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Loss of INPP4B causes a DNA repair defect through loss of BRCA1, ATM and ATR and can be targeted with PARP inhibitor treatment.

Ip LR, Poulogiannis G, Viciano FC, Sasaki J, Kofuji S, Spanswick VJ, Hochhauser D, Hartley JA, Sasaki T, Gewinner CA - Oncotarget (2015)

Bottom Line: The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma.INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models.Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Biology, UCL Cancer Institute, University College London, London, UK.

ABSTRACT
Treatment options for ovarian cancer patients remain limited and overall survival is less than 50% despite recent clinical advances. The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma. Using microarray technology we identified a DNA repair defect in INPP4B-deficient cells, which we further characterized by comet assays and quantification of γH2AX, RAD51 and 53BP1 foci formation. INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models. Mechanistically, we discovered that INPP4B forms a protein complex with the key players of DNA repair, ATR and BRCA1, in GST pulldown and 293T overexpression assays, and INPP4B loss affects BRCA1, ATM and ATR protein stability resulting in the observed DNA repair defect. Given that INPP4B loss has been found in 40% of ovarian cancer patients, this study provides the rationale for establishing INPP4B as a biomarker of PARP inhibitor response, and consequently offers novel therapeutic options for a significant subset of patients. Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

No MeSH data available.


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A model indicating the role of INPP4B in DNA repairINPP4B loss causes a DNA repair defect through loss of BRCA1, ATM and ATR total protein levels.
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Figure 6: A model indicating the role of INPP4B in DNA repairINPP4B loss causes a DNA repair defect through loss of BRCA1, ATM and ATR total protein levels.

Mentions: In agreement with an underlying defect in DDR we found increased accumulation of γH2AX foci in unchallenged INPP4B knockdown cell pools compared to controls. Upon genotoxic stress, induced etoposide treatment, INPP4B-deficient cells revealed an increase and retention of γH2AX, RAD51 and 53BP1 foci relative to controls indicating abnormal DNA repair and dysfunctional HR. While loss of BRCA1 function was shown to result in suppressed RAD51 foci formation, loss of ATR was linked to increased RAD51 foci formation in conjunction with increased γH2AX foci [23, 24]. Intriguingly, INPP4B loss led to concomitant loss of BRCA1, ATM and ATR total protein levels in MEFs. We also observed reduced ATR protein levels in Ovca429 INPP4B knockdown cell pools compared to controls (Supplemental Figure 5G). Additionally we noted in MCF-10A shRNA-BRCA1 cell pools decreased levels of INPP4B. Although the degree of INPP4B loss that is needed for cancer cells to down-modulate ATR and BRCA1 levels and to acquire sensitivity towards PARP inhibitors still needs to be determined, we found that INPP4B loss greater than 50% in MEFs resulted in reduced levels of BRCA1, ATM and ATR proteins. Mechanistically, INPP4B loss may potentially affect ATR and BRCA1 protein stability due to disrupted protein-protein interaction in INPP4B-deficient cells (summarized in Figure 6). In GST pull down assays we identified the N-terminal region of INPP4B (aa1–460) necessary for interaction with ATR or BRCA1. Whether this effect is a result of direct or indirect interaction of INPP4B with ATR and BRCA1, and whether catalytic activity is required for this association will need to be further elucidated. However, our studies reveal that INPP4B plays a crucial role in modulating the stability of key players of the DDR pathway and can be therapeutically exploited for cancer patients, thus providing the rationale to investigate INPP4B as a biomarker of clinical response to PARP inhibition in ovarian cancer. Thus, loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.


Loss of INPP4B causes a DNA repair defect through loss of BRCA1, ATM and ATR and can be targeted with PARP inhibitor treatment.

Ip LR, Poulogiannis G, Viciano FC, Sasaki J, Kofuji S, Spanswick VJ, Hochhauser D, Hartley JA, Sasaki T, Gewinner CA - Oncotarget (2015)

A model indicating the role of INPP4B in DNA repairINPP4B loss causes a DNA repair defect through loss of BRCA1, ATM and ATR total protein levels.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4496374&req=5

Figure 6: A model indicating the role of INPP4B in DNA repairINPP4B loss causes a DNA repair defect through loss of BRCA1, ATM and ATR total protein levels.
Mentions: In agreement with an underlying defect in DDR we found increased accumulation of γH2AX foci in unchallenged INPP4B knockdown cell pools compared to controls. Upon genotoxic stress, induced etoposide treatment, INPP4B-deficient cells revealed an increase and retention of γH2AX, RAD51 and 53BP1 foci relative to controls indicating abnormal DNA repair and dysfunctional HR. While loss of BRCA1 function was shown to result in suppressed RAD51 foci formation, loss of ATR was linked to increased RAD51 foci formation in conjunction with increased γH2AX foci [23, 24]. Intriguingly, INPP4B loss led to concomitant loss of BRCA1, ATM and ATR total protein levels in MEFs. We also observed reduced ATR protein levels in Ovca429 INPP4B knockdown cell pools compared to controls (Supplemental Figure 5G). Additionally we noted in MCF-10A shRNA-BRCA1 cell pools decreased levels of INPP4B. Although the degree of INPP4B loss that is needed for cancer cells to down-modulate ATR and BRCA1 levels and to acquire sensitivity towards PARP inhibitors still needs to be determined, we found that INPP4B loss greater than 50% in MEFs resulted in reduced levels of BRCA1, ATM and ATR proteins. Mechanistically, INPP4B loss may potentially affect ATR and BRCA1 protein stability due to disrupted protein-protein interaction in INPP4B-deficient cells (summarized in Figure 6). In GST pull down assays we identified the N-terminal region of INPP4B (aa1–460) necessary for interaction with ATR or BRCA1. Whether this effect is a result of direct or indirect interaction of INPP4B with ATR and BRCA1, and whether catalytic activity is required for this association will need to be further elucidated. However, our studies reveal that INPP4B plays a crucial role in modulating the stability of key players of the DDR pathway and can be therapeutically exploited for cancer patients, thus providing the rationale to investigate INPP4B as a biomarker of clinical response to PARP inhibition in ovarian cancer. Thus, loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

Bottom Line: The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma.INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models.Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Biology, UCL Cancer Institute, University College London, London, UK.

ABSTRACT
Treatment options for ovarian cancer patients remain limited and overall survival is less than 50% despite recent clinical advances. The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma. Using microarray technology we identified a DNA repair defect in INPP4B-deficient cells, which we further characterized by comet assays and quantification of γH2AX, RAD51 and 53BP1 foci formation. INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models. Mechanistically, we discovered that INPP4B forms a protein complex with the key players of DNA repair, ATR and BRCA1, in GST pulldown and 293T overexpression assays, and INPP4B loss affects BRCA1, ATM and ATR protein stability resulting in the observed DNA repair defect. Given that INPP4B loss has been found in 40% of ovarian cancer patients, this study provides the rationale for establishing INPP4B as a biomarker of PARP inhibitor response, and consequently offers novel therapeutic options for a significant subset of patients. Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

No MeSH data available.


Related in: MedlinePlus