Tissue control of androgen action: The ups and downs of androgen receptor expression

The hormone testosterone plays crucial roles during male development and puberty and throughout life, as an anabolic regulator of muscle and bone structure and function. The actions of testosterone are mediated, primarily, through the androgen receptor, a member of the nuclear receptor superfamily. The androgen receptor gene is located on the X-chromosome and receptor levels are tightly controlled both at the level of transcription of the gene and post-translationally at the protein level. Sp1 has emerged as the major driver of expression of the androgen receptor gene, while auto-regulation by androgens is associated with both positive and negative regulation in a possible cell-selective manner. Research into the networks of positive and negative regulators of the androgen receptor gene are vital in order to understand the temporal and spatial control of receptor levels and the consequences for healthy aging and disease. A clear understanding of the multiple transcription factors participating in regulation of the androgen receptor gene will likely aid in the development and application of hormone therapies to boast or curb receptor activity.

An Sp1 Modulated Regulatory Region Unique to Higher Primates Regulates Human Androgen Receptor Promoter Activity in Prostate Cancer Cells

Androgen receptor (AR) mediated signalling is necessary for normal development of the prostate gland and also drives prostate cancer (PCa) cell growth and survival, with many studies showing a correlation between increased receptor levels and therapy resistance with progression to fatal castrate recurrent PCa (CRPC). Although it has been held for some time that the transcription factor Sp1 is the main stimulator of AR gene transcription, comprehensive knowledge of the regulation of the AR gene remains incomplete. Here we describe and characterise in detail two novel active regulatory elements in the 5’UTR of the human AR gene. Both of these elements contain overlapping binding sites for the positive transcription factor Sp1 and the repressor protein pur-α. Aberrant cell signalling is characteristic of PCa and the transcriptional activity of the AR promoter in PCa cells is dependent upon the relative amounts of the two transcription factors. Together with our corroboration of the dominant role of Sp1, the findings support the rationale of targeting this transcription factor to inhibit tumour progression. This should be of particular therapeutic relevance in CRPC where the levels of the repressor pur-α are reduced.

Functional effects of polymorphisms on glucocorticoid receptor modulation of human anxiogenic substance-P gene promoter activity in primary amygdala neurones

Expression or introduction of the neuropeptide substance-P (SP; encoded by the TAC1 gene in humans and Tac1 in rodents) in the amygdala induces anxiety related behaviour in rodents. In addition, pharmacological antagonism of the main receptor of SP in humans; NK1, is anxiolytic. In the current study, we show that the Tac1 locus is up-regulated in primary rat amygdala neurones in response to activation of the glucocorticoid receptor (GR); a classic component of the stress response. Using a combination of bioinformatics, electrophoretic mobility shift assays (EMSA) and reporter plasmid magnetofection into rat primary amygdala neurones we identified a highly conserved GR response sequence (2GR) in the human TAC1 promoter that binds GR in response to dexamethasone (Dex) or forskolin. We also identified a second GR binding site in the human promoter that was polymorphic and whose T-allele is only found in Japanese and Chinese populations. We present evidence that the T-allele of SNPGR increases the activity of the TAC1 promoter through de-sequestration or de-repression of 2GR. The identification of Dex/forskolin response elements in the TAC1 promoter in amygdala neurones suggests a possible link in the chain of molecular events connecting GR activation and anxiety. In addition, the discovery of a SNP which can alter this response may have implications for our understanding of the role of regulatory variation in susceptibility to stress in specific populations.

