Inhibition of Myoblast Differentiation by Tumor Necrosis Factor α Is Mediated by c-Jun N-terminal Kinase 1 and Leukemia Inhibitory Factor*
- Department of Biochemistry, Rappaport Institute for Research in the Medical Sciences, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel
- 1 To whom correspondence should be addressed: PO Box 9649, Haifa 31096, Israel. Tel.: 972-4-8295-287; Fax: 972-4-8553-299; E mail: bengal{at}tx.technion.ac.il.
Abstract
The proinflammatory cytokine, TNFα plays a major role in muscle wasting occurring in chronic diseases and muscular dystrophies. Among its other functions, TNFα perturbs muscle regeneration by preventing satellite cell differentiation. In the present study, the role of c-Jun N-terminal kinase (JNK), a mediator of TNFα, was investigated in differentiating myoblast cell lines. Addition of TNFα to C2 myoblasts induced immediate and delayed phases of JNK activity. The delayed phase is associated with myoblast proliferation. Inhibition of JNK activity prevented proliferation and restored differentiation to TNFα-treated myoblasts. Studies with cell lines expressing MyoD:ER chimera and lacking JNK1 or JNK2 genes indicate that JNK1 activity mediates the effects of TNFα on myoblast proliferation and differentiation. TNFα does not induce proliferation or inhibit differentiation of JNK1-null myoblasts. However, differentiation of JNK1-null myoblasts is inhibited when they are grown in conditioned medium derived from cell lines affected by TNFα. We investigated the induced synthesis of several candidate growth factors and cytokines following treatment with TNFα. Expression of IL-6 and leukemia inhibitory factor (LIF) was induced by TNFα in wild-type and JNK2-null myoblasts. However, LIF expression was not induced by TNFα in JNK1-null myoblasts. Addition of LIF to the growth medium of JNK1-null myoblasts prevented their differentiation. Moreover, LIF-neutralizing antibodies added to the medium of C2 myoblasts prevented inhibition of differentiation mediated by TNFα. Hence, TNFα promotes myoblast proliferation through JNK1 and prevents myoblast differentiation through JNK1-mediated secretion of LIF.
Footnotes
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↵2 The abbreviations used are: TNFα, tumor necrosis factor α; JNK, c-Jun N-terminal kinase; LIF, leukemia inhibitory factor; ER, estrogen receptor; NFκB, nuclear factor κB; MyHC, myosin heavy chain; BrdU, bromodeoxyuridine; DM, differentiation medium; PBS, phosphate-buffered saline; FACS, fluorescence-activated cell sorting; IL, interleukin; DAPI, 4′,6-diamidino-2-phenylindole; RT, reverse transcriptase.
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↵* This work was supported in part by a grant (to E. B.) from the Israel Science Foundation, by a grant from the Israel Cancer Association (the Todores Moshe & Rachel Dziencielki, & Jacob & Zilpa Bass research fund) (to E. B.), and by funds from the Rappaport Foundation for Medical Research and the Foundation for the Promotion of Research in the Technion, Israel Institute of Technology. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1–S5.
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- Received February 21, 2008.
- Revision received May 26, 2008.
- The American Society for Biochemistry and Molecular Biology, Inc.
