title: Effects of P-glycoprotein and its inhibitors on apoptosis in K562 cells.
abstract: P-glycoprotein (P-gp) is a major factor in multidrug resistance (MDR) which is a serious obstacle in chemotherapy. P-gp has also been implicated in causing apoptosis of tumor cells, which was shown to be another important mechanism of MDR recently. To study the influence of P-gp in tumor cell apoptosis, K562/A cells (P-gp+) and K562/S cells (P-gp-) were subjected to doxorubicin (Dox), serum withdrawal, or independent co-incubation with multiple P-gp inhibitors, including valspodar (PSC833), verapamil (Ver) and H108 to induce apoptosis. Apoptosis was simultaneously detected by apoptotic rate, cell cycle by flow cytometry and cysteine aspartic acid-specific protease 3 (caspase 3) activity by immunoassay. Cytotoxicity and apoptosis induced by PSC833 were evaluated through an MTT method and apoptosis rate, and cell cycle combined with caspase 3 activity, respectively. The results show that K562/A cells are more resistant to apoptosis and cell cycle arrest than K562/S cells after treatment with Dox or serum deprivation. The apoptosis of K562/A cells increased after co-incubation with each of the inhibitors of P-gp. P-gp inhibitors also enhanced cell cycle arrest in K562/A cell. PSC833 most strikingly decreased viability and led to apoptosis and S phase arrest of cell cycle in K562/A cells. Our study demonstrates that P-gp inhibits the apoptosis of tumor cells in addition to participating in the efflux of intracellular chemotherapy drugs. The results of the caspase 3 activity assay also suggest that the role of P-gp in apoptosis avoidance is caspase-related.
authors.affiliation: Department of Health Statistics, School of Public Health, Tianjin Medical University, 22 Qixiangtai Road, Heping District, Tianjin 300070, China. zuyq@tijmu.edu.cn.
authors.forename: Yaqiong
authors.initials: Y
authors.lastname: Zu
authors.affiliation: HUYA Bioscience International LLC, 3 Haidian Avenue, Haidian District, Beijing 100080, China. yzy_lz@hotmail.com.
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Department of Biochemistry and Molecular Biology, School of Basic Courses, Guangdong Pharmaceutical University, 280 Waihuandong Road, Guangzhou Higher Education Mega Center, Guangzhou 510006, China. songstang@hotmail.com.
authors.forename: Songshan
authors.initials: S
authors.lastname: Tang
authors.affiliation: Biotherapy Center of Tianjin Cancer Institute and Hospital, Tianjin Medical University, Tiyuanbei, Huanhuxi Road, Hexi District, Tianjin 300060, China. 13612190539@163.com.
authors.forename: Ying
authors.initials: Y
authors.lastname: Han
authors.affiliation: Department of Health Statistics, School of Public Health, Tianjin Medical University, 22 Qixiangtai Road, Heping District, Tianjin 300070, China. junma@tmu.edu.cn.
authors.forename: Jun
authors.initials: J
authors.lastname: Ma
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000008:administration & dosage; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000096:biosynthesis; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D003524:Cyclosporins / Q000008:administration & dosage; D004317:Doxorubicin / Q000008:administration & dosage; D018432:Drug Resistance, Multiple / Q000187:drug effects / Q000235:genetics*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D005434:Flow Cytometry; D006801:Humans; D020014:K562 Cells; D014700:Verapamil / Q000008:administration & dosage
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D003524:Cyclosporins; D004317:Doxorubicin; D014700:Verapamil; D053148:Caspase 3; C070272:valspodar