Natural Trans-spliced mRNAs Are Generated from the Human Estrogen Receptor-α (hERα) Gene

Abstract

The human estrogen receptor-␣ (hER␣) gene is a complex genomic unit exhibiting alternative splicing and promoter usage in a tissue-specific manner. During the investigation of new hER␣ mRNA variants by rapid amplification of 5 cDNA ends, we identified a cDNA in which the acceptor site of exon 1A, into which the different leader exons are normally alternatively spliced, was spliced accurately the 3 extremity of exon 1A (scrambled 1A31A hER␣ cDNA). Reverse transcription-PCR and S1 nuclease mapping analysis revealed that 1A31A hER␣ transcripts were not circular RNAs constituted by exon 1A only but corresponded to linear polyadenylated hER␣ RNAs composed of the eight coding exons of the hER␣ gene and characterized by a duplication of exon 1A. Genomic Southern blot experiments excluded the hypothesis of duplication of hER␣ exon 1A in the human genome. Therefore, these data suggested that 1A31A hER␣ transcripts were likely generated by trans-splicing. The production of such transcripts by trans-splicing of pre-mRNAs generated from a chimeric gene formed by a single hER␣ exon 1A, exon 2, and their flanking intronic regions was demonstrated in transient transfection experiments. Therefore, in addition to the alternative cis-splicing, the hER␣ gene is also subject to natural trans-splicing. The estrogen receptor-␣ (ER␣)1 is a ligand-inducible transcription factor that belongs to the steroid, thyroid hormone, and retinoic acid receptor family (1-3). As all members of this family, it modulates transcription of specific sets of genes by interacting either in a protein/DNA manner with cognate DNA sequences called responsive elements or in a protein/protein manner with other transcriptional factors (1-5).ER␣ is a key component of a wide range of biological processes. Its main role is in the control of the reproductive functions such as the establishment and maintenance of female sex differentiation characteristics, reproductive cycle, and pregnancy (6, 7). ER␣ is also involved in liver, fat, and bone cell metabolism, cardiovascular and neuronal activity, and embryonic and fetal development (6, 7). Finally, due to the mitogenic effect of its ligand, ER␣ is intimately associated with the biology of endometrium and breast cancers (8 -10).ER status is used clinically both as a prognostic factor and as a target in the therapy of breast cancers (9). Patients with ER-positive tumors have a better prognosis than those with tumors that lack ER expression. The benefits of the anti-estrogen therapy are almost limited to these patients, although quite a number of ER-positive tumors do not respond to endocrine therapy (8, 9). The resistance to hormonal therapy has often been associated with genetic defects within ER biology (11, 12). Thus, the identification of the molecular mechanisms controlling ER␣ expression and function and those that may impair ER␣ biology turned out to be a crucial step for understanding the involvement of the estrogen receptor into several physiological and pathological processes.Mapped to the long arm of chromoso...

Gene Therapy Progress and Prospects: Reprograming gene expression by trans-splicing

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High-Throughput Screening for Highly Functional RNA-Trans-Splicing Molecules: Correction of Plectin in Epidermolysis Bullosa Simplex

“…Pre-mRNA splicing is a naturally occurring process during mRNA maturation, which was first seen in trypanosomes, nematodes and recently also in humans (Murphy et al, 1986;Flouriot et al, 2002;Davis et al, 1995). During trans-splicing, the spliceosome ligates a 5' exon from one pre-mRNA with a 3' exon from another pre-mRNA, thereby producing an "alternative" mature mRNA, composed of exons derived from two different precursors.…”

Chimeric RNAs as potential biomarkers for tumor diagnosis

“…Further studies have indicated that many other RNA chimeras are generated from mechanisms such as transcription read-through and splicing, transcription of short homologous sequence slippage or from so called trans-splicing (Table 1) (1). In the aid of high-throughput sequencing technology and bioinformatics analysis, a growing number of chimeric RNAs have been identified and validated during the last two years (2)(3)(4)(5)(6)(7)(8) …”