title: Semi-high throughput method of measuring proteasome inhibition in vitro and in cultured cells.
abstract: The ubiquitin proteasome-proteolytic pathway has emerged as one of the most significant pathways in modulating protein homeostasis under both normal and disease states. The use of proteasome inhibitors (PI) has played a pivotal role in understanding protein turn over. The main objective of this work was to develop a comprehensive, fast, and reliable, yet simple in vitro assay that would allow for the identification and characterization of a wide range of PIs. The assays consist of a 96-well plate high throughput (HTP) method to assess proteasome activity in Hs578T breast cancer cell extracts, purified 20S proteasome, using a fluorogenic substrate, Suc-leu-leu-val-tyr-7-AMC, specific to the chymotrypsin-like enzymatic activity of the proteasome. We showed that the chymotrypsin-like activity of the proteasome was inhibited in the two in vitro systems, albeit to different degrees. The assay system also includes two cell-based assays consisting of a vector expressing a fusion protein of green fluorescent protein (gfp) and Mouse Ornithine Decarboxylase (MODC) in Zs578T (parental Hs578T carrying the vector that expresses the fusion protein). In the cell-based assay analyses (qualitatively by microscopy and quantitatively by flow cytometry), treatment of Zs578T with PIs prevented the degradation of MODC, accumulated gfp, indicative of increased proteasome inhibition. Because no single assay represents a definitive proof of proteasome inhibitory activity, combined, these assays should serve as a comprehensive benchmark for the identification and partial characterization of novel inhibitors. In summary, the four-step assay protocol can easily be adapted into a high throughput format to rapidly screen unknown inhibitors.
authors.affiliation: Department of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, P. O. Box 66, 1515 Holcombe Blvd., Houston, TX 77030, USA. kkeyomar@mdanderson.org
authors.forename: Khandan
authors.initials: K
authors.lastname: Keyomarsi
authors.forename: Ekem T
authors.initials: ET
authors.lastname: Efuet
authors.forename: Tuyen N
authors.initials: TN
authors.lastname: Bui
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001681:Biological Assay; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D002457:Cell Extracts; D002478:Cells, Cultured; D002918:Chymotrypsin / Q000378:metabolism; D057166:High-Throughput Screening Assays / Q000379:methods*; D020128:Inhibitory Concentration 50; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008954:Models, Biological; D009842:Oligopeptides / Q000494:pharmacology; D009955:Ornithine Decarboxylase / Q000378:metabolism; D011480:Protease Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors
chemical_list: D001897:Boronic Acids; D002457:Cell Extracts; D007976:Leupeptins; D009842:Oligopeptides; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D011993:Recombinant Fusion Proteins; C067713:lactacystin; D000069286:Bortezomib; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex; D009955:Ornithine Decarboxylase; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine; C078846:epoxomicin