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Invertebrates, a key step in the biosynthesis of cholesterol and steroid hormones is the conversion of (S)-2,3-oxidosqualene to lanosterol. The enzyme that catalyzes this complex cyclization/rearrangement step via the protosteryl cation intermediate is lanosterol synthase ((S)-2,3-epoxysqualene mutase (cyclizing, lanosterol forming), EC 5.4.99.7). Because of the crucial role that lanosterol synthase plays in cholesterol biosynthesis, there is great interest in the identification of drugs that target this enzyme for anticholesteremic purposes. Although most studies on lanosterol synthase in the past have focused on the structural and biochemical functions of this enzyme, almost nothing is known concerning how the synthesis of lanosterol synthase is regulated. Here, we report that histone deacetylase 3 (HDAC3) represses transcription from the lanosterol synthase promoter. Overexpression of HDAC3 decreases, whereas knockdown of HDAC3 by small interfering RNA increases, endogenous lanosterol synthase mRNA in cells. Similarly, in transient transfection assays, overexpression of HDAC3 decreases, whereas depletion of HDAC3 increases, expression of a reporter gene under the control of the lanosterol synthase promoter. Stable cell lines that overexpress HDAC3 show a decrease in lanosterol synthase mRNA and have lower cholesterol concentrations compared with parental cells. Extensive promoter analyses coupled with chromatin immunoprecipitation assays reveal that the transcription factor YY1 binds to and recruits HDAC3 to the lanosterol synthase promoter. Together, our results demonstrate that HDAC3 represses the synthesis of a key regulatory enzyme and reveal a novel mechanism by which the cholesterol biosynthetic pathway can be regulated. [ABSTRACT FROM AUTHOR]

Tissue-specific activation of the osteocalcin (OC) gene is associated with changes in chromatin structure at the promoter region. Two nuclease-hypersensitive sites span the key regulatory elements that control basal tissue-specific and vitamin D3-enhanced OC gene transcription. To gain understanding of the molecular mechanisms involved in chromatin remodeling of the OC gene, we have examined the requirement for SWI/SNF activity. We inducibly expressed an ATPase-defective BRG1 catalytic subunit that forms inactive SWI/SNF complexes that bind to the OC promoter. This interaction results in inhibition of both basal and vitamin D3-enhanced OC gene transcription and a marked decrease in nuclease hypersensitivity. We find that SWI/SNF is recruited to the OC promoter via the transcription factor CCAAT/enhancer-binding protein β, which together with Runx2 forms a stable complex to facilitate RNA polymerase II binding and activation of OC gene transcription. Together, our results indicate that the SWI/SNF complex is a key regulator of the chromatin-remodeling events that promote tissue-specific transcription in osteoblasts. [ABSTRACT FROM AUTHOR]

Expression of glycosyltransferase genes is essential for glycosylation. However, the detailed mechanisms of how glycosyltransferase gene expression is regulated in a specific tissue or during disease progression are poorly understood. In particular, epigenetic studies of glycosyltransferase genes are limited, although epigenetic mechanisms, such as histone and DNA modifications, are central to establish tissue-specific gene expression. We previously found that epigenetic histone activation is essential for brain-specific expression of N-acetylglucosaminyltransferase- IX (GnT-IX, also designated GnT-Vb), but the mechanism of brain-specific chromatin activation around GnT-IX gene (Mgat5b) has not been clarified. To reveal the mechanisms regulating the chromatin surrounding GnT-IX, we have investigated the epigenetic factors that are specifically involved with the mouse GnT-IX locus by comparing their involvement with other glycosyltransferase loci. We first found that a histone deacetylase (HDAC) inhibitor enhanced the expression of GnT-IX but not of other glycosyltransferases tested. By overexpression and knockdown of a series of HDACs, we found that HDAC11 silenced GnT-IX. We also identified the O-GlcNAc transferase (OGT) and ten-eleven translocation-3 (TET3) complex as a specific chromatin activator of GnT-IX gene. Moreover, chromatin immunoprecipitation (ChIP) analysis in combination with OGT or TET3 knockdown showed that this OGT-TET3 complex facilitates the binding of a potent transactivator, NeuroD1, to the GnT-IX promoter, suggesting that epigenetic chromatin activation by the OGT-TET3 complex is a prerequisite for the efficient binding of NeuroD1. These results reveal a new epigenetic mechanism of brainspecific GnT-IX expression regulated by defined chromatin modifiers, providing new insights into the tissue-specific expression of glycosyltransferases. [ABSTRACT FROM AUTHOR]