Cancer cells exhibit exacerbated metabolic activity to maintain their accelerated proliferation and microenvironmental adaptation in order to survive under nutrient-deficient conditions. Tumors display an increase in glycolysis, glutaminolysis and fatty acid biosynthesis, which provide their energy source. Glutamine is critical for fundamental cellular processes, where intermediate metabolites produced through glutaminolysis are necessary for the maintenance of mitochondrial metabolism. These include antioxidants to remove reactive oxygen species, and the generation of the nonessential amino acids, purines, pyrimidines and fatty acids required for cellular replication and the activation of cell signaling. Some cancer cells are highly dependent on glutamine consumption since its catabolism provides an anaplerotic pathway to feed the Krebs cycle. Intermediate members of the glutaminolysis pathway have been found to be deregulated in several types of cancers and have been proposed as therapeutic targets and prognostic biomarkers. This review summarizes the main players in the glutaminolysis pathway, how they have been found to be deregulated in cancer and their implications for cancer maintenance. Furthermore, non-coding RNAs are now recognized as new participants in the regulation of glutaminolysis; therefore, their involvement in glutamine metabolism in cancer is discussed in detail.Int. J. Mol. Sci. 2020, 21, 2872 2 of 26 an increased glucose consumption in relation to normal differentiated tissues. Now we know that glutamine metabolism is as important as glucose metabolism for the production of macromolecules in cancer [1].Glutamine is an abundant amino acid involved in energy production, homeostasis in pro/antioxidant species and the activation of signaling pathways in cancer. In addition to the antioxidant glutathione (GSH), nucleotides, lipids and amino acids are formed from glutamine metabolism. All of these are needed for many metabolic functions such as growth, proliferation, cell survival and defense against oxidative stress [2]. Glutamine contributes, with reduced nitrogen, to the de novo biosynthesis of diverse nitrogen-containing compounds, such as purine and pyrimidine nucleotides, glucosamine-6-phosphate and nonessential amino acids.As glutamine is the most abundant amino acid in the blood and muscle tissue, normal proliferating cells use glutamine metabolism as an energy source, mediated by its catabolic products, glutamate and α-ketoglutarate (α-kG), the latter being an intermediate of the tricarboxylic acid cycle (TCA) or Krebs cycle [3]. In 1950, Harry Eagle observed that HeLa tumor cells require an excess of glutamine, in relation to other amino acids in the culture medium, for optimal growth. Furthermore, it has been reported that tumors consume glutamine faster than the surrounding normal tissue [4]. Moreover, most cancer cells are dependent on glutamine being unable to survive under glutamine starvation, an effect that has been termed glutamine addiction [5]. Various types of cancers are high...

Persistent high-risk human papillomavirus infection is the main risk factor for cervical cancer establishment, where the viral oncogenes E6 and E7 promote a cancerous phenotype. Metabolic reprogramming in cancer involves alterations in glutamine metabolism, also named glutaminolysis, to provide energy for supporting cancer processes including migration, proliferation, and production of reactive oxygen species, among others. The aim of this work was to analyze the effect of HPV16 E6 and E7 oncoproteins on the regulation of glutaminolysis and its contribution to cell proliferation. We found that the E6 and E7 oncoproteins exacerbate cell proliferation in a glutamine-dependent manner. Both oncoproteins increased the levels of transporter SNAT1, as well as GLS2 and GS enzymes; E6 also increased LAT1 transporter protein levels, while E7 increased ASCT2 and xCT. Some of these alterations are also regulated at a transcriptional level. Consistently, the amount of SNAT1 protein decreased in Ca Ski cells when E6 and E7 expression was knocked down. In addition, we demonstrated that cell proliferation was partially dependent on SNAT1 in the presence of glutamine. Interestingly, SNAT1 expression was higher in cervical cancer compared with normal cervical cells. The high expression of SNAT1 was associated with poor overall survival of cervical cancer patients. Our results indicate that HPV oncoproteins exacerbate glutaminolysis supporting the malignant phenotype.