Inactivation of eukaryotic initiation factor 5A (eIF5A) by specific acetylation of its hypusine residue by spermidine/spermine acetyltransferase 1 (SSAT1)

Abstract

SYNOPSIS The eukaryotic translation initiation factor 5A (eIF5A) is the only cellular protein containing hypusine, [Nε-(4-amino-2-hydroxybutyl)lysine]. eIF5A is activated by the posttranslational synthesis of hypusine and the hypusine modification is essential for cell proliferation. In this study, we report selective acetylation of the hypusine and/or deoxyhypusine residue of eIF5A by a key polyamine catabolic enzyme, spermidine/spermine- N1-acetyltransferase 1 (SSAT1). This enzyme normally catalyzes the N1-acetylation of spermine and spermidine to form acetyl-derivatives, which in turn are degraded to lower polyamines. Although SSAT1 has been reported to exert other effects in cells by its interaction with other cellular proteins, eIF5A is the first target protein specifically acetylated by SSAT1. Hypusine or deoxyhypusine, as the free amino acid, does not act as a substrate for SSAT1, suggesting a macromolecular interaction between eIF5A and SSAT1. Indeed, the binding of eIF5A and SSAT1 was confirmed by pull-down assays. The effect of the acetylation of hypusine on eIF5A activity was assessed by comparison of acetylated vs non-acetylated bovine testis eIF5A in the methionyl-puromycin synthesis assay. The loss of eIF5A activity by this SSAT1-mediated acetylation confirms the strict structural requirement for the hypusine side chain and suggests a possible regulation of eIF5A by hypusine acetylation/deacetylation.

Depletion of the polyamines spermidine and spermine by overexpression of spermidine/spermine N1-acetyltransferase 1 (SAT1) leads to mitochondria-mediated apoptosis in mammalian cells

“…We previously reported that eIF5A could be acetylated and inactivated by SAT1 in vitro [32]. In order to determine whether the growth inhibition in AdSAT1-transduced cells could be due to a decrease in the level of active eIF5A, hypusinated eIF5A levels were measured, using a hypusine-specific antibody [27] that recognizes eIF5A containing hypusine or deoxyhypusine, but not the unmodified lysine form nor the acetylhypusinated form (Fig.…”

Biological Relevance and Therapeutic Potential of the Hypusine Modification System

“…7B summarizes an hypothesis explaining why eIF-5A1 is differently modified in these scenarios. In a Dohh-deficient background, DHS is constantly linked to eIF-5A1 due to the missing hydroxylation of deoxyhypusine (Dhp50) and subsequently prevents binding of acetyltransferases like HDAC6, SIRT2, p300, and CBP (49,51). In contrast, Dhs depletion prevents DOHH binding and further allows acetylation of eIF-5A1.…”

Overexpression of spermidine/spermine N 1-acetyltransferase impairs osteoblastogenesis and alters mouse bone phenotype

“…Female and male transgenic mice overexpressing SSAT gene governed by its own promoter (SSAT mice) and their wild-type littermates in C57BL/ 6JOlaHsd background and mice deficient for SSAT (SSATKO mice) in C57BL/6J background were used at the age indicated in each experiment (Lee et al 2011;Leeming et al 2006). This study was carried out in strict accordance with the recommendations in the Finnish Act on Animal Experimentation.…”

“…It acetylates the higher polyamines which are then either secreted or oxidized by N 1 -acetylpolyamine oxidase (APAO) to yield smaller polyamines. Increased expression of SSAT is linked to many physiological and pathophysiological processes, including carbohydrate and lipid metabolism, pancreatitis and carcinogenesis (Chen et al 2004;Lee et al 2011;Fredericq et al 1991;Lai and Kondo 2006;Laiosa et al 2006;Janne et al 2006;Liu et al 2001;Long 2011). The effect of SSAT overexpression in these conditions is mediated by altered polyamine levels, deprivation of essential substrates shared with other metabolic pathways or increased oxidative damage as a result of APAO activity.…”