Affinage

NHP2

H/ACA ribonucleoprotein complex subunit 2 · UniProt Q9NX24

Length
153 aa
Mass
17.2 kDa
Annotated
2026-06-10
17 papers in source corpus 12 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NHP2 is an essential, evolutionarily conserved core protein of H/ACA small nucleolar ribonucleoprotein (snoRNP) complexes that couples ribosomal RNA pseudouridylation to telomerase RNA maintenance (PMID:11074001, PMID:2063628). In human cells it co-assembles with GAR1, dyskerin/NOP10, and H/ACA RNAs, including the H/ACA-like 3' domain of the telomerase RNA hTR/TERC, and localizes to the dense fibrillar component of the nucleolus and to Cajal bodies (PMID:11074001). Assembly of the catalytic pre-RNP depends critically on the NHP2–NOP10 interaction and on the integrity of the NHP2 N-terminal domain: disease-associated mutations (V126M, Y139H) disrupt NOP10 binding and abolish pre-RNP formation, while N-terminal variants (A39T, T44M) prevent incorporation into the H/ACA complex and trigger proteasomal degradation of the misfolded protein (PMID:20008900, PMID:37440454). Functionally, NHP2 is required for accumulation and stabilization of TERC—a requirement not shared by GAR1—and its loss reduces telomerase activity and impairs rRNA biogenesis, consistent with dyskeratosis congenita–type pathology arising from biallelic NHP2 mutations (PMID:18523010, PMID:31985013, PMID:37440454). Beyond canonical snoRNP function, NHP2 acts as a chromatin reader of the rDNA histone mark H2AQ105 methylation, bridging rDNA chromatin to the small-subunit processome to coordinate rRNA transcription with processing (PMID:34409714), and in ALT-positive cancer cells its downregulation restrains the DNA damage response at telomeres by limiting 53BP1 recruitment (PMID:33595114).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1991 High

    Established that NHP2 is an essential gene, fixing it as a core requirement for cell proliferation before any molecular role was defined.

    Evidence Gene deletion and spore dissection in S. cerevisiae

    PMID:2063628

    Open questions at the time
    • Molecular function undefined
    • No biochemical partners identified
    • Cause of proliferation arrest unknown
  2. 1999 Medium

    Located NHP2 to the nucleolus throughout the cell cycle, tying its essential role to a stable nucleolar/rDNA-associated activity.

    Evidence Yeast complementation and live-cell GFP imaging in fission and budding yeast

    PMID:10502409

    Open questions at the time
    • Did not define the molecular complex
    • No link to a specific RNA substrate
    • Single lab
  3. 2000 High

    Defined NHP2 as a core H/ACA snoRNP subunit that also associates with telomerase RNA, unifying rRNA modification and telomerase biology under one protein.

    Evidence Co-IP with GAR1/H/ACA RNAs/hTR, yeast complementation, and immunofluorescence in HeLa cells

    PMID:11074001

    Open questions at the time
    • Did not establish whether NHP2 stabilizes hTR or merely co-purifies
    • Stoichiometry/architecture of the complex unresolved
    • Direct vs indirect RNA contacts undefined
  4. 2008 High

    Showed NHP2 is specifically required for TERC accumulation whereas GAR1 is not, dissociating telomerase RNA stabilization from general H/ACA function.

    Evidence siRNA knockdown of NHP2 vs GAR1 with TERC quantification in human cells

    PMID:18523010

    Open questions at the time
    • Mechanism of TERC stabilization not resolved
    • Did not test rRNA pseudouridylation consequences
    • No structural basis
  5. 2009 High

    Mapped disease mutations to the NHP2–NOP10 interface, establishing that this interaction is the assembly-critical step for H/ACA pre-RNP formation.

    Evidence In vivo pre-RNP assembly and co-IP of NHP2 V126M/Y139H mutants with NOP10 and H/ACA RNAs

    PMID:20008900

    Open questions at the time
    • Atomic structure of interface not determined
    • Did not measure downstream pseudouridylation activity directly
    • Patient phenotype-to-assembly correlation incomplete
  6. 2020 Medium

    Demonstrated in patient cells that NHP2 loss impairs rRNA biogenesis, extending its disease-relevant role beyond telomere maintenance.

    Evidence rRNA biogenesis assays in patient-derived cells with biallelic NHP2 mutations

    PMID:31985013

    Open questions at the time
    • Specific pseudouridylation defects not enumerated
    • Single lab
    • Relative contribution of rRNA vs telomere defects to disease unclear
  7. 2020 Medium

    Identified a physical NHP2–TERT interaction supporting telomerase activity, implicating NHP2 in tumor growth.

    Evidence Co-IP, shRNA knockdown, telomerase activity assay, and xenograft in hepatocellular carcinoma cells

    PMID:33044946

    Open questions at the time
    • Directness of NHP2–TERT contact vs RNA-mediated bridging unresolved
    • Single lab
    • Whether effect is general across cancers untested
  8. 2021 Medium

    Revealed a chromatin-reader role: NHP2 binds the rDNA mark H2AQ105me to bridge rDNA chromatin to the SSU processome, coupling rRNA transcription to processing.

    Evidence Proteomic identification of NHP2 as H2AQ105me reader plus chromatin-binding and H2AQ105A mutant rRNA processing assays in yeast

    PMID:34409714

    Open questions at the time
    • Reader function not validated in human cells
    • Structural basis of mark recognition unknown
    • Mild mutant phenotype leaves magnitude of effect uncertain
  9. 2021 Medium

    Uncovered a non-canonical role at ALT telomeres where NHP2 downregulation restrains the DNA damage response by limiting 53BP1 recruitment, independent of hTR's RPA function.

    Evidence NHP2 manipulation in ALT+ cancer cells with 53BP1/p-RPA(S33) foci quantification and hTR epistasis

    PMID:33595114

    Open questions at the time
    • Mechanism linking NHP2 to 53BP1 recruitment undefined
    • Single lab
    • Generality beyond ALT context untested
  10. 2023 Medium

    Showed that N-terminal NHP2 variants block complex incorporation and are cleared by the proteasome, mechanistically explaining how N-terminal mutations destabilize the protein and reduce telomerase activity.

    Evidence Variant expression with co-IP incorporation assays, proteasome inhibition, N-terminal deletion constructs, hTR/telomerase assays, and RoseTTAFold/MD simulation in human cells

    PMID:37440454

    Open questions at the time
    • Structural inference is computational, not experimental
    • Single lab
    • Degradation pathway components not identified
  11. 2025 Medium

    Provided structural insight into NHP2 within a catalytically active H/ACA snoRNP, showing it participates in inter-protomer conformational changes that may gate pseudouridylation.

    Evidence Cryo-EM structures and interface-mutation pseudouridylation assays of an insect H/ACA snoRNP (preprint)

    PMID:bio_10.1101_2025.06.07.658439

    Open questions at the time
    • Preprint, not peer-reviewed
    • Insect rather than human complex
    • Functional consequence of the conformational switch not validated in cells

Open questions

Synthesis pass · forward-looking unresolved questions
  • How NHP2's chromatin-reader and ALT-telomere DDR roles mechanistically integrate with its canonical H/ACA snoRNP function in human cells remains unresolved.
  • Human H2AQ105me reader activity unconfirmed
  • Mechanism of NHP2-dependent 53BP1 recruitment unknown
  • No high-resolution mammalian snoRNP structure linking assembly to catalysis

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003723 RNA binding 3 GO:0005198 structural molecule activity 3 GO:0042393 histone binding 1 GO:0060090 molecular adaptor activity 1
Localization
GO:0005730 nucleolus 3
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-1852241 Organelle biogenesis and maintenance 2
Partners
DKC1GAR1NOP10TERCTERT
Complex memberships
H/ACA snoRNPtelomerase holoenzyme

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 Human NHP2 (hNHP2) is a core protein component of H/ACA snoRNP complexes; epitope-tagged hNHP2 co-immunoprecipitates with hGAR1, H/ACA RNAs, and the RNA subunit of telomerase (hTR, which contains an H/ACA-like domain in its 3' moiety) in HeLa cell extracts. hNHP2 also functionally complements yeast cells depleted of Nhp2p. Immunofluorescence showed hNHP2 localizes to the dense fibrillar component of the nucleolus and Cajal bodies. Immunoprecipitation from transfected HeLa cell extracts; yeast complementation assay; immunofluorescence microscopy Molecular and cellular biology High 11074001
1991 NHP2 in S. cerevisiae encodes an essential 17.1 kDa basic nuclear protein; deletion of one NHP2 copy in diploid yeast followed by sporulation showed that spores lacking NHP2 germinate but form only microcolonies of 12–40 cells, demonstrating NHP2 is essential for normal cell proliferation. Gene deletion / spore dissection in S. cerevisiae; S1 nuclease mapping Yeast (Chichester, England) High 2063628
1999 Fission yeast p17(nhp2) is a nucleolar protein that functionally complements deletion of S. cerevisiae NHP2 and remains associated with nucleolar material throughout the mitotic cell cycle, including during anaphase, suggesting H/ACA snoRNPs are continuously nucleolus-associated during cell division. In S. cerevisiae, Nhp2 co-segregates with bulk chromatin/rDNA during nuclear division. Yeast complementation; live-cell fluorescence microscopy of GFP-tagged Nhp2 through the cell cycle Experimental cell research Medium 10502409
2008 siRNA-mediated knockdown of NHP2 in human cells reduces TERC (telomerase RNA) levels, demonstrating NHP2 is required for TERC accumulation/stability. In contrast, GAR1 knockdown did not reduce TERC levels, establishing a functional difference between these two H/ACA complex components with respect to telomerase RNA stabilization. siRNA knockdown in human cells followed by quantification of TERC levels Proceedings of the National Academy of Sciences of the United States of America High 18523010
2009 Disease-associated NHP2 mutations V126M and Y139H impair NHP2's association with NOP10, causing major pre-RNP assembly defects with all H/ACA RNAs tested, including the H/ACA domain of hTR. This establishes that the NHP2–NOP10 interaction is critical for H/ACA pre-RNP formation. The most prevalent dyskerin DC mutation (A353V) did not affect NAF1-dyskerin-NOP10-NHP2 tetramer formation but slightly reduced assembly with the H/ACA-like domain of hTR. In vivo pre-RNP assembly assays with wild-type and mutant proteins; co-immunoprecipitation of NHP2 mutants with NOP10 and H/ACA RNAs Human molecular genetics High 20008900
2020 Functional deficit of human NHP2 (demonstrated using patient-derived cells with biallelic NHP2 mutations) affects ribosomal RNA (rRNA) biogenesis in addition to telomere maintenance, extending the known molecular consequences of NHP2 loss beyond TERC stabilization. Analysis of patient cells with NHP2 mutations; rRNA biogenesis assays Human molecular genetics Medium 31985013
2021 In ALT-positive cancer cells that retain hTR expression, NHP2 H/ACA ribonucleoprotein levels are downregulated, and this downregulation restrains DNA damage response (DDR) activation at ALT telomeres by reducing 53BP1 recruitment. This role of NHP2 is mechanistically independent from hTR's non-canonical function in modulating telomeric p-RPA(S33). NHP2 knockdown/manipulation in ALT+ cancer cells; 53BP1 and p-RPA(S33) foci quantification at telomeres; epistasis with hTR expression The EMBO journal Medium 33595114
2021 Nhp2 (yeast) functions as a reader of the histone modification H2AQ105 methylation (H2AQ105me) at the rDNA locus, and acts as an adapter bridging rDNA chromatin with components of the small subunit processome to coordinate rRNA transcription with post-transcriptional processing. Nhp2 binding to H2AQ105me depends on a functional mTOR signaling pathway and H3K56 acetylation. An H2AQ105A mutant shows a mild defect in early rRNA processing. Functional and proteomic data; identification of Nhp2 as H2AQ105me reader; chromatin-binding assays; H2AQ105A mutant rRNA processing analysis EMBO reports Medium 34409714
2023 Novel NHP2 variants A39T and T44M fail to be incorporated into the H/ACA RNA-binding complex when competing with wild-type NHP2, and misincorporated variants undergo proteasomal degradation. Molecular dynamics simulations (RoseTTAFold) reveal that A39T causes distortion of residues 33–41 and T44M causes high flexibility of the N-terminal region (residues 1–24); deletion of aa 2–24 reduces NHP2 levels only in presence of wild-type NHP2, while deletion of aa 2–38 completely disrupts stability. Both variants reduce hTR levels and telomerase activity. Expression of NHP2 variants in cells; co-immunoprecipitation to assess complex incorporation; proteasome inhibitor assays; hTR quantification; telomerase activity assay; RoseTTAFold structural prediction + molecular dynamics simulations; N-terminal deletion constructs Human molecular genetics Medium 37440454
2020 NHP2 physically interacts with TERT (telomerase reverse transcriptase) in hepatocellular carcinoma cells, and NHP2 knockdown reduces telomerase activity and TERT protein levels, as well as inhibiting tumor growth in a xenograft model. Co-immunoprecipitation of NHP2 and TERT; shRNA knockdown; telomerase activity assay; xenograft mouse model Aging Medium 33044946
2025 Cryo-EM structures of catalytically active insect H/ACA snoRNPs reveal Nhp2 participates in an asymmetric dimeric complex of two protomers on a two-hairpin H/ACA snoRNA. Coordinated structural changes between Nop10, Nhp2 and the N-terminal extensions of Cbf5 (dyskerin ortholog) in the 3' protomer resemble active and inactive conformations that may regulate pseudouridylation activity. Several DC-associated mutations in H/ACA proteins (including Nhp2 sites) directly impair pseudouridine formation. Cryo-EM structure determination; biochemical characterization of inter-protomer interface mutations; pseudouridylation activity assays bioRxiv (preprint)preprint Medium bio_10.1101_2025.06.07.658439
2018 In Drosophila ovary germline, NHP2 protein is concentrated in nucleoli and its expression decreases abruptly during cyst progression from 2-cell to 4-cell stage. NHP2 knockdown in the germline causes accumulation of 4- and 8-cell cysts and impairs transition to 16-cell cysts, demonstrating a role in controlling germline cell division progression. Sex-lethal (Sxl) protein physically interacts with NHP2 mRNA, suggesting post-transcriptional regulation of NHP2 by Sxl to control cyst formation. NHP2 knockdown (RNAi) in Drosophila germline; immunofluorescence for NHP2 protein localization; RNA immunoprecipitation of Sxl-NHP2 mRNA interaction; cyst staging phenotypic analysis Development, growth & differentiation Medium 29845608

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2008 Mutations in the telomerase component NHP2 cause the premature ageing syndrome dyskeratosis congenita. Proceedings of the National Academy of Sciences of the United States of America 255 18523010
2000 Human H/ACA small nucleolar RNPs and telomerase share evolutionarily conserved proteins NHP2 and NOP10. Molecular and cellular biology 187 11074001
2009 Effects of dyskeratosis congenita mutations in dyskerin, NHP2 and NOP10 on assembly of H/ACA pre-RNPs. Human molecular genetics 49 20008900
2020 NHP2 deficiency impairs rRNA biogenesis and causes pulmonary fibrosis and Høyeraal-Hreidarsson syndrome. Human molecular genetics 47 31985013
1991 Sequence and genetic analysis of NHP2: a moderately abundant high mobility group-like nuclear protein with an essential function in Saccharomyces cerevisiae. Yeast (Chichester, England) 28 2063628
1996 Cloning and mapping of a human novel cDNA (NHP2L1) that encodes a protein highly homologous to yeast nuclear protein NHP2. Cytogenetics and cell genetics 17 8978773
2005 [The NOLA2 and RPS3A genes as highly informative markers for human squamous cell lung cancer]. Bioorganicheskaia khimiia 16 15889794
2021 NHP2 downregulation counteracts hTR-mediated activation of the DNA damage response at ALT telomeres. The EMBO journal 14 33595114
1999 Functional conservation and cell cycle localization of the Nhp2 core component of H + ACA snoRNPs in fission and budding yeasts. Experimental cell research 13 10502409
2018 Long-Term Follow-Up of a Case with Dyskeratosis Congenita Caused by NHP2-V126M/X154R Mutation: Genotype-Phenotype Association. Acta haematologica 10 30472699
2023 Novel pathological variants of NHP2 affect N-terminal domain flexibility, protein stability, H/ACA Ribonucleoprotein (RNP) complex formation and telomerase activity. Human molecular genetics 9 37440454
2021 Nhp2 is a reader of H2AQ105me and part of a network integrating metabolism with rRNA synthesis. EMBO reports 8 34409714
2020 Knockdown of NHP2 inhibits hepatitis B virus X protein-induced hepatocarcinogenesis via repressing TERT expression and disrupting the stability of telomerase complex. Aging 7 33044946
2018 Downregulation of NHP2 promotes proper cyst formation in Drosophila ovary. Development, growth & differentiation 7 29845608
2002 Expression of the human homologue of the small nucleolar RNA-binding protein NHP2 gene during monocytic differentiation of U937 cells. Biochimica et biophysica acta 5 12020816
2024 Siblings with a Homozygous Variant in the NHP2 Gene: A Case Report and Review of Literature. Molecular syndromology 1 40352450
2025 Single-cell transcriptomics reveals that RNA pseudouridylation-related gene NHP2 promotes the progression of uveal melanoma and validated in vivo and in vitro. Experimental eye research 0 40812391

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