Optineurin negatively regulates TNFalpha- induced NF-kappaB activation by competing with NEMO for ubiquitinated RIP.
NF-kappaB essential modulator (NEMO), the regulatory subunit of the IkappaB kinase (IKK) that activates NF-kappaB, is essential for NF-kappaB activation. NEMO was recently found to contain a region that preferentially binds Lys (K)63-linked but not K48-linked polyubiquitin (polyUb) chains, and the ability of NEMO to bind to K63-linked polyUb RIP (receptor-interacting protein) is necessary for efficient tumor necrosis factor alpha (TNFalpha)-induced NF-kappaB activation. Optineurin is a homolog of NEMO, and mutations in the optineurin gene are found in a subset of patients with glaucoma, a neurodegenerative disease involving the loss of retinal ganglion cells. Although optineurin shares considerable homology with NEMO, in resting cells, it is not present in the high-molecular-weight complex containing IKKalpha and IKKbeta, and optineurin cannot substitute for NEMO in lipopolysaccharide (LPS)-induced NF-kappaB activation. On the other hand, the overexpression of optineurin blocks the protective effect of E3-14.7K on cell death caused by the overexpression of TNFalpha receptor 1 (TNFR1). Here we show that optineurin has a K63-linked polyUb-binding region similar to that of NEMO, and like NEMO, it bound K63- but not K48-linked polyUb. Optineurin competitively antagonized NEMO's binding to polyUb RIP, and its overexpression inhibited TNFalpha-induced NF-kappaB activation. This competition occurs at physiologic protein levels because microRNA silencing of optineurin resulted in markedly enhanced TNFalpha-induced NF-kappaB activity. These results reveal a physiologic role for optineurin in dampening TNFalpha signaling, and this role might provide an explanation for its association with glaucoma.
Zhu
Guozhi
G
Laboratory of Immune Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Wu
Chuan-Jin
CJ
Zhao
Yongge
Y
Ashwell
Jonathan D
JD
D018797:Cell Cycle Proteins; D005901:Glaucoma / Q000378:metabolism; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism*; D026901:Membrane Transport Proteins; D016328:NF-kappa B / Q000378:metabolism*; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000378:metabolism*; D035582:Transcription Factor TFIIIA / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
D018797:Cell Cycle Proteins; C491731:IKBKG protein, human; D026901:Membrane Transport Proteins; D016328:NF-kappa B; C409460:OPTN protein, human; D035582:Transcription Factor TFIIIA; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; D051550:I-kappa B Kinase