title: Inhibition of proteasome by MG-132 treatment causes extra phragmoplast formation and cortical microtubule disorganization during M/G1 transition in synchronized tobacco cells.
abstract: The 26S proteasome plays essential roles in cell cycle progression in various types of cell. We previously reported that the inhibition of 26S proteasome activities by a proteasome inhibitor, MG-132, exclusively caused cell cycle arrest in synchronized tobacco BY-2 cells. Here we report a further observation of 26S proteasome involvement during M/G1 transition utilizing a transgenetic BY-2 cell line that stably expresses a GFP-alpha-tubulin fusion protein (BY-GT16). Interestingly, MG-132 treatment caused the arrest of cell cycle progression prior to entering the G1 phase. Indeed, phragmoplast-like structures were formed and cortical microtubules were not organized after the collapse of the original phragmoplasts. Additionally, actin microfilaments showed irregular rearrangements when further incubated with MG-132 and as the phragmoplast-like structures developed. Since these phragmoplast-like structures had a similar configuration and ability to form cell plates to that of the original phragmoplasts, we designated these phragmoplast-like structures as extra phragmoplasts. Furthermore, we showed that a tobacco kinesin-related polypeptide of 125 kDa (TKRP125) localized in the extra phragmoplasts and that its protein level remained unchanged during MG-132 treatment. We propose that TKRP125 might be one of the possible targets of the ubiquitin-proteasome degradation pathway during M/G1 transition.
authors.affiliation: Department of Bioproduction Science, Faculty of Horticulture, Chiba University, Matsudo, Chiba, 271-8510 Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Oka
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yanagawa
authors.forename: Tetsuhiro
authors.initials: T
authors.lastname: Asada
authors.forename: Arata
authors.initials: A
authors.lastname: Yoneda
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Hasezawa
authors.forename: Takahide
authors.initials: T
authors.lastname: Sato
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nakagawa
mesh_terms: D016193:G1 Phase; D007150:Immunohistochemistry; D007976:Leupeptins / Q000494:pharmacology*; D008870:Microtubules / Q000378:metabolism*; D030821:Plants, Genetically Modified; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
chemical_list: D007976:Leupeptins; D011993:Recombinant Fusion Proteins; D014404:Tubulin; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde