Histone deacetylase (HDAC) inhibitors are emerging as a promising new class of cancer therapeutic agents. HDAC inhibitors relieve the deacetylation of histone proteins. However, little is known about the nonhistone targets of HDAC inhibitors and their roles in gene regulation. In this study, we addressed the molecular basis of the down-regulation of the nuclear factor-KB (NF-KB) -responsive gene cyclin D1 by the HDAC inhibitor trichostatin A in mouse JB6 cells. Cyclin D1 plays a critical role

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... cell proliferation and tumor progression. Trichostatin A inhibits cyclin D1 expression in a NF-KB-dependent manner in JB6 cells. Electrophoretic mobility shift assay studies showed that trichostatin A treatment prevents p65 dimer binding to NF-KB sites on DNA. Moreover, a chromatin immunoprecipitation assay shows that trichostatin A treatment inhibits endogenous cyclin D1 gene transcription by preventing p65 binding to the cyclin D1 promoter. However, acetylation of p65 is not affected by trichostatin A treatment. Instead, trichostatin A enhances p52 acetylation and increases p52 protein level by enhancing p100 processing. This is the first report that trichostatin A, a HDAC inhibitor, activates p100 processing and relieves the repression of p52 acetylation. The enhanced acetylation of p52 in the nuclei may operate to cause nuclear retention of p65 by increasing the p52/p65 interaction and preventing IKBA-p65 binding. The enhanced p52 acetylation coincides with decreased p65 DNA binding, suggesting a potential role of p52 acetylation in NF-KB regulation. Together, the results provide the first demonstration that HDAC inhibitor trichostatin A inhibits cyclin D1 gene transcription through targeting transcription factor NF-KB/p65 DNA binding. NF-KB is therefore identified as a transcription factor target of trichostatin A treatment. (Mol Cancer Res 2005;3(2):100 -9)