Browsing by Author "Park, Myung Hee"

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    Deoxyhypusine synthase mutations alter the post-translational modification of eukaryotic initiation factor 5A resulting in impaired human and mouse neural homeostasis
    (Elsevier, 2023-05-18) Padgett, Leah R.; Shinkle, Mollie R.; Rosario, Spencer; Murray Stewart, Tracy; Foley, Jackson R.; Casero, Robert A.. Jr.; Park, Myung Hee; Chung, Wendy K.; Mastracci, Teresa L.; Biology, School of Science
    DHPS deficiency is a rare genetic disease caused by biallelic hypomorphic variants in the Deoxyhypusine synthase (DHPS) gene. The DHPS enzyme functions in mRNA translation by catalyzing the post-translational modification, and therefore activation, of eukaryotic initiation factor 5A (eIF5A). The observed clinical outcomes associated with human mutations in DHPS include developmental delay, intellectual disability, and seizures. Therefore, to increase our understanding of this rare disease, it is critical to determine the mechanisms by which mutations in DHPS alter neurodevelopment. In this study, we have generated patient-derived lymphoblast cell lines and demonstrated that human DHPS variants alter DHPS protein abundance and impair enzyme function. Moreover, we observe a shift in the abundance of the post-translationally modified forms of eIF5A; specifically, an increase in the nuclear localized acetylated form (eIF5AAcK47) and concomitant decrease in the cytoplasmic localized hypusinated form (eIF5AHYP). Generation and characterization of a mouse model with a genetic deletion of Dhps in the brain at birth shows that loss of hypusine biosynthesis impacts neuronal function due to impaired eIF5AHYP-dependent mRNA translation; this translation defect results in altered expression of proteins required for proper neuronal development and function. This study reveals new insight into the biological consequences and molecular impact of human DHPS deficiency and provides valuable information toward the goal of developing treatment strategies for this rare disease.
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    Deoxyhypusine synthase mutations alter the post-translational modification of eukaryotic initiation factor 5A resulting in impaired human and mouse neural homeostasis
    (Elsevier, 2023-05-18) Padgett, Leah R.; Shinkle, Mollie R.; Rosario, Spencer; Murray Stewart, Tracy; Foley, Jackson R.; Casero, Robert A., Jr.; Park, Myung Hee; Chung, Wendy K.; Mastracci, Teresa L.; Biology, School of Science
    DHPS deficiency is a rare genetic disease caused by biallelic hypomorphic variants in the Deoxyhypusine synthase (DHPS) gene. The DHPS enzyme functions in mRNA translation by catalyzing the post-translational modification, and therefore activation, of eukaryotic initiation factor 5A (eIF5A). The observed clinical outcomes associated with human mutations in DHPS include developmental delay, intellectual disability, and seizures. Therefore, to increase our understanding of this rare disease, it is critical to determine the mechanisms by which mutations in DHPS alter neurodevelopment. In this study, we have generated patient-derived lymphoblast cell lines and demonstrated that human DHPS variants alter DHPS protein abundance and impair enzyme function. Moreover, we observe a shift in the abundance of the post-translationally modified forms of eIF5A; specifically, an increase in the nuclear localized acetylated form (eIF5AAcK47) and concomitant decrease in the cytoplasmic localized hypusinated form (eIF5AHYP). Generation and characterization of a mouse model with a genetic deletion of Dhps in the brain at birth shows that loss of hypusine biosynthesis impacts neuronal function due to impaired eIF5AHYP-dependent mRNA translation; this translation defect results in altered expression of proteins required for proper neuronal development and function. This study reveals new insight into the biological consequences and molecular impact of human DHPS deficiency and provides valuable information toward the goal of developing treatment strategies for this rare disease.
