Glutamate-ammonia ligase (GLUL), also known as glutamine synthetase (GS), catalyzes the de novo synthesis of glutamine from glutamate and ammonia. GLUL is ubiquitously expressed with particularly high expression in the muscle, liver, and brain. GLUL expression is elevated in various cancers. Its expression is upregulated by oncogenic c-Myc. High expression of GLUL in breast cancer patients is associated with larger tumor size and high level of HER2 expression. It is a predictor of poor survival in patients with glioma and liver cancers.