Use of G-protein-coupled and -uncoupled CCR5 receptors by CCR5 inhibitor-resistant and -sensitive human immunodeficiency virus type 1 variants

Small-molecule CCR5 inhibitors such as vicriviroc (VVC) and maraviroc (MVC) are allosteric modulators that impair HIV-1 entry by stabilizing a CCR5 conformation that the virus recognizes inefficiently. Viruses resistant to these compounds are able to bind the inhibitor- CCR5 complex while also interacting with the free coreceptor. CCR5 also interacts intracellularly withGproteins, as part of its signal transduction functions, and this process alters its conformation. Here we investigated whether the action ofVVCagainst inhibitor- sensitive and -resistant viruses is affected by whether or not CCR5 is coupled toGproteins such as Gα_i. Treating CD4⁺ T cells with pertussis toxin to uncouple the Gα_i subunit from CCR5 increased the potency of VVCagainst the sensitive viruses and revealed that VVC-resistant viruses use the inhibitor-bound form of Gα_i-coupled CCR5 more efficiently than they use uncoupled CCR5. Supportive evidence was obtained by expressing a signaling-deficient CCR5 mutant with an impaired ability to bind toGproteins, as well as two constitutively active mutants that activateGproteins in the absence of external stimuli. The implication of these various studies is that the association of intracellular domains of CCR5 with the signaling machinery affects the conformation of the external and transmembrane domains and how they interact with small-molecule inhibitors of HIV-1 entry.