Purification and Characterization of a Population of EGFP-Expressing Cells from the Developing Pancreas of a Neurogenin3/EGFP Transgenic Mouse

Neurogenin 3 (ngn3) is a basic helix loop helix transcription factor that is transiently expressed in the developing mouse pancreas with peak expression around E15. In mice lacking the ngn3 gene the endocrine cells of the pancreas fail to develop suggesting that the ngn3-positive cell may represent a progenitor cell for the endocrine pancreas. In order to purify and characterize this cell in detail we have generated a transgenic mouse, in which the ngn3 promoter drives expression of enhanced green fluorescent protein (EGFP). In the E15.5 embryo EGFP was expressed in the dorsal and ventral pancreas, the duodenum, and lower intestine as well as in the brain. This pattern of expression was in keeping with the known expression profile of the endogenous ngn3 gene. Within the pancreas EGFP was localized in close proximity to cells that stained positive for ngn3, insulin, and glucagon, but was absent from regions of the pancreas that stained positive for amylase. EGFP was also present in the pancreas at E18.5, although there was no detectable expression of ngn3. At this stage EGFP did not colocalize with any of the hormones or exocrine markers. EGFP(+) cells were FACS purified (96%) from the E15 pancreas yielding approximately 10,000 cells or 1.6% of the total pancreatic cells from one litter. RT/PCR analysis confirmed that the purified cells expressed EGFP, ngn3, insulin, glucagon, somatostatin and pancreatic polypeptide. The ability to purify ngn3(+) cells provides an invaluable source of material for charactering in detail their properties.

Interactions of abiraterone, eplerenone, and prednisolone with wild-type and mutant androgen receptor: a rationale for increasing abiraterone exposure or combining with MDV3100

Prostate cancer progression can be associated with androgen receptor (AR) mutations acquired following treatment with castration and/or an antiandrogen. Abiraterone, a rationally designed inhibitor of CYP17A1 recently approved for the treatment of docetaxel-treated castration-resistant prostate cancer (CRPC), is often effective, but requires coadministration with glucocorticoids to curtail side effects. Here, we hypothesized that progressive disease on abiraterone may occur secondary to glucocorticoid-induced activation of mutated AR. We found that prednisolone plasma levels in patients with CRPC were sufficiently high to activate mutant AR. Mineralocorticoid receptor antagonists, such as spironolactone and eplerenone that are used to treat side effects related to mineralocorticoid excess, can also bind to and activate signaling through wild-type or mutant AR. Abiraterone inhibited in vitro proliferation and AR-regulated gene expression of AR-positive prostate cancer cells, which could be explained by AR antagonism in addition to inhibition of steroidogenesis. In fact, activation of mutant AR by eplerenone was inhibited by MDV3100, bicalutamide, or greater concentrations of abiraterone. Therefore, an increase in abiraterone exposure could reverse resistance secondary to activation of AR by residual ligands or coadministered drugs. Together, our findings provide a strong rationale for clinical evaluation of combined CYP17A1 inhibition and AR antagonism.

The impact of point mutations in the human androgen receptor: classification of mutations on the basis of transcriptional activity

Androgen receptor mediated signaling drives prostate cancer cell growth and survival. Mutations within the receptor occur infrequently in prostate cancer prior to hormonal therapy but become prevalent in incurable androgen independent and metastatic tumors. Despite the determining role played by the androgen receptor in all stages of prostate cancer progression, there is a conspicuous dearth of comparable data on the consequences of mutations. In order to remedy this omission, we have combined an expansive study of forty five mutations which are predominantly associated with high Gleason scores and metastatic tumors, and span the entire length of the receptor, with a literature review of the mutations under investigation. We report the discovery of a novel prevalent class of androgen receptor mutation that possesses loss of function at low levels of androgen yet transforms to a gain of function at physiological levels. Importantly, mutations introducing constitutive gain of function are uncommon, with the majority of mutations leading to either loss of function or no significant change from wild-type activity. Therefore, the widely accepted supposition that androgen receptor mutations in prostate cancer result in gain of function is appealing, but mistaken. In addition, the transcriptional outcome of some mutations is dependent upon the androgen receptor responsive element. We discuss the consequences of these findings and the role of androgen receptor mutations for prostate cancer progression and current treatment options.

Identification of androgen receptor phosphorylation in the primate ovary in vivo

The androgen receptor (AR) is a member of the nuclear receptor superfamily, and is important for both male and female reproductive health. The receptor is a target for a number of post-translational modifications including phosphorylation, which has been intensively studied in vitro. However, little is known about the phosphorylation status of the receptor in target tissues in vivo. The common marmoset is a useful model for studying human reproductive functions, and comparison of the AR primary sequence from this primate shows high conservation of serines known to be phosphorylated in the human receptor and corresponding flanking amino acids. We have used a panel of phosphospecific antibodies to study AR phosphorylation in the marmoset ovary throughout the follicular phase and after treatment with GNRH antagonist or testosterone propionate. In normal follicular phase ovaries, total AR (both phosphorylated and non-phosphorylated forms) immunopositive staining was observed in several cell types including granulosa cells of developing follicles, theca cells and endothelial cells lining blood vessels. Receptor phosphorylation at serines 81, 308, and 650 was detected primarily in the granulosa cells of developing follicles, surface epithelium, and vessel endothelial cells. Testosterone treatment lead to a modest increase in AR staining in all stages of follicle studied, while GNRH antagonist had no effect. Neither treatment significantly altered the pattern of phosphorylation compared to the control group. These results demonstrate that phosphorylation of the AR occurs, at a subset of serine residues, in a reproductive target tissue in vivo, which appears refractory to hormonal manipulations.

Pancreatic transcription factors and their role in the birth, life and survival of the pancreatic beta cell

In recent years major progress has been made in understanding the role of transcription factors in the development of the endocrine pancreas in the mouse. Here we describe how a number of these transcription factors play a role in maintaining the differentiated phenotype of the beta cell, and in the mechanisms that allow the beta cell to adapt to changing metabolic demands that occur throughout life. Amongst these factors, Pdx1 plays a critical role in defining the region of the primitive gut that will form the pancreas, Ngn3 expression drives cells towards an endocrine lineage, and a number of additional proteins including Pdx1, in a second wave of expression, Pax4, NeuroD1/beta2, and MafA act as beta cell differentiation factors. In the mature beta cell Pdx1, MafA, beta2, and Nkx2.2 play important roles in regulating expression of insulin and to some extent other genes responsible for maintaining beta cell function. We emphasise here that data from gene expression studies in rodents seldom map on to the known structure of the corresponding human promoters. In the adult the beta cell is particularly susceptible to autoimmune-mediated attack and to the toxic metabolic milieu associated with over-eating, and utilises a number of these transcription factors in its defence. Pdx1 has anti-apoptotic and proliferative activities that help facilitate the maintenance of beta cell mass, while Ngn3 may be involved in the recruitment of progenitor cells, and Pax4 (and possibly HNF1alpha and Hnf4alpha) in the proliferation of beta cells in the adult pancreas. Other transcription factors with a more widespread pattern of expression that play a role in beta cell survival or proliferation include Foxo1, CREB family members, NFAT, FoxM1, Snail and Asc-2.

ATF-2 stimulates the human insulin promoter through the conserved CRE2 sequence

The insulin promoter contains a number of dissimilar cis-acting regulatory elements that bind a range of tissue specific and ubiquitous transcription factors. Of the regulatory elements within the insulin promoter, the cyclic AMP responsive element (CRE) binds by far the most diverse array of transcription factors. Rodent insulin promoters have a single CRE site, whereas there are four CREs within the human insulin gene, of which CRE2 is the only one conserved between species. The aim of this study was to characterise the human CRE2 site and to investigate the effects of the two principal CRE-associated transcription factors; CREB-1 and ATF-2. Co-transfection of INS-1 pancreatic beta-cells with promoter constructs containing the human insulin gene promoter placed upstream of the firefly luciferase reporter gene and expression plasmids for ATF-2 or CREB-1 showed that ATF-2 stimulated transcriptional activity while CREB-1 elicited an inhibitory effect. Mutagenesis of CRE2 diminished the effect of ATF-2 but not that of CREB-1. ATF-2 was shown to bind to the CRE2 site by electrophoretic mobility shift assay and by chromatin immunoprecipitation, while siRNA mediated knockdown of ATF-2 diminished the stimulatory effects of cAMP related signalling on promoter activity. These results suggest that ATF-2 may be a key regulator of the human insulin promoter possibly stimulating activity in response to extracellular signals.

