Phosphate-activated glutaminase (GLS2), a p53-inducible regulator of glutamine metabolism and reactive oxygen species

Abstract

We identified a p53 target gene, phosphate-activated mitochondrial glutaminase (GLS2), a key enzyme in conversion of glutamine to glutamate, and thereby a regulator of glutathione (GSH) synthesis and energy production. GLS2 expression is induced in response to DNA damage or oxidative stress in a p53-dependent manner, and p53 associates with the GLS2 promoter. Elevated GLS2 facilitates glutamine metabolism and lowers intracellular reactive oxygen species (ROS) levels, resulting in an overall decrease in DNA oxidation as determined by measurement of 8-OH-dG content in both normal and stressed cells. Further, siRNA down-regulation of either GLS2 or p53 compromises the GSH-dependent antioxidant system and increases intracellular ROS levels. High ROS levels following GLS2 knockdown also coincide with stimulation of p53-induced cell death. We propose that GLS2 control of intracellular ROS levels and the apoptotic response facilitates the ability of p53 to protect cells from accumulation of genomic damage and allows cells to survive after mild and repairable genotoxic stress. Indeed, overexpression of GLS2 reduces the growth of tumor cells and colony formation. Further, compared with normal tissue, GLS2 expression is reduced in liver tumors. Thus, our results provide evidence for a unique metabolic role for p53, linking glutamine metabolism, energy, and ROS homeostasis, which may contribute to p53 tumor suppressor function.glutathione antioxidant | glutaminolysis | tumor suppression | apoptosis

GLS2 is transcriptionally regulated by p73 and contributes to neuronal differentiation

“…9,10 In particular, GLS2 regulates energy metabolism and antioxidant defense in cancer cells. Indeed our results indicate and confirm that GLS2 is a key player in the regulation of, at least, intracellular ATP levels.…”

“…Indeed, it regulates ATP levels and the GSH/GSSG ratio in cells. 9,10,37 Hence, we asked whether GLS2 could also exert the same functions in SH-SY5Y cells. First, we overexpressed GLS2 (Fig.…”

“…However, although GLS distribution has been extensively investigated, the regulation of GLS1/GLS2 expression is poorly understood. Recently, 2 independent groups have shown that GLS2 is a direct target of the tumor suppressor gene p53, 9,10 and that p53 drives the expression of GLS2 under both non-stressed and stressed conditions. Increased levels of GLS2 promote Gln metabolism, and the Glu produced by Gln hydrolysis is a precursor in the biosynthesis of Glutathione (GSH) and therefore promotes antioxidant defense through regulating the GSH/GSSG ratio.…”

Glutamine at focus: versatile roles in cancer

“…The activation of p53 augmented GLS2 expression, resulting in enhanced levels of glutamate and α-KG, increased mitochondrial respiration/ATP production, and decreased ROS levels [65]. Moreover, p53 increased GLS2 expression in response to oxidative stress and accumulation of genome damage, reducing tumor formation [67]. p53 activation represses ME1 and ME2, decreasing glutamine metabolism, rather than glucose metabolism, leading to senescence [66].…”

“…A number of studies have shown that glutaminase enzymes play an important role in regulating intracellular levels of ROS. For instance, genetic downregulation of either GLS2 or p53 compromises the GSH-dependent antioxidant system and increases intracellular ROS levels [67]; however, their activation increase GSH levels and decreases ROS levels, leading to cancer survival [65]. On the other hand, glutamine-fueled mitochondrial metabolism generates ROS by OXPHOS activity, leading to cell proliferation and tumorigenesis [57,143].…”