Leukocyte Ig-like receptor B4 (LILRB4) is a potent inhibitor of FcgammaRI-mediated monocyte activation via dephosphorylation of multiple kinases.
The leukocyte immunoglobulin-like receptor (LILR) B4 belongs to a family of cell surface receptors that possesses cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). LILRB4 is believed to down-regulate activation signals mediated by non-receptor tyrosine kinase cascades through the recruitment of SHP-1. However, the exact mechanisms of LILRB4-mediated inhibition are not fully elucidated. In this study, we demonstrate high level surface expression of LILRB4 on THP-1 cells and primary peripheral blood monocytes, which profoundly inhibited production of a key pro-inflammatory cytokine (TNFalpha) induced by FcgammaRI (CD64). We also report that LILRB4 aggregated to sites of activation upon co-ligation with CD64 and that this may enhance its inhibitory effects. Cross-linking of CD64 on THP-1 cells markedly increased phosphorylation of multiple proteins including tyrosine kinases and signaling molecules (Lck, Syk, LAT, and Erk), an adaptor protein that targets protein-tyrosine kinases for degradation (c-Cbl) and a protein involved in the formation of actin cytoskeletal rearrangement (alpha-actinin-4). Co-ligation of LILRB4 considerably reduced CD64-mediated phosphorylation of Lck, Syk, LAT, Erk, and c-Cbl but not alpha-actinin-4, suggesting selective inhibition of signaling molecules. Treatment of cells with a broad-spectrum phosphatase inhibitor, sodium pervanadate (SP), significantly reversed LILRB4-mediated inhibition of TNFalpha production and protein tyrosine phosphorylation. In comparison, treatment with an SHP-1 specific inhibitor, sodium stibogluconate (SS) has no effects indicating involvement of phosphatase(s) other than SHP-1 in LILRB4 signaling. Collectively, our data show LILRB4 is a potent inhibitor of monocytes activation. This may provide a new potential therapeutic strategy for inflammatory conditions characterized by excessive TNFalpha production.
Lu
Hao Kim
HK
Centre for Infection and Inflammation Research, University of New South Wales, Sydney, New South Wales 2052, Australia.
Rentero
Carles
C
Raftery
Mark J
MJ
Borges
Luis
L
Bryant
Katherine
K
Tedla
Nicodemus
N
D000185:Actinin / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D018189:Immunomagnetic Separation; D008562:Membrane Glycoproteins; D051379:Mice; D009000:Monocytes / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D017452:Receptors, IgG / Q000235:genetics / Q000378:metabolism*; D011971:Receptors, Immunologic; D015398:Signal Transduction / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
C111453:ACTN4 protein, human; D004791:Enzyme Inhibitors; C489017:FCGR1A protein, human; C107907:LILRB4 protein, human; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D017452:Receptors, IgG; D011971:Receptors, Immunologic; D014409:Tumor Necrosis Factor-alpha; D000185:Actinin; D011494:Protein Kinases