Down-regulation of lipids transporter ABCA1 increases the cytotoxicity of nitidine.
OBJECTIVE
Nitidine (NTD) cytotoxicity is highly specific for A549 human lung adenocarcinoma cells. We hypothesized that this cytotoxicity involved the accumulation of NTD in intracellular organelles. However, there have been no reports of NTD transporting factors. In this study, we screened for an NTD transporter and evaluated its association with NTD cytotoxicity.


METHODS
Gene expression analyses were done for A549 and human fetal lung normal diploid fibroblast (WI-38) cells. We screened for ABC transporter, multi-drug resistance-associated genes. Gene expressions of ATP-binding cassette transporter A1 (ABCA1) were confirmed in 8 cell lines by quantitative PCR. The involvement of ABCA1 in NTD cytotoxicity was evaluated using siRNA-mediated ABCA1 gene silencing.


RESULTS
Gene expression analysis indicated that A549 cells expressed higher levels of ABCC1, ABCC2, ABCC3, and ABCG2 and a lower level of ABCA1 compared to WI-38 cells. NTD resistant cell lines uniformly showed higher ABCA1 expression levels. Gene silencing experiments showed that the down-regulation of ABCA1 resulted in increased sensitivity to NTD.


CONCLUSIONS
These results indicated that NTD efflux is controlled by ABCA1 activity, suggesting that ABCA1 transports molecules other than lipids. Thus, there is a possibility that ABCA1 acts as a drug resistance transporter involved in the cytotoxicity of NTD derivatives. This also suggested that the expression level of the ABCA1 gene may be an indicator for the efficiency of NTD treatment.
Center of Molecular Biosciences, Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Okinawa, Japan. hiwasaki@comb.u-ryukyu.ac.jp
Hironori
H
Iwasaki
Takafumi
T
Okabe
Kensaku
K
Takara
Yasuhiko
Y
Yoshida
Kaoru
K
Hanashiro
Hirosuke
H
Oku
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000970:Antineoplastic Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D053119:Benzophenanthridines / Q000493:pharmacokinetics / Q000494:pharmacology*; D001692:Biological Transport; D045744:Cell Line, Tumor; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D016133:Polymerase Chain Reaction; D034741:RNA, Small Interfering / Q000008:administration & dosage
C577836:ABCA1 protein, human; C000715087:ABCC2 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D053119:Benzophenanthridines; D000089762:Multidrug Resistance-Associated Protein 2; D034741:RNA, Small Interfering; C013615:nitidine