CD38 signaling regulates B lymphocyte activation via a phospholipase C (PLC)-gamma 2-independent, protein kinase C, phosphatidylcholine-PLC, and phospholipase D-dependent signaling cascade.
The CD38 cell surface receptor is a potent activator for splenic, B lymphocytes. The molecular mechanisms regulating this response, however, remain incompletely characterized. Activation of the nonreceptor tyrosine kinase, Btk, is essential for CD38 downstream signaling function. The major Btk-dependent substrate in B cells, phospholipase C-gamma2 (PLC-gamma2), functions to generate the key secondary messengers, inositol-1,4,5 trisphosphate and diacylglycerol. Surprisingly, CD38 ligation results in no detectable increase in phosphoinositide metabolism and only a minimal increase in cytosolic calcium. We hypothesized that Btk functioned independently of PLC-gamma2 in the CD38 signaling pathway. Accordingly, we demonstrate that CD38 cross-linking does not result in the functional phosphorylation of PLC-gamma2 nor an increase in inositol-1,4,5 trisphosphate production. Furthermore, splenic B cells exhibit a normal CD38-mediated, proliferative response in the presence of the phosphoinositide-PLC inhibitor, U73122. Conversely, protein kinase C (PKC) beta-deficient mice, or PKC inhibitors, indicated the requirement for diacylglycerol-dependent PKC isoforms in this pathway. Loss of PKC activity blocked CD38-dependent, B cell proliferation, NF-kappaB activation, and subsequent expression of cyclin-D2. These results suggested that an alternate diacylglycerol-producing phospholipase must participate in CD38 signaling. Consistent with this idea, CD38 increased the enzymatic activity of the phosphatidylcholine (PC)-metabolizing enzymes, PC-PLC and phospholipase D. The PC-PLC inhibitor, D609, completely blocked CD38-dependent B cell proliferation, IkappaB-alpha degradation, and cyclin-D2 expression. Analysis of Btk mutant B cells demonstrated a partial requirement for Btk in the activation of both enzymes. Taken together, these data demonstrate that CD38 initiates a novel signaling cascade leading to Btk-, PC-PLC-, and phospholipase D-dependent, PLC-gamma2-independent, B lymphocyte activation.
Moreno-García
Miguel E
ME
Departments of Cell Biology, Centro de Investigación y Estudios Avanzados, Mexico D.F. Mexico.
López-Bojórques
Lucia N
LN
Zentella
Alejandro
A
Humphries
Lisa A
LA
Rawlings
David J
DJ
Santos-Argumedo
Leopoldo
L
D036541:ADP-ribosyl Cyclase / Q000502:physiology*; D051997:ADP-ribosyl Cyclase 1; D000818:Animals; D015703:Antigens, CD / Q000502:physiology*; D001402:B-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000276:immunology*; D001952:Bridged-Ring Compounds / Q000494:pharmacology; D049109:Cell Proliferation; D056742:Cyclin D2; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004075:Diglycerides / Q000502:physiology; D004789:Enzyme Activation / Q000276:immunology; D004790:Enzyme Induction / Q000187:drug effects / Q000276:immunology; D005260:Female; D007527:Isoenzymes / Q000502:physiology; D008213:Lymphocyte Activation / Q000276:immunology*; D008562:Membrane Glycoproteins; D051379:Mice; D008807:Mice, Inbred BALB C; D018345:Mice, Knockout; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D009636:Norbornanes; D051966:Phospholipase C gamma; D010739:Phospholipase D / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D013154:Spleen / Q000166:cytology / Q000201:enzymology / Q000276:immunology; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology; D010738:Type C Phospholipases / Q000502:physiology*
D015703:Antigens, CD; D001952:Bridged-Ring Compounds; C486196:Ccnd2 protein, mouse; D056742:Cyclin D2; D016213:Cyclins; D004075:Diglycerides; D007527:Isoenzymes; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D009636:Norbornanes; D013859:Thiocarbamates; D013871:Thiones; C046498:tricyclodecane-9-yl-xanthogenate; D011493:Protein Kinase C; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D010739:Phospholipase D; D036541:ADP-ribosyl Cyclase; C498155:Cd38 protein, mouse; D051997:ADP-ribosyl Cyclase 1