title: Down-regulation of Raf-1 kinase is associated with paclitaxel resistance in human breast cancer MCF-7/Adr cells.
abstract: Experiments were carried out to determine the role of Raf-1 kinase in the development of drug resistance and apoptosis induced by paclitaxel. In the present study, paclitaxel sensitivity, Raf-1 activity and mitogen-activated protein kinases activation were compared in two cell lines: parental human breast cancer cells and its drug resistant variant (MCF-7/Adr) cells. Paclitaxel treatment of parental MCF-7 cells caused a marked inhibition of Raf-1 kinase activity, concomitant with its mobility shift after 18 h exposure. In addition, paclitaxel greatly increased c-Jun N-terminal protein kinase (JNK) activity whereas showing a small enhancing effect on extracellular-regulated kinases (ERK) activity. Interestingly, MCF-7/Adr cells have lower basal Raf-1 activity, yet have much higher basal ERK activity than parental cells. However, it appeared that PD 98059, which turns off ERK through mitogen-activated protein kinase kinase (MEK) inhibition, enhanced basal Raf-1 kinase activity in MCF-7/Adr cells. Thus, the findings suggest that paclitaxel-induced apoptosis is mediated by JNK and occurs in parallel with suppression of the Raf-1 kinase activity in parental MCF-7 cells. In addition, down-regulation of Raf-1 kinase, which can be induced through the sustained ERK activation, may contribute to the development of acquired resistance in MCF-7/Adr cells.
authors.affiliation: Korea Institute of Toxicology, Korea Research Institute of Chemical Technology, P.O. Box 107,Yusong, Daejeon 305-600, South Korea. mikelee@kitox.re.kr
authors.forename: Michael
authors.initials: M
authors.lastname: Lee
authors.forename: Woo Suk
authors.initials: WS
authors.lastname: Koh
authors.forename: Sang Seop
authors.initials: SS
authors.lastname: Han
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D020935:MAP Kinase Signaling System; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D017239:Paclitaxel / Q000494:pharmacology*; D010766:Phosphorylation; D011233:Precipitin Tests; D019908:Proto-Oncogene Proteins c-raf / Q000096:biosynthesis*; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D017239:Paclitaxel; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one