title: Involvement of C3 exotoxin-sensitive G proteins (rho/rac) in PTH signal transduction in OK cells.
abstract: Parathyroid hormone (PTH) in opossum kidney (OK) cells leads to inhibition of Na-Pi cotransport, to the generation of inositol trisphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) and to a phosphorylation of proteins present in an enriched apical membrane fraction (27, 28; for review see Ref. 23). In the present report we have identified two of these phosphoproteins with molecular weights of approximately 22,000 and approximately 24,000, respectively, as guanosine 5'-triphosphate (GTP)-binding proteins, ADP-ribosylated by the Clostridium botulinum exotoxin C3 and recognized by an anti-rho polyclonal antibody but not by pan-ras monoclonal antibody; as suggested by Western-blot analysis the content of the proteins recognized by the anti-rho antibody did not alter in the membrane fraction as a function of treatment with PTH. Transient permeabilization of OK cells using streptolysin O and including the C3 exotoxin attenuated PTH-dependent inhibition of Na-Pi cotransport at hormone concentrations higher than 10(-10) M; residual PTH-dependent inhibition is equal to that observed after pharmacological activation of protein kinase A and protein kinase C, respectively. C3 exotoxin did not alter PTH-dependent generation of cAMP but modified production of IP3; it was increased at 10(-11) M and reduced at 10(-8) M PTH, respectively. It is suggested that protein kinase A may be involved in the phosphorylation of C3 exotoxin-sensitive G proteins (rho/rac). These proteins could be involved in PTH signal transduction.
authors.affiliation: Department of Physiology, University of Zurich, Switzerland.
authors.forename: S J
authors.initials: SJ
authors.lastname: Reshkin
authors.forename: H
authors.initials: H
authors.lastname: Murer
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism*; D000818:Animals; D001905:Botulinum Toxins; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D007668:Kidney / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology / Q000502:physiology*; D010539:Permeability; D010766:Phosphorylation; D015290:Second Messenger Systems; D015398:Signal Transduction; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D020743:rhoB GTP-Binding Protein
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D010281:Parathyroid Hormone; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020743:rhoB GTP-Binding Protein