Repressive Effects of Resveratrol on Androgen Receptor Transcriptional Activity

The chemopreventive effects of resveratrol (RSV) on prostate cancer have been well established; the androgen receptor (AR) plays pivotal roles in prostatic tumorigenesis. However, the exact underlying molecular mechanisms about the effects of RSV on AR have not been fully elucidated. A model system is needed to determine whether and how RSV represses AR transcriptional activity.The AR cDNA was first cloned into the retroviral vector pOZ-N and then integrated into the genome of AR-negative HeLa cells to generate the AR(+) cells. The constitutively expressed AR was characterized by monitoring hormone-stimulated nuclear translocation, DNA binding, and transcriptional activation, with the AR(-) cells serving as controls. AR(+) cells were treated with RSV, and both AR protein levels and AR transcriptional activity were measured simultaneously. Chromatin immunoprecipitation (ChIP) assays were used to detect the effects of RSV on the recruitment of AR to its cognate element (ARE).AR in the AR (+) stable cell line functions in a manner similar to that of endogenously expressed AR. Using this model system we clearly demonstrated that RSV represses AR transcriptional activity independently of any effects on AR protein levels. However, neither the hormone-mediated nucleus translocation nor the AR/ARE interaction was affected by RSV treatment.We demonstrated unambiguously that RSV regulates AR target gene expression, at least in part, by repressing AR transcriptional activity. Repressive effects of RSV on AR activity result from mechanisms other than the affects of AR nuclear translocation or DNA binding

Human brain glycogen phosphorylase. Cloning, sequence analysis, chromosomal mapping, tissue expression, and comparison with the human liver and muscle isozymes.

We have cloned the cDNA encoding a new isozyme of glycogen phosphorylase (1,4-D-glucan:orthosphosphate D-glucosyltransferase, EC 2.4.1.1) from a cDNA library prepared from a human brain astrocytoma cell line. Blot-hybridization analysis reveals that this message is preferentially expressed in human brain, but is also found at a low level in human fetal liver and adult liver and muscle tissues. Although previous studies have suggested that the major isozyme of phosphorylase found in all fetal tissues is the brain type, our data show that the predominant mRNA in fetal liver (24-week gestation) is the adult liver form. The protein sequence deduced from the nucleotide sequence of the brain phosphorylase cDNA is 862 amino acids long compared with 846 and 841 amino acids for the liver and muscle isozymes, respectively; the greater length of brain phosphorylase is entirely due to an extension at the far C-terminal portion of the protein. The muscle and brain isozymes share greater identity with regard to nucleotide and deduced amino acid sequences, codon usage, and nucleotide composition than either do with the liver sequence, suggesting a closer evolutionary relationship between them. Spot blot hybridization of the brain phosphorylase cDNA to laser-sorted human chromosome fractions, and Southern blot analysis of hamster/human hybrid cell line DNA reveals that the exact homolog of the newly cloned cDNA maps to chromosome 20, but that a slightly less homologous gene is found on chromosome 10 as well. The liver and muscle genes have previously been localized to chromosomes 14 and 11, respectively. This suggests that the phosphorylase genes evolved by duplication and translocation of a common ancestral gene, leading to divergence of elements controlling gene expression and of structural features of the phosphorylase proteins that confer tissue-specific functional properties

Human brain glycogen phosphorylase. Cloning, sequence analysis, chromosomal mapping, tissue expression, and comparison with the human liver and muscle isozymes.

