title: APC(cdh1) mediates degradation of the oncogenic Rho-GEF Ect2 after mitosis.
abstract: BACKGROUND
  Besides 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.
  
  
  RESULTS
  We 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
  Our 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.
authors: Inserm U749, Institut Gustave Roussy, Villejuif, France.
authors: Caroline
authors: C
authors: Liot
authors: Laetitia
authors: L
authors: Seguin
authors: Aurélie
authors: A
authors: Siret
authors: Catherine
authors: C
authors: Crouin
authors: Susanne
authors: S
authors: Schmidt
authors: Jacques
authors: J
authors: Bertoglio
mesh_terms: D015703:Antigens, CD; D015820:Cadherins / Q000502:physiology*; D002460:Cell Line; D004268:DNA-Binding Proteins; D006801:Humans; D008938:Mitosis; D055550:Protein Stability; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D014157:Transcription Factors; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D015703:Antigens, CD; C513384:CDH1 protein, human; D015820:Cadherins; D004268:DNA-Binding Proteins; C489850:ECT2 protein, human; D011518:Proto-Oncogene Proteins; C480633:SLC2A4RG protein, human; D014157:Transcription Factors; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein