title: A Novel BRCA1-Associated Protein-1 Isoform Affects Response of Mesothelioma Cells to Drugs Impairing BRCA1-Mediated DNA Repair.
abstract: BRCA1 associated protein1 (BAP1) is a tumor suppressor involved in multiple cellular processes such as transcriptional regulation, chromatin modification by deubiquitinating histone 2A, and DNA repair. BAP1 mutations are frequent in malignant pleural mesothelioma (MPM). Our aim was to functionally characterize a newly identified isoform of BAP1 and investigate the effects of its expression on drug sensitivity in MPM.
  
  
  
  Expression of BAP1 isoforms was detected by quantitative polymerase chain reaction in MPM and normal mesothelium cell lines and tumor and nontumor samples. Histone H2A ubiquitination levels were analyzed by Western blot after acidic extraction of core histones. Subcellular localization of BAP1 isoforms was examined by immunofluorescence. MPM cell survival in response to poly(adenosine diphosphate-ribose) polymerase (PARP) and dual phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) inhibitors was analyzed by in vitro assays.
  
  
  
  We have identified a novel alternative splice isoform of BAP1 (BAP1Δ) that misses part of the catalytic domain. Cells transfected with BAP1Δ showed reduced deubiquitinating activity compared with full-length BAP1. The expression of BAP1Δ transcript is more abundant in nontumor than in tumor samples. MPM cell lines expressing more than 20% of BAP1Δ are more sensitive to olaparib (a PARP1 inhibitor) cytotoxicity, and this sensitivity is enhanced when olaparib treatment is combined with GDC0980 (a dual PI3K-mTOR inhibitor), which induces downregulation of BRCA1.
  
  
  
  These observations suggest that BAP1Δ does regulate DNA damage response and influences drug sensitivity. It might therefore be relevant to investigate whether patients with high expression of BAP1Δ may be responsive to PARP/PI3K-mTOR inhibitors.
authors.affiliation: Laboratory of Molecular Oncology, Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Rossella
authors.initials: R
authors.lastname: Parrotta
authors.affiliation: Laboratory of Molecular Oncology, Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Agata
authors.initials: A
authors.lastname: Okonska
authors.affiliation: Laboratory of Molecular Oncology, Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Manuel
authors.initials: M
authors.lastname: Ronner
authors.affiliation: Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Walter
authors.initials: W
authors.lastname: Weder
authors.affiliation: Cancer Center Zürich, University Hospital Zürich, Zürich, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Stahel
authors.affiliation: Institute of Molecular Cancer Research, University of Zürich, Zürich, Switzerland.
authors.forename: Lorenza
authors.initials: L
authors.lastname: Penengo
authors.affiliation: Laboratory of Molecular Oncology, Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland. Electronic address: emanuela.felley-bosco@usz.ch.
authors.forename: Emanuela
authors.initials: E
authors.lastname: Felley-Bosco
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000008:administration & dosage / Q000494:pharmacology; D045744:Cell Line, Tumor; D004260:DNA Repair; D004357:Drug Synergism; D006801:Humans; D008654:Mesothelioma / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010793:Phthalazines / Q000008:administration & dosage / Q000494:pharmacology; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D020033:Protein Isoforms; D011743:Pyrimidines / Q000008:administration & dosage / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D043222:Ubiquitin Thiolesterase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
chemical_list: C569670:1-(4-((2-(2-aminopyrimidin-5-yl)-7-methyl-4-morpholinothieno(3,2-d)pyrimidin-6-yl)methyl)piperazin-1-yl)-2-hydroxypropan-1-one; C400134:BAP1 protein, human; D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D019086:Bridged Bicyclo Compounds, Heterocyclic; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D020033:Protein Isoforms; D011743:Pyrimidines; D025521:Tumor Suppressor Proteins; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D043222:Ubiquitin Thiolesterase; C531550:olaparib
keywords: BRCA1; BRCA1 associated protein 1; Mesothelioma; PARP inhibition