ABSTRACT
Alternative splicing is a major source of protein diversity in humans. The human splicing factor zinc finger, Ran-binding domain containing protein 2 (ZRANB2) is a splicing protein whose specific endogenous targets are unknown. Its upregulation in grade III ovarian serous papillary carcinoma could suggest a role in some cancers. To determine whether ZRANB2 is part of the supraspliceosome, nuclear supernatants from human embryonic kidney 293 cells were prepared and then fractioned on a glycerol gradient, followed by Western blotting. The same was done after treatment with a tyrosine kinase to induce phosphorylation. This showed for the first time that ZRANB2 is part of the supraspliceosome, and that phosphorylation affects its subcellular location. Studies were then performed to understand the splicing targets of ZRANB2 at the whole-transcriptome level. HeLa cells were transfected with a vector containing ZRANB2 or with a vector-only control. RNA was extracted, converted to cDNA and hybridized to Affymetrix GeneChip(®) Human Exon 1.0 ST Arrays. At the FDR ≤1.3 significance level we found that ZRANB2 influenced the alternative splicing of primary transcripts of CENTB1, WDR78, C10orf18, CABP4, SMARCC2, SPATA13, OR4C6, ZNF263, CAPN10, SALL1, ST18 and ZP2. Several of these have been implicated in tumor development. In conclusion ZRANB2 is part of the supraspliceosome and causes differential splicing of numerous primary transcripts, some of which might have a role in cancer.
Subject(s)
Alternative Splicing/genetics , RNA-Binding Proteins/metabolism , Spliceosomes/metabolism , Blotting, Western , Cell Fractionation , HEK293 Cells , HeLa Cells , Humans , Oligonucleotide Array Sequence Analysis , Phosphorylation , RNA-Binding Proteins/genetics , Spliceosomes/geneticsABSTRACT
ZRANB2 was identified originally in a differential display experiment on 2-day and 10-day primary cultures of rat juxtaglomerular cells. During prolonged culture it was found to undergo down-regulation in concert with renin, the archetypical constituent of these cells. ZRANB2 has two zinc fingers that form a novel fold and show striking homology to Ran-binding protein domains. Human ZRANB2 mRNA is alternatively spliced to give two variants with different 3' ends. ZRANB2 has homologues across a range of species, the N-terminal end being particularly conserved. ZRANB2 is present in the nucleus of human cells. It binds to mRNA, as well as the essential splicing factors U170K and U2AF35 and the novel splicing component SFRS17A (formerly known as XE7). ZRANB2 is one of 20 genes up-regulated in grade III ovarian serous papillary carcinoma. Here, we review current knowledge surrounding ZRANB2.
Subject(s)
RNA-Binding Proteins/chemistry , RNA-Binding Proteins/metabolism , Animals , Chromosomes, Human, Pair 1 , Humans , Kidney Glomerulus/cytology , Neoplasms/genetics , Neoplasms/metabolism , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , RNA Splicing , RNA-Binding Proteins/geneticsABSTRACT
Pre-mRNA splicing is performed by the spliceosome. SR proteins in this macromolecular complex are essential for both constitutive and alternative splicing. By using the SR-related protein ZNF265 as bait in a yeast two-hybrid screen, we pulled out the uncharacterized human protein XE7, which is encoded by a pseudoautosomal gene. XE7 had been identified in a large-scale proteomic analysis of the human spliceosome. It consists of two different isoforms produced by alternative splicing. The arginine/serine (RS)-rich region in the larger of these suggests a role in mRNA processing. Herein we show for the first time that XE7 is an alternative splicing regulator. XE7 interacts with ZNF265, as well as with the essential SR protein ASF/SF2. The RS-rich region of XE7 dictates both interactions. We show that XE7 localizes in the nucleus of human cells, where it colocalizes with both ZNF265 and ASF/SF2, as well as with other SR proteins, in speckles. We also demonstrate that XE7 influences alternative splice site selection of pre-mRNAs from CD44, Tra2-beta1 and SRp20 minigenes. We have thus shown that the spliceosomal component XE7 resembles an SR-related splicing protein, and can influence alternative splicing.
