title: Mitochondrial localization of ABC transporter ABCG2 and its function in 5-aminolevulinic acid-mediated protoporphyrin IX accumulation.
abstract: Accumulation of protoporphyrin IX (PpIX) in malignant cells is the basis of 5-aminolevulinic acid (ALA)-mediated photodynamic therapy. We studied the expression of proteins that possibly affect ALA-mediated PpIX accumulation, namely oligopeptide transporter-1 and -2, ferrochelatase and ATP-binding cassette transporter G2 (ABCG2), in several tumor cell lines. Among these proteins, only ABCG2 correlated negatively with ALA-mediated PpIX accumulation. Both a subcellular fractionation study and confocal laser microscopic analysis revealed that ABCG2 was distributed not only in the plasma membrane but also intracellular organelles, including mitochondria. In addition, mitochondrial ABCG2 regulated the content of ALA-mediated PpIX in mitochondria, and Ko143, a specific inhibitor of ABCG2, enhanced mitochondrial PpIX accumulation. To clarify the possible roles of mitochondrial ABCG2, we characterized stably transfected-HEK (ST-HEK) cells overexpressing ABCG2. In these ST-HEK cells, functionally active ABCG2 was detected in mitochondria, and treatment with Ko143 increased ALA-mediated mitochondrial PpIX accumulation. Moreover, the mitochondria isolated from ST-HEK cells exported doxorubicin probably through ABCG2, because the export of doxorubicin was inhibited by Ko143. The susceptibility of ABCG2 distributed in mitochondria to proteinase K, endoglycosidase H and peptide-N-glycosidase F suggested that ABCG2 in mitochondrial fraction is modified by N-glycans and trafficked through the endoplasmic reticulum and Golgi apparatus and finally localizes within the mitochondria. Thus, it was found that ABCG2 distributed in mitochondria is a functional transporter and that the mitochondrial ABCG2 regulates ALA-mediated PpIX level through PpIX export from mitochondria to the cytosol.
authors.affiliation: Department of Cell Chemistry, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan. hkobuchi@md.okayama-u.ac.jp
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Kobuchi
authors.forename: Koko
authors.initials: K
authors.lastname: Moriya
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ogino
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Fujita
authors.forename: Keiji
authors.initials: K
authors.lastname: Inoue
authors.forename: Taro
authors.initials: T
authors.lastname: Shuin
authors.forename: Tatsuji
authors.initials: T
authors.lastname: Yasuda
authors.forename: Kozo
authors.initials: K
authors.lastname: Utsumi
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Utsumi
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000622:Aminolevulinic Acid / Q000378:metabolism* / Q000494:pharmacology / Q000633:toxicity; D001692:Biological Transport; D045744:Cell Line, Tumor; D054659:Diketopiperazines; D004317:Doxorubicin / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005294:Ferrochelatase / Q000378:metabolism; D015870:Gene Expression; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D057809:HEK293 Cells; D006576:Heterocyclic Compounds, 4 or More Rings; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D000074011:Peptide Transporter 1; D021381:Protein Transport; D011524:Protoporphyrins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D027981:Symporters / Q000378:metabolism; D020298:U937 Cells
chemical_list: C541506:3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6,7,12,12a-octahydropyrazino(1',2'-1,6)pyrido(3,4-b)indol-3-yl)propionic acid tert-butyl ester; C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D054659:Diketopiperazines; D006576:Heterocyclic Compounds, 4 or More Rings; D009363:Neoplasm Proteins; D000074011:Peptide Transporter 1; D011524:Protoporphyrins; D011993:Recombinant Fusion Proteins; C082186:SLC15A1 protein, human; D027981:Symporters; C093694:hydrogen-coupled oligopeptide transporter PepT2; D004317:Doxorubicin; D000622:Aminolevulinic Acid; C028025:protoporphyrin IX; D005294:Ferrochelatase; D000241:Adenosine