CoChat
Sign Up
Cited by 389DNA Repair MechanismsProtein Tyrosine PhosphatasesCancer-related Molecular Pathways

PPM1D dephosphorylates Chk1 and p53 and abrogates cell cycle checkpoints

Open access
Lu, Xiongbin, Nannenga, Bonnie, Donehower, Lawrence A.·2005·Genes & Development
DOI 10.1101/gad.1291305PMC PMC1132003
Open this paper in CoChat — free accountOpen PDF

Abstract

The ATM (ataxia-telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) kinases respond to DNA damage by phosphorylating cellular target proteins that activate DNA repair pathways and cell cycle checkpoints in order to maintain genomic integrity. Here we show that the oncogenic p53-induced serine/threonine phosphatase, PPM1D (or Wip1), dephosphorylates two ATM/ATR targets, Chk1 and p53. PPM1D binds Chk1 and dephosphorylates the ATR-targeted phospho-Ser 345, leading to decreased Chk1 kinase activity. PPM1D also dephosphorylates p53 at phospho-Ser 15. PPM1D dephosphorylations are correlated with reduced cellular intra-S and G2/M checkpoint activity in response to DNA damage induced by ultraviolet and ionizing radiation. Thus, a primary function of PPM1D may be to reverse the p53 and Chk1-induced DNA damage and cell cycle checkpoint responses and return the cell to a homeostatic state following completion of DNA repair. These homeostatic functions may be partially responsible for the oncogenic effects of PPM1D when it is amplified and overexpressed in human tumors.

Integrity signals

Registry

Crossref · 10.1101/gad.1291305

Cites

Statistics

Nothing to recompute.

Claims the paper makes

0 of 47 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    PPM1D binds Chk1.

    “PPM1D binds Chk1 and dephosphorylates the ATR-targeted phospho-Ser 345”
    • Also stated in: § PPM1D interacts with Chk1 · hedged
      “By this assay, we found that Chk1 is coimmunoprecipitated with PPM1D, indicating a true endogenous interaction between the two proteins (Fig. 1B, left panel).”
    Quote in the paperSubstantial claim
  • Findingown data

    PPM1D dephosphorylation of Chk1 leads to decreased Chk1 kinase activity.

    “leading to decreased Chk1 kinase activity”
    • Also stated in: § Dephosphorylation of Chk1 by PPM1D inhibits Chk1 kinase activity · hedged
      “Preincubation with increasing PPM1D reduced Chk1 kinase activity, indicating that PPM1D inhibits Chk1 kinase function.”
    Quote in the paperSubstantial claim
  • Findingown data

    PPM1D dephosphorylates Chk1 at phospho-Ser345.

    “PPM1D binds Chk1 and dephosphorylates the ATR-targeted phospho-Ser 345”
    • Also stated in: § PPM1D dephosphorylates Chk1 in vitro · plain
      “PPM1D showed high levels of dephosphorylation of phospho-Ser 345, as well as a positive control peptide containing phospho-Thr 180 from p38 MAP kinase previously shown to be a PPM1D target (Fig. 2A; Takekawa et al. 2000).”
    • Also stated in: § PPM1D dephosphorylates Chk1 in vitro · plain
      “To show that PPM1D dephosphorylates the intact Chk1 protein in vitro, we performed a second set of in vitro phosphatase reactions on immunopurified Chk1 and found that increasing PPM1D resulted in increased Ser 345 dephosphorylation (Fig. 2C).”
    Quote in the paperSubstantial claim
  • Findingown data

    PPM1D dephosphorylations are correlated with reduced cellular intra-S and G2/M checkpoint activity in response to DNA damage induced by UV and ionizing radiation.

    “PPM1D dephosphorylations are correlated with reduced cellular intra-S and G2/M checkpoint activity in response to DNA damage induced by ultraviolet and ionizing radiation.”
    • Also stated in: § Abrogation of the intra-S-phase checkpoint by PPM1D · plain
      “Thus, increased levels of PPM1D significantly attenuate the UVinduced intra-S-phase checkpoint, while reduced PPM1D levels dramatically enhance and prolong the intra-S-phase checkpoint.”
    Quote in the paperSubstantial claim
  • Findingown data

    PPM1D dephosphorylates p53 at phospho-Ser15.

    “PPM1D also dephosphorylates p53 at phospho-Ser 15.”
    • Also stated in: § PPM1D dephosphorylates p53 at Ser 15 · plain
      “PPM1D showed high levels of Ser 15 dephosphorylation that was magnesium dependent and okadaic acid independent (Fig. 4A).”
    • Also stated in: § PPM1D dephosphorylates p53 at Ser 15 · plain
      “When intact phospho-p53 was incubated with increasing amounts of PPM1D, phospho-Ser 15 levels were decreased, while phospho-Ser 46, another stress-induced phosphorylation site on p53, showed no reduction in phosphorylation levels (Fig. 4C).”
    Quote in the paperSubstantial claim
  • May combine two claims. 37
  • The quote only partly states this claim. 2
  • Classified as probably not a substantial claim. 18

  • May combine two claims.

    Findingown data

    Addition of PPM1D modestly decreases p53 protein levels, while removal of PPM1D by siRNA results in moderate increases in p53 protein levels.

    “Addition of PPM1D modestly decreased p53 protein levels, while removal of PPM1D by siRNA resulted in moderate increases in p53 protein levels (Fig. 4E, left panel).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingnone given

    PPM1D did not efficiently dephosphorylate Chk1 at Ser317, even though ATM and ATR phosphorylate that site.

    “The correlation between ATM/ATR phosphorylation and PPM1D dephosphorylation is not perfect, since PPM1D did not efficiently dephosphorylate Chk1 at Ser 317, while ATM and ATR phosphorylate that site.”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: ATM and ATR phosphorylate Chk1 at Ser317.

  • May combine two claims.

    Findingown data

    Overexpressed PPM1D reduces CDC25C Ser216 phosphorylation, and PPM1D siRNA induces marginal increases in phospho-Ser216.

    “Overexpressed PPM1D resulted in reduced Ser 216 phosphorylation and siRNA for PPM1D-induced marginal increases in phospho-Ser 216 (Fig. 3C).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Breast cancer cell lines with amplified PPM1D genes (MCF-7, BT474, MDA-MB231) show higher PPM1D protein levels and only modest Chk1 Ser345 phosphorylation induction after UV compared to control cell lines.

    “The three breast cancer lines, MCF-7, BT474, and MDAMB231, showed higher levels of PPM1D protein compared with two control cell lines, human embryonic kidney (HEK) cells and U2OS osteosarcoma cells (Fig. 3D).”
    • Also stated in: § Dephosphorylation of Chk1 by PPM1D inhibits Chk1 kinase activity · plain
      “UV treatment resulted in very high levels of Chk1 Ser 345 phosphorylation in the control cell lines, but only a modest induction of Ser 345 phosphorylation in the three cell lines with PPM1D amplification (Fig. 3D).”
    Quote in the paperSubstantial claim

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    PPM1D dephosphorylates Chk1 at Ser345 in vitro, with only modest activity on Ser317.

    “When another major ATR-targeted serine of Chk1, Ser 317, was tested in the in vitro phosphatase reaction, only modest PPM1D activity was detected on this peptide (Fig. 2A).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Addition of PPM1D results in significant reductions in UV-induced p53 phospho-Ser15, while reduction of PPM1D by siRNA results in dramatic increases in phospho-Ser15.

    “When UV-induced accumulation of p53 phospho-Ser 15 was examined, addition of PPM1D resulted in significant reductions in phospho-Ser 15, while reduction of PPM1D by siRNA resulted in dramatic increases in phospho-Ser 15 (Fig. 4E, middle panel).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Overexpression of PPM1D decreases phospho-Ser317-Chk1, and reduction of PPM1D by siRNA results in marginally increased phospho-Chk1.

    “When the effects of PPM1D on UV-induced phosphorylation of Chk1 at Ser 317 were examined, the results were less dramatic, but overexpression of PPM1D still resulted in decreased phospho-Ser 317-Chk1, and reduction of PPM1D by PPM1D siRNA resulted in marginally increased phospho-Chk1 (Fig. 3B, right panel).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    After 3 Gy ionizing radiation, cells with reduced PPM1D showed an enhanced 95% reduction in M-phase cells as early as 2 hours, and this reduction was prolonged.

    “Finally, the cells with reduced PPM1D displayed an enhanced 95% reduction in M-phase cells as early as 2 h post-irradiation and the M-phase reduction was prolonged.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingnone given

    PP1 protein levels are not induced after DNA damage, although its phosphatase activity could be increased by damage.

    “However, PP1 protein levels are not induced following DNA damage (though its phosphatase activity could be increased by damage).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Transfection of PPM1D eliminates UV-induced Chk1 Ser345 phosphorylation, while phosphatase-dead PPM1D has a slight enhancing effect.

    “Transfection of PPM1D eliminated this UV-induced Ser 345 phosphorylation, while transfection of phosphatase-dead PPM1D had a slight enhancing effect.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Increased PPM1D decreases Cdc2 Tyr15 phosphorylation following UV irradiation, while reduction of PPM1D increases inhibitory tyrosine phosphorylation.

    “In the presence of increased PPM1D, Tyr 15 showed decreased phosphorylation following UV irradiation, while reduction of PPM1D increased the inhibitory tyrosine phosphorylation (Fig. 3C).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Inhibition of PPM1D by siRNA resulted in a much lower thymidine incorporation that was maximal only 4 h post-UV and reached levels of 70% reduction that continued even at 48 h post-irradiation.

    “Inhibition of PPM1D by treatment of U2OS tet on (PPM1D) cells (without doxycycline) with PPM1D siRNA resulted in a much lower thymidine incorporation that was maximal only 4 h post-UV and reached levels of 70% reduction that continued even at 48 h post-irradiation.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: PPM1D siRNA specifically reduces PPM1D without off-target effects on checkpoint proteins.

  • May combine two claims. The quote only partly states this claim.

    Findingown data

    PPM1D dephosphorylation is magnesium-dependent and minimally inhibited by okadaic acid.

    “PPM1D dephosphorylation was minimally inhibited by okadaic acid, an attribute of type 2C phosphatases (Cohen 1989).”
    • Also stated in: § PPM1D dephosphorylates Chk1 in vitro · plain
      “Phosphatase reactions in the absence of magnesium also resulted in little or no phosphatase activity, as expected for the magnesium-dependent PPM1D.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Cohen 1989

      Not checked in the free run.

  • May combine two claims.

    Findingown data

    PPM1D does not affect UV-induced ATRIP mobility shift or ATR-ATRIP interaction.

    “Increased expression of PPM1D appears to have no effect on the mobility of this damage-induced ATRIP shift, suggesting that it does not dephosphorylate ATRIP.”
    • Also stated in: § PPM1D has no apparent effect on damage-induced activation of ATM and ATR · plain
      “immunoprecipitation Western blot analyses of U2OS tet on (PPM1D) cells with and without doxycycline and UV show a slight enhancement of ATRIP binding to ATR following radiation, but no effects of PPM1D on this binding (Fig. 5B).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PPM1D protein levels, and possibly its posttranslational modification state, are altered in cells that incur DNA damage.

    “In contrast, we show that PPM1D protein levels and possibly its posttranslational modification state are altered in cells incurring DNA damage.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    PPM1D protein levels increase by 2-4 h and peak at approximately 8 h in UV-treated U2OS cells.

