The extra domain A of fibronectin activates Toll-like receptor 4.
Cellular fibronectin, which contains an alternatively spliced exon encoding type III repeat extra domain A (EDA), is produced in response to tissue injury. Fragments of fibronectin have been implicated in physiological and pathological processes, especially tissue remodeling associated with inflammation. Because EDA-containing fibronectin fragments produce cellular responses similar to those provoked by bacterial lipopolysaccharide (LPS), we examined the ability of recombinant EDA to activate Toll-like receptor 4 (TLR4), the signaling receptor stimulated by LPS. We found that recombinant EDA, but not other recombinant fibronectin domains, activates human TLR4 expressed in a cell type (HEK 293 cells) that normally lacks this Toll-like receptor. EDA stimulation of TLR4 was dependent upon co-expression of MD-2, a TLR4 accessory protein. Unlike LPS, the activity of EDA was heat-sensitive and persisted in the presence of the LPS-binding antibiotic polymyxin B and a potent LPS antagonist, E5564, which completely suppressed LPS activation of TLR4. These observations provided a mechanism by which EDA-containing fibronectin fragments promote expression of genes involved in the inflammatory response.
Okamura
Y
Y
Center for Research on Reproduction and Women's Health, University of Pennsylvania Medical Center, Philadelphia 19104, USA.
Watari
M
M
Jerud
E S
ES
Young
D W
DW
Ishizaka
S T
ST
Rose
J
J
Chow
J C
JC
Strauss
J F
JF
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000954:Antigens, Surface / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D029721:Drosophila Proteins; D004789:Enzyme Activation; D005091:Exons; D005353:Fibronectins / Q000737:chemistry* / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D007249:Inflammation; D016753:Interleukin-10 / Q000096:biosynthesis; D008050:Lipid A / Q000031:analogs & derivatives* / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051218:Lymphocyte Antigen 96; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D010957:Plasmids / Q000378:metabolism; D011112:Polymyxin B / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology; D013997:Time Factors; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014162:Transfection
D000900:Anti-Bacterial Agents; D000954:Antigens, Surface; D029721:Drosophila Proteins; C404742:E5564; D005353:Fibronectins; C495377:LY96 protein, human; D008050:Lipid A; D008070:Lipopolysaccharides; D051218:Lymphocyte Antigen 96; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D016753:Interleukin-10; D020780:Matrix Metalloproteinase 9; D011112:Polymyxin B