Genetic depletion of Soat2 diminishes hepatic steatosis via genes regulating de novo lipogenesis and by GLUT2 protein in female mice.

Depletion of the cholesterol esterifying enzyme acyl-Coenzyme A: cholesterol acyltransferase 2 (ACAT2, encoded by Soat2) protects mice from atherosclerosis, diet-induced hypercholesterolemia, and hepatic steatosis when fed high-cholesterol diet. The glucose transporter 2 (GLUT2) represents the main gate of glucose uptake by the liver. Lipid synthesis from glucose (de novo lipogenesis; DNL) plays a pivotal role in the development of hepatic steatosis. Inhibition of DNL is a successful approach to reverse hepatic steatosis, as shown by different studies in mice and humans. Here we aimed to investigate whether depletion of Soat2 per se can reduce hepatic steatosis, also in the presence of very low levels of cholesterol in the diet, and the underlying mechanisms. Female Soat2-/- and wild type mice were either fed high-fat or high-carbohydrate diet and both contained <0.05% (w/w) cholesterol. Analysis in serum, liver, muscles and adipose tissues were performed. We found Soat2-/- mice fed high-fat, low-cholesterol diet to have less hepatic steatosis, decreased expression of genes involved in DNL and lower hepatic GLUT2. Similar findings were found in Soat2-/- mice fed high-carbohydrate, low-cholesterol diet. CONCLUSION: Depletion of Soat2 reduces hepatic steatosis independently of the presence of high levels of cholesterol in the diet. Our study provides a link between hepatic cholesterol esterification, DNL, and GLUT2.

Axillary staging for breast cancer during pregnancy: feasibility and safety of sentinel lymph node biopsy.

BACKGROUND: Safety of sentinel lymph node (SLN) biopsy for breast cancer during pregnancy is insufficiently explored. We investigated efficacy and local recurrence rate in a large series of pregnant patients. PATIENTS AND METHODS: Women diagnosed with breast cancer who underwent SLN biopsy during pregnancy were identified from the International Network on Cancer, Infertility and Pregnancy, the German Breast Group, and the Cancer and Pregnancy Registry. Chart review was performed to record technique and outcome of SLN biopsy, locoregional and distant recurrence, and survival. RESULTS: We identified 145 women with clinically N0 disease who underwent SLN during pregnancy. The SLN detection techniques were as follows: 99mTc-labeled albumin nanocolloid only (n = 96; 66.2%), blue dye only (n = 14; 9.7%), combined technique (n = 15; 10.3%), or unknown (n = 20; 13.8%). Mapping was unsuccessful in one patient (0.7%) and she underwent an axillary lymph node dissection (ALND). Mean number of SLNs was 3.2 (interquartile range 1-3; missing n = 15). Positive SLNs were found in 43 (29.7%) patients and 34 subsequently underwent ALND. After a median follow-up of 48 months (range 1-177), 123 (84.8%) patients were alive and free of disease. Eleven patients experienced a locoregional relapse, including 1 isolated ipsilateral axillary recurrence (0.7%). Eleven (7.6%) patients developed distant metastases, of whom 9 (6.2%) died of breast cancer. No neonatal adverse events related to SLN procedure during pregnancy were reported. CONCLUSIONS: SLN biopsy during pregnancy has a comparably low axillary recurrence rate as in nonpregnant women. Therefore, this method can be considered during pregnancy instead of standard ALND for early-stage, clinically node-negative breast cancer.

Using the robust design framework and relative abundance to predict the population size of pallid sturgeon Scaphirhynchus albus in the lower Missouri River.

Several population viability models were constructed to aid recovery in endangered Scaphirhynchus albus, but these models are dependent upon accurate and precise input parameters that are not provided with standard catch per unit effort (CPUE) indices. Nine years of sampling efforts, under the robust design framework, provided 1223 unique captures with an 18·3% recapture rate. The annual population estimates varied from 4·0-7·3 fish rkm-1 for wild and 8·4-18·4 fish rkm-1 for hatchery-reared S. albus. The relationship between abundance (N) and annual trot-line CPUE indices (x = 70.726y + 2·533, R2 = 0·91, P < 0·001) was used to predict an abundance of 13 616 ± 7142 s.e. S. albus in the lower Missouri River. The use of small-scale intensive sampling to develop a relationship with relative abundance indices reported here, may provide a framework for other fisheries management applications where large-scale intensive sampling is not feasible, but catch data are available.

