Affinage

BYSL

Bystin · UniProt Q13895

Length
437 aa
Mass
49.6 kDa
Annotated
2026-06-09
16 papers in source corpus 8 papers cited in narrative 10 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

BYSL (bystin-like) is a conserved nucleolar factor for small (40S) ribosomal subunit biogenesis, acting at the earliest steps of pre-rRNA processing (PMID:12527778, PMID:17242206). Studies of the yeast ortholog Enp1 established that the protein is required for pre-rRNA cleavage at sites A0, A1, and A2 and for production of 20S pre-rRNA and 18S rRNA, and that it co-precipitates with the nucleolar protein Nop1 and with U3 and U14 snoRNAs, embedding it in the early processing machinery (PMID:12527778); the protein concentrates in the nucleus and nucleolus (PMID:9034325, PMID:12527778). The mammalian protein is likewise an integral 40S biogenesis factor whose loss disrupts subunit formation, and it localizes to the nucleolus with diffuse nucleoplasmic distribution (PMID:17242206). This essential housekeeping role is reflected developmentally: targeted disruption of mouse Bysl causes peri-implantation embryonic lethality (PMID:17055491), and Bysl knockdown arrests preimplantation embryos before blastocyst formation with defective trophectoderm differentiation (PMID:17242206). In cancer contexts BYSL is co-opted as a pro-proliferative, pro-invasive factor: it forms a complex with RIOK2 and mTOR and positively regulates AKT/mTOR signaling (PMID:33628587), drives EMT through GSK-3β/β-catenin signaling in glioblastoma (PMID:33178594), and supports proliferation and PI3K/AKT activity in AML, where it is a direct transcriptional target of c-MYC (PMID:41854887). BYSL expression is additionally controlled post-transcriptionally by direct binding of miR-378a-3p to its 3'-UTR (PMID:35154253).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1997 Medium

    Establishing where the protein acts: the yeast ortholog Enp1 was localized to the nucleus, providing the first subcellular framing for its function.

    Evidence Immunohistochemistry of a c-myc-tagged Enp1 fusion in yeast

    PMID:9034325

    Open questions at the time
    • Localization based on a tagged construct in a single study
    • No molecular function assigned at this stage
    • Nucleolar versus broader nuclear residence not resolved
  2. 2003 High

    Defining molecular function: Enp1 was shown to be required for early pre-rRNA processing and to physically associate with the snoRNP machinery, placing it directly in 40S subunit biogenesis.

    Evidence Northern blot and pulse-chase of rRNA precursors in temperature-sensitive enp1-1 mutant plus co-precipitation with Nop1 and U3/U14 snoRNAs; nucleolar localization inferred

    PMID:12527778

    Open questions at the time
    • Whether the association with snoRNAs is direct or indirect not resolved
    • Stoichiometry and structural arrangement within the processing complex unknown
    • Demonstrated in yeast; conservation to mammals not yet tested
  3. 2006 High

    Testing organismal requirement: mouse Bysl knockout established that the gene is essential, with embryonic lethality shortly after implantation.

    Evidence Targeted gene disruption in mouse with immunolocalization in peri-implantation tissues

    PMID:17055491

    Open questions at the time
    • Knockout phenotype not yet mechanistically tied to ribosome biogenesis defect
    • Cell-type-specific contributions not dissected
  4. 2007 High

    Connecting mammalian function and development: mammalian Bysl was confirmed as an integral 40S biogenesis factor, and its knockdown blocked preimplantation development at trophectoderm differentiation, linking ribosome biogenesis to a specific developmental transition.

    Evidence siRNA, dominant-negative mutants, fluorescent tagging, and 40S biogenesis assays in cells; siRNA injection and developmental staging in mouse embryos

    PMID:17242206

    Open questions at the time
    • Precise biochemical step catalyzed by mammalian Bysl not defined
    • Whether trophectoderm defect is solely a consequence of impaired ribosome biogenesis not established
  5. 2020 Medium

    Identifying a disease-context signaling role: BYSL was shown to promote glioblastoma migration, invasion, and EMT via GSK-3β/β-catenin signaling.

    Evidence siRNA/overexpression in GBM cell lines, EMT-marker Western blots, pharmacological GSK-3β inhibition, nuclear fractionation, and immunohistochemistry

    PMID:33178594

    Open questions at the time
    • Pathway placement relies on a pharmacological inhibitor
    • Direct molecular link between BYSL and GSK-3β not demonstrated
    • Single lab, single tumor type
  6. 2021 Medium

    Defining a physical signaling partner: BYSL was found to complex with RIOK2 and mTOR and to positively regulate AKT/mTOR signaling in glioma.

    Evidence Reciprocal Co-IP, double immunofluorescence co-localization, AKT/mTOR Western blots, overexpression/knockdown, and orthotopic xenograft

    PMID:33628587

    Open questions at the time
    • Direct binary interactions within the BYSL–RIOK2–mTOR complex not resolved
    • Relationship between this signaling role and the canonical ribosome biogenesis role unclear
    • Single lab
  7. 2022 Medium

    Establishing post-transcriptional control: miR-378a-3p was shown to directly target the BYSL 3'-UTR, and BYSL was linked to Nrf2 induction under hypoxia.

    Evidence Dual-luciferase reporter and rescue assays with Western blot in osteosarcoma cells

    PMID:35154253

    Open questions at the time
    • Mechanism linking BYSL to Nrf2 not defined
    • Single lab, single cancer type
  8. 2026 Medium

    Identifying transcriptional control and a proliferative requirement: c-MYC was shown to directly bind the BYSL promoter, and BYSL suppression caused G0/G1 arrest and reduced PI3K/AKT phosphorylation in AML.

    Evidence shRNA knockdown, ChIP-qPCR, cell cycle and colony-formation assays, and PI3K/AKT Western blots in AML cell lines

    PMID:41854887

    Open questions at the time
    • Whether PI3K/AKT changes are direct or secondary to reduced ribosome biogenesis not resolved
    • Single study

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the conserved nucleolar 40S-biogenesis function mechanistically connects to the AKT/mTOR, GSK-3β/β-catenin, and c-MYC signaling roles reported in cancer remains unresolved.
  • No structural model of BYSL within the pre-rRNA processing machinery in the corpus
  • Direct binding partners of mammalian BYSL during ribosome biogenesis not enumerated
  • Causal ordering between ribosome biogenesis defects and signaling outputs not established

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 1
Localization
GO:0005634 nucleus 2 GO:0005730 nucleolus 2
Pathway
R-HSA-162582 Signal Transduction 2 R-HSA-8953854 Metabolism of RNA 2
Partners
MTORNOP1RIOK2
Complex memberships
mTORC2

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Yeast Enp1 protein (ortholog of human BYSL) is localized to the nucleus, as demonstrated by immunohistochemical studies using a c-myc-tagged fusion construct. Immunohistochemistry with epitope-tagged protein (c-myc fusion) Gene Medium 9034325
2003 Yeast Enp1 is required for early pre-rRNA processing at sites A0, A1, and A2, and for synthesis of 20S pre-rRNA and 18S rRNA, leading to reduced 40S ribosomal subunit formation. Enp1 co-precipitates with Nop1 protein and with U3 and U14 snoRNAs, placing it in the early pre-rRNA processing machinery. Northern blot analysis of rRNA precursors in temperature-sensitive enp1-1 mutant; pulse-chase analysis; co-precipitation assay Nucleic acids research High 12527778
2003 Yeast Enp1 is concentrated in the nucleolus, consistent with its role in ribosome biogenesis. Subcellular localization by co-precipitation and inferred from nucleolar protein Nop1 association Nucleic acids research Medium 12527778
2006 Targeted disruption of the mouse Bysl gene results in embryonic lethality shortly after implantation, establishing that bystin is essential for post-implantation mouse embryo survival. Bystin expression was detected in uterine epithelia at peri-implantation stages and in blastocysts. Gene knockout (targeted disruption) in mouse; immunolocalization FEBS letters High 17055491
2007 Mammalian Bysl (bystin-like) is an integral factor for 40S ribosomal subunit biogenesis. Loss of Bysl function via siRNA or dominant-negative mutants caused defects in 40S ribosomal subunit biogenesis. Exogenously expressed Bysl is concentrated in the nucleolus with diffuse nucleoplasmic distribution. siRNA knockdown; dominant-negative mutants; fluorescent protein tagging and live-cell imaging; 40S subunit biogenesis assay Molecular and cellular biology High 17242206
2007 Bysl siRNA knockdown in mouse preimplantation embryos arrests development just prior to blastocyst formation, resulting in a defect in trophectoderm differentiation, establishing Bysl as essential for this developmental transition. siRNA injection into embryos; developmental staging Molecular and cellular biology High 17242206
2020 BYSL promotes glioblastoma cell migration, invasion, and epithelial-mesenchymal transition (EMT) via the GSK-3β/β-catenin signaling pathway. BYSL overexpression increased phosphorylation of GSK-3β and nuclear distribution of β-catenin; GSK-3β inhibition partially reversed the effects of BYSL downregulation on β-catenin transcriptional activity and EMT markers. siRNA knockdown and overexpression in GBM cell lines; Western blot for EMT markers (β-catenin, N-cadherin, E-cadherin); pharmacological inhibition of GSK-3β (1-Azakenpaullone); nuclear fractionation; immunohistochemistry Frontiers in oncology Medium 33178594
2021 BYSL forms a complex with RIOK2 and mTOR (mTORC2 complex components), and co-localizes with RIOK2 in glioma cells. Overexpression of BYSL or RIOK2 increased AKT/mTOR signaling activity, while knockdown decreased it, placing BYSL as a positive regulator of AKT/mTOR signaling through its association with RIOK2 and mTOR. Co-immunoprecipitation; double immunofluorescence co-localization; Western blot for AKT/mTOR signaling; overexpression and siRNA knockdown; orthotopic xenograft model Cancer biology & medicine Medium 33628587
2022 miR-378a-3p directly binds to the 3'-UTR of BYSL mRNA and suppresses BYSL expression, establishing BYSL as a direct target of miR-378a-3p. BYSL upregulation under hypoxia enhanced Nrf2 expression in osteosarcoma cells. Dual-luciferase reporter assay; rescue assay; Western blot Frontiers in genetics Medium 35154253
2026 BYSL knockdown in AML cell lines inhibits cell proliferation, reduces colony-forming ability, and induces G0/G1 cell cycle arrest. Mechanistically, BYSL suppression decreases PI3K and AKT phosphorylation. ChIP-qPCR confirmed that c-MYC directly binds to the BYSL promoter, establishing BYSL as a transcriptional target of c-MYC. shRNA knockdown in AML cell lines; Western blot for PI3K/AKT phosphorylation; ChIP-qPCR; cell cycle analysis; colony formation assay Clinical and experimental medicine Medium 41854887

