Developing treatment modalities for, and characterization of splicing of IKBKAP exon 20 in, individuals with familial dysautonomia
Familial Dysautonomia (FD), also known as Riley-Day Syndrome or Hereditary sensory neuropathy type III (HSAN type III, MIM 223900), is an autosomal recessive disorder that is caused by the mutation, IVS20+6T→C, in IKBKAP, which changes the intron 20 donor splice site sequence and causes exon 20 skipping. Using FD-derived cell line, we demonstrated that tocotrienols elevate the level of full-length IKBKAP exon 20-containing transcripts in FD-derived cells in a dosage and time dependent manner. This effect is due to the up-regulation of the transcription of IKAP by the tocotrienols. Examination of the exon 20 nucleotide sequence revealed two potential exonic splicing silencers (ESSs). As (-)-epigallocatechin gallate (EGCG) was reported to down-regulate hnRNP A2/B1, a factor that binds ESS elements and promotes exon skipping, we studied the effect of EGCG treatment on FD-derived cells and observed a decreased presence of hnRNP A2/B1 in these cells. We further noted an increase in the level of the exon 20-containing IKBKAP transcript, while no appreciable effect was observed on the level of the exon 20-lacking transcript. These results suggest that EGCG treatment impacts the splicing of the IKBKAP transcript rather than the transcription rate of this gene. FD-derived cells treated with a combination of δ-tocotrienol and EGCG, at doses that by themselves do not result in a significant elevation in the level of the wild-type IKBKAP transcript, showed a clear synergistic increase in the level of the IKAP transcript and protein. FD patients may benefit from the combined use of these two compounds. Mutagenesis analysis on FD-derived and wild-type minigenes generated with genomic sequences from exon 19 to 21 from affected and normal individuals respectively, revealed several potential exonic splicing enhancers (ESEs) in the exon 20 sequence. In addition, TTAG sequences located at bases 16-19 and 46-49 of exon 20 of IKBKAP were demonstrated to act as ESSs. Identification of these cis elements should lead to a better understanding of the modulation by which the splicing of exon 20 of IKBKAP is regulated.
Molecular biology|Genetics|Cellular biology
Qiu, Jinsong, "Developing treatment modalities for, and characterization of splicing of IKBKAP exon 20 in, individuals with familial dysautonomia" (2009). ETD Collection for Fordham University. AAI3353776.