Soluble G protein of respiratory syncytial virus inhibits Toll-like receptor 3/4-mediated IFN-beta induction.
Monocyte-derived dendritic cells (mDCs) recognize viral RNA extrinsically by Toll-like receptor (TLR) 3 on the membrane and intrinsically retinoic acid-inducible gene I (RIG-I)/melanoma differentiation-associated gene 5 (MDA5) in the cytoplasm to induce type I IFNs and mDC maturation. When mDCs were treated with live or UV-irradiated respiratory syncytial virus (RSV), early ( approximately 4 h) induction of IFN-beta usually occurs in other virus infections was barely observed. Live RSV subsequently replicated to activate the cytoplasmic IFN-inducing pathway leading to robust type I IFN induction. We found that RSV initial attachment to cells blocked polyI:C-mediated IFN-beta induction, and this early IFN-beta-modulating event was abrogated by antibodies against envelope proteins of RSV, demonstrating the presence of a IFN-regulatory mode by early RSV attachment to host cells. By IFN-stimulated response element (ISRE) reporter analysis in HEK293 cells, polyI:C- or LPS-mediated ISRE activation was dose dependently inhibited by live and inactive RSV to a similar extent. Of the RSV envelope proteins, simultaneously expressed or exogenously added RSV G or soluble G (sG) proteins inhibited TLR3/4-mediated ISRE activation in HEK293 cells. sG proteins expressed in cells did not affect the RIG-I/MDA5 pathway but inhibited the TLR adaptor TRIF/TICAM-1 pathway for ISRE activation. Finally, extrinsically added sG protein suppressed the production of IFN-beta in mDCs. Although the molecular mechanism of this extrinsic functional mode of the RSV G glycoprotein (G protein) remains undetermined, G proteins may neutralize the fusion glycoprotein function that promotes IFN-mediated mDC modulation via TLR4 and may cause insufficient raising cell-mediated immunity against RSV.
Shingai
Masashi
M
Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita-ku, Sapporo 060-8638, Japan.
Azuma
Masahiro
M
Ebihara
Takashi
T
Sasai
Miwa
M
Funami
Kenji
K
Ayata
Minoru
M
Ogura
Hisashi
H
Tsutsumi
Hiroyuki
H
Matsumoto
Misako
M
Seya
Tsukasa
T
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D003713:Dendritic Cells / Q000276:immunology; D005786:Gene Expression Regulation; D006801:Humans; D016899:Interferon-beta / Q000235:genetics / Q000378:metabolism*; D018113:Respiratory Syncytial Virus, Human / Q000378:metabolism / Q000472:pathogenicity*; D051196:Toll-Like Receptor 3 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014759:Viral Envelope Proteins / Q000276:immunology / Q000378:metabolism*
C495344:TLR3 protein, human; C495345:TLR4 protein, human; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D014759:Viral Envelope Proteins; C116204:attachment protein G; D016899:Interferon-beta