SUMMARYGlutamate-ammonia ligase (GLUL) is highly expressed in many cancer cells. Synthesizing glutamine by its enzyme function has been found to be important for supporting cancer cell survival and growth under glutamine restriction. However, GLUL’s functions under a glutamine-sufficient condition still have not been uncovered. Here we find that GLUL is highly expressed in lung cancer cells and provides survival and growth advantages under both glutamine restriction and adequacy conditions. Knocking down GLUL can block lung cancer cell growth in an enzyme-independent way when glutamine is sufficient. Mechanistically, GLUL regulates Calcium/Calmodulin Dependent Protein Kinase II Gamma (CaMK2G) expression at the transcription level, and CaMK2G is a major mediator in controlling cell growth under GLUL. The transcriptional regulation of CaMK2G is partially mediated by SMAD4. Our data unveil a new enzyme-independent function of GLUL in lung cancer cells under a glutamine-sufficient condition.