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Absence of Wip1 partially rescues Atm deficiency phenotypes in mice.

Darlington Y, Nguyen TA, Moon SH, Herron A, Rao P, Zhu C, Lu X, Donehower LA - Oncogene (2011)

Bottom Line: WIP1 may have a homeostatic role in ATM signaling by returning the cell to a normal pre-stress state following completion of DNA repair.Additionally, double knockout splenocytes displayed reduced chromosomal instability compared with Atm mice.These results indicate that inhibition of WIP1 may represent a useful strategy for cancer treatment in general and A-T patients in particular.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Graduate Program in Cell and Molecular Biology, Houston, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Wild-type p53-induced phosphatase 1 (WIP1) is a serine/threonine phosphatase that dephosphorylates proteins in the ataxia telangiectasia mutated (ATM)-initiated DNA damage response pathway. WIP1 may have a homeostatic role in ATM signaling by returning the cell to a normal pre-stress state following completion of DNA repair. To better understand the effects of WIP1 on ATM signaling, we crossed Atm-deficient mice to Wip1-deficient mice and characterized phenotypes of the double knockout progeny. We hypothesized that the absence of Wip1 might rescue Atm deficiency phenotypes. Atm mice, like ATM-deficient humans with the inherited syndrome ataxia telangiectasia, exhibit radiation sensitivity, fertility defects, and are T-cell lymphoma prone. Most double knockout mice were largely protected from lymphoma development and had a greatly extended lifespan compared with Atm mice. Double knockout mice had increased p53 and H2AX phosphorylation and p21 expression compared with their Atm counterparts, indicating enhanced p53 and DNA damage responses. Additionally, double knockout splenocytes displayed reduced chromosomal instability compared with Atm mice. Finally, doubly mice were partially rescued from gametogenesis defects observed in Atm mice. These results indicate that inhibition of WIP1 may represent a useful strategy for cancer treatment in general and A-T patients in particular.

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Absence of Wip1 increases genomic stability of Atm  splenocytes(A-F) SKY analysis of Atm+/+Wip1+/+ (N=4) (A), Atm+/+Wip1−/− (N=4) (B), Atm−/−Wip1+/+ (N=6) (C,D), and Atm−/−Wip1−/− (N=5) (E,F) splenocytes. Aberrant chromosomes (either non-diploid numbers or translocations) are indicated by red boxes. Atm−/−Wip1−/− splenocytes have decreased genomic instability compared to Atm−/−Wip1+/+ splenocytes. (G) Graph comparing the average number of chromosomal aberrations observed per mouse (12-20 metaphase profiles analyzed per mouse and normalized) using SKY analysis. Atm−/−Wip1−/− splenocytes have a decreased number of chromosomal aberrations per mouse compared to Atm−/−Wip1+/+ splenocytes. **P = 0.009. (H) Graph comparing the average number of chromosomal aberrations per cell for each genotype. Atm−/−Wip1−/− splenocytes have a reduced number of chromosomal aberrations per cell observed compared to Atm−/−Wip1+/+ splenocytes. *P = 0.03.
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Figure 3: Absence of Wip1 increases genomic stability of Atm splenocytes(A-F) SKY analysis of Atm+/+Wip1+/+ (N=4) (A), Atm+/+Wip1−/− (N=4) (B), Atm−/−Wip1+/+ (N=6) (C,D), and Atm−/−Wip1−/− (N=5) (E,F) splenocytes. Aberrant chromosomes (either non-diploid numbers or translocations) are indicated by red boxes. Atm−/−Wip1−/− splenocytes have decreased genomic instability compared to Atm−/−Wip1+/+ splenocytes. (G) Graph comparing the average number of chromosomal aberrations observed per mouse (12-20 metaphase profiles analyzed per mouse and normalized) using SKY analysis. Atm−/−Wip1−/− splenocytes have a decreased number of chromosomal aberrations per mouse compared to Atm−/−Wip1+/+ splenocytes. **P = 0.009. (H) Graph comparing the average number of chromosomal aberrations per cell for each genotype. Atm−/−Wip1−/− splenocytes have a reduced number of chromosomal aberrations per cell observed compared to Atm−/−Wip1+/+ splenocytes. *P = 0.03.

