Multiple components of the spliceosome regulate Mcl1 activity in neuroblastoma

• Type of Material: Article
• Authors: T.W. Laetsch, Childrens Hospital of Philadelphia; X. Liu, Childrens Hospital of Philadelphia; A. Vu, Childrens Hospital of Philadelphia; M. Sliozberg, Childrens Hospital of Philadelphia; M. Vido, Childrens Hospital of Philadelphia; O.U. Elci, The Children's Hospital of Philadelphia/Westat; Kelly Goldsmith, Emory University; M.D. Hogarty, Childrens Hospital of Philadelphia
• Language: English
• Date: 2014-02-01
• Publisher: Nature Publishing Group: Open Access Journals - Option C
• Publication Version: Final Published Version
• Copyright Statement: © 2014 Macmillan Publishers Limited.
• License: Creative Commons Attribution-NonCommerical-NoDerivs 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1038/cddis.2014.40
• Title of Journal or Parent Work: Cell Death and Disease
• ISSN: 2041-4889
• Volume: 5
• Issue: 2
• Start Page: e1072
• End Page: e1072
• Grant/Funding Information: This work was supported by NIH CA97323, Alex's Lemonade Stand Foundation, Cookies for Kids Cancer Foundation (to MDH) and Bear Necessities Pediatric Cancer Foundation and NIH T32-HD0433021 (to TWL).
• Keywords: Bcl2 inhibitors; CELL BIOLOGY; Bcl2 family; experimental therapeutics; REVEALS; embryonal tumor; Life Sciences & Biomedicine; Cell Biology; Science & Technology; CANCER; PROTEIN; NUCLEAR RIBONUCLEOPROTEIN PARTICLE; PRE-MESSENGER-RNA; CHRONIC LYMPHOCYTIC-LEUKEMIA; MYELOMA CELLS; alternative splicing; APOPTOSIS; FAMILY; SURVIVAL
• Research Categories: Health Sciences, General; Health Sciences, Oncology

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. © 2014 Macmillan Publishers Limited.