pH dependence of methotrexate transport by the reduced folate carrier and the folate receptor in L1210 leukemia cells - Further evidence for a third route mediated at low pH

被引:58
作者
Sierra, EE
Brigle, KE
Spinella, MJ
Goldman, ID
机构
[1] YESHIVA UNIV ALBERT EINSTEIN COLL MED, DEPT MED, BRONX, NY 10461 USA
[2] YESHIVA UNIV ALBERT EINSTEIN COLL MED, DEPT MOL PHARMACOL, BRONX, NY 10461 USA
[3] YESHIVA UNIV ALBERT EINSTEIN COLL MED, EINSTEIN CANC CTR, BRONX, NY 10461 USA
[4] VIRGINIA COMMONWEALTH UNIV, MED COLL VIRGINIA, MASSEY CANC CTR, RICHMOND, VA 23298 USA
关键词
reduced folate carrier; folate receptor; methotrexate; transport; binding;
D O I
10.1016/S0006-2952(96)00730-7
中图分类号
R9 [药学];
学科分类号
1007 ;
摘要
F2-MTX(r)A is an L1210 leukemia cell line with a functional defect in the reduced folate carrier and high level expression of folate receptor beta. The pH-dependence of methotrexate (MTX) influx by folate receptor beta in F2-MTX(r)A cells was characterized and compared with that of the reduced folate carrier in parental L1210 cells. MTX influx by folate receptor beta had a pH optimum of 6.5, whereas influx mediated by the reduced folate carrier showed a pH optimum of 7.5. Increased folate receptor beta-mediated MTX influx at pH 6.5 relative to pH 7.5 was accompanied by a 5-fold increase in binding affinity of the receptor for MTX without a change in the number of binding sites. At pH 6.2, approximately 24% of MTX influx in F2-MTX(r)A cells proceeded by another mechanism. This transport route became active at pH <7.5, operated optimally at pH 6.0 to 6.5, and, unlike folate receptor beta-mediated MTX influx, was insensitive to the presence of low levels of folic acid (100 nM). MTX influx by the low pH system showed saturability, with a K-t, of 5.3 mu M and a V-max of 1.53 nmol/g dry wt/min, was energy dependent, was inhibited by sulfobromophthalein with a K-t of 148 mu M, and had similar relative affinities for folic acid, leucovorin, and 5-methyltetrahydrofolate. Influx of 5-methyltetrahydrofolate was also mediated by this route. The data provide further confirmatory evidence for an MTX influx route in F2-MTX(r)A cells, optimal at low pH and distinct from the reduced folate carrier or the folate receptor. Copyright (C) 1996 Elsevier Science Inc.
引用
收藏
页码:223 / 231
页数:9
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