Agonist-Biased Signaling at the Histamine H4 Receptor: JNJ7777120 Recruits β-Arrestin without Activating G Proteins

The G(i/o)-coupled histamine H-4 receptor is highly expressed in hemopoietic cells and is a promising new target for the treatment of chronic inflammatory diseases. 1-[(5-Chloro-1H-indol-2-yl)carbonyl]-4-methyl-piperazine (JNJ7777120) has been described as a selective antagonist at the H-4 receptor and is widely used to characterize the physiological role of the H-4 receptor. We have investigated the pharmacological properties of JNJ7777120 using two distinct downstream signaling measurements, G protein activation and beta-arrestin recruitment. The H-4 receptor agonists histamine and clobenpropit, but not JNJ7777120, were able to induce [S-35]GTP gamma S binding in membranes prepared from U2OS-H-4 cells. Thioperamide, a dual H-3/H-4 receptor antagonist, and JNJ7777120 were both able to inhibit the [S-35]GTP gamma S binding induced by clobenpropit. Agonists and antagonists specific for other members of the histamine receptor family had no effect in this assay format. Histamine and clobenpropit increased beta-arrestin recruitment to the H-4 receptor in a concentration-dependent manner. This beta-arrestin recruitment could be inhibited by preincubation with thioperamide. We were surprised to find that preincubation with the H-4-selective antagonist JNJ7777120 potentiated rather than antagonized the response to a submaximal concentration of clobenpropit. JNJ7777120 treatment alone resulted in an increase in beta-arrestin recruitment, which again could be inhibited by preincubation with thioperamide. Schild analysis demonstrated competitive antagonism between thioperamide and both clobenpropit and JNJ7777120. Histamine and clobenpropit had comparable potencies for both [S-35]GTP gamma S binding and beta-arrestin recruitment, suggesting little difference in the levels of receptor reserve between the two assays. In conclusion, we have demonstrated that JNJ7777120 recruits beta-arrestin to the H-4 receptor, independent of G protein activation.