Role of calcium, protein kinase C and MAP kinase in the activation of mast cells

Abstract

The mechanisms of activation of mast cells have been studied in most detail in rat RBL-2H3 cells. These cells respond to antigen via the IgE receptor (FcεRl) through sequential activation of the tyrosine kinases, Lyn and Syk, and to adenosine analogs via the adenosine A₃ receptor (A₃R) and a pertussis toxin-sensitive G protein, most likely G_i-3. Other receptors, introduced through gene transfection, include the muscarinic m1 receptor (m1R) which acts via G_q/11. Stimulation of cells via FcεRl, A₃R or m1R leads to the activation of phospholipase (PL) C, PLD and mitogen-activated protein (MAP) kinase resulting in the generation of inositol phosphates and diglycerides, an increase of cytosolic Ca²⁺, the activation of protein kinase C (PKC) and the phosphorylation of various proteins by PKC and MAP kinase. The extent and time course of these events varies for each receptor. These variations, as well as the effects of pharmacologic probes, gene transfection and reconstitution of responses in washed permeabilized cells, indicate how these events relate to functional responses. A modest but sustained elevation of cytosolic Ca²⁺ through an influx of extracellular Ca²⁺ and activation of PKCβ and PKCδ are sufficient for optimal release of preformed secretory granules. Phosphorylation of a cytosolic PLA₂ by MAP kinase (p42^mapk) and a modest increase in cytosolic Ca²⁺ are necessary for the activation of PLA₂ and the binding of PLA₂ to membranes, respectively. Finally, both de novo generation and secretion via Golgi-derived vesicles of certain cytokines are dependent on Ca²⁺ and PKC as well as additional signals most probably phosphorylation of proteins by Syk and p42^mapk.