title: Spindle pole fragmentation due to proteasome inhibition.
abstract: During interphase, the centrosome concentrates cell stress response molecules, including chaperones and proteasomes, into a proteolytic center. However, whether the centrosome functions as proteolytic center during mitosis is not known. In this study, cultured mammalian cells were treated with the proteasome inhibitor MG 132 and spindle morphology in mitotic cells was characterized in order to address this issue. Proteasome inhibition during mitosis leads to the formation of additional asters that cause the assembly of multipolar spindles. The cause of this phenomenon was investigated by inhibiting microtubule-based transport and protein synthesis. These experimental conditions prevented the formation of supernumerary asters during mitosis. In addition, the expression of dsRed without proteasome inhibition led to the fragmentation of spindle poles. These experiments showed that the formation of extra asters depends on intact microtubule-based transport and protein synthesis. These results suggest that formation of supernumerary asters is due to excessive accumulation of proteins at the spindle poles and consequently fragmentation of the centrosome. Together, this leads to the conclusion that the centrosome functions as proteolytic center during mitosis and proteolytic activity at the spindle poles is necessary for maintaining spindle pole integrity.
authors.affiliation: Department of Cell Biology, University of Massachusetts Medical School, Worcester, 01605, USA. anka.ehrhardt@umassmed.edu
authors.forename: Anka G
authors.initials: AG
authors.lastname: Ehrhardt
authors.forename: Greenfield
authors.initials: G
authors.lastname: Sluder
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear; D001692:Biological Transport; D018797:Cell Cycle Proteins; D002460:Cell Line; D018385:Centrosome / Q000378:metabolism; D006224:Cricetinae; D004398:Dyneins / Q000378:metabolism; D006801:Humans; D007399:Interphase / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D008938:Mitosis; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011485:Protein Binding; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism*; D014158:Transcription, Genetic; D014404:Tubulin / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D034961:Antigens, Nuclear; D018797:Cell Cycle Proteins; D007976:Leupeptins; C050045:NUMA1 protein, human; D034521:Nuclear Matrix-Associated Proteins; D009687:Nuclear Proteins; D061988:Proteasome Inhibitors; D014404:Tubulin; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex; D004398:Dyneins; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde