title: Functional and molecular characteristics of system L in human breast cancer cells.
abstract: The functional and molecular properties of system L in human mammary cancer cells (MDA-MB-231 and MCF-7) have been examined. All transport experiments were conducted under Na(+)-free conditions. alpha-Aminoisobutyric acid (AIB) uptake by MDA-MB-231 and MCF-7 cells was almost abolished by BCH (2-amino-2-norbornane-carboxylic acid). AIB uptake by MDA-MB-231 cells was also inhibited by L-alanine (83.6%), L-lysine (75.6%) but not by L-proline. Similarly, L-lysine and L-alanine, respectively, reduced AIB influx into MCF-7 cells by 45.3% and 63.7%. The K(m) of AIB uptake into MDA-MB-231 and MCF-7 cells was, respectively, 1.6 and 8.8 mM, whereas the V(max) was, respectively, 9.7 and 110.0 nmol/mg protein/10 min. AIB efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH, L-glutamine, L-alanine, L-leucine, L-lysine and AIB (all at 2 mM). In contrast, L-glutamate, L-proline, L-arginine and MeAIB had no effect. The interaction between L-lysine and AIB efflux was one of low affinity. The fractional release of AIB from MDA-MB-231 cells was trans-accelerated by D-leucine and D-tryptophan but not by D-alanine. MDA-MB-231 and MCF-7 cells expressed LAT1 and CD98 mRNA. MCF-7 cells also expressed LAT2 mRNA. The results suggest that AIB transport in mammary cancer cells under Na(+)-free conditions is predominantly via system L which acts as an exchange mechanism. The differences in the kinetics of AIB transport between MDA-MB-231 and MCF-7 cells may be due to the differential expression of LAT2.
authors.affiliation: Hannah Research Institute, Ayr, Scotland KA6 5HL, UK. shennan@hri.sari.ac.uk
authors.forename: D B
authors.initials: DB
authors.lastname: Shennan
authors.forename: J
authors.initials: J
authors.lastname: Thomson
authors.forename: M C
authors.initials: MC
authors.lastname: Barber
authors.forename: M T
authors.initials: MT
authors.lastname: Travers
mesh_terms: D027062:Amino Acid Transport System L / Q000737:chemistry / Q000378:metabolism*; D027182:Amino Acid Transport System y+; D000598:Amino Acids, Cyclic / Q000494:pharmacology; D000621:Aminoisobutyric Acids / Q000737:chemistry / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D027301:Fusion Regulatory Protein 1, Light Chains / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D027283:Large Neutral Amino Acid-Transporter 1 / Q000096:biosynthesis / Q000378:metabolism; D011960:Receptors, Estrogen / Q000032:analysis; D014407:Tumor Cells, Cultured
chemical_list: D027062:Amino Acid Transport System L; D027182:Amino Acid Transport System y+; D000598:Amino Acids, Cyclic; D000621:Aminoisobutyric Acids; D027301:Fusion Regulatory Protein 1, Light Chains; D027283:Large Neutral Amino Acid-Transporter 1; D011960:Receptors, Estrogen; C420646:SLC7A8 protein, human; C100049:2-aminoisobutyric acid; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid