Biomedical subjects

Y Huang

Publications and source records attributed to Y Huang.

At least 505 records · Page 28Linked to original sources

PubMed1999

Jasmine green tea epicatechins are hypolipidemic in hamsters (Mesocricetus auratus) fed a high fat diet.

These studies were designed to test the hypolipidemic activity of green tea epicatechins (GTE) isolated from jasmine green tea. In Experiment 1, three groups of hamsters were given a semisynthetic diet containing 200 g lard/kg and 1 g cholesterol/kg for 4 wk. The control group received distilled water, and the other two groups received either 15 g/L green tea water extract (GTWE) or 5.0 g/L GTE solution. Both the GTWE and GTE groups had lower concentrations of serum total cholesterol (TC) and triacylglycerols (TG) than the controls (P < 0.05). In Experiment 2, four groups of hamsters received tap water as the drinking fluid, but they were given the same high fat and cholesterol diet supplemented with 0 (control), 1.1, 3.4 or 5.7 g GTE/kg diet. The hypolipidemic effect of jasmine GTE was dose dependent. In Experiment 3, the time-course of changes in serum TC and TG was monitored in hamsters given the high fat diet supplemented with 5.7 g GTE/kg in comparison with that of controls. The hypolipidemic effects of dietary GTE were evident after feeding for 2 wk. Dietary supplementation of GTE did not affect liver fatty acid synthase. However, GTE-supplemented hamsters had higher fecal excretions of total fatty acids, neutral sterols and acidic sterols compared with the control group. In Experiment 4, hamsters were fed nonpurified diet; the control group drank distilled water, and the GTE group drank distilled water containing 5.0 g GTE/L. No differences in activities of 3-hydroxy-3-methyl glutaryl coenzyme A reductase and intestinal acyl CoA:cholesterol acyltransferase were observed. This study suggests that the hypolipidemic activity of GTE is not due to inhibition of synthesis of cholesterol or fatty acid but is most likely mediated by its influence on absorption of dietary fat and cholesterol.

Animals↗

PubMed1999

Potassium channel activity recorded from the apical membrane of freshly isolated epithelial cells in rat caudal epididymis.

K+ channels were recorded in excised, inside-out patches from the apical membrane of the freshly isolated tubule of the caudal portion of the rat epididymis. With asymmetric K+ concentrations in bath and pipette (140 mM K+in/6 mM K+out), the channels had a slope conductance of 54.2 pS at 0 mV. The relative permeability of K+ over Na+ was about 171 to 1. The channels were activated by intracellular Ca2+ and by membrane depolarization. These channels belong to a class defined as "intermediate-conductance Ca2+-activated K+ channel. " External tetraethylammonium ions (TEA+) caused a flickery block of the channel with reduction in single-channel current amplitude measured at a range of holding membrane potentials (-40 to 60 mV). Activity of the K+ channels was inhibited by intracellular ATP (KD =1.188 mM). The channel activity was detected only occasionally in patches from the apical membrane (about 1 in 17 patches containing active channels). The presence of the intermediate-conductance Ca2+-activated K+ channels indicates that they could provide a route for K+ secretion in a Ca2+-dependent process responsible for a high luminal K+ concentration found in the epididymal duct of the rat.

Adenosine Triphosphate↗

PubMed1999

Gastrointestinal symptoms and use of medical care associated with child day care and health care plan among preschool children.

OBJECTIVES: This study examined whether out-of-home day care increases the risk of gastrointestinal symptoms for children <6 years of age and whether there is an association between gastrointestinal symptoms and medical care utilization. METHODS: The study population comprised members of 2 health plans residing in 2 South Carolina counties: 417 families from an health maintenance organization (HMO) plan; and 643 families from a Medicaid plan. Participants were followed for 18 months by either bimonthly telephone interviews or personal interviews. The survey/interview collected familial, personal, day-care and disease-related information and medical care utilization. The analyses controlled for both family characteristics and the type of health care plan. RESULTS: Children attending out-of-home day care had higher incidence rates for most gastrointestinal symptoms studied than did children staying at home (2.51 vs. 1.61 episodes of mild gastrointestinal symptoms and 1.63 vs. 1.08 episodes of moderate gastrointestinal symptoms for the HMO group; 1.72 vs. 1.28 episodes of moderate gastrointestinal symptoms for the Medicaid group). Nearly one-fourth of the annual physician visits by children younger than 6 years were attributed to gastrointestinal symptoms, and more than one-fourth of the children with gastrointestinal symptoms were prescribed antibiotics. When displaying gastrointestinal symptoms, children in the Medicaid group were significantly more likely to visit a doctor and receive antibiotics than those in the HMO group. CONCLUSIONS: Although the type of health plan has negligible influence on the frequency of reported gastrointestinal symptoms, it exerts a strong influence on medical care utilization.

Child Care↗

PubMed1999

Apolipoprotein E: from atherosclerosis to Alzheimer's disease and beyond.

Apolipoprotein E is a key regulator of plasma lipid levels. Our appreciation of its role continues to expand as additional aspects of its function are discovered. Apolipoprotein E affects the levels of all lipoproteins, either directly or indirectly by modulating their receptor-mediated clearance or lipolytic processing and the production of hepatic very low density lipoproteins. Furthermore, it plays a critical role in neurobiology. The apolipoprotein E4 allele is the major susceptibility gene related to the occurrence and early age of onset of Alzheimer's disease. It is probable that one of the major functions of apolipoprotein E in the central nervous system is to mediate neuronal repair, remodeling, and protection, with apolipoprotein E4 being less effective than the E3 and E2 alleles. The isoform-specific effects of apolipoprotein E are currently being unraveled through detailed structure and function studies of this protein.

Alzheimer Disease↗

PubMed1999

Crystallization and preliminary x-ray diffraction studies of guanidinoacetate methyltransferase from rat liver.

Guanidinoacetate methyltransferase is the enzyme which catalyzes the last step of creatine biosynthesis. The enzyme is found ubiquitously and in abundance in the livers of all vertebrates. Recombinant rat-liver guanidinoacetate methyltransferase has been crystallized with guanidinoacetate and S-adenosylhomocysteine. The crystals belong to the monoclinic space group P2(1), with unit-cell parameters a = 54.8, b = 162.5, c = 56.1 A, beta = 96.8 (1) degrees at 93 K, and typically diffract beyond 2.8 A.

Animals↗

PubMed1999

A new strategy for controlling the level of activation in artificially stimulated muscle.

Distributed stimulation of slow skeletal muscle has previously been used to produce smooth tetanic contractions at low stimulus rates. This involved distributed or interleaved stimulation of portions of the muscle with near equal tension contributions. Extending this to fast and mixed muscle encounters difficulties in getting and maintaining equal twitch responses for the portions. This need has now been circumvented by using distributed stimulation with unequal interpulse intervals. Described here is a microprocessor-based eight channel distributed muscle stimulator that can adjust stimulation timing to produce an optimally smooth tension over a range of stimulus rates even when the portions are unequal. This design is based on modeling results. Distributed stimulation experiments performed on skeletal muscle show that this method can be used to achieve smooth tension at physiological stimulus rates, which should reduce fatigue. This has important implications in functional neuromuscular stimulation (FNS) as well as in enabling experiments to be conducted to characterize the biomechanical behavior of partially activated fast and mixed muscle.

Animals↗

PubMed1999

The two-sample problem with induced dependent censorship.

Induced dependent censorship is a general phenomenon in health service evaluation studies in which a measure such as quality-adjusted survival time or lifetime medical cost is of interest. We investigate the two-sample problem and propose two classes of nonparametric tests. Based on consistent estimation of the survival function for each sample, the two classes of test statistics examine the cumulative weighted difference in hazard functions and in survival functions. We derive a unified asymptotic null distribution theory and inference procedure. The tests are applied to trial V of the International Breast Cancer Study Group and show that long duration chemotherapy significantly improves time without symptoms of disease and toxicity of treatment as compared with the short duration treatment. Simulation studies demonstrate that the proposed tests, with a wide range of weight choices, perform well under moderate sample sizes.

Biometry↗

PubMed1999

Identification of calcium-activated potassium channels in cultured equine sweat gland epithelial cells.

The patch-clamp recording technique was used to examine the properties of the K+ channels in cultured equine sweat gland epithelial cells. With symmetric K+ solutions (140 mM), a single population of K+ channels was identified with a slope conductance of 187 pS and a reversal potential of around 0 mV. The channel was selective for K+ over Na+. Channel activity was increased by membrane depolarization. A 10-fold increase in [Ca2+]i produced an approximate 60 mV negative shift in the open state probability (Popen)-voltage curve. Externally applied tetraethylammonium ions (TEA+) caused a rapid and flickery block of the channel and reduced the unitary current amplitude. TEA+ bound to the blocking site with stoichiometry of 1:1 and with a dissociation constant (Kd) of 186 +/- 27 microM at +40 mV. A weak voltage dependence of Kd was observed. Iberiotoxin (100 nM) reduced Popen but had no effect on single-channel conductance. Neither glibenclamide (10 microM) nor intracellular adenosine 5'-triphosphate (ATP, 1 mM) altered channel activity. In addition, ATP, when applied extracellularly, transiently activated the channel by increasing Popen. Channel activity was low around the resting membrane potential in the intact epithelia, indicating that these channels might not contribute to the resting K+ conductance. However, the channel could be activated in a regulated manner. The K+ channels may play a role in transepithelial fluid secretion in sweat gland.

Adenosine Triphosphate↗

PubMed1999

Protective immunity against Streptococcus mutans infection in mice after intranasal immunization with the glucan-binding region of S. mutans glucosyltransferase.

Here we present the construction and characterization of a chimeric vaccine protein combining the glucan-binding domain (GLU) of the gtfB-encoded water-insoluble glucan-synthesizing glucosyltransferase enzyme (GTF-I) from Streptococcus mutans and thioredoxin from Escherichia coli, which increases the solubility of coexpressed recombinant proteins and stimulates proliferation of murine T cells. The protective potential of intranasal (i.n.) immunization with this chimeric immunogen was compared to that of the GLU polypeptide alone in a mouse infection model. Both immunogens were able to induce statistically significant mucosal (salivary and vaginal) and serum responses (P < 0.01) which were sustained to the end of the study (experimental day 100). Following infection with S. mutans, sham-immunized mice maintained high levels of this cariogenic organism ( approximately 60% of the total oral streptococci) for at least 5 weeks. In contrast, animals immunized with the thioredoxin-GLU chimeric protein (Thio-GLU) showed significant reduction (>85%) in S. mutans colonization after 3 weeks (P < 0.05). The animals immunized with GLU alone required 5 weeks to demonstrate significant reduction (>50%) of S. mutans infection (P < 0.05). Evaluation of dental caries activity at the end of the study showed that mice immunized with either Thio-GLU or GLU had significantly fewer carious lesions in the buccal enamel or dentinal surfaces than the sham-immunized animals (P < 0.01). The protective effects against S. mutans colonization and caries activity following i.n. immunization with GLU or Thio-GLU are attributed to the induced salivary immunoglobulin A (IgA) anti-GLU responses. Although in general Thio-GLU was not significantly better than GLU alone in stimulating salivary IgA responses and in protection against dental caries, the finding that the GLU polypeptide alone, in the absence of any immunoenhancing agents, is protective against disease offers a promising and safe strategy for the development of a vaccine against caries.

Administration, Intranasal↗

PubMed1999

A polymorphism in the regulatory region of the CC-chemokine receptor 5 gene influences perinatal transmission of human immunodeficiency virus type 1 to African-American infants.

There are natural mutations in the coding and noncoding regions of the human immunodeficiency virus type 1 (HIV-1) CC-chemokine coreceptor 5 (CCR5) and in the related CCR2 protein (the CCR2-64I mutation). Individuals homozygous for the CCR5-Delta32 allele, which prevents CCR5 expression, strongly resist HIV-1 infection. Several genetic polymorphisms have been identified within the CCR5 5' regulatory region, some of which influence the rate of disease progression in adult AIDS study cohorts. We genotyped 1,442 infants (1,235 uninfected and 207 HIV-1 infected) for five CCR5 and CCR2 polymorphisms: CCR5-59353-T/C, CCR5-59356-C/T CCR5-59402-A/G, CCR5-Delta32, and CCR2-64I. The clinical significance of each genotype was assessed by measuring whether it influenced the rate of perinatal HIV-1 transmission among 667 AZT-untreated mother-infant pairs (554 uninfected and 113 HIV-1 infected). We found that the mutant CCR5-59356-T allele is relatively common in African-Americans (20.6% allele frequency among 552 infants) and rare in Caucasians and Hispanics (3.4 and 5.6% of 174 and 458 infants, respectively; P < 0.001). There were 38 infants homozygous for CCR5-59356-T, of whom 35 were African-Americans. Among the African-American infants in the AZT-untreated group, there was a highly significant increase in HIV-1 transmission to infants with two mutant CCR5-59356-T alleles (47.6% of 21), compared to those with no or one mutant allele (13.4 to 14.1% of 187 and 71, respectively; P < 0.001). The increased relative risk was 5.9 (95% confidence interval, 2.3 to 15.3; P < 0.001). The frequency of the CCR5-59356-T mutation varies between population groups in the United States, a low frequency occurring in Caucasians and a higher frequency occurring in African-Americans. Homozygosity for CCR5-59356-T is strongly associated with an increased rate of perinatal HIV-1 transmission.

5' Untranslated Regions↗

PubMed1999

The role of Pr55(gag) in the annealing of tRNA3Lys to human immunodeficiency virus type 1 genomic RNA.

During human immunodeficiency virus type 1 (HIV-1) assembly, the primer tRNA for the reverse transcriptase-catalyzed synthesis of minus-strand strong-stop cDNA, tRNA3Lys, is selectively packaged into the virus and annealed onto the primer binding site on the RNA genome. Annealing of tRNA3Lys in HIV-1 is independent of polyprotein processing and is facilitated in vitro by p7 nucleocapsid (NCp7). We have previously shown that mutations in clusters of basic amino acids flanking the first Cys-His box in NC sequence inhibit annealing of tRNA3Lys in vivo by 70 to 80%. In this report, we have investigated whether these NC mutations act through Pr55(gag) or Pr160(gag-pol). In vivo placement of tRNA3Lys is measured with total viral RNA as the source of primer tRNA-template in an in vitro reverse transcription assay. Cotransfection of COS cells with a plasmid coding for either mutant Pr55(gag) or mutant Pr160(gag-pol), and with a plasmid containing HIV-1 proviral DNA, shows that only the NC mutations in Pr55(gag) inhibit tRNA3Lys placement. The NC mutations in Pr55(gag) reduce viral infectivity by 95% and are trans-dominant-negative, i.e., they inhibit genomic placement of tRNA3Lys even in the presence of wild-type Pr55(gag). This dominant phenotype may indicate that the mutant Pr55(gag) is disrupting an ordered Pr55(gag) structure responsible for the annealing of tRNA3Lys to genomic RNA.

Animals↗

PubMed1999

Role for caspase-mediated cleavage of Rad51 in induction of apoptosis by DNA damage.

We report here that the Rad51 recombinase is cleaved in mammalian cells during the induction of apoptosis by ionizing radiation (IR) exposure. The results demonstrate that IR induces Rad51 cleavage by a caspase-dependent mechanism. Further support for involvement of caspases is provided by the finding that IR-induced proteolysis of Rad51 is inhibited by Ac-DEVD-CHO. In vitro studies show that Rad51 is cleaved by caspase 3 at a DVLD/N site. Stable expression of a Rad51 mutant in which the aspartic acid residues were mutated to alanines (AVLA/N) confirmed that the DVLD/N site is responsible for the cleavage of Rad51 in IR-induced apoptosis. The functional significance of Rad51 proteolysis is supported by the finding that, unlike intact Rad51, the N- and C-terminal cleavage products fail to exhibit recombinase activity. In cells, overexpression of the Rad51(D-A) mutant had no effect on activation of caspase 3 but did abrogate in part the apoptotic response to IR exposure. We conclude that proteolytic inactivation of Rad51 by a caspase-mediated mechanism contributes to the cell death response induced by DNA damage.

Animals↗

PubMed1999

Anaphylactic response to parasite antigens: IgE and IgG1 independently induce death in Trichinella-infected mice.

The response of animals infected with different Trichinella species (T. spiralis, T. britovi, T. pseudospiralis) to antigens of different Trichinella species was evaluated in outbred mice (CD1) and inbred mice (BALB/c, C3H, SJL, C57BL/6). In mice deficient for IgE or IgG1, T. spiralis only was used. In homologous conditions (i. e., same Trichinella species for antigens and infectious agent) mortality was very high (up to 100% in SJL and C57BL/6). The anaphylactic response in heterologous conditions was much lower and death was observed only in C57BL/6 and SJL mice. Experiments with deficient mice have shown that both specific IgE and IgG1 independently induce a fatal anaphylactic response.

Anaphylaxis↗

PubMed1999

Oxidized LDL stimulates matrix metalloproteinase-1 expression in human vascular endothelial cells.

It has been well documented that acute myocardial infarction is triggered by disruption of atherosclerotic plaques. Immunocytochemistry studies have shown that matrix metalloproteinase-1 (MMP-1) is specifically expressed by cells present in atherosclerotic plaques, including luminal and neovascular endothelial cells. Since MMP-1 degrades type I collagen, a major type of collagen in atherosclerotic lesions, it is likely that MMP-1 is involved in promoting destabilization of plaques. To date, however, the stimulatory factors that induce MMP-1 expression in endothelial cells have not been well defined. In the present study, we found that oxidized low density lipoprotein (LDL) stimulated MMP-1 release from both human umbilical vein and aortic endothelial cells. We also found that oxidized LDL markedly stimulated MMP-1 expression in these cells and that the degree of LDL oxidation was positively correlated with the level of MMP-1 mRNA expression. Furthermore, our data showed that stimulated MMP-1 secretion was inhibited by actinomycin D and that the nascent MMP-1 mRNA synthesis was stimulated by oxidized LDL, indicating that oxidized LDL activated transcription of the MMP-1 gene. Finally, both zymography and activity assays demonstrated that collagenase activity in conditioned medium was stimulated by oxidized LDL. Taken together, these results have shown for the first time that oxidized LDL stimulates MMP-1 transcription and secretion by vascular endothelial cells, suggesting that oxidized LDL may be a potent stimulator for MMP-1 expression in atherosclerotic plaques, thus promoting plaque rupture.

Arteriosclerosis↗

PubMed1999

Overexpression of apolipoprotein E3 in transgenic rabbits causes combined hyperlipidemia by stimulating hepatic VLDL production and impairing VLDL lipolysis.

The differential effects of overexpression of human apolipoprotein (apo) E3 on plasma cholesterol and triglyceride metabolism were investigated in transgenic rabbits expressing low (<10 mg/dL), medium (10 to 20 mg/dL), or high (>20 mg/dL) levels of apoE3. Cholesterol levels increased progressively with increasing levels of apoE3, whereas triglyceride levels were not significantly affected at apoE3 levels up to 20 mg/dL but were markedly increased at levels of apoE3 >20 mg/dL. The medium expressers had marked hypercholesterolemia (up to 3- to 4-fold over nontransgenics), characterized by an increase in low density lipoprotein (LDL) cholesterol, while the low expressers had only slightly increased plasma cholesterol levels. The medium expressers displayed an 18-fold increase in LDL but also had a 2-fold increase in hepatic very low density lipoprotein (VLDL) triglyceride production, an 8-fold increase in VLDL apoB, and a moderate decrease in the ability of the VLDL to be lipolyzed. However, plasma clearance of VLDL was increased, likely because of the increased apoE3 content. The increase in LDL appears to be due to an enhanced competition of VLDL for LDL receptor binding and uptake, resulting in the accumulation of LDL. The combined hyperlipidemia of the apoE3 high expressers (>20 mg/dL) was characterized by a 19-fold increase in LDL cholesterol but also a 4-fold increase in hepatic VLDL triglyceride production associated with a marked elevation of plasma VLDL triglycerides, cholesterol, and apoB100 (4-, 9-, and 25-fold over nontransgenics, respectively). The VLDL from the high expressers was much more enriched in apoE3 and markedly depleted in apoC-II, which contributed to a >60% inhibition of VLDL lipolysis. The combined effects of stimulated VLDL production and impaired VLDL lipolysis accounted for the increases in plasma triglyceride and VLDL concentrations in the apoE3 high expressers. The hyperlipidemic apoE3 rabbits have phenotypes similar to those of familial combined hyperlipidemia, in which VLDL overproduction is a major biochemical feature. Overall, elevated expression of apoE3 appears to determine plasma lipid levels by stimulating hepatic VLDL production, enhancing VLDL clearance, and inhibiting VLDL lipolysis. Thus, the differential expression of apoE may, within a rather narrow range of concentrations, play a critical role in modulating plasma cholesterol and triglyceride levels and may represent an important determinant of specific types of hyperlipoproteinemia.

Animals↗

PubMed1999

Oxidized LDL-containing immune complexes induce Fc gamma receptor I-mediated mitogen-activated protein kinase activation in THP-1 macrophages.

Our previous studies have shown that Fc gamma receptor (FcgammaR)-mediated uptake of LDL-containing immune complexes (oxLDL-ICs) by human monocyte-derived macrophages leads to not only transformation of macrophages into foam cells but also macrophage activation and release of cytokines. It has been shown that cross-linking of FcgammaR triggers activation of signal transduction pathways that alter gene expression in macrophages. In this study, we determined whether engagement of FcgammaR by oxLDL-ICs leads to activation of mitogen-activated protein (MAP) kinase pathway, a signaling cascade serving many important functions, including the regulation of gene expression, in THP-1 macrophage-like cells. Our results from immunoblotting, using specific anti-phosphorylated MAP kinase antibodies, showed that oxLDL-ICs induced extracellular signal regulated kinase 2 (ERK2) MAP kinase phosphorylation in THP-1 macrophage-like cells in time- and dose-dependent manners. Cholesterol loading before stimulation led to a longer phosphorylation of ERK2. Nuclear translocation of phosphorylated ERK was markedly increased after the stimulation. Moreover, our data showed that oxLDL-IC induction of MAP kinase was prevented by human monomeric IgG1, suggesting that the specific engagement of type I FcgammaR by oxLDL-IC is responsible for the MAP kinase activation. Finally, we showed that human anti-oxLDL autoantibody-containing immune complexes immobilized on type I collagen induced MAP kinase activation in THP-1 cells. These results strongly suggest that oxLDL-IC, which has been detected in atherosclerotic plaques, may play an important role in macrophage activation and atherogenesis.

Animals↗

PubMed1999

Phase II trial of weekly irinotecan plus cisplatin in advanced esophageal cancer.

PURPOSE: To evaluate the response, toxicity, survival, and quality of life in patients with unresectable or metastatic esophageal cancer treated with weekly irinotecan and cisplatin. PATIENTS AND METHODS: Thirty-five patients with metastatic or unresectable esophageal adenocarcinoma (23 patients) or squamous cell carcinoma (12 patients) were treated. No prior chemotherapy was allowed. The majority of patients had metastatic and bidimensionally measurable disease (34 patients each [97%]). Patients were treated with cisplatin 30 mg/m(2) and irinotecan 65 mg/m(2), repeated weekly for 4 weeks, followed by a 2-week rest period. Treatment was recycled every 6 weeks. Degree of dysphagia relief was monitored, and quality of life was measured prospectively using the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire C-30 and Functional Assessment of Cancer Therapy-General instruments. RESULTS: Thirty-five patients were assessable for response and toxicity. Major objective responses were observed in 20 patients (57%; 95% confidence interval, 41% to 73%), including two complete responses (6%). Similar response rates were observed for adenocarcinoma (12 of 23 patients; 52%) and squamous carcinoma (eight of 12 patients; 66%). The median duration of response was 4.2 months (range, 1 to 8.8+ months). Median actuarial survival was 14.6 months (range, 1 to 15.2+ months). In 20 patients with dysphagia assessable at baseline, 18 (90%) noted either improvement or resolution of dysphagia on chemotherapy. Global quality of life improved in responding patients, primarily because of improvements in pain, emotional state, and relationships with family and friends. Toxicity was relatively mild and included only three patients (9%) with grade 4 neutropenia and four (11%) with grade 3 diarrhea. There were no treatment-related deaths. CONCLUSION: The combination of weekly cisplatin plus irinotecan had significant activity in metastatic esophageal carcinoma and resulted in significant relief of dysphagia. The regimen was well tolerated, with acceptable myelosuppression and rare treatment-related diarrhea. Further evaluation of the combination of weekly irinotecan and cisplatin, including the addition of other agents to this regimen, is indicated.

Adenocarcinoma↗

PubMed1999

Opposing effects of corepressor and coactivators in determining the dose-response curve of agonists, and residual agonist activity of antagonists, for glucocorticoid receptor-regulated gene expression.

A distinguishing, but unexplained, characteristic of steroid hormone action is the dose-response curve for the regulation of gene expression. We have previously reported that the dose-response curve for glucocorticoid induction of a transfected reporter gene in CV-1 and HeLa cells is repositioned in the presence of increasing concentrations of glucocorticoid receptors (GRs). This behavior is now shown to be independent of the reporter, promoter, or enhancer, consistent with our proposal that a transacting factor(s) was being titrated by added receptors. Candidate factors have been identified by the observation that changes in glucocorticoid induction parameters in CV-1 cells could be reproduced by varying the cellular levels of coactivators [transcriptional intermediary factor 2 (TIF2), steroid receptor coactivator 1 (SRC-1), and amplified in breast cancer 1 (AIB1)], comodulator [CREB-binding protein (CBP)], or corepressor [silencing mediator for retinoid and thyroid-hormone receptors (SMRT)] without concomitant increases in GR. Significantly, the effects of TIF2 and SMRT were mutually antagonistic. Similarly, additional SMRT could reverse the action of increased levels of GRs in HeLa cells, thus indicating that the effects of cofactors on transcription may be general for GR in a variety of cells. These data further indicate that GRs are yet an additional target of the corepressor SMRT. At the same time, these cofactors were found to be capable of regulating the level of residual agonist activity displayed by antiglucocorticoids. Finally, these observations suggest that a novel role for cofactors is to participate in processes that determine the dose-response curve, and partial agonist activity, of GR-steroid complexes. This new activity of cofactors is disconnected from their ability to increase or decrease GR transactivation. An equilibrium model is proposed in which the ratio of coactivator-corepressor bound to either receptor-agonist or -antagonist complexes regulates the final transcriptional properties.

Cell Line↗