title: Ca2+-independent protein kinase Cs mediate heterologous desensitization of leukocyte chemokine receptors by opioid receptors.
abstract: Heterologous desensitization of chemokine receptors by opioids has been considered to contribute to their immunosuppressive effects. Previous studies show that Met-enkephalin, an endogenous opioid, down-regulates chemotaxis of selected chemokine receptors via phosphorylation. In the present study, we further investigated the molecular mechanism of such cross-regulation. Our data showed that preincubation with Met-enkephalin inhibited both MIP-1 alpha-mediated chemotaxis and Ca(2+) flux of monocytes in a dose-dependent manner. The inhibitory effects were maximal using nanomolar concentrations of activating chemokines, a concentration found in physiological conditions. A decrease both in chemokine receptor affinity and in coupling efficiency between receptors and G protein were observed, which directly contributed to the desensitization effects. However, comparing with chemokines such as MIP-1 alpha and MCP-1, opioids did not elicit a calcium flux, failed to induce MIP-1 alpha receptors internalization, and mediated a less potent heterologous desensitization. We hypothesized that these differences might originate from the involvement of different protein kinase C (PKC) isotypes. In our studies, opioid-mediated down-regulation of MIP-1 alpha receptors could be blocked by the general PKC inhibitor calphostin C, but not by the calcium-dependent classic PKC inhibitor Go6976. Western blotting analysis and immunofluorescent staining further showed that only calcium-independent PKCs were activated upon opioid stimulation. Thus, opioids achieve desensitization of chemokine receptors via a unique pathway, involving only calcium-independent PKC isotypes.
authors.affiliation: Laboratory of Molecular Immunoregulation, Intramural Research Support Program, Frederick, Maryland 21702-1201, USA.
authors.forename: Ning
authors.initials: N
authors.lastname: Zhang
authors.forename: Dave
authors.initials: D
authors.lastname: Hodge
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Rogers
authors.forename: Joost J
authors.initials: JJ
authors.lastname: Oppenheim
mesh_terms: D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D054407:Chemokine CCL4; D002634:Chemotaxis, Leukocyte / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D006706:Homeostasis; D006801:Humans; D007962:Leukocytes / Q000276:immunology*; D019402:Macrophage Inflammatory Proteins / Q000502:physiology; D009000:Monocytes / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D011493:Protein Kinase C / Q000097:blood*; D019707:Receptors, Chemokine / Q000097:blood*; D011957:Receptors, Opioid / Q000502:physiology*
chemical_list: D054407:Chemokine CCL4; D019402:Macrophage Inflammatory Proteins; D019707:Receptors, Chemokine; D011957:Receptors, Opioid; D004744:Enkephalin, Methionine; D011493:Protein Kinase C; D002118:Calcium