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Biomedical subjects

T M Willson

Publications and source records attributed to T M Willson.

At least 55 records · Page 3Linked to original sources
PubMed2000

A synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), is a ligand for the peroxisome proliferator-activated receptor gamma.

A novel synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO), previously reported to have potent differentiating, antiproliferative, and antiinflammatory activities, has been identified as a ligand for the peroxisome proliferator-activated receptor gamma (PPARgamma). CDDO induces adipocytic differentiation in 3T3-L1 cells, although it is not as potent as the full agonist of PPARgamma, rosiglitazone. Binding studies of CDDO to PPARgamma using a scintillation proximity assay give a Ki between 10(-8) to 10(-7) M. In transactivation assays, CDDO is a partial agonist for PPARgamma. The methyl ester of CDDO, CDDO-Me, binds to PPARgamma with similar affinity, but is an antagonist. Like other PPARgamma ligands, CDDO synergizes with a retinoid X receptor (RXR)-specific ligand to induce 3T3-L1 differentiation, while CDDO-Me is an antagonist in this assay. The partial agonism of CDDO and the antagonism of CDDO-Me reflect the differences in their capacity to recruit or displace cofactors of transcriptional regulation; CDDO and rosiglitazone both release the nuclear receptor corepressor, NCoR, from PPARgamma, while CDDO-Me does not. The differences between CDDO and rosiglitazone as either partial or full agonists, respectively, are seen in the weaker ability of CDDO to recruit the coactivator CREB-binding protein, CBP, to PPARgamma. Our results establish the triterpenoid CDDO as a member of a new class of PPARgamma ligands.

3T3 Cells↗
PubMed1999

Synthesis and biological activity of a novel series of indole-derived PPARgamma agonists.

The synthesis and structure-activity relationships of a novel series of indole 5-carboxylic acids that bind and activate peroxisome proliferator-activated receptor gamma (PPARgamma) are reported. These new analogs are selective for PPARgamma vs the other PPAR subtypes, and the most potent compounds in this series are comparable to in vitro potencies at PPARgamma reported for the thiazolidinedione-based antidiabetic drugs currently in clinical use.

Animals↗
PubMed1999

A new ligand for the peroxisome proliferator-activated receptor-gamma (PPAR-gamma), GW7845, inhibits rat mammary carcinogenesis.

We have tested a new ligand for peroxisome proliferator-activated receptor-gamma, GW7845, as an inhibitor of experimental mammary carcinogenesis, using the classic rat model with nitrosomethylurea as carcinogen. Rats were first treated with a single dose of nitrosomethylurea (50 mg/kg body weight, i.p.). Starting 1 week later, they were fed GW7845, at either 60 or 30 mg/kg of diet, for 2 months. This agent significantly reduced tumor incidence, tumor number, and tumor weight at both doses. This is the first report of the use of a ligand for peroxisome proliferator-activated receptor-gamma to prevent experimental breast cancer.

Animals↗
PubMed1999

Expression of wild-type estrogen receptor beta and variant isoforms in human breast cancer.

It has been shown in previous studies that a variety of estrogen receptor (ER) beta mRNA transcripts are expressed in human breast cancer cell lines and tumors. To complement the RNA expression studies, we have developed ER-beta-specific antibodies to characterize ER-beta protein expression in breast cancer cell lines and tumors. Monoclonal antibodies were made against a peptide representing the first 18 amino acids of the longest ER-beta open reading frame reported to date, and polyclonal antibodies were made against a peptide within the ER-beta B domain. By Western blot analysis, we show that ER-beta protein is expressed in all cancer cell lines tested and in three of five breast tumor samples. The breast cancer cell lines showed variation in the size of the expressed ER-beta protein. The longest form detected was consistent with the 530-amino acid, full-length ER-beta sequence. Shorter ER-beta isoforms were detected in the ER-alpha-negative MDA-MB-231 and MDA-MB-435 breast cancer cell lines, likely corresponding to previously described COOH-terminal RNA variant isoforms.

Blotting, Western↗
PubMed1999

Identification of a bile acid-responsive element in the human ileal bile acid-binding protein gene. Involvement of the farnesoid X receptor/9-cis-retinoic acid receptor heterodimer.

Intestinal bile acid-binding protein (I-BABP) is a cytosolic protein that binds bile acids (BAs) with a high affinity. In the small intestine, its expression is restricted to the ileum where it is involved in the enterohepatic circulation of BAs. Using the human enterocyte-like Caco-2 cell line, we have recently shown that BAs increased I-BABP gene expression. To determine whether this regulation occurs in vivo, the effect of BA depletion or supplementation was studied in mice. A dramatic drop in I-BABP mRNA levels was observed in mice treated with the BA-binding resin cholestyramine, whereas an increase was found in animals fed with taurocholic acid. BAs are physiological ligands for the nuclear farnesoid X receptor (FXR). Both FXR and I-BABP are co-expressed along the small intestine and in Caco-2 cells. To determine the role of FXR in the regulation of I-BABP expression, the promoter of the human I-BABP gene was cloned. In Caco-2 cells, cotransfection of FXR and RXRalpha is required to obtain the full transactivation of the I-BABP promoter by BAs. Deletion and mutation analyses demonstrate that the FXR/RXRalpha heterodimer activates transcription through an inverted repeat bile acid responsive element located in position -160/-148 of the human I-BABP promoter. In conclusion, we show that FXR is a physiological BA sensor that is likely to play an essential role in BA homeostasis through the regulation of genes involved in their enterohepatic circulation.

Animals↗
PubMed1999

Interleukin-4-dependent production of PPAR-gamma ligands in macrophages by 12/15-lipoxygenase.

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-dependent nuclear receptor that has been implicated in the modulation of critical aspects of development and homeostasis, including adipocyte differentiation, glucose metabolism and macrophage development and function. PPAR-gamma is activated by a range of synthetic and naturally occurring substances, including antidiabetic thiazolidinediones, polyunsaturated fatty acids, 15-deoxy-delta prostaglandin J2 and components of oxidized low-density lipoprotein, such as 13-hydroxyoctadecadienoic acid (13-HODE) and 15-hydroxyeicosatetraenoic acid (15-HETE). However, the identities of endogenous ligands for PPAR-gamma and their means of production in vivo have not been established. In monocytes and macrophages, 13-HODE and 15-HETE can be generated from linoleic and arachidonic acids, respectively, by a 12/15-lipoxygenase that is upregulated by the TH2-derived cytokine interleukin-4. Here we show that interleukin-4 also induces the expression of PPAR-gamma and provide evidence that the coordinate induction of PPAR-gamma and 12/15-lipoxygenase mediates interleukin-4-dependent transcription of the CD36 gene in macrophages. These findings reveal a physiological role of 12/15-lipoxygenase in the generation of endogenous ligands for PPAR-gamma, and suggest a paradigm for the regulation of nuclear receptor function by cytokines.

Animals↗
PubMed1999

A peroxisome proliferator-activated receptor gamma ligand inhibits adipocyte differentiation.

The peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate glucose and lipid homeostasis. The PPARgamma subtype plays a central role in the regulation of adipogenesis and is the molecular target for the 2, 4-thiazolidinedione class of antidiabetic drugs. Structural studies have revealed that agonist ligands activate the PPARs through direct interactions with the C-terminal region of the ligand-binding domain, which includes the activation function 2 helix. GW0072 was identified as a high-affinity PPARgamma ligand that was a weak partial agonist of PPARgamma transactivation. X-ray crystallography revealed that GW0072 occupied the ligand-binding pocket by using different epitopes than the known PPAR agonists and did not interact with the activation function 2 helix. In cell culture, GW0072 was a potent antagonist of adipocyte differentiation. These results establish an approach to the design of PPAR ligands with modified biological activities.

