Quercetin sensitizes RBL-2H3 cells to polybasic mast cell secretagogues through increased expression of Gi GTP-binding proteins linked to a phospholipase C signaling pathway.

Polybasic secretagogues such as mastoparan, compound 48/80, substance P, and somatostatin stimulate secretion in rat peritoneal mast cells through direct activation of the heterotrimeric G protein, G(i-3). Cultured RBL-2H3 mast cells do not normally respond to these secretagogues, but, as reported here, they do so after prolonged exposure to the kinase inhibitor, quercetin. This inhibitor, which causes phenotypic changes in RBL-2H3 cells, induces a substantial increase (more than sevenfold) in the expression of alpha subunits of the pertussis toxin-sensitive G proteins, G(i-2) and G(i-3). Compound 48/80-induced secretion is associated with transient hydrolysis of phosphoinositides and a transient increase in cytosolic calcium ions. These responses are inhibited by pertussis toxin, and in addition, secretion is blocked by calcium chelation and the protein kinase C inhibitor, Ro31-7549. These results delineate a pathway for compound 48/80-induced secretion in mast cells via Gi protein(s), phospholipase C, calcium, and protein kinase C. The results also imply that phospholipase C, most likely phospholipase Cbeta3, can be transiently activated in RBL-2H3 cells by subunits of Gi proteins to induce cellular responses.