title: Effect of phorbol 12-myristate 13-acetate on function and gene expression of P-glycoprotein in adriamycin-resistant K562/ADM cells.
abstract: OBJECTIVE
  Multidrug resistance (MDR) is a critical issue during chemotherapy of cancers. Phorbol 12-myristate 13-acetate (PMA), a diester of phorbol, is a typical activator of protein kinase C (PKC). In the present study, we investigated the effect of PMA on MDR and P-glycoprotein (P-gp) gene expression in K562/ADM cells.
  
  
  METHODS
  3-(4,5-dimethylthiazol-2-thiazolyl)-2,5-diphenyltetrazolium bromide assay was used to assess adriamycin (Adr)-induced cytotoxicity towards K562/ADM cells in the absence or presence of PMA. The intracellular accumulation of Adr was measured by determining the mean fluorescence intensity. The effect of PMA on P-gp activity was investigated by rhodamine-123 accumulation and efflux experiment. Protein expression and mRNA expression of P-gp in K562/ADM cells were determined by Western blot analysis and real-time qPCR, respectively.
  
  
  RESULTS
  Adr-induced cytotoxicity towards K562/ADM cells was significantly decreased by PMA at 5 μmol/l. Furthermore, intracellular Adr-associated mean fluorescence intensity was attenuated by 53.8% 1 h after exposure to PMA at 5 μmol/l compared with the control group (p < 0.05). A dose-dependent decrease of intracellular rhodamine-123 and increase of efflux activity of P-gp were also observed in K562/ADM cells incubation with PMA. In addition, P-gp mRNA and protein expression were significantly induced by PMA.
  
  
  CONCLUSIONS
  Activation of PKC pathway by PMA can significantly induce expression and activity of P-gp, and thus decrease intracellular Adr level and strengthen MDR in K562/ADM cells.
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou, PR China.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Li
authors.forename: Huichang
authors.initials: H
authors.lastname: Bi
authors.forename: Guoping
authors.initials: G
authors.lastname: Zhong
authors.forename: Ling
authors.initials: L
authors.lastname: Huang
authors.forename: Gelin
authors.initials: G
authors.lastname: Li
authors.forename: Yanzhe
authors.initials: Y
authors.lastname: Xia
authors.forename: Xiao
authors.initials: X
authors.lastname: Chen
authors.forename: Min
authors.initials: M
authors.lastname: Huang
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics* / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D020014:K562 Cells; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D012333:RNA, Messenger; D004317:Doxorubicin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate