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Plant and Cell Physiology 2004 45(11):1623-1632; doi:10.1093/pcp/pch183
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© 2004 Oxford University Press

Inhibition of Proteasome by MG-132 Treatment Causes Extra Phragmoplast Formation and Cortical Microtubule Disorganization during M/G1 Transition in Synchronized Tobacco Cells

Masayoshi Oka1, Yuki Yanagawa2, Tetsuhiro Asada3, Arata Yoneda4, Seiichiro Hasezawa4, Takahide Sato1 and Hiroki Nakagawa1,5

1 Department of Bioproduction Science, Faculty of Horticulture, Chiba University, Matsudo, Chiba, 271-8510 Japan
2 Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8104, U.S.A.
3 Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka, 560-0043 Japan
4 Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba, 277-8562 Japan

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.

5 Corresponding author: E-mail, hirokinakagawa{at}faculty.chiba-u.jp; Fax, +81-473-08-8862.


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