Comparative analysis of insulin gene promoters: implications for diabetes research

DNA sequences that regulate expression of the insulin gene are located within a region spanning approximately 400 bp that flank the transcription start site. This region, the insulin promoter, contains a number of cis-acting elements that bind transcription factors, some of which are expressed only in the beta-cell and a few other endocrine or neural cell types, while others have a widespread tissue distribution. The sequencing of the genome of a number of species has allowed us to examine the manner in which the insulin promoter has evolved over a 450 million-year period. The major findings are that the A-box sites that bind PDX-1 are among the most highly conserved regulatory sequences, and that the conservation of the C1, E1, and CRE sequences emphasize the importance of MafA, E47/beta2, and cAMP-associated regulation. The review also reveals that of all the insulin gene promoters studied, the rodent insulin promoters are considerably dissimilar to the human, leading to the conclusion that extreme care should be taken when extrapolating rodent-based data on the insulin gene to humans.

Presence of endocrine and exocrine markers in EGFP-positive cells from the developing pancreas of a nestin/EGFP mouse

In order to purify and characterize nestin-positive cells in the developing pancreas a transgenic mouse was generated, in which the enhanced green fluorescent protein (EGFP) was driven by the nestin second intronic enhancer and upstream promoter. In keeping with previous studies on the distribution of nestin, EGFP was expressed in the developing embryo in neurones in the brain, eye, spinal cord, tail bud and glial cells in the small intestine. In the pancreas there was no detectable EGFP at embryonic day 11.5 (E11.5). EGFP expression appeared at E12.5 and increased in intensity through E14.5, E18.5 and post-natal day 1. Flow cytometry was used to quantify and purify the EGFP positive population in the E15.5 pancreas. The purified (96%) EGFP-expressing cells, which represent 20% of the total cell population, were shown by RT/PCR to express exocrine cell markers (amylase and P48) and endocrine cell markers (insulin 1, insulin 2, and Ngn3). They also expressed, at a lower level, PDX-1, Isl-1, and the islet hormones pancreatic polypeptide, glucagon and somatostatin as well as GLUT2, the stem cell marker ABCG2 and PECAM, a marker of endothelial cells. It was further shown by immunocytochemistry of the E15.5 pancreas that EGFP colocalised in separate subpopulations of cells that expressed nestin, insulin and amylase. These results support the conclusion that nestin expressing cells can give rise to both endocrine and exocrine cells. The ability to purify these putative progenitor cells may provide further insights into their properties and function.

Transcription factor cycling on the insulin promoter

Using MIN6 beta-cells and chromatin immunoprecipitation (ChIP) assays, the chronological sequence of binding of MafA, E47/beta2 and PDX-1 to the insulin promoter in living beta-cells were investigated. All four factors were shown to bind to the mouse insulin 2 promoter in a cyclical manner with a periodicity of approximately 10-15 min. The cyclical binding of MafA, E47 and beta2 was largely unaffected by the glucose or insulin concentration in the media. However, the binding and cycling of PDX-1 was markedly abolished in low glucose (1 mM), and this was reversed in the presence of low concentrations of insulin.

Glucagon-like peptide-1 stimulates human insulin promoter activity in part through cAMP-responsive elements that lie upstream and downstream of the transcription start site

