title: Disruption of RhoGDI and RhoA regulation by a Rac1 specificity switch mutant.
abstract: Rho family GTPases are important regulators of the actin cytoskeleton. Activation of these proteins can be promoted by guanine nucleotide exchange factors containing Dbl and Pleckstrin homology domains resulting in membrane insertion of a Rho family member, whereas the inactive GDP-bound form is sequestered primarily in the cytoplasm, bound to the guanosine dissociation inhibitor RhoGDI. Dominant interfering variants of Rac1, but not Cdc42, inhibit beta1 integrin-promoted uptake of Yersinia pseudotuberculosis. Unexpectedly, we found that the Rac1(W56F) guanine nucleotide exchange factors specificity switch mutant blocked invasin-promoted uptake as well as Cdc42-dependent uptake of enteropathogenic Escherichia coli. Fluorescence resonance energy transfer experiments demonstrated that Rac1(W56F) retained the ability to be loaded with GTP, bind a downstream effector, and interact with RhoGDI. Mutational analyses of intragenic suppressors and coexpression studies demonstrated that binding of the Rac1(W56F) mutant to RhoGDI appeared to play a role in the inhibition of uptake. As RhoGDI inhibits RhoA, overactivation of RhoA may account for the uptake interference caused by Rac1(W56F). Consistent with this model, a dominant interfering form of RhoA restored significant uptake in the presence of the Rac1(W56F) mutant but had no effect on another interfering Rac1 form. Furthermore, the cellular GTP-RhoA level was elevated by the presence of Rac1(W56F) mutant protein. These data are consistent with the proposition that Rac1(W56F) blocks invasin-promoted uptake by preventing RhoGDI from inactivating RhoA. We conclude that RhoGDI allows cross-talk between Rho family members that promote potentially antagonistic processes, and disruption of this cross-talk can interfere with invasin-promoted uptake.
authors.affiliation: Howard Hughes Medical Institute, Department of Molecular Biology and Microbiology, Tufts University Medical School, Boston, Massachusetts 02111, USA.
authors.forename: Ka-Wing
authors.initials: KW
authors.lastname: Wong
authors.forename: Sina
authors.initials: S
authors.lastname: Mohammadi
authors.forename: Ralph R
authors.initials: RR
authors.lastname: Isberg
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics*; D000818:Animals; D001216:Asparagine / Q000235:genetics; D019556:COS Cells; D002522:Chlorocebus aethiops; D004926:Escherichia coli / Q000378:metabolism / Q000472:pathogenicity; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000037:antagonists & inhibitors* / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D010649:Phenylalanine / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics; D013912:Threonine / Q000235:genetics; D014364:Tryptophan / Q000235:genetics; D015011:Yersinia pseudotuberculosis / Q000201:enzymology / Q000235:genetics; D020764:cdc42 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000235:genetics* / Q000502:physiology; D020741:rho GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology*; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: C569638:ARHGDIA protein, human; D020730:Guanine Nucleotide Dissociation Inhibitors; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D013912:Threonine; D010649:Phenylalanine; D001216:Asparagine; D014364:Tryptophan; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020741:rho GTP-Binding Proteins