title: Cardiac glycosides inhibit p53 synthesis by a mechanism relieved by Src or MAPK inhibition.
abstract: p53 is regulated at multiple levels. We report here that p53, in multiple lines of human cancer cells, is down-regulated by cardiac glycoside drugs digoxin and ouabain, potent inhibitors of Na(+)/K(+)-ATPase. These drugs reduced the basal levels of p53 protein at nanomolar concentrations in a dose-, time-, and cancer cell line-dependent manner, but independent of p53 status of wild-type or mutant. The drugs also reduced the levels of p53 induced by its activators as well as p53 transfected into human cancer cells, regardless of its status. Interestingly, the drugs had no effect on endogenous p53 in two immortalized human cell lines. Mechanistically, p53 reduction occurred not at the mRNA levels but at the protein levels, as a result of reduced protein synthesis rather than enhanced degradation. The cellular sensitivity to drug-induced p53 reduction was not associated with the levels of alphasubunits of Na(+)/K(+)-ATPase in different cell lines. Although lowering extracellular K(+) did not reduce p53 as did ouabain and digoxin, it did potentiate both digoxin- and ouabain-induced p53 reduction in sensitive lines. Finally, p53 reduction seems to be triggered by activation of Src/mitogen-activated protein kinase (MAPK) signaling pathways upon drug binding to the Na(+)/K(+)-ATPase and can be completely blocked by the inhibitors of Src or MAP/ERK kinase. This is the first report that cardiac glycoside drugs, by initiating the Src/MAPK signaling pathways, reduce the p53 levels via inhibition of p53 protein synthesis. The drugs may be useful in the treatment of human cancers with a gain-of-function p53 mutation.
authors.affiliation: Department of Radiation Oncology, University of Michigan Comprehensive Cancer Center, Ann Arbor, 48109, USA.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Min
authors.initials: M
authors.lastname: Zheng
authors.forename: Zhichuan
authors.initials: Z
authors.lastname: Li
authors.forename: Ruiguo
authors.initials: R
authors.lastname: Li
authors.forename: Lijun
authors.initials: L
authors.lastname: Jia
authors.forename: Xiufang
authors.initials: X
authors.lastname: Xiong
authors.forename: Noel
authors.initials: N
authors.lastname: Southall
authors.forename: Shaomeng
authors.initials: S
authors.lastname: Wang
authors.forename: Menghang
authors.initials: M
authors.lastname: Xia
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Austin
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.forename: Zijian
authors.initials: Z
authors.lastname: Xie
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
mesh_terms: D002301:Cardiac Glycosides / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D045325:HCT116 Cells; D019073:HT29 Cells; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism / Q000473:pathology; D008954:Models, Biological; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000037:antagonists & inhibitors*; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D002301:Cardiac Glycosides; D016159:Tumor Suppressor Protein p53; D016392:Proto-Oncogene Proteins pp60(c-src); D048049:Extracellular Signal-Regulated MAP Kinases
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