IKKepsilon (Ik2, dTBK1) is the single Drosophila member of the TBK1/IKK-epsilon branch of the IKK kinase family, a 720-residue cytoplasmic serine/threonine protein kinase with an N-terminal kinase domain followed by ubiquitin-like and coiled-coil scaffold domains. It is activated locally at the distal tip of growing mechanosensory bristles, where the adaptor Spindle-F links it to dynein and retains it. There it phosphorylates Spn-F and Nuclear fallout, the Rab11/dynein adaptor, controlling the shuttling of recycling endosomes, and it regulates F-actin and microtubule organization needed for polarized cell elongation of bristles, arista laterals and tracheal terminal cells. In bristle cells its kinase activity also restrains protein kinase C, preventing membrane translocation of PKC53E and so protecting the actin cross-linker Fascin from inhibitory phosphorylation; excess PKC activity underlies the actin-bundle defects of IKKepsilon-deficient bristles. It also phosphorylates DIAP1 and promotes its degradation, setting the threshold of nonapoptotic caspase activity during sensory organ development. Further roles in oocyte cytoskeletal polarity and in local severing of sensory neuron dendrites during pruning have been shown. In intestinal enterocytes dTBK1 is required for cyclic-dinucleotide/dSTING-dependent antiviral protection and induced antiviral gene expression, a conserved innate immune function of the TBK1 clade.
Summary: ATP is the phosphate donor for this experimentally active protein kinase. ATP binding is more specific than generic nucleotide binding and is consistent with its conserved kinase domain and measured protein phosphorylation.
Reason: ATP is the phosphate donor for this experimentally active protein kinase. ATP binding is more specific than generic nucleotide binding and is consistent with its conserved kinase domain and measured protein phosphorylation.
IMP PMID:16887350 IKK epsilon regulates F actin assembly and interacts with Dr...
KEEP AS NON CORE
Summary: The kinase regulates polarized cellular elongation through cytoskeletal remodeling and endosomal traffic. Cell morphogenesis is a correct downstream process but is less informative than these mechanisms.
Reason: The kinase regulates polarized cellular elongation through cytoskeletal remodeling and endosomal traffic. Cell morphogenesis is a correct downstream process but is less informative than these mechanisms.
IMP PMID:19917727 Asymmetric microtubule function is an essential requirement ...
KEEP AS NON CORE
Summary: ik2 mutants disrupt bristle microtubule organization; Ik2 acts as a regulator rather than a microtubule-bundling component.
Reason: The mutant phenotype (PMID:19917727) shows that Ik2 is required for the polarized organization of bristle shaft microtubules, so the annotation is supported by target-specific genetics. Ik2 is a kinase that acts at the bristle tip through Spn-F and recycling-endosome traffic; it is not itself a microtubule-binding or bundling protein. Its mechanistic contribution is better represented by the accepted regulation of cytoskeleton organization (GO:0051493) and endocytic recycling annotations, so this row is retained as non-core.
Summary: Inherited from the bilaterian TBK1/IKBKE node PTN000540338, for which fly IKKepsilon is itself an IBD seed; independently supported by fly dSTING/dTBK1 genetics.
Reason: PAINT placed this term at PTN000540338 (taxon Bilateria), the TBK1/IKBKE clade that contains human TBK1 and IKBKE and fly IKKepsilon (PANTHER subfamily SF15, a fly-specific subfamily inside the same family). Fly IKKepsilon is among the IBD seeds, which reflects its own experimental grounding rather than circularity. Target-specific depletion of dTBK1 in enterocytes abolishes cyclic-dinucleotide/dSTING-dependent antiviral protection and induced srg3 expression (PMID:34965418). The IkappaB kinase activity, IKK complex and NF-kappaB-activation terms sit on a different node (PTN000540281, the IKKalpha/beta clade that contains fly IKKbeta) and are not inherited by this gene, a placement this review respects.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
c-di-GMP-induced expression of srg3 was dTBK1 dependent
GO:0004674 protein serine/threonine kinase activity
IBA GO_REF:0000033
ACCEPT
Summary: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
Reason: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
We show that DmIKKvarepsilon promotes degradation of DIAP1 through direct phosphorylation.
