Down-regulation of CD98 in melphalan-resistant myeloma cells with reduced drug uptake.
Although melphalan has been used as a therapeutic reagent for multiple myeloma, many patients become refractory. To elucidate the mechanism of resistance to melphalan, we generated a melphalan-resistant myeloma cell line, KHM-11(EMS), by treating a parental line, KHM-11, with a mutagen, ethylmethanesulfonate. KHM-11(EMS) is 55 times more resistant to melphalan. gamma-Glutamylcysteine synthetase, P-glycoprotein, multidrug-resistance-associated protein, lung-resistance-related protein and the Bcl-2 family of proteins were not responsible for the drug resistance in KHM-11(EMS). Intracellular incorporation of melphalan to myeloma cells was determined by using [(14)C]-labeled melphalan. Accumulation of melphalan in KHM-11(EMS) was 43% of KHM-11, while the efflux rates were comparable in both cell lines. The uptake of melphalan was inhibited by the addition of L-phenylalanine, indicating that melphalan is incorporated through the L-phenylalanine transporter as reported previously. Expression of CD98, which was recently cloned as an L-phenylalanine transporter, was 6-fold decreased in KHM-11(EMS), suggesting that CD98 may be correlated with the incorporation of melphalan. CD98 expression and incorporation of melphalan were analyzed in fresh purified myeloma cells from 5 patients. All myeloma cells from 4 cases expressed CD98 at a high level and incorporated melphalan. However, tumor cells from 1 case expressed CD98 at low levels and did not incorporate melphalan. Taken together, reduced melphalan uptake could be responsible for the drug resistance in KHM-11(EMS), and down-regulation of CD98 may be related to this phenomenon. Further investigation of the correlation between impaired drug uptake and down-regulation of CD98 in myeloma cells should be important to understand the mechanism of resistance to melphalan.
Department of Internal Medicine II, Kumamoto University School of Medicine, Kumamoto, Japan.
N
N
Harada
A
A
Nagasaki
H
H
Hata
H
H
Matsuzaki
F
F
Matsuno
H
H
Mitsuya
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis / Q000235:genetics; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics; D015703:Antigens, CD / Q000096:biosynthesis* / Q000235:genetics; D000951:Antigens, Neoplasm / Q000096:biosynthesis* / Q000235:genetics; D018906:Antineoplastic Agents, Alkylating / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects / Q000235:genetics; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D018432:Drug Resistance, Multiple / Q000235:genetics; D019008:Drug Resistance, Neoplasm; D005020:Ethyl Methanesulfonate; D027261:Fusion Regulatory Protein-1; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D005721:Glutamate-Cysteine Ligase / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D008558:Melphalan / Q000378:metabolism / Q000494:pharmacology*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009101:Multiple Myeloma / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D010649:Phenylalanine / Q000378:metabolism / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D020394:Vault Ribonucleoprotein Particles / Q000096:biosynthesis / Q000235:genetics; D000099187:Major Vault Protein
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D018906:Antineoplastic Agents, Alkylating; D002352:Carrier Proteins; D005020:Ethyl Methanesulfonate; D027261:Fusion Regulatory Protein-1; D005721:Glutamate-Cysteine Ligase; D008558:Melphalan; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D010649:Phenylalanine; D020394:Vault Ribonucleoprotein Particles; D000099187:Major Vault Protein