The IkB kinases (IKKs) IKK-a and IKK-b, and the IKK-related kinases TBK1 and IKK-e, have essential roles in innate immunity through signal-induced activation of NF-kB, IRF3 and IRF7, respectively. Although the signaling events within these pathways have been extensively studied, the mechanisms of IKK and IKK-related complex assembly and activation remain poorly defined. Recent data provide insight into the requirement for scaffold proteins in complex assembly; NF-kB essential modulator coordinates some IKK complexes, whereas TANK, NF-kB-activating kinase-associated protein 1 (NAP1) or similar to NAP1 TBK1 adaptor (SINTBAD) assemble TBK1 and IKK-e complexes. The different scaffold proteins undergo similar post-translational modifications, including phosphorylation and non-degradative polyubiquitylation. Moreover, increasing evidence indicates that distinct scaffold proteins assemble IKK, and potentially TBK1 and IKK-e subcomplexes, in a stimulus-specific manner, which might be a mechanism to achieve specificity. Review GlossaryCaspase-recruitment domain (CARD): the CARD is found in some initiator caspases, but also in some adaptor proteins, and mediates protein-protein interactions. Classical and alternative NF-kB-activating pathways: the classical pathway is triggered by various stimuli, including proinflammatory cytokines and TLR ligands, and leads to the activation of the IKK complex that includes IKK-a and IKK-b and also the scaffold protein NEMO. This complex targets the inhibitory IkBa protein for phosphorylation, which is followed by its degradation through the proteasome pathway. NF-kB heterodimers (typically composed of p50 and p65) subsequently move into the nucleus to drive the expression of proinflammatory molecules and chemokines. The alternative pathway is triggered by stimuli such as lymphotoxin-b and requires the kinase NIK in addition to an IKK-a homodimer. NEMO is dispensable for this pathway to be activated. The targeted inhibitory molecule is p100 instead of IkBa, and the NFkB heterodimers are typically composed of p52 and RelB. The target genes of this pathway are required for adaptive immunity. Conventional myeloid and plasmacytoid dendritic cells: dendritic cells (DCs) take up antigens, are activated and migrate to lymphoid tissues in order to present the antigenic peptides on the MHC molecules. They can be broadly divided into plasmacytoid DCs (pDCs) and conventional myeloid DCs, based on the expression of a variety of cell surface markers and their responses to pathogen molecules. pDCs are defined as a subset of cells, the appearance under the microscope of which is similar to that of plasmablasts. These cells are the main producers of type I IFNs in response to viral infections. CpG DNAs: CpG DNAs are DNA oligodeoxynucleotide sequences that include a cytosine-guanosine sequence and some flanking nucleotides. The CpG DNAs induce innate immunity through binding to the TLR9 receptor. Cytosolic NF-kB and IRF activating pathways: these pathways include the RIG-I family (comprising MDA5 and RI...

Type I interferon gene induction relies on IKK-related kinase TBK1 and IKK⑀-mediated phosphorylations of IRF3/7 through the Toll-like receptor-dependent signaling pathways. The scaffold proteins that assemble these kinase complexes are poorly characterized. We show here that TANK/I-TRAF is required for the TBK1-and IKK⑀-mediated IRF3/7 phosphorylations through some Toll-like receptor-dependent pathways and is part of a TRAF3-containing complex. Moreover, TANK is dispensable for the early phase of doublestranded RNA-mediated IRF3 phosphorylation. Interestingly, TANK is heavily phosphorylated by TBK1-IKK⑀ upon lipopolysaccharide stimulation and is also subject to lipopolysaccharide-and TBK1-IKK⑀-mediated Lys 63 -linked polyubiquitination, a mechanism that does not require TBK1-IKK⑀ kinase activity. Thus, we have identified TANK as a scaffold protein that assembles some but not all IRF3/7-phosphorylating TBK1-IKK⑀ complexes and demonstrated that these kinases possess two functions, namely the phosphorylation of both IRF3/7 and TANK as well as the recruitment of an E3 ligase for Lys 63 -linked polyubiquitination of their scaffold protein, TANK.

Restoration of p53 tumor suppressor function through inhibition of its interaction and/or enzymatic activity of its E3 ligase, MDM2, is a promising therapeutic approach to treat cancer. However, because the MDM2 targetome extends beyond p53, MDM2 inhibition may also cause unwanted activation of oncogenic pathways. Accordingly, we identified the microtubuleassociated HPIP, a positive regulator of oncogenic AKT signaling, as a novel MDM2 substrate. MDM2-dependent HPIP degradation occurs in breast cancer cells on its phosphorylation by the estrogen-activated kinase TBK1. Importantly, decreasing Mdm2 gene dosage in mouse mammary epithelial cells potentiates estrogen-dependent AKT activation owing to HPIP stabilization. In addition, we identified HPIP as a novel p53 transcriptional target, and pharmacological inhibition of MDM2 causes p53-dependent increase in HPIP transcription and also prevents HPIP degradation by turning off TBK1 activity. Our data indicate that p53 reactivation through MDM2 inhibition may result in ectopic AKT oncogenic activity by maintaining HPIP protein levels. Cell Death and Differentiation (2014) 21, 811-824; doi:10.1038/cdd.2014.2; published online 31 January 2014Restoration of p53 tumor suppressor function in cancer cells expressing wild-type (WT) p53 is a promising therapeutic approach. 1 Reactivation of p53 activity can be achieved by small molecular inhibitors that disrupt the interaction between p53 and its main E3 ligase MDM2. As a result, targeted cells undergo cell cycle arrest and apoptosis through p53 stabilization. 2 A potential drawback associated with this approach is that, besides p53, MDM2 targets other substrates for degradation. 3 In this context, accumulative evidence show that MDM2 promotes the degradation of FOXO3a, a tumor-suppressing transcription factor as well as the apoptosome activator CAS and the ubiquitin E3 ligase HUWE1. 4,5 Although it is currently unclear whether MDM2 targets positive regulators of oncogenic pathways, an exhaustive characterization of MDM2 substrates will help to anticipate undesired side effects of MDM2 inhibitors used in cancer therapy.Oncogenic pathways include AKT-dependent signaling cascades. Indeed, AKT promotes cell proliferation, survival, migration and angiogenesis by targeting numerous substrates ranging from anti-apoptotic transcription factors to regulators of protein synthesis. 6,7 Mutations or altered expressions of various AKT-activating signaling molecules have been described in human malignancies, thereby defining AKT as a hallmark of tumor development and progression. 8,9 AKT activation by estrogens requires the microtubule-binding protein hematopoietic PBX-interaction protein (HPIP). 10 Initially identified as a corepressor of pre-B-cell leukemia homeobox protein 1 (PBX1), 11 HPIP assembles a signaling complex that connects the p85 subunit of PI3K and ERa to microtubules in order to properly activate AKT. 10 Likewise, HPIP also promotes the growth and differentiation of hematopoietic cells through AKT. 12 Because correct reg...