The t-SNARE syntaxin 4 is regulated during macrophage activation to function in membrane traffic and cytokine secretion.
Activation of macrophages with lipopolysaccharide (LPS) induces the rapid synthesis and secretion of proinflammatory cytokines, such as tumor necrosis factor (TNFalpha), for priming the immune response. TNFalpha plays a key role in inflammatory disease; yet, little is known of the intracellular trafficking events leading to its secretion. In order to identify molecules involved in this secretory pathway, we asked whether any of the known trafficking proteins are regulated by LPS. We found that the levels of SNARE proteins were rapidly and significantly up- or downregulated during macrophage activation. A subset of t-SNAREs (Syntaxin 4/SNAP23/Munc18c) known to control regulated exocytosis in other cell types was substantially increased by LPS in a temporal pattern coinciding with peak TNFalpha secretion. Syntaxin 4 formed a complex with Munc18c at the cell surface of macrophages. Functional studies involving the introduction of Syntaxin 4 cDNA or peptides into macrophages implicate this t-SNARE in a rate-limiting step of TNFalpha secretion and in membrane ruffling during macrophage activation. We conclude that, in macrophages, SNAREs are regulated in order to accommodate the rapid onset of cytokine secretion and for membrane traffic associated with the phenotypic changes of immune activation. This represents a novel regulatory role for SNAREs in regulated secretion and in macrophage-mediated host defense.
Pagan
Julia K
JK
Institute for Molecular Bioscience and Special Research Centre for Functional and Applied Genomics, QLD 4072, Brisbane, Australia.
Wylie
Fiona G
FG
Joseph
Shannon
S
Widberg
Charlotte
C
Bryant
Nia J
NJ
James
David E
DE
Stow
Jennifer L
JL
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D016207:Cytokines / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D033921:Vesicular Transport Proteins
D016207:Cytokines; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050600:SNARE Proteins; D014409:Tumor Necrosis Factor-alpha; D033921:Vesicular Transport Proteins