Biomedical subjects

Marc I Diamond

Publications and source records attributed to Marc I Diamond.

5 recordsLinked to original sources

PubMed2006

Soluble androgen receptor oligomers underlie pathology in a mouse model of spinobulbar muscular atrophy.

In polyglutamine diseases such as X-linked spinobulbar muscular atrophy (SBMA), it is unknown whether the toxic form of the protein is an insoluble or soluble aggregate or a monomer. We have addressed this question by studying a full-length androgen receptor (AR) mouse model of SBMA. We used biochemistry and atomic force microscopy to immunopurify oligomers soluble after ultracentrifugation that are comprised of a single approximately 50-kDa N-terminal polyglutamine-containing AR fragment. AR oligomers appeared several weeks prior to symptom onset, were distinct and temporally dissociated from intranuclear inclusions, and disappeared rapidly after castration, which halts disease. This is the first demonstration of soluble AR oligomers in vivo and suggests that they underlie neurodegeneration in SBMA.

Aging↗

PubMed2006

Selective activation of estrogen receptor-beta transcriptional pathways by an herbal extract.

Novel estrogenic therapies are needed that ameliorate menopausal symptoms and have the bone-sparing effects of endogenous estrogens but do not promote breast or uterine cancer. Recent evidence suggests that selective activation of the estrogen receptor (ER)-beta subtype inhibits breast cancer cell proliferation. To establish whether ERbeta-selective ligands represent a viable approach to improve hormone therapy, we investigated whether the estrogenic activities present in an herbal extract, MF101, used to treat hot flashes, are ERbeta selective. MF101 promoted ERbeta, but not ERalpha, activation of an estrogen response element upstream of the luciferase reporter gene. MF101 also selectively regulates transcription of endogenous genes through ERbeta. The ERbeta selectivity was not due to differential binding because MF101 binds equally to ERalpha and ERbeta. Fluorescence resonance energy transfer and protease digestion studies showed that MF101 produces a different conformation in ERalpha from ERbeta when compared with the conformations produced by estradiol. The specific conformational change induced by MF101 allows ERbeta to bind to an estrogen response element and recruit coregulatory proteins that are required for gene activation. MF101 did not activate the ERalpha-regulated proliferative genes, c-myc and cyclin D1, or stimulate MCF-7 breast cancer cell proliferation or tumor formation in a mouse xenograft model. Our results demonstrate that herbal ERbeta-selective estrogens may be a safer alternative for hormone therapy than estrogens that nonselectively activate both ER subtypes.

Anemarrhena↗

PubMed2006

Biologically active molecules that reduce polyglutamine aggregation and toxicity.

Polyglutamine expansion in certain proteins causes neurodegeneration in inherited disorders such as Huntington disease and X-linked spinobulbar muscular atrophy. Polyglutamine tracts promote protein aggregation in vitro and in vivo with a strict length-dependence that strongly implicates alternative protein folding and/or aggregation as a proximal cause of cellular toxicity and neurodegeneration. We used an intracellular polyglutamine protein aggregation assay based on fluorescence resonance energy transfer (FRET) to identify inhibitors of androgen receptor (AR) aggregation in three libraries of biologically active small molecules: the Annotated Compound Library, the NINDS Custom Collection and a kinase inhibitor collection. In the primary screen 10 compounds reduced AR aggregation. While 10/10 also reduced huntingtin (Htt) exon 1 aggregation, only 2/10 reduced aggregation of pure polyglutamine peptides. In a PC-12 model 9/10 compounds reduced aggregation. Five out of nine compounds tested in an Htt exon 1 assay of neurodegeneration in Drosophila partially rescued the phenotype. Three of the five compounds effective in flies are FDA-approved drugs. These compounds provide new leads for therapeutic development for the polyglutamine diseases based on their efficacy in mammalian cells and a Drosophila model. The high predictive value of the primary screen suggests that the FRET-based screening assay may be useful for further primary and secondary screens for genes or small molecules that inhibit polyglutamine protein aggregation.

Androgen Receptor Antagonists↗

PubMed2005

The structural basis of androgen receptor activation: intramolecular and intermolecular amino-carboxy interactions.

Nuclear receptors (NRs) are ligand-regulated transcription factors important in human physiology and disease. In certain NRs, including the androgen receptor (AR), ligand binding to the carboxy-terminal domain (LBD) regulates transcriptional activation functions in the LBD and amino-terminal domain (NTD). The basis for NTD-LBD communication is unknown but may involve NTD-LBD interactions either within a single receptor or between different members of an AR dimer. Here, measurement of FRET between fluorophores attached to the NTD and LBD of the AR established that agonist binding initiated an intramolecular NTD-LBD interaction in the nucleus and cytoplasm. This intramolecular folding was followed by AR self-association, which occurred preferentially in the nucleus. Rapid, ligand-induced intramolecular folding and delayed association also were observed for estrogen receptor-alpha but not for peroxisome proliferator activated receptor-gamma2. An antagonist ligand, hydroxyflutamide, blocked the NTD-LBD association within AR. NTD-LBD association also closely correlated with the transcriptional activation by heterologous ligands of AR mutants isolated from hormone-refractory prostate tumors. Intramolecular folding, but not AR-AR affinity, was disrupted by mutation of an alpha-helical ((23)FQNLF(27)) motif in the AR NTD previously described to interact with the AR LBD in vitro. This work establishes an intramolecular NTD-LBD conformational change as an initial component of ligand-regulated NR function.

Amino Acid Motifs↗

PubMed2003

A rapid cellular FRET assay of polyglutamine aggregation identifies a novel inhibitor.

Many neurodegenerative diseases, including tauopathies, Parkinson's disease, amyotrophic lateral sclerosis, and the polyglutamine diseases, are characterized by intracellular aggregation of pathogenic proteins. It is difficult to study modifiers of this process in intact cells in a high-throughput and quantitative manner, although this could facilitate molecular insights into disease pathogenesis. Here we introduce a high-throughput assay to measure intracellular polyglutamine protein aggregation using fluorescence resonance energy transfer (FRET). We screened over 2800 biologically active small molecules for inhibitory activity and have characterized one lead compound in detail. Y-27632, an inhibitor of the Rho-associated kinase p160ROCK, diminished polyglutamine protein aggregation (EC(50) congruent with 5 microM) and reduced neurodegeneration in a Drosophila model of polyglutamine disease. This establishes a novel high-throughput approach to study protein misfolding and aggregation associated with neurodegenerative diseases and implicates a signaling pathway of previously unrecognized importance in polyglutamine protein processing.

Amides↗