RhoA-GDP regulates RhoB protein stability. Potential involvement of RhoGDIalpha.
RhoA plays a significant role in actin stress fibers formation. However, silencing RhoA alone or RhoA and RhoC did not completely suppress the stress fibers suggesting a residual "Rho-like" activity. RhoB, the third member of the Rho subclass, is a shortlived protein barely detectable in basal conditions. In various cell types, the silencing of RhoA induced a strong up-regulation of both total and active RhoB protein levels that were rescued by re-expressing RhoA and related to an enhanced half-life of the protein. The RhoA-dependent regulation of RhoB does not depend on the activity of RhoA but is mediated by its GDP-bound form. The stabilization of RhoB was not dependent on isoprenoid biosynthesis, Rho kinase, extracellular signal-regulated kinase, p38 mitogen-activated kinase, or phosphatidylinositol 3'-OH kinase pathways but required RhoGDIalpha. The forced expression of RhoGDIalpha increased RhoB half-life, whereas its knock-down antagonized the induction of RhoB following RhoA silencing. Moreover, a RhoA mutant (RhoAR68E) unable to bind RhoGDIalpha was significantly less efficient as compared with wild-type RhoA in reversing RhoB up-regulation upon RhoA silencing. These results suggest that, in basal conditions, RhoGDIalpha is rate-limiting and the suppression of RhoA makes it available to stabilize RhoB. Our results highlight RhoGDIalpha-dependent cross-talks that regulate the stability of RhoGTPases.
Laboratory of Connective Tissues Biology, GIGA-R, University of Liège, Tour de Pathologie, Sart Tilman, Belgium.
T T Giang
TT
Ho
Sofia D
SD
Merajver
Charles M
CM
Lapière
Betty V
BV
Nusgens
Christophe F
CF
Deroanne
D000818:Animals; D020868:Gene Silencing; D005822:Genetic Vectors; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000737:chemistry*; D006801:Humans; D008954:Models, Biological; D021381:Protein Transport; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014162:Transfection; D015854:Up-Regulation; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020742:rhoA GTP-Binding Protein / Q000378:metabolism / Q000502:physiology*; D020743:rhoB GTP-Binding Protein / Q000378:metabolism*; D000075024:rhoC GTP-Binding Protein
D020730:Guanine Nucleotide Dissociation Inhibitors; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D006153:Guanosine Diphosphate; C066690:RHOC protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein; D000075024:rhoC GTP-Binding Protein