scholarly journals Activation of the Heterodimeric IκB Kinase α (IKKα)-IKKβ Complex Is Directional: IKKα Regulates IKKβ under Both Basal and Stimulated Conditions

2000 ◽  
Vol 20 (4) ◽  
pp. 1170-1178 ◽  
Author(s):  
Alison O'Mahony ◽  
Xin Lin ◽  
Romas Geleziunas ◽  
Warner C. Greene
Keyword(s):  
Protein Kinase ◽  
Kinase Activity ◽  
Leukemia Virus ◽  
Mitogen Activated Protein Kinase ◽  
Activation Loop ◽  
Stimulatory Action ◽  
Necrosis Factor Alpha ◽  
Cell Leukemia Virus Type ◽  
Iκb Kinase ◽  
Human T Cell

ABSTRACT Signal-induced nuclear expression of the eukaryotic NF-κB transcription factor involves the stimulatory action of select mitogen-activated protein kinase kinase kinases on the IκB kinases (IKKα and IKKβ) which reside in a macromolecular signaling complex termed the signalsome. While genetic studies indicate that IKKβ is the principal kinase involved in proinflammatory cytokine-induced IκB phosphorylation, the function of the equivalently expressed IKKα is less clear. Here we demonstrate that assembly of IKKα with IKKβ in the heterodimeric signalsome serves two important functions: (i) in unstimulated cells, IKKα inhibits the constitutive IκB kinase activity of IKKβ; (ii) in activated cells, IKKα kinase activity is required for the induction of IKKβ. The introduction of kinase-inactive IKKα, activation loop mutants of IKKα, or IKKα antisense RNA into 293 or HeLa cells blocks NIK (NF-κB-inducing kinase)-induced phosphorylation of the IKKβ activation loop occurring in functional signalsomes. In contrast, catalytically inactive mutants of IKKβ do not block NIK-mediated phosphorylation of IKKα in these macromolecular signaling complexes. This requirement for kinase-proficient IKKα to activate IKKβ in heterodimeric IKK signalsomes is also observed with other NF-κB inducers, including tumor necrosis factor alpha, human T-cell leukemia virus type 1 Tax, Cot, and MEKK1. Conversely, the θ isoform of protein kinase C, which also induces NF-κB/Rel, directly targets IKKβ for phosphorylation and activation, possibly acting through homodimeric IKKβ complexes. Together, our findings indicate that activation of the heterodimeric IKK complex by a variety of different inducers proceeds in a directional manner and is dependent on the kinase activity of IKKα to activate IKKβ.

scholarly journals Ssp2 Binding Activates the Smk1 Mitogen-Activated Protein Kinase

2017 ◽  
Vol 37 (10) ◽  
Author(s):  
Chong Wai Tio ◽  
Gregory Omerza ◽  
Timothy Phillips ◽  
Hua Jane Lou ◽  
Benjamin E. Turk ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Chromosome Segregation ◽  
Kinase Activity ◽  
Specific Protein ◽  
Mitogen Activated Protein Kinase ◽  
Activation Loop ◽  
Cyclin Dependent Kinase ◽  
Content Type ◽  
Dual Specificity ◽  
Mitogen Activated Protein

ABSTRACT Smk1 is a meiosis-specific mitogen-activated protein kinase (MAPK) in Saccharomyces cerevisiae that couples spore morphogenesis to the completion of chromosome segregation. Similar to other MAPKs, Smk1 is controlled by phosphorylation of a threonine (T) and a tyrosine (Y) in its activation loop. However, it is not activated by a dual-specificity MAPK kinase. Instead, T207 in Smk1's activation loop is phosphorylated by the cyclin-dependent kinase (CDK)-activating kinase (Cak1), and Y209 is autophosphorylated in an intramolecular reaction that requires the meiosis-specific protein Ssp2. In this study, we show that Smk1 is catalytically inert unless it is bound by Ssp2. While Ssp2 binding activates Smk1 by a mechanism that is independent of activation loop phosphorylation, binding also triggers autophosphorylation of Y209 in Smk1, which, along with Cak1-mediated phosphorylation of T207, further activates the kinase. Autophosphorylation of Smk1 on Y209 also appears to modify the specificity of the MAPK by suppressing Y kinase and enhancing S/T kinase activity. We also found that the phosphoconsensus motif preference of Ssp2/Smk1 is more extensive than that of other characterized MAPKs. This study therefore defines a novel mechanism of MAPK activation requiring binding of an activator and also shows that MAPKs can be diversified to recognize unique phosphorylation motifs.

scholarly journals The Human T-cell Leukemia Virus Type-1 Tax Protein Regulates the Activity of the IκB Kinase Complex

1999 ◽  
Vol 274 (48) ◽  
pp. 34417-34424 ◽  
Author(s):  
Xiao Hua Li ◽  
Kathleen M. Murphy ◽  
Kevin T. Palka ◽  
Rama Mohan Surabhi ◽  
Richard B. Gaynor
Keyword(s):  
T Cell ◽  
Virus Type ◽  
Leukemia Virus ◽  
Cell Leukemia ◽  
Cell Leukemia Virus Type ◽  
Tax Protein ◽  
Iκb Kinase ◽  
Human T Cell ◽  
T Cell Leukemia Virus

scholarly journals Human T-Cell Leukemia Virus Type 1 Tax Induction of NF-κB Involves Activation of the IκB Kinase α (IKKα) and IKKβ Cellular Kinases

1998 ◽  
Vol 18 (9) ◽  
pp. 5157-5165 ◽  
Author(s):  
Romas Geleziunas ◽  
Sharon Ferrell ◽  
Xin Lin ◽  
Yajun Mu ◽  
Emmett T. Cunningham ◽  
...  
Keyword(s):  
T Cell ◽  
Leukemia Virus ◽  
T Cell Leukemia ◽  
Cell Leukemia ◽  
Cell Leukemia Virus Type ◽  
Iκb Kinase ◽  
Human T Cell ◽  
Tnf Α ◽  
T Cell Leukemia Virus

ABSTRACT Tax corresponds to a 40-kDa transforming protein from the pathogenic retrovirus human T-cell leukemia virus type 1 (HTLV-1) that activates nuclear expression of the NF-κB/Rel family of transcription factors by an unknown mechanism. Tax expression promotes N-terminal phosphorylation and degradation of IκBα, a principal cytoplasmic inhibitor of NF-κB. Our studies now demonstrate that HTLV-1 Tax activates the recently identified cellular kinases IκB kinase α (IKKα) and IKKβ, which normally phosphorylate IκBα on both of its N-terminal regulatory serines in response to tumor necrosis factor alpha (TNF-α) and interleukin-1 (IL-1) stimulation. In contrast, a mutant of Tax termed M22, which does not induce NF-κB, fails to activate either IKKα or IKKβ. Furthermore, endogenous IKK enzymatic activity was significantly elevated in HTLV-1-infected and Tax-expressing T-cell lines. Transfection of kinase-deficient mutants of IKKα and IKKβ into either human Jurkat T or 293 cells also inhibits NF-κB-dependent reporter gene expression induced by Tax. Similarly, a kinase-deficient mutant of NIK (NF-κB-inducing kinase), which represents an upstream kinase in the TNF-α and IL-1 signaling pathways leading to IKKα and IKKβ activation, blocks Tax induction of NF-κB. However, plasma membrane-proximal elements in these proinflammatory cytokine pathways are apparently not involved since dominant negative mutants of the TRAF2 and TRAF6 adaptors, which effectively block signaling through the cytoplasmic tails of the TNF-α and IL-1 receptors, respectively, do not inhibit Tax induction of NF-κB. Together, these studies demonstrate that HTLV-1 Tax exploits a distal part of the proinflammatory cytokine signaling cascade leading to induction of NF-κB. The pathological alteration of this cytokine pathway leading to NF-κB activation by Tax may play a central role in HTLV-1-mediated transformation of human T cells, clinically manifested as the adult T-cell leukemia.

scholarly journals An Alternative Splice Product of IκB Kinase (IKKγ), IKKγ-Δ, DifferentiallyMediates Cytokine and Human T-Cell Leukemia Virus Type 1 Tax-Induced NF-κB Activation

2006 ◽  
Vol 80 (9) ◽  
pp. 4227-4241 ◽  
Author(s):  
Tao Hai ◽  
Man-Lung Yeung ◽  
Thomas G. Wood ◽  
Yuanfen Wei ◽  
Shoji Yamaoka ◽  
...  
Keyword(s):  
T Cell ◽  
Leukemia Virus ◽  
Cell Leukemia ◽  
Cell Leukemia Virus Type ◽  
The Core ◽  
Iκb Kinase ◽  
Human T Cell ◽  
T Cell Leukemia Virus ◽  
Alternatively Spliced

ABSTRACT NF-κB is an inducible transcription factor mediating innate immune responses whose activity is controlled by the multiprotein IκB kinase (IKK) “signalsome”. The core IKK consists of two catalytic serine kinases, IKKα and IKKβ, and a noncatalytic subunit, IKKγ. IKKγ is required for IKK activity by mediating kinase oligomerization and serving to couple the core catalytic subunits to upstream mitogen-activated protein 3-kinase cascades. We have discovered an alternatively spliced IKKγ mRNA isoform, encoding an in-frame deletion of exon 5, termed IKKγ-Δ. Using a specific reverse transcription-PCR assay, we find that IKKγ-Δ is widely expressed in cultured human cells and normal human tissues. Because IKKγ-Δ protein is lacking a critical coiled-coil domain important in protein-protein interactions, we sought to determine its signaling properties by examining its ability to self associate, couple to activators of the canonical pathway, and mediate human T-cell leukemia virus type 1 (HTLV-1) Tax-induced NF-κB activity. Coimmunoprecipitation and confocal colocalization assays indicate IKKγ-Δ has strong homo- and heterotypic association with wild-type (WT) IKKγ and, like IKKγ WT, associates with the IKKβ kinase. Similarly, IKKγ-Δ mediates IKK kinase activity and downstream NF-κB-dependent transcription in response to tumor necrosis factor (TNF) and the NF-κB-inducing kinase-IKKα signaling pathway. Surprisingly, however, in contrast to IKKγ WT, IKKγ-Δ is not able to mediate HTLV-1 Tax-induced NF-κB-dependent transcription, even though IKKγ-Δ binds and colocalizes with Tax. These observations suggest that IKKγ-Δ is a functionally distinct alternatively spliced mRNA product differentially mediating TNF-induced, but not Tax-induced, signals converging on the IKK signalsome. Differing levels of IKKγ-Δ expression, therefore, may affect signal transduction cascades coupling to IKK.

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