Role of human CD36 in bacterial recognition, phagocytosis, and pathogen-induced JNK-mediated signaling.
Scavenger receptor CD36 mediates Staphylococcus aureus phagocytosis and initiates TLR2/6 signaling. We analyzed the role of CD36 in the uptake and TLR-independent signaling of various bacterium, including Escherichia coli, Klebsiella pneumoniae, Salmonella typhimurium, S. aureus, and Enterococcus faecalis. Expression of human CD36 in HeLa cells increased the uptake of both gram-positive and gram-negative bacteria compared with the control mock-transfected cells. Bacterial adhesion was associated with pathogen phagocytosis. Upon CD36 transfection, HEK293 cells, which demonstrate no TLR2/4 expression, acquired LPS responsiveness as assessed by IL-8 production. The cells demonstrated a marked 5- to 15-fold increase in cytokine release upon exposure to gram-negative bacteria, while the increase was much smaller (1.5- to 3-fold) with gram-positive bacteria and lipoteichoic acid. CD36 down-regulation utilizing CD36 small interfering RNA reduced cytokine release by 40-50% in human fibroblasts induced by both gram-negative and gram-positive bacteria as well as LPS. Of all MAPK signaling cascade inhibitors tested, only the inhibitor of JNK, a stress-activated protein kinase, potently blocked E. coli/LPS-stimulated cytokine production. NF-kappaB inhibitors were ineffective, indicating direct TLR-independent signaling. JNK activation was confirmed by Western blot analyses of phosphorylated JKN1/2 products. Synthetic amphipathic peptides with an alpha-helical motif were shown to be efficient inhibitors of E. coli- and LPS-induced IL-8 secretion as well as JNK1/2 activation/phosphorylation in CD36-overexpressing cells. These results indicate that CD36 functions as a phagocytic receptor for a variety of bacteria and mediates signaling induced by gram-negative bacteria and LPS via a JNK-mediated signaling pathway in a TLR2/4-independent manner.
Baranova
Irina N
IN
Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
Kurlander
Roger
R
Bocharov
Alexander V
AV
Vishnyakova
Tatyana G
TG
Chen
Zhigang
Z
Remaley
Alan T
AT
Csako
Gyorgy
G
Patterson
Amy P
AP
Eggerman
Thomas L
TL
D000818:Animals; D001424:Bacterial Infections / Q000276:immunology* / Q000378:metabolism; D015153:Blotting, Western; D018955:CD36 Antigens / Q000276:immunology* / Q000378:metabolism; D002460:Cell Line; D016207:Cytokines / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D005455:Fluorescent Antibody Technique; D006801:Humans; D008070:Lipopolysaccharides / Q000276:immunology; D048670:MAP Kinase Kinase 4 / Q000276:immunology* / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D018613:Microscopy, Confocal; D010587:Phagocytosis / Q000187:drug effects / Q000276:immunology*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D014162:Transfection
D018955:CD36 Antigens; D016207:Cytokines; D004791:Enzyme Inhibitors; D008070:Lipopolysaccharides; D048670:MAP Kinase Kinase 4