Lipopolysaccharide (LPS)-induced production of tumor necrosis factor (TNF)-α requires the recruitment of two pairs of adaptors to the Toll-like receptor 4 cytoplasmic domain. The contribution of one pair – Toll-interleukin-1 receptor domain-containing adaptor inducing interferon-β (TRIF) and TRIF-related adaptor molecule (TRAM) – to TNF-α expression is not well understood. To clarify this issue, we studied TRAM knockout bone marrow-derived macrophages (BMDM). LPS-stimulated TRAM-deficient BMDM had decreased TNF-α protein expression even at times when TNF-α mRNA levels were normal, suggesting impaired translation. Consistent with this idea, knockdown of TRAM in RAW264.7 macrophages decreased translation of a reporter controlled by the TNF-α 3′ untranslated region, while transfection of TRAM in HEK293T cells increased translation of this reporter. Also consistent with a role for TRAM in TNF-α translation, LPS-induced activation of MK2, a kinase involved in this process, was impaired in TRAM-deficient BMDM. TRIF did not increase translation of the TNF-α 3′ untranslated region reporter when expressed in HEK293T cells. However, BMDM that lacked functional TRIF produced reduced levels of TNF-α protein in response to LPS despite normal amounts of the mRNA. Unlike BMDM, LPS-stimulated TRAM-deficient peritoneal macrophages displayed equivalent reductions in TNF-α protein and mRNA. Our results indicate that TRAM- and TRIF-dependent signals have a previously unappreciated, cell type-specific role in regulating TNF-α translation.
© 2011 S. Karger AG, Basel
- Toll-like receptor
- Signal transduction
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Dr. Bobby J. Cherayil
Pediatric Gastroenterology Unit, Massachusetts General Hospital
Building 114, 16th Street
Charlestown, MA 02129 (USA)
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Received: November 19, 2010
Accepted after revision: February 3, 2011
Published online: April 14, 2011
Number of Print Pages : 10
Number of Figures : 8, Number of Tables : 1, Number of References : 32
Journal of Innate Immunity
Vol. 3, No. 5, Year 2011 (Cover Date: August 2011)
Journal Editor: Herwald H. (Lund), Egesten A. (Lund)
ISSN: 1662-811X (Print), eISSN: 1662-8128 (Online)
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