title: Repression of mitogen-activated protein kinase (MAPK) phosphatase-1 by anthracyclines contributes to their antiapoptotic activation of p44/42-MAPK.
abstract: Anthracyclines are commonly used chemotherapeutics, and in some models enhance p44/42-mitogen-activated protein kinase (MAPK) pathway signaling by effects on upstream kinases. To evaluate the impact of anthracyclines on p44/42-MAPK in breast cancer, A1N4-myc human mammary and BT-474 and MDA-MB-231 breast carcinoma cells were studied. Treatment with doxorubicin or epirubicin resulted in increased phospho-p44/42-MAPK levels in a time- and concentration-dependent manner. This was associated with p44/42 activation, as reflected by increased p90 ribosomal protein S6 kinase and Bad phosphorylation. Activation of p44/42 appeared to be antiapoptotic, since MAPK stimulation with epidermal growth factor or a dominant-positive p42 construct inhibited apoptosis. Modest activation of the upstream MAPK kinase MEK was noted under some conditions, but inhibition of MEK did not abolish p44/42 activation, suggesting a contribution from another mechanism. Anthracyclines were found to decrease expression of MAPK phosphatase-1 (MKP-1) both in vitro and in vivo. MKP-1 mRNA levels were decreased in anthracycline-treated cells, and transcription from the MKP-1 promoter was repressed. Inhibition of MKP-1 expression through the use of small interfering RNAs decreased the ability of anthracyclines to induce phospho-p44/42. Wild-type mouse embryo fibroblasts (MEFs) treated with doxorubicin showed increased phospho-p44/42-MAPK levels, but MEFs from MKP-1 heterozygous and homozygous knockout mice had blunted p44/42 activation. These studies support the ability of anthracyclines to activate antiapoptotic p44/42-MAPK phosphorylation in breast cancer, and indicate that this occurs in part through the novel mechanism of repression of MKP-1 transcription.
authors.affiliation: University of North Carolina at Chapel Hill, 22-003 Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599-7295, USA.
authors.forename: George W
authors.initials: GW
authors.lastname: Small
authors.forename: Sivagurunathan
authors.initials: S
authors.lastname: Somasundaram
authors.forename: Dominic T
authors.initials: DT
authors.lastname: Moore
authors.forename: Yue Y
authors.initials: YY
authors.lastname: Shi
authors.forename: Robert Z
authors.initials: RZ
authors.lastname: Orlowski
mesh_terms: D000818:Animals; D018943:Anthracyclines / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000201:enzymology; D045744:Cell Line, Tumor; D002999:Clone Cells; D054638:Dual Specificity Phosphatase 1; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology; D005260:Female; D005455:Fluorescent Antibody Technique; D020868:Gene Silencing / Q000187:drug effects; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic
chemical_list: D018943:Anthracyclines; D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D008156:Luciferases; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D054645:Protein Phosphatase 1; C517019:DUSP1 protein, human; D054638:Dual Specificity Phosphatase 1; C517020:Dusp1 protein, mouse; D017027:Protein Tyrosine Phosphatases