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Cited by 26Nuclear Structure and FunctionDNA Repair MechanismsEffects of Radiation Exposure

UV-Induced Nuclear Import of XPA Is Mediated by Importin-α4 in An ATR-Dependent Manner

Open access
Li, Zhengke, Musich, Phillip R., Cartwright, Brian M., Wang, Hui, Zou, Yue·2013·PLoS ONE
DOI 10.1371/journal.pone.0068297PMC PMC3704644
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Abstract

Xeroderma pigmentosum Group A (XPA) is a crucial factor in mammalian nucleotide excision repair (NER) and nuclear import of XPA from the cytoplasm for NER is regulated in cellular DNA damage responses in S-phase. In this study, experiments were carried out to determine the transport mechanisms that are responsible for the UV (ultraviolet)-induced nuclear import of XPA. We found that, in addition to the nuclear localization signal (NLS) of XPA, importin-α4 or/and importin-α7 are required for the XPA nuclear import. Further investigation indicated that, importin-α4 and importin-α7 directly interacted with XPA in cells. Interestingly, the binding of importin-α4 to XPA was dependent on UV-irradiation, while the binding of importin-α7 was not, suggesting a role for importin-α7 in nuclear translocation of XPA in the absence of DNA damage, perhaps with specificity to certain non-S-phases of the cell-cycle. Consistent with the previous report of a dependence of UV-induced XPA nuclear import on ataxia telangiectasia and Rad3-related protein (ATR) in S-phase, knockdown of ATR reduced the amount of XPA interacting with importin-α4. In contrast, the GTPase XPA binding protein 1 (XAB1), previously proposed to be required for XPA nuclear import, showed no effect on the nuclear import of XPA in our siRNA knockdown analysis. In conclusion, our results suggest that upon DNA damage transport adaptor importin-α4 imports XPA into the nucleus in an ATR-dependent manner, while XAB1 has no role in this process. In addition, these findings reveal a potential new therapeutic target for the sensitization of cancer cells to chemotherapy.

AI snapshot

Written from the paper’s full text.

TL;DR

UV-induced nuclear import of XPA requires its N-terminal NLS and is mediated by importin-α4 in an ATR-dependent manner. Importin-α7 also interacts with XPA, likely for DNA-damage-independent nuclear import, while XAB1 is dispensable for UV-induced XPA import.

Key findings

  • XPA nuclear import after UV-C (20 J/m²) depended on an intact N-terminal NLS; mutating Q33/R34 to alanine (XPA-ΔNLS) prevented nuclear accumulation even after UV.
  • siRNA knockdown of importin-α4 and/or importin-α7 inhibited UV-induced XPA nuclear import, whereas knockdown of importins-α1, -α3, or -α5 did not.
  • Importin-α4 and importin-α7 directly interacted with XPA in vitro; endogenous XPA–importin-α4 binding was UV-induced, while XPA–importin-α7 binding occurred without UV. ATR knockdown reduced XPA interaction with importin-α4.
  • XAB1 knockdown had no effect on UV-induced XPA nuclear import, contrary to its prior proposed role; the paper reports a 2.8-fold average increase in XPA–importin-α4 interaction after UV irradiation in at least three independent experiments.

Methods

  • Cell lines: H1299 for most experiments, A549 for ATR-dependence studies, and GM04429 (XPA−/−) for XPA-free extracts; cells were mock- or UV-C-irradiated (254 nm, 20 J/m²) with recovery times including 0.5 or 2 h.
  • Approaches: siRNA knockdown of importin-α isoforms, ATR, and XAB1; subcellular fractionation with western blotting; co-immunoprecipitation; in vitro protein–protein interaction assays with recombinant XPA; and immunofluorescence microscopy.
  • Main analysis: cytoplasmic-to-nuclear XPA distribution was assessed by western blot and reported as cXPA/nXPA ratios; protein interactions were assessed by co-immunoprecipitation and pull-down.

Limitations

  • Stated: the identity of cytoplasmic factors that may mask the XPA NLS and regulate XPA–importin-α4 binding was beyond the scope and merits future investigation; the XAB1 discrepancy may reflect differences between human cells and the yeast two-hybrid system.
  • Stated: XPA localization is cell-cycle-dependent, and unsynchronized populations contain only about 15–20% G2 cells; fixation method can affect anti-XPA immunofluorescence patterns, and basal nuclear XPA may vary between experiments.
  • Evident: most mechanistic work used H1299 cells, with ATR-dependence tested in A549 cells; the study relies on siRNA knockdown rather than knockout or in vivo models, and importin-β is not shown in the proposed model.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1371/journal.pone.0068297

Cites

52 of 52 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 76 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    Without UV, siRNA-knockdown of importin α4 has no effect on XPA subcellular localization.

