title: Quantitative cell-based protein degradation assays to identify and classify drugs that target the ubiquitin-proteasome system.
abstract: We have generated a set of dual-reporter human cell lines and devised a chase protocol to quantify proteasomal degradation of a ubiquitin fusion degradation (UFD) substrate, a ubiquitin ligase CRL2(VHL) substrate, and a ubiquitin-independent substrate. Well characterized inhibitors that target different aspects of the ubiquitin-proteasome system can be distinguished by their distinctive patterns of substrate stabilization, enabling assignment of test compounds as inhibitors of the proteasome, ubiquitin chain formation or perception, CRL activity, or the UFD-p97 pathway. We confirmed that degradation of the UFD but not the CRL2(VHL) or ubiquitin-independent substrates depends on p97 activity. We optimized our suite of assays to establish conditions suitable for high-throughput screening and then validated their performance by screening against 160 cell-permeable protein kinase inhibitors. This screen identified Syk inhibitor III as an irreversible p97/vasolin containing protein inhibitor (IC(50) = 1.7 μM) that acts through Cys-522 within the D2 ATPase domain. Our work establishes a high-throughput screening-compatible pipeline for identification and classification of small molecules, cDNAs, or siRNAs that target components of the ubiquitin-proteasome system.
authors.affiliation: Division of Biology, California Institute of Technology, Pasadena, California 91125, USA. tfchou@caltech.edu
authors.forename: Tsui-Fen
authors.initials: TF
authors.lastname: Chou
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Deshaies
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry; D018929:Cell Culture Techniques / Q000379:methods; D002460:Cell Line; D002626:Chemistry, Pharmaceutical / Q000379:methods; D049452:Green Fluorescent Proteins / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D009687:Nuclear Proteins / Q000737:chemistry; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D034741:RNA, Small Interfering / Q000378:metabolism; D013678:Technology, Pharmaceutical / Q000379:methods; D025801:Ubiquitin / Q000737:chemistry*
chemical_list: D009687:Nuclear Proteins; D011506:Proteins; D034741:RNA, Small Interfering; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C404942:p97 ATPase