Clopidogrel-Paclitaxel Drug-Drug Interaction: A Pharmacoepidemiologic Study.

Paclitaxel is mainly eliminated by CYP2C8 in the liver. CYP2C8 is strongly inhibited by the clopidogrel metabolite acyl-ß-D-glucuronide. To determine if this interaction has clinical relevance, we identified 48 patients treated with clopidogrel and paclitaxel using databases and a prescription register. Peripheral sensory neuropathy was retrospectively evaluated from medical charts and compared to that of 88 age- and sex-matched controls treated with paclitaxel and low-dose aspirin. By a cumulative dose of 1,500 mg paclitaxel, 35% of the patients had developed severe neuropathy. The overall hazard ratio between clopidogrel use and severe paclitaxel neuropathy was 1.7 (95% confidence interval, 0.9-3.0). Among those receiving a high-dose paclitaxel regimen, the hazard ratio was 2.3 (95% confidence interval, 1.1-4.5). Our study indicates that clopidogrel is associated with a clinically relevant increased risk of neuropathy in patients treated with high-dose paclitaxel.

Emerging role of thyroid hormone metabolites.

Thyroid hormones (THs) are essential for the regulation of development and metabolism in key organs. THs produce biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). Such activations can be either direct, in the case of ion channels, or mediated by membrane or cytoplasmic receptors. Short-term-activated signalling pathways often play a role in the regulation of genomic effects. Several TH intermediate metabolites, which were previously considered without biological activity, have now been associated with a broad range of actions, mostly attributable to short-term effects. Here, we give an overview of the physiological roles and mechanisms of action of THs, focusing on the emerging position that TH metabolites are acquiring as important regulators of physiology and metabolism.

The oxysterol receptor LXRß protects against DSS- and TNBS-induced colitis in mice.

We examined the function of the oxysterol receptors (LXRs) in inflammatory bowel disease (IBD) through studying dextran sodium sulfate (DSS)- and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice and by elucidating molecular mechanisms underlying their anti-inflammatory action. We observed that Lxr-deficient mice are more susceptible to colitis. Clinical indicators of colitis including weight loss, diarrhea and blood in feces appeared earlier and were more severe in Lxr-deficient mice and particularly LXRß protected against symptoms of colitis. Addition of an LXR agonist led to faster recovery and increased survival. In contrast, Lxr-deficient mice showed slower recovery and decreased survival. In Lxr-deficient mice, inflammatory cytokines and chemokines were increased together with increased infiltration of immune cells in the colon epithelium. Activation of LXRs strongly suppressed expression of inflammatory mediators including TNFα. While LXRα had anti-inflammatory effects in CD11b(+) immune cell populations, LXRß in addition had anti-inflammatory effects in colon epithelial cells. Lack of LXRß also induced CD4(+)/CD3(+) immune cell recruitment to the inflamed colon. Expression of both LXRA and LXRB was significantly suppressed in inflamed colon from subjects with IBD compared with non-inflamed colon. Taken together, our observations suggest that the LXRs could provide interesting targets to reduce the inflammatory responses in IBD.

Soy protein isoflavones differentially regulate liver X receptor isoforms to modulate lipid metabolism and cholesterol transport in the liver and intestine in mice.

AIMS/HYPOTHESIS: Liver X receptor (LXR)α regulates the genes involved in cholesterol, fatty acid and glucose metabolism. Soy protein (SP) consumption reduces the hepatic accumulation of cholesterol and triacylglycerol, and improves insulin sensitivity. However, it is not known whether these effects are mediated via LXRα. We therefore investigated whether the consumption of SP regulates metabolic changes in cholesterol metabolism and insulin sensitivity via LXRα. METHODS: Wild-type (WT) and Lxrα(-/-) (Lxrα, also known as Nr1h3) mice were fed an SP diet with or without cholesterol for 28 days. The expression of LXRα target genes was measured in liver and intestine, as were hepatic lipid content and faecal bile acid concentration. Oral glucose and insulin tolerance tests were also performed. Hepatocytes were used to study the effect of isoflavones on LXR activity. RESULTS: The livers of WT and Lxrα(-/-) mice fed an SP high-cholesterol diet showed less steatosis than those fed casein. The SP diet increased the expression of the ATP-binding cassette (ABC) sub-family genes Abca1, Abcg5 and Abcg8 in the liver and intestine, as well as increasing total faecal bile acid excretion and insulin sensitivity in WT mice compared with mice fed a casein diet. However, these effects of SP were not observed in Lxrα(-/-) mice. The SP isoflavone, genistein, repressed the activation of LXRα target genes by T0901317, whereas it stimulated the activation of LXRß target genes. The AMP-activated protein kinase inhibitor, compound C, had the opposite effects to those of genistein. CONCLUSIONS/INTERPRETATION: Our results suggest that SP isoflavones stimulate the phosphorylation of LXRα or LXRß, resulting in different biological effects for each LXR isoform.

