Secretion of the human Toll-like receptor 3 ectodomain is affected by single nucleotide polymorphisms and regulated by Unc93b1.
The innate immune receptor Toll-like receptor 3 (TLR3) can be present on the surface of the plasma membranes of cells and in endolysosomes. The Unc93b1 protein has been reported to facilitate localization of TLR7 and 9 and is required for TLR3, -7, and -9 signaling. We demonstrate that siRNA knockdown of Unc93b1 reduced the abundance of TLR3 on the cell surface without altering total TLR3 accumulation. In addition, siRNA to Unc93b1 reduced the secretion of the TLR3 ectodomain (T3ECD) into the cell medium. Furthermore, two human single nucleotide polymorphisms that affected herpesvirus and influenza virus encephalopathy as well as a natural isoform generated by alternative splicing were found to be impaired for T3ECD secretion and decreased the abundance of TLR3 on the cell surface. The locations of the SNP P554S and the deletion in the isoform led to the identification of a loop in the TLR3 ectodomain that is required for secretion and a second whose presence decreased secretion. Finally, a truncated protein containing the N-terminal 10 leucine-rich repeats of T3ECD was sufficient for secretion in an Unc93b1-dependent manner.
Qi
Rongsu
R
Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana 47401-3700, USA.
Hoose
Scott
S
Schreiter
Jessica
J
Sawant
Kirti V
KV
Lamb
Roberta
R
Ranjith-Kumar
C T
CT
Mills
Juliane
J
San Mateo
Lani
L
Jordan
Jarrat L
JL
Kao
C Cheng
CC
D000595:Amino Acid Sequence; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D006031:Glycosylation; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051196:Toll-Like Receptor 3 / Q000235:genetics* / Q000378:metabolism*
D026901:Membrane Transport Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C495344:TLR3 protein, human; D051196:Toll-Like Receptor 3; C454130:UNC93B1 protein, human; D008156:Luciferases