    “we show here that PPM1D protein levels increase by 2-4 h and peak at ∼8 h in UV-treated U2OS cells (Fig. 3A).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Human PP1 dephosphorylates both Chk1 Ser317 and Chk1 Ser345.

    “We confirmed here that human PP1 does target both Ser 317 and Ser 345 for dephosphorylation (Fig. 2B; data not shown).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Reduction of PPM1D levels by siRNA displayed a 58% reduction by 2 h post-irradiation and incorporation levels remained low for up to 48 h.

    “In contrast, reduction of PPM1D levels by PPM1D siRNA transfection displayed a 58% reduction by 2 h post-irradiation and incorporation levels remained low for up to 48 h.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: PPM1D siRNA specifically reduces PPM1D without off-target effects on checkpoint proteins.

  • May combine two claims.

    Findingown data

    In UV-treated cells, PPM1D overexpression delayed and weakened the fall in M-phase cells, with the largest reduction being only 30% at 16 hours after irradiation.

    “Overexpression of PPM1D in UV-treated cells delayed and attenuated the reduction in M-phase cells with a maximal reduction of only 30% by 16 h post-irradiation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Increased PPM1D levels are associated with reduced inhibitory phosphorylation of the mitotic kinase Cdc2 and with abrogation of intra-S and G2/M checkpoints after UV and ionizing irradiation.

    “We have shown that increased PPM1D levels are also associated with reduced inhibitory phosphorylation of the mitotic kinase Cdc2 and with abrogation of intra-S and G2/M checkpoints following UV and ionizing irradiation.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning

    Overexpression of PPM1D in vivo is correlated with reduced Chk1 kinase activity on key substrates such as CDC25C and appears to modestly reduce Chk1 stability.

    “Overexpression of PPM1D in vivo is correlated with reduced Chk1 kinase activity on key substrates such as CDC25C and appears to modestly reduce Chk1 stability.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    PPM1D protein has Mg2+-dependent serine/threonine protein phosphatase activity and is insensitive to okadaic acid.

    “In vitro studies confirmed that the PPM1D protein has Mg 2+ -dependent serine/threonine protein phosphatase activity and is insensitive to the inhibitor okadaic acid, characteristics of PP2Cs (Fiscella et al. 1997).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Fiscella et al. 1997

      Not checked in the free run.

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

    Premisecitation

    PPM1D sequence shows significant region-specific homology with type 2C protein phosphatases (PP2Cs).

    “The PPM1D sequence shows significant region-specific homology with type 2C protein phosphatases (PP2Cs) (Fiscella et al. 1997;Choi et al. 2000).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Fiscella et al. 1997

      Not checked in the free run.

    • cites Choi et al. 2000

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    In approximately 15% of human breast cancers the PPM1D gene is amplified and its RNA overexpressed.

    “In ∼15% of human breast cancers the PPM1D gene is amplified and its RNA overexpressed (Bulavin et al. 2002b;Li et al. 2002;Harrison et al. 2004).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Bulavin et al. 2002b

      Not checked in the free run.

    • cites Li et al. 2002

      Not checked in the free run.

    • cites Harrison et al. 2004

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    ATM/ATR kinases phosphorylate target proteins to activate DNA repair pathways and cell cycle checkpoints.

    “The ATM (ataxia-telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) kinases respond to DNA damage by phosphorylating cellular target proteins that activate DNA repair pathways and cell cycle checkpoints in order to maintain genomic integrity.”
    • Also stated in: § Abstract · plain
      “DNA damage mobilizes an intricate signaling network by activating the ATM/ATR protein kinases, which, in turn, orchestrate this network by phosphorylating their target proteins in each pathway.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Shiloh 2003

      Not checked in the free run.

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

    Premisecitation

    The first identified target of PPM1D was p38 MAP kinase.

    “The first identified target of PPM1D was also p38 MAP kinase (Takekawa et al. 2000).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Takekawa et al. 2000

      Not checked in the free run.

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

    Premisecitation

    PPM1D amplification occurs in other human tumors, including ovarian clear cell adenocarcinomas and neuroblastomas.

    “Recent evidence indicates that PPM1D amplification occurs in other human tumors, including ovarian clear cell adenocarcinomas and neuroblastomas (Hirasawa et al. 2003;Saito-Ohara et al. 2003).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Hirasawa et al. 2003

      Not checked in the free run.

    • cites Saito-Ohara et al. 2003

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Interpretationnone given

    After a cell has arrested and repaired its DNA damage, a mechanism must exist to return it to a homeostatic state.

    “Once the cell is arrested and the DNA damage is repaired, a mechanism to return the cell to a homeostatic state must exist.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Premisecitation

    Chk1 is phosphorylated and activated by ATR at Ser345 and Ser317 in response to UV radiation.

    “It is phosphorylated and activated by ATR at Ser 345 and Ser 317 in response to UV radiation (Shiloh 2003).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Shiloh 2003

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    PPM1D affects ATM/ATR targets Chk1 and p53, but has minimal effects on ATM or ATR activation itself.

    “Thus, the preliminary evidence suggests that PPM1D affects ATM/ ATR targets Chk1 and p53, but has minimal effects on ATM or ATR activation itself.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Phosphorylation of Chk1 Ser345 is important for Chk1 activation after genotoxic stress and for nuclear retention after DNA damage.

    “Moreover, phosphorylation of Ser 345 has been shown to be important for Chk1 activation in response to genotoxic stress and for nuclear retention after DNA damage (Lopez-Girona et al. 2001;Zhao and Piwnica-Worms 2001;Jiang et al. 2003).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Lopez-Girona et al. 2001

      Not checked in the free run.

    • cites Zhao and Piwnica-Worms 2001

      Not checked in the free run.

    • cites Jiang et al. 2003

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    Increased levels of PPM1D significantly attenuate the UV-induced intra-S-phase checkpoint, while reduced PPM1D levels dramatically enhance and prolong the intra-S-phase checkpoint.

    “Thus, increased levels of PPM1D significantly attenuate the UVinduced intra-S-phase checkpoint, while reduced PPM1D levels dramatically enhance and prolong the intra-S-phase checkpoint.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    PP2A may regulate autophosphorylation of ATM.

    “Recent data also indicate that PP2A may regulate autophosphorylation of ATM (Goodarzi et al. 2004).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Goodarzi et al. 2004

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    ATM and ATR are important for starting and propagating the signaling pathways that mediate cell cycle checkpoints and DNA damage repair by phosphorylating critical target proteins.

    “ATM and ATR clearly play an important role in initiating and propagating the signaling pathways that mediate cell cycle checkpoints and DNA damage repair through their ability to phosphorylate an array of critical target proteins (Shiloh 2003).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Shiloh 2003

      Not checked in the free run.

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

    Premisecitation

    PP5 and PP1 have been proposed as alternative phosphatases that may reverse ATM/ATR phosphorylation effects.

    “Recently, phosphatases such as protein phosphatase 5 (PP5) and PP1 have emerged as alternative candidates that may reverse ATM/ATR phosphorylation effects (Ali et al. 2004;Bakkenist and Kastan 2004b;Den Elzen et al. 2004)”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites Ali et al. 2004

      Not checked in the free run.

    • cites Bakkenist and Kastan 2004b

      Not checked in the free run.

    • cites Den Elzen et al. 2004

      Not checked in the free run.

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

    Premisecitation

    PP5 is involved in regulation of ATM and DNA-PK, and PP1 may dephosphorylate Chk1 and allow yeast cells to recover from a DNA damage-induced G2 checkpoint.

    “Recent evidence has shown that PP5 is involved in the regulation of ATM and DNA-PK, and another phosphatase, PP1, may dephosphorylate Chk1 and allow yeast cells to recover from a DNA damage-induced G2 checkpoint (Ali et al. 2004;Bakkenist and Kastan 2004b).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Ali et al. 2004

      Not checked in the free run.

    • cites Bakkenist and Kastan 2004b

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    p53 Ser15 is phosphorylated by ATM and ATR in response to IR and UV irradiation.

    “p53 Ser 15 is phosphorylated by ATM and ATR in response to IR and UV irradiation (Banin et al. 1998;Canman et al. 1998;Tibbetts et al. 1999).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Banin et al. 1998

      Not checked in the free run.

    • cites Canman et al. 1998

      Not checked in the free run.

    • cites Tibbetts et al. 1999

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    Starting the DNA damage response and engaging cell cycle checkpoints are critical for preventing damaged DNA templates from being propagated.

    “Initiation of the DNA damage response and engagement of cell cycle checkpoints are critical for protecting the cell from propagation of damaged DNA templates (Sancar et al. 2004).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Sancar et al. 2004

      Not checked in the free run.

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

    Premisecitation

    PP2A could help activate ATM.

    “while PP2A could assist in activating ATM (Goodarzi et al. 2004).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Goodarzi et al. 2004

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    Chk1 phosphorylates Ser216 of CDC25C, preventing its activation at G2 through 14-3-3-mediated translocation to the cytoplasm.

    “Chk1, in turn, phosphorylates Ser 216 of the phosphatase CDC25C, which prevents its activation at G2 through 14-3-3-mediated translocation to the cytoplasm (Bartek and Lukas 2003).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Bartek and Lukas 2003

      Not checked in the free run.

  • May combine two claims.

    Interpretationown data

    PPM1D overexpression attenuates the G2/M checkpoint, while reducing PPM1D strengthens and prolongs the G2/M checkpoint.

    “Thus, it appears that PPM1D overexpression attenuates the G2/M checkpoint, while reduction of PPM1D exacerbates and prolongs the G2/M checkpoint.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    PPM1D accumulation takes at least several hours, which allows enough time for DNA damage repair before PPM1D relaxes cell cycle checkpoints.

    “The accumulation of PPM1D appears to take at least several hours, allowing sufficient time for DNA damage to be repaired prior to PPM1Dmediated relaxation of the cell cycle checkpoints.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisereasoning

    G2 arrest ensues due to the inability of CDC25C to dephosphorylate inhibitory phosphorylation sites on Cdc2 (CDK1).

    “G2 arrest ensues due to the inability of CDC25C to dephosphorylate inhibitory phosphorylation sites on Cdc2 (CDK1), a primary mitotic kinase.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    Chk1 is a critical mediator of ATM/ATR signaling and phosphorylates key cell cycle effectors such as CDC25A and CDC25C to facilitate S-phase and G2/M checkpoints.

    “Chk1 is a critical mediator of the ATM/ATR signal and phosphorylates key cell cycle effectors such as CDC25A and CDC25C to facilitate S-phase and G2/M checkpoints (Bartek and Lukas 2003).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Bartek and Lukas 2003

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    By abrogating cell cycle checkpoints, PPM1D overexpression would likely result in increased proliferation and chromosomal instability.

    “By abrogating cell cycle checkpoints, PPM1D overexpression would likely result in increased proliferation and chromosomal instability.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    PPM1D may deactivate p53 directly by dephosphorylating ATM/ATR-phosphorylated Ser15, and indirectly by reducing Chk1 phosphorylation of Ser20, which could facilitate p53 degradation by MDM2.

    “PPM1D may contribute to p53 deactivation directly by dephosphorylating the ATM/ATR phosphorylated Ser 15, and indirectly through decreased Chk1 phosphorylation of Ser 20, which could facilitate p53 degradation by MDM2.”
    Quote in the paperSubstantial claim

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

    Premisecitation

    ATM and ATR kinases preferentially target sequences containing an S/TQ motif.

    “The ATM and ATR kinases have a specificity for targets containing an S/TQ motif (Kim et al. 1999).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Kim et al. 1999

      Not checked in the free run.

  • May combine two claims.

    Interpretationreasoning

    PPM1D may have multiple sequence specificities in its target sites and can dephosphorylate substrates of both the ATM/ATR and MAP kinase stress response pathways.

    “This suggests that PPM1D may have multiple sequence specificities in its target sites and can dephosphorylate substrates of both the ATM/ATR and MAP kinase stress response pathways.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationreasoning

    By inhibiting the DNA damage response, PPM1D overexpression could increase mutation accumulation through abrogation of checkpoint control proteins and through direct suppression of DNA repair.

    “By inhibiting the DNA damage response, PPM1D overexpression could result in increased accumulation of mutations, not only through abrogation of checkpoint control proteins, but also through direct suppression of DNA repair.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    Accumulated PPM1D reverses p53 activation by dephosphorylating p53, completing the feedback loop.

    “Accumulation of PPM1D reverses p53 activation by dephosphorylation of p53, completing the feedback loop.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Phosphorylated p53 is more active and increases PPM1D expression.

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

    Premisecitation

    PPM1D has been shown to dephosphorylate p38 MAP kinase and uracil DNA glycosylase at the phosphothreonine of dual phosphorylated TXY motifs.

    “PPM1D has been shown to dephosphorylate p38 MAP kinase and uracil DNA glycosylase at the phosphothreonine of dual phosphorylated TXY motifs (Takekawa et al. 2000;Lu et al. 2004).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites Takekawa et al. 2000

      Not checked in the free run.

    • cites Lu et al. 2004

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    The U2OS Tet-on PPM1D clonal lines used for the experiments had high inducible PPM1D expression and no detectable basal Flag-PPM1D without doxycycline.

    “Clonal lines with high levels of inducible PPM1D expression and nondetectable basal levels of Flag-PPM1D in the absence of doxycycline were used for the experiments described in this paper.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    PPM1D suppresses DNA base excision repair, and recent studies indicate it may also inhibit nucleotide excision repair.

    “In a previous study, we have shown that PPM1D suppresses DNA base excision repair, and recent studies in our laboratory indicate that it may also inhibit nucleotide excision repair (Lu et al. 2004;T.A. Nguyen, unpubl.).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites Lu et al. 2004

      Not checked in the free run.

    • cites T.A. Nguyen, unpubl.

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S1 (asserted).

    Interpretationreasoning

    PPM1D binding to Chk1 and dephosphorylation of Ser345 may be a primary mechanism by which Chk1 kinase activity is inhibited.

    “We hypothesize that PPM1D binding to Chk1 and dephosphorylation of Ser 345 may be a primary mechanism of Chk1 kinase inhibition.”
    Quote in the paperNot a substantial claim
54 of 54

  • The paper relies on this without support.

    Virtually none of the tumors with PPM1D amplification carried a p53 mutation, while human breast cancers generally have a 30%-40% p53 mutation frequency.

    “Interestingly, virtually none of the tumors with PPM1D amplification carried a p53 mutation, though human breast cancers usually exhibit a 30%-40% frequency in p53 mutations.”

  • The paper relies on this without support.

    PPM1D siRNA specifically reduces PPM1D without off-target effects on checkpoint proteins.

    “Introduction of two different PPM1D siRNAs resulted in very high levels of phospho-Ser 345, indicating that PPM1D is likely to be a primary phosphatase that dephosphorylates Chk1 at Ser 345 following UV irradiation.”

  • The paper relies on this without support.

    SB203580 specifically inhibits p38 MAP kinase without affecting other kinases that regulate CDC25C phosphorylation.

    “To test this possibility, we treated U20S cells with SB203580, a known inhibitor of p38 MAP kinase, and examined phosphorylation of CDC25C, a G2/M checkpoint control protein, in the presence of overexpressed PPM1D.”
    “We confirmed that p38 activation was completely inhibited by SB203580 by measuring p38 MAP kinase activity in the presence and absence of the drug (Fig. 5D).”

