title: Multiple components of the spliceosome regulate Mcl1 activity in neuroblastoma.
abstract: Cancer treatments induce cell stress to trigger apoptosis in tumor cells. Many cancers repress these apoptotic signals through alterations in the Bcl2 proteins that regulate this process. Therapeutics that target these specific survival biases are in development, and drugs that inhibit Bcl2 activities have shown clinical activity for some cancers. Mcl1 is a survival factor for which no effective antagonists have been developed, so it remains a principal mediator of therapy resistance, including to Bcl2 inhibitors. We used a synthetic-lethal screening strategy to identify genes that regulate Mcl1 survival activity using the pediatric tumor neuroblastoma (NB) as a model, as a large subset are functionally verified to be Mcl1 dependent and Bcl2 inhibitor resistant. A targeted siRNA screen identified genes whose knockdown restores sensitivity of Mcl1-dependent NBs to ABT-737, a small molecule inhibitor of Bcl2, BclXL and BclW. Three target genes that shifted the ABT-737 IC50 >1 log were identified and validated: PSMD14, UBL5 and PRPF8. The latter two are members of a recently characterized subcomplex of the spliceosome that along with SART1 is responsible for non-canonical 5'-splice sequence recognition in yeast. We showed that SART1 knockdown similarly sensitized Mcl1-dependent NB to ABT-737 and that triple knockdown of UBL5/PRPF8/SART1 phenocopied direct MCL1 knockdown, whereas having no effect on Bcl2-dependent NBs. Both genetic spliceosome knockdown or treatment with SF3b-interacting spliceosome inhibitors like spliceostatin A led to preferential pro-apoptotic Mcl1-S splicing and reduced translation and abundance of Mcl1 protein. In contrast, BN82865, which inhibits the second transesterification step in terminal spliceosome processing, did not have this effect. These findings demonstrate a prominent role for the spliceosome in mediating Mcl1 activity and suggest that drugs that target either the specific UBL5/PRPF8/SART1 subcomplex or SF3b functions may have a role as cancer therapeutics by attenuating the Mcl1 survival bias present in numerous cancers.
authors.affiliation: Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Laetsch
authors.affiliation: Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.affiliation: Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
authors.forename: A
authors.initials: A
authors.lastname: Vu
authors.affiliation: Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
authors.forename: M
authors.initials: M
authors.lastname: Sliozberg
authors.affiliation: Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA.
authors.forename: M
authors.initials: M
authors.lastname: Vido
authors.affiliation: The Children's Hospital of Philadelphia/Westat, Biostatistics and Data Management Core, 3535 Market Street, Philadelphia, PA 19104, USA.
authors.forename: O U
authors.initials: OU
authors.lastname: Elci
authors.affiliation: 1] Division of Hematology/Oncology, Aflac Children's Cancer Center, Children's Healthcare of Atlanta, 2015 Uppergate Drive, ECC 460, Atlanta, GA 30322, USA [2] Department of Pediatrics, Emory University School of Medicine, Atlanta, GA 30322, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Goldsmith
authors.affiliation: 1] Division of Oncology, The Children's Hospital of Philadelphia, 3501 Civic Center Boulevard, Philadelphia, PA 19104-4318, USA [2] Department of Pediatrics, Perelman School of Medicine, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, PA 19104-6055, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Hogarty
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D005136:Eye Proteins; C579095:MCL1 protein, human; D046912:Multiprotein Complexes; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C115374:PRPF8 protein, human; C109285:PSMD14 protein, human; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; C431323:SART1 protein, human; D015534:Trans-Activators; C429294:UBL5 protein, human; D014452:Ubiquitins; D046988:Proteasome Endopeptidase Complex