Role of human CD36 in bacterial recognition, phagocytosis, and pathogen-induced JNK-mediated signaling

IN Baranova, R Kurlander, AV Bocharov… - The Journal of …, 2008 - journals.aai.org
IN Baranova, R Kurlander, AV Bocharov, TG Vishnyakova, Z Chen, AT Remaley, G Csako…
The Journal of Immunology, 2008journals.aai.org
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 …
Abstract
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-κB 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 α-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.
journals.aai.org