Histamine H[sub.1] Receptor-Mediated JNK Phosphorylation Is Regulated by G[sub.q] Protein-Dependent but Arrestin-Independent Pathways

Arrestins are known to be involved not only in the desensitization and internalization of G protein-coupled receptors but also in the G protein-independent activation of mitogen-activated protein (MAP) kinases, such as extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), to regulate cell proliferation and inflammation. Our previous study revealed that the histamine H[sub.1] receptor-mediated activation of ERK is dually regulated by G[sub.q] proteins and arrestins. In this study, we investigated the roles of G[sub.q] proteins and arrestins in the H[sub.1] receptor-mediated activation of JNK in Chinese hamster ovary (CHO) cells expressing wild-type (WT) human H[sub.1] receptors, the G[sub.q] protein-biased mutant S487TR, and the arrestin-biased mutant S487A. In these mutants, the Ser487 residue in the C-terminus region of the WT was truncated (S487TR) or mutated to alanine (S487A). Histamine significantly stimulated JNK phosphorylation in CHO cells expressing WT and S487TR but not S487A. Histamine-induced JNK phosphorylation in CHO cells expressing WT and S487TR was suppressed by inhibitors against H[sub.1] receptors (ketotifen and diphenhydramine), G[sub.q] proteins (YM-254890), and protein kinase C (PKC) (GF109203X) as well as an intracellular Ca[sup.2+] chelator (BAPTA-AM) but not by inhibitors against G protein-coupled receptor kinases (GRK2/3) (cmpd101), β-arrestin2 (β-arrestin2 siRNA), and clathrin (hypertonic sucrose). These results suggest that the H[sub.1] receptor-mediated phosphorylation of JNK is regulated by G[sub.q]-protein/Ca[sup.2+]/PKC-dependent but GRK/arrestin/clathrin-independent pathways.