Membrane-anchored CD14 is required for LPS-induced TLR4 endocytosis in TLR4/MD-2/CD14 overexpressing CHO cells.
Lipopolysaccharide (LPS) induces inflammatory activation through TLR4 (toll-like receptor-4)/MD-2 (myeloid differentiation-2)/CD14 (cluster of differentiation-14) complex. Although optimal LPS signaling is required to activate our innate immune systems against gram-negative bacterium, excessive amount of LPS signaling develops a detrimental inflammatory response in gram-negative bacterial infections. Downregulation of surface TLR4 expression is one of the critical mechanisms that can restrict LPS signaling. Here, we found that membrane-anchored CD14 is required for LPS-induced downregulation of TLR4 and MD-2 in CHO cells. Moreover, pretreatment of the cells with sterol-binding agent filipin reduced LPS-induced TLR4 downregulation, suggesting the involvement of caveolae-mediated endocytosis pathway. Involvement of caveolae in LPS-induced TLR4 endocytosis was further confirmed by immunoprecipitation. Thus, our data indicate that caveolae-dependent endocytosis pathway is involved in LPS-induced TLR4 downregulation and that this is dependent on membrane-anchored CD14 expression.
Shuto
Tsuyoshi
T
Department of Molecular Medicine, Kumamoto University, Kumamoto 862-0973, Japan.
Kato
Kosuke
K
Mori
Yoko
Y
Viriyakosol
Suganya
S
Oba
Mariko
M
Furuta
Takashi
T
Okiyoneda
Tsukasa
T
Arima
Hidetoshi
H
Suico
Mary Ann
MA
Kai
Hirofumi
H
D000818:Animals; D016466:CHO Cells; D022461:Caveolins / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D015536:Down-Regulation / Q000187:drug effects; D004705:Endocytosis / Q000187:drug effects*; D005786:Gene Expression Regulation; D018950:Lipopolysaccharide Receptors / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D051218:Lymphocyte Antigen 96 / Q000235:genetics / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
D022461:Caveolins; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D051197:Toll-Like Receptor 4