Abstract
Intrinsic expression of the multidrug resistance (MDR) transporter P-glycoprotein (Pgp) may be regulated by reactive oxygen species (ROS). A transient expression of Pgp was observed during the growth of multicellular tumor spheroids. Maximum Pgp expression occurred in tumor spheroids with a high percentage of quiescent, Ki-67-negative cells, elevated glutathione levels, increased expression of the cyclin-dependent kinase inhibitors p27Kip1 and p21WAF-1 as well as reduced ROS levels and minor activity of the mitogen-activated kinase (MAPK) members c-Jun amino-terminal kinase (JNK), extracellular signal-regulated kinase ERK1,2, and p38 MAPK. Raising intracellular ROS by depletion of glutathione with buthionine sulfoximine (BSO) or glutamine starvation resulted in down-regulation of Pgp and p27Kip1, whereas ERK1,2 and JNK were activated. Down-regulation of Pgp was furthermore observed with low concentrations of hydrogen peroxide and epidermal growth factor, indicating that ROS may regulate Pgp expression. The down-regulation of Pgp following BSO treatment was abolished by agents interfering with receptor tyrosine kinase signaling pathways, i.e. the protein kinase C inhibitors bisindolylmaleimide I (BIM-1) and Ro-31-8220, the p21ras farnesyl protein transferase inhibitor III, the c-Raf inhibitor ZM 336372 and PD98059, which inhibits ERK1,2 activation. ROS involved as second messengers in receptor tyrosine kinase signaling pathways may act as negative regulators of Pgp expression.
MeSH terms
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ATP Binding Cassette Transporter, Subfamily B, Member 1 / genetics*
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Buthionine Sulfoximine / pharmacology*
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Carcinoma, Hepatocellular
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Cell Cycle Proteins*
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Cell Division
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclin-Dependent Kinase Inhibitor p27
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Cyclins / genetics
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Cyclins / metabolism
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Drug Resistance, Multiple / genetics
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Enzyme Inhibitors / metabolism
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Enzyme Inhibitors / pharmacology
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Epidermal Growth Factor / pharmacology
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Gene Expression Regulation, Neoplastic / drug effects
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Gene Expression Regulation, Neoplastic / physiology*
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Glutathione / metabolism
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Humans
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Hydrogen Peroxide / pharmacology
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JNK Mitogen-Activated Protein Kinases
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Kinetics
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Liver Neoplasms
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MAP Kinase Signaling System / drug effects
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MAP Kinase Signaling System / physiology
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Male
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Melanoma
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Microtubule-Associated Proteins / genetics
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Microtubule-Associated Proteins / metabolism
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases / metabolism
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Prostatic Neoplasms / genetics
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Prostatic Neoplasms / pathology
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Protein-Tyrosine Kinases / metabolism
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Reactive Oxygen Species / physiology*
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Tumor Cells, Cultured
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Tumor Suppressor Proteins*
Substances
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ATP Binding Cassette Transporter, Subfamily B, Member 1
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CDKN1A protein, human
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Cell Cycle Proteins
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Enzyme Inhibitors
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Microtubule-Associated Proteins
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Reactive Oxygen Species
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Tumor Suppressor Proteins
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Cyclin-Dependent Kinase Inhibitor p27
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Buthionine Sulfoximine
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Epidermal Growth Factor
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Hydrogen Peroxide
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Protein-Tyrosine Kinases
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JNK Mitogen-Activated Protein Kinases
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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Glutathione