Direct binding of Toll-like receptor 2 to zymosan, and zymosan-induced NF-kappa B activation and TNF-alpha secretion are down-regulated by lung collectin surfactant protein A.
The lung collectin surfactant protein A (SP-A) has been implicated in the regulation of pulmonary host defense and inflammation. Zymosan induces proinflammatory cytokines in immune cells. Toll-like receptor (TLR)2 has been shown to be involved in zymosan-induced signaling. We first investigated the interaction of TLR2 with zymosan. Zymosan cosedimented the soluble form of rTLR2 possessing the putative extracellular domain (sTLR2). sTLR2 directly bound to zymosan with an apparent binding constant of 48 nM. We next examined whether SP-A modulated zymosan-induced cellular responses. SP-A significantly attenuated zymosan-induced TNF-alpha secretion in RAW264.7 cells and alveolar macrophages in a concentration-dependent manner. Although zymosan failed to cosediment SP-A, SP-A significantly reduced zymosan-elicited NF-kappaB activation in TLR2-transfected human embryonic kidney 293 cells. Because we have shown that SP-A binds to sTLR2, we also examined whether SP-A affected the binding of sTLR2 to zymosan. SP-A significantly attenuated the direct binding of sTLR2 to zymosan in a concentration-dependent fashion. From these results, we conclude that 1) TLR2 directly binds zymosan, 2) SP-A can alter zymosan-TLR2 interaction, and 3) SP-A down-regulates TLR2-mediated signaling and TNF-alpha secretion stimulated by zymosan. This study supports an important role of SP-A in controlling pulmonary inflammation caused by microbial pathogens.
Sato
Morihito
M
Department of Biochemistry, Sapporo Medical University School of Medicine, Sapporo, Japan.
Sano
Hitomi
H
Iwaki
Daisuke
D
Kudo
Kazumi
K
Konishi
Masanori
M
Takahashi
Hiroki
H
Takahashi
Toru
T
Imaizumi
Hitoshi
H
Asai
Yasufumi
Y
Kuroki
Yoshio
Y
D000818:Animals; D002460:Cell Line; D015536:Down-Regulation / Q000502:physiology*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary; D037662:Pulmonary Surfactant-Associated Protein A / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015054:Zymosan / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology*
D008562:Membrane Glycoproteins; D016328:NF-kappa B; D037662:Pulmonary Surfactant-Associated Protein A; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495343:Tlr2 protein, rat; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D015054:Zymosan