The influence of UBE3A, NEDD4L, and ARFGEF2 on the progression of Angelman syndrome and sickle cell anemia
Wu, Katie Jennifer
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This project investigates the impact of UBE3A, NEDD4L, and ARFGEF2 on disorder and disease in humans. UBE3A is a member of the homologous to E6AP COOH-terminus (HECT) E3 ubiquitin ligase family and is parentally imprinted in certain cell types. Mutation of the gene causes Angelman syndrome (AS), which is characterized by developmental delays, mental retardation, motor ataxia, and seizures. Patients frequently display excitable behavior, laughing, and a happy appearance. I found a previously unreported UBE3A candidate mutation, F606S, in twin boys diagnosed with AS.To test the change's clinical significance, I looked at its presence throughout the probands' family by sequencing, its influence on expression levels by qRT-PCR, and structure change predictions. The S606 is located in the functional domain of the enzyme, and its inheritance pattern correlates with disorder expression. The expression data is inconclusive, however, which highlights problems of using human experimental subjects. Nevertheless, there are indications that the F606S missense change could be responsible for AS. Another HECT E3 ligase, NEDD4L influences hypertension severity. Hypertension and inflammation are a complication of sickle cell anemia (SCA) and can affect patient outcome. Mutations in the gene increase epithelial Na+ channel surface expression and thus raise sodium uptake in epithelial cells. It is possible NEDD4L is a component of hypertension in a system instrumental to SCA development, endothelial cells. I conducted a pilot study to determine the effectiveness of NEDD4L knockdown by siRNA as a model for gene dysfunction and found that expression levels were significantly reduced in human pulmonary artery endothelial cells (HPAEC). I also did a preliminary study of the knockdown's influence on other genes that showed no change in ACTB, ARFGEF2, NOS3, or TNFRSFJA expression. Inflammation is a key component in hypertension. ARFGEF2 is a gene that could modulate endothelial inflammation response in sickle cell anemia. It is a GDP-GTP exchange factor involved in the downregulation of the TNF-α receptor, TNFRSF IA, a significant part of the inflammatory signaling pathway. Data from a gene chip expression assay yielded genes with four-fold expression change after ARFGEF2 knockdown. There is a strong inflammatory trend in the functional connections between these genes. It is a promising indication that ARFGEF2 has a role in inflammation, especially in immune response and intercellular signaling.
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