Abstract
Overexpression of ErbB-2/Neu has been causally associated with mammary epithelial transformation. Here we report that blockade of the epidermal growth factor receptor (EGFR) kinase with AG-1478 markedly delays breast tumor formation in mouse mammary tumor virus (MMTV)/Neu + MMTV/transforming growth factor alpha bigenic mice. This delay was associated with inhibition of EGFR and Neu signaling, reduction of cyclin-dependent kinase 2 (Cdk2) and mitogen-activated protein kinase (MAPK) activities and cyclin D1, and an increase in the levels of the Cdk inhibitor p27(Kip1). In addition, BrdUrd incorporation into tumor cell nuclei was prevented with no signs of tumor cell apoptosis. These observations prompted us to investigate the stability of p27. Recombinant p27 was degraded rapidly in vitro by untreated but not by AG-1478-treated tumor lysates. Proteasome depletion of the tumor lysates, addition of the specific MEK1/2 inhibitor U-0126, or a T187A mutation in recombinant p27 all prevented p27 degradation. Cdk2 and MAPK precipitates from untreated tumor lysates phosphorylated recombinant wild-type p27 but not the T187A mutant in vitro. Cdk2 and MAPK precipitates from AG-1478-treated tumors were unable to phosphorylate p27 in vitro. These data suggest that increased signaling by ErbB receptors up-regulates MAPK activity, which, in turn, phosphorylates and destabilizes p27, thus contributing to dysregulated cell cycle progression.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, Non-P.H.S.
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Animals
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Butadienes / pharmacology
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CDC2-CDC28 Kinases*
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Cell Cycle Proteins*
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Cell Division / drug effects
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Cell Transformation, Neoplastic* / drug effects
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Cyclin D1 / metabolism
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase Inhibitor p27
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Cyclin-Dependent Kinases / metabolism
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Cysteine Endopeptidases / metabolism
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DNA / biosynthesis
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Dimerization
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Down-Regulation / drug effects
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ErbB Receptors / antagonists & inhibitors*
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ErbB Receptors / metabolism*
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Female
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Humans
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Mammary Neoplasms, Experimental / genetics
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Mammary Neoplasms, Experimental / metabolism
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Mammary Neoplasms, Experimental / pathology*
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Mammary Tumor Virus, Mouse / genetics
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Mammary Tumor Virus, Mouse / physiology
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Mice
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Mice, Transgenic
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Microtubule-Associated Proteins / genetics
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Microtubule-Associated Proteins / metabolism
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Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors
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Mitogen-Activated Protein Kinase Kinases / metabolism
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Mitogen-Activated Protein Kinases / metabolism
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Multienzyme Complexes / metabolism
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Nitriles / pharmacology
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Phosphorylation / drug effects
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Proteasome Endopeptidase Complex
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Protein Serine-Threonine Kinases / metabolism
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Quinazolines
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Receptor, ErbB-2 / genetics
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Receptor, ErbB-2 / metabolism*
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Signal Transduction / drug effects
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Time Factors
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Transforming Growth Factor alpha / genetics
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Transforming Growth Factor alpha / metabolism*
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Tumor Cells, Cultured
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Tumor Suppressor Proteins*
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Tyrphostins / pharmacology
Substances
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Butadienes
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Cdkn1b protein, mouse
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Cell Cycle Proteins
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Microtubule-Associated Proteins
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Multienzyme Complexes
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Nitriles
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Quinazolines
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Transforming Growth Factor alpha
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Tumor Suppressor Proteins
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Tyrphostins
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U 0126
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Cyclin D1
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Cyclin-Dependent Kinase Inhibitor p27
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RTKI cpd
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DNA
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ErbB Receptors
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Receptor, ErbB-2
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Protein Serine-Threonine Kinases
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CDC2-CDC28 Kinases
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CDK2 protein, human
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Cdk2 protein, mouse
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinases
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Mitogen-Activated Protein Kinases
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Mitogen-Activated Protein Kinase Kinases
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex