title: ADP-ribosylation of Rho proteins by Clostridium botulinum exoenzyme C3 is influenced by phosphorylation of Rho-associated factors.
abstract: Specific [32P]ADP-ribosylation by Clostridium botulinum exoenzyme C3 was used to study the involvement of phosphorylation in the regulation of the low-molecular-mass GTP-binding protein Rho. Dephosphorylation of CHO cell extracts by alkaline phosphatase treatment resulted in a 80-90% reduction in the C3-catalysed [32P]ADP-ribosylation of Rho proteins in both cytosolic and membrane fractions. Similar results were obtained after dephosphorylation with protein phosphatase type-1 from bovine retina, whereas type-2B and type-2C phosphatases had no effect on the level of subsequent [32P]ADP-ribosylation of Rho by C3. Incubation of CHO cell lysate under phosphorylation conditions increased the subsequent C3-mediated [32P]ADP-ribosylation of Rho proteins. The protein kinase inhibitors H7 and H9 had no effect on [32P]ADP-ribosylation at concentrations which are specific for inhibition of protein kinase A or C. Recombinant glutathione S-transferase-RhoA fusion protein (GST-RhoA) was phosphorylated by protein kinase A; however, the phosphorylation had no stimulatory effect on the ADP-ribosylation of GST-RhoA by C3. An approx. 48 kDa phosphoprotein was identified which bound specifically to recombinant GST-RhoA fusion protein. By gel-permeation chromatography, Rho-containing complexes of approx. 50 kDa and 130-170 kDa were detected. The ADP-ribosylation of Rho in the 130-170 kDa complex was reduced by alkaline phosphatase pretreatment. The data suggest that Rho activity is influenced by phosphorylation of Rho-associated regulatory factors. Phosphorylation/dephosphorylation of these Rho-regulating factors appears to alter the ability of Rho to serve as a substrate for C3-induced [32P]ADP-ribosylation.
authors.affiliation: Institut für Pharmakologie und Toxikologie, Universität des Saarlandes, Homburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Fritz
authors.forename: K
authors.initials: K
authors.lastname: Aktories
mesh_terms: D016475:3T3 Cells; D036002:ADP Ribose Transferases / Q000378:metabolism*; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001685:Biological Factors / Q000378:metabolism; D001905:Botulinum Toxins; D016466:CHO Cells; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020730:Guanine Nucleotide Dissociation Inhibitors; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020742:rhoA GTP-Binding Protein
chemical_list: D001685:Biological Factors; D020730:Guanine Nucleotide Dissociation Inhibitors; D010750:Phosphoproteins; D011994:Recombinant Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D000246:Adenosine Diphosphate Ribose; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein