NRP/Optineurin Cooperates with TAX1BP1 to potentiate the activation of NF-kappaB by human T-lymphotropic virus type 1 tax protein

Nuclear factor (NF)-kB is a major survival pathway engaged by the Human T-Lymphotropic Virus type 1 (HTLV-1) Tax protein. Tax1 activation of NF-kB occurs predominantly in the cytoplasm, where Tax1 binds NF-kB Essential Modulator (NEMO/IKKc) and triggers the activation of IkB kinases. Several independent studies have shown that Tax1-mediated NF-kB activation is dependent on Tax1 ubiquitination. Here, we identify by co-immunoprecipitation assays NEMO-Related Protein (NRP/Optineurin) as a binding partner for Tax1 in HTLV-1 infected and Tax1/NRP co-expressing cells. Immunofluorescence studies reveal that Tax1, NRP and NEMO colocalize in Golgi-associated structures. The interaction between Tax1 and NRP requires the ubiquitin-binding activity of NRP and the ubiquitination sites of Tax1. In addition, we observe that NRP increases the ubiquitination of Tax1 along with Tax1-dependent NF-kB signaling. Surprisingly, we find that in addition to Tax1, NRP interacts cooperatively with the Tax1 binding protein TAX1BP1, and that NRP and TAX1BP1 cooperate to modulate Tax1 ubiquitination and NF-kB activation. Our data strongly suggest for the first time that NRP is a critical adaptor that regulates the assembly of TAX1BP1 and post-translationally modified forms of Tax1, leading to sustained NF-kB activation. Citation: Journo C, Filipe J, About F, Chevalier SA, Afonso PV, et al. (2009) NRP/Optineurin Cooperates with TAX1BP1 to Potentiate the Activation of NF-kB by Human T-Lymphotropic Virus Type 1 Tax Protein. PLoS Pathog 5(7): e1000521. doi:10.1371/journal.ppat.1000521 Editor: Susan Ross, University of Pennsylvania School of Medicine, United States of America Received March 31, 2009; Accepted June 22, 2009; Published July 17, 2009 This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. Funding: RM was supported by INSERM and is now supported by École Normale Supérieure de Lyon. RW is supported by CNRS. CJ, SAL and PVA were supported by the Ministère de la Recherche. JF is a recipient of the Fundação para a Ciência e a Tecnologia PhD fellowship. DF was supported by a Fulbright Fellowship through the U.S. Department of State Bureau of Educational and Cultural Affairs. This work was supported by PTR214 from the Pasteur Institute and by the Rubicon FP6 European Network of Excellence to AI. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: [email protected] . These authors contributed equally to this work. " These authors are joint senior authors on this work.