Affinage

TXLNG

Gamma-taxilin · UniProt Q9NUQ3

Length
528 aa
Mass
60.6 kDa
Annotated
2026-06-10
16 papers in source corpus 13 papers cited in narrative 13 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

TXLNG (FIAT/gamma-taxilin) is a nuclear leucine zipper protein that functions as a transcriptional repressor controlling osteoblast activity and bone mass accrual (PMID:15911876, PMID:27906582). Lacking a basic DNA-binding domain, FIAT heterodimerizes with the bZIP transcription factor ATF4 through its second leucine zipper (LZ2, residues 194–222), forming transcriptionally inactive dimers that cannot bind DNA and thereby blocking ATF4-mediated transcription of the osteocalcin gene; mutation of LZ2 abolishes both the ATF4 interaction and repression of mineralization (PMID:15911876, PMID:18680144). Loss-of-function studies confirm this repressor role: FIAT knockdown increases ATF4 occupancy on the osteocalcin promoter and enhances osteoblast differentiation (PMID:19016261), and Fiat-knockout mice display increased bone mass alongside increased susceptibility to fat accumulation and metabolic disturbance (PMID:27906582). FIAT also represses FRA-1/c-JUN heterodimer-driven transcription through LZ2, extending its repressor activity to a second bZIP target (PMID:20392257). Maximal repression of osteocalcin requires interaction with SUMOylated αNAC associated with HDAC2 at the target promoter (PMID:24375853), and Fiat expression itself is controlled by opposing Sp1/Sp3 inputs at a proximal GC-box and by miR-98 (PMID:23463631, PMID:29949140). Beyond bone, TXLNG improves insulin sensitivity in adipocytes by inhibiting ATF4 transcriptional activity, linking the same repressor mechanism to metabolic regulation (PMID:37028586).

Mechanistic history

Synthesis pass · year-by-year structured walk · 13 steps
  1. 2005 High

    Established that FIAT acts as a dominant-negative repressor of ATF4 by forming inactive dimers, defining a molecular brake on osteoblast activity in vivo.

    Evidence In vitro transcription/reporter assays plus transgenic osteoblast-targeted overexpression with bone densitometry and mineralization readouts

    PMID:15911876

    Open questions at the time
    • Did not map the interaction interface
    • Did not test endogenous loss-of-function
  2. 2006 Medium

    Confirmed nuclear localization and leucine-zipper-mediated ATF4 dimerization and identified αNAC as an additional FIAT partner contributing to repression.

    Evidence Immunofluorescence, co-immunoprecipitation, and luciferase reporter assays in osteoblasts

    PMID:16831913

    Open questions at the time
    • αNAC interaction mechanism not resolved
    • abstract-level detail only
  3. 2007 Medium

    Extended FIAT's repressor specificity beyond ATF4 to the AP-1 family by showing it inhibits c-Jun/Fra-1 heterodimers but not c-Jun homodimers.

    Evidence AP-1-tk-luciferase reporter assays in MC3T3-E1 osteoblastic cells

    PMID:18083929

    Open questions at the time
    • Did not map binding region for Fra-1
    • single reporter system
  4. 2008 High

    Mapped the ATF4-binding and repressor activity to the second leucine zipper (LZ2), defining the functional interaction module.

    Evidence Deletion and L-to-A site-specific mutagenesis with reporter and mineralization assays in osteoblastic cells

    PMID:18680144

    Open questions at the time
    • No structural model of the heterodimer interface
    • LZ1/LZ3 functions undefined
  5. 2009 High

    Demonstrated by loss-of-function that endogenous FIAT restrains ATF4 promoter occupancy and osteoblast differentiation, validating it as a negative regulator.

    Evidence siRNA knockdown with ChIP, reporter, endogenous gene expression, and mineralization assays

    PMID:19016261

    Open questions at the time
    • In vivo knockdown not addressed
    • effect on Fra-1 targets endogenously untested
  6. 2009 Medium

    Showed reciprocal FIAT/ATF4 protein dynamics and cell-type partitioning across osteoblastogenesis, linking FIAT downregulation to osteoblast maturation.

    Evidence Immunofluorescence, immunoblotting, RT-qPCR, ChIP, and immunohistochemistry of mouse long bones

    PMID:19232401

    Open questions at the time
    • Mechanism driving FIAT downregulation not yet defined
    • correlative in adult bone
  7. 2010 Medium

    Confirmed FIAT represses FRA-1/c-JUN heterodimer activity via LZ2 using natural target promoters, generalizing its bZIP repressor mechanism.

    Evidence Luciferase reporters on natural FRA-1 targets (Mmp-9, Mgp) with LZ2 mutagenesis in MC3T3-E1 cells

    PMID:20392257

    Open questions at the time
    • Physiological role of Fra-1 repression in bone not established
  8. 2013 High

    Defined upstream transcriptional control of Fiat by antagonistic Sp1 (activating) and Sp3 (repressing) binding at a proximal GC-box.

    Evidence EMSA, ChIP, reporter assays, siRNA knockdown, and pharmacological inhibition in osteoblasts

    PMID:23463631

    Open questions at the time
    • Signals controlling Sp1/Sp3 balance unknown
  9. 2014 High

    Established that maximal FIAT repression requires SUMOylated, HDAC2-associated αNAC bound at the target promoter, adding a co-repressor layer to the mechanism.

    Evidence In vitro SUMOylation, site-specific mutagenesis (K127, S132D), co-IP, ChIP, and reporter assays in osteoblasts/calvaria

    PMID:24375853

    Open questions at the time
    • How SUMOylation is regulated in vivo not addressed
  10. 2014 Medium

    Demonstrated in vivo genetic epistasis between Fiat and Naca, placing them in a common pathway controlling bone physiology.

    Evidence Compound heterozygous mice analyzed by microCT and RT-qPCR

    PMID:24440290

    Open questions at the time
    • Cell-type and molecular basis of cortical porosity phenotype unresolved
  11. 2017 High

    Genetic deletion confirmed FIAT as a negative regulator of bone mass in vivo and revealed an unexpected metabolic role in fat accumulation and lipid handling.

    Evidence Fiat-knockout mice with microCT, histomorphometry, biomechanics, and metabolic phenotyping on high-fat diet

    PMID:27906582

    Open questions at the time
    • Tissue source of metabolic phenotype not dissected
    • molecular link to Scd1 not mapped
  12. 2018 Medium

    Identified post-transcriptional control of FIAT by miR-98 within an Sp7-driven regulatory loop modulating osteoblast mineralization.

    Evidence miR-98 target reporter validation, EMSA, ChIP, promoter reporters, and overexpression/knockdown

    PMID:29949140

    Open questions at the time
    • Loop dynamics in vivo untested
    • abstract-level mechanistic detail
  13. 2023 Medium

    Extended the ATF4-repressor mechanism to adipocytes, showing TXLNG improves insulin sensitivity by inhibiting ATF4 transcriptional activity.

    Evidence Gain/loss-of-function in 3T3-L1 adipocytes and HFD mice with glucose uptake, GLUT4/Akt readouts, and ATF4 epistasis rescue

    PMID:37028586

    Open questions at the time
    • Direct ATF4 targets in adipocytes not mapped
    • single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unknown what signals dynamically control FIAT abundance and bZIP partner choice across tissues, and whether its repressor function operates in non-bone, non-adipose contexts.
  • No structural model of FIAT-bZIP heterodimers
  • Tissue-specific partner spectrum undefined
  • Human disease relevance not established in the corpus

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140110 transcription regulator activity 4 GO:0098772 molecular function regulator activity 3
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-74160 Gene expression (Transcription) 3 R-HSA-1266738 Developmental Biology 2 R-HSA-1430728 Metabolism 2
Partners
ATF4FOSL1HDAC2JUNNACA

Evidence

Reading pass · 13 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 FIAT (TXLNG) is a leucine zipper nuclear protein that interacts with ATF4 to form inactive dimers, preventing ATF4 from binding to DNA and blocking ATF4-mediated transcription of the osteocalcin gene in vitro. Transgenic overexpression in osteoblasts reduced osteocalcin expression, decreased bone mineral density, and reduced mineral apposition rate, demonstrating cell-autonomous decrease in osteoblast activity. In vitro transcription assay, transgenic mouse overexpression, primary osteoblast cultures (alkaline phosphatase activity, mineralization), immunodetection The Journal of cell biology High 15911876
2006 FIAT/gamma-taxilin localizes to the nucleus in osteoblasts and dimerizes with ATF4 through its leucine zipper to form inactive dimers (lacking DNA-binding basic domain), thereby inhibiting ATF4-mediated transcription. FIAT also interacts with the transcriptional co-activator alphaNAC, suggesting an additional mechanism contributing to inhibition of ATF4-dependent osteocalcin gene transcription. Subcellular localization by immunofluorescence, co-immunoprecipitation, luciferase reporter assay Annals of the New York Academy of Sciences Medium 16831913
2007 FIAT interacts with Fra-1 (but not c-Jun) and specifically inhibits transcriptional activation by a c-Jun/Fra-1 heterodimer, without affecting c-Jun homodimer-mediated transcription. This identifies Fra-1 as a second transcriptional target of FIAT repressor activity. Transient transfection with AP-1-tk-luciferase reporter in MC3T3-E1 osteoblastic cells Annals of the New York Academy of Sciences Medium 18083929
2008 FIAT interacts with ATF4 through its second leucine zipper (LZ2, amino acids 194–222). Deletion or leucine-to-alanine mutation of LZ2 (L208A/L215A/L222A) abolished FIAT-ATF4 interaction and inhibition of ATF4-mediated transcription, as well as FIAT-mediated inhibition of mineralization. Mutations in LZ1 or LZ3 did not affect these activities. Deletion mutagenesis, site-specific mutagenesis, luciferase reporter assay in MC3T3-E1 cells, mineralization assay in stably transfected osteoblastic cells Journal of cellular biochemistry High 18680144
2009 siRNA knockdown of FIAT in osteoblastic cells increased ATF4 occupancy on the osteocalcin promoter, enhanced osteocalcin reporter and endogenous gene expression, increased bone sialoprotein and type I collagen protein synthesis, and enhanced mineralization, confirming that FIAT negatively regulates ATF4 activity and osteoblast function. siRNA knockdown, chromatin immunoprecipitation (ChIP), luciferase reporter assay, immunoblotting, mineralization assay in MC3T3-E1 cells and primary osteoblasts Journal of cellular biochemistry High 19016261
2009 FIAT protein levels are inversely correlated with ATF4 protein levels during osteoblastogenesis. Decreased FIAT protein in mature osteoblasts coincides with increased ATF4 binding to the osteocalcin promoter and increased osteocalcin expression. In adult bone, FIAT is expressed in osteocytes while ATF4 is in active osteoblasts and lining cells but not osteocytes. Immunofluorescence, immunoblotting, RT-qPCR, chromatin immunoprecipitation (ChIP), immunohistochemistry of mouse long bones Gene expression patterns : GEP Medium 19232401
2010 FIAT represses transcriptional activation by a FRA-1/c-JUN heterodimer (but not c-JUN homodimer) through its second leucine zipper. Natural FRA-1 target genes Mmp-9 and Mgp were used as reporters. This confirms FRA-1 as a second transcriptional target of FIAT. Luciferase reporter assays with natural FRA-1 target promoters (Mmp-9, Mgp), mutagenesis of FIAT LZ2, transient transfection in MC3T3-E1 cells Annals of the New York Academy of Sciences Medium 20392257
2013 Sp1 and Sp3 (but not Sp7/OSTERIX) bind a canonical GC-box in the proximal Fiat promoter. Sp1 dose-dependently activates Fiat expression while both Sp3 isoforms dose-dependently repress it; Sp1 knockdown reduces and Sp3 knockdown increases endogenous FIAT expression, establishing Sp1/Sp3 interplay as a regulatory mechanism controlling Fiat gene expression in osteoblasts. EMSA, chromatin immunoprecipitation (ChIP), transient transfection luciferase reporter, siRNA knockdown, pharmacological inhibition (WP631) Journal of cellular biochemistry High 23463631
2014 SUMOylated αNAC (at K127, enhanced by phosphomimetic S132D mutation) specifically interacts with HDAC2 and potentiates FIAT-mediated transcriptional repression of the osteocalcin gene. This effect requires binding of SUMOylated αNAC to the target promoter, establishing a mechanism whereby maximal FIAT repression requires interaction with SUMOylated, HDAC2-associated αNAC. In vitro SUMOylation assay, mutagenesis (K127 and S132D), co-immunoprecipitation, luciferase reporter assay, ChIP in osteoblasts and calvarial tissue Journal of cellular biochemistry High 24375853
2014 Genetic interaction between FIAT and αNAC is demonstrated in vivo: compound Naca(+/-); Fiat(+/-) heterozygous mice show increased cortical porosity and elevated Dmp1 expression compared to single heterozygotes, confirming FIAT and αNAC act in a common genetic pathway controlling bone physiology. Compound heterozygous mouse model, microcomputed tomography (μCT), RT-qPCR Gene Medium 24440290
2017 FIAT knockout (Fiat-/Y) mice show increased trabecular and cortical bone mass with increased mineral apposition rate and osteoblast function, confirming FIAT is a negative regulator of osteoblast activity in vivo. Loss of FIAT also increased susceptibility to fat accumulation and metabolic disturbance (reduced fatty acid oxidation and lipolysis, upregulated Scd1) on high-fat diet. Fiat knockout mice, microcomputed tomography, histomorphometry, biomechanical testing, gene expression analysis, metabolic phenotyping Endocrinology High 27906582
2018 FIAT (TXLNG) is a direct target of miR-98; miR-98 overexpression reduces FIAT protein and promotes osteoblast mineralization. Sp7 promotes miR-98 transcription by binding the miR-98 promoter region, creating a miR-98/FIAT/Sp7 regulatory loop in osteoblast mineralization. Luciferase reporter assay (miR-98 target validation), EMSA, ChIP, promoter luciferase assay, overexpression and knockdown experiments European review for medical and pharmacological sciences Medium 29949140
2023 TXLNG overexpression in adipocytes reverses high-glucose/high-insulin-induced insulin resistance by restoring glucose uptake, GLUT4 surface levels, and Akt phosphorylation, and reducing IL-6 and TNF-α expression. This effect is mediated through inhibition of ATF4 transcriptional activity; ATF4 overexpression abolishes the improvements in insulin-resistant adipocyte dysfunction caused by TXLNG overexpression. TXLNG overexpression in HFD mice reduced body weight, adipose weight, adipocyte size, and pro-inflammatory markers. TXLNG overexpression and knockdown in 3T3-L1 adipocytes, HFD mouse model, glucose uptake assay, immunoblotting (GLUT4, Akt phosphorylation), RT-qPCR Molecular and cellular endocrinology Medium 37028586

