using transcriptomic and metabolomic analyses, we determined that loss of GCN2 or p53 in PCa cells impacted multiple metabolic pathways, specifically those involved in amino acid and nucleotide metabolism, supporting the importance of GCN2 and p53 in metabolic homeostasis. In addition, deletion of p53 in PCa cells exacerbates the activation of GCN2 and the ISR, suggesting that loss of p53 results in amino acid imbalances that further activate GCN2. Importantly, inhibition of GCN2 in combination with loss of p53 resulted in increased cell death and apoptosis in PCa. Our study suggests that GCN2 and p53 can be activated in parallel in PCa and these stress response pathways are crucial for PCa cells to maintain homeostasis and adapt to metabolic stress. We propose that GCN2 and p53 function to coordinate PCa growth and progression by regulating metabolism and cell cycle control. Targeting these stress pathways in combination may provide enhanced efficacy for the treatment of PCa.
Citation Format: Ricardo A. Cordova, Noah R. Sommers, Angela J. Klunk, Haroon M. Mohiuddin, Roberto Pili, Ronald C. Wek, Kirk A. Staschke. GCN2 eIF2 kinase and p53 coordinate amino acid homeostasis and metabolism in prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4818.