title: 14-3-3Tau regulates ubiquitin-independent proteasomal degradation of p21, a novel mechanism of p21 downregulation in breast cancer.
abstract: 14-3-3 proteins regulate many cellular functions, including proliferation. However, the detailed mechanisms by which they control the cell cycle remain to be fully elucidated. We report that one of the 14-3-3 isoforms, 14-3-3tau, is required for the G(1)/S transition through its role in ubiquitin-independent proteasomal degradation of p21. 14-3-3tau binds to p21, MDM2, and the C8 subunit of the 20S proteasome in G(1) phase and facilitates proteasomal targeting of p21. This function of 14-3-3tau may be deregulated in cancer. The overexpression of 14-3-3tau is frequently found in primary human breast cancer and correlates with lower levels of p21 and shorter patient survival. Tenascin-C, an extracellular matrix protein involved in tumor initiation and progression and a known 14-3-3tau inducer, decreases p21 and abrogates adriamycin-induced G(1)/S arrest. It has been known that p21 is required for a proper tamoxifen response in breast cancer. We show that the overexpression of 14-3-3tau inhibits tamoxifen-induced p21 induction and growth arrest in MCF7 cells. Together, the findings of our studies strongly suggest a novel oncogenic role of 14-3-3tau by downregulating p21 in breast cancer. Therefore, 14-3-3tau may be a potential therapeutic target in breast cancer.
authors.affiliation: Division of Hematology and Oncology, Department of Medicine,1 Medical Statistics Section, University of Alabama at Birmingham, Birmingham, Alabama 35294-2182, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Wang
authors.forename: Kang
authors.initials: K
authors.lastname: Liu
authors.forename: Hui-Yi
authors.initials: HY
authors.lastname: Lin
authors.forename: Naresh
authors.initials: N
authors.lastname: Bellam
authors.forename: Shiyun
authors.initials: S
authors.lastname: Ling
authors.forename: Weei-Chin
authors.initials: WC
authors.lastname: Lin
mesh_terms: D048948:14-3-3 Proteins / Q000378:metabolism*; D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D005260:Female; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D016019:Survival Analysis; D013629:Tamoxifen / Q000494:pharmacology; D019063:Tenascin / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D048948:14-3-3 Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D021122:Protein Subunits; D019063:Tenascin; D025801:Ubiquitin; D013629:Tamoxifen; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D046988:Proteasome Endopeptidase Complex