Glucagon-like peptide-1 (GLP-1) is a peptide hormone secreted from the enteroendocrine L-cells of the gut and which acts primarily to potentiate the effects of glucose on insulin secretion from pancreatic beta-cells. It also stimulates insulin gene expression, proinsulin biosynthesis and affects the growth and differentiation of the islets of Langerhans. Previous studies on the mechanisms whereby GLP-1 regulates insulin gene transcription have focused on the rat insulin promoter. The aim of this study was to determine whether the human insulin promoter was also responsive to GLP-1, and if so to investigate the possible role of cAMP-responsive elements (CREs) that lie upstream (CRE1 and CRE2) and downstream (CRE3 and CRE4) of the transcription start site. INS-1 pancreatic beta-cells were transfected with promoter constructs containing fragments of the insulin gene promoter placed upstream of the firefly luciferase reporter gene. GLP-1 was found to stimulate the human insulin promoter, albeit to a lesser degree than the rat insulin promoter. Mutagenesis of CRE2, CRE3 and CRE4 blocked the stimulatory effect of GLP-1 while mutagenesis of CRE1 had no effect. Analysis of nuclear protein binding to the four CREs showed that, while they share some proteins, each CRE site is unique. Stimulation of transcription by GLP-1 through CRE2, CRE3 and CRE4 resulted in altered protein binding that was different for each of the CRE sites involved. Collectively, these data show that the four human CREs are not simply multiple copies of the rat CRE site and further emphasise that the human insulin promoter is distinct from the rodent promoter.

Enhanced expression of a furin-cleavable proinsulin

Cell engineering or gene therapy may represent an alternative to current methods of treating diabetes mellitus. Cells could be engineered to secrete insulin ex vivo for transplantation or the insulin gene could be administered directly by injection into muscle. A problem has been that non-neuroendocrine cells lack the endoproteases (PC3/1 and PC2) that are responsible for the processing of proinsulin to insulin. This can be surmounted by engineering the paired basic amino acid processing sites within proinsulin to sites that would be recognized by the ubiquitously expressed protease, furin. However, in every study to date, the expression of the furin-cleavable construct was greatly reduced relative to that of the unmodified proinsulin construct. We investigated possible causes for this, including mRNA stability, the presence of additional CpG islands, and the amino acid substitutions within furin-cleavable proinsulin. Several furin-cleavable rat proinsulin I cDNAs were engineered and used to transfect human HEK293, rat L6 and mouse C(2)C(12) cell lines. The stability of wild-type and furin-cleavable proinsulin mRNA in transfected C(2)C(12) cells was measured by RT-PCR. Comparison of the decay rates in the presence of actinomycin D showed no significant difference between the two species of mRNA. A furin-cleavable proinsulin cDNA was created to contain the same distribution of CpG islands as wild-type proinsulin. Comparison of insulin-like immunoreactivity in all three cell lines transfected with either this construct or a widely used furin-cleavable proinsulin containing additional CpG islands showed that the presence of the extra CpG islands had no effect. Studies to examine amino acid substitutions used to create furin consensus sequences showed that the addition of basic residues at the C-peptide/A-chain junction was responsible for the reduced production of furin-cleavable proinsulin. Using this information, we engineered a cDNA for furin-cleavable rat proinsulin I that was efficiently processed to mature insulin and expressed at the same level as wild-type proinsulin.

Para-aural abscessation following traumatic ear canal separation in a dog

Traumatic ear canal separation is rare in animals, with only eight dogs and one cat reported with the condition in the English language literature. Para-aural abscessation occurred in six of these nine animals. Diagnosis was made on otoscopic observation of a shortened, abruptly ending external ear canal that was free from advanced disease. Radiographs in those cases which have been described showed a disruption of the normal air opacity of the affected ear canal. Drainage, by creating a separate opening for the horizontal ear canal, or total ear canal ablation and lateral bulla osteotomy (TECA/LBO), have led to resolution of the clinical signs. This report adds a further case to the literature in which TECA/LBO was employed successfully.

Tearing of the dura mater in three dogs

Tearing of the thoracolumbar dura mater was diagnosed after myelography in three large breed dogs. All three dogs lost the ability to walk suddenly, after a period of vigorous running or struggling. Radiographic changes suggested that the tearing of the dura was associated with intervertebral disc injury in two dogs. These dogs regained the ability to walk after medical treatment. Postmortem findings suggested that the tearing of the dura mater in the third dog was associated with nerve root injury and spinal cord haemorrhage after an episode of violent struggling.

Idiopathic multifocal osteopathy in four Scottish terriers (1991-1996)

This case series describes four Scottish terriers with an osteopathic condition, characterized by multifocal absence of bone in the skull, cervical spine, and proximal radii, ulnae, and femora. All dogs were affected clinically; two dogs were euthanized due to progression of the disease, one died acutely, and one was euthanized for an oral melanoma. Histopathology in one case was characterized by osteoclastic osteolysis and replacement of bone with fibrous tissue. This disease has some characteristics of human osteolysis syndromes. Three of the dogs were related through pedigree analysis, and the pedigree of the other dog was not available. The name, idiopathic multifocal osteopathy, is used to describe a new disease in dogs, found particularly in Scottish terriers.

Synovial fluid interleukin 6, tumor necrosis factor, and nitric oxide values in dogs with osteoarthritis secondary to cranial cruciate ligament rupture

OBJECTIVE

To measure and compare values of interleukin 6 (IL-6), tumor necrosis factor (TNF), and nitric oxide (NO) metabolites in synovial fluid from canine joints with osteoarthritis (OA) secondary to naturally acquired cranial cruciate ligament (CCL) rupture and experimental CCL transection.

ANIMALS

57 dogs (clinical group) with OA secondary to CCL rupture; 5 dogs (experimental group) with OA secondary to CCL transection; 19 control dogs with normal joints.

PROCEDURE

Joints were radiographed and graded for seventy of OA. Synovial fluid was collected from dogs: at surgery from the clinical group, at 90 days after surgery from the experimental group, and at necropsy from the control group. Activities of IL-6 and TNF, as well as concentration of the NO metabolites (NO2-/NO3-) were measured, and results were reported as mean +/- SEM.

RESULTS

IL-6 activity in dogs of the clinical (290 +/- 40 U/ml) and experimental (494 +/- 165 U/ml) groups was greater than that in control dogs (6 +/- 1.6 U/ml; P < 0.05). The TNF values in dogs of the clinical (3.0 +/- 0.5 pg/ml) and experimental (2.0 +/- 0.9 pg/ml) groups were lower than those in control dogs (8.6 +/- 2.3 pg/ml; P < 0.05). The IL-6 values were negatively associated with radiographic score of OA and were positively associated with age (R2 = 26.5%, P < 0.05).

CONCLUSION

Dogs with OA secondary to naturally acquired CCL rupture and experimental CCL transection had significantly different alterations in synovial fluid IL-6 and TNF values. The decrease in IL-6 activity with advancing OA was independent of the increase in IL-6 activity with aging.

CLINICAL RELEVANCE

IL-6 and TNF may be involved in pathogenesis of OA secondary to naturally acquired and experimentally induced CCL rupture.

Use of the Wagner apparatus to lengthen the antebrachium of a growing dog

A six-month-old male golden retriever was presented with a shortened radius and ulna and valgus deformity of the carpus secondary to premature closure of the distal radial and ulnar physes. Osteotomies of the radius and ulna were performed and the antebrachium was lengthened over eight weeks using a Wagner apparatus. This external fixation distractor is used in humans for limb-lengthening procedures. In this case, it was used to correct the angular deformity and to lengthen the limb.

Isolation of a human von Willebrand factor cDNA from the hybrid endothelial cell line EA.hy926

A permanent human hybrid endothelial cell line (EA.hy926) was shown to produce the von Willebrand factor, a protein of 250,000 relative mass (Mr) which was secreted into the medium as a 220,000 Mr protein. A cDNA library was constructed in lambda gt11 using mRNA from these hybrid cells. Several von Willebrand factor cDNA clones were isolated from this library using a synthetic oligodeoxyribonucleotide as a hybridization probe. These cDNA clones were used to analyze the von Willebrand factor gene in normal individuals and in cultured cells.

RFLPs for PstI and EcoRI in the human blood clotting factor X gene

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Use of a BamHI polymorphism in the factor IX gene for the determination of hemophilia B carrier status

A BamHI polymorphism has been identified in the human factor IX gene. This polymorphism, which occurs in approximately 6% of X chromosomes, has been used to determine the carrier status of a female in a family with a history of hemophilia B. This family was uninformative for the previously reported TaqI and Xmnl polymorphisms in the factor IX gene.

