Post-translational formation of hypusine in eIF5A: implications in human neurodevelopment

Abstract

Hypusine [Nε-(4-amino-2-hydroxybutyl)lysine] is a derivative of lysine that is formed post-translationally in the eukaryotic initiation factor 5A (eIF5A). Its occurrence at a single site in one cellular protein defines hypusine synthesis as one of the most specific post-translational modifications. Synthesis of hypusine involves two enzymatic steps: first, deoxyhypusine synthase (DHPS) cleaves the 4-aminobutyl moiety of spermidine and transfers it to the ε-amino group of a specific lysine residue of the eIF5A precursor protein to form an intermediate, deoxyhypusine [Nε-(4-aminobutyl)lysine]. This intermediate is subsequently hydroxylated by deoxyhypusine hydroxylase (DOHH) to form hypusine in eIF5A. eIF5A, DHPS, and DOHH are highly conserved in all eukaryotes, and both enzymes exhibit a strict specificity toward eIF5A substrates. eIF5A promotes translation elongation globally by alleviating ribosome stalling and it also facilitates translation termination. Hypusine is required for the activity of eIF5A, mammalian cell proliferation, and animal development. Homozygous knockout of any of the three genes, Eif5a, Dhps, or Dohh, leads to embryonic lethality in mice. eIF5A has been implicated in various human pathological conditions. A recent genetic study reveals that heterozygous germline EIF5A variants cause Faundes–Banka syndrome, a craniofacial–neurodevelopmental malformations in humans. Biallelic variants of DHPS were identified as the genetic basis underlying a rare inherited neurodevelopmental disorder. Furthermore, biallelic DOHH variants also appear to be associated with neurodevelopmental disorder. The clinical phenotypes of these patients include intellectual disability, developmental delay, seizures, microcephaly, growth impairment, and/or facial dysmorphisms. Taken together, these findings underscore the importance of eIF5A and the hypusine modification pathway in neurodevelopment in humans.

Neuron-specific ablation of eIF5A or deoxyhypusine synthase leads to impairments in growth, viability, neurodevelopment, and cognitive functions in mice

“…Furthermore, individuals with DOHH variants who display similar developmental delay and intellectual disability have also been identified (Ziegler A. et al. , unpublished results), underscoring the importance of each step of the hypusine modification pathway and thereby the critical role of the hypusinated eIF5A in neurodevelopment in humans ( 29 ). These findings led us to generate the four CKO mouse models, with temporal- and region-specific deletion of either Eif5a or Dhps in the forebrain, and to assess the impact on development.…”

“…In these studies, a reduction of hypusinated eIF5A by using a DHPS inhibitor or DHPS RNAi attenuated neurite outgrowth and neuronal survival ( 26 ). Only recently, definitive genetic evidence for their importance in human neurodevelopment was reported ( 27 , 28 , 29 ). From whole-exome sequencing and genetic analysis, biallelic DHPS variants were identified as the cause of a rare autosomal recessive neurodevelopmental disorder ( 28 ).…”

Role of eIF5A in Mitochondrial Function

“…The overexpression of both eIF5A isoforms has been observed in several tumors and triggers cell migration, invasion, and cancer metastasis (see review [51] for details), but EIF5A2 is considered a potential oncogene and diagnostic or prognostic marker [61,62] because it is associated with poor survival, advanced disease stage, poor response to chemotherapeutic drugs, and metastasis. Genetic variants of eIF5A genes have been identified as the basis of certain rare neurodevelopmental disorders in humans [63].…”

Specific and sensitive GC–MS analysis of hypusine, Nε-(4-amino-2-hydroxybutyl)lysine, a biomarker of hypusinated eukaryotic initiation factor eIF5A, and its application to the bi-ethnic ASOS study

“…Nevertheless, the differences found between the correlations of many urinary amino acids including their AGEs and urinary Hyp in the children of the ASOS study suggest that not yet known differences in amino acid homoeostasis including metabolism to polyamine and excretion may depend upon ethnicity. Spermidine is the biological precursor of Hyp (Park et al 1981(Park et al , 2021. At high mM concentrations, spermidine was reported to enhance weakly hypusination in flies and mice (Liang et al 2021).…”

“…This is subsequently hydroxylated by deoxyhypusine hydroxylase (DOHH) to form hypusinated eIF5A. In vivo, proteolysis of hypusinated eIF5A releases hypusine, i.e., N ε -(4-amino-2hydroxybutyl)lysine (not shown) implicated in various human pathological conditions including infectious diseases, diabetes, neurodevelopment disorders and cancer (Nakanishi and Cleveland 2016;McNamara et al 2021;Park et al 2021). The two-step biosynthesis of hypusine is illustrated in Scheme 1.…”