Nagamori Shushi, Wiriyasermkul Pattama, Okuda Suguru, Kojima Naoto, Hari Yoshiyuki, Kiyonaka Shigeki, Mori Yasuo, Tominaga Hideyuki, Ohgaki Ryuichi, Kanai Yoshikatsu
Department of Bio-System Pharmacology, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Department of Pharmaceutical Manufacturing Chemistry, Kyoto Pharmaceutical University, Kyoto, Japan.
Amino Acids. 2016 Apr;48(4):1045-1058. doi: 10.1007/s00726-015-2158-z. Epub 2016 Jan 2.
Among amino acids, leucine is a potential signaling molecule to regulate cell growth and metabolism by activating mechanistic target of rapamycin complex 1 (mTORC1). To reveal the critical structures of leucine molecule to activate mTORC1, we examined the structure-activity relationships of leucine derivatives in HeLa S3 cells for cellular uptake and for the induction of phosphorylation of p70 ribosomal S6 kinase 1 (p70S6K), a downstream effector of mTORC1. The activation of mTORC1 by leucine and its derivatives was the consequence of two successive events: the cellular uptake by L-type amino acid transporter 1 (LAT1) responsible for leucine uptake in HeLa S3 cells and the activation of mTORC1 following the transport. The structural requirement for the recognition by LAT1 was to have carbonyl oxygen, alkoxy oxygen of carboxyl group, amino group and hydrophobic side chain. In contrast, the requirement for mTORC1 activation was more rigorous. It additionally required fixed distance between carbonyl oxygen and alkoxy oxygen of carboxyl group, and amino group positioned at α-carbon. L-Configuration in chirality and appropriate length of side chain with a terminal isopropyl group were also important. This confirmed that LAT1 itself is not a leucine sensor. Some specialized leucine sensing mechanism with rigorous requirement for agonistic structures should exist inside the cells because leucine derivatives not transported by LAT1 did not activate mTORC1. Because LAT1-mTOR axis is involved in the regulation of cell growth and cancer progression, the results from this study may provide a new insight into therapeutics targeting both LAT1 and leucine sensor.
在氨基酸中，亮氨酸是一种潜在的信号分子，可通过激活雷帕霉素复合物1（mTORC1）的机制性靶点来调节细胞生长和代谢。为了揭示亮氨酸分子激活mTORC1的关键结构，我们研究了亮氨酸衍生物在HeLa S3细胞中的结构-活性关系，包括细胞摄取以及对mTORC1下游效应物p70核糖体S6激酶1（p70S6K）磷酸化的诱导作用。亮氨酸及其衍生物对mTORC1的激活是两个连续事件的结果：由负责HeLa S3细胞中亮氨酸摄取的L型氨基酸转运体1（LAT1）进行细胞摄取，以及转运后mTORC1的激活。LAT1识别所需的结构要求是具有羰基氧、羧基的烷氧基氧、氨基和疏水侧链。相比之下，mTORC1激活的要求更为严格。它还需要羧基的羰基氧和烷氧基氧之间有固定距离，且氨基位于α-碳上。手性中的L-构型以及带有末端异丙基的侧链的适当长度也很重要。这证实了LAT1本身不是亮氨酸传感器。由于未被LAT1转运的亮氨酸衍生物不会激活mTORC1，因此细胞内应该存在一些对激动剂结构有严格要求的特殊亮氨酸传感机制。因为LAT1-mTOR轴参与细胞生长和癌症进展的调节，本研究结果可能为针对LAT1和亮氨酸传感器的治疗提供新的见解。
