Abstract 5418: Deciphering the dynamics of alternative pre-mRNA processing of glutaminase in metastatic ovarian cancer
Authors: Masamha Chioniso P. , LaFontaine Patrick , Gibbs Bettine E. 
Published: July 2017

Abstract
The chronically proliferative cancer phenotype requires metabolic reprogramming to meet the increased energy and biosynthetic demands of rapid cell division. This results in increased glucose uptake and usage (the Warburg effect). Cancer cells that undergo the Warburg effect may also become reliant on glutamine, a term called ‘glutamine addiction’. Recent studies in ovarian cancer suggest that highly invasive ovarian cancer cells show a remarkable dependence on glutamine, hence implicating glutamine metabolism in metastasis. Glutaminase is the first enzyme that is involved in glutaminolysis and it catalyzes the rate-limiting conversion of glutamine to glutamate and ammonia. There are two genes that code for glutaminase in the human genome, glutaminase 1 (GLS1), and glutaminase 2 (GLS2). GLS2 is associated with cell differentiation whereas GLS1 expression is up-regulated in cancer. Hence, GLS1 had been proposed to be better adapted to meet the altered metabolic needs of the tumor phenotype. GLS1 can be alternatively spliced into two isoforms, KGA and GAC. Although both KGA and GAC have been implicated in cancer cell metabolism, there is still controversy over the actual isoform that is most important for tumorigenesis. Whereas the KGA isoform is repressed by miR-23, there is no documented miRNA repression of GAC suggesting that GAC is more tumorigenic. Using next-generation sequencing, we recently identified an unannotated novel KGA transcript with a truncated 3′ untranslated region (3′UTR) which is more stable than the traditionally known KGA transcript. Our goal is to determine the expression profile of different glutaminase isoforms in the highly lethal gynecological malignancy, ovarian cancer, and their role in tumorigenesis and metastasis. We have developed amplicons to measure total GLS1 and GLS2 transcripts using quantitative real time PCR (qRT-PCR). Although we unexpectedly detected both GLS2 and GLS1 transcripts, the mRNA levels of GLS2 were significantly lower than those of GLS1. To determine the specific GLS1 isoforms expressed we used isoform specific amplicons and detected both GAC and KGA using qRT-PCR. Western blot analysis was able to detect both GAC and KGA protein in one cell line only suggesting that the KGA mRNA we detected was subject to miR-23 repression. Inhibition of total GLS1 activity with a glutaminase inhibitor resulted in decreased colony formation as shown by soft agar assays. In conclusion, the expression profile of different GLS1 isoforms in highly invasive ovarian cancer supports the role of glutamine metabolism in maintaining the metastatic phenotype. This makes glutamine metabolism a viable therapeutic target for metastatic ovarian cancer.
Citation Format: Chioniso P. Masamha, Patrick LaFontaine, Bettine E. Gibbs. Deciphering the dynamics of alternative pre-mRNA processing of glutaminase in metastatic ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5418. doi:10.1158/1538-7445.AM2017-5418