GTP-binding protein G alpha Z: its down-regulation by dexamethasone and its credentials as a mediator of antigen-induced responses in RBL-2H3 cells.
We have investigated the possible role of guanine nucleotide-binding proteins in the process of antigen-induced exocytosis in a cultured rat mast cell line, RBL-2H3 cells. The mRNAs for the alpha subunits of the guanine nucleotide-binding proteins G alpha S (short and long forms), G alpha i-2, G alpha i-3, and G alpha Z were detected by hybridization with G alpha-specific oligonucleotide probes. The corresponding proteins were identified in membranes of RBL-2H3 cells on the basis of size, immunoreactivity with specific antibodies, and their ability to serve as substrates for ADP-ribosylation by cholera toxin or pertussis toxin. Treatment of cells with as little as 10(-9) to 10(-7) M dexamethasone markedly decreased the amount of G alpha Z mRNA and membrane G alpha Z, as well as the responsiveness of the cells to antigen stimulation. In the same cells, the exposure to dexamethasone caused an increase in the amounts of certain other G alpha subunits, particularly G alpha i-3, and in the responsiveness of the cells to an adenosine analog, N(ethylcarboxamido)-adenosine. Because of the apparent decrease in G alpha Z mRNA and protein in dexamethasone-treated cells and the fact that neither cholera toxin nor pertussis toxin inhibits the stimulatory signals to antigen [J. Biol. Chem. 265:745-753 (1990)], we suggest that G alpha Z is a potential candidate for regulating the early signals in antigen-stimulated RBL-2H3 cells.
Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, Bethesda, MD 20892.
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D000244:Adenosine Diphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects*; D005089:Exocytosis; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D046911:Macromolecular Substances; D008407:Mast Cells / Q000166:cytology / Q000378:metabolism; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D037342:Pertussis Toxin; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D046911:Macromolecular Substances; D008565:Membrane Proteins; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D010566:Virulence Factors, Bordetella; D000244:Adenosine Diphosphate; D003907:Dexamethasone; D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins