The Orphan G Protein-coupled Receptor 75 Signaling is Activated by the Chemokine CCL5

The chemokine CCL5 prevents neuronal cell death mediated both by amyloid β, as well as the human immunodeficiency virus (HIV) viral proteins gp120 and Tat. Because CCL5 binds to CCR5, CCR3 and/or CCR1 receptors, it is unclear which of these receptors plays a role in neuroprotection. Indeed, CCL5 also has neuroprotective activity in cells lacking these receptors. CCL5 may bind to a G protein-coupled receptor 75 (GPR75), which encodes for a 540 amino-acid orphan receptor of the Gqα family. In this study, we have used SH-SY5Y human neuroblastoma cells to characterize whether CCL5 could activate a Gq signaling through GPR75. Both qPCR and flow cytometry show that these cells express GPR75 but do not express CCR5, CCR3 or CCR1 receptors. SY-SY5Y cells were then used to examine CCL5-mediated signaling. We report that CCL5 promotes a time- and concentration-dependent phosphorylation of protein kinase B (AKT), glycogen synthase kinase 3β and extracellular signal-regulated kinase (ERK) 1/2. Specific antagonists of CCR5, CCR3 and CCR1 did not prevent CCL5 from increasing phosphorylated AKT or ERK. Moreover, CCL5 promotes a time-dependent internalization of GPR75. Lastly, knocking down GPR75 expression by a CRISPR-Cas9 approach inhibited the ability of CCL5 to activate pERK in SH-SY5Y cells. Therefore, we propose that GPR75 is a novel receptor for CCL5 that could explain some of the pharmacological action of this chemokine. These findings may help in the development of small molecule GPR75 agonists that mimic CCL5.