Adipocytes↗
PubMed1999

Bile acids: natural ligands for an orphan nuclear receptor.

Bile acids regulate the transcription of genes that control cholesterol homeostasis through molecular mechanisms that are poorly understood. Physiological concentrations of free and conjugated chenodeoxycholic acid, lithocholic acid, and deoxycholic acid activated the farnesoid X receptor (FXR; NR1H4), an orphan nuclear receptor. As ligands, these bile acids and their conjugates modulated interaction of FXR with a peptide derived from steroid receptor coactivator 1. These results provide evidence for a nuclear bile acid signaling pathway that may regulate cholesterol homeostasis.

Animals↗
PubMed1999

Orphan nuclear receptors: shifting endocrinology into reverse.

Steroid and thyroid hormones and vitamin A metabolites (retinoids) regulate the expression of complex gene programs by binding to members of the nuclear receptor family of ligand-activated transcription factors. The nuclear receptor family also includes many "orphan" members that currently lack known ligands but that represent candidate receptors for new hormones. Recently, natural and synthetic ligands have been identified for several orphan receptors and used to dissect their biological roles. This "reverse endocrinology" strategy has resulted in the discovery of unanticipated nuclear signaling pathways for retinoids, fatty acids, eicosanoids, and steroids with important physiological and pharmacological ramifications.

Animals↗
PubMed1999

Molecular recognition of fatty acids by peroxisome proliferator-activated receptors.

The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors for fatty acids (FAs) that regulate glucose and lipid homeostasis. We report the crystal structure of the PPAR delta ligand-binding domain (LBD) bound to either the FA eicosapentaenoic acid (EPA) or the synthetic fibrate GW2433. The carboxylic acids of EPA and GW2433 interact directly with the activation function 2 (AF-2) helix. The hydrophobic tail of EPA adopts two distinct conformations within the large hydrophobic cavity. GW2433 occupies essentially the same space as EPA bound in both conformations. These structures provide molecular insight into the propensity for PPARs to interact with a variety of synthetic and natural compounds, including FAs that vary in both chain length and degree of saturation.

Animals↗
PubMed1999

A novel N-aryl tyrosine activator of peroxisome proliferator-activated receptor-gamma reverses the diabetic phenotype of the Zucker diabetic fatty rat.

The discovery that peroxisome proliferator-activated receptor (PPAR)-gamma was the molecular target of the thiazolidinedione class of antidiabetic agents suggested a key role for PPAR-gamma in the regulation of carbohydrate and lipid metabolism. Through the use of high-throughput biochemical assays, GW1929, a novel N-aryl tyrosine activator of human PPAR-gamma, was identified. Chronic oral administration of GW1929 or troglitazone to Zucker diabetic fatty (ZDF) rats resulted in dose-dependent decreases in daily glucose, free fatty acid, and triglyceride exposure compared with pretreatment values, as well as significant decreases in glycosylated hemoglobin. Whole body insulin sensitivity, as determined by the euglycemic-hyperinsulinemic clamp technique, was significantly increased in treated animals. Comparison of the magnitude of glucose lowering as a function of serum drug concentrations showed that GW1929 was 2 orders of magnitude more potent than troglitazone in vivo. These data were consistent with the relative in vitro potencies of GW1929 and troglitazone. Isolated perfused pancreas studies performed at the end of the study confirmed that pancreata from vehicle-treated rats showed no increase in insulin secretion in response to a step change in glucose from 3 to 10 mmol/l. In contrast, pancreata from animals treated with GW1929 showed a first- and second-phase insulin secretion pattern. Consistent with the functional data from the perfusion experiments, animals treated with the PPAR-gamma agonist had more normal islet architecture with preserved insulin staining compared with vehicle-treated ZDF rats. This is the first demonstration of in vivo efficacy of a novel nonthiazolidinedione identified as a high-affinity ligand for human PPAR-gamma. The increased potency of GW1929 compared with troglitazone both in vitro and in vivo may translate into improved clinical efficacy when used as monotherapy in type 2 diabetic patients. In addition, the significant improvement in daily meal tolerance may impact cardiovascular risk factor management in these patients.

