Characterization of novel inhibitors of histone acetyltransferases.

Modification of proteins by histone acetyltransferases (HAT) or histone deacetylases plays an important role in the control of gene expression, and its dysregulation has been linked to malignant transformation and other diseases. Although histone deacetylase inhibitors have been extensively studied and several are currently in clinical trials, there is little information available on inhibitors of HATs (HATi). Starting from the natural product lead HATi anacardic acid, a series of 28 analogues was synthesized and investigated for HAT-inhibitory properties and effects on cancer cell growth. The compounds inhibited up to 95% HAT activity in vitro, and there was a clear correlation between their inhibitory potency and cytotoxicity toward a broad panel of cancer cells. Interestingly, all tested compounds were relatively nontoxic to nonmalignant human cell lines. Western blot analysis of MCF7 breast carcinoma cells treated with HATi showed significant reduction in acetylation levels of histone H4. To directly show effect of the new compounds on HAT activity in vivo, MCF7 cells were cotransfected with the p21 promoter fused to firefly luciferase and a full-length p300 acetyltransferase, and luciferase activity was determined following treatment with HATi. Significant inhibition of p300 activity was detected after treatment with all tested compounds except one. Effects of the new HATi on protein acetylation and HAT activity in vivo make them a suitable tool for discovery of molecular targets of HATs and, potentially, for development of new anticancer therapeutics.

Cytoplasmic sequestration of HDAC7 from mitochondrial and nuclear compartments upon initiation of apoptosis.

Control of global histone acetylation status is largely governed by the opposing enzymatic activities of histone acetyltransferases and deacetylases (HDACs). HDACs were originally identified as modulators of nuclear histone acetylation status and have been linked to chromosomal condensation and subsequent gene repression. Accumulating evidence highlights HDAC modification of non-histone targets. Mitochondria were first characterized as intracellular organelles responsible for energy production through the coupling of oxidative phosphorylation to respiration. More recently, mitochondria have been implicated in programmed cell death whereby release of pro-apoptotic inner membrane space factors facilitates apoptotic progression. Here we describe the novel discovery that the nuclear encoded Class II human histone deacetylase HDAC7 localizes to the mitochondrial inner membrane space of prostate epithelial cells and exhibits cytoplasmic relocalization in response to initiation of the apoptotic cascade. These results highlight a previously unrecognized link between HDACs, mitochondria, and programmed cell death.