The context of HLA-DR/CD18 complex in the plasma membrane governs HLA-DR-derived signals in activated monocytes.
HLA-DR-derived signals in activated monocytes mediate both pro-inflammatory cytokine production and caspase-independent death, and have been postulated to play a role in inflammation and in its resolution, respectively. Herein, using the monocytic/macrophagic human cell line THP-1 primed with IFNgamma (IFNgamma-primed THP-1), we investigated how HLA-DR may integrate both signals. Our inhibition studies demonstrated that if cell death is dependent on PKCbeta activation, the induction of TNFalpha gene expression relies on PTK activation, in particular the Src family of kinases, but both cell responses implicate the beta2-integrin CD18. Accordingly, sequential immunoprecipitation experiments demonstrated that following engagement of HLA-DR on IFNgamma-primed THP-1 cells, the HLA-DR/CD18 complex physically associates with PKCbeta and with PTK. Pharmacological disruption of lipid rafts microdomains abolished the assembly of HLA-DR/CD18/PTK signaling complex, HLA-DR-mediated tyrosine activation, and the PTK-dependent TNFalpha expression in IFNgamma-primed THP-1 cells. In contrast, HLA-DR/CD18/PKCbeta complex was still formed and able to mediate cell death after cholesterol depletion of these cells. These results indicate that while the integrity of lipid rafts is necessary for the transduction of cytokine gene expression through the HLA-DR/CD18 complex, it is not necessary for the induction of the HLA-DR/CD18-dependent cell death. Thus, our study provides experimental evidence indicating the compartmentalization of HLA-DR/CD18 complex within or outside lipid rafts as a mechanism through which HLA-DR can integrate both PTK and PKCbeta signals leading to activation and death, respectively, of activated monocytes. This might provide new insights into how MHC class II signaling may regulate inflammatory response.
Doisne
Jean-Marc
JM
INSERM U662, Réponses Immunes: Régulation et Développement, Institut Universitaire d'Hématologie, Université Paris 7, Hôpital St. Louis, 1 Av Claude Vellefaux, 75010 Paris, France.
Castaigne
Jean-Gabriel
JG
Deruyffelaere
Carine
C
Dieu-Nosjean
Marie-Caroline
MC
Chamot
Christophe
C
Alcaide-Loridan
Catherine
C
Charron
Dominique
D
Al-Daccak
Reem
R
D018821:CD18 Antigens / Q000276:immunology*; D016923:Cell Death / Q000187:drug effects / Q000276:immunology; D002460:Cell Line; D002784:Cholesterol / Q000276:immunology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D006684:HLA-DR Antigens / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology; D006801:Humans; D007249:Inflammation / Q000276:immunology; D007371:Interferon-gamma / Q000276:immunology / Q000494:pharmacology; D020930:MAP Kinase Kinase Kinases / Q000276:immunology; D021962:Membrane Microdomains / Q000276:immunology*; D009000:Monocytes / Q000276:immunology*; D046912:Multiprotein Complexes / Q000276:immunology*; D011493:Protein Kinase C / Q000276:immunology; D064546:Protein Kinase C beta; D015398:Signal Transduction / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology
D018821:CD18 Antigens; D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; D046912:Multiprotein Complexes; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D002784:Cholesterol; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D020930:MAP Kinase Kinase Kinases