GO:0004674 protein serine/threonine kinase activity
IDA PMID:21316589 IKKΞ΅ regulates cell elongation through recycling endosome sh...
ACCEPT
Summary: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
Reason: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
We show that DmIKKvarepsilon promotes degradation of DIAP1 through direct phosphorylation.
GO:0004674 protein serine/threonine kinase activity
IEA GO_REF:0000120
ACCEPT
Summary: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
Reason: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
Summary: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
Reason: Direct studies establish phosphorylation of Spn-F, Nuclear fallout and DIAP1 by Drosophila Ik2/IKKepsilon. These substrate experiments support the serine/threonine kinase activity independently of family labels and electronic mappings.
IPI PMID:14605208 A protein interaction map of Drosophila melanogaster.
REMOVE
Summary: High-throughput detection of the Ik2-Spn-F interaction; bare protein binding is uninformative.
Reason: The partner recorded here (Spn-F, Q9V9Y9) is a well-validated binding partner and substrate of Ik2, so the interaction is not in doubt; low-throughput studies show direct binding and phosphorylation of Spn-F (PMID:18796167). Bare GO:0005515 protein binding nevertheless carries no functional information, and no more specific molecular-function term describes binding of a kinase to its own substrate/adaptor beyond the protein serine/threonine kinase activity already accepted. Removal does not mean the reported interaction is false.
Summary: DIAP1 binding reflects the kinase-substrate relationship; bare protein binding is uninformative.
Reason: Ik2 binds and directly phosphorylates DIAP1, promoting its degradation. That relationship is captured by the accepted protein serine/threonine kinase activity; the generic GO:0005515 row adds no functional information and is removed under the protein-binding policy. Removal does not mean the interaction is false.
IPI PMID:18796167 The Drosophila IKK-related kinase (Ik2) and Spindle-F protei...
REMOVE
Summary: Ik2 binds Spn-F directly and in a complex; the interaction is real, but bare protein binding is uninformative.
Reason: Direct binding of Ik2 to Spn-F, and Spn-F acting as the adaptor that links Ik2 to dynein for distal-tip transport, are well supported. The informative content of this relationship is captured by the accepted protein serine/threonine kinase activity (Spn-F is an Ik2 substrate) and by the cytoskeleton-regulation, cell-tip and endocytic-recycling annotations. Following the GO:0005515 policy, the generic protein-binding row is removed; removal does not mean the interaction is false.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IPI PMID:24019068 Drosophila oocyte polarity and cytoskeleton organization req...
REMOVE
Summary: Ik2 binds Spn-F directly and in a complex; the interaction is real, but bare protein binding is uninformative.
Reason: Direct binding of Ik2 to Spn-F, and Spn-F acting as the adaptor that links Ik2 to dynein for distal-tip transport, are well supported. The informative content of this relationship is captured by the accepted protein serine/threonine kinase activity (Spn-F is an Ik2 substrate) and by the cytoskeleton-regulation, cell-tip and endocytic-recycling annotations. Following the GO:0005515 policy, the generic protein-binding row is removed; removal does not mean the interaction is false.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IPI PMID:26092846 A transport and retention mechanism for the sustained distal...
REMOVE
Summary: Ik2 binds Spn-F directly and in a complex; the interaction is real, but bare protein binding is uninformative.
Reason: Direct binding of Ik2 to Spn-F, and Spn-F acting as the adaptor that links Ik2 to dynein for distal-tip transport, are well supported. The informative content of this relationship is captured by the accepted protein serine/threonine kinase activity (Spn-F is an Ik2 substrate) and by the cytoskeleton-regulation, cell-tip and endocytic-recycling annotations. Following the GO:0005515 policy, the generic protein-binding row is removed; removal does not mean the interaction is false.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IPI PMID:38944040 Next-generation Drosophila protein interactome map and its f...
REMOVE
Summary: High-throughput detection of the Ik2-Spn-F interaction; bare protein binding is uninformative.
Reason: The partner recorded here (Spn-F, Q9V9Y9) is a well-validated binding partner and substrate of Ik2, so the interaction is not in doubt; low-throughput studies show direct binding and phosphorylation of Spn-F (PMID:18796167). Bare GO:0005515 protein binding nevertheless carries no functional information, and no more specific molecular-function term describes binding of a kinase to its own substrate/adaptor beyond the protein serine/threonine kinase activity already accepted. Removal does not mean the reported interaction is false.
Summary: The conserved protein-kinase domain and multiple direct phosphorylation assays support ATP binding as part of catalysis. No alternative nucleotide-specific chemistry is inferred.
Reason: The conserved protein-kinase domain and multiple direct phosphorylation assays support ATP binding as part of catalysis. No alternative nucleotide-specific chemistry is inferred.
Summary: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
Reason: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IDA PMID:21316589 IKKΞ΅ regulates cell elongation through recycling endosome sh...
ACCEPT
Summary: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
Reason: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
Summary: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
Reason: Ik2 acts on cytoplasmic substrates and is localized to punctate structures, cortical regions and the growing bristle tip. These primary observations support cytoplasmic localization.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IMP PMID:16887350 IKK epsilon regulates F actin assembly and interacts with Dr...
ACCEPT
Summary: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
Reason: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
IMP PMID:24019068 Drosophila oocyte polarity and cytoskeleton organization req...
KEEP AS NON CORE
Summary: Ik2-dependent regulation of Spn-F/Javelin-like supports oocyte cytoskeleton polarity and oskar/gurken localization. Retain axis specification as a developmental consequence of the underlying transport/cytoskeletal mechanism.
Reason: Ik2-dependent regulation of Spn-F/Javelin-like supports oocyte cytoskeleton polarity and oskar/gurken localization. Retain axis specification as a developmental consequence of the underlying transport/cytoskeletal mechanism.
IMP PMID:19917727 Asymmetric microtubule function is an essential requirement ...
KEEP AS NON CORE
Summary: Bristle morphology depends on local kinase-controlled microtubule, actin and endosome organization. The tissue-level morphogenesis term is retained as noncore relative to those direct mechanisms.
Reason: Bristle morphology depends on local kinase-controlled microtubule, actin and endosome organization. The tissue-level morphogenesis term is retained as noncore relative to those direct mechanisms.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
IKKΙ regulates the localization of recycling endosome regulators Rab11 and Dynein and phosphorylates their adaptor molecule, Nuclear fallout (Nuf).
GO:0009967 positive regulation of signal transduction
IEA GO_REF:0000117
MODIFY
Summary: Ik2/dTBK1 acts as a kinase within STING-dependent signaling, not as a generic positive regulator of signal transduction; replace with the specific pathway it participates in.
Reason: This ARBA-derived term frames Ik2 as an upstream positive regulator of unspecified signalling. The only signalling context with fly evidence is the cyclic-dinucleotide/dSTING antiviral pathway, in which dTBK1 is required for protection and for induced gene expression in enterocytes (PMID:34965418), i.e. it is a pathway component. That role is captured by GO:0140896 cGAS/STING signaling pathway (IMP, accepted). The broad regulatory umbrella is therefore replaced by the specific pathway term. Ik2 also acts in bristle elongation and dendrite pruning, but those contexts are not signal transduction regulation.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
Summary: Induced antiviral gene expression is a downstream output of dSTING signalling, already covered by the accepted pathway and antiviral response terms.
Reason: c-di-GMP-induced srg3 expression is dTBK1-dependent (PMID:34965418), so the claim is not false. However, the kinase does not act directly on gene expression; the transcriptional output is executed downstream by NF-kappaB factors. Positive regulation of gene expression is a broad, indirect consequence that the ARBA rule applies to many signalling kinases and adds nothing beyond GO:0140896 and GO:0140374.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
Summary: Ik2 is required for dendrite severing during metamorphic pruning, and premature kinase activation induces precocious severing. Neuron remodeling is retained as a context-specific consequence of cytoskeletal regulation.
Reason: Ik2 is required for dendrite severing during metamorphic pruning, and premature kinase activation induces precocious severing. Neuron remodeling is retained as a context-specific consequence of cytoskeletal regulation.
IPI PMID:25453831 Toward a comprehensive map of the effectors of rab GTPases.
KEEP AS NON CORE
Summary: Ik2 was recovered as a GTP-specific interactor of Rab30 in S2-cell affinity chromatography; a supported but non-core trafficking interaction.
Reason: In the Rab effector screen (PMID:25453831), Ik2 was found in both Rab30 affinity datasets and the interaction was confirmed to be GTP specific by immunoblotting, which is the hallmark of a Rab effector interaction. The same study shows that the punctate Ik2/Spn-F structures in S2 cells correspond to the Golgi. Affinity chromatography from lysate does not establish that binding is direct, and no function of the Rab30 interaction for Ik2 activity has been shown, so it is kept as non-core.
IMP PMID:21316589 IKKΞ΅ regulates cell elongation through recycling endosome sh...
ACCEPT
Summary: Phosphorylation of the Rab11/dynein adaptor Nuf regulates recycling-endosome transport, providing a direct mechanistic role in endocytic recycling.
Reason: Phosphorylation of the Rab11/dynein adaptor Nuf regulates recycling-endosome transport, providing a direct mechanistic role in endocytic recycling.
IKKΙ regulates the localization of recycling endosome regulators Rab11 and Dynein and phosphorylates their adaptor molecule, Nuclear fallout (Nuf).
GO:0032481 positive regulation of type I interferon production
IBA GO_REF:0000033
REMOVE
Summary: Taxon-incompatible propagation; Drosophila has no type I interferons, so the fly kinase cannot positively regulate their production.
Reason: This IBA comes from PAINT node PTN000540338, placed at Bilateria, but every IBD seed for this term is vertebrate (human TBK1 Q9UHD2, human IKBKE Q14164, mouse Ikbke); fly IKKepsilon is a seed for activation of innate immune response at the same node but not for this term. Type I interferons and IRF3/IRF7 are vertebrate innovations, and flies are described as devoid of interferons (PMID:30119996). The process therefore cannot occur in Drosophila, so this is a lineage-specific function propagated too deep in the tree. The conserved antiviral role of dTBK1 is retained through GO:0002218, GO:0140374 and GO:0140896.
Propagation Review
Root cause:PROPAGATION BAD
Failure modes:LINEAGE OR TAXON MISMATCH
Sources checked:
PANTHER:PTN000540338 Β· TBK1/IKBKE clade node (Bilateria) SUPPORTS SOURCE BUT NOT TARGET
All IBD seeds for GO:0032481 at this node are vertebrate (UniProtKB:Q9UHD2, UniProtKB:Q14164, MGI:MGI:1929658); fly IKKepsilon seeds only GO:0002218 here. Type I interferon production is vertebrate-restricted and absent from Drosophila.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
GO:0035160 maintenance of epithelial integrity, open tracheal system
IMP PMID:16887350 IKK epsilon regulates F actin assembly and interacts with Dr...
UNDECIDED
Summary: The accessible abstract reports aberrant branching of tracheal terminal cells, not loss of tracheal epithelial integrity; the full text was not available to check what the curator saw.