Source papers

Stage 0 corpus · 16 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2007 EnP1, a microsporidian spore wall protein that enables spores to adhere to and infect host cells in vitro. Eukaryotic cell 80 17557882
2005 EnP1 and EnP2, two proteins associated with the Encephalitozoon cuniculi endospore, the chitin-rich inner layer of the microsporidian spore wall. International journal for parasitology 54 16368098
2003 Enp1, a yeast protein associated with U3 and U14 snoRNAs, is required for pre-rRNA processing and 40S subunit synthesis. Nucleic acids research 53 12527778
2005 Identification of CCND3 and BYSL as candidate targets for the 6p21 amplification in diffuse large B-cell lymphoma. Clinical cancer research : an official journal of the American Association for Cancer Research 36 16322284
2007 Crucial role of Bysl in mammalian preimplantation development as an integral factor for 40S ribosome biogenesis. Molecular and cellular biology 28 17242206
2021 BYSL contributes to tumor growth by cooperating with the mTORC2 complex in gliomas. Cancer biology & medicine 27 33628587
2020 BYSL Promotes Glioblastoma Cell Migration, Invasion, and Mesenchymal Transition Through the GSK-3β/β-Catenin Signaling Pathway. Frontiers in oncology 27 33178594
1997 ENP1, an essential gene encoding a nuclear protein that is highly conserved from yeast to humans. Gene 24 9034325
2006 The Bysl gene product, bystin, is essential for survival of mouse embryos. FEBS letters 12 17055491
2021 DDX10 and BYSL as the potential targets of chondrosarcoma and glioma. Medicine 9 34797290
2024 Microsporidian EnP1 alters host cell H2B monoubiquitination and prevents ferroptosis facilitating microsporidia survival. Proceedings of the National Academy of Sciences of the United States of America 8 39141344
2022 Hypoxia-Induced miR-378a-3p Inhibits Osteosarcoma Invasion and Epithelial-to-Mesenchymal Transition via BYSL Regulation. Frontiers in genetics 8 35154253
2018 Bystin (BYSL) as a possible marker of severe hypoxic-ischemic changes in neuropathological examination of forensic cases. Forensic science, medicine, and pathology 6 29349722
2023 Sarcomatoid renal cell tumor harboring a novel BYSL::TFEB fusion with concurrent TFEB amplification. Genes, chromosomes & cancer 3 36704911
2026 EnP1 exploits H2Aub-dependent epigenetic reprogramming to promote microsporidia proliferation in host cells. PLoS pathogens 1 41499632
2026 Investigation of the expression and potential mechanistic role of BYSL in acute myeloid leukemia. Clinical and experimental medicine 0 41854887

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