Affinage

PNO1

RNA-binding protein PNO1 · UniProt Q9NRX1

Length
252 aa
Mass
27.9 kDa
Annotated
2026-04-28
23 papers in source corpus 14 papers cited in narrative 15 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PNO1 is a KH-domain RNA-binding protein essential for 18S rRNA maturation and 40S ribosomal subunit biogenesis, with additional roles in proteasome assembly and multiple oncogenic signaling pathways. In yeast and mammalian cells, PNO1 localizes to the nucleolus (via residues 92–230) and, in complex with NOB1, directs cleavage of 20S pre-rRNA to generate mature 18S rRNA; loss of PNO1 depletes 40S/60S subunits and 80S ribosomes, reduces global translation, and triggers nucleolar stress that stabilizes p53 by blocking MDM2-mediated ubiquitination (PMID:12736301, PMID:30862720, PMID:40157618). PNO1 is essential for early mammalian embryogenesis, as homozygous knockout in mice causes pre-compaction lethality (PMID:23029399). PNO1 transcription is repressed by EBF1 and activated by MYC and E2F6, while its mRNA is post-transcriptionally targeted by miR-340-5p and miR-326; PNO1 also participates in proteasome assembly, and its depletion stabilizes the CDK inhibitor p27 (PMID:30862720, PMID:35870038, PMID:39414903, PMID:32483111).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2003 High

    The fundamental question of whether PNO1/RRP20 participates in pre-rRNA processing was answered: the yeast ortholog is a nucleolar protein whose KH domain is required for early cleavage at sites A1 and A2 to produce 18S rRNA, establishing PNO1 as a core 40S biogenesis factor.

    Evidence Point mutagenesis (Gly235Asp in KH domain), northern blot, and primer extension in Saccharomyces cerevisiae

    PMID:12736301

    Open questions at the time
    • Mechanism by which PNO1 facilitates cleavage at A1/A2 was not defined
    • Direct RNA substrates not identified
    • Human ortholog function not yet tested
  2. 2004 Medium

    Mapping the nucleolar targeting determinants of human PNO1 showed that residues 92–230, rather than the KH domain itself, are required for nucleolar retention, separating RNA-binding capacity from subnuclear localization.

    Evidence GFP-tagged deletion constructs and live-cell imaging in mammalian cells

    PMID:15497447

    Open questions at the time
    • Interacting nucleolar partners responsible for retention not identified
    • Functional consequence of mislocalization not tested
  3. 2012 Medium

    Establishing in vivo essentiality, Pno1 knockout in mice caused pre-compaction embryonic lethality, demonstrating that Pno1 is indispensable for the earliest cell divisions; biochemical fractionation placed Pno1 in ~20S–26S complexes distinct from mature ribosomes or proteasomes.

    Evidence Gene-trap knockout mouse, ex vivo embryo culture, density-gradient sedimentation of tagged Pno1

    PMID:23029399

    Open questions at the time
    • Identity of the 20S–26S complexes containing Pno1 was unknown
    • Whether lethality is due to ribosome biogenesis defects specifically was not demonstrated
  4. 2019 High

    The link between PNO1's ribosome biogenesis function and tumor suppression was established: PNO1 depletion in cancer cells reduced 18S rRNA, 40S subunits, and global translation, triggering nucleolar stress that blocked MDM2-mediated p53 degradation and activated p53/p21 signaling. EBF1 was identified as a transcriptional repressor of PNO1, connecting upstream regulation to this axis.

    Evidence shRNA knockdown, ribosome profiling, p53/MDM2 western blot with p53-KO and PFT-α rescue, EBF1 overexpression with promoter-reporter assay in colorectal cancer cells and xenografts

    PMID:30862720

    Open questions at the time
    • Direct structural basis for PNO1 in 18S maturation unresolved
    • Whether p53 pathway is the sole growth-inhibitory mechanism of PNO1 loss unknown
    • EBF1 binding site on PNO1 promoter not mapped at nucleotide resolution
  5. 2020 Medium

    Post-transcriptional regulation of PNO1 was defined: miR-340-5p directly targets the PNO1 3′ UTR, and PNO1 promotes lung adenocarcinoma progression through Notch signaling and EMT, placing PNO1 downstream of a miRNA regulatory node.

    Evidence Luciferase 3′ UTR reporter assay, miRNA gain/loss-of-function rescue, Notch pathway protein analysis in lung adenocarcinoma cells

    PMID:32483111

    Open questions at the time
    • Mechanism connecting PNO1 to Notch pathway activation not defined
    • Whether Notch activation depends on PNO1's ribosome biogenesis function is unclear
  6. 2021 Medium

    A direct protein interaction between PNO1 and THBS1 was identified, with MYC driving PNO1 transcription; PNO1-THBS1 activates FAK/Akt signaling in glioma, extending PNO1's oncogenic reach beyond ribosome biogenesis.

