Isoprenoid pathway activity is required for IgE receptor-mediated, tyrosine kinase-coupled transmembrane signaling in permeabilized RBL-2H3 rat basophilic leukemia cells.
Previously, we reported that the isoprenoid pathway inhibitor, lovastatin, blocks the activation by IgE receptor cross-linking of 45Ca2+ influx, 1,4,5-inositol trisphosphate production, secretion, and membrane changes (ruffling, spreading) in intact RBL-2H3 rat basophilic leukemia cells. These results indicated that an isoprenoid pathway intermediate, very likely an isoprenylated protein, is importantly involved in the control of IgE receptor-mediated signal transduction. Here, we show that 20 h of pretreatment with lovastatin also inhibits antigen-induced secretion and membrane responses in streptolysin O-(SLO)-permeabilized cells. However, lovastatin does not inhibit secretion stimulated by the nonhydrolyzable GTP analog, GTP gamma S. Furthermore, the membrane responses to GTP gamma S persist, although in an attenuated form, in lovastatin-treated permeabilized cells. The relative insensitivity of GTP gamma S-induced responses to lovastatin was one of several indications that antigen and GTP gamma S may activate separate pathways leading to transmembrane responses in permeabilized cells. Further experiments showed that the beta-thio derivative of GDP, GDPBAS, inhibits the secretory and membrane responses to GTP gamma S, as expected for a GTP-binding protein-dependent signaling pathway, while having little effect on antigen-induced responses. Conversely, genistein blocks the secretory and membrane responses to antigen, as expected for a tyrosine kinase-dependent pathway, without altering the GTP gamma S-induced responses. From these results, and from additional data from cells treated with tyrphostins and sodium orthovanadate, we propose that IgE receptor-mediated secretion from permeabilized RBL-2H3 cells occurs by a tyrosine kinase-dependent pathway that requires isoprenoid pathway activity for function. We propose further that RBL-2H3 cells contain a separate GTP-binding protein-mediated signaling pathway whose direct activation by GTP gamma S is either independent of isoprenoid pathway activity or depends on the activity of an isoprenylated protein that is not significantly depleted after 20 h of lovastatin treatment.
Deanin
G G
GG
Department of Pathology, University of New Mexico, Albuquerque 87131, USA.
Pfeiffer
J R
JR
Cutts
J L
JL
Fore
M L
ML
Oliver
J M
JM
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008148:Lovastatin / Q000494:pharmacology; D008407:Mast Cells / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D011106:Polyisoprenyl Phosphates / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011971:Receptors, Immunologic / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000378:metabolism
D011106:Polyisoprenyl Phosphates; D011971:Receptors, Immunologic; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008148:Lovastatin; D011505:Protein-Tyrosine Kinases