Investigating the Role of SLC45A4 in GABA Metabolism

摘要 溶质载体（SLC）蛋白是控制葡萄糖跨膜交换的膜转运蛋白， 氨基酸、无机离子和其它小分子代谢物。许多SLC基因已被证明是 许多SLC转运蛋白是重要的药物靶点。 然而，由于无数的技术困难，SLC家族成员中的很大一部分仍然是孤儿运输者 没有已知的基质，这既代表了一个重大的知识差距，也代表了一个巨大的机会， 药物开发为了系统研究孤儿SLC转运蛋白的生化功能， 我们实验室开发了计算工作流程，它结合了公共转录组学和代谢组学 数据集来揭示SLC转运蛋白的代谢功能。使用这种关联分析， SLC 45 A4基因是γ-氨基丁酸的最大决定因子 （GABA）在人类癌细胞中的水平。GABA，这是最为人所知的抑制性神经递质，在 哺乳动物中枢神经系统，在外周组织中起调节细胞增殖，分化， 和移民。鉴于这些功能在癌症和正常细胞中的重要性， 了解SLC 45 A4在非神经元细胞中GABA代谢的背景下如何发挥作用。使用稳定 通过同位素示踪，发现SLC 45 A4不是通过促进GABA摄取而增加细胞GABA水平， 通过促进GABA从头合成，提出了一种全新的GABA调节机制， 合成.因此，假设SLC 45 A4编码一种亚细胞鸟氨酸转运蛋白， GABA生产。该计划将朝着三个方向前进：目标1，确定生物化学 SLC 45 A4促进细胞GABA产生的机制;目的2，确定亚细胞 SLC 45 A4转运蛋白和GABA合成的区室化;以及Aim 3，确定底物 SLC 45 A4的偏好和酶性质。总的目标是确定SLC 45 A4如何调节细胞凋亡。 novo GABA合成，这有助于人类生物化学的基础知识，并可能提供 针对GABA代谢的新疗法。

ABSTRACT Solute carrier (SLC) proteins are membrane transporters that govern the cross-membrane exchanges of glucose, amino acids, inorganic ions, and other small molecule metabolites. Many SLC genes have been shown to be causes of Mendelian diseases in humans, and a number of SLC transporters are important drug targets. However, due to myriad technical difficulties, a large fraction of SLC family members are still orphan transporters without known substrates, which represents both a significant knowledge gap and a huge opportunity for new drug development. In order to systematically study the biochemical functions of the orphan SLC transporters, a computational workflow was developed in our lab, which combines public transcriptomic and metabolomic datasets to uncover the metabolic function of SLC transporters. Using this association analysis, an uncharacterized gene, SLC45A4, was identified to be the single greatest determinant of γ-Aminobutyric acid (GABA) levels in human cancer cells. GABA, which is mostly known as an inhibitory neurotransmitter in the mammalian central nervous system, functions in peripheral tissues to regulate cell proliferation, differentiation, and migration. Given the importance of these functions in both cancer and normal cells, it is essential to understand how SLC45A4 functions in the context of GABA metabolism in non-neuronal cells. Using stable isotope tracing, it was found that SLC45A4 increases cellular GABA levels not by promoting GABA uptake but by facilitating GABA de novo synthesis, suggesting an entirely new mechanism of the regulation of GABA synthesis. Therefore, it is hypothesized that SLC45A4 encodes a subcellular ornithine transporter that supports GABA production. This program will move forward in three directions: Aim 1, determining the biochemical mechanism by which SLC45A4 promotes cellular GABA production; Aim 2, determining the subcellular compartmentalization of SLC45A4 transporter and GABA synthesis; and Aim 3, determining substrate preference and enzymatic properties of SLC45A4. The overall goal is to determine how SLC45A4 regulates de novo GABA synthesis, which contributes to the fundamental knowledge of human biochemistry and may provide new therapeutics targeting GABA metabolism.