Abstract 1007: The amino acid transporter SNAT4: Potential role as a tumor suppressor in melanoma
Authors: Otte Nicholas J. , Broer Angelika , O’Young Patrick , van Geldermalsen Michelle , Wang Qian , Bailey Charles G. , Broer Stefan , Holst Jeff 
Published: July 2016

Abstract
Cancer cells utilize amino acids to satisfy their need for nutrients and fuel their accelerated growth. The amino acid glutamine has been identified as one of the key building blocks in cancer cells, utilized for macromolecular synthesis and energy production. Due to the increased requirement for glutamine and other amino acids, cancer cells commonly increase expression of amino acid transporters, such as SLC1A5 (ASCT2). Amino acid transporters are membrane transport proteins that are used by cells to move important amino acids in and out of the cell. Interestingly, most amino acid transporters are upregulated in cancer to ensure continued access to nutrients.
We have recently shown that ASCT2 plays a critical role in regulating glutamine uptake in melanoma, prostate and breast cancer. Many other glutamine transporters are upregulated in different cancers, including SLC38 family members SNAT1, SNAT2 and SNAT3. The role of SLC38A4 (SNAT4) in amino acid uptake and cancer growth, however, has not been examined. Like the other SNATs, SNAT4 is a sodium-dependent amino acid transporter that transports neutral amino acids, such as alanine, across the plasma membrane, although it has low affinity for glutamine. Interestingly, unlike the other SNAT family members, our analysis showed that SNAT4 expression is downregulated in 879/917 cancer cell lines in Oncomine. Analysis of SNAT4 mutations in patient samples using cBioPortal showed infrequent mutations in the majority of cancers. However, the TCGA melanoma data (cBioPortal) showed that 32 of 278 melanoma cases (11.5%) have a point mutation in SNAT4 suggesting an important role in melanoma. These mutations included 9 SNAT4 hotspot mutations, present in 2-4 patients each. Using a SNAT4 homology model to predict loss-of-function mutants, we selected five of these mutations to assess in a SNAT4 transport assay in Xenopus oocytes. Two of the five hotspot mutations (G31E, S76F, G78E, G150E and S371F) were able to completely inactivate SNAT4 alanine transport in oocytes. Further analysis of 52 melanoma patient samples in Oncomine showed SNAT4 downregulation in all patients, suggesting that, in contrast to most amino acid transporters, SNAT4 plays a tumor suppressor role in melanoma.
We are currently examining these mutations in melanoma cell lines to determine their effects on cell growth. We are also examining how SNAT4 is involved in either the import or export of amino acids and the downstream metabolic consequences that may directly inhibit melanoma cell growth. Through this research we will gain a better understanding of the role of SNAT4- mediated amino acid metabolism in preventing melanoma cell growth.
Citation Format: Nicholas J. Otte, Angelika Broer, Patrick O’Young, Michelle van Geldermalsen, Qian Wang, Charles G. Bailey, Stefan Broer, Jeff Holst. The amino acid transporter SNAT4: Potential role as a tumor suppressor in melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1007.