Affinage

IFT57

Intraflagellar transport protein 57 homolog · UniProt Q9NWB7

Length
429 aa
Mass
49.1 kDa
Annotated
2026-04-28
25 papers in source corpus 17 papers cited in narrative 17 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

IFT57 is a bifunctional protein that operates both as an intraflagellar transport (IFT) complex component essential for ciliogenesis and as a nuclear transcriptional regulator and apoptosis initiator (under its alias HIPPI). Within the IFT-B complex, IFT57 is required for IFT20 association with the IFT particle and for ATP-dependent kinesin-II dissociation, stabilizes assembled IFT-B against cytoplasmic degradation, and transports specific motility-related axonemal cargo; its loss causes shortened cilia/photoreceptor outer segments, randomized left–right patterning due to absent node monocilia, and impaired Sonic Hedgehog signaling in mammals (PMID:18492793, PMID:28104816, PMID:17027958, PMID:27060890). In its HIPPI role, IFT57 heterodimerizes with HIP-1 through pseudo death-effector domains (pDEDs) to recruit procaspase-8 and activate extrinsic apoptosis, and uses the same pDED to bind specific promoter motifs (AAAGACATG) and transcriptionally activate caspase-1, caspase-8, caspase-10, and REST/NRSF—a pathway amplified in Huntington's disease models where expanded polyglutamine huntingtin liberates HIP-1 (PMID:11788820, PMID:17623017, PMID:21832040). Hypomorphic and missense mutations in human IFT57 cause ciliary transport defects and skeletal ciliopathy features, with cell-type-specific severity in retinal cells (PMID:27060890, PMID:40273360).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2002 High

    Establishing the apoptotic identity of HIPPI/IFT57: the discovery that HIPPI heterodimerizes with HIP-1 via pDEDs and recruits procaspase-8 to activate caspase-8-dependent apoptosis revealed an unexpected link between huntingtin-interacting protein biology and the extrinsic death pathway.

    Evidence Co-IP, in vitro binding, caspase-8 activation and apoptosis assays in mammalian cells

    PMID:11788820

    Open questions at the time
    • Physiological relevance of HIPPI-mediated apoptosis in vivo not established
    • Whether pDED functions as a bona fide death effector domain or an atypical coiled coil was unresolved
  2. 2006 High

    Connecting HIPPI/IFT57 to transcriptional regulation: the finding that HIPPI directly binds the caspase-1 promoter (−151 to −92) and activates its transcription, combined with the demonstration that mouse Hippi knockout eliminates node monocilia and disrupts Shh signaling and left–right patterning, established IFT57 as both a transcription factor and an essential ciliogenesis gene in mammals.

    Evidence EMSA, ChIP, reporter assay for caspase-1 promoter binding; Hippi-KO mouse with cilia IF, in situ hybridization for Shh targets, embryo phenotyping

    PMID:17027958 PMID:17173859

    Open questions at the time
    • How a single protein partitions between nuclear transcriptional and cytoplasmic IFT functions was unclear
    • Whether caspase-1 transcriptional activation occurs in vivo during development or disease not shown
  3. 2007 Medium

    Defining the DNA-binding specificity: identification of the AAAGACATG motif at −101 to −93 of the caspase-1 promoter as the pDED-binding element, and extension to caspase-8 and caspase-10 promoters, refined HIPPI as a sequence-specific transcription factor for multiple caspase genes; structural analysis of HIP-1 revealed the interaction module is a coiled coil rather than a canonical DED.

    Evidence Promoter mutagenesis + EMSA, luciferase reporters for caspase-1/8/10; X-ray crystallography of HIP-1 coiled-coil domain at 2.8 Å

    PMID:17623017 PMID:18155047

    Open questions at the time
    • No crystal structure of HIPPI itself or of the HIPPI–DNA complex
    • Functional validation of predicted HIP-1 residues (F432, K474) for HIPPI binding was modeled, not experimentally mutated
  4. 2008 High

    Establishing IFT57's molecular role within the IFT particle: demonstration that IFT57 is required for IFT20 incorporation into the complex and for ATP-dependent kinesin-II release identified the specific biochemical steps IFT57 mediates in anterograde transport.

    Evidence Co-IP from IFT57-mutant vs. wild-type zebrafish whole-animal extracts, comparison with IFT88 mutants

    PMID:18492793

    Open questions at the time
    • Whether IFT57 or IFT20 is the direct effector of kinesin-II dissociation was not resolved
    • Mechanism of IFT20 anchoring to IFT57 at the structural level unknown
  5. 2009 Medium

    Resolving species-specific differences and expanding nuclear function: zebrafish ift57 mutants form short but detectable outer segments (unlike ift88 null), establishing IFT57 as a modulator of IFT efficiency rather than an obligate component; simultaneously, zebrafish IFT57 was shown dispensable for Hedgehog signaling unlike in mouse, and R393 in the pDED was identified as critical for DNA binding and caspase-1 activation, with HIP-1 acting as the nuclear transporter for HIPPI.

    Evidence Zebrafish ift57 mutant TEM and IHC; site-directed mutagenesis R393E, ChIP, HIP-1 knockdown/NLS-mutation experiments

    PMID:19136023 PMID:19517571 PMID:19934260

    Open questions at the time
    • Basis for species-specific Hedgehog requirement (mouse vs. zebrafish) not mechanistically explained
    • How HIP-1 controls nuclear vs. cytoplasmic partitioning of HIPPI at endogenous levels not fully characterized
  6. 2011 Medium

    Linking IFT57/HIPPI to Huntington's disease transcriptional pathology: the finding that HIPPI–HIP-1 binds the REST/NRSF promoter and drives REST expression, with enhanced occupancy in an HD cell model, connected the HIPPI pathway to neuronal gene silencing in neurodegeneration.

    Evidence ChIP, promoter-reporter assay, HIP-1 knockdown/overexpression in HD cell model, RT-PCR for BDNF and PENK

    PMID:21832040

    Open questions at the time
    • In vivo validation in HD animal models not reported
    • Direct contribution of HIPPI-driven REST to HD pathology vs. other REST-regulatory mechanisms unknown
  7. 2017 High

    Redefining IFT57 as a complex stabilizer and cargo adaptor: Chlamydomonas ift57 mutant analysis showed IFT57 protects the assembled IFT complex from cytoplasmic proteolysis rather than bridging B1–B2, and selectively transports motility-related axonemal proteins, explaining waveform defects without loss of IFT movement per se.

    Evidence Chlamydomonas ift57-1 mutant: mass spectrometry, Western blot of flagellar vs. whole-cell fractions, IFT motility assays, flagellar waveform analysis

    PMID:28104816

    Open questions at the time
    • Identity of the protease(s) degrading IFT-B in the absence of IFT57 not determined
    • Structural basis for selective cargo recognition by IFT57 unknown
  8. 2025 Medium

    Demonstrating cell-type-specific cilia dependence on IFT57: the p.(Val397Glu) variant partially rescues anterograde transport in kidney-derived cells but fails to rescue cilia in retinal RPE1 cells, revealing that retinal cells have a more stringent requirement for IFT57 function.

    Evidence IFT57-KO RPE1 and mIMCD3 cells, variant complementation, patient fibroblast cilia assays

    PMID:40273360

    Open questions at the time
    • Molecular basis of cell-type-specific IFT57 dependence not identified
    • Whether the V397E variant affects HIPPI transcriptional function is untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • A unifying structural and regulatory model that explains how a single polypeptide partitions between IFT-B complex stabilization/cargo transport in cilia and pDED-mediated transcriptional activation/apoptosis in the nucleus remains unresolved.
  • No high-resolution structure of IFT57 alone or within the IFT-B complex
  • Signals controlling cytoplasmic (IFT) vs. nuclear (transcription/apoptosis) partitioning are poorly defined
  • Whether HIPPI transcriptional and apoptotic functions are relevant in ciliated cell types in vivo is unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 3 GO:0140110 transcription regulator activity 3 GO:0060090 molecular adaptor activity 2
Localization
GO:0005929 cilium 4 GO:0005634 nucleus 2 GO:0005829 cytosol 2
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 4 R-HSA-74160 Gene expression (Transcription) 3 R-HSA-162582 Signal Transduction 2 R-HSA-5357801 Programmed Cell Death 2
Partners
BLOC1S2CASP8HIP1HOMER1IFT20RESTRYBP
Complex memberships
HIPPI–HIP-1 heterodimerIFT-B complex

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2008 IFT57 is required for IFT20 association with the IFT particle; in the absence of IFT57, IFT20 does not co-immunoprecipitate with the IFT particle, and kinesin II fails to exhibit ATP-dependent dissociation from the IFT particle, indicating IFT57 and/or IFT20 mediate kinesin II dissociation. Co-immunoprecipitation from whole-animal extracts of IFT57 mutant zebrafish; genetic comparison of IFT57 and IFT88 mutant phenotypes Journal of cell science High 18492793
2009 IFT57 is required for efficient cilia/outer segment formation but is not essential for IFT per se; ift57 mutant zebrafish form short outer segments with reduced opsin, whereas ift88 mutants fail to form outer segments entirely, establishing IFT57 as a modulator of IFT efficiency rather than an obligate IFT component. Genetic analysis of zebrafish ift57, ift88, and ift172 mutants using transmission electron microscopy and immunohistochemistry Vision research High 18492793 19136023
2017 In Chlamydomonas, IFT57 stabilizes the assembled IFT complex against degradation rather than providing an essential structural bridge between IFT-B1 and IFT-B2 subcomplexes; loss of IFT57 reduces IFT-B protein levels at the whole-cell level but not in the protease-free flagellar compartment, and IFT particle movement is unchanged. Additionally, IFT57 is required for transport of specific motility-related axonemal proteins, and its loss disrupts flagellar waveform. Analysis of Chlamydomonas ift57-1 mutant: flagellar protein composition by mass spectrometry/Western blot, IFT movement assays, flagellar waveform analysis Journal of cell science High 28104816
2016 A hypomorphic homozygous mutation in human IFT57 causes ciliary transport defect: anterograde ciliary transport and Sonic Hedgehog signaling are significantly decreased in patient-derived fibroblasts, establishing IFT57 as required for both anterograde IFT and ciliary Shh signaling in human cells. Patient fibroblast functional assays: anterograde ciliary transport measured by IFT particle imaging; Shh pathway activity by target gene expression; splicing anomaly confirmed by RT-PCR Clinical genetics Medium 27060890
2025 The IFT57 p.(Val397Glu) variant causes primary cilia structural and functional defects; exogenous expression of p.(Val397Glu) partially restores anterograde transport in Ift57-KO mIMCD3 cells but fails to rescue primary cilia in retinal IFT57-KO RPE1 cells, demonstrating a cell-type-specific requirement for IFT57 in retinal cells. IFT57-knockout RPE1 and mIMCD3 cells, patient-derived fibroblasts; cilia immunofluorescence, anterograde IFT rescue assays, variant complementation Human molecular genetics Medium 40273360
2002 HIPPI (IFT57) forms a heterodimer with HIP-1 through pseudo death-effector domains (pDEDs), and this heterodimer recruits procaspase-8 into a ternary complex (Hippi–Hip-1–procaspase-8), activating the extrinsic apoptosis pathway. Polyglutamine expansion in huntingtin reduces HIP-1 binding to Htt, freeing HIP-1 to bind HIPPI and initiate this caspase-8 recruitment cascade. Co-immunoprecipitation, in vitro binding assays, caspase-8 activation assays, cell biological apoptosis assays Nature cell biology High 11788820
2006 HIPPI (IFT57) directly binds the 60 bp upstream sequence (−151 to −92) of the caspase-1 gene in vitro and in vivo (by EMSA, fluorescence quenching, and chromatin immunoprecipitation), and increases caspase-1 promoter-driven reporter gene expression, establishing HIPPI as a transcriptional regulator of caspase-1. EMSA, fluorescence quenching, chromatin immunoprecipitation (ChIP), luciferase reporter assay Biochemical and biophysical research communications Medium 17173859
2007 The pseudo death-effector domain (pDED) of HIPPI interacts with specific upstream motif AAAGACATG (−101 to −93) at the caspase-1 promoter; mutation of this motif abolished interaction and reduced reporter activity. HIPPI also interacts with similar motifs in putative promoters of caspase-8 and caspase-10, increasing their expression. Mutagenesis of promoter sequence + EMSA, luciferase reporter assay, domain mapping The FEBS journal Medium 17623017
