Cancer-associated missplicing of exon 4 influences the subnuclear distribution of the DNA replication factor CIZ1.
Cip1-interacting zinc finger protein 1 (CIZ1, also known as CDKN1A-interacting zinc finger protein 1) stimulates initiation of mammalian DNA replication and is normally tethered to the nuclear matrix within DNA replication foci. Here, we show that an alternatively spliced human CIZ1 variant, lacking exon 4 (Delta E4), is misexpressed as a consequence of intronic mutation in Ewing tumor (ET) cell lines. In all ET lines tested, exon 4 is skipped and an upstream mononucleotide repeat element is expanded to contain up to 28 thymidines, compared to 16 in controls. In exon-trap experiments, a 24T variant produced three-fold more exon skipping than a 16T variant, demonstrating a direct effect on splicing. In functional assays, Delta E4 protein retains replication activity, but fails to form subnuclear foci. Furthermore, coexpression of mouse Delta E4 with Ciz1 prevents Ciz1 from localizing appropriately, having a dominant negative effect on foci formation. The data show that conditional exclusion of exon 4 influences the spatial distribution of the Ciz1 protein within the nucleus, and raise the possibility that CIZ1 alternative splicing could influence organized patterns of DNA replication.
Rahman
Faisal  Abdel
F
Biology Department, University of York, Heslington, York, United Kingdom.
Ainscough
Justin F-X
JF
Copeland
Nikki
N
Coverley
Dawn
D
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D045744:Cell Line, Tumor; D004261:DNA Replication; D005091:Exons; D014644:Genetic Variation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009369:Neoplasms / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
C400423:Ciz1 protein, human; D009687:Nuclear Proteins