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

ABSTRACTThe 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 (FceRI) 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 Gi-3. Other receptors, introduced through gene transfection, include the muscarinic ml receptor (mlR) which acts via Gq/11. Stimulation of cells via FceRI, A3R or ml R 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 PLAj by AMP kinase (p42mapk) and a modest increase in cytosolic Ca2+ are necessary for the activation of Pl^ 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 p42mapk