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S. Chen, G.–H. Peng; Histone Deacetylase Inhibitors Can Compensate for Low Levels of CRX to Induce Photoreceptor Gene Expression in Y79 Retinoblastoma Cells . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5411.
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© ARVO (1962-2015); The Authors (2016-present)
Y79 retinoblastoma cells do not express opsins and many other photoreceptor cell markers, although transcripts from a few photoreceptor genes, such as RBP3 and PDE6B, are detectable. Consistent with this, Y79 cells express a low level of CRX, a transcription factor that is essential for photoreceptor gene expression. We found recently that CRX is required for the acetylation of histones on the chromatin of target genes during transcriptional activation (2004 ARVO, Abstract 2253). To determine whether insufficient CRX in Y79 cells results in hypoacetylation and transcriptional silencing of target genes, we either altered CRX levels or increased histone acetylation and measured photoreceptor gene transcription in Y79 cells.
Y79 cells were transiently transfected with a CRX expression plasmid or treated with various doses of three histone deacetylase inhibitors (HDACi): sodium butyrate (NaB), trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA). RT–PCR was used to measure target gene transcription. Chromatin immunoprecipitation (ChIP) was performed to detect the association of CRX, acetylated histone H3 (AcH3) and an active form of RNA polymerase II (Pol II) with selected CRX target genes.
In Y79 cells, the transcription of several silenced photoreceptor genes, including three opsins, was significantly enhanced by expressing recombinant CRX or by administering HDACi drugs. The increase in transcription was drug– and dose–dependent. Furthermore, the enhanced transcription correlated with increased Pol II occupancy and elevated levels of AcH3 in the promoter/enhancer regions of these target genes. In contrast, the treatments did not significantly alter the transcription of genes that were already expressed in Y79 cells, RBP3, PDE6B and ß–ACTIN, nor Pol II occupancy or AcH3 levels on the chromatin of these genes. These results suggest that chromatin structural changes, especially histone acetylation, are important for regulating the transcription of many photoreceptor genes.
In Y79 cells, pharmacologically increasing histone acetylation by administering HDACi can complement low levels of CRX (or other related transcription factors) to activate photoreceptor gene expression. Thus, HDACi may be beneficial in treating diseases that are associated with CRX deficiency.
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