| Summary: | <p>Abstract</p> <p>Background</p> <p>The active copy of the imprinted gene <it>H19</it> is turned off by inappropriate methylation in several pediatric tumors including Wilms' Tumour and embryonal rhabdomyosarcoma. <it>H19</it> controls in <it>cis</it> the linked <it>Insulin-like Growth Factor 2</it> (<it>IGF2</it>) gene, encoding an important growth factor. Recent work has suggested that methylation of a gene may lead to deacetylation of its associated histones and that silenced genes can be reactivated by increasing histone acetylation levels.</p> <p>Results</p> <p>Treatment of a rhabdomyosarcoma cell line which has a silent, methylated <it>H19</it> gene with histone deacetylase (HDAC) inhibitors under conditions which gave maximal hyperacetylation of histone 4, both globally and at the <it>H19</it> gene itself could not reactivate <it>H19</it> or affect the active <it>Insulin-like Growth Factor 2</it> (<it>IGF2</it>) gene, but caused clear up-regulation of the <it>Tissue-type Plasminogen Activator</it> (<it>TPA</it>) gene, a non-imprinted gene known to respond to changes in histone acetylation. In contrast, mild treatment of the cells with the methylation inhibitor 5-AzaC-2'-deoxycytidine (AzaC) on its own was able to reactivate <it>H19</it>. Combining AzaC treatment with HDAC inhibitors gave a reduced rather than enhanced reactivation. These findings were confirmed in mouse primary liver and kidney explants which maintain normal imprinting, where we also found that the silent <it>Igf2</it> gene could not be reactivated by HDAC inhibitors.</p> <p>Conclusion</p> <p>These results suggest that DNA methylation rather than histone acetylation is the primary determinant of silencing of <it>H19</it> in rhabdomyosarcoma.</p>
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