title: Differential expression and activity of phosphatases and protein kinases in adriamycin sensitive and resistant human breast cancer MCF-7 cells.
abstract: Multidrug resistance is one of the major obstacles in cancer chemotherapy. In tumor cells, overexpression of the transmembrane P-glycoprotein 170 (P-gp) is associated with the multidrug resistance phenotype and serves as a drug efflux pump. The activation of P-gp has been suggested to occur at the post-translational level. Protein kinase C mediated phosphorylation may be associated with the drug effux mechanism but the overall phosphorylation pathway has not been completely defined. we report the novel finding of an increase in phosphatase 1B (a tyrosine phosphatase) and a decrease in PP1 and PP2A (serine/threonine phosphatases) expression and activity in our series of early (R65) and late (R500) stage adriamycin resistant MCF-7 cells. In addition, we show a decrease in protein kinase A (PKA) activity and an increase in protein kinase C (PKC) in our drug resistant cells. Analyses of PKC isoforms alpha through epsilon revealed that PKCbeta was not expressed and that all other isoforms increased with increasing resistance, except PKCgamma which was detected only in R65 cells. Our findings suggest that in drug resistant cells, there is a pattern consistant with the maintenance of serine and threonine residues in a phosphorylated state.
authors.affiliation: Cellular Defense and Carcinogenesis Section, Laboratory of Nutritional and Molecular Regulation, National Cancer Institute, Frederick, MD 21702, USA.
authors.forename: D
authors.initials: D
authors.lastname: Ratnasinghe
authors.forename: J M
authors.initials: JM
authors.lastname: Phang
authors.forename: G C
authors.initials: GC
authors.lastname: Yeh
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000201:enzymology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000903:Antibiotics, Antineoplastic; D007527:Isoenzymes; D004317:Doxorubicin; D011494:Protein Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010744:Phosphoric Monoester Hydrolases