L-leucine transport in human breast cancer cells (MCF-7 and MDA-MB-231): kinetics, regulation by estrogen and molecular identity of the transporter.
The transport of L-leucine by two human breast cancer cell lines has been examined. L-leucine uptake by MDA-MB-231 and MCF-7 cells was via a BCH-sensitive, Na+ -independent pathway. L-leucine uptake by both cell lines was inhibited by L-alanine, D-leucine and to a lesser extent by L-lysine but not by L-proline. Estrogen (17beta-estradiol) stimulated L-leucine uptake by MCF-7 but not by MDA-MB-231 cells. L-leucine efflux from MDA-MB-231 and MCF-7 cells was trans-stimulated by BCH in a dose-dependent fashion. The effect of external BCH on L-leucine efflux from both cell types was almost abolished by reducing the temperature from 37 to 4 degrees C. There was, however, a significant efflux of L-leucine under zero-trans conditions which was also temperature-sensitive. L-glutamine, L-leucine, D-leucine, L-alanine, AIB and L-lysine all trans-stimulated L-leucine release from MDA-MB-231 and MCF-7 cells. In contrast, D-alanine and L-proline had little or no effect. The anti-cancer agent melphalan inhibited L-leucine uptake by MDA-MB-231 cells but had no effect on L-leucine efflux. Quantitative real-time PCR revealed that LAT1 mRNA was approximately 200 times more abundant than LAT2 mRNA in MCF-7 cells and confirmed that MDA-MB-231 cells express LAT1 but not LAT2 mRNA. LAT1 mRNA levels were higher in MCF-7 cells than in MDA-MB-231 cells. Furthermore, LAT1 mRNA was more abundant than CD98hc mRNA in both MDA-MB-231 and MCF-7 cells. The results suggest that system L is the major transporter for L-leucine in both MDA-MB-231 and MCF-7 cells. It is possible that LAT1 may be the major molecular correlate of system L in both cell types. However, not all of the properties of system L reflected those of LAT1/LAT2/CD98hc.
Shennan
D B
DB
Hannah Research Institute, Ayr, Scotland, KA6 5HL, UK. shennand@hri.sari.ac.uk
Thomson
J
J
Gow
I F
IF
Travers
M T
MT
Barber
M C
MC
D027182:Amino Acid Transport System y+ / Q000235:genetics; D001692:Biological Transport / Q000187:drug effects; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D004967:Estrogens / Q000494:pharmacology*; D027301:Fusion Regulatory Protein 1, Light Chains / Q000235:genetics; D027261:Fusion Regulatory Protein-1 / Q000235:genetics; D006801:Humans; D007700:Kinetics; D027283:Large Neutral Amino Acid-Transporter 1 / Q000235:genetics; D007930:Leucine / Q000378:metabolism*; D008558:Melphalan / Q000493:pharmacokinetics / Q000494:pharmacology
D027182:Amino Acid Transport System y+; D004967:Estrogens; D027301:Fusion Regulatory Protein 1, Light Chains; D027261:Fusion Regulatory Protein-1; D027283:Large Neutral Amino Acid-Transporter 1; C420646:SLC7A8 protein, human; D007930:Leucine; D008558:Melphalan