title: P-glycoprotein (MDR1) expression in leukemic cells is regulated at two distinct steps, mRNA stabilization and translational initiation.
abstract: Multidrug resistance in acute myeloid leukemia is often conferred by overexpression of P-glycoprotein, encoded by the MDR1 gene. We have characterized the key regulatory steps in the development of multidrug resistance in K562 myelogenous leukemic cells. Unexpectedly, up-regulation of MDR1 levels was not due to transcriptional activation but was achieved at two distinct post-transcriptional steps, mRNA turnover and translational regulation. The short-lived (half-life 1 h) MDR1 mRNA of naive cells (not exposed to drugs) was stabilized (half-life greater than 10 h) following short-term drug exposure. However, this stabilized mRNA was not associated with translating polyribosomes and did not direct P-glycoprotein synthesis. Selection for drug resistance, by long-term exposure to drug, led to resistant lines in which the translational block was overcome such that the stabilized mRNA was translated and P-glycoprotein expressed. The absence of a correlation between steady-state MDR1 mRNA and P-glycoprotein levels was not restricted to K562 cells but was found in other lymphoid cell lines. These findings have implications for the avoidance or reversal of multidrug resistance in the clinic.
authors.affiliation: Medical Research Council Clinical Sciences Centre, Imperial College Faculty of Medicine, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.
authors.forename: Ernesto
authors.initials: E
authors.lastname: Yague
authors.forename: Angel L
authors.initials: AL
authors.lastname: Armesilla
authors.forename: Georgina
authors.initials: G
authors.lastname: Harrison
authors.forename: James
authors.initials: J
authors.lastname: Elliott
authors.forename: Alessandro
authors.initials: A
authors.lastname: Sardini
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Higgins
authors.forename: Selina
authors.initials: S
authors.lastname: Raguz
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D015973:Gene Expression Regulation, Leukemic; D015321:Gene Rearrangement; D006801:Humans; D020014:K562 Cells; D014176:Protein Biosynthesis; D021381:Protein Transport; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015533:Transcriptional Activation
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D012333:RNA, Messenger; D013755:Tetradecanoylphorbol Acetate