[The Mechanism Study on Histone Acetylation Activating Glioblastoma-derived Neurotrophic Factor Transcription].

OBJECTIVE: To study the regulation role and mechanism of protein acetylation on the expression of glioblastoma-derived neurotrophic factor (GDNF) in human glioma. METHODS: Six normal brain tissue samples, six low-grade glioma brain tissue (LG-glioma), and six high-grade glioma brain tissue (HG-glioma) were collected for study. Human glioma U251 cells were treated with histone acetylase inhibitor and histone deacetylase inhibition. The mRNA level of GDNF in glioma and normal controls was detected by Real-time PCR. H3K9 acetylation level of cAMP-response element binding protein (CREB) binding region on GDNF promoter and the ability of CREB combining to GDNF promoter were detected by ChIP-PCR. The effects of histone acetylase and deacetylase inhibitors on transcription factor binding ability and GDNF expression were detected. RESULTS: The mRNA level of GDNF in HG-glioma was significantly higher than those in normal brain tissue and LG-glioma (P < 0.01). The H3K9 acetylation level of GDNF promoter region in the glioma was increased compared to that in the normal brain tissue (P < 0.01), and the acetylation level in CREB-binding region on the GDNF promoter was higher than that in the non-CREB-binding region (P < 0.01). The binding activity of CREB and GDNF promoter in HG-glioma was higher than those in normal brain tissue and LG-glioma (P < 0.05). After treatment of U251 cells with histone acetyltransferase inhibition, the level of acetylation in CREB-binding region on GDNF promoter, the binding activity of CREB and GDNF promoter was decreased, and GDNF transcription and expression were down-regulated, while histone deacetylase inhibitors had the opposite effect (P < 0.01). CONCLUSION: Histone acetylation promotes the transcription expression of GDNF in glioma by promoting the binding of transcription factor CREB to the promoter region of GDNF gene.

Hyperacetylation of histone H3K9 involved in the promotion of abnormally high transcription of the gdnf gene in glioma cells.

The mechanism underlying abnormally high transcription of the glial cell line-derived neurotrophic factor (GDNF) gene in glioma cells is not clear. In this study, to assess histone H3K9 acetylation levels in promoters I and II of the gdnf gene in normal human brain tissue, low- and high-grade glioma tissues, normal rat astrocytes, and rat C6 glioblastoma cells, we employed chromatin immunoprecipitation-polymerase chain reaction (ChIP-PCR), real-time PCR, and a pGL3 dual fluorescence reporter system. We also investigated the influence of treatment with curcumin, a histone acetyltransferase inhibitor, and trichostatin A (TSA), a deacetylase inhibitor, on promoter acetylation and activity and messenger RNA (mRNA) expression level of the gdnf gene in C6 cells. Compared to normal brain tissue, H3K9 acetylation in promoters I and II of the gdnf gene increased significantly in high-grade glioma tissues but not in low-grade glioma tissues. Moreover, H3K9 promoter acetylation level of the gdnf gene in C6 cells was also remarkably higher than in normal astrocytes. In C6 cells, curcumin markedly decreased promoter II acetylation and activity and GDNF mRNA expression. Conversely, all three measurements were significantly increased following TSA treatment. Our results suggest that histone H3K9 hyperacetylation in promoter II of the gdnf gene might be one of the reasons for its abnormal high transcription in glioma cells.

Changes in transcriptional factor binding capacity resulting from promoter region methylation induce aberrantly high GDNF expression in human glioma.

Glial cell line-derived neurotrophic factor (GDNF), which belongs to transforming growth factor ß superfamily, plays important roles in glioma pathogenesis. Gdnf mRNA is aberrantly increased in glioma cells, but the underlying transcription mechanism is unclear. Here, we found that although the base sequence in the promoter region of the gdnf gene was unchanged in glioma cells, there were significant changes in the methylation level of promoter region I (P < 0.05) in both high- and low-grade glioma tissues. However, the methylation degree in promoter region II was notably decreased in low-grade glioma tissue compared to normal brain tissue (P < 0.05), and the demethylation sites were mainly located in the enhancer region. Conversely, methylation was markedly increased in high-grade glioma tissue (P < 0.05), and the sites with decreased methylation level were mainly located in the silencer region. The binding capacities of several transcriptional factors, such as activating protein 2, specificity protein 1, ETS-related gene 2, and cAMP response element binding protein, which specifically bind to regions with altered methylation status decreased along with the pathological grade of glioma, and the differences between high-grade glioma and normal brain tissue were significant (P < 0.05). The results suggest that changes in transcriptional factor binding capacity are due to changes in promoter region methylation and might be the underlying mechanism for aberrantly high gdnf expression in glioma.