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-1α-mediated chemotaxis and Ca2+ 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-1α and MCP-1, opioids did not elicit a calcium flux, failed to induce MIP-1α 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-1α 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. 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-1α-mediated chemotaxis and Ca2+ 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-1α and MCP-1, opioids did not elicit a calcium flux, failed to induce MIP-1α 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-1α 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. G protein-coupled receptor protein kinase C diacylglycerol classical PKC novel PKC phosphate-buffered saline Dulbecco's modified Eagle's medium guanosine 5′-3-O-(thio)triphosphate Cys2, Tyr3, Orn5, Pen7 amide green fluorescent protein Long term opioid usage induces immunosuppression by modulating a spectrum of immune activities, such as inhibition of lymphocyte proliferation, decreased production of interferon γ, interleukin 2, and interleukin 4 by activated lymphocytes, enhanced synthesis of tumor necrosis factor α and interleukin 1β in activated macrophage, enhanced production of MCP-1, RANTES (regulated on activation normal T-cell expressed and secreted), and IP-10 in peripheral blood mononuclear cells, and reduction in antibody production (1Novick D.M.O.M. Ghali V. Croxson T.S. Mercer W.D. Chiorazzi N. Kreek M.J. J. Pharmacol. Exp. Ther. 1989; 250: 606-610PubMed Google Scholar, 2Taub D.D., E.T. Geller E.B. Adler M.W. Rogers T.J. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 360-364Crossref PubMed Scopus (169) Google Scholar, 3Wang J Charboneau R. Balasubramanian S. Barke R.A. Loh H.H. Roy S. J. Leukocyte Biol. 2002; 71: 782-790PubMed Google Scholar, 4McCarthy L. Szabo I. Nitsche J.F. Pintar J.E. Rogers T.J. J. Neuroimmunol. 2001; 114: 173-180Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar, 5McCarthy L, W.M. Sliker J.K. Eisenstein T.K. Rogers T.J. Drug Alcohol Depend. 2001; 62: 111-123Crossref PubMed Scopus (337) Google Scholar). The fact that accelerated human immunodeficiency virus pathogenesis occurred in patients who abuse heroin is consistent with the immunosuppressive activity of the opioids (6Donahoe R.M. Falek A. Adv. Biochem. Psychopharmacol. 1988; 44: 145-158PubMed Google Scholar). Although previous studies indicate that opioids may regulate immune responses through their action on central nervous system or sympathetic nervous system, the discovery of opioid receptors on peripheral blood mononuclear cells suggested that these opioid receptors could directly modify the response of proinflammatory receptors (2Taub D.D., E.T. Geller E.B. Adler M.W. Rogers T.J. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 360-364Crossref PubMed Scopus (169) Google Scholar, 3Wang J Charboneau R. Balasubramanian S. Barke R.A. Loh H.H. Roy S. J. Leukocyte Biol. 2002; 71: 782-790PubMed Google Scholar, 4McCarthy L. Szabo I. Nitsche J.F. Pintar J.E. Rogers T.J. J. Neuroimmunol. 2001; 114: 173-180Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar, 7Grimm M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google Scholar). Data from knock-out mice and in vitro studies suggest that such suppression is mediated largely by μ, δ, and κ opioid receptors. Opioids receptors, members of the seven-transmembrane receptor family, perform their function by coupling to heterotrimeric Gi/o proteins. Their activation leads to inhibition of adenylyl cyclase by Gα, inhibition of voltage-dependent calcium channels, and activation of G protein-coupled inwardly rectifying K+channels by Gβγ. In cells expressing multiple G protein-coupled receptors (GPCRs),1 prolonged activation of one receptor has been shown to result in the down-regulation of other GPCR through a process called heterologous desensitization. Accumulating data have demonstrated that heterologous down-regulation of GPCR is mediated by protein kinase A and protein kinase C (PKC) (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 9Richmond A, M.S. White J.R. Schraw W. Methods Enzymol. 