Characterization of an almost full-length cDNA coding for human blood coagulation factor X

A human liver cDNA library was screened by colony hybridization with a bovine factor X cDNA probe. Three of the positive plasmids contained overlapping DNA that coded for most of human factor X mRNA. DNA sequence analysis of these three clones allowed the prediction of the complete amino acid sequence of plasma factor X. From these studies, we predict that human factor X is synthesized as a single polypeptide chain precursor in which the light and heavy chains of plasma factor X are linked by the tripeptide Arg-Lys-Arg. The cDNA sequence also predicts that human factor X is synthesized as a preproprotein having an amino-terminal leader peptide of at least 28 amino acid residues. A comparison of the amino acid sequences of human and bovine factor X shows high sequence identity around the calcium-binding regions and catalytic regions but low sequence identity around the nonfunctional regions.

Histone deacetylase from HeLa cells: properties of the high molecular weight complex

In previous work [Hay, C. W., & Candido, E. P. M. (1983) J. Biol. Chem. 258, 3726-3734], we have shown that the histone deacetylase from HeLa cell nuclei is associated with a high molecular weight, nuclease-resistant complex. This complex was found to contain a variety of non-histone proteins, and indirect evidence for the importance of protein-protein interactions in the maintenance of its structure was obtained. In the present report, we examine the effects of beta-mercaptoethanol and neocuproine on the deacetylase complex and present data on the level of histone acetylation and the presence of satellite DNA sequences in this material. HeLa cell histone deacetylase complex partially dissociates in 10 mM beta-mercaptoethanol, resulting in a loss of non-histone proteins. The presence of 10 mM beta-mercaptoethanol during the micrococcal nuclease digestion of HeLa cell nuclei results in a greatly reduced yield of histone deacetylase complex, with a correspondingly large increase in the production of small oligonucleosomes and mononucleosomes. Histone deacetylase activity on endogenous labeled histone within the complex is strongly inhibited by either 1 or 10 mM beta-mercaptoethanol or 3 mM neocuproine. This loss of histone deacetylase activity does not seem to be due to an inactivation of the enzyme but appears to be a consequence of the disruption of the structure of the deacetylase complex itself. Histone H4 in the deacetylase complex prepared from HeLa cell nuclei by micrococcal nuclease digestion was more highly acetylated than H4 in bulk nucleosomes. Restriction enzyme analysis of the DNA associated with the histone deacetylase complex revealed neither an enrichment nor a depletion of major satellite sequences in this material.

Histone deacetylase. Association with a nuclease resistant, high molecular weight fraction of HeLa cell chromatin

The chromatin-bound histone deacetylase of HeLa cells has been studied using endogenous [3H]acetyl-labeled polynucleosomes containing the enzyme, prepared in the presence of 40 mM butyrate. Histone deacetylase was assayed upon removal of the butyrate, and it was found that active enzyme is found only in association with a high molecular weight complex. This deacetylase-containing complex is relatively resistant to digestion with micrococcal nuclease. No activity is found on mononucleosomes or oligonucleosomes. Up to 90% of labeled acetyl groups are removed from histone deacetylase complexes incubated in the absence of butyrate. Free histones are a poor substrate under these conditions, but histones in mononucleosomes are deacetylated when they are incubated with histone deacetylase complex. Histone deacetylase remains bound to this complex in 1-2 M NaCl and does not dissociate from it during its reaction with acetylated core histones. Under typical nuclease digestion conditions, the histone deacetylase complex contains DNA with a size distribution of 5-11 kilobase pairs and a variety of nonhistone proteins. Comparison of the protein composition of histone deacetylase complexes with that of nuclear matrix preparations shows some similarities. Taken together, the results on the chromatographic behavior, the DNA fragment sizes, and the protein composition of the deacetylase complex suggest that protein-protein interactions may be important in maintaining its structure and also in the binding of the deacetylase itself to the complex.