title: Autocrine tumor necrosis factor (TNF) and lymphotoxin (LT) alpha differentially modulate cellular sensitivity to TNF/LT-alpha cytotoxicity in L929 cells.
abstract: Tumor necrosis factor (TNF) and lymphotoxin (LT) alpha are structurally and functionally related cytokines. We expressed the TNF and LT-alpha genes in murine fibrosarcoma L929r2 cells, which can be sensitized to TNF/LT-alpha-dependent necrosis by inhibitors of transcription or translation. Autocrine production of murine TNF in L929r2 cells completely downmodulated the expression of the 55- and 75-kD TNF receptors, resulting in resistance to TNF/LT-alpha cytotoxicity. Partial downmodulation of the 55-kD receptor was observed in human TNF-producing L929r2 cells. In contrast, an unaltered TNF receptor expression was found on LT-alpha L929r2 transfectants. Hence, although similar cytotoxic effects are induced by extracellularly administered TNF and LT-alpha, endogenous expression of these cytokines fundamentally differs in the way they modulate TNF receptor expression. Unlike LT-alpha, secreted by the classical pathway, TNF is first formed as a membrane-bound protein, which is responsible for receptor downmodulation. To explore whether the different pathways for secretion of TNF and LT-alpha explain this difference, we examined the effect of membrane-bound LT-alpha expression. This was obtained by exchange of the classical signal sequence of LT-alpha for the membrane anchor of chicken hepatic lectin. Membrane retention of LT-alpha resulted indeed in receptor downmodulation and TNF/LT-alpha resistance. We conclude that membrane retention of newly synthesized TNF or LT-alpha is absolutely required for receptor downmodulation and TNF/LT-alpha resistance.
authors.affiliation: Department of Molecular Biology, Flanders Interuniversity Institute for Biotechnology and University of Ghent, B-9000 Ghent, Belgium.
authors.forename: E
authors.initials: E
authors.lastname: Decoster
authors.forename: S
authors.initials: S
authors.lastname: Cornelis
authors.forename: B
authors.initials: B
authors.lastname: Vanhaesebroeck
authors.forename: W
authors.initials: W
authors.lastname: Fiers
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D003602:Cytotoxicity, Immunologic; D015536:Down-Regulation / Q000187:drug effects; D004351:Drug Resistance; D005354:Fibrosarcoma / Q000473:pathology; D005786:Gene Expression Regulation / Q000187:drug effects; D008233:Lymphotoxin-alpha / Q000378:metabolism / Q000502:physiology* / Q000633:toxicity; D051379:Mice; D010641:Phenotype; D021382:Protein Sorting Signals / Q000502:physiology; D018124:Receptors, Tumor Necrosis Factor / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D011993:Recombinant Fusion Proteins / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism / Q000502:physiology* / Q000633:toxicity
chemical_list: D015703:Antigens, CD; D008233:Lymphotoxin-alpha; D021382:Protein Sorting Signals; D018124:Receptors, Tumor Necrosis Factor; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; D011993:Recombinant Fusion Proteins; D014409:Tumor Necrosis Factor-alpha