Impaired secretion and increased insolubilization of IgE-receptor complexes in mycophenolic acid-treated (guanine nucleotide-depleted) RBL-2H3 mast cells.
In RBL-2H3 rat leukemic mast cells, cross-linking anti-DNP IgE-receptor complexes with multivalent antigen (DNP-BSA) activates a signal transduction pathway leading to Ca2+ influx and secretion. Cross-linking IgE-receptor complexes also stimulates a pathway that inactivates (desensitizes) receptors; this pathway becomes important at high concentrations of cross-linking antigen. Recent evidence that antigen-induced secretion is impaired by mycophenolic acid (MPA), an inhibitor of guanine nucleotide synthesis de novo, has implicated a GTP-binding protein (G protein) in the signaling pathway. Other recent studies have indicated that the conversion of cross-linked receptors to a detergent-insoluble (cytoskeleton-associated) form at high antigen concentrations is correlated with the loss of signaling activity. Here we show that secretion elicited by an optimal concentration of antigen (0.05 micrograms/ml DNP-BSA) is only inhibited by about 25% in guanine nucleotide-depleted cells, whereas secretion elicited by 5 micrograms/ml DNP-BSA, a concentration in the range that causes the high-dose inhibition of secretion, is inhibited by more than 60%. We also show that IgE-receptor complexes are insolubilized in response to 5 but not 0.05 micrograms/ml DNP-BSA in both control and guanine nucleotide-depleted cells. Importantly, the extent of insolubilization elicited by 5 micrograms/ml DNP-BSA is increased by more than 60% in the guanine nucleotide-depleted samples. These results raise the possibility that guanine nucleotide depletion reduces the secretory response to high antigen concentrations in two ways: by inhibiting the G protein-coupled signaling pathway and by increasing the availability of receptors to the pathway leading to receptor insolubilization and inactivation.
Wilson
B S
BS
Department of Pathology, University of New Mexico, Albuquerque 87131.
Seagrave
J
J
Oliver
J M
JM
D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004140:Dinitrophenols / Q000494:pharmacology; D006150:Guanine Nucleotides / Q000096:biosynthesis*; D007073:Immunoglobulin E / Q000378:metabolism; D007700:Kinetics; D008407:Mast Cells; D009173:Mycophenolic Acid / Q000494:pharmacology*; D051381:Rats; D011961:Receptors, Fc / Q000187:drug effects / Q000378:metabolism*; D017455:Receptors, IgE; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects
D000944:Antigens, Differentiation, B-Lymphocyte; D004140:Dinitrophenols; D006150:Guanine Nucleotides; D011961:Receptors, Fc; D017455:Receptors, IgE; C034638:dinitrophenyl-bovine serum albumin; D012710:Serum Albumin, Bovine; D007073:Immunoglobulin E; D009173:Mycophenolic Acid; D002118:Calcium