The heterodimeric amino acid transporter family is a subfamily of SLC7 solute transporter family which includes 14-transmembrane cationic amino acid transporters and 12-transmembrane heterodimeric amino acid transporters. The members of heterodimeric amino acid transporter family are linked via a disulfide bond to single membrane spanning glycoproteins such as 4F2hc (4F2 heavy chain) and rBAT (related to b0, +-amino acid transporter). Six members are associated with 4F2hc and one is linked to rBAT. Two additional members were identified as ones associated with unknown heavy chains. The members of heterodimeric amino acid transporter family exhibit diverse substrate selectivity and are expressed in variety of tissues. They play variety of physiological roles including epithelial transport of amino acids as well as the roles to provide cells in general with amino acids for cellular nutrition. The dysfunction or hyperfunction of the members of the heterodimeric amino acid transporter family are involved in some diseases and pathologic conditions. The genetic defects of the renal and intestinal transporters b0, +AT/BAT1 (b0, +-type amino acid transporter/b0, +-type amino acid transporter 1) and y+LAT1 (y+L-type amino acid transporter 1) result in the amino aciduria with sever clinical symptoms such as cystinuria and lysin uric protein intolerance, respectively. LAT1 is proposed to be involved in the progression of malignant tumor. xCT (x-C-type transporter) functions to protect cells against oxidative stress, while its over-function may be damaging neurons leading to the exacerbation of brain damage after brain ischemia. Because of broad substrate selectivity, system L transporters such as LAT1 transport amino acid-related compounds including L-Dopa and function as a drug transporter. System L also interacts with some environmental toxins with amino acid-related structure such as cysteine-conjugated methylmercury. Therefore, these transporter would be candidates for drug targets based on new therapeutic strategies.
Amino Acid Transport Systems* ; Amino Acid Transport Systems, Basic ; Amino Acids ; Brain ; Brain Ischemia ; Cystinuria ; Glycoproteins ; Humans ; Levodopa ; Membranes ; Neurons ; Oxidative Stress

The continuous growth and proliferation of cells are essential for the wound healing process, and the amino acid transporters plays an important role in the continuous growing and proliferating cells. Among the amino acid transport systems, the amino acid transport system L, which is a Na+/-independent neutral amino acid transport system, is a major route for providing living cells including tumor cells with neutral amino acids including several essential amino acids. In the present study, to elucidate the role of amino acid transport system L in the wound healing process, we investigated the expression pattern of LAT1 and LAT2 in the healing process after inflicting the wound on skin of rat. The expression of LAT1 was increased at 12 hours after inflicting the wound and was similar to the control group getting closer to 7 days. The expression of LAT2 was increased at 1 day and 3 days after inflicting the wound and was similar to the control group getting closer to 7 days. These results suggest that the LAT1 and LAT2 play important roles at the early stage and at the middle stage getting closer to normal skin in the wound healing process after inflicting the wound, respectively.
Amino Acid Transport System L ; Amino Acid Transport Systems* ; Amino Acids, Essential ; Amino Acids, Neutral ; Animals ; Rats* ; Skin* ; Wound Healing* ; Wounds and Injuries*

Chronic immobilization stress (CIS) induces low levels of glutamate (Glu) and glutamine (Gln) and hypoactive glutamatergic signaling in the mouse prefrontal cortex (PFC), which is closely related to the Glu-Gln cycle. A Gln-supplemented diet ameliorates CIS-induced deleterious changes. Here, we investigated the effects of CIS and Gln supplementation on Glu-Gln cycle-related proteins to characterize the underlying mechanisms. Using the CIS-induced depression mouse model, we examined the expression of 11 proteins involved in the Glu-Gln cycle in the PFC. CIS decreased levels of glutamate transporter 1 (GLT1) and sodium-coupled neutral amino acid transporter (SNAT) 1, SANT2, SNAT3, and SNAT5. Gln supplementation did not affect the non-stressed group but significantly increased GLT1 and SNATs of the stressed group. By immunohistochemical analysis, we confirmed that SNAT1 and SNAT2 were decreased in neurons and GLT1, SNAT3, and SNAT5 were decreased in astrocytes in the medial PFC of the stressed group, but Gln-supplemented diet ameliorated these decrements. Collectively, these results suggest that CIS may cause depressive-like behaviors by decreasing Glu and Gln transportation in the PFC and that a Gln-supplemented diet could prevent the deleterious effects of CIS.
Amino Acid Transport System X-AG ; Amino Acid Transport Systems ; Animals ; Astrocytes ; Depression ; Depressive Disorder ; Diet ; Glutamic Acid ; Glutamine ; Immobilization ; Mice ; Neurons ; Prefrontal Cortex ; Transportation

A boy, aged 1 year and 6 months, was found to have persistent positive urine glucose at the age of 4 months, with polydipsia, polyuria, and growth retardation. Laboratory examinations suggested that the boy had low specific weight urine, anemia, hypokalemia, hyponatremia, hypomagnesemia, metabolic acidosis, glycosuria, acidaminuria, increased fractional excretion of potassium, and decreased tubular reabsorption of phosphate. X-ray examinations of the head, thorax, and right hand showed changes of renal rickets. The slit-lamp examination showed a large number of cystine crystals in the cornea. The genetic testing showed a suspected pathogenic homozygous mutation of the
Amino Acid Transport Systems, Neutral/genetics* ; Cornea ; Cystinosis/genetics* ; Humans ; Hypokalemia ; Infant ; Male ; Mutation ; Rare Diseases

The periodontium is a topographically complex organ consisting of epithelial tissue, soft and mineralized tissues. Structures comprising the periodontium include the gingiva, periodontal ligament (PDL), cementum and the alveolar bone. The molecular mechanism of differentiation in PDL fibroblast cells remain unclear. Amino acid transporters play an important role in supplying nutrition to normal and cancer cells and for cell proliferation. Amino acid transport system L is a major nutrient transport system responsible for the Na+-independent transport of neutral amino acids including several essential amino acids. The system L is divided into two major subgroups, the L-type amino acid transporter 1 (LAT1) and the L-type amino acid transporter 2 (LAT2). In this study, the expression pattern of amino acid transport system L was, therefore, investigated in the differentiation of PDL fibroblast cells. To determine the expression level of amino acid transport system L participating in intracellular transport of amino acids in the differentiation of PDL fibroblast cells, it was examined by RT-PCR, observation of cell morphology, Alizaline red-S staining and uptake analysis after inducing experimental differentiation in PDL fibroblast cells isolated from mouse molar teeth. The results are as follows. 1. The LAT1 mRNA was expressed in the early stage of PDL fibroblast cell differentiation. This expression level was gradually reduced by differentiation-inducing time and it was not observed after the late stage. 2. The expression level of LAT2 mRNA was increased in time-dependent manner during differentiation induction of PDL fibroblast cells. 3. There was no changes in the expression level of 4F2hc mRNA, the cofactor of LAT1 and LAT2, during differentiation of PDL fibroblast cells. 4. The expression level of ALP mRNA was gradually increased and the expression level of Col I mRNA was decreased during differentiation of PDL fibroblast cells. 5. The L-leucine transport was reduced by time from the early stage to the late stage in PDL fibroblast cell differentiation. As the results, it is considered that among neutral amino acid transport system L in differentiation of PDL fibroblast cells, the LAT1 has a key role in cell proliferation in the early stage of cell differentiation and the LAT2 has an important role in the late stage of cell differentiation for providing cells with neutral amino acids including several essential amino acids.
Amino Acid Transport System L* ; Amino Acid Transport Systems ; Amino Acids ; Amino Acids, Essential ; Amino Acids, Neutral ; Animals ; Cell Differentiation ; Cell Proliferation ; Dental Cementum ; Fibroblasts* ; Gingiva ; Leucine ; Mice ; Molar ; Periodontal Ligament* ; Periodontium ; RNA, Messenger ; Tooth

The characteristics of Na+/-dependent cycloleucine uptake was investigated in OK cells with regard to substrate specificity and regulation by protein kinase C (PKC). Inhibition studies with different synthetic and natural amino acids showed a broad spectrum affinity to neutral amino acids regardless of their different side chains including branched or aromatic, indicating that the Na+/-dependent cycloleucine uptake in OK cells is mediated by System B-o or System B degree -like transporter rather than the classical System A or ASC. Phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate, but not 4 alpha-PMA elicited a time-dependent biphasic stimulation of Na+/-dependent cycloleucine uptake, which produced early transient peak at 30 min and late sustained peak at 180 min. Both the early and late stimulations by PMA were due to an increase in Vmax and not due to a change in Km. PKC inhibitors blocked both the early and late stimulation by PMA, while protein synthesis inhibitors blocked the late stimulation only. These results suggest the existence and regulation by PKC of System B degree or System B degree -like broad spectrum transport system for neutral amino acids in OK cells.
Amino Acid Transport Systems* ; Amino Acids ; Amino Acids, Neutral ; Cycloleucine ; Kidney* ; Opossums* ; Phorbol 12,13-Dibutyrate ; Protein Kinase C ; Protein Synthesis Inhibitors ; Substrate Specificity

Most normal cells express L-type amino acid transporter 2 (LAT2). However, L-type amino acid transporter 1 (LAT1) is highly expressed in many tumor cells and presumed to support their increased growth and proliferation. This study examined the effects of JPH203, a selective LAT1 inhibitor, on cell growth and its mechanism for cell death in Saos2 human osteosarcoma cells. FOB human osteoblastic cells and Saos2 cells expressed LAT1 and LAT2 together with their associating protein 4F2 heavy chain, but the expression of LAT2 in the Saos2 cells was especially weak. JPH203 and BCH, a non-selective L-type amino acid transporter inhibitor, potently inhibited L-leucine uptake in Saos2 cells. As expected, the intrinsic ability of JPH203 to inhibit L-leucine uptake was far more efficient than that of BCH in Saos2 cells. Likewise, JPH203 and BCH inhibited Saos2 cell growth with JPH203 being superior to BCH in this regard. Furthermore, JPH203 increased apoptosis rates and formed DNA ladder in Saos2 cells. Moreover, JPH203 activated the mitochondria-dependent apoptotic signaling pathway by upregulating pro-apoptotic factors, such as Bad, Bax, and Bak, and the active form of caspase-9, and downregulating anti-apoptotic factors, such as Bcl-2 and Bcl-xL. These results suggest that the inhibition of LAT1 activity via JPH203, which may act as a potential novel anti-cancer agent, leads to apoptosis mediated by the mitochondria-dependent intrinsic apoptotic signaling pathway by inducing the intracellular depletion of neutral amino acids essential for cell growth in Saos2 human osteosarcoma cells.
Amino Acid Transport Systems* ; Amino Acids, Neutral ; Antigens, CD98 Heavy Chain ; Apoptosis* ; Caspase 9 ; Cell Death ; DNA ; Humans* ; Leucine ; Osteoblasts ; Osteosarcoma*

Cystinuria is an inherited renal and intestinal disease characterized by defective amino acids reabsorption and cystine urolithiasis. It is unusually associated with neurologic symptoms. Mutations in two genes, SLC3A1 and SLC7A9, have been identified in cystinuric patients. This report presents a 13-yr-old boy with cystinuria who manifested difficulty in walking, ataxia, and mental retardation. Somatosensory evoked potential of posterior tibial nerve stimulation showed the central conduction dysfunction through the posterior column of spinal cord. He was diagnosed non-type I cystinuria by urinary amino acid analysis and oral cystine loading test. We screened him and his family for gene mutation by direct sequencing of SLC3A1 and SLC7A9 genes. In this patient, we identified new missence mutation G173R in SLC7A9 gene.
Adolescent ; Amino Acid Substitution ; Amino Acid Transport Systems, Basic/*genetics ; Amino Acids/urine ; Ataxia/complications/diagnosis/*genetics ; Base Sequence ; Cystine/blood ; Cystinuria/complications/diagnosis/*genetics ; Humans ; Intellectual Disability/complications/diagnosis/*genetics ; Male ; *Mutation, Missense ; Pedigree ; Republic of Korea

In Escherichia coli, uptake of L-tryptophan is done by three distinct permeases, encoded by mtr, tnaB, and aroP. Based on the mtr single-gene knockout, we constructed the mtr.tnaB and mtr.aroP double-gene knockout mutants and the mtr.tnaB.aroP triple-gene knockout mutant. The fermentation results showed that the mtr.tnaB and mtr.aroP knockout mutants produced 1.38 g/L and 1.27 g/L L-tryptophan, respectively, which was 17% and 9% higher than that of the mtr knockout mutant. However, the mtr.tnaB.aroP knockout mutant was significantly affected on cell growth and only produced 0.63 g/L L-tryptophan. During the fed-batch fermentation in a 3-L fermentor, the mtr.tnaB knockout mutant produced 12.2 g/L L-tryptophan, which was 27% higher than that of the mtr knockout mutant. This study demonstrates the effect of multi-gene knockouts of L-tryptophan transport system of Escherichia coli on the biosynthesis of L-tryptophan.
Amino Acid Transport Systems ; genetics ; Biological Transport ; Escherichia coli ; genetics ; metabolism ; Escherichia coli Proteins ; genetics ; Fermentation ; Gene Knockout Techniques ; Membrane Transport Proteins ; genetics ; metabolism ; Mutant Proteins ; metabolism ; Tryptophan ; biosynthesis ; genetics ; metabolism

Rapid ammonia elevation in blood with accompanying mental change should be considered as a true medical emergency. In such a case, action leading to immediate diagnosis and the earliest possible treatment must occur in order to minimize permanent brain damage. Hyperornithinemia- Hyperammonemia-Homocitrullinuria (HHH) syndrome is a rare inborn errors of metabolism and autosomal recessive metabolic disorder caused by a deficiency of the mitochondrial ornithine transporter at the cellular level. Emergency physicians should take account of the possibility of HHH syndrome in patients with unreasonable hyperammonemia coupled with altered mental status. We report a case of a 59-year old man who presented with headache, nausea, vomiting and altered mental status. His serologic test showed hyperornithinemia, hyperammomemia, and homocitrullinuria. He was treated with fluid therapy and hemodialysis. His clinical manifestation improved and he was discharged after hemodialysis
Amino Acid Transport Systems, Basic ; Ammonia ; Brain ; Emergencies ; Fluid Therapy ; Headache ; Humans ; Hyperammonemia ; Metabolism, Inborn Errors ; Nausea ; Ornithine ; Renal Dialysis ; Serologic Tests ; Urea Cycle Disorders, Inborn ; Vomiting