title: Dual regulation of soluble tumor necrosis factor-alpha induced activation of human monocytic cells via modulating transmembrane TNF-alpha-mediated 'reverse signaling'.
abstract: Transmembrane tumor necrosis factor-alpha (mTNF-alpha) is known to be the precursor of soluble TNF-alpha (sTNF-alpha). mTNF-alpha can act as a ligand on the TNF receptor- (TNFR)- bearing cell through 'forward signaling' or as a receptor on the TNF producing cell through 'reverse signaling'. In the current study, we investigated the role of mTNF-alpha-mediated reverse signaling in regulating sTNF-alpha-induced activation of human monocytic U937 cells. We demonstrated that pretreatment with sTNFRI, for inducing reverse signaling through mTNF-alpha, sensitized U937 cells to sTNF-alpha stimulation, as evidenced by an increase in reactive oxygen production and mRNA levels of proinflammatory cytokines (TNF-alpha, IL-1beta, and IL-8) in these cells. Further experiments revealed that IkappaB-alpha degradation was increased in the monocytic cells primed with sTNFRI, implying that reverse signaling of mTNF-alpha sensitizes U937 cells via an NF-kappaB-dependent mechanism. On the other hand, binding of sTNFRI to mTNF-alpha after sTNF-alpha-induced activation of U937 cells reduced mRNA stability (half-life) of IL-1beta and IL-8. The involvement of reverse signaling in the process was verified by using a mutated form of mTNF-alpha lacking the majority of the cytoplasmic domain. Our results clearly showed that enhanced mRNA degradation of the cytokines occurred only in U937 cells transfected with a wild-type mTNF-alpha, but not in those cells transfected with the mutant mTNF-alpha. Taken together, these data suggest that reverse signaling through mTNF-alpha may exert a double role in modulating sTNF-alpha bioactivity. It is positive when reverse signaling occurs prior to sTNF-alpha stimulation, while it is negative when reverse signaling occurs after the sTNF-alpha signal. Thus, our findings strengthen a role of mTNF-alpha-mediated reverse signaling in the regulation of immune-inflammatory response and control of inflammatory reaction.
authors.affiliation: Department of Immunology, Tongji Medical College, Central China University of Science and Technology, Wuhan 430030, PR China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Xin
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Hailong
authors.initials: H
authors.lastname: Zhang
authors.forename: Wenfang
authors.initials: W
authors.lastname: Shi
authors.forename: Mingxia
authors.initials: M
authors.lastname: Yu
authors.forename: Qingfen
authors.initials: Q
authors.lastname: Li
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Jiang
authors.forename: Feili
authors.initials: F
authors.lastname: Gong
authors.forename: Kevin
authors.initials: K
authors.lastname: Gardner
authors.forename: Qingdi Q
authors.initials: QQ
authors.lastname: Li
authors.forename: Zhuoya
authors.initials: Z
authors.lastname: Li
mesh_terms: D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism; D008262:Macrophage Activation; D009000:Monocytes / Q000187:drug effects / Q000276:immunology*; D000072000:NF-KappaB Inhibitor alpha; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D020298:U937 Cells
chemical_list: D020672:I-kappa B Proteins; D007375:Interleukin-1; D016209:Interleukin-8; C000606204:NFKBIA protein, human; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha