HDAC9 and breast cancer: We have previously shown that the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) induces the rapid ubiquitin-dependent degradation of cyclin D1 in MCF-7 breast cancer cells prior to repression of cyclin D1 gene (CCND1) transcription [15] TSA-induced cyclin D1 degradation is associated with Skp2 upregulation and Skp2 siRNA inhibits this response.