2009 R393 of HIPPI within the pDED is critical for DNA binding and caspase-1 transcriptional activation; R393E mutation reduces promoter interaction and caspase-1 expression. Nuclear translocation of HIPPI requires HIP-1 (acting as nuclear transporter), and the HIPPI–HIP-1 heterodimer associates with the transcription complex in the nucleus. Site-directed mutagenesis, ChIP, HIP-1 knockdown and overexpression with NLS mutations, co-immunoprecipitation of nuclear complex Nucleic acids research Medium 19934260
2011 HIPPI binds the promoter of REST/NRSF and increases REST expression, which in turn represses REST target genes (BDNF, PENK). In a Huntington's disease cell model, increased free HIP-1 (due to reduced Htt binding) promotes nuclear accumulation of HIPPI–HIP-1, greater occupancy at the REST promoter, and consequent transcriptional activation of REST. ChIP, promoter-reporter assay, HIP-1 knockdown/overexpression, HD cell model, RT-PCR for target gene expression The Journal of biological chemistry Medium 21832040
2007 Crystal structure at 2.8 Å of the HIP-1 coiled-coil domain (residues 371–481) reveals a partially opened coiled-coil with a basic surface predicted to bind HIPPI; residues F432 and K474 are identified as important for HIPPI binding. The structure demonstrates that the HIP-1/HIPPI interaction module is a coiled coil, not a canonical death-effector domain. X-ray crystallography, structural modeling Journal of molecular biology Medium 18155047
2006 Hippi (IFT57) knockout mice lack motile monocilia at the embryonic node, causing randomized left-right axis patterning (randomized turning and heart looping) and defective Sonic Hedgehog signaling in the neural tube, establishing Hippi as essential for node cilia assembly and Shh-dependent ventral neural cell fate. Knockout mouse model; immunofluorescence for cilia, in situ hybridization for Shh target genes, embryo phenotyping Developmental biology High 17027958
2009 In zebrafish, mutations in ift57 (as well as ift88 and ift172) disrupt cilia but do not affect Hedgehog target gene expression in the neural tube or forebrain, demonstrating that in zebrafish (unlike mouse), IFT57 function in cilia is not required for Hh signal transduction. Genetic analysis of zebrafish ift57 mutants and morphants; in situ hybridization for Hh target genes; craniofacial and motor neuron phenotyping Developmental dynamics Medium 19517571
2003 Apoptin (chicken anemia virus protein) interacts with HIPPI both in vitro and in human cells; Apoptin binds the C-terminal half of HIPPI including its pDED, and HIPPI binds within the self-multimerization domain of Apoptin. In normal cells, HIPPI and Apoptin co-localize in the cytoplasm; in cancer cells, they largely separate (Apoptin nuclear, HIPPI cytoplasmic). Yeast two-hybrid, in vitro binding assay, co-immunoprecipitation in human cells, subcellular localization by fluorescence microscopy, domain mapping Biochemical and biophysical research communications Medium 12745083
2007 Rybp (DEDAF) physically interacts with HIPPI and synergizes with HIPPI to enhance caspase-8-mediated apoptosis; Rybp appears essential for HIPPI-mediated apoptosis and may mediate or regulate the HIPPI–caspase-8 interaction. Rybp and HIPPI co-localize in a subset of neurons in the developing mouse brain. Co-immunoprecipitation, apoptosis assays (caspase-8 activation), overexpression and knockdown, immunofluorescence in mouse brain sections Apoptosis Medium 17874297
2008 BLOC1S2 interacts with HIPPI (but not HIP-1) by yeast two-hybrid and co-immunoprecipitation; co-expression of BLOC1S2 and HIPPI sensitizes glioblastoma cells to staurosporine and TRAIL-induced apoptosis by enhancing caspase activation and cytochrome c release, without inducing apoptosis alone. Yeast two-hybrid, co-immunoprecipitation, apoptosis/caspase activation assays, subcellular co-localization Apoptosis Low 18188704
2006 Homer1c interacts specifically with HIPPI (but not Homer2) in a yeast two-hybrid screen of mouse brain cDNA; co-expression of Homer1c with HIPPI prevents HIPPI-induced apoptosis in cultured striatal neurons, and deletion of the HIPPI-binding domain of Homer1c abolishes this protection. Yeast two-hybrid, co-expression in primary striatal neurons, apoptosis assay, deletion mutagenesis Biochemical and biophysical research communications Low 17107665

