The association of mutations in deoxyhypusine synthase (DHPS) with a human neurodevelopmental disorder (Collaboration with Dr. Wendy Chung, Columbia University) From exome sequencing, three independent biallelic pathogenic variants in DHPS were identified in four affected individuals from three unrelated families. The patients all have a neurodevelopmental disorder that includes global developmental delay, seizures, and short stature. All four affected children share a recurrent missense variant (c.518A>G;p.N173S, substitution of Asn173 with serine) in trans with a gene disrupting variant, either c.1014+1G>A (splice mutation), c.912_917delTTACAT;p.Y305_I306del (deletion of Tyr305 and Ile306) or p.M1? (substitution of 1A to G (initiation codon change to GUG). Expression studies demonstrated that the c.1014+1G>A variant causes aberrant splicing resulting in a truncated DHPS lacking the active site Lys residue, K329. Recombinant DHPS enzymes with either the p.N173S or p.Y305_I306del mutation were produced and their activities were tested in vitro. The DHPSN173S enzyme had approximately 20% of wildtype enzyme activity, whereas the DHPSY305_I306del enzyme had no activity. A lymphoblastoid cell line derived from an affected patient contained a reduced amount of hypusinated eIF5A compared to the wild type, due to low activities of DHPS. These data suggest that rare biallelic variants in DHPS, which limit the hypusination of eIF5A, are associated with a neurodevelopmental disorder in humans. In line with these results, haploinsufficiency in eIF5A or certain mutations in eIF5A (Christopher Gordon, personal communication) also lead to a neurodevelopmental disorder with clinical phenotypes including microcephaly, craniofacial and skeletal anomaly, and seizure. Our future efforts will be directed towards the identification of the downstream targets of eIF5A that are important in neurodevelopment and the delineation of the molecular pathways leading to the human disease. Sensitization of cisplatin-resistant bladder cancer (BC) cells through epigenetic regulation of metabolic genes (Collaboration with Jayoung Kim, Cedars-Sinai Medical Center). Alterations in DNA methylation are important epigenetic markers. These epigenome modifications may drive the mechanisms of aggressive chemo-resistant BC. In order to determine whether DNA methylation of certain metabolic enzymes is significantly altered in cisplatin-resistant BC cells, the Illumina Infinium HM450 DNA methylation assay was performed. Arginosuccinate synthase 1 (ASS1) and SAT1, genes for amino acid and polyamine metabolism catalysts, respectively, were found to be vastly hypermethylated, resulting in greatly downregulated expression. ASS1 expression is of particular interest as it has been associated with BC stage and recurrence. Aberrant expression or induced stimulation of SAT1 restored cisplatin sensitivity in the cell culture system. This study demonstrates a novel mechanistic link between the epigenetic perturbation of SAT1 and ASS1 and cancer metabolism in cisplatin-resistant bladder cancer cells.
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