    Evidence Co-immunoprecipitation (PNO1-THBS1), MYC promoter-reporter assay, THBS1 epistasis rescue in glioma cells and xenografts

    PMID:33664245

    Open questions at the time
    • Co-IP not validated by reciprocal pull-down or structural data
    • Whether PNO1-THBS1 interaction is direct or bridged is unresolved
    • Relevance outside glioma not tested
  7. 2022 Medium

    E2F6 was established as a transcriptional activator that directly binds the PNO1 promoter, and a circRNA/miR-377-3p/E2F6 axis was mapped as an upstream regulatory circuit controlling PNO1 levels in breast cancer.

    Evidence ChIP for E2F6 at PNO1 promoter, RIP and RNA pulldown for circRNA-miRNA interaction, epistasis rescue in triple-negative breast cancer cells

    PMID:35870038

    Open questions at the time
    • Exact E2F6 binding element not mutagenized
    • Whether E2F6-mediated PNO1 regulation operates in non-cancer contexts unknown
  8. 2024 Medium

    PNO1's role was extended to proteasome biology: PNO1 depletion suppressed proteasome activities and assembly and stabilized the CDK inhibitor p27; miR-326 was shown to directly target the PNO1 CDS to downregulate it, revealing a second post-transcriptional silencing mechanism.

    Evidence Proteasome activity assays, miR-326 luciferase CDS reporter, p27 stability assay, shRNA knockdown in colorectal cancer cells

    PMID:39414903

    Open questions at the time
    • How a ribosome biogenesis factor mechanistically promotes proteasome assembly is unknown
    • Whether proteasome defect is a direct or indirect consequence of translation impairment not resolved
  9. 2024 Medium

    Proximity proteomics defined the PNO1-NOB1 partnership in 40S maturation and identified translation initiation factors EIF4B and EIF4G2 as interaction partners, linking 18S rRNA processing to the translation machinery.

    Evidence TurboID proximity labeling/mass spectrometry, co-immunoprecipitation validation, immunofluorescence

    PMID:40157618

    Open questions at the time
    • Functional consequence of EIF4B/EIF4G2 interaction not tested
    • Structure of PNO1-NOB1 complex on pre-40S particle in human cells not determined

Open questions

Synthesis pass · forward-looking unresolved questions
  • The structural basis for PNO1's role in 18S rRNA cleavage in human cells, the mechanism by which PNO1 influences proteasome assembly, and whether PNO1's diverse oncogenic signaling outputs are all downstream of impaired ribosome biogenesis or reflect independent moonlighting functions remain unresolved.
  • No high-resolution structure of human PNO1 on a pre-40S particle
  • Proteasome assembly role lacks mechanistic reconstitution
  • Separation of ribosome-dependent versus ribosome-independent oncogenic functions not achieved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 2
Localization
GO:0005730 nucleolus 2 GO:0005634 nucleus 1
Pathway
R-HSA-392499 Metabolism of proteins 3 R-HSA-8953854 Metabolism of RNA 3 R-HSA-5357801 Programmed Cell Death 2
Partners
EIF4BEIF4G2NOB1THBS1
Complex memberships
pre-40S ribosomal subunit

Evidence

Reading pass · 15 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 The yeast ortholog of PNO1 (RRP20/Yor145c) is a nucleolar protein required for pre-18S rRNA processing; a point mutation (Gly235Asp) in its KH-type RNA-binding domain impairs early pre-rRNA cleavage at sites A1 and A2, leading to accumulation of a 22S dead-end processing product and marked deficiency in 18S rRNA production, without destabilizing U3, U14, snR10, or snR30 snoRNAs. Point mutagenesis, northern blotting, primer extension analysis, nucleolar localization confirmed; yeast genetic model Nucleic acids research High 12736301
2004 Human PNO1 protein (~35 kDa) localizes to the nucleus and specifically to nucleoli; the region of amino acids 92–230 is solely responsible for nucleolar retention, whereas the KH domain alone is not sufficient for this localization. GFP fusion protein expression and live-cell imaging of deletion constructs in mammalian cells DNA sequence : the journal of DNA sequencing and mapping Medium 15497447
2012 Mouse Pno1 is essential for early embryonic development; homozygous knockout causes lethality with arrest before the compaction stage, while heterozygous mice with ~50% Pno1 are viable and fertile. Tagged Pno1 by density-gradient fractionation exists in large complexes (sedimentation between 20S and 26S) that do not co-fractionate with 40S or 60S ribosomal subunits or mature 26S proteasomes. Gene knockout/transgenic mouse generation, ex vivo embryo development assay, density-gradient fractionation of tagged Pno1 PloS one Medium 23029399
2019 PNO1 knockdown in colorectal cancer cells (HCT116) decreases levels of 18S rRNA, 40S and 60S ribosomal subunits, and the 80S ribosome, reduces global protein synthesis, increases nucleolar stress, and thereby inhibits MDM2-mediated ubiquitination and degradation of p53, leading to p53/p21 pathway activation. shRNA knockdown, rRNA quantification, ribosome profile analysis, p53/MDM2 western blot, rescue with p53 knockout and PFT-α inhibitor Cancer research High 30862720
2019 EBF1 functions as an upstream transcription factor that suppresses PNO1 promoter activity, decreasing PNO1 mRNA and protein levels; EBF1 overexpression in colorectal cancer cells downregulates PNO1 and upregulates p53/p21, inhibiting proliferation and inducing apoptosis. Lentiviral EBF1 overexpression, PNO1 promoter-reporter assay, RT-PCR, western blot, in vitro/in vivo tumor assays Cancer research Medium 30862720
2019 PNO1 knockdown in HCC cells reduces AKT/mTOR signaling, identifying this pathway as a mediator of PNO1's oncogenic activity. shRNA knockdown, western blot for AKT/mTOR pathway components, in vitro and xenograft tumor growth assays Medical science monitor Low 31568401
2020 miR-340-5p directly binds the 3′ UTR of PNO1 mRNA to suppress PNO1 expression; PNO1 acts downstream of miR-340-5p and promotes lung adenocarcinoma progression via the Notch signaling pathway, which modulates EMT. Luciferase reporter assay (3′UTR binding), gain/loss-of-function rescue experiments, Notch pathway protein analysis Oncogenesis Medium 32483111
2020 EBF1 overexpression downregulates PNO1 transcriptional activity and protein expression, upregulates p53 and p21, and suppresses colorectal cancer cell growth, confirming EBF1→PNO1→p53/p21 axis. Lentiviral transduction, promoter activity assay, western blot, in vitro and xenograft assays Frontiers in oncology Medium 32676457
2021 PNO1 promotes HCC progression by activating the MAPK signaling pathway; PNO1 overexpression increases autophagy and inhibits apoptosis of HCC cells through this pathway. RNA-seq analysis, functional assays (overexpression/knockdown), in vitro and in vivo tumor models Cell death & disease Low 34050137
2021 PNO1 interacts with THBS1 in glioma cells and promotes tumor growth and invasion via activation of the FAK/Akt pathway; silencing THBS1 attenuates or reverses the pro-tumorigenic effects of PNO1 overexpression. MYC overexpression increases PNO1 promoter activity and drives this axis. Co-immunoprecipitation (PNO1-THBS1 interaction), MYC promoter activity assay, epistasis rescue by THBS1 silencing, in vitro/in vivo tumor assays Cell death & disease Medium 33664245
2022 PNO1 knockdown in breast cancer cells arrests the cell cycle at G2/M phase and downregulates cyclin B1 (CCNB1) and CDK1 protein expression, identifying cell cycle regulation as a downstream mechanism. Lentiviral shRNA knockdown, flow cytometry cell-cycle analysis, western blot for CCNB1/CDK1 Oncology reports Low 35445733
2022 The transcription factor E2F6 directly binds the PNO1 promoter to upregulate PNO1 expression; circ_0004676 acts as a sponge for miR-377-3p, which otherwise suppresses E2F6, thereby indirectly increasing PNO1 levels in triple-negative breast cancer. FISH, RIP, RNA pulldown, ChIP (E2F6 binding to PNO1 promoter), gain/loss-of-function rescue experiments Cell biology and toxicology Medium 35870038
2024 PNO1 knockdown in colorectal cancer cells suppresses proteasome activities and assembly, reduces CDKN1B/p27Kip1 degradation (thus stabilizing p27), and inhibits cell growth; miR-326 directly targets the CDS region of PNO1 mRNA to downregulate PNO1 protein, mimicking these effects. shRNA knockdown, proteasome activity assays, miR-326 overexpression with western blot validation, luciferase reporter for CDS binding, p27 stability assay Scientific reports Medium 39414903
2024 PNO1 collaborates with NOB1 in the maturation of the 40S ribosomal small subunit, transitioning 20S pre-rRNA into functional 18S rRNA; PNO1 and NOB1 interact with the translation-related proteins EIF4B and EIF4G2 as identified by TurboID proximity labeling and validated by co-IP. TurboID proximity labeling/mass spectrometry, co-immunoprecipitation (PNO1/NOB1 with EIF4B and EIF4G2), immunofluorescence for subcellular localization Gene Medium 40157618
2025 PNO1 promotes stemness and progression of breast cancer via activation of the NF-κB signaling pathway; JSH-23 (NF-κB inhibitor) suppresses PNO1-mediated stem-like properties. RNA-seq, sphere-formation assays, western blot, flow cytometry, pharmacological inhibition of NF-κB (JSH-23), in vitro and in vivo tumor assays Stem cells Low 40971713

