The effects of pertussis toxin and cholera toxin on mitogen-induced interleukin-2 production: evidence for G protein involvement in signal transduction.
GTP-binding proteins, known as G proteins, play important roles in transducing signals generated by the binding of specific ligands to cell surface receptors. We examined the possibility that a G protein is involved in transducing the concanavalin A (Con A) signal for IL-2 production using a T-cell hybridoma, FS6-14.13, and the bacterial toxins, pertussis toxin (PTX) and cholera toxin (CTX). These toxins are known to interact with and modify the functions of G proteins. High concentrations of PTX (25-50 micrograms/ml) stimulated IL-2 production in the FS-6 cells in the absence of Con A, presumably due to the ability of its B subunit to crosslink membrane proteins. However, in the presence of Con A, PTX inhibited IL-2 production at concentrations ranging from 0.05 to 50 micrograms/ml. It is unlikely that this inhibition was due to a competitive interaction between Con A and PTX for binding sites at the cell surface, since high concentrations of PTX only minimally reduced Con A-FITC binding, evaluated by FACS analysis. In addition, concentrations of PTX which were not able to stimulate IL-2 production in the absence of Con A, retained their ability to inhibit IL-2 production in the presence of Con A. These data suggest the involvement of the PTX A subunit in this activity. In support of this possibility, PTX catalyzed ADP-ribosylation of a Mr = 41,000-Da protein in FS-6 membranes. This strongly suggests that a PTX substrate is involved in transducing the Con A signal for IL-2 production in FS-6 cells. CTX also inhibited Con A-induced IL-2 production, an effect mimicked by the addition of dibutyryl-cAMP. This suggests that a CTX substrate linked to the adenylyl cyclase-cAMP pathway is probably not involved in transducing the stimulatory Con A signal, but may play a role in downregulating T-cell activation.
Gilmore
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Department of Neurology, University of Southern California, School of Medicine, Los Angeles 90033.
Weiner
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LP
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D037361:Adenylate Cyclase Toxin; D003994:Bucladesine / Q000494:pharmacology; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology*; D003208:Concanavalin A / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019204:GTP-Binding Proteins / Q000502:physiology*; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000096:biosynthesis*; D008213:Lymphocyte Activation / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D008766:Methylmannosides / Q000494:pharmacology; D037342:Pertussis Toxin; D011952:Receptors, Concanavalin A / Q000378:metabolism; D013601:T-Lymphocytes / Q000502:physiology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D037361:Adenylate Cyclase Toxin; D007376:Interleukin-2; D008565:Membrane Proteins; D008766:Methylmannosides; D011952:Receptors, Concanavalin A; D010566:Virulence Factors, Bordetella; D003208:Concanavalin A; D000246:Adenosine Diphosphate Ribose; C008466:methylmannoside; D003994:Bucladesine; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins