title: Novel functions of Ect2 in polar lamellipodia formation and polarity maintenance during "contractile ring-independent" cytokinesis in adherent cells.
abstract: 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.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Kanada
authors.forename: Akira
authors.initials: A
authors.lastname: Nagasaki
authors.forename: Taro Q P
authors.initials: TQ
authors.lastname: Uyeda
mesh_terms: D036002:ADP Ribose Transferases / Q000494:pharmacology; D001905:Botulinum Toxins / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability / Q000187:drug effects; D016764:Cell Polarity / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D048749:Cytokinesis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005799:Genes, Dominant; D006801:Humans; D008954:Models, Biological; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000378:metabolism*; D011554:Pseudopodia / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: C489850:ECT2 protein, human; D011518:Proto-Oncogene Proteins; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D020742:rhoA GTP-Binding Protein