Noncompetitive antagonism and inverse agonism as mechanism of action of nonpeptidergic antagonists at primate and rodent CXCR3 chemokine receptors

Nonpeptidergic allosteric antagonists differentially bind to the CXCR2 chemokine receptor

The chemokine receptor CXCR2 is involved in different inflammatory diseases, like chronic obstructive pulmonary disease, psoriasis, rheumatoid arthritis, and ulcerative colitis; therefore, it is considered an attractive drug target. Different classes of small CXCR2 antagonists have been developed. In this study, we selected seven CXCR2 antagonists from the diarylurea, imidazolylpyrimide, and thiazolopyrimidine class and studied their mechanisms of action at human CXCR2. All compounds are able to displace (125)I-CXCL8 and inhibit CXCL8-induced beta-arrestin2 recruitment. Detailed studies with representatives of each class showed that these compounds displace and antagonize CXCL8, most probably via a noncompetitive, allosteric mechanism. In addition, we radiolabeled the high-affinity CXCR2 antagonist SB265610 [1-(2-bromophenyl)-3-(4-cyano-1H-benzo[d] [1,2,3]-triazol-7-yl)urea] and subjected [(3)H]SB265610 to a detailed analysis. The binding of this radioligand was saturable and reversible. Using [(3)H]SB265610, we found that compounds of the different chemical classes bind to distinct binding sites. Hence, the use of a radiolabeled low-molecular weight CXCR2 antagonist serves as a tool to investigate the different binding sites of CXCR2 antagonists in more detail.

Viral hijacking of human receptors through heterodimerization

Epstein-Barr virus (EBV) is a human herpesvirus that primarily infects B lymphocytes and is associated with tumor development. Like other herpesviruses, EBV has pirated and modified host genes encoding important regulatory cellular proteins to take over cellular control after infection. One of these genes (BILF1) encodes a G protein-coupled receptor (GPCR). It is currently accepted that GPCRs exist and function as dimers. B lymphocyte migration and functioning is regulated by chemokines acting on their cognate receptors. In this study, we show that BILF1 heterodimerizes with various chemokine receptors using BRET, trFRET and co-immunoprecipitation. Importantly, heterodimerization of BILF1 with chemokine receptors may alter the responsiveness of B lymphocytes to chemokines thereby altering homing and homeostasis of infected B lymphocytes and might be essential for EBV dissemination and/or involved in EBV-induced pathogenesis.