Roles of the TRAF6 and Pellino E3 ligases in MyD88 and RANKL signaling

Strickson, S. et al. (2017) Roles of the TRAF6 and Pellino E3 ligases in MyD88 and RANKL signaling. Proceedings of the National Academy of Sciences of the United States of America, 114(17), E3481-E3489. (doi: 10.1073/pnas.1702367114) (PMID:28404732)

Abstract

It is widely accepted that the essential role of TRAF6 in vivo is to generate the Lys63-linked ubiquitin (K63-Ub) chains needed to activate the "master" protein kinase TAK1. Here, we report that TRAF6 E3 ligase activity contributes to but is not essential for the IL-1-dependent formation of K63-Ub chains, TAK1 activation, or IL-8 production in human cells, because Pellino1 and Pellino2 generate the K63-Ub chains required for signaling in cells expressing E3 ligase-inactive TRAF6 mutants. The IL-1-induced formation of K63-Ub chains and ubiquitylation of IRAK1, IRAK4, and MyD88 was abolished in TRAF6/Pellino1/Pellino2 triple-knockout (KO) cells, but not in TRAF6 KO or Pellino1/2 double-KO cells. The reexpression of E3 ligase-inactive TRAF6 mutants partially restored IL-1 signaling in TRAF6 KO cells, but not in TRAF6/Pellino1/Pellino2 triple-KO cells. Pellino1-generated K63-Ub chains activated the TAK1 complex in vitro with similar efficiently to TRAF6-generated K63-Ub chains. The early phase of TLR signaling and the TLR-dependent secretion of IL-10 (controlled by IRAKs 1 and 2) was only reduced modestly in primary macrophages from knockin mice expressing the E3 ligase-inactive TRAF6[L74H] mutant, but the late-phase production of IL-6, IL-12, and TNFα (controlled only by the pseudokinase IRAK2) was abolished. RANKL-induced signaling in macrophages and the differentiation of bone marrow to osteoclasts was similar in TRAF6[L74H] and wild-type cells, explaining why the bone structure and teeth of the TRAF6[L74H] mice was normal, unlike TRAF6 KO mice. We identify two essential roles of TRAF6 that are independent of its E3 ligase activity.

• Item Type: Articles
• Keywords: IL-1, Pellino, TAK1, TRAF6, ubiquitin.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Marchesi, Dr Francesco
• Authors: Strickson, S., Emmerich, C. H., Goh, E. T.H., Zhang, J., Kelsall, I. R., Macartney, T., Hastie, C. J., Knebel, A., Peggie, M., Marchesi, F., Arthur, J. S. C., and Cohen, P.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Proceedings of the National Academy of Sciences of the United States of America
• Publisher: National Academy of Sciences
• ISSN: 1091-6490
• ISSN (Online): 1091-6490
• Published Online: 12 April 2017
• Copyright Holders: Copyright © 2017 The Authors
• First Published: First published in Proceedings of the National Academy of Sciences of the United States of America 114(17):E3481-E3489
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher