Glutamine synthetase limits β-catenin–mutated liver cancer growth by maintaining nitrogen homeostasis and suppressing mTORC1
Weiwei Dai, … , Shenglan Gao, Wei-Xing Zong
Weiwei Dai, … , Shenglan Gao, Wei-Xing Zong
Published October 18, 2022
Citation Information: J Clin Invest. 2022;132(24):e161408. https://doi.org/10.1172/JCI161408.
View: Text | PDF
Research Article Hepatology Metabolism

Glutamine synthetase limits β-catenin–mutated liver cancer growth by maintaining nitrogen homeostasis and suppressing mTORC1

Abstract

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.

Authors

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 Valvezan, Wen-Xing Ding, Xin Chen, Xiaoyang Su, Shenglan Gao, Wei-Xing Zong

×

Figure 8

Inhibition of GPT1 suppresses HCC development in Glul-KO livers.

Options: View larger image (or click on image) Download as PowerPoint
Inhibition of GPT1 suppresses HCC development in Glul-KO livers. (A–D) G...
(A–D) Glul-KO mice were injected with c-Met/ΔN90-β-catenin, together with sgCtrl (n = 8) or sgGpt1 (n = 10) plasmids, via SB-HTVI. Mice were sacrificed 6 weeks later (endpoint of the sgCtrl mice). (A) Successful GPT1 knockdown. (B) Representative gross liver images (n = 8–10). (C) Liver/body weight ratios (n = 8–10). (D) Liver tissues were stained with H&E and by IHC and IF. Note that while sgCtrl mice developed full-blown tumors that were positive for both GPT1 and β-catenin, sgGpt1 mice showed smaller tumor nodules with reduced GPT1 expression and low p-S6 (S235/236) despite high β-catenin expression. Scale bars: 50 μm (left panels), 100 μm (right panels). (E–I) Glul-KO male mice were injected with c-Met/ΔN90-β-catenin/SB10. On the same day, half of each group of mice were i.p. injected with β-CLA (20 mg/kg; 3 times per week), while the other half received PBS. (E) Two weeks later, mice were i.p. injected with 5 mmol/kg 15N-NH4Cl and sacrificed after 30 minutes. Total labeled and unlabeled metabolite ion counts for Glu and Ala were determined by LC-MS. (F–I) Mice were sacrificed 6 weeks later (endpoint of PBS-treated mice). (F) Representative gross liver images. (G) Liver/body weight ratios (n = 5 or 6). (H) Immunoblotting of liver lysates. (I) Liver tissue H&E and IHC. Scale bars: 50 μm. *P < 0.05; ****P < 0.0001 by 2-tailed t test (C, E, and G).