CNF1-induced Ubiquitylation and Proteasome Destruction of Activated RhoA Is Impaired in Smurf1-/- Cells

Boyer L, Turchi L, Desnues B, Doye A, Ponzio G, Mege JL, Yamashita M, Zhang YE, Bertoglio J, Flatau G, Boquet P, Lemichez E
Source: Mol Biol Cell
Publication Date: (2006)
Issue: 17(6): 2489-2497
Research Area:
Cancer Research/Cell Biology
Cells used in publication:
Embryonic fibroblast, mouse (MEF) immort
Species: mouse
Tissue Origin: embryo
Nucleofector® I/II/2b
Ubiquitylation of RhoA has emerged as an important aspect of both the virulence of Escherichia coli producing CNF1-toxin and the establishment of the polarity of eukaryotic cells. Owing to the molecular activity of CNF1, we have investigated the relationship between permanent activation of RhoA catalyzed by CNF1 and subsequent ubiquitylation of RhoA by Smurf1. Using Smurf1-deficient cells and by RNAi-mediated Smurf1 knock-down we demonstrate that Smurf1 is a rate-limiting and specific factor of the ubiquitin-mediated proteasomal degradation of activated-RhoA. We further show that the cancer cell lines HEp-2, HEK293 and Vero are specifically deficient in ubiquitylation of either activated-Rac, Cdc42 or Rho, respectively. In contrast, CNF1 produced the cellular depletion of all three isoforms of Rho proteins in the primary human cell types we have tested. We demonstrate that ectopic expression of Smurf1 in Vero cells, deficient for RhoA ubiquitylation, restores ubiquitylation of the activated forms of RhoA. We conclude here that Smurf1 ubiquitylates activated-RhoA and that, in contrast to human primary cell types, some cancer cell lines have a lower ubiquitylation capacity of specific Rho proteins. Thus, both CNF1 and TGF-beta trigger activated-RhoA ubiquitylation through Smurf1 ubiquitin-ligase.