Leslie Herd

 Introductions: Hepatocellular carcinoma (HCC) involves tumor formation in the liver and it has the third highest death rate for any cancer due to increasing rates of hepatitis B, hepatitis C, and nonalcoholic fatty liver disease.¹  Importantly, HCC is possible through overutilization of aerobic glycolysis, which relies on cancer cells’ ability to intentionally break down glutamine into intermediates used in different biosynthetic pathways.²  Additionally, HCC cells specifically utilize Epithelial-Mesenchymal Transition (EMT), wherein epithelial cells become more undifferentiated into mesenchymal cells so that they can metastasize to other tissues.³  In particular, Snail protein is known to upregulate factors that promote EMT.³  A pivotal study investigates the link between metabolism of glutamine through glutaminase enzymes (mainly GLS2, which has tumor-suppressor activity) and its role in preventing EMT through the use of miRNAs (regulatory RNAs that prevent overexpression of mRNAs).⁴  Methods: First, the role of GLS2 in the progression of HCC was determined using immunohistochemical staining with IgG antibodies against GLS2 in non-diseased liver tissue, early stage HCC tumors, and late stage HCC tumors.⁴  Then, the relationship between GLS2, miR-34 (a specific miRNA), and Snail expression in HCC patient tumors was explored using Western blotting.⁴  Lastly, luciferase enzyme activity and degree of metastasis was measured in primary tumors excised from mice that had either GLS2 knockout cell lines (Mahlavu-GL/pcDNA3.1) or GLS2-overexpressing cell lines (Mahlavu-GL/GLS2) injected.⁴  Results: As expected with immunohistochemical staining, GLS2 expression was greater in normal liver tissue and was moderate in early stage HCC tumors, but late stage HCC tumors had little to no expression of GLS2, further corroborating the inhibitory action of GLS2 in HCC.⁴  Using Western blotting, it was found that patients with high expression of GLS2 also had high expression of miR-34 and low expression of Snail protein.⁴  Patients with this tumor phenotype also had greater rates of survival over an 80-month period.⁴  The link between GLS2 and miR-34 was found to be Dicer, a protein that promotes maturation of miRNAs and was also highly expressed when GLS2 is expressed.⁴  Measurements of luciferase activity in tumors grown from Mahlavu-GL/pcDNA3.1 cell lines in mice showed an increase in Snail activity and greater metastasis in the liver and lungs versus the Mahlavu-GL/GLS2 cell lines.⁴  Conclusions: The downregulation of GLS2 in advanced HCC conveys it may have a role in suppressing tumor activity, especially due to its interaction with regulatory miRNAs.  Therefore, GLS2 is a novel target for therapeutic treatments in HCC.

1. Bruix J, Reig M, Sherman, M. Evidence-Based diagnosis, staging, and treatment of patients with hepatocellular carcinoma.  2016; 150: 835-853.  http://dx.doi.org/10.1053/j.gastro.2015.12.041.  Accessed May 28, 2019.
2. Altman, BJ, Stine, ZE, Dang, CV. From Krebs to clinic: Glutamine metabolism to cancer therapy. Nat Rev Cancer. 2016; 16(10): 619-634. https://doi.org/10.1038/nrc.2016.71.  Accessed May 28, 2019.
3. Dongre A, Weinberg R. New insights into the mechanisms of epithelial-mesenchymal transition and implications for cancer. Nature Reviews Molecular Cell Biology. 20: 69-84. https://doi.org/10.1038/s41580-018-0080-4. Accessed May 28, 2019.
4. Kuo T, Chen C, Hua K, et al. Glutaminase 2 stabilizes Dicer to repress Snail and metastasis in hepatocellular carcinoma cells. Cancer Letters.  2016; 383: 282-294.  http://dx.doi.org/10.1016/j.canlet.2016.10.012.  Accessed May 28, 2019.