Activity of an intracellular lymphocyte stimulator is independent of G-protein interactions, [Ca2+]i elevation, phosphoinositide hydrolysis, and protein kinase C translocation.
We have evaluated potential molecular mechanisms by which a group of synthetic lymphokine-like molecules, the 7,8-disubstituted guanine ribonucleosides, acts on second messenger pathways to augment the responses of murine B lymphocytes. Despite its extensive structural homology with GTP, 7-methyl-8-oxoguanosine (7-Me-8-oGuo), a prototypical disubstituted nucleoside, does not inhibit the binding of guanosine 5'-3-O-(thio)triphosphate either to purified G-proteins, or to G-proteins in situ in the plasma membrane. In contrast to anti-IgM antibodies, 7-Me-8-oGuo fails to induce elevation of intracellular free calcium in B lymphocytes. It does not elicit enhanced production of inositol phosphates in either unfractionated or large, cycling B cells (the cells on which it acts preferentially). It is unable to modify the cellular distribution or activity of protein kinase C, whereas phorbol 12-myristate 13-acetate, anti-IgD antibodies, and lipopolysaccharide do activate protein kinase C. Inhibitors of protein kinase C activity diminish stimulation of mRNA transcription by anti-IgD antibodies and lipopolysaccharide but not by 7-Me-8-oGuo. These data demonstrate that 7-Me-8-oGuo either uses a pathway distinct from that mediated by G-proteins, intracellular free calcium, inositol phosphates, and protein kinase C, or else bypasses the early events of this pathway, activating the cell at a point beyond their involvement. In either event, these nucleosides represent the only class of activator to date that is capable of driving B cell proliferation and differentiation without involvement of protein kinase C.
Goodman
M G
MG
Department of Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037.
Speizer
L
L
Bokoch
G
G
Kanter
J
J
Brunton
L L
LL
D000818:Animals; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D006151:Guanosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D051379:Mice; D010716:Phosphatidylinositols / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction
D010716:Phosphatidylinositols; D012333:RNA, Messenger; D006151:Guanosine; C050068:7-methyl-8-oxoguanosine; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D002118:Calcium