APCcdh1 Mediates Degradation of the Oncogenic Rho-GEF Ect2 after Mitosis

Abstract

BackgroundBesides regulation of actin cytoskeleton-dependent functions, Rho GTPase pathways are essential to cell cycle progression and cell division. Rho, Rac and Cdc42 regulate G1 to S phase progression and are involved in cytokinesis. RhoA GDP/GTP cycling is required for normal cytokinesis and recent reports have shown that the exchange factor Ect2 and the GTPase activating protein MgcRacGAP regulate RhoA activity during mitosis. We previously showed that the transcription factors E2F1 and CUX1 regulate expression of MgcRacGAP and Ect2 as cells enter S-phase.Methodology/Principal FindingsWe now report that Ect2 is subject to proteasomal degradation after mitosis, following ubiquitination by the APC/C complex and its co-activator Cdh1. A proper nuclear localization of Ect2 is necessary for its degradation. APC-Cdh1 assembles K11-linked poly-ubiquitin chains on Ect2, depending upon a stretch of ∼25 amino acid residues that contain a bi-partite NLS, a conventional D-box and two TEK-like boxes. Site-directed mutagenesis of target sequences generated stabilized Ect2 proteins. Furthermore, such degradation-resistant mutants of Ect2 were found to activate RhoA and subsequent signalling pathways and are able to transform NIH3T3 cells.Conclusions/SignificanceOur results identify Ect2 as a bona fide cell cycle-regulated protein and suggest that its ubiquitination-dependent degradation may play an important role in RhoA regulation at the time of mitosis. Our findings raise the possibility that the overexpression of Ect2 that has been reported in some human tumors might result not only from deregulated transcription, but also from impaired degradation.

Cytokinesis in Animal Cells

“…As discussed in the abscission section, loss of Plk1 activity is thought to dictate abscission timing by triggering the recruitment of the abscission regulator CEP55 (Bastos & Barr 2010). The Ect2 RhoGEF (Liot et al 2011), the CPC component Aurora B (Floyd et al 2008, Stewart & Fang 2005, and anillin (Zhao & Fang 2005a) are all targeted for degradation by APC/C Cdh1 . Inhibiting the degradation of Ect2 or Aurora B has been shown to result in cell transformation (Liot et al 2011, which highlights the importance of APC/C Cdh1 -mediated degradation of key regulators after cytokinesis is complete.…”

Spatiotemporal organization of Aurora-B by APC/CCdh1 after mitosis coordinates cell spreading via FHOD1

“…2C, supplementary material Movie 6). It is possible that ZM is added too late in these experiments to influence cell polarity (it cannot be added earlier than late telophase without causing cytokinesis to fail) and also likely that the effects of Cdh1-i depend on additional targets, such as Rho regulators p190rhoGAP and Ect2 (Liot et al, 2011;Naoe et al, 2010). We also reasoned that cell-wide inhibition of AurB might not be able to rescue effects on cell spreading that depend on spatial organization of AurB activity.…”

Rho GTPases as regulators of mitosis and cytokinesis in mammalian cells

“…151,152 The mechanism of dissociation remains unknown but could involve dephosphorylation of MgcRacGAP 80,81 or ubiquitin-mediated degradation of Ect2. 153 During the secondary ingression, FIP3 endosomes deliver p50RhoGAP to the intracellular bridge to regulate depolymerization of the cortical actin network for abscission. 141 In contrast to previous dogma, an active pool of RhoA exists at the midbody ring indicating that its role during abscission may not only be associated with cortical actin disassembly.…”