Genome-wide silencing screen in mesothelioma cells reveals that loss of function of BAP1 induces chemoresistance to ribonucleotide reductase inhibition: implication for therapy

Abstract

IntroductionLoss 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.\n\nMethodsA genetically engineered model was established expressing either functional or nonfunctional BAP1 and whole-genome siRNA screens were performed assessing impaired survival between the two cell lines. Cytotoxity induced by gemcitabine and hydroxyurea were assessed in a panel of BAP1-WT and BAP1-mut/del cell lines. Functional studies were carried out in BAP1 mut/del cell line reconstituted with BAP1 WT or BAP1 C91A (catalytically dead mutant) and in BAP1 WT cell line upon siRNA-mediated knock-down of BAP1.\n\nResultsThe whole-genome siRNA screen unexpectedly revealed 11 hits (FDR<0.05) more cytotoxic for BAP1-proficient cells. Two actionable targets, RRM1 and RRM2, were validated and their inhibition mediated by gemcitabine or hydroxyurea respectively, was more cytotoxic in BAP1-proficient cell lines. Upregulation of RRM2 upon gemcitabine and hydroxyurea was more profound in BAP1 mut/del cell lines. Increased lethality mediated by gemcitabine and hydroxyurea was observed in NCI-H2452 cells reconstituted with BAP1 WT but not with C91A mutant and upregulation of RRM2 in NCI-H2452-BAP1 WT spheroids was modest compared to control or C91A mutant. Finally, the opposite was observed after BAP1 knockdown in BAP1-proficient SPC111 cell line.\n\nConclusionWe found that BAP1 is involved in the regulation of RRM2 levels during replication stress. These observations reveal a potential therapeutic approach where MPM patients to be stratified depending on BAP status for gemcitabine treatment.