title: Recognition by TNF-alpha of the GPI-anchor glycan induces apoptosis of U937 cells.
abstract: Tumor necrosis factor-alpha (TNF-alpha) binds to TNF-alpha receptors (TNFR) to produce a hexameric (TNF-alpha)(3)-(TNFR)(3) structure that stimulates apoptosis. We found by using ELISA that TNF-alpha binds to the glycosylphosphatidylinositol (GPI) anchor glycans of carcinoembryonic antigen, human placental alkaline phosphatase (hAP), and Tamm-Horsfall glycoprotein. These binding abilities were inhibited by 10(-6)M mannose-6-phosphate. Treatment of hAP with mild acid and phosphatase, which releases the N-acetylglucosamine (GlcNAc) beta1 -->phosphate-->6 residue from the GPI-anchor glycan of hAP, abrogated the binding of TNF-alpha to hAP. Thus, TNF-alpha binds to the GlcNAcbeta1-->phosphate-->6Man residue in GPI-anchor glycans. To investigate whether the carbohydrate-binding ability of TNF-alpha is related to its physiological functions, human lymphoma U937 cells were used. TNF-alpha stimulates U937 cell apoptosis in a dose-dependent manner and the presence of mannose-6-phosphate inhibited this. TNF-alpha-dependent tyrosine phosphorylation of several proteins in U937 cells was also diminished by mannose-6-phosphate. Phosphatidylinositol-specific phospholipase C-pretreatment also inhibited this tyrosine phosphorylation. These data suggest that TNF-alpha stimulates U937 cell apoptosis by forming a high-affinity nanomeric (TNF-alpha)(3)-(TNFR)(3)-(GPI-anchored glycan)(3) complex. The GPI-anchored glycoprotein involved remains to be identified.
authors.affiliation: Department of Biochemistry, Sasaki Institute, 2-2 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Fukushima
authors.forename: Chikako
authors.initials: C
authors.lastname: Ishiyama
authors.forename: Katsuko
authors.initials: K
authors.lastname: Yamashita
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D058851:GPI-Linked Proteins; D006801:Humans; D008360:Mannosephosphates / Q000378:metabolism* / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D011485:Protein Binding; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D020298:U937 Cells
chemical_list: D018797:Cell Cycle Proteins; C102519:GML protein, human; D058851:GPI-Linked Proteins; D008360:Mannosephosphates; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D014409:Tumor Necrosis Factor-alpha; C027693:mannose-6-phosphate