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MBC in Press, published online ahead of print October 17, 2007
Mol. Biol. Cell 10.1091/mbc.E07-04-0370

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Submitted on April 24, 2007
Revised on September 27, 2007
Accepted on October 10, 2007

Novel Functions of Ect2 in Polar Lamellipodia Formation and Polarity Maintenance during "Contractile Ring-Independent" Cytokinesis in Adherent Cells

Masamitsu Kanada,*{dagger} Akira Nagasaki,{dagger} and Taro Q.P. Uyeda*{dagger}

*Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan; {dagger}Research Institute for Cell Engineering, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8562, Japan

Monitoring Editor: Yu-Li Wang

Some mammalian cells are able to divide via both the classic contractile ring-dependent method (cytokinesis A) and a contractile ring-independent, adhesion-dependent method (cytokinesis B). Cytokinesis A is triggered by RhoA, which, in HeLa cells, is activated by the guanine nucleotide-exchange factor Ect2 localized at the central spindle and equatorial cortex. Here, we show that in HT1080 cells undergoing cytokinesis A, Ect2 does not localize in the equatorial cortex, though RhoA accumulates there. Moreover, Ect2 depletion resulted in only modest multinucleation of HT1080 cells, enabling us to establish cell lines in which Ect2 was constitutively depleted. Thus, RhoA is activated via an Ect2-independent pathway during cytokinesis A in HT1080 cells. During cytokinesis B, Ect2-depleted cells showed narrower accumulation of RhoA at the equatorial cortex, accompanied by compromised pole-to-equator polarity, formation of ectopic lamellipodia in regions where RhoA normally would be distributed, and delayed formation of polar lamellipodia. Furthermore, C3 exoenzyme inhibited equatorial RhoA activation and polar lamellipodia formation. Conversely, expression of dominant active Ect2 in interphase HT1080 cells enhanced RhoA activity and suppressed lamellipodia formation. These results suggest that equatorial Ect2 locally suppresses lamellipodia formation via RhoA activation, which indirectly contributes to restricting lamellipodia formation to polar regions during cytokinesis B.

Address correspondence to: Taro Q.P. Uyeda (t-uyeda{at}aist.go.jp)






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