Receptor-mediated activation of human B lymphocytes in a nonphosphotyrosine-dependent manner.
The B cell AgR regulates two signal transduction pathways: the tyrosine kinase and the phosphatidylinositol (PtdIns) pathways. Stimulation of B cells with Ag or anti-Ig antibody results in a rapid increase in tyrosine phosphorylation of multiple substrates. The AgR also mediates the activation of phospholipase C-gamma 1 (PLC-gamma 1) thus producing the second messengers, inositol trisphosphate and diacylglycerol. Although the detailed relationship between these two signaling pathways remains unclear, it has recently become apparent that PLC-gamma 1 might be a target for the AgR-associated protein tyrosine kinase. To address the question of whether tyrosine kinase activity is essential for B cell activation, we studied early biochemical changes and later cellular events induced by ligation of the purinoceptor (P2R). Ligation of ATP to its receptor on B cells has been previously shown to elicit increases in cytosolic free Ca2+ and inositol phosphate production as well as induction of c-fos mRNA expression and increased expression of IL-2 and transferrin receptors. We show here that ATP in a wide range of concentrations did not increase protein tyrosine kinase activity. In contrast with the AgR, P2R did not mediate tyrosine phosphorylation of PLC-gamma 1, thus suggesting that it may use another phosphoinositide-specific PLC that does not require phosphorylation on tyrosine residues for its activation. The results were supported by experiments with a specific tyrosine kinase inhibitor, tyrphostin AG-126. Preincubation with this inhibitor blocked AgR but not P2R-mediated inositol phosphate production, cytosolic free Ca2+ changes, and IL-2 and transferrin receptor expression. The results indicate that the PtdIns pathway may be sufficient to induce activation of B cells and that the tyrosine phosphorylation pathway is not necessary for nonantigenic B cell activation.
Roifman
C M
CM
Division of Immunology/Allergy, Hospital for Sick Children, Toronto, Ontario, Canada.
Wang
G
G
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001402:B-Lymphocytes / Q000276:immunology*; D001597:Benzylidene Compounds / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D016762:Genes, fos; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000502:physiology; D008213:Lymphocyte Activation; D009570:Nitriles / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000502:physiology; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D015375:Receptors, Interleukin-2 / Q000378:metabolism; D011983:Receptors, Purinergic / Q000502:physiology*; D011990:Receptors, Transferrin / Q000378:metabolism; D015290:Second Messenger Systems; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D020032:Tyrphostins
D001597:Benzylidene Compounds; D007295:Inositol Phosphates; D009570:Nitriles; D010716:Phosphatidylinositols; D012333:RNA, Messenger; D011947:Receptors, Antigen, B-Cell; D015375:Receptors, Interleukin-2; D011983:Receptors, Purinergic; D011990:Receptors, Transferrin; D020032:Tyrphostins; C069028:AG 127; D019000:Phosphotyrosine; D014443:Tyrosine; D000255:Adenosine Triphosphate; D011505:Protein-Tyrosine Kinases; D010738:Type C Phospholipases