LXRß activation increases intestinal cholesterol absorption, leading to an atherogenic lipoprotein profile.

OBJECTIVES: Liver X receptors (LXRs) are essential for the regulation of intestinal cholesterol absorption. Because two isoforms exist, LXRα and LXRß, with overlapping but not identical functions, we investigated whether LXRα and LXRß exert different effects on intestinal cholesterol absorption. DESIGN: Wild-type (WT), LXRα(-/-) and LXRß(-/-) mice were fed control diet, 0.2% cholesterol-enriched diet or 0.2% cholesterol-enriched diet plus the LXR agonist GW3965. RESULTS: When fed a control diet, all three genotypes showed similar levels of cholesterol absorption. Of interest, a significant increase in cholesterol absorption was found in the LXRα(-/-) mice, but not in the WT or LXRß(-/-) animals, when fed a diet enriched with 0.2% cholesterol or 0.2% cholesterol + GW3965. Reduced faecal neutral sterol excretion and a hydrophobic bile acid profile were also observed in LXRα(-/-) mice. Greater increases in the apolipoprotein (apo)B-containing lipoproteins in serum were seen in the LXRα(-/-) mice. A 0.2% cholesterol +GW3965 diet suppressed intestinal Npc1l1 protein expression to the same extent for all genotypes, while Abca1 and Abcg5 were elevated to the same degree. CONCLUSIONS: In the intestine, LXRα and LXRß seem to exert similar effects on expression of cholesterol-transporting proteins such as Npc1l1. Selective activation of LXRß may generate effects such as increased cholesterol absorption and elevated serum levels of apoB-containing lipoproteins, which seem to be counteracted by LXRα. Therefore, an intestinal LXRß-specific pathway might exist in terms of cholesterol transportation in addition to the main pathway.

The predictive value of serum VEGF in multiresistant ovarian cancer patients treated with bevacizumab.

OBJECTIVE: Bevacizumab, a humanized monoclonal antibody against VEGF (vascular endothelial growth factor), has shown antitumor activity, but so far no biomarkers have been identified to predict outcome. The purpose of the present study was to investigate the efficacy of bevacizumab in patients with multiresistant ovarian cancer and, furthermore, to investigate the possible predictive value of serum VEGF, VEGFR1-2 and VEGF gene polymorphisms. METHODS: Patients received single-agent bevacizumab 10 mg/kg every 3 weeks. All patients were followed with CA 125 measurements and serum VEGF/VEGFR1-2 levels prior to each cycle. Endpoints were response rate (RR), progression-free survival (PFS) and overall survival (OS). RESULTS: Thirty-eight patients were included. All patients were heavily pre-treated with a median of five prior regimens. The median number of bevacizumab treatments was 4. Overall response rate was 30% according to CA 125 (GCIG criteria). Median PFS was 5.9 months (95% CI, 3.5-9.4) and median OS was 8.6 months (95% CI, 6.6-12.8). The VEGF serum level decreased during treatment in all patients. A low pre-treatment VEGF level was predictive to response. The median value was 540 pg/ml and divided the patients into two groups with a response rate of 60% and 0%, respectively (p=0.0007). The difference translated to a significant difference in PFS (p=0.047) and OS (p=0.01). VEGF gene polymorphisms -2578, -1154, -460, +405, +936 did not reveal any association with response or survival and the same applied to serum VEGFR1-2. CONCLUSIONS: Single agent bevacizumab has activity in ovarian cancer patients. Pre-treatment serum VEGF seems to have predictive value.

The relationship of VEGF polymorphisms with serum VEGF levels and progression-free survival in patients with epithelial ovarian cancer.

