title: Anomalous expression of P-glycoprotein in highly drug-resistant human KB cells.
abstract: KB-A1 and KB-A10 are 2 multi-drug-resistant cell lines which are 100- and 1,000-fold resistant to Adriamycin, respectively. We have examined the expression of P-glycoprotein at the molecular and cellular levels in these human carcinoma cells. Both MDR cell lines, when compared to the parental KB-3-1, show characteristic increases in mdr 1 gene copy number, an increase in mdr 1 mRNA expression, a corresponding increase in transcription rate and a consequent over-expression of P-glycoprotein. However, the more highly resistant KB-A10 cells have a lower gene copy number, express less mdr 1 mRNA and contain less P-glycoprotein than the A1 cell line. To determine whether higher levels of cellular resistance were attributable to enhanced efficacy of P-glycoprotein or to other cellular regulatory mechanisms, we examined other major cellular properties known to be associated with the mdr phenotype. Both the KB-A1 and KB-A10 lines exhibit similar increases in protein kinase C activity as compared to the drug-sensitive parent. In addition, neither glutathione-S-transferase nor topoisomerase II activities account for enhanced resistance of the KB-A10 cells. The above observations are contrary to the premise that the level of drug resistance is necessarily proportional to expression of P-glycoprotein or to other common factors thought to participate in drug insensitivity; consequently, new mechanisms of resistance must be in operation in these cells.
authors.affiliation: Department of Pharmacology, University of Vermont, College of Medicine, Burlington 05405.
authors.forename: E D
authors.initials: ED
authors.lastname: Dolci
authors.forename: R
authors.initials: R
authors.lastname: Abramson
authors.forename: Y
authors.initials: Y
authors.lastname: Xuan
authors.forename: J
authors.initials: J
authors.lastname: Siegfried
authors.forename: K A
authors.initials: KA
authors.lastname: Yuenger
authors.forename: D S
authors.initials: DS
authors.lastname: Yassa
authors.forename: T R
authors.initials: TR
authors.lastname: Tritton
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D015153:Blotting, Western; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology; D004351:Drug Resistance; D015870:Gene Expression; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007624:KB Cells / Q000187:drug effects* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D010750:Phosphoproteins; D004317:Doxorubicin; D005982:Glutathione Transferase; D011493:Protein Kinase C; D004250:DNA Topoisomerases, Type II