Differential Roles for Extracellularly Regulated Kinase-Mitogen-Activated Protein Kinase in B Cell Antigen Receptor-Induced Apoptosis and CD40-Mediated Rescue of WEHI-231 Immature B Cells

Abstract

One of the major unresolved questions in B cell biology is how the B cell Ag receptor (BCR) differentially signals to transduce anergy, apoptosis, proliferation, or differentiation during B cell maturation. We now report that extracellularly regulated kinase-mitogen-activated protein kinase (Erk-MAP kinase) can play dual roles in the regulation of the cell fate of the immature B cell lymphoma, WEHI-231, depending on the kinetics and context of Erk-MAP kinase activation. First, we show that the BCR couples to an early (≤2 h) Erk-MAP kinase signal which activates a phospholipase A2 pathway that we have previously shown to mediate collapse of mitochondrial membrane potential, resulting in depletion of cellular ATP and cathepsin B execution of apoptosis. Rescue of BCR-driven apoptosis by CD40 signaling desensitizes such early extracellularly regulated kinase (Erk) signaling and hence uncouples the BCR from the apoptotic mitochondrial phospholipase A2 pathway. A second role for Erk-MAP kinase in promoting the growth and proliferation of WEHI-231 immature B cells is evidenced by data showing that proliferating and CD40-stimulated WEHI-231 B cells exhibit a sustained cycling pattern (8–48 h) of Erk activation that correlates with cell growth and proliferation. This growth-promoting role for Erk signaling is supported by three key pieces of evidence: 1) signaling via the BCR, under conditions that induce growth arrest, completely abrogates sustained Erk activation; 2) CD40-mediated rescue from growth arrest correlates with restoration of cycling Erk activation; and 3) sustained inhibition of Erk prevents CD40-mediated rescue of BCR-driven growth arrest of WEHI-231 immature B cells. Erk-MAP kinase can therefore induce diverse biological responses in WEHI-231 cells depending on the context and kinetics of activation.

The Extracellular Membrane-Proximal Domain of Human Membrane IgE Controls Apoptotic Signaling of the B Cell Receptor in the Mature B Cell Line A20

“…Similar cases have been described previously also in mature T lymphocytes upon engagement of CD99 and in human monocytes and dendritic cells by anti-CD47 treatment (40,41). Moreover, in the immature B cell line WEHI-231, signaling through IgM induced growth arrest and apoptosis in a caspaseindependent mode that could be prevented by rescue signals mediated by CD40 (26,27,42). In this cell line, although IgM crosslinking induced caspase and cathepsin activities, these proteases were not responsible for BCR-mediated apoptosis, suggesting the existence of an alternative proteolytic pathway (43).…”

“…Despite this, ERK1/2 phosphorylation, which has been implicated in BCR activation (34,35) as well as in BCR-mediated apoptosis (25,26), was nevertheless activated in the ⌬EMPD receptors, although with a different kinetics. Consistent with these characteristics was the observation that costimulation of -⌬EMPD BCR and CD40 produced partial rescue of the apoptotic signaling and partial change of ERK phosphorylation kinetics.…”

“…Apoptotic signaling through IgM BCR in the immature WEHI-231 B cell line was reported to be inhibited by simultaneous engagement of CD40 (26). As shown in Fig.…”

The Adaptor Protein HSH2 Attenuates Apoptosis in Response to Ligation of the B Cell Antigen Receptor Complex on the B Lymphoma Cell Line, WEHI-231

“…CD40-mediated signaling has been shown to confer protec- tion against BCR-induced apoptosis in WEHI-231 cells, as well as normal B cells (35,48,50,51). When experiments were performed to compare the ability of HSH2 and CD40-mediated signaling to prevent BCR-induced mitochondrial depolarization in WEHI-231 cells, they were found to be comparable in their effectiveness (Fig.…”

CCR3 Expression Induced by IL-2 and IL-4 Functioning as a Death Receptor for B Cells

“…For Western blots, cells were lysed and total protein content was electrophoresed and blotted, as described in Materials and Methods. Numbers indicate the quantity of total cellular protein from the tested samples loaded in each lane (g) (27,41). Arrows indicate markers used to verify equivalent m.w.…”