1997; 288: 3-15Crossref PubMed Scopus (7) Google Scholar, 11Lefkowitz R. J. Biol. Chem. 1998; 273: 18677-18680Abstract Full Text Full Text PDF PubMed Scopus (908) Google Scholar). Calcium flux, a potent activator of PKC, has been considered essential for heterologous desensitization of chemokine receptors in peripheral blood mononuclear cells (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 9Richmond A, M.S. White J.R. Schraw W. Methods Enzymol. 1997; 288: 3-15Crossref PubMed Scopus (7) Google Scholar, 10Mueller S.G. Schraw W.P. Richmond A. J. Biol. Chem. 1995; 270: 10439-10448Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar). Interaction of chemokine receptors with their ligands activates Giproteins, induces the production of DAG, and releases Ca2+, followed by activation and translocation of PKC to the plasma membrane. This process is associated with desensitization of other GPCRs in the same cell by phosphorylation of their consensus sites (10Mueller S.G. Schraw W.P. Richmond A. J. Biol. Chem. 1995; 270: 10439-10448Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar, 13Mueller S.G. White J.R. Schraw W.P. Lam V. Richmond A. J. Biol. Chem. 1997; 272: 8207-8214Abstract Full Text Full Text PDF PubMed Scopus (101) Google Scholar). The family of PKC consists of more than 12 isozymes, and each of them exhibits a unique pattern of tissue distribution, subcellular translocation, and function (14Mochly-Rosen D. Science. 1995; 268: 247-251Crossref PubMed Scopus (835) Google Scholar). For instance, PKCζ is essential in mediating neutrophil chemotaxis and in regulating the polarity of astrocytes during wound healing process (15Laudanna C. Mochly-Rosen D. Liron T. Constantin G. Butcher E.C. J. Biol. Chem. 1998; 273: 30306-30315Abstract Full Text Full Text PDF PubMed Scopus (209) Google Scholar, 16Etienne-Manneville S. Hall A. Cell. 2001; 106: 489-498Abstract Full Text Full Text PDF PubMed Scopus (866) Google Scholar). PKCθ is predominantly expressed in lymphocytes and is recruited to the membrane during antigen presentation to T-cells (17Meller N. Elitzur Y. Isakov N. Cell. Immunol. 1999; 193: 185-193Crossref PubMed Scopus (57) Google Scholar). The 12 PKC isozymes be classical PKCs such as and γ, both Ca2+ and for novel PKCs such as δ, and but and such as and Ca2+ or PKC isozymes, δ, μ, and have been in human blood monocytes G. J. 1998; PubMed Google Scholar). However, their to heterologous desensitization of chemokine receptors has not been with or has been shown to MIP-1α-mediated chemotaxis of monocytes and M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google M.C. Ben-Baruch A. Taub D.D. Howard O.M. Wang J.M. Oppenheim J.J. N. Y. Acad. Sci. 1998; PubMed Scopus Google Scholar). inhibition be blocked by the opioid or the or and M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google Scholar). with opioids has been shown to phosphorylation of with of with other chemokines, opioids less of mediating heterologous desensitization. Heterologous desensitization of chemokine receptors to a receptors more potent in than Richardson R.M. J.R. L. Snyderman R. Ali H. J. Immunol. Google R.M. Haribabu B. Ali H. Snyderman R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The of a receptor to GPCRs has been to with to induce a (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar). We to the that the may be to the PKC isotypes. In study, we show in opioid-mediated heterologous desensitization not only chemotaxis but Ca2+ in a dose-dependent manner. inhibitory effects result from a decrease in chemokine receptor affinity and their coupling efficiency to G we chemokine receptors, opioid receptors to elicit a calcium flux and only novel and PKC, in suppression of chemokine receptor Our data suggest that the of G protein-coupled receptors in heterologous desensitization is on which of PKC is A heterologous desensitization both calcium-dependent and kinase C. Opioids unique and only a calcium-independent PKC to and heterologous receptors. and MIP-1α were from and were from Met-enkephalin from from calphostin C and were from chemotaxis and membrane were from and were from and were from of the other were and were from peripheral monocytes were from blood and from of by The monocytes were by staining or by monocytes were in and for on the same and cells were in with and and cells were in the same with were in vitro by monocytes in medium and in the of human factor in a for with the of human medium D. Y. Wang J.M. Oppenheim J.J. J. Immunol. 2001; PubMed Scopus Google Scholar). of were to with and with the by Western and a with of selected to receptor to The as a cells were in with to Ther. PubMed Scopus Google Scholar). of each the were for cells by using to the Ther. PubMed Scopus Google Scholar, J.J. H. Cell. Immunol. 1999; PubMed Scopus Google Scholar). The via of the protein and a the of the for of cells by the cells were selected with of for which the of were by cell with as in to and with of medium to cells to virus the same cell were by cells tissue and the with of the were with to in virus the cells were by and as as by the In the monocytes were with MCP-1, Met-enkephalin, or for The cells were with medium from and and the chemotaxis to concentrations were the The were and for The between the and The cells that through the were by The chemotaxis the of cell in a chemokine the cell in a medium For cells, the with of in medium 4 of cells The analysis of responses by Calcium flux as by J.J. Wang J.M. D. Oppenheim J.J. J. Immunol. 1995; Google Scholar). In the cells were for in The cells were with with and The cells were a and the of fluorescent by and by a For desensitization the cells were with Met-enkephalin or chemokines for The were as by M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google with The cells were with MCP-1, or Met-enkephalin for and in medium The were on using in the of concentration of The cells were 4 for and ligands were from cells by a The of in a analysis of data by a by the The as by Richardson R.M. Haribabu B. Ali H. Snyderman R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google with The cells were with MCP-1, Met-enkephalin, or medium for the cell were for of PKC translocation in monocytes were as by C. Mochly-Rosen D. Liron T. Constantin G. Butcher E.C. J. Biol. Chem. 1998; 273: 30306-30315Abstract Full Text Full Text PDF PubMed Scopus (209) Google with In monocytes were in for to decrease the PKC stimulation. of were The cells were by by and for The as the The were in one of with and for The were as the membrane The were on followed by Western blotting analysis of immunofluorescent staining of PKC as by S. Hall A. Cell. 2001; 106: 489-498Abstract Full Text Full Text PDF PubMed Scopus (866) Google Scholar). The cells were with or Met-enkephalin for and by antibody to PKC followed by The cells were using a fluorescent we the of chemotaxis of monocytes to by chemokines, MIP-1α and shown in MCP-1, by activating chemokine a chemotaxis which the endogenous for receptor and a potent of However, the response of Met-enkephalin on less with an from to a of chemotaxis not The activity of opioids may be to the receptor on cell or to coupling between opioid receptors and proteins. and MIP-1α the of with a concentration from to not opioid receptors to and induce we to their to elicit a Ca2+ shown in both and MIP-1α a potent Ca2+ flux in that the Ca2+ flux is Med. 1999; PubMed Scopus Google Scholar). However, Met-enkephalin, concentrations from to failed to a in monocytes and data not did not induce Ca2+ not The of is to production of by activated data further suggest that the receptors less potent in in monocytes than chemokine receptors. the of the inhibitory effects of Met-enkephalin on chemotaxis were with the effects of MIP-1α and on chemokine receptors. monocytes with MIP-1α a reduction of more than of the response to of desensitization This desensitization dose-dependent with for showed a decrease in their response to of heterologous desensitization of chemokine receptors and with of Met-enkephalin MIP-1α-mediated chemotaxis but to a Met-enkephalin dose-dependent heterologous desensitization effects with inhibitory activity of the of opioid mediated heterologous desensitization on Ca2+ flux, we the of the Ca2+ response of which were cells with of MCP-1, or and Ca2+ flux in monocytes in a dose-dependent and data not directly and heterologous the maximal of each Ca2+ flux to the response of the with MIP-1α for followed by failed to a response to and MIP-1α desensitization decreased the response to MIP-1α and the but the inhibitory effects decreased as the concentration of and of MIP-1α with Met-enkephalin in inhibition of Ca2+ flux with of the Ca2+ response to inhibitory effects were maximal chemokine concentration and decreased as the chemokine concentration chemotaxis and calcium flux data show that the heterologous desensitization of the MIP-1α response by Met-enkephalin but less potent than or heterologous desensitization of chemokine receptors by We further the on MIP-1α-mediated chemotaxis vitro shown in opioids did not induce calcium flux in activated macrophage, heterologous desensitization of chemokine receptors in activated of seven-transmembrane receptors may of receptors, decrease in or with R. J. Biol. Chem. 1998; 273: 18677-18680Abstract Full Text Full Text PDF PubMed Scopus (908) Google Scholar, Chem. 2001; PubMed Scopus Google Scholar, 13Mueller S.G. White J.R. Schraw W.P. Lam V. Richmond A. J. Biol. Chem. 1997; 272: 8207-8214Abstract Full Text Full Text PDF PubMed Scopus (101) Google M.J. D. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Biochem. J. 1989; PubMed Scopus Google Scholar, W. Wang D. Richmond A. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar, W. Schraw W.P. S.G. Richmond A. 1997; PubMed Scopus Google Scholar). to the of Met-enkephalin on the of sites and affinity on showed a decrease in MIP-1α affinity Met-enkephalin the of sites A and In preincubation with MIP-1α the of sites by of receptor during desensitization of receptors decreased the of MIP-1α receptors by more than In with our did not affinity M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google Scholar). Our were 4 to desensitization. chemokine receptors heterotrimeric G by the of to A GPCR a decrease in to induce the of to membrane G proteins. with Met-enkephalin for in a of on the an of the coupling efficiency between chemokine receptors and G protein In the of MIP-1α receptors to membrane inhibited to with or MIP-1α The decrease in both receptor affinity and coupling efficiency to G protein may directly contribute to the desensitization of MIP-1α-mediated calcium flux, and other The of opioid receptors on monocytes and is to that of chemokine receptors. that sites were not Thus, of a opioid-mediated Ca2+ response or opioid inhibition of chemokine receptor function may be to the of opioid receptors. we the receptors in both and analysis showed in both and cells, the of sites for and the cells expressed an of receptors in The of by chemotaxis Met-enkephalin concentration chemotaxis in both and cells not the of upon Met-enkephalin or Ca2+ flux in or cells and data not In MIP-1α and Ca2+ flux response in both and cells, the of is with that of the Thus, the in opioid calcium flux be on their activation of We the of receptors to induce heterologous desensitization in with previous data from opioids chemotaxis to and did not induce receptor and further that term activation of opioid receptors leads to a of down-regulation of chemokine receptor function through heterologous desensitization. protein kinase A and PKC, in heterologous desensitization of G protein-coupled receptors via (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 9Richmond A, M.S. White J.R. Schraw W. Methods Enzymol. 1997; 288: 3-15Crossref PubMed Scopus (7) Google Scholar, 11Lefkowitz R. J. Biol. Chem. 1998; 273: 18677-18680Abstract Full Text Full Text PDF PubMed Scopus (908) Google Scholar). Previous studies have shown upon chemokine receptors elicit a Ca2+ flux which in activates PKC, in heterologous desensitization of other of chemokine receptors. However, Met-enkephalin did not induce a Ca2+ We calphostin C, an inhibitor of and to PKCs in opioid monocytes were with calphostin C, the inhibition of MIP-1α chemotaxis by opioids largely the involvement of PKCs in heterologous desensitization heterologous desensitization blocked by calphostin C However, calphostin C did not with MIP-1α-mediated chemotaxis but only with heterologous desensitization. which of PKCs were we a inhibitor for but not This only the inhibition by and on the inhibition by opioids data suggest that only PKC in opioid-mediated heterologous consistent with a of Ca2+ flux upon opioid The translocation of PKCs from to different membrane is a of PKC activation (14Mochly-Rosen D. Science. 1995; 268: 247-251Crossref PubMed Scopus (835) Google Scholar). The activation of each be by to the membrane. the with PKC we investigated the translocation of different PKC isozymes in monocytes upon and Met-enkephalin stimulation. shown in Western blotting in PKCs in the with MCP-1, monocytes with a membrane of both and such as δ, and isozymes The translocation occurred in as as not activation were found in cells not However, only such as and were activated by We further the Western blotting data by immunofluorescent staining of PKC translocation in monocytes In the different PKC to different pattern in with Western blotting Met-enkephalin translocation of but not calcium-dependent PKC both and to the membrane upon stimulation. data that the activation of classical PKC isozymes is in the of Met-enkephalin, and only PKCs in heterologous desensitization. The of PKC and may for the of chemokine receptor and the of opioid-mediated heterologous desensitization. Opioids chemokine receptor function through calcium-independent studies have shown the essential of PKC in heterologous desensitization (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar, 9Richmond A, M.S. White J.R. Schraw W. Methods Enzymol. 1997; 288: 3-15Crossref PubMed Scopus (7) Google Scholar). However, is the of different PKC to indicate that 12 PKC not but each has unique activation process and function (14Mochly-Rosen D. Science. 1995; 268: 247-251Crossref PubMed Scopus (835) Google Scholar, C. Mochly-Rosen D. Liron T. Constantin G. Butcher E.C. J. Biol. Chem. 1998; 273: 30306-30315Abstract Full Text Full Text PDF PubMed Scopus (209) Google Scholar, 16Etienne-Manneville S. Hall A. Cell. 2001; 106: 489-498Abstract Full Text Full Text PDF PubMed Scopus (866) Google Scholar, N. Elitzur Y. Isakov N. Cell. Immunol. 1999; 193: 185-193Crossref PubMed Scopus (57) Google Scholar). comparing Met-enkephalin, MCP-1, and MIP-1α-mediated down-regulation of MIP-1α receptors, our data the the of PKC in heterologous desensitization. The fact that calphostin C blocked the inhibitory effects of both and Met-enkephalin that PKCs were in both and heterologous desensitization. However, the of Ca2+ the that were not in desensitization by The of to inhibition further for the of effects. these we directly activation of PKC by a translocation Western blotting analysis and immunofluorescent staining showed that only were activated by of PKCθ is in monocytes and to the not to be (17Meller N. Elitzur Y. Isakov N. Cell. Immunol. 1999; 193: 185-193Crossref PubMed Scopus (57) Google Scholar, G. J. 1998; PubMed Google C. G. G. G. J. Biol. Chem. 1995; 270: Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, we that only δ, μ, and may be in heterologous desensitization in chemokines calcium-dependent further the of PKC we that of PKCs may be to the isozymes (14Mochly-Rosen D. Science. 1995; 268: 247-251Crossref PubMed Scopus (835) Google Scholar). Heterologous desensitization of chemokine receptors to a receptors, such as the have a to other opioid receptors have a Richardson R.M. J.R. L. Snyderman R. Ali H. J. Immunol. Google Scholar, R.M. Haribabu B. Ali H. Snyderman R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The of a receptor to GPCRs to with to induce and calcium (8Ali H. Richardson R.M. Haribabu B. Snyderman R. J. Biol. Chem. 1999; 274: 6027-6030Abstract Full Text Full Text PDF PubMed Scopus (232) Google Scholar). Our data suggest that calcium-dependent PKCs for heterologous desensitization. a calcium which is for the of sites and a decrease in the coupling efficiency between receptors and G inhibitory effects could be blocked by the PKC inhibitor calphostin C. In Met-enkephalin failed to classic PKC and inhibitory effects and receptor Thus, we that the of heterologous desensitization on the of receptors to different of opioid receptors that to only heterologous desensitization. less from activated receptors than Ca2+ chemokines induce both chemotaxis and a Ca2+ flux response in a suggested that chemotaxis a Ca2+ Our data show that chemotaxis by opioids in the of our data suggest that chemotaxis is more to stimulation. We that Met-enkephalin receptors induce a of for but to elicit a Ca2+ other such as to elicit receptors may as a between immune and nervous by modulating PKC activity of In opioids elicit activation of G protein-coupled inwardly rectifying channels, inhibition of and adenylyl cyclase in Loh H.H. Pharmacol. PubMed Scopus Google Scholar). coupling to opioid receptors on that may with chemokine receptors M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google Scholar). have been to opioid-mediated activation of opioid receptors in the central nervous system may the of which in the immune system J.R. 1991; PubMed Scopus Google Scholar, J. Pharmacol. Exp. Ther. 270: Google Scholar). opioids may the sympathetic nervous system to the of or J. Pharmacol. PubMed Scopus Google Scholar, G. J. Pharmacol. PubMed Scopus Google Scholar). The discovery of opioid receptors in peripheral blood mononuclear cells a mechanism on data that these receptors directly modify the response of proinflammatory receptors (2Taub D.D., E.T. Geller E.B. Adler M.W. Rogers T.J. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 360-364Crossref PubMed Scopus (169) Google Scholar, 3Wang J Charboneau R. Balasubramanian S. Barke R.A. Loh H.H. Roy S. J. Leukocyte Biol. 2002; 71: 782-790PubMed Google Scholar, 4McCarthy L. Szabo I. Nitsche J.F. Pintar J.E. Rogers T.J. J. Neuroimmunol. 2001; 114: 173-180Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholar, 7Grimm M.C. Ben-Baruch A. Taub D.D. Howard O.M. Resau J.H. Wang J.M. Ali H. Richardson R. Snyderman R. Oppenheim J.J. J. Exp. Med. 1998; 188: 317-325Crossref PubMed Scopus (188) Google Scholar). Our data suggest that term usage of opioids directly with chemokine receptor function and a molecular mechanism for such heterologous desensitization. The of inhibition showed that Met-enkephalin inhibited chemotaxis concentrations as as with the blood of in patients or Chem. 2001; PubMed Scopus Google Scholar). In prolonged to has been shown to the of opioid receptors, which may to inhibitory effects. heterologous desensitization chemokine responses in the concentration of chemokine is in the nanomolar For instance, of Ca2+ showed that opioid inhibition the concentration of MIP-1α between to in This leads to suggest that such in may directly contribute to opioid-mediated immunosuppression (1Novick D.M.O.M. Ghali V. Croxson T.S. Mercer W.D. Chiorazzi N. Kreek M.J. J. Pharmacol. Exp. Ther. 1989; 250: 606-610PubMed Google Scholar, 2Taub D.D., E.T. Geller E.B. Adler M.W. Rogers T.J. Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 360-364Crossref PubMed Scopus (169) Google Scholar, 3Wang J Charboneau R. Balasubramanian S. Barke R.A. Loh H.H. Roy S. J. Leukocyte Biol. 2002; 71: 782-790PubMed Google Scholar). down-regulation of chemokine receptor function is not to monocytes in the The fact that Met-enkephalin the chemotaxis response of a inhibitory of opioids during the inhibitory effects of heterologous desensitization to be and only one of the effects of our studies have PKCs as in opioid desensitization of chemokine receptors and of the molecular mechanism of opioid-mediated This is a on the different of and in heterologous desensitization. on our for isozymes be to to immunosuppressive effects. that not have effects on endogenous heterologous desensitization of chemokine receptors. We and for We for for