    “without UV the siRNA-knockdown of importin α4 had no effect on XPA subcellular localization”
    Quote in the paperSubstantial claim
  • Findingown data

    Recombinant wild-type XPA accumulates in the nucleus after UV-irradiation.

    “the recombinant wild-type XPA also accumulated in the nucleus”
    Quote in the paperSubstantial claim
  • Findingown data

    Replacing the two last amino acids of the XPA NLS with alanine (XPA-ΔNLS) prevents nuclear accumulation of the mutated XPA protein even after UV-irradiation.

    “no mutated XPA protein (His-V5-XPA) was detected in the nuclear fractions of these mutated transfectants even after UV-irradiation.”
    • Also stated in: § The N-terminal NLS of XPA is Required for UV-induced Nuclear Import · plain
      “XPA-ΔNLS remained in the cytoplasm even after the cells were irradiated with UV, while the wild-type XPA accumulated normally in the nucleus”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The XPA-ΔNLS mutant is properly folded and functional except for the NLS, so its failure to enter the nucleus reflects loss of NLS-dependent import rather than misfolding or other defects.
  • Findingown data

    The N-terminal NLS-like motif of XPA is required for UV-induced nuclear import of XPA.

    “These results suggest a dependence of the DNA damage-induced XPA nuclear import on the protein’s NLS motif.”
    • Also stated in: § The N-terminal NLS of XPA is Required for UV-induced Nuclear Import · plain
      “no mutated XPA protein (His-V5-XPA) was detected in the nuclear fractions of these mutated transfectants even after UV-irradiation.”
    • Also stated in: § The N-terminal NLS of XPA is Required for UV-induced Nuclear Import · plain
      “XPA-ΔNLS remained in the cytoplasm even after the cells were irradiated with UV, while the wild-type XPA accumulated normally in the nucleus”
    Quote in the paperSubstantial claim
  • Findingown data

    XPA interacts preferentially with importin-α4 and importin-α7 over importin-α1 and importin-α5.

    “probing the same blot with importin-α1 and importin-α5 antibodies showed no bands in the Western blotting (Figure 3B), indicating the preferred interactions of XPA with importin-α4 and importin-α7.”
    Quote in the paperSubstantial claim
  • May combine two claims. 23
  • Classified as probably not a substantial claim. 28

  • May combine two claims.

    Findingown data

    Knockdown of importin-α1, -α3, or -α5 does not inhibit UV-induced XPA nuclear import.

    “XPA was present primarily in the cytoplasm without UV-irradiation in control cells, and was transported into the nucleus after UV-irradiation in the control and importins-α1, -α3 or -α5 siRNA-knocked down cells”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    After UV-irradiation, endogenous XPA increases in the nucleus as it decreases in the cytoplasm.

    “after UV-irradiation the endogenous XPA increased in the nucleus as it decreased in the cytoplasm”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Importin-α4 and importin-α7 directly interact with XPA in cells.

    “Further investigation indicated that, importin-α4 and importin-α7 directly interacted with XPA in cells.”
    • Also stated in: § Interaction of Importin-α4 and Importin-α7 with XPA · plain
      “XPA was co-immunoprecipitated with importin-α4 or importin-α7 antibodies.”
    • Also stated in: § Interaction of Importin-α4 and Importin-α7 with XPA · plain
      “importin-α4 and importin-α7 were co-immunoprecipitated with XPA.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Importin-α4 and/or importin-α7 are required for the UV-induced nuclear import of XPA.

    “We found that, in addition to the nuclear localization signal (NLS) of XPA, importin-α4 or/and importin-α7 are required for the XPA nuclear import.”
    • Also stated in: § Importin-α4 and Importin-α7 are Involved in the UV-induced XPA Nuclear Import · plain
      “knockdown of importin-α4 or/and importin-α7 inhibited the XPA nuclear import”
    • Also stated in: § Importin-α4 and Importin-α7 are Involved in the UV-induced XPA Nuclear Import · plain
      “in cells with importin-α4 and/or importin-α7 silenced with siRNAs, a significant amount of XPA remained in the cytoplasm.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Substantial XPA-importin-α7 interaction is observed in the absence of DNA damage, and DNA damage appears to have no effect on this interaction.

    “In contrast, substantial XPA-importin-α7 interaction was observed in the absence of DNA damage and, thus, the DNA damage appeared to have no effect on the interaction (Figure 3A, right panel).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    XPA is predominantly located in the cytoplasm of undamaged cells fixed with methanol, whereas formaldehyde fixation results in a predominantly nuclear localization in undamaged cells.

    “XPA is predominately located in the cytoplasm of undamaged cells fixed with methanol; in contrast, formaldehyde fixation resulted in a predominately nuclear localization in undamaged cells (data not shown).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingown data

    The same monoclonal anti-XPA antibody yields distinctly different XPA distribution patterns depending on the method of cell fixation.

    “we recently found that the same monoclonal anti-XPA antibody yields distinctly different XPA distribution patterns depending on the method of cell fixation.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S2 (checkable).

    Interpretationreasoning

    The findings reveal a potential new therapeutic target for sensitization of cancer cells to chemotherapy.

    “In addition, these findings reveal a potential new therapeutic target for the sensitization of cancer cells to chemotherapy.”
    • Also stated in: § Introduction · hedged
      “The therapeutic disruption of this transport process may provide a means of sensitizing cancer cells to chemotherapeutic drugs.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data

    The binding affinity of XPA to importin-α4 itself is not affected by UV-irradiation of cells, but the binding is regulated in a UV-dependent manner.

    “This difference suggests that the binding affinity of XPA to importin-α4 itself is not affected by UV-irradiation of cells, but the binding is regulated in a UV-dependent manner”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Cargo protein with a classic NLS requires a direct interaction with importin-α to be transported through the nuclear pore complex.

    “Cargo protein with a classic NLS requires a direct interaction with importin-α to be transported through the nuclear pore complex [31], [40], [45], [46], [47]”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [31] NO Knudsen, 2009, Nuclear translocation contributes to regulation of DNA excision repair activities, DNA Repair (Amst) source

      Not checked in the free run.

    • cites [40] M Stewart, 2007, Molecular mechanism of the nuclear protein import cycle, Nat Rev Mol Cell Biol source

      Not checked in the free run.

    • cites [45] W Wickner, 2005, Protein translocation across biological membranes, Science source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The NER pathway is the primary mechanism in cells for removal of helix-distorting, replication-blocking bulky DNA adducts induced by exogenous agents such as UV radiation and genotoxic chemicals.

    “The NER pathway is the primary mechanism in cells for removal of helix-distorting, replication-blocking bulky DNA adducts that are induced by exogenous agents such as UV radiation and a variety of genotoxic chemicals [1], [2].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [1] A Sancar, 2004, Molecular mechanisms of mammalian DNA repair and the DNA damage checkpoints, Annu Rev Biochem source

      Not checked in the free run.

    • cites [2] D Branzei, 2008, Regulation of DNA repair throughout the cell cycle, Nat Rev Mol Cell Biol source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    In unstressed cells, XPA is primarily restricted to the cytoplasm in G1 and S phases, but is present predominantly in the nucleus during G2 phase.

    “However, more recent biochemical fractionation and immunofluorescence studies demonstrate that in unstressed cells XPA is primarily restricted to the cytoplasm of cells in G1 and S phases, though it is present predominately in the nucleus during the G2 phase [24], [25], [31], [32].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] X Wu, 2007, ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation, Oncogene source

      Not checked in the free run.

    • cites [25] SM Shell, 2009, Checkpoint kinase ATR promotes nucleotide excision repair of UV-induced DNA damage via physical interaction with xeroderma pigmentosum group A. J Biol Chem

      Not checked in the free run.

    • cites [31] NO Knudsen, 2009, Nuclear translocation contributes to regulation of DNA excision repair activities, DNA Repair (Amst) source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    XPA is an indispensable factor for both transcription-coupled NER and global genome NER.

    “XPA is an indispensable factor both for transcription-coupled NER and global genome NER [7], [8].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [7] VA Bohr, 1985, DNA repair in an active gene: removal of pyrimidine dimers from the DHFR gene of CHO cells is much more efficient than in the genome overall, Cell source

      Not checked in the free run.

    • cites [8] I Mellon, 1987, Selective removal of transcription-blocking DNA damage from the transcribed strand of the mammalian DHFR gene, Cell source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The activity of NER and sensitization of cancer cells to chemotherapy can be regulated by transcriptional and post-transcriptional control of the XPA protein.

    “Because of XPA’s crucial functions in NER, the activity of NER and sensitization of cancer cells to chemotherapy can be regulated by transcriptional and post-transcriptional control of the XPA protein [19], [20], [21], [22], [23], [24], [25], [26].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [19] Lee TH, Park JM, Leem SH, Kang TH (2013) Coordinated regulation of XPA stability by ATR and HERC2 during nucleotide excision repair. Oncogene (advance online publication, 26 November 2012; doi:<ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://dx.doi.org/10.1038/onc.2012.539" xlink:type="simple">10.1038/onc.2012.539</ext-link>). source

      Not checked in the free run.

    • cites [20] Lee TH, Park JM, Leem SH, Kang TH (2012) Coordinated regulation of XPA stability by ATR and HERC2 during nucleotide excision repair. Oncogene. source

      Not checked in the free run.

    • cites [21] TH Kang, 2011, Regulation of nucleotide excision repair activity by transcriptional and post-transcriptional control of the XPA protein, Nucleic Acids Research source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    The DNA damage-induced nuclear import of cytoplasmic XPA for NER during S-phase is a DNA damage checkpoint-dependent process mediated by ATR and p53.

    “It was shown previously that the DNA damage-induced nuclear import of cytoplasmic XPA for NER during S-phase is a DNA damage checkpoint-dependent process mediated by ataxia telangiectasia and Rad3-related (ATR) protein and p53 tumor suppressor protein [24], [25], [33].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] X Wu, 2007, ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation, Oncogene source

      Not checked in the free run.

    • cites [25] SM Shell, 2009, Checkpoint kinase ATR promotes nucleotide excision repair of UV-induced DNA damage via physical interaction with xeroderma pigmentosum group A. J Biol Chem

      Not checked in the free run.

    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    XPA localization to the nucleus depends on DNA damage and cell cycle stage.

    “XPA has an N-terminal NLS (Figure 1), but its localization to the nucleus where it functions also depends on DNA damage and cell cycle stage [24], [32], [33].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] X Wu, 2007, ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation, Oncogene source

      Not checked in the free run.

    • cites [32] Z Li, 2011, Differential DNA damage responses in p53 proficient and deficient cells: cisplatin-induced nuclear import of XPA is independent of ATR checkpoint in p53-deficient lung cancer cells, Int J Biochem Mol Biol

      Not checked in the free run.

    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    There may be two stages of XPA nuclear import: one occurs naturally in the absence of DNA damage, and another massive transport (particularly in S-phase) is initiated by specific DNA damage signaling.

    “These observations indicate that there maybe two stages of XPA nuclear import: one occurs naturally in the absence of DNA damage, and another, the massive transport (particularly in S-phase), is initiated by specific DNA damage signaling [24], [32], [33].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [24] X Wu, 2007, ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation, Oncogene source

      Not checked in the free run.

    • cites [32] Z Li, 2011, Differential DNA damage responses in p53 proficient and deficient cells: cisplatin-induced nuclear import of XPA is independent of ATR checkpoint in p53-deficient lung cancer cells, Int J Biochem Mol Biol

      Not checked in the free run.

    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    In humans, six importin-α isoforms are known.

    “In humans, six importin-α isoforms are known [41], [42], [43], [44].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [41] P Cortes, 1994, RAG-1 interacts with the repeated amino acid motif of the human homologue of the yeast protein SRP1, Proc Natl Acad Sci U S A source

      Not checked in the free run.

    • cites [42] CA Cuomo, 1994, Rch1, a protein that specifically interacts with the RAG-1 recombination-activating protein, Proc Natl Acad Sci U S A source

      Not checked in the free run.

    • cites [43] M Kohler, 1997, Cloning of two novel human importin-alpha subunits and analysis of the expression pattern of the importin-alpha protein family, FEBS Lett source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Importin-α acts as an adaptor protein that recognizes the NLS of cargo proteins and is transported as a ternary complex with importin-β into the nucleus.

    “Importin-α is a constituent of the classical nuclear import pathway. It acts as an adaptor protein that recognizes the NLS of cargo proteins and is transported as a ternary complex with importin-β into the nucleus [39], [40]”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [39] IW Mattaj, 1998, Nucleocytoplasmic transport: the soluble phase, Annu Rev Biochem source

      Not checked in the free run.

    • cites [40] M Stewart, 2007, Molecular mechanism of the nuclear protein import cycle, Nat Rev Mol Cell Biol source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Importin-α7 could be involved in the nuclear import of XPA independent of DNA damage, while importin-α4 participates in the damage-dependent import of XPA.

    “a possible scenario is that importin-α7 could be involved in the nuclear import of XPA independent of DNA damage (Figure S1D), while importin-α4 participated in the damage-dependent import of XPA.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S1 (asserted), S3 (load-bearing).

    Premisecitation

    XAB1 was proposed to be the GTPase involved in XPA nuclear import.

    “and was proposed to be the GTPase involved in XPA nuclear import [50].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [50] M Nitta, 2000, A novel cytoplasmic GTPase XAB1 interacts with DNA repair protein XPA, Nucleic Acids Res source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    XPA-deficient cells exhibit the highest UV sensitivity among XP cells.

    “the XPA-deficient cells exhibit the highest UV sensitivity among the XP cells [6].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [6] LJ Niedernhofer, 2006, A new progeroid syndrome reveals that genotoxic stress suppresses the somatotroph axis, Nature source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationown data

    The fixation method affects antigen display, with methanol revealing the same antigens as seen in western blots of SDS-denatured proteins.

    “Apparently, the fixation method affects the antigen display with methanol revealing the same antigens as seen in the western blots of SDS-denatured proteins.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationreasoning

    Importin-α7 is mainly responsible for nuclear import of XPA in G2 phase, while importin-α4 is for S phase.

    “Thus, it is possible that importin-α7 is mainly responsible for nuclear import of XPA in G2 phase, while importin-α4 for S phase.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Transportation of cargo protein in importin-α/−β protein complexes through the NPC requires energy derived from the activities of GTPases.

    “Transportation of cargo protein in importin-α/−β protein complexes through the NPC requires energy derived from the activities of GTPases [40], [45] (Figure 2A).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [40] M Stewart, 2007, Molecular mechanism of the nuclear protein import cycle, Nat Rev Mol Cell Biol source

      Not checked in the free run.

    • cites [45] W Wickner, 2005, Protein translocation across biological membranes, Science source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Formaldehyde rather than methanol was employed in the reports of a nucleus-only location for XPA.

    “Formaldehyde rather than methanol was employed in the reports of a nucleus-only location for XPA [38], [51], [52].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [38] I Miyamoto, 1992, Mutational analysis of the structure and function of the xeroderma pigmentosum group A complementing protein. Identification of essential domains for nuclear localization and DNA excision repair, J Biol Chem source

      Not checked in the free run.

    • cites [51] LL Solimando, 2009, Spatial organization of nucleotide excision repair proteins after UV-induced DNA damage in the human cell nucleus, J Cell Sci source

      Not checked in the free run.

    • cites [52] S Rademakers, 2003, Xeroderma pigmentosum group A protein loads as a separate factor onto DNA lesions, Mol Cell Biol source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    XPA plays roles in verifying DNA damage, stabilizing repair intermediates, and recruiting other NER factors to damaged DNA.

    “Functionally, XPA is believed to play roles in verifying DNA damage, stabilizing repair intermediates, and recruiting other NER factors to the damaged DNA [1], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [1] A Sancar, 2004, Molecular mechanisms of mammalian DNA repair and the DNA damage checkpoints, Annu Rev Biochem source

      Not checked in the free run.

    • cites [9] B Orelli, 2010, The XPA-binding domain of ERCC1 is required for nucleotide excision repair but not other DNA repair pathways, J Biol Chem source

      Not checked in the free run.

    • cites [10] CH Park, 1994, Formation of a ternary complex by human XPA, ERCC1, and ERCC4(XPF) excision repair proteins, Proc Natl Acad Sci U S A source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    Knockdown of importin-α7 has less effect on XPA nuclear import because the percentage of G2 cells in an unsynchronized cell population is only about 15-20%.

    “This also may provide a possible explanation for the observation that knockdown of importin-α7 had less effect on the XPA nuclear import because the percentage of G2 cells in an unsynchronized cell population is only about 15–20%.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The percentage of G2 cells in an unsynchronized cell population is only about 15–20%.

  • Classified as probably not a substantial claim.

    Premisecitation

    In a yeast two-hybrid system, XAB1 was observed to bind XPA.

    “In a yeast two-hybrid system XAB1 was observed to bind XPA and it has been proposed to be the GTPase involved in XPA nuclear import [50].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [50] M Nitta, 2000, A novel cytoplasmic GTPase XAB1 interacts with DNA repair protein XPA, Nucleic Acids Res source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Defects of NER lead to xeroderma pigmentosum characterized by increased sensitivity to UV radiation and predisposition to skin cancers.

    “In humans, defects of NER lead to the clinical disorder xeroderma pigmentosum (XP) which is characterized by an increased sensitivity to UV radiation and a predisposition to development of skin cancers [3], [4].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [3] KH Kraemer, 1994, The role of sunlight and DNA repair in melanoma and nonmelanoma skin cancer. The xeroderma pigmentosum paradigm, Arch Dermatol source

      Not checked in the free run.

    • cites [4] JE Cleaver, 2005, Cancer in xeroderma pigmentosum and related disorders of DNA repair, Nat Rev Cancer source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    ATR phosphorylates XPA at Ser196 in cells in response to UV damage.

    “Although ATR phosphorylates XPA at Ser196 in cells in responses to UV damage [26]”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [26] X Wu, 2006, Phosphorylation of nucleotide excision repair factor xeroderma pigmentosum group A by ataxia telangiectasia mutated and Rad3-related-dependent checkpoint pathway promotes cell survival in response to UV irradiation, Cancer Res source

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    Although both importin-α4 and/or importin-α7 are required for XPA nuclear import, the requirement of importin-α4 is DNA damage-dependent while that of importin-α7 is not.

    “These results indicate that although both importin-α4 and/or importin-α7 were required for XPA nuclear import, the requirement of importin-α4 was DNA damage-dependent while that of importin-α7 was not.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductcitation

    Immunofluorescence images may accurately depict XPA distribution within an individual cell but do not reflect the subcellular localization of XPA within a population of cells, whereas biochemical fractionation studies represent the average XPA distribution within millions of cells.

    “Though immunofluorescence images may accurately depict XPA distribution within an individual cell they do not reflect the subcellular localization of XPA within a population of cells as do our biochemical fractionation studies which represent the average XPA distribution within millions of cells [24], [32], [33].”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [24] X Wu, 2007, ATR-dependent checkpoint modulates XPA nuclear import in response to UV irradiation, Oncogene source

      Not checked in the free run.

    • cites [32] Z Li, 2011, Differential DNA damage responses in p53 proficient and deficient cells: cisplatin-induced nuclear import of XPA is independent of ATR checkpoint in p53-deficient lung cancer cells, Int J Biochem Mol Biol

      Not checked in the free run.

    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    In response to UV-C irradiation, XPA forms a complex with importin-α4 and importin-β for nuclear import in a process facilitated by a GTPase other than XAB1.

    “In response to UV-C irradiation XPA forms a complex with importin-α4 (Imp α4) and importin-β (not shown) for nuclear import in a process facilitated by a GTPase other than XAB1.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationcitation

    The basal level of nuclear XPA in the fractionation assays may vary somewhat between experiments, likely due to culture variations affecting the proportion of cells in the G2 phase.

    “Even the basal level of nuclear XPA in the fractionation assays may vary somewhat between experiments, likely due to culture variations affecting the proportion of cells in the G2 phase [32], [33].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [32] Z Li, 2011, Differential DNA damage responses in p53 proficient and deficient cells: cisplatin-induced nuclear import of XPA is independent of ATR checkpoint in p53-deficient lung cancer cells, Int J Biochem Mol Biol

      Not checked in the free run.

    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    XAB1 is a GTP-binding protein that was identified as an interacting partner with XPA in a yeast two-hybrid system.

    “the protein XAB1 is a GTP-binding protein that was identified as an interacting partner with XPA in a yeast two-hybrid system”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [50] M Nitta, 2000, A novel cytoplasmic GTPase XAB1 interacts with DNA repair protein XPA, Nucleic Acids Res source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Reports of immunofluorescence microscopic analyses showed that XPA was fully localized to the nucleus even in the absence of DNA damage.

    “reports of immunofluorescence microscopic analyses that showed that XPA was fully localized to the nucleus even in the absence of DNA damage [38], [51], [52].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [38] I Miyamoto, 1992, Mutational analysis of the structure and function of the xeroderma pigmentosum group A complementing protein. Identification of essential domains for nuclear localization and DNA excision repair, J Biol Chem source

      Not checked in the free run.

    • cites [51] LL Solimando, 2009, Spatial organization of nucleotide excision repair proteins after UV-induced DNA damage in the human cell nucleus, J Cell Sci source

      Not checked in the free run.

    • cites [52] S Rademakers, 2003, Xeroderma pigmentosum group A protein loads as a separate factor onto DNA lesions, Mol Cell Biol source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    The DNA damage-induced nuclear import of XPA is cell cycle dependent, primarily occurring in S phase.

    “the DNA damage-induced nuclear import of XPA was cell cycle dependent, primarily occurring in S phase [33].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    XAB1 has been proposed to be the GTPase involved in XPA nuclear import.

    “it has been proposed to be the GTPase involved in XPA nuclear import [50]”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [50] M Nitta, 2000, A novel cytoplasmic GTPase XAB1 interacts with DNA repair protein XPA, Nucleic Acids Res source

      Not checked in the free run.

  • May combine two claims.

    Interpretationcitation

    The nuclear import of XPA depends on its NLS in cells, which excludes the possibility that XPA is co-imported with other proteins containing a NLS or imported by alternative import mechanisms.

    “The observation that the nuclear import of XPA depended on its NLS in cells excludes the possibility that XPA was co-imported with other proteins containing a NLS, or imported by “alternative import mechanisms” [31].”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [31] NO Knudsen, 2009, Nuclear translocation contributes to regulation of DNA excision repair activities, DNA Repair (Amst) source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    XPA may participate in other cellular events in the absence of genotoxic insults, such as facilitating chromatin modification for transcription, inhibiting DNA double-strand break repair in progeria, and potential involvement in DNA replication.

    “In addition, recent studies demonstrated that besides its anticipated functions in NER, XPA also may participate in other cellular events in the absence of genotoxic insults, such as facilitating chromatin modification for transcription [27], inhibiting DNA double-strand break repair in progeria [28], and potential involvement in DNA replication [29].”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [27] N Le May, 2010, NER factors are recruited to active promoters and facilitate chromatin modification for transcription in the absence of exogenous genotoxic attack, Mol Cell source

      Not checked in the free run.

    • cites [28] Y Liu, 2008, Involvement of xeroderma pigmentosum group A (XPA) in progeria arising from defective maturation of prelamin A. Faseb J

      Not checked in the free run.

    • cites [29] KM Gilljam, 2012, Nucleotide Excision Repair Is Associated with the Replisome and Its Efficiency Depends on a Direct Interaction between XPA and PCNA, PLoS One source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S3 (load-bearing).

    Interpretationnone given

    The inconsistency between the XAB1 knockdown result and the yeast two-hybrid proposal could be due to the different environments within human cells and the yeast model system.

    “This inconsistency could be due to the different environments within human cells and the yeast model system.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    Targeted disruption of the XPA-importin-α4 complex could be a potential strategy to reduce the nuclear level of XPA given that NER occurs exclusively in the nucleus.

    “The results from this study suggest that targeted disruption of the XPA-importin-α4 complex could be a potential strategy to reduce the nuclear level of XPA given that NER occurs exclusively in the nucleus.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: NER occurs exclusively in the nucleus.

  • May combine two claims.

    Interpretationcitation

    Since the DNA damage-induced nuclear import of XPA occurs primarily in S-phase, the inhibition is expected to be specific to replicative cells, typically cancer cells, without interruption of XPA functions in cells in other cell cycle phases.

    “Since the DNA damage-induced nuclear import of XPA occurs primarily in S-phase [33], the inhibition is expected to be specific to replicative cells, typically cancer cells, without interruption of XPA functions in cells in other cell cycle phases.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [33] Z Li, 2011, XPA-mediated regulation of global nucleotide excision repair by ATR Is p53-dependent and occurs primarily in S-phase, PLoS One source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Targeting protein-trafficking pathways alters the sensitivity of melanoma cells to chemotherapy.

    “recent studies indicate that targeting protein-trafficking pathways altered the sensitivity of melanoma cells to chemotherapy [34].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [34] ZM Huang, 2012, Targeting protein-trafficking pathways alters melanoma treatment sensitivity, Proc Natl Acad Sci U S A source

      Not checked in the free run.

45 of 45

  • The paper relies on this without support.

    The XPA-ΔNLS mutant is properly folded and functional except for the NLS, so its failure to enter the nucleus reflects loss of NLS-dependent import rather than misfolding or other defects.

    “no mutated XPA protein (His-V5-XPA) was detected in the nuclear fractions of these mutated transfectants even after UV-irradiation.”
    “XPA-ΔNLS remained in the cytoplasm even after the cells were irradiated with UV”

  • The paper relies on this without support.

    The siRNA knockdown of importin-α4 and importin-α7 specifically reduces the targeted proteins without off-target effects that independently impair XPA nuclear import.

    “Western blotting confirms the efficiency of siRNA knockdown of each of the five importin-α proteins.”

  • The paper relies on this without support.

    The in vitro binding of recombinant XPA to immunoprecipitated importin-α4 reflects the direct interaction that mediates XPA nuclear import in cells.

    “The ability of added recombinant XPA to bind to the immunoprecipitated importin-α4 was demonstrated by Western blotting of the bead-associated protein complexes.”

  • The paper relies on this without support.

    The antibodies against importin-α4 and importin-α7 are specific and do not cross-react with other importin-α isoforms.

    “Antibodies against importins-α1, -α3, -α4, -α5, or -α7 were from Genetex Biotechnology Co.”

  • The paper relies on this without support.

    NER depends on XPA functioning within the nucleus.

    “as NER depends on XPA functioning within the nucleus”

  • The paper relies on this without support.

    XPA has crucial functions in NER.

    “XPA has crucial functions in NER.”

  • The paper relies on this without support.

    NER occurs exclusively in the nucleus.

    “given that NER occurs exclusively in the nucleus”

  • The paper relies on this without support.

    The percentage of G2 cells in an unsynchronized cell population is only about 15–20%.

    “the percentage of G2 cells in an unsynchronized cell population is only about 15–20%”
8 of 8

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Figure 1 cells described as both stably and transiently transfected

    Minor

    The Figure 1 caption identifies the H1299 cells as stably transfected, but the discussion of the Figure 1B result explains it by referring to a transient transfection.

  • GM04429 experiment did not use isolated, washed importin-α4

    Minor

    The discussion says isolated and washed importin-α4 bound recombinant XPA in both cell types, citing Figure 3B for GM04429 cells. Figure 3B instead describes adding XPA to cell lysates and immunoprecipitating XPA, not isolating and washing importin-α4 before the binding test.

2 of 2

Cites

Flagged first, then by citations

1 of the 53 references couldn’t be matched to a known paper.

Research works printed but not linked: 4

  1. Lee TH, Park JM, Leem SH, Kang TH (2012) Coordinated regulation of XPA stability by ATR and HERC2 during nucleotide excision repair. Oncogene. · DOI · Paper page
  2. GR Kumar, 2011, Importin alpha-mediated nuclear import of cytoplasmic poly(A) binding protein occurs as a direct consequence of cytoplasmic mRNA depletion, Mol Cell Biol, 31, 3113, 10.1128/MCB.05402-11 · DOI · Paper page
  3. TH Kang, 2011, Circadian control of XPA and excision repair of cisplatin-DNA damage by cryptochrome and HERC2 ubiquitin ligase, Proc Natl Acad Sci U S A, 107, 4890, 10.1073/pnas.0915085107 · DOI · Paper page
  4. TH Kang, 2011, Regulation of nucleotide excision repair activity by transcriptional and post-transcriptional control of the XPA protein, Nucleic Acids Res, 39, 3176, 10.1093/nar/gkq1318 · DOI · Paper page

Cited by

Sorted by citations

Related

Authors
Li, Z., Musich, P. R., Cartwright, B. M., Wang, H., & Zou, Y.
Affiliations
East Tennessee State University (US)
Corresponding author
Zou, Yue
ORCID
Venue
PLoS ONE
Publisher
Public Library of Science (PLoS)
Published
2013-07-08
Volume
8
Issue
7
Pages
e68297
ISSN
1932-6203 (ISSN-L)
DOI
10.1371/journal.pone.0068297
PMC
PMC3704644
OpenAlex
W2038144270
Cited by
26
References
53
Citations by year
2022: 2 · 2021: 3 · 2020: 4 · 2018: 5 · 2017: 6 · 2016: 2 · 2015: 3 · 2014: 1
FWCI
0.90
Type
journal article
Language
en
Open access
Licence
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • Europe PMC (PubMed Central) (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • Digital Commons - East Tennessee State University (East Tennessee State University) (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • National Institutes of Health (R01CA86927)
  • National Cancer Institute (R01CA86927, R01CA086927)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Nuclear Structure and Function
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › DNA Repair Mechanisms
  • Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Effects of Radiation Exposure
Keywords
XPA, nuclear import, ATR, nucleotide excision repair, UV-induced DNA damage, nuclear localization signal, protein-protein interaction, S phase, DNA damage response, chemosensitization
MeSH terms
Cell Line, Cell Nucleus, Humans, Models, Biological, Protein Binding, Recombinant Proteins, Ultraviolet Rays, GTP-Binding Proteins, Nuclear Localization Signals, Active Transport, Cell Nucleus, alpha Karyopherins, Xeroderma Pigmentosum Group A Protein, Gene Knockdown Techniques, Ataxia Telangiectasia Mutated Proteins

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-06.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-06.

Statistics and arithmetic are recomputed, not judged.

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