Mentions: Previously, spectral karyotyping (SKY) analysis revealed that both murine Atm fibroblasts and A-T cells from humans display increased chromosomal instability (Barlow et al., 1996; Chun and Gatti, 2004). Since the Atm−/−Wip1−/− mice have enhanced DNA damage responses, we hypothesized that cells from these mice might also have reduced chromosomal instability. To test this, splenocytes from Atm+/+Wip1+/+, Atm+/+Wip1−/−, Atm−/−Wip1+/+, and Atm−/−Wip1−/− eight week old mice were isolated, mitogen-activated, and subjected to SKY analysis. No aberrations were detected in metaphase chromosomes from 12-20 metaphase profiles prepared from each of four Atm+/+Wip1+/+ and four Atm+/+Wip1−/− mice (Fig. 3A,B). SKY analysis of splenocyte metaphase spreads from six Atm−/−Wip1+/+ mice revealed multiple chromosomal aberrations, including translocations, chromosome losses, and chromosome gains (Fig. 3C,D). Conversely, metaphase spreads from splenocytes of five Atm−/−Wip1−/− mice averaged fewer chromosomal abnormalities than those from Atm−/−Wip1+/+ mice (Fig. 3E,F). Overall, Atm splenocytes averaged 18.3 chromosomal aberrations per mouse analyzed, whereas Atm−/−Wip1−/− splenocytes averaged 6.8 chromosomal aberrations per mouse (Fig. 3G). This difference was statistically significant (P = 0.009). Atm−/−Wip1+/+ mice averaged 1.42 chromosomal aberrations per individual metaphase, while Atm−/−Wip1−/− mice averaged 0.59 chromosomal aberrations per individual metaphase, which was statistically significant (P = 0.03) (Fig. 3H). Thus, the absence of Wip1 significantly decreases the genomic instability of Atm cells.


Absence of Wip1 partially rescues Atm deficiency phenotypes in mice.

Darlington Y, Nguyen TA, Moon SH, Herron A, Rao P, Zhu C, Lu X, Donehower LA - Oncogene (2011)

Absence of Wip1 increases genomic stability of Atm  splenocytes(A-F) SKY analysis of Atm+/+Wip1+/+ (N=4) (A), Atm+/+Wip1−/− (N=4) (B), Atm−/−Wip1+/+ (N=6) (C,D), and Atm−/−Wip1−/− (N=5) (E,F) splenocytes. Aberrant chromosomes (either non-diploid numbers or translocations) are indicated by red boxes. Atm−/−Wip1−/− splenocytes have decreased genomic instability compared to Atm−/−Wip1+/+ splenocytes. (G) Graph comparing the average number of chromosomal aberrations observed per mouse (12-20 metaphase profiles analyzed per mouse and normalized) using SKY analysis. Atm−/−Wip1−/− splenocytes have a decreased number of chromosomal aberrations per mouse compared to Atm−/−Wip1+/+ splenocytes. **P = 0.009. (H) Graph comparing the average number of chromosomal aberrations per cell for each genotype. Atm−/−Wip1−/− splenocytes have a reduced number of chromosomal aberrations per cell observed compared to Atm−/−Wip1+/+ splenocytes. *P = 0.03.
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Figure 3: Absence of Wip1 increases genomic stability of Atm splenocytes(A-F) SKY analysis of Atm+/+Wip1+/+ (N=4) (A), Atm+/+Wip1−/− (N=4) (B), Atm−/−Wip1+/+ (N=6) (C,D), and Atm−/−Wip1−/− (N=5) (E,F) splenocytes. Aberrant chromosomes (either non-diploid numbers or translocations) are indicated by red boxes. Atm−/−Wip1−/− splenocytes have decreased genomic instability compared to Atm−/−Wip1+/+ splenocytes. (G) Graph comparing the average number of chromosomal aberrations observed per mouse (12-20 metaphase profiles analyzed per mouse and normalized) using SKY analysis. Atm−/−Wip1−/− splenocytes have a decreased number of chromosomal aberrations per mouse compared to Atm−/−Wip1+/+ splenocytes. **P = 0.009. (H) Graph comparing the average number of chromosomal aberrations per cell for each genotype. Atm−/−Wip1−/− splenocytes have a reduced number of chromosomal aberrations per cell observed compared to Atm−/−Wip1+/+ splenocytes. *P = 0.03.
Mentions: Previously, spectral karyotyping (SKY) analysis revealed that both murine Atm fibroblasts and A-T cells from humans display increased chromosomal instability (Barlow et al., 1996; Chun and Gatti, 2004). Since the Atm−/−Wip1−/− mice have enhanced DNA damage responses, we hypothesized that cells from these mice might also have reduced chromosomal instability. To test this, splenocytes from Atm+/+Wip1+/+, Atm+/+Wip1−/−, Atm−/−Wip1+/+, and Atm−/−Wip1−/− eight week old mice were isolated, mitogen-activated, and subjected to SKY analysis. No aberrations were detected in metaphase chromosomes from 12-20 metaphase profiles prepared from each of four Atm+/+Wip1+/+ and four Atm+/+Wip1−/− mice (Fig. 3A,B). SKY analysis of splenocyte metaphase spreads from six Atm−/−Wip1+/+ mice revealed multiple chromosomal aberrations, including translocations, chromosome losses, and chromosome gains (Fig. 3C,D). Conversely, metaphase spreads from splenocytes of five Atm−/−Wip1−/− mice averaged fewer chromosomal abnormalities than those from Atm−/−Wip1+/+ mice (Fig. 3E,F). Overall, Atm splenocytes averaged 18.3 chromosomal aberrations per mouse analyzed, whereas Atm−/−Wip1−/− splenocytes averaged 6.8 chromosomal aberrations per mouse (Fig. 3G). This difference was statistically significant (P = 0.009). Atm−/−Wip1+/+ mice averaged 1.42 chromosomal aberrations per individual metaphase, while Atm−/−Wip1−/− mice averaged 0.59 chromosomal aberrations per individual metaphase, which was statistically significant (P = 0.03) (Fig. 3H). Thus, the absence of Wip1 significantly decreases the genomic instability of Atm cells.

Bottom Line: WIP1 may have a homeostatic role in ATM signaling by returning the cell to a normal pre-stress state following completion of DNA repair.Additionally, double knockout splenocytes displayed reduced chromosomal instability compared with Atm mice.These results indicate that inhibition of WIP1 may represent a useful strategy for cancer treatment in general and A-T patients in particular.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Graduate Program in Cell and Molecular Biology, Houston, Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT
Wild-type p53-induced phosphatase 1 (WIP1) is a serine/threonine phosphatase that dephosphorylates proteins in the ataxia telangiectasia mutated (ATM)-initiated DNA damage response pathway. WIP1 may have a homeostatic role in ATM signaling by returning the cell to a normal pre-stress state following completion of DNA repair. To better understand the effects of WIP1 on ATM signaling, we crossed Atm-deficient mice to Wip1-deficient mice and characterized phenotypes of the double knockout progeny. We hypothesized that the absence of Wip1 might rescue Atm deficiency phenotypes. Atm mice, like ATM-deficient humans with the inherited syndrome ataxia telangiectasia, exhibit radiation sensitivity, fertility defects, and are T-cell lymphoma prone. Most double knockout mice were largely protected from lymphoma development and had a greatly extended lifespan compared with Atm mice. Double knockout mice had increased p53 and H2AX phosphorylation and p21 expression compared with their Atm counterparts, indicating enhanced p53 and DNA damage responses. Additionally, double knockout splenocytes displayed reduced chromosomal instability compared with Atm mice. Finally, doubly mice were partially rescued from gametogenesis defects observed in Atm mice. These results indicate that inhibition of WIP1 may represent a useful strategy for cancer treatment in general and A-T patients in particular.

Show MeSH
Related in: MedlinePlus