Protein Kinase Cζ Mediates μ-Opioid Receptor-induced Cross-desensitization of Chemokine Receptor CCR5

We have previously shown that the mu-opioid receptor (MOR) is capable of mediating cross-desensitization of several chemokine receptors including CCR5, but the biochemical mechanism of this process has not been fully elucidated. We have carried out a series of functional and biochemical studies and found that the mechanism of MOR-induced cross-desensitization of CCR5 involves the activation of PKC zeta. Inhibition of PKC zeta by its pseudosubstrate inhibitor, or its siRNA, or dominant negative mutants suppresses the cross-desensitization of CCR5. Our results further indicate that the activation of PKC zeta is mediated through a pathway involving phosphoinositol-dependent kinase-1 (PDK1). In addition, activation of MOR elevates the phosphorylation level and kinase activity of PKC zeta. The phosphorylation of PKC zeta can be suppressed by a dominant negative mutant of PDK1. We observed that following MOR activation, the interaction between PKC zeta and PDK1 is immediately increased based on the analysis of fluorescent resonance energy transfer in cells with the expression of PKC zeta-YFP and PDK1-CFP. In addition, cells expressing PKC zeta kinase motif mutants (Lys-281, Thr-410, Thr-560) fail to exhibit full MOR-induced desensitization of CCR5 activity. Taken together, we propose that upon DAMGO treatment, MOR activates PKC zeta through a PDK1-dependent signaling pathway to induce CCR5 phosphorylation and desensitization. Because CCR5 is a highly proinflammatory receptor, and a critical coreceptor for HIV-1, these results may provide a novel approach for the development of specific therapeutic agents to treat patients with certain inflammatory diseases or AIDS.