Genomic organization of the human mi-er1 gene and characterization of alternatively spliced isoforms: regulated use of a facultative intron determines subcellular localization

• Published in: Gene 2002-07, Vol.295 (1), p.79-88
• Main Authors: Paterno, Gary D., Ding, Zhihu, Lew, Yuan-Y., Nash, Gord W., Mercer, F.Corinne, Gillespie, Laura L.
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Alternative Splicing; Amino Acid Sequence; Animals; Base Sequence; Cell Nucleus - metabolism; Cytoplasm - metabolism; Female; Fibroblast growth factor; Gene Expression; Gene structure; Genes - genetics; Humans; Immediate-early gene; Immediate-Early Proteins - genetics; Introns - genetics; Male; Mice; Molecular Sequence Data; Nuclear Proteins - genetics; Nuclear targeting; Protein Isoforms - genetics; Sequence Homology, Amino Acid; Transcription factor; Transcription Factors; Transcription, Genetic
• ISSN: 0378-1119; 1879-0038
• DOI: 10.1016/S0378-1119(02)00823-5

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-ER1α and hMI-ER1β. In all tissues except testis, transcripts encoding the β isoform were predominant. hMI-ER1α lacks the predicted nuclear localization signal and transfection assays revealed that, unlike hMI-ER1β, 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.