Abstract 283: AHCYL1 is crucial for NRAS mutant-expressing melanoma tumor growth by governing ER calcium homeostasis
Authors: Cai Chufan , Tu Jiayi , Najarro Jeronimo , Zhang Rukang , Gao Xue , Fan Hao , Zhang Freya , Li Jiacheng , Ciboddo Michele , Elf Shannon , Wu Rong , Chen Jing 
Published: April 2023

Abstract
Cancer cells apply metabolic adaptations for proliferation and survival such as the Warburg Effect and the maintenance of redox balance, which are common for different cancer types. However, it remains elusive whether different cancer oncogenic backgrounds require oncogene-specific metabolic adaptations, which could represent unique cancer vulnerabilities for novel therapy development. Herein we report that, using a shRNA library designed to target a subset of genes related to cell metabolism, we identified adenosylhomocysteinase like 1 (AHCYL1) as a “synthetic lethal” partner of oncogenic NRAS mutations, which is selectively important for the proliferation and survival of NRAS mutant-expressing melanoma cells, but not for cells harboring BRAF mutations. AHCYL1 is an inhibitory binding partner of endoplasmic reticulum (ER) calcium channel protein inositol trisphosphate receptor (IP3R) by competing off its agonist inositol triphosphate (IP3) and consequently blocking ER calcium release. In consonance with our finding, AHCYL1 expression levels correlate with mutational status of NRAS but not with BRAF in diverse human melanoma cell lines. In addition, exogenous expression of mutant NRAS but not BRAF in immortal melanocytes MEL-ST cells results in upregulated AHCYL1 transcription and protein expression. Notably, these findings are consistent with the results of Cancer Genome Atlas (TCGA) database analysis, which reveal elevated AHCYL1 transcription in melanoma patients harboring NRAS mutations but not BRAF V600E mutation. Further transcription factor screening studies suggested that the transcription of AHCYL1 is regulated by activating transcription factor 2 (ATF2), which is supported by TCGA database analysis results showing that ATF2 transcription level is selectively higher in NRAS-mutant melanoma patients. Furthermore, AHCYL1-deficiency by shRNA-mediated knockdown and CRISPR/Cas9-mediated knockout significantly reduces in vitro cell proliferation and in vivo tumor growth potential of NRAS mutant-expressing melanoma cells, but not for control melanoma cells expressing BRAF V600E mutant. Mechanistically, AHCYL1 deficiency in NRAS mutant-expressing melanoma cells triggers calcium leakage from the ER, leading to sustained activation of the ER unfolded protein response (UPR) that subsequently attenuates cell proliferation and initiates apoptosis. Altogether, these findings suggest a positive feedback mechanism by which mutant NRAS enhances AHCYL1 expression that contributes to NRAS mutation-dependent melanoma transformation and tumor growth. The AHCYL1-IP3R axis may represent a novel therapeutic target for treatment of NRAS mutant-expressing tumors including melanoma.
Citation Format: Chufan Cai, Jiayi Tu, Jeronimo Najarro, Rukang Zhang, Xue Gao, Hao Fan, Freya Zhang, Jiacheng Li, Michele Ciboddo, Shannon Elf, Rong Wu, Jing Chen. AHCYL1 is crucial for NRAS mutant-expressing melanoma tumor growth by governing ER calcium homeostasis [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 283.