Carcinogenesis Advance Access originally published online on September 26, 2008
Carcinogenesis 2008 29(12):2289-2297; doi:10.1093/carcin/bgn223
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Analysis of ABCG2 expression and side population identifies intrinsic drug efflux in the HCC cell line MHCC-97L and its modulation by Akt signaling
Department of General Surgery, the First Affiliated Hospital, School of Medicine, Zhejiang University, 79 Qingchun Road, Hangzhou 310003, People’s Republic of China
1 State Key Laboratory of Oncogenes and Related Genes, Shanghai Cancer Institute and Cancer Institute of Shanghai Jiao Tong University, 25/Ln 2200 Xietu Road, Shanghai 200032, People’s Republic of China
* To whom correspondence should be addressed. Tel: +86 21 64432140; Fax: +86 21 64432140; Email: jjli{at}shsci.org
Correspondence may also be addressed to Shusen Zheng. Tel: +86 571 87236466; Fax: +86 571 87236609;Email: shusenzheng{at}zju.edu.cn
Active drug efflux by the adenosine triphosphate-binding cassette (ABC) transporter ABCG2 is one of the common mechanisms causing multiple drug resistance in various human cancers. In the intrinsic drug resistance of hepatocellular carcinoma (HCC), the role of ABCG2 is closely associated with ‘side population (SP)’, a minor subset of cancer stem-like cells with unique capacity to extrude lipophilic dye Hoechst 33342 and many chemotherapeutic agents. In this study, we showed that ABCG2 was intrinsically expressed in a subgroup of HCC tissues and its expression pattern significantly influenced the levels of drug efflux from HCC cell lines. In MHCC-97L HCC cell line with intrinsic ABCG2 expression, we confirmed the importance of SP cells to the drug efflux-related chemotherapy resistance and found that the SP analysis provided an efficient method to evaluate the functional activity of ABCG2 transporter. In this cell line, we discovered that the SP proportion was modulated by the treatments of Akt signaling inhibitors and serum supplement, which led to the finding that Akt signaling was able to regulate the SP cells’ efflux activity via altering the subcellular localization of ABCG2 transporter. We further demonstrated that the Akt signaling inhibition attenuated the doxorubicin efflux from MHCC-97L cells and increased the drug efficacy. Our results indicate the protective role of intrinsic ABCG2 expression in HCC cells and suggest that suppressing Akt signaling could help overcome the drug efflux by ABCG2 transporter.
Abbreviations: ABC, adenosine triphosphate-binding cassette; DMEM, Dulbecco’s modified Eagle’s medium; FBS, fetal bovine serum; FTC, fumitremorgin C; HCC, hepatocellular carcinoma; mTOR, mammalian target of rapamycin; PBS, phosphate-buffered saline; PCR, polymerase chain reaction; PI3K, phosphoinositide 3-kinase; siRNA, small-interfering RNA; SP, side population
These authors contributed equally to this work. Received April 1, 2008; revised September 12, 2008; accepted September 19, 2008.