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Recruitment and activation of caspase-8 by the Huntingtin-interacting protein Hip-1 and a novel partner Hippi. Nature cell biology 232 11788820
2008 The intraflagellar transport protein IFT57 is required for cilia maintenance and regulates IFT-particle-kinesin-II dissociation in vertebrate photoreceptors. Journal of cell science 109 18492793
2009 Early defects in photoreceptor outer segment morphogenesis in zebrafish ift57, ift88 and ift172 Intraflagellar Transport mutants. Vision research 80 19136023
2006 Hippi is essential for node cilia assembly and Sonic hedgehog signaling. Developmental biology 77 17027958
2009 Zebrafish ift57, ift88, and ift172 intraflagellar transport mutants disrupt cilia but do not affect hedgehog signaling. Developmental dynamics : an official publication of the American Association of Anatomists 60 19517571
2008 Huntington's disease: roles of huntingtin-interacting protein 1 (HIP-1) and its molecular partner HIPPI in the regulation of apoptosis and transcription. The FEBS journal 35 18637945
2003 The viral death protein Apoptin interacts with Hippi, the protein interactor of Huntingtin-interacting protein 1. Biochemical and biophysical research communications 32 12745083
2005 Induction of apoptosis in cells expressing exogenous Hippi, a molecular partner of huntingtin-interacting protein Hip1. Neurobiology of disease 24 16364650
2007 Rybp interacts with Hippi and enhances Hippi-mediated apoptosis. Apoptosis : an international journal on programmed cell death 23 17874297
2016 Autosomal recessive IFT57 hypomorphic mutation cause ciliary transport defect in unclassified oral-facial-digital syndrome with short stature and brachymesophalangia. Clinical genetics 19 27060890
2011 Regulation of RE1 protein silencing transcription factor (REST) expression by HIP1 protein interactor (HIPPI). The Journal of biological chemistry 19 21832040
2008 BLOC1S2 interacts with the HIPPI protein and sensitizes NCH89 glioblastoma cells to apoptosis. Apoptosis : an international journal on programmed cell death 17 18188704
2007 Crystal structure at 2.8 A of Huntingtin-interacting protein 1 (HIP1) coiled-coil domain reveals a charged surface suitable for HIP1 protein interactor (HIPPI). Journal of molecular biology 15 18155047
2017 The Ciliary Protein IFT57 in the Macronucleus of Paramecium. The Journal of eukaryotic microbiology 13 28474836
2016 HIPPI: highly accurate protein family classification with ensembles of HMMs. BMC genomics 13 28185571
2002 Hip1 and Hippi participate in a novel cell death-signaling pathway. Developmental cell 11 11832235
2017 IFT57 stabilizes the assembled intraflagellar transport complex and mediates transport of motility-related flagellar cargo. Journal of cell science 10 28104816
2009 Transcription regulation of caspase-1 by R393 of HIPPI and its molecular partner HIP-1. Nucleic acids research 10 19934260
2007 Interactions of HIPPI, a molecular partner of Huntingtin interacting protein HIP1, with the specific motif present at the putative promoter sequence of the caspase-1, caspase-8 and caspase-10 genes. The FEBS journal 10 17623017
2006 Interaction of HIPPI with putative promoter sequence of caspase-1 in vitro and in vivo. Biochemical and biophysical research communications 10 17173859
2006 Homer1c interacts with Hippi and protects striatal neurons from apoptosis. Biochemical and biophysical research communications 8 17107665
2021 Silencing HIPPI Suppresses Tumor Progression in Non-Small-Cell Lung Cancer by Inhibiting DNA Replication. OncoTargets and therapy 6 34079292
2025 Defective IFT57 underlies a novel cause of Bardet-Biedl syndrome. Human molecular genetics 2 40273360
2024 CD47 and IFT57 Are Colinear Genes That Are Highly Coexpressed in Most Cancers and Exhibit Parallel Cancer-Specific Correlations with Survival. International journal of molecular sciences 1 39201643
2006 Cloning, expression, purification, crystallization and preliminary crystallographic analysis of pseudo death-effector domain of HIPPI, a molecular partner of Huntingtin-interacting protein HIP-1. Acta crystallographica. Section F, Structural biology and crystallization communications 1 17142908