Animals↗
PubMed1999

The PPARs and PXRs: nuclear xenobiotic receptors that define novel hormone signaling pathways.

Traditional pharmacologic approaches had identified several classes of xenobiotics that elicited characteristic biological effects in vivo but that lacked defined molecular mechanisms of action. Among these xenobiotics were the peroxisome proliferators, the thiazolidinediones (TZDs), and a set of compounds that induced the expression of cytochrome P450 (CYP) 3A genes and promoted the metabolism of other xenobiotics. All three classes of xenobiotics are now known to exert their actions through activation of orphan members of the nuclear receptor family of ligand-activated transcription factors. Peroxisome proliferators are a diverse group of amphipathic acids that include the fibrate class of triglyceride- and cholesterol-lowering drugs. TZDs sensitize tissues such as skeletal muscle, liver, and adipose to the actions of insulin and lower glucose and lipid levels in type 2 diabetics. The peroxisome proliferators and TZDs are now known to mediate their effects through the peroxisome proliferator-activated receptors (PPARs) alpha and gamma, respectively. The activities of these compounds established the PPARs as key regulators of glucose and lipid homeostasis. We and others have recently shown that various naturally occurring fatty acids and eicosanoids serve as PPAR ligands, suggesting a novel regulatory mechanism whereby dietary lipids and their metabolites can regulate gene transcription and impact overall energy balance. The third class of xenobiotics we have studied induces the expression of CYP3A genes, mono-oxygenases responsible for the metabolism of natural steroids as well as a variety of xenobiotics, including > 60% of all drugs. We have recently shown that compounds that induce CYP3A gene expression do so through activation of novel orphan receptors, termed the pregnane X receptors (PXRs). Many of the PXR activators are widely used drugs such as dexamethasone, lovastatin, and rifampicin, whose induction of CYP3A levels causes them to promote the metabolism of other drugs, often with adverse consequences. Thus, the finding that the PXRs regulate CYP3A gene expression provides a basis for the efficient identification and elimination of candidate drugs that will interact with other medicines. Searches for natural ligands have revealed that the PXRs are activated by C21 steroids, including pregnenolone and progesterone, suggesting that these orphan receptors define a novel steroid hormone signaling pathway. In sum, work from our laboratories and others has demonstrated that peroxisome proliferators, TZDs, and inducers of CYP3A gene expression exert their biological actions through the activation of orphan nuclear receptors. These findings provide insights into new endocrine signaling pathways and have important implications for the discovery of safer and more efficacious drugs for the treatment of a variety of diseases.

Animals↗
PubMed1998

N-(2-Benzoylphenyl)-L-tyrosine PPARgamma agonists. 1. Discovery of a novel series of potent antihyperglycemic and antihyperlipidemic agents.

We have identified a novel series of antidiabetic N-(2-benzoylphenyl)-L-tyrosine derivatives which are potent, selective PPARgamma agonists. Through the use of in vitro PPARgamma binding and functional assays (2S)-3-(4-(benzyloxy)phenyl)-2-((1-methyl-3-oxo-3-phenylpropenyl)+ ++amin o)propionic acid (2) was identified as a structurally novel PPARgamma agonist. Structure-activity relationships identified the 2-aminobenzophenone moiety as a suitable isostere for the chemically labile enaminone moiety in compound 2, affording 2-((2-benzoylphenyl)amino)-3-(4-(benzyloxy)phenyl)propionic acid (9). Replacement of the benzyl group in 9 with substituents known to confer in vivo potency in the thiazolidinedione (TZD) class of antidiabetic agents provided a dramatic increase in the in vitro functional potency and affinity at PPARgamma, affording a series of potent and selective PPARgamma agonists exemplified by (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(methylpyridin-2-ylamino+ ++)ethoxy ]phenyl¿propionic acid (18), 3-¿4-[2-(benzoxazol-2-ylmethylamino)ethoxy]phenyl¿-(2S)-((2- benzoylph enyl)amino)propanoic acid (19), and (2S)-((2-benzoylphenyl)amino)-3-¿4-[2-(5-methyl-2-phenyloxazol-4-y l)e thoxy]phenyl¿propanoic acid (20). Compounds 18 and 20 show potent antihyperglycemic and antihyperlipidemic activity when given orally in two rodent models of type 2 diabetes. In addition, these analogues are readily prepared in chiral nonracemic fashion from L-tyrosine and do not show a propensity to undergo racemization in vitro. The increased potency of these PPARgamma agonists relative to troglitazone may translate into superior clinical efficacy for the treatment of type 2 diabetes.

