title: Reciprocal changes in p27(Kip1) and p21(Cip1) in growth inhibition mediated by blockade or overstimulation of epidermal growth factor receptors.
abstract: Many human epithelial tumors express high levels of epidermal growth factor (EGF) receptors. A human-mouse chimeric version of anti-EGF receptor monoclonal antibody (mAb) C225, which blocks receptor activation and produces inhibition of cell proliferation, is currently being investigated in clinical trials. When cells bear high numbers of EGF receptors, either complete blockade of receptors with mAb 225 or full activation of receptors with EGF results in inhibition of proliferation. In the present study, we have explored the molecular mechanisms explaining how a receptor inhibitor, mAb 225, and a receptor activator, EGF, can both produce growth inhibition of A431 human squamous epithelial carcinoma cells. We reported previously that inhibition of A431 cells by EGF is associated with up-regulation of p21(Cip1). We now demonstrate that mAb 255-mediated inhibition is associated with up-regulation of p27(Kip1), which binds to and inactivates cyclin-dependent kinase-2 activity and produces cell cycle arrest in G1. Furthermore, inhibition by mAb 225 can be overcome by titrating the cultures with increasing concentrations of EGF, which is accompanied by a concurrent fall in the level of p27(Kip1). At properly titrated concentrations of mAb 225 and EGF, the inhibitory activities of both mAb 225 and EGF are counterbalanced and abolished. When EGF concentrations reach levels high enough to compete with mAb to produce near-saturating levels of receptor activation, p27(Kip1) falls below basal levels; however, the concomitant marked rise in the level of p21(Cip1) results in growth inhibition. Our data suggest that although p27(Kip1) and p21(Cip1) are induced and act independently, they play reciprocal roles in mediating inhibition of A431 cell growth by blockade of EGF receptors with mAb 225 and by activation of receptors with saturating concentrations of EGF.
authors.affiliation: The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Fan
authors.forename: B Y
authors.initials: BY
authors.lastname: Shang
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: J L
authors.initials: JL
authors.lastname: Chou
authors.forename: J
authors.initials: J
authors.lastname: Mendelsohn
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D016213:Cyclins / Q000502:physiology*; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: D000911:Antibodies, Monoclonal; C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D018844:Cyclin-Dependent Kinases