title: FBXO32 suppresses breast cancer tumorigenesis through targeting KLF4 to proteasomal degradation.
abstract: Krüppel-like factor 4 (KLF4, GKLF) is a zinc-finger transcription factor involved in a large variety of cellular processes, including apoptosis, cell cycle progression, as well as stem cell renewal. KLF4 is critical for cell fate decision and has an ambivalent role in tumorigenesis. Emerging data keep reminding us that KLF4 dysregulation either facilitates or impedes tumor progression, making it important to clarify the regulating network of KLF4. Like most transcription factors, KLF4 has a rather short half-life within the cell and its turnover must be carefully orchestrated by ubiquitination and ubiquitin-proteasome system. To better understand the mechanism of KLF4 ubiquitination, we performed a genome-wide screen of E3 ligase small interfering RNA library based on western blot and identified SCF-FBXO32 to be a new E3 ligase, which is responsible for KLF4 ubiquitination and degradation. The F-box domain is critical for FBXO32-dependent KLF4 ubiquitination and degradation. Furthermore, we demonstrated that FBXO32 physically interacts with the N-terminus (1-60 aa) of KLF4 via its C-terminus (228-355 aa) and directly targets KLF4 for ubiquitination and degradation. We also found out that p38 mitogen-activated protein kinase pathway may be implicated in FBXO32-mediated ubiquitination of KLF4, as p38 kinase inhibitor coincidently abrogates endogenous KLF4 ubiquitination and degradation, as well as FBXO32-dependent exogenous KLF4 ubiquitination and degradation. Finally, FBXO32 inhibits colony formation in vitro and primary tumor initiation and growth in vivo through targeting KLF4 into degradation. Our findings thus further elucidate the tumor-suppressive function of FBXO32 in breast cancer. These results expand our understanding of the posttranslational modification of KLF4 and of its role in breast cancer development and provide a potential target for diagnosis and therapeutic treatment of breast cancer.
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: H
authors.initials: H
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: R
authors.initials: R
authors.lastname: Zhu
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: F
authors.initials: F
authors.lastname: Ding
authors.affiliation: Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.|Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pennsylvania, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Wan
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.affiliation: State Key Laboratory of Molecular Oncology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Collaborative Innovation Center for Cancer Medicine, Beijing, China.
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
mesh_terms: D000818:Animals; D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D005260:Female; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination; D023041:Xenograft Model Antitumor Assays; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; C000715467:KLF4 protein, human; C000715468:Klf4 protein, mouse; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D009124:Muscle Proteins; D025801:Ubiquitin; C440907:FBXO32 protein, human; D044843:SKP Cullin F-Box Protein Ligases; D048051:p38 Mitogen-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex