Trichostatin A (TSA) is a well characterized histone deacetylase (HDAC) inhibitor. TSA modifies the balance between HDAC and histone acetyltransferase (HAT) activities that is important in chromatin remodeling and gene expression. Although several previous studies have demonstrated the role of TSA in regulation of ER alpha, the precise mechanism by which TSA affects ER alpha activity remains unclear.

Transient transfection was performed using the Welfect-EXTMPlus procedure. The mRNA expression was determined using the reverse transcriptase-polymerase chain reaction (RT-PCR). Protein expression and interaction were determined by western blotting and immunoprecipitation. The transfection of siRNAs was performed using the OligofectamineTM reagent procedure.

TSA treatment increased acetylation of ER alpha in a dose-dependent manner. The TSA-induced acetylation of ER alpha was accompanied by an increased stability of ER alpha protein. Interestingly, TSA also increased the acetylation and the stability of p300 protein. Overexpression of p300 induced acetylation and stability of ER alpha by blocking ubiquitination. Knock-down of p300 by RNA interference decreased acetylation as well as the protein level of ER alpha, indicating that p300 mediated the TSA-induced stabilization of ER alpha.

We report that TSA enhanced acetylation as well as the stability of the ER alpha protein by modulating stability of p300. These results may provide the molecular basis for pharmacological functions of histone deacetylase inhibitors in the treatment of human breast cancer.

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