title: Digitalis-induced signaling by Na+/K+-ATPase in human breast cancer cells.
abstract: Because beneficial effects of digitalis treatment in breast cancer patients have been suggested by epidemiological studies, we explored the mechanism of the growth inhibitory effects of these drugs on the estrogen receptor-negative human breast cancer cell line MDA-MB-435 s. Ouabain concentrations (100 nM or lower) that caused less than 25% inhibition of the pumping function of Na+/K+-ATPase had no effect on cell viability but inhibited proliferation. At the same concentrations, ouabain 1) activated Src kinase and stimulated the interaction of Src and Na+/K+-ATPase with epidermal growth factor receptor (EGFR); 2) caused a transient and then a sustained activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2); 3) increased the expression of p21Cip1 but decreased that of p53; and 4) activated c-Jun NH2-terminal kinase (JNK) but not p38 kinase. These data, in conjunction with our previous findings on the signaling role of Na+/K+-ATPase in other cells, suggest that ouabain-induced activation/transactivation of Src/EGFR by Na+/K+-ATPase leads to activation of ERK1/2, the resulting increase in the level of cell cycle inhibitor p21Cip1, and growth arrest. Cooperation of JNK with ERK1/2 in this process is also suggested. Digoxin and digitoxin concentrations close to or at the therapeutic plasma levels had effects on proliferation and ERK1/2 similar to those of ouabain, supporting the proposed potential value of digitalis drugs for the treatment of breast cancer.
authors.affiliation: Department of Pharmacology, Medical College of Ohio, 3035 Arlington Ave., Toledo, OH 43614-5804, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Kometiani
authors.forename: Lijun
authors.initials: L
authors.lastname: Liu
authors.forename: Amir
authors.initials: A
authors.lastname: Askari
mesh_terms: D001943:Breast Neoplasms; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004071:Digitalis Glycosides / Q000494:pharmacology*; D066246:ErbB Receptors / Q000502:physiology; D005260:Female; D006801:Humans; D007700:Kinetics; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D004071:Digitalis Glycosides; D010042:Ouabain; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000254:Sodium-Potassium-Exchanging ATPase