Common and Distinct Signaling Pathways Mediate the Induction of TNF-α and IL-5 in IgE Plus Antigen-Stimulated Mast Cells

A small number of signaling cascades represented by mitogen-activated protein kinases, phosphoinositol-3-kinase, protein kinase C, signal transducers and activators of transcription, Ca2+/calcineurin, and a few other molecules are linked to an incomparably large number of surface receptors. Parallel activation of several of these pathways and the existence of isozymes for a number of signal transmitting molecules generate the required complexity and specificity matching the receptor variety. Here we show that the proinflammatory mediator TNF-α and the growth factor IL-5 are activated along common and distinct signaling cascades in allergically stimulated murine mast cells. Both of them are dependent on Ca2+ influx, activation of calcineurin and nuclear factor of activated T cells as well as a member of the atypical PKC family, most likely PKCμ. Additionally, mitogen-activated protein kinases for TNF-α and members of the classical or nonclassical PKCs for IL-5, respectively, were identified as additional required pathways. Inhibition of the classical and nonclassical PKCs, however, does not abrogate IL-5 induction but instead leads to a switch to mitogen-activated protein kinases, which then become essential. The activated branches of this “salvage” signaling cascade are represented by extracellular signal-regulated kinase 1/2 and c-jun NH2 terminal kinase 1 in allergically stimulated mast cells.