Introduction: Trichostatin A (TSA) is a well-characterized histone deacetylase (HDAC) inhibitor. TSA modifies the balance between HDAC and histone acetyltransferase activities that is important in chromatin remodeling and gene expression. Although several previous studies have demonstrated the role of TSA in regulation of estrogen receptor alpha (ERalpha), the precise mechanism by which TSA affects ERalpha activity remains unclear.
Methods: Transient transfection was performed using the Welfect-EX Plus procedure. The mRNA expression was determined using RT-PCR. Protein expression and interaction were determined by western blotting and immunoprecipitation. The transfection of siRNAs was performed using the Oligofectamine reagent procedure.
Results: TSA treatment increased acetylation of ERalpha in a dose-dependent manner. The TSA-induced acetylation of ERalpha was accompanied by an increased stability of ERalpha protein. Interestingly, TSA also increased the acetylation and the stability of p300 protein. Overexpression of p300 induced acetylation and stability of ERalpha by blocking ubiquitination. Knockdown of p300 by RNA interference decreased acetylation as well as the protein level of ERalpha, indicating that p300 mediated the TSA-induced stabilization of ERalpha.
Conclusions: We report that TSA enhanced acetylation as well as the stability of the ERalpha protein by modulating stability of p300. These results may provide the molecular basis for pharmacological functions of HDAC inhibitors in the treatment of human breast cancer.