Administration, Oral↗
PubMed1998

Ligand binding and co-activator assembly of the peroxisome proliferator-activated receptor-gamma.

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a ligand-dependent transcription factor that is important in adipocyte differentiation and glucose homeostasis and which depends on interactions with co-activators, including steroid receptor co-activating factor-1 (SRC-1). Here we present the X-ray crystal structure of the human apo-PPAR-gamma ligand-binding domain (LBD), at 2.2 A resolution; this structure reveals a large binding pocket, which may explain the diversity of ligands for PPAR-gamma. We also describe the ternary complex containing the PPAR-gamma LBD, the antidiabetic ligand rosiglitazone (BRL49653), and 88 amino acids of human SRC-1 at 2.3 A resolution. Glutamate and lysine residues that are highly conserved in LBDs of nuclear receptors form a 'charge clamp' that contacts backbone atoms of the LXXLL helices of SRC-1. These results, together with the observation that two consecutive LXXLL motifs of SRC-1 make identical contacts with both subunits of a PPAR-gamma homodimer, suggest a general mechanism for the assembly of nuclear receptors with co-activators.

Amino Acid Sequence↗
PubMed1998

The human orphan nuclear receptor PXR is activated by compounds that regulate CYP3A4 gene expression and cause drug interactions.

The cytochrome P-450 monooxygenase 3A4 (CYP3A4) is responsible for the oxidative metabolism of a wide variety of xenobiotics including an estimated 60% of all clinically used drugs. Although expression of the CYP3A4 gene is known to be induced in response to a variety of compounds, the mechanism underlying this induction, which represents a basis for drug interactions in patients, has remained unclear. We report the identification of a human (h) orphan nuclear receptor, termed the pregnane X receptor (PXR), that binds to a response element in the CYP3A4 promoter and is activated by a range of drugs known to induce CYP3A4 expression. Comparison of hPXR with the recently cloned mouse PXR reveals marked differences in their activation by certain drugs, which may account in part for the species-specific effects of compounds on CYP3A gene expression. These findings provide a molecular explanation for the ability of disparate chemicals to induce CYP3A4 levels and, furthermore, provide a basis for developing in vitro assays to aid in predicting whether drugs will interact in humans.

Amino Acid Sequence↗
PubMed1998

Cloning and characterization of human estrogen receptor beta isoforms.

Multiple transcripts which arise from the human estrogen receptor beta (ER beta) gene have been characterized. Three full length isoforms of the hER beta gene, designated hER beta 1-3, were identified in a testis cDNA library. An additional two isoforms, designated hER beta 4 and hER beta 5, were identified by PCR amplification from testis cDNA and from the MDA-MB 435 cell line. hER beta 1 corresponds to the previously described hER beta. All five isoforms diverge at a common position within the predicted helix 10 of the ligand binding domain of hER beta, with nucleotide sequences consistent with differential exon usage. The hER beta isoform mRNAs displayed a differential pattern of expression in human tissues and in tumor cell lines when analyzed by RT-PCR. Further characterization of the three full length isoforms, hER beta 1-3, by in vitro band shift studies indicated that the isoforms were able to form DNA-binding homodimers and heterodimers with each other and with the ER alpha subtype.

Alternative Splicing↗