OBJECTIVE: The vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis and vascular permeability of tumors. In the present study we evaluated the relation of five single nucleotide polymorphisms (SNPs) in the VEGF gene with progression-free survival. Furthermore, we evaluated the functional significance of the SNPs as determined by the influence on serum VEGF levels in ovarian cancer. METHODS: Serum from 143 consecutive ovarian cancer patients referred for first line platinum/paclitaxel treatment were analyzed for serum VEGF levels using commercially available enzyme-linked immunosorbent assay (ELISA). VEGF gene polymorphisms (-2578 C/A, -1154 G/A, -460 T/C, +405 G/C and +936C/T) were determined by real time PCR using genomic DNA extracted from whole blood samples. RESULTS: VEGF serum levels were significantly higher in carriers of the 2578C, 460T and 405C, alleles compared to non-carriers (p=0.003, p=0.003 and p=0.001, respectively). There was no significant correlation between VEGF SNP genotypes and progression-free survival. In haplotype analysis, the multivariate survival analysis showed that progression-free survival (PFS) for the patients with the AGCGC haplotype was significantly improved compared to patients with other haplotypes (HR 1.9, p=0.036). CONCLUSIONS: VEGF polymorphisms were found to be significantly related with serum VEGF levels. The AGCGC haplotype was found to be independently associated with improved PFS.

Self-assembling microparticles with controllable disruption properties based on cyclodextrin interactions.

In this paper, we present the formation of particles by self-assembly of cyclodextrin polymers and hydrophobically modified dextran followed by a controlled disruption of the particles by addition of a trigger molecule competing for the cyclodextrin cavities. The produced particles are formed from poly(vinylpyrrolidone)-co-beta-cyclodextrin and dextran-benzoate, both biocompatible polymers, and are all in the nano-/micrometer range and hence suitable for drug delivery purposes. The particle formation was studied in different ratios of poly(vinylpyrrolidone)-co-beta-cyclodextrin and dextran-benzoate by visual inspections, dynamic light scattering, isothermal titration calorimetry and SEM. The triggering of particle disruption was achieved by addition of hydroxyadamantane which has a very strong affinity towards the beta-cyclodextrin cavities. The stepwise addition of hydroxyadamantane was followed by dynamic light scattering and SEM measurements, revealing a disruption of the particles due to the addition of this competitor. These particles are believed to be promising candidates for controlled drug delivery systems, due to their unique ability to disrupt in a controlled manner.

Cancers take their Toll--the function and regulation of Toll-like receptors in cancer cells.

Cancer could be deemed as an abnormal and uncontrolled tissue repair process. Therefore, it would not be surprising that factors that function in the tissue repair process, such as cytokines, chemokines, growth factors and Toll-like receptor (TLR) ligands, as well as growth signals for compensatory proliferation, would also be key factors in regulating and enhancing cancer progression. The TLR pathways, which play a critical role in tissue repair, are also key regulators in cancer progression as well as chemoresistance. TLRs serve as cell surface sensors that can initiate pathways leading to proliferation and chemoresistance; as well as mediators that are able to regulate the infiltrating immune cells to provide further support for cancer progression.

Prediction of response to chemotherapy by ERCC1 immunohistochemistry and ERCC1 polymorphism in ovarian cancer.

The response of tumor cells to platinum-based chemotherapy involves DNA repair mechanisms. Excision repair cross-complementation group 1 (ercc1) is one of the leading genes involved in DNA repair, and several studies have linked ercc1 to platinum resistance in cell lines and in human cancers. A common single nucleotide polymorphism (SNP) of ercc1 at codon 118 has been proposed to impair ercc1 translation and reduce ERCC1 protein expression and consequently influence the response to platinum-based chemotherapy. The primary aim of the present study was to evaluate ERCC1 expression and ercc1 codon 118 polymorphism in epithelial ovarian cancer (EOC) and their possible predictive value in patients treated with platinum-based chemotherapy. Formalin-fixed, paraffin-embedded tissue sections from 159 patients with advanced EOC were used for immunohistochemistry. Ercc1 codon 118 SNP genotyping was performed by real-time polymerase chain reaction. ERCC1 protein overexpression was found in 37.7% of the tumors. The CA-125 response rate was 94.5% (52/55) in patients with ERCC1-negative tumors compared to 80% (36/45) in patients with ERCC1-positive tumors (P = 0.026, chi(2)). The T/T genotype (44%) signalized a better response to chemotherapy than C/C (15%) + C/T (41%) variants (P = 0.045, trend test). Patients with ERCC1-negative tumors appear to have significantly better response to platinum-based chemotherapy compared to patients with ERCC1-positive tumors, but the differences in response rates did not translate into differences in survival. In addition, the TT genotype seems to be favorable toward better response to platinum-based chemotherapy.