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    Neuron-specific ablation of eIF5A or deoxyhypusine synthase leads to impairments in growth, viability, neurodevelopment, and cognitive functions in mice
    (Elsevier, 2021) Kar, Rajesh Kumar; Hanner, Ashleigh S.; Starost, Matthew F.; Springer, Danielle; Mastracci, Teresa L.; Mirmira, Raghavendra G.; Park, Myung Hee; Biology, School of Science
    Eukaryotic initiation factor 5A (eIF5A)†, ‡ is an essential protein that requires a unique amino acid, hypusine, for its activity. Hypusine is formed exclusively in eIF5A post-translationally via two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase. Each of the genes encoding these proteins, Eif5a, Dhps, and Dohh, is required for mouse embryonic development. Variants in EIF5A or DHPS were recently identified as the genetic basis underlying certain rare neurodevelopmental disorders in humans. To investigate the roles of eIF5A and DHPS in brain development, we generated four conditional KO mouse strains using the Emx1-Cre or Camk2a-Cre strains and examined the effects of temporal- and region-specific deletion of Eif5a or Dhps. The conditional deletion of Dhps or Eif5a by Emx1 promotor–driven Cre expression (E9.5, in the cortex and hippocampus) led to gross defects in forebrain development, reduced growth, and premature death. On the other hand, the conditional deletion of Dhps or Eif5a by Camk2a promoter–driven Cre expression (postnatal, mainly in the CA1 region of the hippocampus) did not lead to global developmental defects; rather, these KO animals exhibited severe impairment in spatial learning, contextual learning, and memory when subjected to the Morris water maze and a contextual learning test. In both models, the Dhps-KO mice displayed more severe impairment than their Eif5a-KO counterparts. The observed defects in the brain, global development, or cognitive functions most likely result from translation errors due to a deficiency in active, hypusinated eIF5A. Our study underscores the important roles of eIF5A and DHPS in neurodevelopment.
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    Recessive Rare Variants in Deoxyhypusine Synthase, an Enzyme Involved in the Synthesis of Hypusine, Are Associated with a Neurodevelopmental Disorder
    (Elsevier, 2019-02-07) Ganapathi, Mythily; Padgett, Leah R.; Yamada, Kentaro; Devinsky, Orrin; Willaert, Rebecca; Person, Richard; Au, Ping-Yee Billie; Tagoe, Julia; McDonald, Marie; Karlowicz, Danielle; Wolf, Barry; Lee, Joanna; Shen, Yufeng; Okur, Volkan; Deng, Liyong; LeDuc, Charles A.; Wang, Jiayao; Hanner, Ashleigh; Mirmira, Raghavendra G.; Park, Myung Hee; Mastracci, Teresa L.; Chung, Wendy K.; Pediatrics, School of Medicine
    Hypusine is formed post-translationally from lysine and is found in a single cellular protein, eukaryotic translation initiation factor-5A (eIF5A), and its homolog eIF5A2. Biosynthesis of hypusine is a two-step reaction involving the enzymes deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). eIF5A is highly conserved throughout eukaryotic evolution and plays a role in mRNA translation, cellular proliferation, cellular differentiation, and inflammation. DHPS is also highly conserved and is essential for life, as Dhps-null mice are embryonic lethal. Using exome sequencing, we identified rare biallelic, recurrent, predicted likely pathogenic variants in DHPS segregating with disease in five affected individuals from four unrelated families. These individuals have similar neurodevelopmental features that include global developmental delay and seizures. Two of four affected females have short stature. All five affected individuals share a recurrent missense variant (c.518A>G [p.Asn173Ser]) in trans with a likely gene disrupting variant (c.1014+1G>A, c.912_917delTTACAT [p.Tyr305_Ile306del], or c.1A>G [p.Met1?]). cDNA studies demonstrated that the c.1014+1G>A variant causes aberrant splicing. Recombinant DHPS enzyme harboring either the p.Asn173Ser or p.Tyr305_Ile306del variant showed reduced (20%) or absent in vitro activity, respectively. We co-transfected constructs overexpressing HA-tagged DHPS (wild-type or mutant) and GFP-tagged eIF5A into HEK293T cells to determine the effect of these variants on hypusine biosynthesis and observed that the p.Tyr305_Ile306del and p.Asn173Ser variants resulted in reduced hypusination of eIF5A compared to wild-type DHPS enzyme. Our data suggest that rare biallelic variants in DHPS result in reduced enzyme activity that limits the hypusination of eIF5A and are associated with a neurodevelopmental disorder.