title: Genomic organization of the human mi-er1 gene and characterization of alternatively spliced isoforms: regulated use of a facultative intron determines subcellular localization.
abstract: mi-er1 (previously called er1) is a fibroblast growth factor-inducible early response gene activated during mesoderm induction in Xenopus embryos and encoding a nuclear protein that functions as a transcriptional activator. The human orthologue of mi-er1 was shown to be upregulated in breast carcinoma cell lines and breast tumours when compared to normal breast cells. In this report, we investigate the structure of the human mi-er1 (hmi-er1) gene and characterize the alternatively spliced transcripts and protein isoforms. hmi-er1 is a single copy gene located at 1p31.2 and spanning 63 kb. It contains 17 exons and includes one skipped exon, a facultative intron and three polyadenylation signals to produce 12 transcripts encoding six distinct proteins. hmi-er1 transcripts were expressed at very low levels in most human adult tissues and the mRNA isoform pattern varied with the tissue. The 12 transcripts encode proteins containing a common internal sequence with variable N- and C-termini. Three distinct N- and two distinct C-termini were identified, giving rise to six protein isoforms. The two C-termini differ significantly in size and sequence and arise from alternate use of a facultative intron to produce hMI-ER1alpha and hMI-ER1beta. In all tissues except testis, transcripts encoding the beta isoform were predominant. hMI-ER1alpha lacks the predicted nuclear localization signal and transfection assays revealed that, unlike hMI-ER1beta, it is not a nuclear protein, but remains in the cytoplasm. Our results demonstrate that alternate use of a facultative intron regulates the subcellular localization of hMI-ER1 proteins and this may have important implications for hMI-ER1 function.
authors.affiliation: Terry Fox Cancer Research Laboratories, Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, 300 Prince Phillip Drive, St. John's, Newfoundland A1B 3V6, Canada.
authors.forename: Gary D
authors.initials: GD
authors.lastname: Paterno
authors.forename: Zhihu
authors.initials: Z
authors.lastname: Ding
authors.forename: Yuan-Y
authors.initials: YY
authors.lastname: Lew
authors.forename: Gord W
authors.initials: GW
authors.lastname: Nash
authors.forename: F Corinne
authors.initials: FC
authors.lastname: Mercer
authors.forename: Laura L
authors.initials: LL
authors.lastname: Gillespie
mesh_terms: D016475:3T3 Cells; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins; D005260:Female; D015870:Gene Expression; D005796:Genes / Q000235:genetics; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D017874:Immediate-Early Proteins; C470480:MIER1 protein, human; D009687:Nuclear Proteins; D020033:Protein Isoforms; D014157:Transcription Factors