We have cloned the cDNA encoding a new isozyme of glycogen phosphorylase (1,4-D-glucan:orthosphosphate D-glucosyltransferase, EC 2.4.1.1) from a cDNA library prepared from a human brain astrocytoma cell line. Blot-hybridization analysis reveals that this message is preferentially expressed in human brain, but is also found at a low level in human fetal liver and adult liver and muscle tissues. Although previous studies have suggested that the major isozyme of phosphorylase found in all fetal tissues is the brain type, our data show that the predominant mRNA in fetal liver (24-week gestation) is the adult liver form. The protein sequence deduced from the nucleotide sequence of the brain phosphorylase cDNA is 862 amino acids long compared with 846 and 841 amino acids for the liver and muscle isozymes, respectively; the greater length of brain phosphorylase is entirely due to an extension at the far C-terminal portion of the protein. The muscle and brain isozymes share greater identity with regard to nucleotide and deduced amino acid sequences, codon usage, and nucleotide composition than either do with the liver sequence, suggesting a closer evolutionary relationship between them. Spot blot hybridization of the brain phosphorylase cDNA to laser-sorted human chromosome fractions, and Southern blot analysis of hamster/human hybrid cell line DNA reveals that the exact homolog of the newly cloned cDNA maps to chromosome 20, but that a slightly less homologous gene is found on chromosome 10 as well. The liver and muscle genes have previously been localized to chromosomes 14 and 11, respectively. This suggests that the phosphorylase genes evolved by duplication and translocation of a common ancestral gene, leading to divergence of elements controlling gene expression and of structural features of the phosphorylase proteins that confer tissue-specific functional properties

The FKBP52 Cochaperone Acts in Synergy with β-Catenin to Potentiate Androgen Receptor Signaling

© 2015 Storer Samaniego et al.FKBP52 and β-catenin have emerged in recent years as attractive targets for prostate cancer treatment. β-catenin interacts directly with the androgen receptor (AR) and has been characterized as a co-Activator of AR-mediated t

The human orphan nuclear receptor tailless (TLX, NR2E1) is druggable

Nuclear receptors (NRs) are an important group of ligand-dependent transcriptional factors. Presently, no natural or synthetic ligand has been identified for a large group of orphan NRs. Small molecules to target these orphan NRs will provide unique resou

Structural changes in glycogen phosphorylase induced by phosphorylation.

A comparison of the refined crystal structures of dimeric glycogen phosphorylase b and a reveals structural changes that represent the first step in the activation of the enzyme. On phosphorylation of serine-14, the N-terminus of each subunit assumes an ordered helical conformation and binds to the surface of the dimer. The consequent structural changes at the N- and C-terminal regions lead to strengthened interactions between subunits and alter the binding sites for allosteric effectors and substrates

Ligand selectivity by seeking hydrophobicity in thyroid hormone receptor

Selective therapeutics for nuclear receptors would revolutionize treatment for endocrine disease. Specific control of nuclear receptor activity is challenging because the internal cavities that bind hormones can be virtually identical. Only one highly selective hormone analog is known for the thyroid receptor, GC-24, an agonist for human thyroid hormone receptor beta. The compound differs from natural hormone in benzyl, substituting for an iodine atom in the 3' position. The benzyl is too large to fit into the enclosed pocket of the receptor. The crystal structure of human thyroid hormone receptor beta at 2.8-A resolution with GC-24 bound explains its agonist activity and unique isoform specificity. The benzyl of GC-24 is accommodated through shifts of 3-4 A in two helices. These helices are required for binding hormone and positioning the critical helix 12 at the C terminus. Despite these changes, the complex associates with coactivator as tightly as human thyroid hormone receptor bound to thyroid hormone and is fully active. Our data suggest that increased specificity of ligand recognition derives from creating a new hydrophobic cluster with ligand and protein components

Design of thyroid hormone receptor antagonists from first principles

It is desirable to obtain TR antagonists for treatment of hyperthyroidism and other conditions. We have designed TR antagonists from first principles based on TR crystal structures. Since agonist ligands are buried in the fold of the TR ligand binding domain (LBD), we reasoned that ligands that resemble agonists with large extensions should bind the LBD, but would prevent its folding into an active conformation. In particular, we predicted that extensions at the 5' aryl position of ligand should reposition helix (H) 12, which forms part of the co-activator binding surface, and thereby inhibit TR activity. We have found that some synthetic ligands with 5' aryl ring extensions behave as antagonists (DIBRT, NH-3), or partial antagonists (GC-14, NH-4). Moreover, one compound (NH-3) represents the first potent TR antagonist with nanomolar affinity that also inhibits TR action in an animal model. However, the properties of the ligands also reveal unexpected aspects of TR behavior. While nuclear receptor antagonists generally promote binding of co-repressors, NH-3 blocks co-activator binding and also prevents co-repressor binding. More surprisingly, many compounds with extensions behave as full or partial agonists. We present hypotheses to explain both behaviors in terms of dynamic equilibrium of H12 position