Synergistic effect of histone hyperacetylation and DNA demethylation in the reactivation of the FMR1 gene

Most fragile X syndrome patients have expansion of a (CGG)(n) sequence with >200 repeats (full mutation) in the FMR1 gene responsible for this conditi on, Hypermethylation of the expanded repeat and of the FMR1 promoter is alm ost always present and apparently suppresses transcription, resulting in ab sence of the FMR1 protein. We recently showed that transcriptional reactiva tion of FMR1 full mutations can be achieved by inducing DNA demethylation w ith 5-azadeoxycytidine (5-azadC). The level of histone acetylation is anoth er important factor in regulating gene expression; therefore, we treated ly mphoblastoid cell lines of non-mosaic full mutation patients with three dru gs capable of inducing histone hyperacetylation, We observed a consistent, although modest, reactivation of the FMR1 gene with 4-phenylbutyrate, sodiu m butyrate and trichostatin A, as shown by RT-PCR, However, we report that combining these drugs with 5-azadC results in a 2- to 5-fold increase in FM R1 mRNA levels obtained with 5-azadC alone, thus showing a marked synergist ic effect of histone hyperacetylation and DNA demethylation in the reactiva tion of FMR1 full mutations.