Polyamines upregulate the mRNA expression of cationic amino acid transporter-1 in human retinal pigment epithelial cells.
We previously showed that ornithine was mainly transported via cationic amino acid transporter (CAT)-1 in human retinal pigment epithelial (RPE) cell line, human telomerase RT (hTERT)-RPE, and that CAT-1 was involved in ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient cell produced by a OAT specific inhibitor, 5-fluoromethylornithine (5-FMO). We showed here that CAT-1 mRNA expression was increased by ornithne in OAT-deficient RPE cells, which was reversed by an inhibitor of ornithine decarboxylase (ODC), alpha-difluoromethylornithine (DFMO). Polyamines, especially spermine, one of the metabolites of ODC, also enhanced the expression of CAT-1 mRNA. ODC mRNA expression was also increased by ornithine and polyamines, and gene silencing of ODC by siRNA decreased ornithine transport activity and its cytotoxicity. In addition, the mRNA of nuclear protein c-myc was also increased in 5-FMO- and ornithine-treated hTERT-RPE cells, and gene silencing of c-myc prevented the induction of CAT-1 and ODC. Increases in expression of CAT-1, ODC, and c-myc, and the inhibition of these stimulated expression by DFMO were also observed in primary porcine RPE cells. These results suggest that spermine plays an important role in stimulation of mRNA expression of CAT-1, which is a crucial role in ornithine cytotoxicity in OAT-deficient hTERT-RPE cells.
Kaneko
Shiho
S
Department of Ophthalmology, Kansai Medical University, Moriguchi, Osaka, Japan.
Okuda-Ashitaka
Emiko
E
Ando
Akira
A
Nishimura
Kazuhiro
K
Igarashi
Kazuei
K
Maeda
Masahide
M
Furuta
Kyoji
K
Suzuki
Masaaki
M
Matsumura
Miyo
M
Ito
Seiji
S
D000818:Animals; D027201:Cationic Amino Acid Transporter 1 / Q000096:biosynthesis* / Q000235:genetics; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D000518:Eflornithine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D027283:Large Neutral Amino Acid-Transporter 1 / Q000096:biosynthesis / Q000235:genetics; D009952:Ornithine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology / Q000633:toxicity; D009955:Ornithine Decarboxylase / Q000235:genetics / Q000378:metabolism; D065108:Ornithine Decarboxylase Inhibitors; D009953:Ornithine-Oxo-Acid Transaminase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D011700:Putrescine / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis*; D034741:RNA, Small Interfering / Q000378:metabolism; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism; D013552:Swine; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
D027201:Cationic Amino Acid Transporter 1; D004791:Enzyme Inhibitors; D027283:Large Neutral Amino Acid-Transporter 1; C489427:MYC protein, human; D065108:Ornithine Decarboxylase Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C420825:SLC7A1 protein, human; C057405:5-fluoromethylornithine; D013096:Spermine; D009952:Ornithine; D009953:Ornithine-Oxo-Acid Transaminase; D019098:Telomerase; D009955:Ornithine Decarboxylase; D013095:Spermidine; D011700:Putrescine; D000518:Eflornithine