Fukuhara Daisuke, Kanai Yoshikatsu, Chairoungdua Arthit, Babu Ellappan, Bessho Fumio, Kawano Toshio, Akimoto Yoshihiro, Endou Hitoshi, Yan Kunimasa
Department of Pediatrics, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan.
Am J Pathol. 2007 Mar;170(3):888-98. doi: 10.2353/ajpath.2007.060428.
We recently cloned the human Na(+)-independent system L neutral amino acid transporter LAT3. The aim of the present study was to characterize the molecular nature of mouse LAT3 at the protein level. Isolated mouse LAT3 showed 83% identity to human LAT3. Xenopus oocytes injected with mouse LAT3 cRNA showed the same functional property as human LAT3. Reverse transcriptase-polymerase chain reaction revealed apparent transcripts of mouse LAT3 in the liver, skeletal muscle, and pancreas, an expression pattern identical to that found in humans. Antibody generated against mouse LAT3 detected both approximately 58-kd and 48-kd bands in the sample from liver and only a 48-kd band in skeletal muscle and pancreas. Immunohistochemical study showed its clear localization in the plasma membrane of liver and skeletal muscle, whereas it was only detectable in the endoplasmic reticulum and in crystalline inclusions in pancreatic acinar cells. Starvation induced up-regulation of mouse LAT3 protein and mRNA in both liver and skeletal muscle but not in pancreas. These results suggest that LAT3 may indeed function as an amino acid transporter, transporting branched-chain amino acids from liver and skeletal muscle to the bloodstream and thereby participating in the regulatory system of interorgan amino acid nutrition.
我们最近克隆了人钠非依赖性系统L中性氨基酸转运体LAT3。本研究的目的是在蛋白质水平上表征小鼠LAT3的分子特性。分离得到的小鼠LAT3与人LAT3有83%的同一性。注射了小鼠LAT3 cRNA的非洲爪蟾卵母细胞表现出与人LAT3相同的功能特性。逆转录聚合酶链反应显示小鼠LAT3在肝脏、骨骼肌和胰腺中有明显的转录本，其表达模式与在人类中发现的相同。针对小鼠LAT3产生的抗体在肝脏样本中检测到约58-kd和48-kd两条带，而在骨骼肌和胰腺中仅检测到一条48-kd的带。免疫组织化学研究表明，它在肝脏和骨骼肌的质膜中有明确的定位，而在胰腺腺泡细胞的内质网和晶体包涵体中仅可检测到。饥饿诱导肝脏和骨骼肌中小鼠LAT3蛋白和mRNA上调，但胰腺中未出现上调。这些结果表明，LAT3可能确实作为一种氨基酸转运体发挥作用, 将支链氨基酸从肝脏和骨骼肌转运到血液中，从而参与器官间氨基酸营养的调节系统。
