Spinocerebellar ataxia type 8 larger triplet expansion alters histone modification and induces RNA foci.
BACKGROUND
Spinocerebellar ataxia type 8 (SCA8) involves the expression of an expanded CTG/CAG combined repeats (CR) from opposite strands producing CUG expansion transcripts (ataxin 8 opposite strand, ATXN8OS) and a polyglutamine expansion protein (ataxin 8, ATXN8). The pathogenesis of SCA8 is complex and the spectrum of clinical presentations is broad.


RESULTS
Using stably induced cell models expressing 0, 23, 88 and 157 CR, we study the role of ATXN8OS transcripts in SCA8 pathogenesis. In the absence of doxycycline, the stable ATXN8OS CR cell lines exhibit low levels of ATXN8OS expression and a repeat length-related increase in staurosporine sensitivity and in the number of annexin positive cells. A repeat length-dependent repression of ATXN8OS expression was also notable. Addition of doxycycline leads to 25 approximately 50 times more ATXN8OS RNA expression with a repeat length-dependent increase in fold of ATXN8OS RNA induction. ChIP-PCR assay using anti-dimethyl-histone H3-K9 and anti-acetyl-histone H3-K14 antibodies revealed increased H3-K9 dimethylation and reduced H3-K14 acetylation around the ATXN8OS cDNA gene in 157 CR line. The repeat length-dependent increase in induction fold is probably due to the increased RNA stability as demonstrated by monitoring ATXN8OS RNA decay in cells treated with the transcriptional inhibitor, actinomycin D. In cells stably expressing ATXN8OS, RNA FISH experiments further revealed ribonuclear foci formation in cells carrying expanded 88 and 157 CR.


CONCLUSIONS
The present study demonstrates that the expanded CUG-repeat tracts are toxic to human cells and may affect ATXN8OS RNA expression and stability through epigenetic and post-transcriptional mechanisms.
Chen
I-Cheng
IC
Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan. ichen910@yahoo.com.tw
Lin
Hsuan-Yuan
HY
Lee
Ghin-Chueh
GC
Kao
Shih-Huan
SH
Chen
Chiung-Mei
CM
Wu
Yih-Ru
YR
Hsieh-Li
Hsiu-Mei
HM
Su
Ming-Tsan
MT
Lee-Chen
Guey-Jen
GJ
D000107:Acetylation; D002460:Cell Line; D044127:Epigenesis, Genetic; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008745:Methylation; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D012313:RNA / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability; D020754:Spinocerebellar Ataxias / Q000235:genetics* / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion
C539186:ATXN8 protein, human; D006657:Histones; D009419:Nerve Tissue Proteins; D012313:RNA