Cyclin E associates with components of the pre-mRNA splicing machinery in mammalian cells.
Cyclin E-cdk2 is a critical regulator of cell cycle progression from G1 into S phase in mammalian cells. Despite this important function little is known about the downstream targets of this cyclin-kinase complex. Here we have identified components of the pre-mRNA processing machinery as potential targets of cyclin E-cdk2. Cyclin E-specific antibodies coprecipitated a number of cyclin E-associated proteins from cell lysates, among which are the spliceosome-associated proteins, SAP 114, SAP 145, and SAP 155, as well as the snRNP core proteins B' and B. The three SAPs are all subunits of the essential splicing factor SF3, a component of U2 snRNP. Cyclin E antibodies also specifically immunoprecipitated U2 snRNA and the spliceosome from splicing extracts. We demonstrate that SAP 155 serves as a substrate for cyclin E-cdk2 in vitro and that its phosphorylation in the cyclin E complex can be inhibited by the cdk-specific inhibitor p21. SAP 155 contains numerous cdk consensus phosphorylation sites in its N terminus and is phosphorylated prior to catalytic step II of the splicing pathway, suggesting a potential role for cdk regulation. These findings provide evidence that pre-mRNA splicing may be linked to the cell cycle machinery in mammalian cells.
Department of Cell Signaling, DNAX Research Institute, Palo Alto, California 94304-1104, USA. seghezzi@dnax.org
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Seghezzi
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Chua
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Shanahan
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Gozani
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Reed
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D000595:Amino Acid Sequence; D042846:CDC2-CDC28 Kinases; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010750:Phosphoproteins / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012322:RNA Precursors; D012326:RNA Splicing; D000072260:RNA Splicing Factors; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000378:metabolism*; D017381:Spliceosomes / Q000378:metabolism; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D019927:Cyclin E; D010750:Phosphoproteins; D012322:RNA Precursors; D000072260:RNA Splicing Factors; D017413:Ribonucleoprotein, U2 Small Nuclear; C112491:SF3B1 protein, human; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases