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Translational efficiency is up-regulated by alternative exon in murine IL-15 mRNA
H Nishimura1, J Washizu, N Nakamura
1Laboratory of Host Defense and Germfree Life, Research Institute for Disease Mechanism and Control, Nagoya University School of Medicine, Japan.
Abstract:
IL-15 promotes the growth of T cells and shares properties of IL-2. IL-2 is produced exclusively by T cells, while IL-15 message is expressed by a variety of tissues. However, it has been difficult to demonstrate IL-15 in the supernatants of many cells that express message for this cytokine. This suggests that IL-15 production is regulated by post-transcriptional controls. In this study, we cloned three types of murine IL-15 cDNA isoforms generated by alternative splicing and compared the translational efficiency among these isoforms. The translational efficiency of isoforms with alternative exon 5 containing another 3' splice site was significantly higher than that of IL-15 cDNA with originally described exon 5, which is generated by internal splicing of alternative exon 5. The translation product of the isoform containing alternative exon 5 has a shorter open reading frame due to stop codons in additional sequence, followed by a new AUG codon, and displays a shorter leader sequence. The shorter isoform of the IL-15 was detected in peritoneal macrophages stimulated with IFN-gamma and LPS, which expressed an abundant level of alternative exon 5. These results suggest that normal IL-15 production in stimulated macrophages is regulated by splicing of alternative exon 5.
Insights
Interleukin-15 (IL-15) production in macrophages is controlled by alternative splicing of exon 5. This post-transcriptional regulation results in a shorter, more efficiently translated IL-15 isoform.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- Interleukin-15 (IL-15) is crucial for T cell growth, sharing functions with Interleukin-2 (IL-2).
- While IL-15 mRNA is widespread, secreted IL-15 protein is often undetectable, suggesting post-transcriptional regulation.
- Understanding IL-15 regulation is key to controlling immune responses.
Purpose of the Study:
- To investigate the role of alternative splicing in regulating IL-15 production.
- To compare the translational efficiency of different murine IL-15 cDNA isoforms.
- To identify the specific IL-15 isoform produced by stimulated macrophages.
Main Methods:
- Cloning of three murine IL-15 cDNA isoforms generated by alternative splicing.
- Comparison of translational efficiency among the cloned isoforms.
- Detection of IL-15 isoforms in IFN-gamma and LPS-stimulated peritoneal macrophages.
Main Results:
- Isoforms with alternative exon 5 showed significantly higher translational efficiency compared to the original exon 5.
- The alternative exon 5 isoform results in a shorter open reading frame and leader sequence.
- A shorter IL-15 isoform, utilizing alternative exon 5, was detected in stimulated macrophages.
Conclusions:
- Alternative splicing of exon 5 is a key post-transcriptional mechanism regulating IL-15 production.
- This splicing event leads to a more efficiently translated, shorter IL-15 isoform.
- The findings elucidate a novel regulatory pathway for IL-15 in immune cells.