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2005 FIAT represses ATF4-mediated transcription to regulate bone mass in transgenic mice. The Journal of cell biology 43 15911876
2006 Inhibition of ATF4 transcriptional activity by FIAT/gamma-taxilin modulates bone mass accrual. Annals of the New York Academy of Sciences 26 16831913
2008 FIAT represses bone matrix mineralization by interacting with ATF4 through its second leucine zipper. Journal of cellular biochemistry 13 18680144
2009 FIAT inhibition increases osteoblast activity by modulating Atf4-dependent functions. Journal of cellular biochemistry 12 19016261
2009 FIAT is co-expressed with its dimerization target ATF4 in early osteoblasts, but not in osteocytes. Gene expression patterns : GEP 12 19232401
2013 Control of Fiat (factor inhibiting ATF4-mediated transcription) expression by Sp family transcription factors in osteoblasts. Journal of cellular biochemistry 9 23463631
2014 Altered gene dosage confirms the genetic interaction between FIAT and αNAC. Gene 6 24440290
2007 Identification of additional dimerization partners of FIAT, the factor inhibiting ATF4-mediated transcription. Annals of the New York Academy of Sciences 6 18083929
2014 SUMOylated αNAC potentiates transcriptional repression by FIAT. Journal of cellular biochemistry 5 24375853
2018 Improving interpretation of publically reported statistics on health and healthcare: the Figure Interpretation Assessment Tool (FIAT-Health). Health research policy and systems 4 29514711
2010 FIAT control of osteoblast activity. Journal of cellular biochemistry 4 20013796
2010 FIAT, the factor-inhibiting ATF4-mediated transcription, also represses the transcriptional activity of the bZIP factor FRA-1. Annals of the New York Academy of Sciences 4 20392257
2023 TXLNG improves insulin resistance in obese subjects in vitro and in vivo by inhibiting ATF4 transcriptional activity. Molecular and cellular endocrinology 3 37028586
2017 FIAT Deletion Increases Bone Mass But Does Not Prevent High-Fat-Diet-Induced Metabolic Complications. Endocrinology 2 27906582
2013 Fiat lux! Phylogeny and bioinformatics shed light on GABA functions in plants. Plant signaling & behavior 2 23518583
2018 miR-98-TXLNG1 (FIAT)/Sp7 function loop mediates osteoblast mineralization. European review for medical and pharmacological sciences 1 29949140

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