The prognostic importance of cyclooxygenase 2 and HER2 expression in epithelial ovarian cancer.

Both cyclooxygenase 2 (COX2) and human epidermal growth factor receptor 2 (HER2, also called c-erbB-2) overexpression have been related to a worse prognosis in epithelial ovarian cancer (EOC), but the data are conflicting and the percentage of tumors with overexpression varies widely in different studies. The aim of this study was to investigate the potential prognostic value of COX2 and HER2 expression in EOC. A further purpose was to investigate a possible coexpression of the two markers, and finally, to elucidate the agreement between fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) for evaluation of the HER2 status in EOC. Immunostaining was performed for COX2/HER2 together with FISH analysis for HER2 gene amplification in 160 patients with EOC, FIGO stages IIB-IV. Follow-up was more than 10 years. COX2 overexpression was found in 20.0% of the tumors. With HER2 staining, 64.4% were scored as 0, 24.4% as 1+, 6.9% as 2+, and 4.4% as 3+. Median survival time for COX2-negative tumors was 21.6 versus 36 months for COX2-positive tumors. The longer survival for COX2 positive was significant by both univariate analysis (P= 0.015) and multivariate analysis (P= 0.025). Positive immunostaining for HER2 was associated with poor overall survival (P= 0.03). Agreement between IHC and FISH was seen in all cases (P < 0.0000001). With long-term observation, patients with negative COX2 expression had significantly shorter survival compared to patients with COX2-positive tumors. Positive HER2 expression also notified a grave prognosis, but the low rate of overexpression reduces its potential clinical application.

Gene expression profiling identifies liver X receptor alpha as an estrogen-regulated gene in mouse adipose tissue.

Estrogens reduce adipose tissue mass in both humans and animals. The molecular mechanisms for this effect are, however, not well characterized. We took a gene expression profiling approach to study the direct effects of estrogen on mouse white adipose tissue (WAT). Female ovariectomized mice were treated for 10, 24 and 48 h with 17beta-estradiol or vehicle. RNA was extracted from gonadal fat and hybridized to Affymetrix MG-U74Av2 arrays. 17beta-Estradiol was shown to decrease mRNA expression of liver X receptor (LXR) alpha after 10 h of treatment compared with the vehicle control. The expression of several LXRalpha target genes, such as sterol regulatory element-binding protein 1c, apolipoprotein E, phospholipid transfer protein, ATP-binding cassette A1 and ATP-binding cassette G1, was similarly decreased. We furthermore identified a 1.5 kb LXRalpha promoter fragment that is negatively regulated by estrogen. Several genes involved in lipogenesis and lipolysis were identified as novel targets that could mediate estrogenic effects on adipose tissue. Finally, we show that ERalpha is the main estrogen receptor expressed in mouse white adipose tissue (WAT) with mRNA levels several hundred times higher than those of ERbeta mRNA.

TACC3 expression is tightly regulated during early differentiation.

Transforming acidic coiled-coil (TACC) proteins are hypothesized to play a role in normal cellular growth and differentiation and to be involved in centrosomal microtubule stabilization. Our current studies aim to delineate the expression pattern of TACC3 protein during cellular differentiation and in a variety of normal human tissues. TACC3 is known to be upregulated in differentiating erythroid progenitor cells following treatment with erythropoietin and is required for replication of hematopoietic stem cells. However, we demonstrate that a dramatic upregulation of TACC3 also occurs during the early differentiation of NIH 3T3-L1 cells into adipocytes and PC12 cells into neurons, indicating that TACC3 mediates cellular differentiation in several cell types. Using real-time PCR, we quantitated the mRNA levels of TACC3 compared to TACC1 and TACC2 in various human adult tissues. We observed the highest expression of TACC3 mRNA in testis, spleen, thymus and peripheral blood leukocytes, all tissues undergoing high rates of differentiation, and a lower level of expression in ovary, prostate, pancreas, colon, small intestine, liver and kidney. In contrast, TACC1 and TACC2 mRNA levels are more widespread. By immunohistochemistry, we confirm that the TACC3 protein localizes to differentiating cell types, including spermatocytes, oocytes, epithelial cells, bone marrow cells and lymphocytes. Thus, these observations are concordant with a basic role for TACC3 during early stages of differentiation in normal tissues.

