Neu1 desialylation of sialyl alpha-2,3-linked beta-galactosyl residues of TOLL-like receptor 4 is essential for receptor activation and cellular signaling.
The ectodomain of TOLL-like receptors (TLR) is highly glycosylated with several N-linked gylcosylation sites located in the inner concave surface. The precise role of these sugar N-glycans in TLR receptor activation is unknown. Recently, we have shown that Neu1 sialidase and not Neu2, -3 and -4 forms a complex with TLR-2, -3 and -4 receptors on the cell-surface membrane of naïve and activated macrophage cells (Glycoconj J DOI 10.1007/s10719-009-9239-8). Activation of Neu1 is induced by TLR ligands binding to their respective receptors. Here, we show that endotoxin lipopolysaccharide (LPS)-induced MyD88/TLR4 complex formation and subsequent NFkappaB activation is dependent on the removal of alpha-2,3-sialyl residue linked to beta-galactoside of TLR4 by the Neu1 activity associated with LPS-stimulated live primary macrophage cells, macrophage and dendritic cell lines but not with primary Neu1-deficient macrophage cells. Exogenous alpha-2,3 sialyl specific neuraminidase (Streptoccocus pneumoniae) and wild-type T. cruzi trans-sialidase (TS) but not the catalytically inactive mutant TSAsp98-Glu mediate TLR4 dimerization to facilitate MyD88/TLR4 complex formation and NFkappaB activation similar to those responses seen with LPS. These same TLR ligand-induced NFkappaB responses are not observed in TLR deficient HEK293 cells, but are re-established in HEK293 cells stably transfected with TLR4/MD2, and are significantly inhibited by alpha-2,3-sialyl specific Maackia amurensis (MAL-2) lectin, alpha-2,3-sialyl specific galectin-1 and neuraminidase inhibitor Tamiflu but not by alpha-2,6-sialyl specific Sambucus nigra lectin (SNA). Taken together, the findings suggest that Neu1 desialylation of alpha-2,3-sialyl residues of TLR receptors enables in removing a steric hinderance to receptor association for TLR activation and cellular signaling.
Amith
Schammim Ray
SR
Department of Microbiology & Immunology, Queen's University, Kingston, Ontario, Canada. ray.amith@gmail.com
Jayanth
Preethi
P
Franchuk
Susan
S
Finlay
Trisha
T
Seyrantepe
Volkan
V
Beyaert
Rudi
R
Pshezhetsky
Alexey V
AV
Szewczuk
Myron R
MR
D000818:Animals; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006023:Glycoproteins / Q000494:pharmacology; D006031:Glycosylation; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D009439:Neuraminidase / Q000378:metabolism* / Q000494:pharmacology; D053139:Oseltamivir / Q000494:pharmacology; D010766:Phosphorylation; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000737:chemistry / Q000378:metabolism*
D004791:Enzyme Inhibitors; D006023:Glycoproteins; D008070:Lipopolysaccharides; D016328:NF-kappa B; D051197:Toll-Like Receptor 4; D053139:Oseltamivir; C069715:trans-sialidase; D009439:Neuraminidase