Modulation of the acetylation state of histones plays a pivotal role in the regulation of gene expression. Histone deacetylases (HDACs) catalyze the removal of acetyl groups from lysines near the N termini of histones. This reaction promotes the condensation of chromatin, leading to repression of transcription. HDAC deregulation has been linked to several types of cancer, suggesting a potential use for HDAC inhibitors in oncology. Here we describe the first crystal structures of a human HDAC: the structures of human HDAC8 complexed with four structurally diverse hydroxamate inhibitors. This work sheds light on the catalytic mechanism of the HDACs, and on differences in substrate specificity across the HDAC family. The structure also suggests how phosphorylation of Ser39 affects HDAC8 activity.

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In response to heat stress, Bacillus subtilis activates the transcription of well over 100 different genes. Many of these genes are members of a general stress response regulon controlled by the secondary sigma factor, B , while others are under control of the HrcA or CtsR heat shock regulators. We have used DNA microarrays to monitor the global transcriptional response to heat shock. We find strong induction of known B -dependent genes with a characteristic rapid induction followed by a return to near prestimulus levels. The HrcA and CtsR regulons are also induced, but with somewhat slower kinetics. Analysis of DNA sequences proximal to newly identified heat-induced genes leads us to propose ϳ70 additional members of the B regulon. We have also identified numerous heat-induced genes that are not members of known heat shock regulons. Notably, we observe very strong induction of arginine biosynthesis and transport operons. Induction of several genes was confirmed by quantitative reverse transcriptase PCR. In addition, the transcriptional responses measured by microarray hybridization compare favorably with the numerous previous studies of heat shock in this organism. Since many different conditions elicit both specific and general stress responses, knowledge of the heat-induced general stress response reported here will be helpful for interpreting future microarray studies of other stress responses.DNA microarray technology provides a powerful tool for the analysis of global transcriptional responses elicited by various physical and chemical stresses. One challenge in this sort of analysis is to distinguish stress-specific responses from more general stress responses. For example, in Bacillus subtilis, many different stresses (including heat shock, osmotic stress, and energy stress) activate the large general stress response controlled by the B transcription factor (20,44,45). While others have used two-dimensional protein gels to classify cellular stress responses (55, 58), DNA-based methods have several advantages: they can be rapidly adapted to new organisms, they provide greater coverage of the genome, and data processing is comparatively easy to automate. Ultimately, it may be possible to integrate both technologies, at least for well-studied model organisms (19,41,56).We have initiated a series of studies to characterize the global transcriptional responses of B. subtilis, a model grampositive microorganism. Here, we document the heat-induced general stress response. Heat shock was chosen for this initial study since it is arguably the best-studied stress response in this organism and includes activation of the large general stress response under the control of B (20, 44). In addition, a subset of antibiotics that inhibit translation have been reported to induce heat shock genes in other organisms (57). It is anticipated that knowledge of transcriptional responses to antimicrobial compounds will be useful for both antibacterial discovery and characterization (47).Analysis of the transcriptional profile of B...

The management of sodium intake is clinically important in many disease states including heart failure, kidney disease, and hypertension. Tenapanor is an inhibitor of the sodium-proton (Na(+)/H(+)) exchanger NHE3, which plays a prominent role in sodium handling in the gastrointestinal tract and kidney. When administered orally to rats, tenapanor acted exclusively in the gastrointestinal tract to inhibit sodium uptake. We showed that the systemic availability of tenapanor was negligible through plasma pharmacokinetic studies, as well as autoradiography and mass balance studies performed with (14)C-tenapanor. In humans, tenapanor reduced urinary sodium excretion by 20 to 50 mmol/day and led to an increase of similar magnitude in stool sodium. In salt-fed nephrectomized rats exhibiting hypervolemia, cardiac hypertrophy, and arterial stiffening, tenapanor reduced extracellular fluid volume, left ventricular hypertrophy, albuminuria, and blood pressure in a dose-dependent fashion. We observed these effects whether tenapanor was administered prophylactically or after disease was established. In addition, the combination of tenapanor and the blood pressure medication enalapril improved cardiac diastolic dysfunction and arterial pulse wave velocity relative to enalapril monotherapy in this animal model. Tenapanor prevented increases in glomerular area and urinary KIM-1, a marker of renal injury. The results suggest that therapeutic alteration of sodium transport in the gastrointestinal tract instead of the kidney--the target of current drugs--could lead to improved sodium management in renal disease.

The expression of members of the family of matrix-degrading metalloproteinases (MMPs) is believed to contribute to the complex process of invasion and metastasis. In this study, specific cDNA probes for three members of the stromelysin subfamily of MMPs--stromelysin (MMP-3), stromelysin-2 (MMP-10), and pump-1 (MMP-7)--were used to examine the expression of these three different MMPs in human gastric and colonic carcinomas and in adjacent normal mucosa. The expression of pump-1 mRNA in malignant colon and stomach samples was striking. In a total of 10 gastric carcinoma samples examined, eight (80%) expressed pump-1 transcripts; similarly, 6 of 8 (75%) colon carcinoma samples were also positive. Stromelysin and stromelysin-2 mRNAs were not detected in any of these samples. Expression of the MMPs examined was not detected in any of the adjacent, grossly normal tissue samples. Using in situ hybridization and affinity purified anti-pump-1 antibodies, the expression of pump-1 mRNA and protein was localized to tumor cells and was not detected in stromal or lymphocytic cells. This data suggests that the inappropriate expression of pump-1 by malignant cells may contribute to the neoplastic phenotype.