Suppression of exogenous gene expression by spermidine/spermine N 1-acetyltransferase 1 (SSAT1) cotransfection

Seung Bum Lee, Jong Hwan Park, Patrick M. Woster, Robert A. Casero, Myung Hee Park

Research output: Contribution to journalArticlepeer-review

Abstract

Spermidine/spermine N1-acetyltransferase 1 (SSAT1), which catalyzes the N1-acetylation of spermidine and spermine to form acetyl derivatives, is a rate-limiting enzyme in polyamine catabolism. We now report a novel activity of transiently transfected SSAT1 in suppressing the exogenous expression of other proteins, i.e. green fluorescent protein (GFP) or GFP-eIF5A. Spermidine/spermine N1-acetyltransferase 2 (SSAT2) or inactive SSAT1 mutant enzymes (R101A or R101K) were without effect. The loss of exogenous gene expression is not due to accelerated protein degradation, because various inhibitors of proteases, lysosome, or autophagy did not mitigate the effects. This SSAT1 effect cannot be attributed to the depletion of overall cellular polyamines or accumulation of N1-acetylspermidine (N 1-AcSpd) because of the following: (i) addition of putrescine, spermidine, spermine, or N1-AcSpd did not restore the expression of GFP or GFP-eIF5A; (ii) depletion of cellular polyamines with α-difluoromethylornithine, an inhibitor of ornithine decarboxylase, did not inhibit exogenous gene expression; and (iii) N1,N 11-bis(ethyl)norspermine caused a drastic depletion of cellular polyamines through induction of endogenous SSAT1 but did not block exogenous gene expression. SSAT1 transient transfection did not affect stable expression of GFP, and stably expressed SSAT1 did not affect exogenous expression of GFP, suggesting that only transiently (episomally) expressed SSAT1 blocks exogenous (episomal) expression of other proteins. SSAT1 may regulate exogenous gene expression by blocking steps involved in transcription/translation from an episomal vector by targeting non-polyamine substrate(s) critical for this pathway.

Original languageEnglish (US)
Pages (from-to)15548-15556
Number of pages9
JournalJournal of Biological Chemistry
Volume285
Issue number20
DOIs
StatePublished - May 14 2010

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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