  • The paper relies on this without support.

    Phosphorylated p53 is more active and increases PPM1D expression.

    “Phosphorylated p53 is more active and up-regulates PPM1D expression.”

  • The paper relies on this without support.

    ATM and ATR phosphorylate Chk1 at Ser317.

    “while ATM and ATR phosphorylate that site.”

  • The paper relies on this without support.

    PPM1D mRNA up-regulation after DNA damage is p53-dependent.

    “PPM1D mRNA was up-regulated in a p53-dependent manner following UV, IR, and other DNA damaging agents.”
6 of 6

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?

  • PPM1D (WIP1) is also a p53 target and encodes for a phosphatase that confers a negative feedback loop through p53 dephosphorylation and cell cycle checkpoint abrogation.

    “PPM1D (WIP1) is also a p53 target and encodes for a phosphatase that confers a negative feedback loop through p53 dephosphorylation and cell cycle checkpoint abrogation.40, 220, 221”

    From Census and evaluation of p53 target genes (2017) · cites this paper as [220]

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.

  • Negative-control peptide result points to the wrong figure

    Minor

    The text directs readers to Figure 1A for the phosphopeptide result, whereas the figure descriptions place that assay in Figure 2A. Figure 1A describes a Chk1-PPM1D binding experiment.

  • Checkpoint UV dose conflicts with the methods

    Minor

    The results describe an intra-S-phase checkpoint experiment using 30 J/m2 UV, but the methods say all checkpoint experiments used 5 J/m2.

2 of 2

The citation lists haven’t been fetched yet

References 48 · Cited by 389

Research works printed but not linked: 3

  1. 2004, Cell Cycle, 3, 529
  2. 2003, Clin. Cancer Res., 9, 1995
  3. 2003, Cancer Res., 63, 1876

Authors
Lu, X., Nannenga, B., & Donehower, L. A.
Affiliations
Baylor College of Medicine (US)
ORCID
Lu, Xiongbin
Venue
Genes & Development
Publisher
Cold Spring Harbor Laboratory
Published
2005-05-03
Volume
19
Issue
10
Pages
1162-1174
ISSN
  • 0890-9369 (ISSN-L)
  • 1549-5477
DOI
10.1101/gad.1291305
PMC
PMC1132003
OpenAlex
W2162369786
Semantic Scholar
c15a0d98cdd8c39f028470c5a58ca174b668da61
Cited by
389
References
48
Citations by year
2026: 7 · 2025: 10 · 2024: 16 · 2023: 18 · 2022: 14 · 2021: 13 · 2020: 20 · 2019: 15 · 2018: 21 · 2017: 16 · 2016: 16 · 2015: 21 · 2014: 27 · 2013: 27 · 2012: 21
Type
posted content
Language
en
Open access
Locations
  • Genes & Development (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • HighWire Press Open Archive (submittedVersion)
Funders
National Cancer Institute
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › DNA Repair Mechanisms
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Tyrosine Phosphatases
  • Health Sciences › Medicine › Oncology › Cancer-related Molecular Pathways
Keywords
PPM1D, Wip1, Chk1, p53, dephosphorylation, ATM kinase, ATR kinase, DNA damage response, cell cycle checkpoints, S-phase checkpoint, G2/M checkpoint, DNA repair, ultraviolet radiation, ionizing radiation
MeSH terms
Protein Phosphatase 2C, Checkpoint Kinase 1, Cell Cycle, DNA Damage, DNA Repair, DNA-Binding Proteins, Homeostasis, Humans, Neoplasm Proteins, Phosphoprotein Phosphatases, Protein Kinases, Ultraviolet Rays, Signal Transduction, Tumor Suppressor Protein p53, Protein Serine-Threonine Kinases, Cell Cycle Proteins, Tumor Suppressor Proteins, Cell Line, Tumor, 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.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review