Source papers

Stage 0 corpus · 23 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2019 EBF1-Mediated Upregulation of Ribosome Assembly Factor PNO1 Contributes to Cancer Progression by Negatively Regulating the p53 Signaling Pathway. Cancer research 65 30862720
2021 PNO1 regulates autophagy and apoptosis of hepatocellular carcinoma via the MAPK signaling pathway. Cell death & disease 42 34050137
2020 PNO1, which is negatively regulated by miR-340-5p, promotes lung adenocarcinoma progression through Notch signaling pathway. Oncogenesis 31 32483111
2019 Celecoxib Inhibits Hepatocellular Carcinoma Cell Growth and Migration by Targeting PNO1. Medical science monitor : international medical journal of experimental and clinical research 27 31568401
2003 RRP20, a component of the 90S preribosome, is required for pre-18S rRNA processing in Saccharomyces cerevisiae. Nucleic acids research 22 12736301
2021 MYC-mediated upregulation of PNO1 promotes glioma tumorigenesis by activating THBS1/FAK/Akt signaling. Cell death & disease 19 33664245
2019 Importance of PNO1 for growth and survival of urinary bladder carcinoma: Role in core-regulatory circuitry. Journal of cellular and molecular medicine 19 31800162
2004 Cloning and characterization in Pichia pastoris of PNO1 gene required for phosphomannosylation of N-linked oligosaccharides. Gene 18 14693378
2020 Transcription Factor EBF1 Over-Expression Suppresses Tumor Growth in vivo and in vitro via Modulation of the PNO1/p53 Pathway in Colorectal Cancer. Frontiers in oncology 14 32676457
2004 Cloning and characterization of a novel human RNA binding protein gene PNO1. DNA sequence : the journal of DNA sequencing and mapping 14 15497447
2022 Ribosome assembly factor PNO1 is associated with progression and promotes tumorigenesis in triple‑negative breast cancer. Oncology reports 12 35445733
2022 Circ_0004676 exacerbates triple-negative breast cancer progression through regulation of the miR-377-3p/E2F6/PNO1 axis. Cell biology and toxicology 11 35870038
2012 Pno1 tissue-specific expression and its functions related to the immune responses and proteasome activities. PloS one 11 23029399
2021 Knockdown of PNO1 inhibits esophageal cancer progression. Oncology reports 10 33864661
2023 Inhibition of ribosome assembly factor PNO1 by CRISPR/Cas9 technique suppresses lung adenocarcinoma and Notch pathway: Clinical application. Journal of cellular and molecular medicine 8 36625087
2023 PNO1 promotes the progression of osteosarcoma via TGF-β and YAP/TAZ pathway. Scientific reports 7 38071381
2024 Pien Tze Huang Inhibits Proliferation of Colorectal Cancer Cells through Suppressing PNO1 Expression and Activating p53/p21 Signaling Pathway. Chinese journal of integrative medicine 5 38216838
2024 Clinical significance of PNO1 as a novel biomarker and therapeutic target of hepatocellular carcinoma. Journal of cellular and molecular medicine 4 38722284
2025 PNO1 enhances ovarian cancer cell growth, invasion, and stemness via activating the AKT/Wnt/β-catenin pathway. Scientific reports 3 40113869
2024 Ribosome Biogenesis and Cancer: Insights into NOB1 and PNO1 Mechanisms. Current pharmaceutical design 1 39143880
2024 miR-326 overexpression inhibits colorectal cancer cell growth and proteasome activity by targeting PNO1: unveiling a novel therapeutic intervention strategy. Scientific reports 1 39414903
2025 The proximity proteome of pre-40S pre-ribosomal particle components PNO1 and NOB1 using turboID proximity labeling technology. Gene 0 40157618
2025 PNO1 served as a potential biomarker to promote the stemness and progression of breast cancer via the NF-κB signaling pathway. Stem cells (Dayton, Ohio) 0 40971713