[대학원 생명과학과 세미나 안내] 

연사 : 성인식 교수(Harvard Medical School/Massachusetts General Hospital)

연제 : Lessons from a novel huntingtin gene mutation family for huntingtin regulation

일시 : 2018년 4월 25일 (수) 오전 10시 

장소 : 하나과학관 A동 207호

초청교수 : 윤봉준 교수

Abstract

Huntington’s Disease (HD) is triggered by an expanded polyglutamine (polyQ) tract in the huntingtin protein (HTT). While genetic studies have revealed the causal mutation and modifiers of the disease, the underlying disease mechanism remains unexplained. The gain of toxic function of mutant HTT should be the trigger of HD but the molecular mechanism seems to involve multiple pathways and be very challenged to tease out a meaningful therapeutic target out of them. Thus, lowering mutant HTT is an appealing therapeutic strategy.  Particularly, understanding the regulation mechanism of the disease protein level through its posttranslational modification (PTM), such as phosphorylation, would be important to advance HD interventions along with current HTT lowering strategies by RNAi or ASOs, such as IONIS HTT-Rx clinical trial, for this complicated chronic disease. 
The recent clinical exome sequencing project found two novel mutations, mutation at a conserved splicing site and missense mutation, in huntingtin gene (HTT) with very severe developmental abnormalities in affected children (compound heterozygotes). Our initial western blot data from these affected children patients’ cells revealed dramatically reduced HTT levels compared to their parental cells and a heterozygous HTT knock-out cell line as well as control cells. With our allele-specific HTT mRNA and protein measurement using Mi-Seq and target mass spectrometry (SRM), respectively, we found that the splicing mutation resulted in little or no mRNA probably through nonsense mediated decay and the missense mutation affected the protein stability only. To further investigate the effect of the missense mutation on HTT, we generated pFastBac-Q23-HTT clone having this mutation and purified it with control Q23-HTT, which we have previously developed a panel of human recombinant full-length HTT with different polyQ lengths using insect expression system. Interestingly, we found this mutant protein dramatically hyperphosphorylated at two specific sites using our PTM-specific SRM assay, strongly suggesting the phosphorylation at either of or both specific sites are involved in regulating HTT stability. 
This rare and novel missense mutation from the patients and our knowledge and resources of full-length HTT will lead us to deeper understanding of HTT structure and regulation and contribute to provide a potential druggable target to lower mutant HTT for HD treatment.