Spt4 Is Selectively Required for Transcription of Extended Trinucleotide Repeats

Abstract

Lengthy trinucleotide repeats encoding polyglutamine (polyQ) stretches characterize the variant proteins of Huntington's disease and certain other inherited neurological disorders. Using a phenotypic screen to identify events that restore functionality to polyQ proteins in S. cerevisiae, we discovered that transcription elongation factor Spt4 is required to transcribe long trinucleotide repeats located either in ORFs or nonprotein-coding regions of DNA templates. Mutation of SPT4 selectively decreased synthesis of and restored enzymatic activity to expanded polyQ protein without affecting protein lacking long-polyQ stretches. RNA-seq analysis revealed limited effects of Spt4 on overall gene expression. Inhibition of Supt4h, the mammalian ortholog of Spt4, reduced mutant huntingtin protein in neuronal cells and decreased its aggregation and toxicity while not altering overall cellular mRNA synthesis. Our findings identify a cellular mechanism for transcription through repeated trinucleotides and a potential target for countermeasures against neurological disorders attributable to expanded trinucleotide regions.

Transcriptional elongation checkpoint control in development and disease

“…Even within the same complex, different factors have context-specific roles. For example, SPT4, which, with SPT5, forms DSIF, has a particular requirement for transcription of tracts of trinucleotide repeats (Liu et al 2012). Like DSIF, which has both positive and negative elongation activities, the PAF complex, which is generally thought of as a positive elongation factor, is antagonistic to the productive elongation of erythroid genes, as evidenced by the suppression of the TIF1g mutant in zebrafish (Schuh et al 2005;Bai et al 2010).…”

Tissue-dependent regulation of RNAP II dynamics

“…Interestingly, depleting SPT4 in yeast and mammalian cells specifically decreased transcription of CAGexpanded genes, thereby reducing toxicity of the gene products. 30 Our results suggest that decreasing transcription elongation might also reduce toxicity, limiting repeat instability. Thus, targeting transcription elongation might represent an attractive therapeutic perspective.…”

The CAA Repeat Polymorphism in the <i>ZFHX3</i> Gene Is Associated with Risk of Coronary Heart Disease in a Chinese Population

“…The other properties of trinucleotide repeat sequences that manifest themselves on the levels of DNA, RNA, or both may also contribute to the functional importance of these sequences and their prevalence in exons . These properties of trinucleotide repeats may include their ability to form higher order structures in single-stranded DNA and transcripts (Liu et al 2012). Higher order structures may play an important regulatory role in numerous cellular processes, such as DNA replication repair and at various steps of gene expression ranging from transcription to mRNA decay (Gannon et al 2012).…”