title: Inhibition of TRIP1/S8/hSug1, a component of the human 19S proteasome, enhances mitotic apoptosis induced by spindle poisons.
abstract: Mitotic spindle poisons (e.g., Taxol and vinblastine), used as chemotherapy drugs, inhibit mitotic spindle function, activate the mitotic spindle checkpoint, arrest cells in mitosis, and then cause cell death by mechanisms that are poorly understood. By expression cloning, we identified a truncated version of human TRIP1 (also known as S8, hSug1), an AAA (ATPases associated with diverse cellular activities) family ATPase subunit of the 19S proteasome regulatory complex, as an enhancer of spindle poison-mediated apoptosis. Stable expression of the truncated TRIP1/S8/hSug1 in HeLa cells [OP-TRIP1(88-406)] resulted in a decrease of measurable cellular proteasome activity, indicating that OP-TRIP1(88-406) had a dominant-negative effect on proteasome function. OP-TRIP1(88-406) revealed an increased apoptotic response after treatment with spindle poisons or with proteasome inhibitors. The increased apoptosis coincided with a significant decrease in expression of BubR1, a kinase required for activation and maintenance of the mitotic spindle checkpoint in response to treatment with spindle poisons. Small interfering RNA (siRNA)-mediated knockdown of TRIP1/S8/hSug1 resulted in a reduction of general proteasome activity and an increase in mitotic index. The siRNA treatment also caused increased cell death after spindle poison treatment. These results indicate that inhibition of TRIP1/S8/hSug1 function by expression of a truncated version of the protein or by siRNA-mediated suppression enhances cell death in response to spindle poison treatment. Current proteasome inhibitor drugs in trial as anticancer agents target elements of the 20S catalytic subcomplex. Our results suggest that targeting the ATPase subunits in 19S regulatory complex in the proteasome may enhance the antitumor effects of spindle poisons.
authors.affiliation: Molecular, Cell, and Developmental Biology Research Program, Oklahoma Medical Research Foundation, 825 Northeast 13th Street, MS48, Oklahoma City, 73104-5097, USA. Hiroshi-yamada@omrf.ouhsc.edu
authors.forename: Hiroshi Y
authors.initials: HY
authors.lastname: Yamada
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Gorbsky
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D048868:Adaptor Proteins, Signal Transducing / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D060588:LIM Domain Proteins; D007976:Leupeptins / Q000494:pharmacology; D008938:Mitosis; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D034741:RNA, Small Interfering / Q000494:pharmacology; D008941:Spindle Apparatus / Q000187:drug effects*; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015853:Cysteine Proteinase Inhibitors; D060588:LIM Domain Proteins; D007976:Leupeptins; C092282:PSMC5 protein, human; D010446:Peptide Fragments; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D014157:Transcription Factors; D011494:Protein Kinases; C584277:BUB1 protein, human; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases; D046988:Proteasome Endopeptidase Complex; D000074183:ATPases Associated with Diverse Cellular Activities; D017239:Paclitaxel; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D015739:Nocodazole