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The function of spliceosome components in open mitosis.

ABSTRACT: Spatial separation of eukaryotic cells into the nuclear and cytoplasmic compartment permits uncoupling of DNA transcription from translation of mRNAs and allows cells to modify newly transcribed pre mRNAs extensively. Intronic sequences (introns), which interrupt the coding elements (exons), are excised ("spliced") from pre-mRNAs in the nucleus to yield mature mRNAs. This not only enables alternative splicing as an important source of proteome diversity, but splicing is also an essential process in all eukaryotes and knock-out or knock-down of splicing factors frequently results in defective cell proliferation and cell division. However, higher eukaryotes progress through cell division only after breakdown of the nucleus ("open mitosis"). Open mitosis suppresses basic nuclear functions such as transcription and splicing, but allows separate, mitotic functions of nuclear proteins in cell division. Mitotic defects arising after loss-of-function of splicing proteins therefore could be an indirect consequence of compromised splicing in the closed nucleus of the preceding interphase or reflect a direct contribution of splicing proteins to open mitosis. Although experiments to directly distinguish between these two alternatives have not been reported, indirect evidence exists for either hypotheses. In this review, we survey published data supporting an indirect function of splicing in open mitosis or arguing for a direct function of spliceosomal proteins in cell division.

SUBMITTER: Hofmann JC

PROVIDER: S-EPMC3027046 | biostudies-literature | 2010 Nov-Dec

REPOSITORIES: biostudies-literature

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The function of spliceosome components in open mitosis.

Hofmann Jennifer C JC Husedzinovic Alma A Gruss Oliver J OJ

Nucleus (Austin, Tex.) 20100813 6

Spatial separation of eukaryotic cells into the nuclear and cytoplasmic compartment permits uncoupling of DNA transcription from translation of mRNAs and allows cells to modify newly transcribed pre mRNAs extensively. Intronic sequences (introns), which interrupt the coding elements (exons), are excised ("spliced") from pre-mRNAs in the nucleus to yield mature mRNAs. This not only enables alternative splicing as an important source of proteome diversity, but splicing is also an essential process ...[more]

PMID: 21327086

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Project description: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.

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The function of spliceosome components in open mitosis.

Publications

The function of spliceosome components in open mitosis.

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