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  • Title: Differential coupling of membrane Ig and CD40 to the extracellularly regulated kinase signaling pathway.
    Author: Purkerson JM, Parker DC.
    Journal: J Immunol; 1998 Mar 01; 160(5):2121-9. PubMed ID: 9498749.
    Abstract:
    Coupling of membrane Ig (mIg) and CD40 to the extracellularly regulated kinase (ERK) signal transduction pathway was examined in the WEHI-231 B lymphoma and normal mouse B cells. Cross-linking mIg induces ERK activation in both WEHI-231 and normal B cells. In contrast, CD40 cross-linking failed to induce ERK activation in WEHI-231, but signals through CD40 were more effective than mIg as a stimulus for ERK activation in normal B cells. However, several lines of evidence suggest that CD40 and the B cell Ag regulate ERK through distinct pathways that converge at the level of MEK-1, mitogen-activated protein kinase kinase. Abs to mIg or CD40 induced MEK-1 activation with different kinetics. Cross-linking of mIg, but not CD40, induced tyrosine phosphorylation of the SHC adapter molecule that couples receptors to Ras-dependent signaling pathways. Finally, agents that elevate cAMP, causing protein kinase A-mediated inhibition of Raf-1, inhibited activation of ERK in response to mIg cross-linking, but had no affect on ERK activation in response to anti-CD40 or Jun N-terminal kinase activation by signals through either receptor. Thus, CD40 uses an unidentified protein kinase A-insensitive MEK kinase, rather than Raf-1, to regulate ERK activity.
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