Low Temperatures and Hypertonicity Do Not Block Cytokine-induced Stimulation of the Sphingomyelin Pathway but Inhibit Nuclear
Factor-
B Activation (*)
- From the (1)Laboratoire de Biochimie, “Maladies Métaboliques,” CJF INSERM 9206, Institut Louis Bugnard, C.H.U. Rangueil, Toulouse, France and
- (2) CNRS, Centre Claudius Régaud, Toulouse, France
- § To whom correspondence should be addressed: CJF INSERM 9206, Laboratoire de Biochimie, “Maladies Métaboliques”, Institut Louis Bugnard, Bât. L3, C.H.U. Rangueil, 1 Avenue Jean Poulhès, F-31054 Toulouse Cédex, France. Tel.: 33-61-32-29-84; Fax: 33-61-32-29-53.
Abstract
In order to better understand the significance of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β)-receptor internalization
in the sphingomyelin pathway signal transduction, we investigated receptor signaling under conditions in which receptor internalization
is blocked. We demonstrate that human recombinant TNF-α and IL-1β both induced sphingomyelin and phosphatidylcholine hydrolysis
at either 4, 14, or 37°C in human skin fibroblasts and U937 monocytic cells. Cytokine-induced sphingomyelin degradation also
occurred when endocytosis was inhibited by incubating the cells in hypertonic medium. While internalization was not required
for the production of ceramide, activation of the transcription factor NF-κB was strongly reduced when cells were stimulated
with TNF at low temperature or in hypertonic medium. Under these conditions, activation of NF-κB by the cell-permeant C
-ceramide (N-acetylsphingosine), by exogenous sphingomyelinase or by phorbol myristate acetate was also inhibited. These results suggest
that low temperature and hypertonicity, two inhibitors of receptor internalization: (i) do not affect the TNF-α- or IL-1β-induced
sphingomyelin hydrolysis, but (ii) do inhibit a step distal to ceramide of the intracellular signaling pathway leading to
NF-κB activation.
Footnotes
-
↵* This work was supported by grants from the INSERM (CJF 9206), Faculté de Médecine-Rangueil, Université Paul Sabatier, Toulouse-3 (JE DRED-174), the “Association pour la Recherche sur le Cancer” (ARC 3002 and 6749), and the “Ligue Nationale contre le Cancer.” The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵1 The abbreviations used are:
- SPM
-
sphingomyelin
- TNF-α
-
tumor necrosis factor α
- IL-1β
-
interleukin-1β
- NF-κB
-
nuclear factor-κB
- DiI
-
1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate
- LDL
-
low density lipoprotein
- C
-ceramide -
N-acetylsphingosine.
-
↵2We also observed two cycles of phosphatidylcholine and SPM hydrolysis in U937 cells after treatment with a chemotherapeutic agent (Jaffrézou, J. P., Levade, T., Bettaïeb, A., Maestre, N., Rousse, A., and Laurent, G., submitted for publication).
-
↵3N. Andrieu, R. Salvayre, and T. Levade, submitted for publication.
-
↵4H. Chap, personal communication.
-
↵5This result might explain why, in all the conditions we tested for blocking endocytosis, TNF-α was unable to induce apoptosis of U937 cells as followed by DNA fragmentation (data not shown).
-
- Received March 8, 1995.
- Revision received August 9, 1995.
- © 1995 by The American Society for Biochemistry and Molecular Biology, Inc.
