H4R activation utilizes distinct signaling pathways for the production of RANTES and IL-13 in human mast cells.

The histamine H4 receptor functionally expressed on human mast cells and their signaling pathways for the production of IL-13 and RANTES have never been analyzed side by side in a directly comparable manner. Therefore, the aim of the study was to investigate signaling transduction pathways of H4R via ERK1/2, Akt and NFκB leading to the induction of inflammatory cytokine expression. In the present study, HMC-1 cells and CBMCs were pretreated individually with H4R antagonist JNJ7777120, H1R antagonist mepyramine and signaling molecule inhibitors PD 98059, LY294002, Bay 117082 followed by stimulation was done with or without histamine or 4-MH. Furthermore, the siRNA mediated H4R gene silencing effects are studied at the H4R protein expression level and also signal transduction level. We found that the pretreatment with JNJ7777120 and H4R gene silencing decreased histamine, 4-MH induced phosphorylation of ERK1/2, Akt and NFκB-p65. Moreover, PD 98059, LY294002 and Bay 117082, which respectively inhibited the histamine and 4-methylhistamine induced phosphorylation of ERK1/2, Akt and NFκB-p65 respectively. We also found that the activation of H4R caused the release of IL-13 and RANTES on human mast cells. The MEK inhibitor PD98059 blocked H4R mediated RANTES/CCL5 production by 20.33 pg/ml and inhibited IL-13 generation by 95.71 pg/ml. In contrast, PI3 kinase inhibitor LY294002 had no effect on 4-MH induced RANTES/CCL5 production but blocked IL-13 generation by 117.58 pg/ml. These data demonstrate that the H4R activates divergent signaling pathways to induce cytokine and chemokine production in human mast cells.