Browsing by Subject "DHPS"

Now showing 1 - 3 of 3
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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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    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.
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    Understanding the Role of Hypusine Biosynthesis in Endocrine-Exocrine Crosstalk
    (2022-08) Dale, Dorian J.; Mastracci, Teresa L.; Berbari, Nicolas; Balakrishnan, Lata; Spaeth, Jason
    Traditionally, the exocrine and endocrine cellular compartments of the pancreas have been considered distinct functional systems. However, recent studies suggest a more intricate relationship between the exocrine and endocrine, which may impact pancreatic growth and health. Additionally, translational control mechanisms have been linked to organ development. Our lab has shown that the mRNA translation factor eukaryotic initiation factor 5A (eIF5A), when in its post-translationally modified “hypusinated” form, plays a role in pancreas development. The hypusination of eIF5A requires the rate-limiting enzyme deoxyhypusine synthase (Dhps) to post- translationally modify a critical lysine residue which in turn produces the active form of eIF5A that functions in mRNA translation. When we generated animals with a deletion of Dhps in the pancreatic progenitor cells, there was no alteration in islet mass but significant exocrine insufficiency at embryonic (E) day 18.5 concomitant with downregulation of proteins required for exocrine pancreas development and function. Resultantly these animals died by 6 weeks-of-age. These observations prompted the question, is the phenotype caused by the absence of hypusinated eIF5A or the increase of unhypusinated eIF5A? To address this, we generated a mouse model wherein Eif5a is deleted in the pancreas (eIF5A∆PANC) and these mutant animals also display exocrine insufficiency. Interestingly, beta cell mass is increased at E18.5, and the mutant animals maintain euglycemia and survive up to 2 years. Ongoing analyses are interrogating the differences between these animal models with the goal to determine if mRNA translation facilitates cellular communication between the exocrine and endocrine pancreas.