Journal
JOURNAL OF EXPERIMENTAL MEDICINE
Volume 202, Issue 10, Pages 1363-1374Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1084/jem.20051283
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Funding
- NCRR NIH HHS [P51 RR000166, RR00166] Funding Source: Medline
- NIAID NIH HHS [R01 AI045088, AI45088] Funding Source: Medline
- NIGMS NIH HHS [GM67905, R01 GM037905] Funding Source: Medline
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The B cell activating factor belonging to the tumor necrosis factor family ( BAFF) is required for B cell survival and maturation. The mechanisms by which BAFF mediates B cell survival are less understood. We found that BAFF and a proliferation-inducing ligand (APRIL), which are related, block B cell antigen receptor (BCR) - induced apoptosis upstream of mitochondrial damage, which is consistent with a role for Bcl-2 family proteins. BCR ligation strongly increased expression of the proapoptotic Bcl-2 homology 3-only Bcl-2 protein Bim in both WEHI-231 and splenic B cells, and increases in Bim were reversed by BAFF or APRIL. Small interfering RNA vector - mediated suppression of Bim blocked BCR-induced apoptosis. BAFF also induced Bim phosphorylation and inhibited BCR-induced association of Bim with Bcl-2. BAFF induced delayed but sustained stimulation of extracellular signal - regulated kinase (ERK) and its activators, mitogen-activated protein kinase/ERK activating kinase (MEK) and c-Raf, and MEK inhibitors promoted accumulation and dephosphorylation of Bim. These results suggest that BAFF inhibits BCR-induced death by down-regulating Bim via sustained ERK activation, demonstrating that BAFF directly regulates Bim function. Although transitional immature type 1 ( T1) B cell numbers are normal in Bim(-/-) mice, T2 and follicular mature B cells are elevated and marginal zone B cells are reduced. Our results suggest that mature B cell homeostasis is maintained by BAFF-mediated regulation of Bim.
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