title: B cell receptor (BCR) cross-talk: CD40 engagement enhances BCR-induced ERK activation.
abstract: Bystander B cells may be initially stimulated through CD40, which enhances susceptibility to Fas-mediated apoptosis, before encountering Ag, which produces Fas resistance. A key issue in this process is to what extent CD40 cross-talk might affect subsequent BCR signaling. It has previously been shown that CD40 engagement bypasses or mitigates the need for Bruton's tyrosine kinase in subsequent BCR signaling for NF-kappaB activation. However, the full extent of the effects of CD40 on BCR signaling has not been delineated. In the present study we evaluated the possibility that CD40-mediated cross-talk also affects another principal outcome of BCR signaling: MAPK activation. We found that prior stimulation of primary murine B cells with CD40L markedly enhanced the level of ERK and JNK (but not p38 MAPK) phosphorylation produced by subsequently added anti-Ig Ab, and much, but not all, of this enhancement was independent of PI3K and phospholipase C. CD40L treatment similarly enhanced BCR-induced MAPK kinase (MEK) phosphorylation, and MEK was required for enhancement of ERK. Although BCR-induced c-Raf phosphorylation was also enhanced by prior CD40L treatment, c-Raf was not required for MEK/ERK phosphorylation. These results identify a novel system of receptor cross-talk between CD40 and BCR and indicate that the effects of CD40 engagement on subsequent BCR stimulation spread beyond NF-kappaB to involve the MAPK pathway.
authors.affiliation: Department of Medicine, Boston University School of Medicine, Boston, MA 02118, USA.
authors.forename: Takuya
authors.initials: T
authors.lastname: Mizuno
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Rothstein
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology*; D019013:CD40 Antigens / Q000378:metabolism*; D023201:CD40 Ligand / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D066298:In Vitro Techniques; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D018448:Models, Immunological; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051966:Phospholipase C gamma; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D020239:Receptor Cross-Talk; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D019013:CD40 Antigens; D004791:Enzyme Inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011947:Receptors, Antigen, B-Cell; D023201:CD40 Ligand; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma