title: Identification of RBCK1 as a novel regulator of FKBPL: implications for tumor growth and response to tamoxifen.
abstract: FKBPL has been implicated in processes associated with cancer, including regulation of tumor growth and angiogenesis with high levels of FKBPL prognosticating for improved patient survival. Understanding how FKBPL levels are controlled within the cell is therefore critical. We have identified a novel role for RBCK1 as an FKBPL-interacting protein, which regulates FKBPL stability at the post-translational level via ubiquitination. Both RBCK1 and FKBPL are upregulated by 17-β-estradiol and interact within heat shock protein 90 chaperone complexes, together with estrogen receptor-α (ERα). Furthermore, FKBPL and RBCK1 associate with ERα at the promoter of the estrogen responsive gene, pS2, and regulate pS2 levels. MCF-7 clones stably overexpressing RBCK1 were shown to have reduced proliferation and increased levels of FKBPL and p21. Furthermore, these clones were resistant to tamoxifen therapy, suggesting that RBCK1 could be a predictive marker of response to endocrine therapy. RBCK1 knockdown using targeted small interfering RNA resulted in increased proliferation and increased sensitivity to tamoxifen treatment. Moreover, in support of our in vitro data, analysis of mRNA microarray data sets demonstrated that high levels of FKBPL and RBCK1 correlated with increased patient survival, whereas high RBCK1 predicted for a poor response to tamoxifen. Our findings support a role for RBCK1 in the regulation of FKBPL with important implications for estrogen receptor signaling, cell proliferation and response to endocrine therapy.
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: C
authors.initials: C
authors.lastname: Donley
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: K
authors.initials: K
authors.lastname: McClelland
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: H D
authors.initials: HD
authors.lastname: McKeen
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: L
authors.initials: L
authors.lastname: Nelson
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: A
authors.initials: A
authors.lastname: Yakkundi
authors.affiliation: Liverpool Cancer Research UK Centre, University of Liverpool, Liverpool, UK.
authors.forename: P V
authors.initials: PV
authors.lastname: Jithesh
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: J
authors.initials: J
authors.lastname: Burrows
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: L
authors.initials: L
authors.lastname: McClements
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: A
authors.initials: A
authors.lastname: Valentine
authors.affiliation: Centre for Cancer Research and Cell Biology, Queen's University, Belfast, Northern Ireland.
authors.forename: K M
authors.initials: KM
authors.lastname: Prise
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: H O
authors.initials: HO
authors.lastname: McCarthy
authors.affiliation: School of Pharmacy, McClay Research Centre, Queen's University, Belfast, Northern Ireland.
authors.forename: T
authors.initials: T
authors.lastname: Robson
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology / Q000627:therapeutic use*; D014408:Biomarkers, Tumor / Q000235:genetics; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000401:mortality; D019556:COS Cells; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis*; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004958:Estradiol / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D020104:Immunophilins / Q000096:biosynthesis / Q000235:genetics*; D009389:Neovascularization, Pathologic / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D034622:RNA Interference; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D022021:Tacrolimus Binding Proteins; D013629:Tamoxifen / Q000494:pharmacology / Q000627:therapeutic use*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D015533:Transcriptional Activation; D016896:Treatment Outcome; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis / Q000235:genetics; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination
chemical_list: D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; C400101:FKBPL protein, human; D018841:HSP90 Heat-Shock Proteins; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; C051838:TFF1 protein, human; D014157:Transcription Factors; D000071163:Trefoil Factor-1; D025521:Tumor Suppressor Proteins; D013629:Tamoxifen; D004958:Estradiol; C504507:RBCK1 protein, human; D044767:Ubiquitin-Protein Ligases; D022021:Tacrolimus Binding Proteins; D020104:Immunophilins