Reason: The cached abstract of PMID:16887350 describes aberrantly branched morphology of tracheal terminal cells (a polarized cell-elongation defect) with no apparent change in cell viability. Maintenance of epithelial integrity in the open tracheal system describes preserving the tracheal epithelium against breakage or leakage, which the abstract does not mention. The full text may contain such data, so the experimental annotation is not overruled; it is left unresolved pending the full paper. If the only tracheal phenotype is terminal-cell branching, a terminal-branching/cell-morphogenesis term would fit better.
tracheal terminal cells, bristles, and arista laterals, which require accurate F actin assembly for their polarized elongation, all exhibited aberrantly branched morphology.
GO:0043065 positive regulation of apoptotic process
Summary: The accessible abstract establishes phosphorylation-dependent DIAP1 degradation and explicitly emphasizes nonapoptotic caspase functions. That does not by itself demonstrate positive regulation of apoptosis, but the full original experiment has not been inspected and may include a relevant context. Retain the experimental annotation unresolved rather than infer cell death from any caspase activation.
Reason: The accessible abstract establishes phosphorylation-dependent DIAP1 degradation and explicitly emphasizes nonapoptotic caspase functions. That does not by itself demonstrate positive regulation of apoptosis, but the full original experiment has not been inspected and may include a relevant context. Retain the experimental annotation unresolved rather than infer cell death from any caspase activation.
IGI PMID:19822670 Temporal regulation of Drosophila IAP1 determines caspase fu...
MARK AS OVER ANNOTATED
Summary: The full primary study places the demonstrated Ik2-dependent DIAP1 degradation effect after the final SOP division, during shaft elongation. It explicitly reports that phase-I degradation during division was not disturbed by Ik2 downregulation and calls for further work on cell division. This annotation overstates the demonstrated temporal role; shaft morphogenesis and nonapoptotic caspase regulation are supported.
Reason: The full primary study places the demonstrated Ik2-dependent DIAP1 degradation effect after the final SOP division, during shaft elongation. It explicitly reports that phase-I degradation during division was not disturbed by Ik2 downregulation and calls for further work on cell division. This annotation overstates the demonstrated temporal role; shaft morphogenesis and nonapoptotic caspase regulation are supported.
however, its degradation pattern was not disturbed in phase I, suggesting that there may be one or more other regulators of DIAP1 turnover during SOP cell division.
GO:0045089 positive regulation of innate immune response
IEA GO_REF:0000117
MODIFY
Summary: Correct but general; the gene already carries the more specific child term activation of innate immune response (GO:0002218).
Reason: dTBK1 is required for dSTING-dependent antiviral protection and induced immune gene expression in enterocytes (PMID:34965418), so a positive role in innate immunity is supported. GO:0002218 activation of innate immune response is an is_a descendant of this term (verified in OLS), is carried by this gene via IBA from PAINT node PTN000540338 (for which fly IKKepsilon is itself an IBD seed), and is the more precise statement; the ARBA-level parent is refined to it.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
IDA PMID:21316589 IKKΞ΅ regulates cell elongation through recycling endosome sh...
ACCEPT
Summary: The kinase is specifically activated and retained at the distal tip of growing bristles through Spn-F/Javelin-like-dependent transport and retention.
Reason: The kinase is specifically activated and retained at the distal tip of growing bristles through Spn-F/Javelin-like-dependent transport and retention.
IKKΞ΅ distal tip localization is regulated by Spindle-F (Spn-F), which is stably retained at the distal tip and functions as an adaptor linking IKKΞ΅ to cytoplasmic dynein.
GO:0051493 regulation of cytoskeleton organization
IPI PMID:18796167 The Drosophila IKK-related kinase (Ik2) and Spindle-F protei...
ACCEPT
Summary: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
Reason: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
IMP PMID:21316589 IKKΞ΅ regulates cell elongation through recycling endosome sh...
ACCEPT
Summary: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
Reason: The kinase controls F-actin turnover and polarized cytoskeletal organization. Spn-F binding and phosphorylation, together with target mutant phenotypes, support this cytoskeletal regulatory mechanism.
Summary: Target-specific depletion of dTBK1/Ik2 in enterocytes blocks cyclic-dinucleotide/STING-dependent antiviral protection and affects induced immune gene expression. This directly supports an innate antiviral signaling role in flies, without implying mammalian interferon production.
Reason: Target-specific depletion of dTBK1/Ik2 in enterocytes blocks cyclic-dinucleotide/STING-dependent antiviral protection and affects induced immune gene expression. This directly supports an innate antiviral signaling role in flies, without implying mammalian interferon production.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
Summary: Target-specific depletion of dTBK1/Ik2 in enterocytes blocks cyclic-dinucleotide/STING-dependent antiviral protection and affects induced immune gene expression. This directly supports an innate antiviral signaling role in flies, without implying mammalian interferon production.
Reason: Target-specific depletion of dTBK1/Ik2 in enterocytes blocks cyclic-dinucleotide/STING-dependent antiviral protection and affects induced immune gene expression. This directly supports an innate antiviral signaling role in flies, without implying mammalian interferon production.
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
CDN-mediated protection from enteric SINV infection was lost in dSTING-enterocyte-depleted flies and in dTBK1-enterocyte-depleted flies compared to control flies
c-di-GMP-induced expression of srg3 was dTBK1 dependent
Phosphorylates DIAP1 to promote its degradation, setting the threshold of nonapoptotic caspase activity during sensory organ and bristle shaft development.
Q: Which residues of DIAP1, Spn-F and Nuf are phosphorylated by Ik2, and is there a shared substrate motif with the mammalian TBK1/IKBKE phospho-sites on Rab11-FIP3?
Q: Does dTBK1 act on Relish, IKKbeta or dSTING itself in the enterocyte antiviral pathway, i.e. which substrate links it to NF-kappaB-dependent antiviral gene expression in a lineage without IRFs?
Suggested Experiments
Experiment: In vitro kinase assays with recombinant Ik2 and dSTING, IKKbeta and Relish, combined with phospho-site mutant rescue in enterocyte-specific dTBK1 knockdown flies, to identify the antiviral substrate of dTBK1.
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
Ik2/IKKepsilon is a cytoplasmic IKK-related serine/threonine kinase that directly phosphorylates Spn-F, Nuclear fallout and DIAP1; the single ProtNLM2 prediction, protein phosphorylation, is supported by these substrate experiments and is absent from the gene's GOA process annotations.
Review rationale: Protein phosphorylation is directly established by experiments showing that fly Ik2/IKKepsilon phosphorylates its substrates Spn-F, Nuclear fallout and DIAP1, and the Q9V3Y8 protein retains the complete kinase domain. GOA carries experimentally supported protein serine/threonine kinase activity (GO:0004674) for this gene, but no protein phosphorylation process term or descendant of it, and the molecular-function term does not entail the process term in the ontology, so the process annotation is novel. It does not entail every mammalian TBK1 downstream pathway, particularly interferon production.
Supporting Evidence:
PMID:18796167: "We showed that Ik2 phosphorylates Spn-F and demonstrated that this phosphorylation does not lead to Spn-F degradation."
PMID:21316589: "IKKΙ regulates the localization of recycling endosome regulators Rab11 and Dynein and phosphorylates their adaptor molecule, Nuclear fallout (Nuf)."
PMID:16887178: "We show that DmIKKvarepsilon promotes degradation of DIAP1 through direct phosphorylation."
FlyBase gene description for IKKepsilon (DROME)FlyBase
FlyBase gene description for IKKepsilon (DROME)
I-kappaB kinase &egr; (IKK&egr;) encodes a serine-threonine kinase that targets the inhibitor of apoptosis encoded by Diap1 for degradation. It also negatively regulates protein kinase C and the dynein adaptor encoded nuf. The product of IKK&egr; contributes to the specification of bristle cells, bristle cell morphogenesis, oocyte polarity, and dendrite development.