Members of the nuclear factor 1 family reduce the transcriptional potential of the nuclear receptor LXRalpha promoter.

Expression of the LXRalpha nuclear receptor in liver is predicted to affect cholesterol and lipid metabolism. Here we show that a short fragment from the LXRalpha gene promoter spanning the region from -144 to +43 relative to the mRNA initiation site can drive transcription of a reporter gene. Under basal conditions, in vitro DNase I footprinting demonstrated interaction between nuclear proteins and an NF1 recognition site in close vicinity to the transcriptional initiation. Both supershift, mutational analyses in EMSA and transfections provided evidence that the NF1 (nuclear factor I) transcription factor interacts with the LXRalpha promoter. All four members of the NF1 family were found to suppress the transcriptional activity indicating a general inhibitory effect on LXRalpha expression. A similar regulation by NF1 was also observed when using a fragment from the LXRalpha promoter extending up to position -3033 therefore giving the inhibitory effect of NF1 a significant impact on LXRalpha gene expression.

Structural characterisation of the mouse nuclear oxysterol receptor genes LXRalpha and LXRbeta.

Oxysterols are important regulatory molecules of diverse biological processes such as cholesterol homeostasis, bile acid synthesis and apoptosis. Recent findings led to the suggestion that some of these functions are mediated by the nuclear receptors LXRalpha and LXRbeta owing to their potential to bind a group of naturally occurring oxysterols as their ligands. In this report, we compare the genomic structure and the promoter regions of the two mouse LXR genes. In addition, we show evidence for the presence of a processed, but truncated LXRbeta pseudogene in the mouse genome. RACE-PCR on mouse liver cDNA demonstrates the presence of more than one defined transcription initiation site for both genes. The LXRalpha and LXRbeta promoter regions are GC-rich and contain a number of putative Sp1 binding sites but lack obvious TATA and CAAT boxes. A database search revealed several sequence motifs in the LXR promoter regions that resemble known transcription factor binding sites. Most striking is the identification of one potential NFkappaB and seven potential Ets-protein binding sites in the LXRbeta promoter, suggesting an important role for this receptor in the haematopoietic/immune system.

Ligand-independent coregulator recruitment by the triply activatable OR1/retinoid X receptor-alpha nuclear receptor heterodimer.

OR1 is a member of the superfamily of steroid/thyroid hormone nuclear receptors and recognizes DNA as a heterodimer with the 9-cis-retinoic acid receptor RXR (retinoid X receptor). The heterodimeric complex has been shown to be transcriptionally activatable by the RXR ligand as well as certain oxysterols via OR1, but to date uniquely also by heterodimerization itself. Recent studies on other members of the superfamily of nuclear receptors have led to the identification of a number of nuclear receptor-interacting proteins that mediate their regulatory effects on transcription. Here, we address the question of involvement of some of these cofactors in the three modes of activation by the OR1/RXRalpha complex. We show that in vitro the steroid receptor coactivator SRC-1 can be recruited by RXRalpha upon addition of its ligand, and to OR1 upon addition of 22(R)-OH-cholesterol, demonstrating that the latter can act as a direct ligand to OR1. Additionally, heterodimerization is sufficient to recruit SRC-1 to OR1/RXRalpha, indicating SRC-1 as a molecular mediator of dimerization-induced activation. In transfection experiments, coexpression of a nuclear receptor-interacting fragment of SRC-1 abolishes constitutive activation by OR1/RXRalpha, which can be restored by over-expression of full-length SRC-1. This constitutes evidence for an in vivo role of SRC-1 in dimerization-induced activation by OR1/RXRalpha. Additionally, we show that the nuclear receptor-interacting protein RIP140 binds in vitro to OR1 and RXRalpha with requirements distinct from those of SRC-1, and that binding of the two cofactors is competitive. Taken together, our results suggest a complex modulation of differentially induced transactivation by OR1/RXR coregulatory molecules.