Polyamine-regulated unproductive splicing and translation of spermidine/spermine N1-acetyltransferase

Mervi T. Hyvönen; Anne Uimari; Tuomo A. Keinänen; Sami Heikkinen; Riikka Pellinen; Tiina Wahlfors; Arja Korhonen; Ale Närvänen; Jarmo Wahlfors; Leena Alhonen; Juhani Jänne

doi:10.1261/rna.39806

Polyamine-regulated unproductive splicing and translation of spermidine/spermine N¹-acetyltransferase

¹Department of Biotechnology and Molecular Medicine, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, FI-70211 Kuopio, Finland
²Department of Chemistry, University of Kuopio, FI-70211 Kuopio, Finland

Abstract

Spermidine/spermine N¹-acetyltransferase (SSAT), the rate-controlling enzyme in the interconversion of spermidine and spermine, is regulated by polyamines and their analogs at many levels of gene expression. Recently, SSAT pre-mRNA has been shown to undergo alternative splicing by inclusion of an exon that contains premature termination codons. In the present study, we show that alterations in the intracellular polyamine level resulted in a change in the relative abundance of SSAT transcripts. Addition of polyamines or their N-diethylated analogs reduced the amount of the variant transcript, whereas polyamine depletion by 2-difluoromethylornithine or MG-132 enhanced the exon inclusion. Experiments performed with protein synthesis inhibitors and siRNA-mediated down-regulation of Upf1 protein verified that the variant transcript was degraded by nonsense-mediated mRNA decay (NMD). Interestingly, several proteins have been shown to regulate their expression by alternative splicing-coupled NMD, termed regulated unproductive splicing and translation (RUST). Our present results suggest that in the case of SSAT, RUST is mediated by polyamines, and this system functions to fine-tune the polyamine metabolism.

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Footnotes

Reprint requests to: Mervi T. Hyvönen, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, P.O. Box 1627, Kuopio, FI-70211, Finland; e-mail: Mervi.Hyvonen{at}uku.fi; fax: +358-17-163025.
Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.39806.
Abbreviations: SSAT, spermidine/spermine N¹-acetyltransferase; MT, metallothionein; NMD, nonsense-mediated mRNA decay; DENSpd, N¹,N⁷-diethylnorspermidine; DESpd, N¹N⁸-diethylspermidine; DENSpm, N¹N¹¹-diethylnorspermine; DESpm, N¹,N¹²-diethylspermine; DFMO, 2-difluoromethylornithine; Me₂Spm, Bis-α,ω-methylspermine; SFV, Semliki Forest virus; CHX, cycloheximide; PUR, puromycin; Upf1, Up-frameshift protein 1; ABCC4, multidrug resistance associated protein 4; RUST, regulated unproductive splicing and translation; PTC, premature termination codon.
- Received January 24, 2006.
- Accepted May 12, 2006.