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Updated: Jan 5, 2026
Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1
Published on: February 17, 2011
Functional Genomic Screen in Mesothelioma Reveals that Loss of Function of BRCA1-Associated Protein 1 Induces
Agata Okonska1, Saskja Bühler1, Vasundhara Rao1
1Laboratory of Molecular Oncology, Lungen- und Thoraxonkologie Zentrum, University Hospital Zürich, Zürich, Switzerland.
Abstract:
Loss of function of BRCA1-associated protein 1 (BAP1) is observed in about 50% of malignant pleural mesothelioma (MPM) cases. The aim of this study was to investigate whether this aspect could be exploited for targeted therapy. A genetically engineered model was established expressing either functional or nonfunctional BAP1, and whole-genome siRNA synthetic lethality screens were performed assessing differentially impaired survival between the two cell lines. The whole-genome siRNA screen unexpectedly revealed 11 hits (FDR < 0.05) that were more cytotoxic to BAP1-proficient cells. Two actionable targets, ribonucleotide reductase (RNR) catalytic subunit M1 (RRM1) and RNR regulatory subunit M2 (RRM2), were validated. In line with the screen results, primary mesothelioma (BAP1 +/-) overexpressing BAP1 C91A (catalytically dead mutant) was more resistant to RNR inhibition, while BAP1 knockdown in the BAP1-proficient cell lines rescued the cells from their vulnerability to RNR depletion. Gemcitabine and hydroxyurea were more cytotoxic in BAP1-proficient cell line-derived spheroids compared with BAP1 deficient. Upregulation of RRM2 upon gemcitabine and hydroxyurea treatment was more profound in BAP1 mut/del cell lines. Increased lethality mediated by RNR inhibition was observed in NCI-H2452 cells reconstituted with BAP1-WT but not with BAP1 C91A. Upregulation of RRM2 in NCI-H2452-BAP1 WT spheroids was modest compared with control or C91A mutant. Together, we found that BAP1 is involved in the regulation of RNR levels during replication stress. Our observations reveal a potential clinical application where BAP1 status could serve as predictive or stratification biomarker for RNR inhibition-based therapy in MPM.
Insights
Loss of function in BRCA1-associated protein 1 (BAP1) creates vulnerability to ribonucleotide reductase (RNR) inhibition in malignant pleural mesothelioma (MPM). BAP1 status can predict response to RNR-targeted therapies.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Therapeutics
Background:
- Loss of function of BRCA1-associated protein 1 (BAP1) occurs in approximately 50% of malignant pleural mesothelioma (MPM) cases.
- Understanding the therapeutic implications of BAP1 dysfunction is crucial for developing targeted treatments for MPM.
Purpose of the Study:
- To investigate the potential of exploiting BAP1 loss of function for targeted therapy in MPM.
- To identify synthetic lethal interactions associated with BAP1 deficiency in MPM.
Main Methods:
- Establishment of genetically engineered models with functional or non-functional BAP1.
- Whole-genome siRNA synthetic lethality screens to identify genes differentially affecting cell survival.
- Validation of identified targets, including ribonucleotide reductase (RNR) subunits RRM1 and RRM2, using cell lines and spheroids.
Main Results:
- Whole-genome siRNA screens identified 11 hits more cytotoxic to BAP1-proficient cells, including RRM1 and RRM2.
- BAP1-proficient cells showed increased sensitivity to RNR inhibition, while BAP1 knockdown conferred resistance.
- Gemcitabine and hydroxyurea (RNR inhibitors) were more cytotoxic in BAP1-proficient MPM models; RRM2 upregulation varied with BAP1 status and drug treatment.
Conclusions:
- BAP1 plays a role in regulating RNR levels during replication stress.
- BAP1 status can serve as a predictive or stratification biomarker for RNR inhibition-based therapy in MPM.
- This study reveals a potential therapeutic strategy targeting MPM based on BAP1 mutational status.
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