Glutaminase

Glutaminase is the initial enzyme in glutamine metabolism, which catalyzes the hydrolysis of glutamine to glutamate in cells. Glutaminase plays a key role in cancer cell metabolism, growth, and proliferation. In mammalian cells, there are two paralogous GLS genes, GLS1 (or GLS) and GLS2. GLS1 encodes two alternatively spliced isozymes: kidney glutaminase (KGA) and glutaminase C (GAC). GLS2 also encodes two isozymes: liver glutaminase (LGA) and glutaminase B.

GLS1 is ubiquitously expressed in various tissues, and its expression can be induced by the oncogene MYC. GLS1 is frequently activated and/or overexpressed in various types of cancer, including hepatocellular carcinoma (HCC). GLS1 has been reported to promote tumorigenesis in different types of cancer, including HCC, which is mainly attributable to its glutaminase activity and role in promoting glutamine metabolism. GLS has emerged as a critical enzyme in a number of cancer types. Elevated GLS2 enzymatic activity has also been correlated with tumor cell growth in vitro and in vivo. N-Myc activates GLS2 to promote conversion of glutamine to glutamate in MYCN-amplified neuroblastoma cells. Abrogation of GLS2 function profoundly inhibits glutaminolysis and dramatically decreases cell proliferation and survival in vitro and in vivo. However, there is controversy over the role of GLS2 as a tumor suppressor. Enzymatic activity independent of GLS2 is up-regulated via p53 or p63 and plays a role of tumor suppressor.