Figure 5.

BAFF induces Bim phosphorylation via sustained activation of the MEK–ERK pathway. (A) WEHI-231 cells were treated for 24 h with medium, anti-IgM, BAFF, or anti-CD40. Cell lysates were incubated with or without λ protein phosphatase. Immunoblots were probed with anti-Bim serum. (B) WEHI-231 cells were pretreated for 2 h with DMSO vehicle, 5 μM MEK inhibitor U0126 (U), or 5 μM p38 MAPK inhibitor SB203580 (SB) before incubation with BAFF for 24 h. Blots were probed with anti-Bim, anti–phospho-ERK, or anti-actin (loading control). (C and D) WEHI-231 cells were treated for 0–24 h with anti-IgM in the presence or absence of BAFF. Immunoblots were probed with either anti–phospho-ERK, anti–phospho-MEK, anti–phospho–c-Raf (Ser 338), anti-MKP2, anti-Bim, or anti–Bcl-2 serum. In (D), immunoblots for ERK2 (top) or MEK1/2 (bottom) were quantified by scanning densitometry to measure the fold change in each phosphorylated protein.