B cell receptor (BCR) cross-talk: IL-4 creates an alternate pathway for BCR-induced ERK activation that is phosphatidylinositol 3-kinase independent

IL-4 has pleiotropic effects on B cells. These effects include alteration of subsequent BCR-triggered responses. To identify a molecular basis for this receptor cross-talk, we examined ERK activation and NF-kappa B induction. We found that treatment with IL-4, but not other cytokines, affected subsequent BCR signaling by creating a new pathway in which the need for PI3K in ERK activation was eliminated. In contrast, the need for PI3K in NF-kappa B induction was not altered. The new-pathway for ERK required time to develop, depended on STAT6, and was blocked by inhibition of macromolecular synthesis. As in the classical pathway, BCR-induced ERK activation in the new, PI3K-independent pathway required MEK and was reflected in c-Raf. Thus, IL-4 promotes an alternate pathway through which BCR is coupled to Raf/MEK/ERK that may function to heighten the responsiveness of B cells during times of immunological stress.