title: p27 phosphorylation by Src regulates inhibition of cyclin E-Cdk2.
abstract: The kinase inhibitor p27Kip1 regulates the G1 cell cycle phase. Here, we present data indicating that the oncogenic kinase Src regulates p27 stability through phosphorylation of p27 at tyrosine 74 and tyrosine 88. Src inhibitors increase cellular p27 stability, and Src overexpression accelerates p27 proteolysis. Src-phosphorylated p27 is shown to inhibit cyclin E-Cdk2 poorly in vitro, and Src transfection reduces p27-cyclin E-Cdk2 complexes. Our data indicate that phosphorylation by Src impairs the Cdk2 inhibitory action of p27 and reduces its steady-state binding to cyclin E-Cdk2 to facilitate cyclin E-Cdk2-dependent p27 proteolysis. Furthermore, we find that Src-activated breast cancer lines show reduced p27 and observe a correlation between Src activation and reduced nuclear p27 in 482 primary human breast cancers. Importantly, we report that in tamoxifen-resistant breast cancer cell lines, Src inhibition can increase p27 levels and restore tamoxifen sensitivity. These data provide a new rationale for Src inhibitors in cancer therapy.
authors.affiliation: Braman Family Breast Cancer Institute of the University of Miami Sylvester Comprehensive Cancer Center and Department of Biochemistry and Molecular Biology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Isabel
authors.initials: I
authors.lastname: Chu
authors.forename: Jun
authors.initials: J
authors.lastname: Sun
authors.forename: Angel
authors.initials: A
authors.lastname: Arnaout
authors.forename: Harriette
authors.initials: H
authors.lastname: Kahn
authors.forename: Wedad
authors.initials: W
authors.lastname: Hanna
authors.forename: Steven
authors.initials: S
authors.lastname: Narod
authors.forename: Ping
authors.initials: P
authors.lastname: Sun
authors.forename: Cheng-Keat
authors.initials: CK
authors.lastname: Tan
authors.forename: Ludger
authors.initials: L
authors.lastname: Hengst
authors.forename: Joyce
authors.initials: J
authors.lastname: Slingerland
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000378:metabolism / Q000494:pharmacology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000628:therapy; D002277:Carcinoma / Q000235:genetics / Q000378:metabolism* / Q000628:therapy; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D025461:Feedback, Physiological / Q000235:genetics; D005260:Female; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013629:Tamoxifen / Q000378:metabolism / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D018797:Cell Cycle Proteins; D019927:Cyclin E; D013629:Tamoxifen; D050760:Cyclin-Dependent Kinase Inhibitor p27; D014443:Tyrosine; D016392:Proto-Oncogene Proteins pp60(c-src); D051357:Cyclin-Dependent Kinase 2