Glutamate-ammonia ligase and reduction of G0 population in PANC-1 cells

The effect of bta-miR-1296 on the proliferation and extracellular matrix synthesis of bovine mammary fibroblasts

Mammary fibrosis in dairy cows is a chronic condition caused by mastitis, and can lead to serious culling of dairy cows resulting in huge economic losses in the dairy industry. MicroRNAs (miRNAs) exert an important role in regulating mammary gland health in dairy cows. This study investigated whether exosomal miRNAs in mammary epithelial cells can regulate the proliferation of bovine mammary fibroblasts (BMFBs) in mastitis. Liposome transfection technology was used to construct a cellular model of the overexpression and inhibition of miRNAs. The STarMir software, dual luciferase reporter gene test, real-time quantitative PCR (qRT-PCR), a Cell Counting Kit-8 (CCK-8), and a Western Blot and plate clone formation test were used to investigate the mechanism by which bta-miR-1296 regulates the proliferation of BMFBs. Target gene prediction results revealed that glutamate-ammonia ligase was a direct target gene by which bta-miR-1296 regulates cell proliferation. It was found that bta-miR-1296 significantly inhibited the proliferation of BMFBs. After BMFBs were transfected with a bta-miR-1296 mimic, mRNA expression in the extracellular matrix (ECM), α-smooth muscle actin (α-SMA), collagen type I alpha 1 chain (COL1α1) and collagen type III alpha 1 chain (COL3α1), and various cell growth factors (basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), and transforming growth factor-β1 (TGF-β1)) were down-regulated, and the expressions of α-SMA, COL1α1, COL3α1, phospho-extracellular regulated protein kinases, phospho-protein kinase B, TGF-β1, and phospho-Smad family member3 proteins were inhibited. In conclusion, bta-miR-1296 can inhibit the proliferation of BMFBs and the synthesis of ECM in BMFBs, thus affecting the occurrence and development of mammary fibrosis in dairy cows and laying the foundation for further studies to clarify the regulatory mechanism of mammary fibrosis.

GLUL stabilizes N-Cadherin by antagonizing β-Catenin to inhibit the progresses of gastric cancer

Glutamate-ammonia ligase (GLUL, also known as glutamine synthetase) is a crucial enzyme that catalyzes ammonium and glutamate into glutamine in the ATP-dependent condensation. Although GLUL plays a critical role in multiple cancers, the expression and function of GLUL in gastric cancer remain unclear. In the present study, we have found that the expression level of GLUL was significantly lower in gastric cancer tissues compared with adjacent normal tissues, and correlated with N stage and TNM stage, and low GLUL expression predicted poor survival for gastric cancer patients. Knockdown of GLUL promoted the growth, migration, invasion and metastasis of gastric cancer cells in vitro and in vivo, and vice versa, which was independent of its enzyme activity. Mechanistically, GLUL competed with β-Catenin to bind to N-Cadherin, increased the stability of N-Cadherin and decreased the stability of β-Catenin by alerting their ubiquitination. Furthermore, there were lower N-Cadherin and higher β-Catenin expression levels in gastric cancer tissues compared with adjacent normal tissues. GLUL protein expression was correlated with that of N-Cadherin, and could be the independent prognostic factor in gastric cancer. Our findings reveal that GLUL stabilizes N-Cadherin by antagonizing β-Catenin to inhibit the progress of gastric cancer.

Glutamine synthetase facilitates cancer cells to recover from irradiation-induced G2/M arrest

Resistance to radiation of cancer cells can be either intrinsic or acquired, leading to treatment failure. In response to DNA damage caused by IR, cancer cells are arrested in cell cycle showing limited proliferation and increased apoptosis. However, radiation-resistant cells are able to overcome the cell cycle block and proceed to proliferation, for which the detailed mechanism remains to be elucidated. In the present study, we showed that radioresistant cells exhibited a recoverable G2/M phase during prolonged cell cycle and manifested lower apoptosis rate and more colony formation. RNA-seq analysis revealed that glutamine synthetase (GS, GLUL) gene was highly expressed in radioresistant cancer cells in comparison with the parental cells, which was in accordance with the G2/M arrest after ionizing radiation. Knocking out of GS in radioresistant cells resulted in a delayed G2/M recovery and lowered proliferation rate after ionizing radiation treatment, which was accompanied with increased inhibitory phosphorylation of CDK1 at Y15 and downregulated Cdc25B, a dual specific phosphatase of CDK1. Moreover, there was an enhanced complex formation of CDK1 and Cyclin B1 when the cells were rescued by re-introducing GS. In vivo, knocking down of GS significantly sensitized CNE2-R xenografts to RT in mice. In this study, we demonstrate a novel role of glutamine synthetase independent of metabolic function in promoting recovery from G2/M arrest caused by ionizing radiation, thus, causing cancer cell resistance to radiotherapy.

High expression of glutamate-ammonia ligase is associated with unfavorable prognosis in patients with ovarian cancer

Glutamate-ammonia ligase (GLUL), which is also called GS (glutamine synthetase), is the enzyme that catalyzes the synthesis of glutamine from glutamate and ammonia in an ATP-dependent reaction. Here, we found higher expression of GLUL in the ovarian cancer patients was associated with worse disease-free survival (DFS) and overall survival (OS). In addition, GLUL was heterogeneously expressed in various ovarian cancer cells. The mRNA and protein expression levels of GLUL in NIH:OVCAR-3 and ES-2 cells were obviously higher than that in the other types of ovarian cancer cells. Knockdown of GLUL in NIH:OVCAR-3 or ES-2 cells could significantly decrease the proliferation ability. Furthermore, GLUL knockdown markedly inhibited the p38 MAPK signaling pathway in NIH:OVCAR-3 or ES-2 cells. Our findings suggest that decreasing expression of GLUL may be a new approach that can be used for ovarian cancer treatment.

GLUL Promotes Cell Proliferation in Breast Cancer

Glutamate-ammonia ligase (GLUL) belongs to the glutamine synthetase family. It catalyzes the synthesis of glutamine from glutamate and ammonia in an ATP-dependent reaction. Here, we found higher expression of GLUL in the breast cancer patients was associated with larger tumor size and higher level of HER2 expression. In addition, GLUL was heterogeneously expressed in various breast cancer cells. The mRNA and protein expression levels of GLUL in SK-BR-3 cells were obviously higher than that in the other types of breast cancer cells. Results showed GLUL knockdown in SK-BR-3 cells could significantly decrease the proliferation ability. Furthermore, GLUL knockdown markedly inhibited the p38 MAPK and ERK1/ERK2 signaling pathways in SK-BR-3 cells. Thus, GLUL may represent a novel target for selectively inhibiting p38 MAPK and ERK1/ERK2 signaling pathways and the proliferation potential of breast cancer cells. J. Cell. Biochem. 118: 2018-2025, 2017. © 2016 Wiley Periodicals, Inc.