Biomedical subjects

Paul Webb

Publications and source records attributed to Paul Webb.

42 records · Page 3Linked to original sources

PubMed2002

p300 Modulates the BRCA1 inhibition of estrogen receptor activity.

We previously reported that expression of the breast cancer susceptibility gene BRCA1 strongly inhibits the transcriptional activity of the estrogen receptor (ER-alpha) in human breast and prostate cancer cell lines but only weakly inhibits ER-alpha activity in cervical cancer cells (S. Fan et al., Science (Wash. DC), 284: 1354-1356, 1999). We now report that the ability of BRCA1 to repress ER-alpha activity correlates with its ability to induce down-regulation of the cellular levels of the transcriptional coactivator p300 in breast and prostate, but not in cervical cancer cells. On the other hand, BRCA1 failed to alter the expression of the CREB binding protein (CBP), the structural and functional homologue of p300, in any of these cell types. Ectopic expression of either p300 or CBP "rescued" (i.e., reversed) the BRCA1 inhibition of ER-alpha activity, whereas two other nuclear receptor coactivators, the p300/CBP-associated factor (PCAF) and the glucocorticoid receptor-interacting protein-1 (GRIP1), failed to rescue the ER-alpha activity. The rescue function mapped to the cysteine-histidine rich domain CH3, a region of p300/CBP that we found to interact directly with the conserved COOH-terminal activation domain (AF-2) of ER-alpha. p300 and ER-alpha were also found to interact in vivo and to colocalize within the nucleus in breast cancer cells. These findings suggest that the cofactors p300 and CBP modulate the ability of the BRCA1 protein to inhibit ER-alpha signaling. They further suggest that the BRCA1 inhibition of ER-alpha activity may be attributable, at least in part, to the down-regulation of p300.

BRCA1 Protein↗

PubMed2002

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.

Animals↗

PubMed2002

Structure-based design and synthesis of a thyroid hormone receptor (TR) antagonist.

Antagonists have been developed for several nuclear receptors but not for others, including TRs. TR antagonists may have significant clinical utility for treating hormone excess states and other conditions. A structure derived "extension hypothesis" was applied to synthesize a TR antagonist. The principal design feature was to attach an extension group to a TR agonist whose structure would perturb formation of the TR coactivator-binding surface. The compound, 3,5-dibromo-4-(3',5'-diisopropyl-4'-hydroxyphenoxy)benzoic acid, has no (TRalpha) or very weak partial (TRbeta) TR agonist activity and blocks TR binding of T3, formation of the coactivator-binding surface, and both a positive T3 response on a thyroid hormone response element and a negative T3 response on the TSHbeta promoter in cultured cells. The results suggest that 3,5-dibromo-4-(3',5'-diisopropyl-4'-hydroxyphenoxy)benzoic acid is a TR antagonist for thyroid hormone response element-mediated responses, this approach can be used more generally to generate nuclear receptor antagonists, and this compound or analogues may have medical and research utility.

Alkaline Phosphatase↗

PubMed2002

Skin microvascular flow during hypobaric exposure with and without a mechanical counter-pressure space suit glove.

INTRODUCTION: Current space suits are rigid, gas-pressurized shells that protect astronauts from the vacuum of space. A tight elastic garment or mechanical-counter-pressure (MCP) suit generates pressure by compression and may have several advantages over current space suit technology. In this study, we investigated local microcirculatory effects produced with and without a prototype MCP glove. METHODS: The right hand of eight normal volunteers was studied at normal ambient pressure and during exposure to -50, -100 and -150 mm Hg with and without the MCP glove. Measurements included the pressure against the hand, skin microvascular flow, temperature on the dorsum of the hand, and middle finger girth. RESULTS: Without the glove, skin microvascular flow and finger girth significantly increased with negative pressure, and the skin temperature decreased compared with the control condition. The MCP glove generated approximately 200 mm Hg at the skin surface; all measured values remained at control levels during exposure to negative pressure. DISCUSSION: Without the glove, skin microvascular flow and finger girth increased with negative pressure, probably due to a blood shift toward the hand. The elastic compression of the material of the MCP glove generated pressure on the hand similar to that in current gas-pressurized space suit gloves. The MCP glove prevented the apparent blood shift and thus maintained baseline values of the measured variables despite exposure of the hand to negative pressure.

Adult↗

PubMed2002

Compression under a mechanical counter pressure space suit glove.

BACKGROUND: Current gas-pressurized space suits are bulky stiff shells severely limiting astronaut function and capability. A mechanical counter pressure (MCP) space suit in the form of a tight elastic garment could dramatically improve extravehicular activity (EVA) dexterity, but also be advantageous in safety, cost, mass and volume. The purpose of this study was to verify that a prototype MCP glove exerts the design compression of 200 mmHg, a pressure similar to the current NASA EVA suit. METHODS: Seven male subjects donned a pressure measurement array and MCP glove on the right hand, which was placed into a partial vacuum chamber. Average compression was recorded on the palm, the bottom of the middle finger, the top of the middle finger and the dorsum of the hand at pressures of 760 (ambient), 660 and 580 mmHg. The vacuum chamber was used to simulate the pressure difference between the low breathing pressure of the current NASA space suits (approximately 200 mmHg) and an unprotected hand in space. RESULTS: At ambient conditions, the MCP glove compressed the dorsum of the hand at 203.5 +/- 22.7 mmHg, the bottom of the middle finger at 179.4 +/- 16.0 mmHg, and the top of the middle finger at 183.8 +/- 22.6 mmHg. The palm compression was significantly lower (59.6 +/- 18.8 mmHg, p<0.001). There was no significant change in glove compression with the chamber pressure reductions. CONCLUSIONS: The MCP glove compressed the dorsum of the hand and middle finger at the design pressure.

Adult↗

PubMedDate not supplied

Selective activation of thyroid hormone signaling pathways by GC-1: a new approach to controlling cholesterol and body weight.

The current report describes progress in development of a selective thyroid hormone receptor modulator, GC-1. This compound binds selectively to the beta-isoform of the thyroid hormone receptor, and its uptake into the heart is relatively low. Studies in rats, mice and monkeys show that GC-1 lowers cholesterol with 600- to 1400-fold more potency and approximately two- to threefold more efficacy than atorvastatin, a compound that blocks HMG-CoA reductase. GC-1 also decreases plasma levels of triglyceride and lipoprotein (a), and induces loss of fat. These effects can be observed under conditions where there is either no or minimal effect on heart rate, and no detectable loss of muscle. Although more study is required, compounds of this class deserve further investigation for treating lipid disorders and obesity.

Acetates↗