尿素循环
mTORC1型
谷氨酰胺
谷氨酰胺合成酶
癌变
高氨血症
生物
癌症研究
化学
生物化学
氨基酸
信号转导
基因
PI3K/AKT/mTOR通路
精氨酸
作者
Weiwei Dai,Jianliang Shen,Junrong Yan,Alex J. Bott,Sara Maimouni,Heineken Q. Daguplo,Yujue Wang,Khoosheh Khayati,Jessie Yanxiang Guo,Lanjing Zhang,Yongbo Wang,Alexander J. Valvezan,Wen‐Xing Ding,Xin Chen,Xiaoyang Su,Shu‐Qin Gao,Wei‐Xing Zong
摘要
Glutamine synthetase (GS) catalyzes de novo synthesis of glutamine that facilitates cancer cell growth. In the liver, GS functions next to the urea cycle to remove ammonia waste. As a dysregulated urea cycle is implicated in cancer development, the impact of GS's ammonia clearance function has not been explored in cancer. Here, we show that oncogenic activation of β-catenin (encoded by CTNNB1) led to a decreased urea cycle and elevated ammonia waste burden. While β-catenin induced the expression of GS, which is thought to be cancer promoting, surprisingly, genetic ablation of hepatic GS accelerated the onset of liver tumors in several mouse models that involved β-catenin activation. Mechanistically, GS ablation exacerbated hyperammonemia and facilitated the production of glutamate-derived nonessential amino acids, which subsequently stimulated mechanistic target of rapamycin complex 1 (mTORC1). Pharmacological and genetic inhibition of mTORC1 and glutamic transaminases suppressed tumorigenesis facilitated by GS ablation. While patients with hepatocellular carcinoma, especially those with CTNNB1 mutations, have an overall defective urea cycle and increased expression of GS, there exists a subset of patients with low GS expression that is associated with mTORC1 hyperactivation. Therefore, GS-mediated ammonia clearance serves as a tumor-suppressing mechanism in livers that harbor β-catenin activation mutations and a compromised urea cycle.
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