Deviation from major codons in the Toll-like receptor genes is associated with low Toll-like receptor expression.
Microbial structures activate Toll-like receptors (TLRs) and TLR-mediated cell signalling elicits and regulates host immunity. Most TLRs are poorly expressed but the underlying expression mechanism is not clear. Examination TLR sequences revealed that most human TLR genes deviated from using major human codons. CD14 resembles TLRs in sequence but its gene preferentially uses major codons. Indeed, CD14 expression on monocytes was higher than expression of TLR1 and TLR2. The TLR9 gene is abundant in major codons and it also showed higher expression than TLR1, TLR2 and TLR7 in transfected 293T cells. Change of the 5'-end 302 base pairs of the TLR2 sequence into major human codons markedly increased TLR2 expression, which led to increased TLR2-mediated constitutive nuclear factor-kappaB activation. Change of the 5'-end 381 base pairs of the CD14 sequence into prevalent TLR codons markedly reduced CD14 expression. These results collectively show that the deviation of TLR sequences from using major codons dictates the low TLR expression and this may protect the host against excessive inflammation and tissue damages.
Zhong
Fei
F
Department of Microbiology, Faculty of Medicine, National University of Singapore, Singapore 117597.
Cao
Weiping
W
Chan
Edmund
E
Tay
Puei Nam
PN
Cahya
Florence Feby
FF
Zhang
Haifeng
H
Lu
Jinhua
J
D001483:Base Sequence; D002478:Cells, Cultured; D003062:Codon; D006801:Humans; D018950:Lipopolysaccharide Receptors / Q000097:blood / Q000235:genetics; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009000:Monocytes / Q000276:immunology; D016328:NF-kappa B / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051199:Toll-Like Receptor 7; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D014162:Transfection
D003062:Codon; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495348:TLR7 protein, human; C495371:TLR9 protein, human; D051194:Toll-Like Receptor 1; D051195:Toll-Like Receptor 2; D051199:Toll-Like Receptor 7; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors