Vitamin A Deficiency Induces Autistic-Like Behaviors in Rats by Regulating the RARß-CD38-Oxytocin Axis in the Hypothalamus.

SCOPE: Vitamin A (VA) is an essential nutrient for the development of the brain. We previously found that children with autism spectrum disorder (ASD) have a significant rate of VA deficiency (VAD). In the current study, we aim to determine whether VAD is a risk factor for the generation of autistic-like behaviors via the transcription factor retinoic acid receptor beta (RARß)-regulated cluster of differentiation 38 (CD38)-oxytocin (OXT) axis. METHODS AND RESULTS: Gestational VAD or VA supplementation (VAS) rat models are established, and the autistic-like behaviors in the offspring rats are investigated. The different expression levels of RARß and CD38 in hypothalamic tissue and serum retinol and OXT concentration are tested. Primary cultured rat hypothalamic neurons are treated with all-trans retinoic acid (atRA), and recombinant adenoviruses carrying the rat RARß (AdRARß) or RNA interference virus RARß-siRNA (siRARß) are used to infect neurons to change RARß signal. Western blotting, chromatin immunoprecipitation (ChIP), and intracellular Ca2+ detections are used to investigate the primary regulatory mechanism of RARß in the CD38-OXT signaling pathway. We found that gestational VAD increases autistic-like behaviors and decreases the expression levels of hypothalamic RARß and CD38 and serum OXT levels in the offspring. VAS ameliorates these autistic-like behaviors and increases the expression levels of RARß, CD38, and OXT in the gestational VAD pups. In vitro, atRA increases the Ca2+ excitability of neurons, which might further promote the release of OXT. Different CD38 levels are induced in the neurons by infection with different RARß adenoviruses. Furthermore, atRA enhances the binding of RARß to the proximal promoter of CD38, indicating a potential upregulation of CD38 transcriptional activity by RARß. CONCLUSIONS: Gestational VAD might be a risk factor for autistic-like behaviors due to the RARß signal suppression of CD38 expression in the hypothalamus of the offspring, which improves with VAS during the early-life period. The nutritional status during pregnancy and the early-life period is important in rats.

Dual-probe electrochemical DNA biosensor based on the "Y" junction structure and restriction endonuclease assisted cyclic enzymatic amplification for detection of double-strand DNA of PML/RARα related fusion gene.

Taking advantage of "Y" junction structure and restriction endonuclease assisted cyclic enzymatic amplification, a dual-probe electrochemical DNA (DE-DNA) biosensor was designed to detect double-stranded DNA (dsDNA) of acute promyelocytic leukemia (APL) related gene. Two groups of detection probes were designed, and each group was composed of a biotinylated capture probe and an assisted probe. They were separately complementary with two strands of target dsDNA in order to prevent the reannealing of the two separate strands from target dsDNA. First, thiol functionalized capture probes (C1 and C2) were severally assembled onto two different gold electrodes, followed by hybridizing with target dsDNA (S1a-S1b) and assistant probes to form two Y-junction-structure ternary complexes. Subsequently, restriction sites on the ternary complexes were digested by Rsa I, which can release S1a, S1b and biotins from the electrode surfaces. Meanwhile, the released S1a and S1b can further hybridize with the unhybridized corresponding detection probes and then initiate another new hybridization-cleavage-separation cycle. Finally, the current signals were produced by the enzyme-catalyzed reaction of streptavidin-horse reddish peroxidase (streptavidin-HRP). The distinct difference in current signals between different sequences allowed detection of target dsDNA down to a low detection limit of 47 fM and presented excellent specificity with discriminating only a single-base mismatched dsDNA sequence. Moreover, this biosensor was also used for assay of polymerase chain reaction (PCR) samples with satisfactory results. According to the results, the power of the DE-DNA biosensor as a promising tool for the detection of APL and other diseases.

Effects of beta-carotene supplementation on molecular markers of lung carcinogenesis in male smokers.

Two primary prevention trials unexpectedly showed adverse effects of supplemental beta-carotene on lung cancer incidence in cigarette smokers. To elucidate the molecular mechanisms that might underlie these effects, we studied the immunohistochemical expression of cytochrome P450 1A1, 1A2, and 2E1, retinoic acid receptor beta, activated protein-1 elements, cyclin D1, and Ki67 in lung tumors and, when available, adjacent normal tissues obtained from incident cases in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. Archival lung tissue was available from 52 men randomized to receive 20 mg of beta-carotene per day and 30 men randomized to the placebo arm, all of whom were diagnosed with incident non-small-cell lung carcinoma during the course of the trial and subsequently underwent radical pulmonary resection. In normal-appearing bronchial epithelium, positive staining for cyclin D1 was observed in 23% of cases in the beta-carotene group and 0% of cases in the placebo group (based on only 3 of 13 versus 0 of 11 cases staining positively, however; P = 0.04), with no differences in expression noted in lung tumor tissue (P = 0.48). There were no statistically significant differences in Ki67 expression in normal or cancerous lung tissue between intervention groups, although a small increase in staining in tumors was noted among cases in the beta-carotene versus placebo group (88% versus 71% of cases stained positive, respectively; P = 0.13). Contrary to expectation, beta-carotene supplementation had no apparent effect on retinoic acid receptor-beta expression. These findings suggest that male smokers supplemented with beta-carotene may have had an increased risk of lung cancer due to aberrant cell growth, although our results are based on a relatively small number of cases and require confirmation in other completed trials of beta-carotene supplementation.

Detection of nucleic acid-nuclear hormone receptor complexes with mass spectrometry.

Nuclear receptors, such as the retinoic acid receptor (RAR) or the 9-cis retinoic acid receptor (RXR), interact not only with their ligands but also with other types of receptors and with DNA. Here, two complementary mass spectrometry (MS) methods were used to study the interactions between retinoic receptors (RXR/RAR) and DNA: non-denaturing nano-electrospray (nanoESI MS), and high-mass matrix-assisted laser desorption ionization (MALDI MS) combined with chemical cross-linking. The RAR x RXR heterodimer was studied in the presence of a specific DNA sequence (DR5), and a specific RAR x RXR x DNA complex was detected with both MS techniques. RAR by itself showed no significant homodimerization. A complex between RAR and the double stranded DR5 was detected with nanoESI. After cross-linking, high-mass MALDI mass spectra showed that the RAR binds the single stranded DR5, and the RAR dimer binds both single and double stranded DR5. Moreover, the MALDI mass spectrum shows a larger RAR dimer signal in the presence of DNA. These results suggest that a gene-regulatory site on DNA can induce quaternary structural changes in a transcription factor such as RAR.

Characterization of cellular retinoid-binding proteins in human myometrium during pregnancy.

Many complementary or competing signalling pathways bear an influence on the myometrium at any one time, and because the retinoic acid signalling pathway influences differentiation of a wide array of human tissues, this may be one of the determinants of myometrial differentiation during pregnancy. We have explored the novel hypothesis that the retinoids may act as important regulators in controlling the differentiated state of the human myometrium during pregnancy by characterizing the expression profiles for cellular retinoid-binding proteins CRBPI, CRABPI and CRABPII in non-pregnant, pregnant (non-labouring) and labouring human myometrium taken from the functionally distinct upper and lower uterine segments. In addition, we have investigated the effect of all-trans retinoic acid (ATRA) on the expression of several retinoic acid response genes including cyclooxygenase-2 (COX-2) and connexin-43 (Cx-43). Different spatial and temporal patterns of expression were observed for CRBPI, CRABPI and CRABPII within the upper and lower uterine segments through the three trimesters of pregnancy and in labour. Furthermore, the expression of COX-2, Cx-43, CRABPI, the transcription factor c-Jun and the retinoic acid receptor RARbeta altered in response to different concentrations of ATRA, suggesting that the differential expression of cellular retinoid-binding proteins may lead to different levels of retinoic acid being delivered to its nuclear targets, leading to the differential expression of specific target genes within the myometrium during pregnancy.

Transforming growth factor-beta1 signaling participates in the physiological and pathological regulation of mouse inner ear development by all-trans retinoic acid.

BACKGROUND: Retinoic acid (RA) is a vitamin A derivative that participates in patterning and regulation of inner ear development. Either excess RA or RA deficiency during a critical stage of inner ear development can produce teratogenic effects. Previous studies have shown that in utero exposure of the developing mouse inner ear to a high dose of all-trans RA (atRA) results in severe malformations of the inner ear that are associated with diminished levels of endogenous transforming growth factor-beta1 (TGF-beta(1)) protein. METHODS: In this study, the effects of a teratogenic level of atRA on levels and patterns of expression of TGFbeta receptor II (TGFbetaRII) and Smad2, a downstream component of the TGFbeta signal transduction pathway, are investigated in the developing mouse inner ear. The expression pattern of endogenous RA receptor alpha (RARalpha) and the ability of an RARalpha(1)-specific antisense oligonucleotide (AS) to modulate otic capsule chondrogenesis are demonstrated in the inner ear and in culture. RESULTS: Endogenous TGFbetaRII and Smad2 are downregulated in the inner ear following in utero atRA treatment. In addition, a reduction in endogenous TGFbeta(1) and a marked suppression of chondrogenesis occur in RARalpha(1) AS-treated cultures in comparison to untreated or oligonucleotide-treated control cultures. This chondrogenic suppression can be partially overcome by supplementation of RARalpha(1) AS-treated cultures with exogenous TGFbeta(1) protein. CONCLUSIONS: Our findings support a role for TGFbeta in the physiological and pathological effects of RA on inner ear development.

Expression of vitamin D3 receptor and retinoid receptors in human breast cancer: identification of potential heterodimeric receptors.

Vitamin D3 (VD) and all-trans-retinoic acid (ATRA) have been postulated as a novel treatment option for breast carcinoma. Since the combined effects of retinoids and VD derivatives are attributed to heterodimeric interactions between members of the nuclear receptor family, the expression patterns of the heterodimers formed by vitamin D3 receptor (VDR) and the retinoid receptors RARs (RAR-alpha, RAR-beta and RAR-gamma) and RXRs (RXR-alpha, RXR-beta and RXR-gamma) have been studied by immunohistochemistry in benign and malignant breast tissues. Present results revealed that immunoexpressions to all receptor types studied were higher in both in situ and infiltrative carcinomas than in benign breast diseases. In a variable number of cases of infiltrative carcinoma, immunostaining appeared in the nucleus, whereas in the other two disorders immunostaining was only cytoplasmic. The correlation established between VDR and the different isoforms of retinoid receptors revealed that VDR seems to select mainly RAR-alpha to form heterodimers and to exert their properties as transcription factor. The results of this study suggest that this heterodimer plays a critical role in cancer malignancy, and its presence indicates those patient groups presenting a better response to adjuvant therapies based on the combination of vitamin D and ATRA.

Phase II clinical trial of N-(4-Hydroxyphenyl)retinamide and tamoxifen administration before definitive surgery for breast neoplasia.

PURPOSE: Surrogate end point biomarkers (SEBs) that can be measured in ductal carcinoma in situ or early-stage invasive cancer are needed to improve the efficiency and reduce the cost of chemoprevention trials. EXPERIMENTAL DESIGN: We conducted a prospective study to develop SEBs for tamoxifen and N-[4-hydroxyphenyl]retinamide by administering either a placebo or both drugs for 2-4 weeks to women with ductal carcinoma in situ or early invasive cancers in the interval between the initial diagnostic core biopsy and definitive surgery. The major statistical end point of the study was pre- versus posttreatment change in cell proliferation, as measured by changes in Ki67 labeling indices. In addition, estrogen receptor (ER), HER2/neu, p53, retinoid receptors, and DNA index were measured. RESULTS: Between February 1997 and April 200, 52 patients were registered on the study, and 36 (20 in the placebo arm and 16 in the treatment arm) were available for analysis. No statistically significant pre- versus posttreatment differences in Ki67 labeling index or in the other markers were observed in the treatment arm compared with the placebo arm. There was a trend toward increased treatment response in ER-positive versus ER-negative patients, but this could not be rigorously analyzed because of the low sample size and the unequal distribution of ER-positive patients in the two study arms. CONCLUSION: Future SEB trials for breast carcinoma must (a) incorporate information about patient hormonal status into the study design and (b) resolve problems in patient accrual.

Carnosic acid and promotion of monocytic differentiation of HL60-G cells initiated by other agents.

BACKGROUND: Carnosic acid is a plant-derived polyphenol food preservative with chemoprotective effects against carcinogens when tested in animals. Recently, we showed that carnosic acid potentiates the effects of 1alpha,25-dihydroxyvitamin D3 (1alpha,25[OH]2D3) and of all-trans-retinoic acid (ATRA) on differentiation of human leukemia cells. We now examine the mechanisms associated with carnosic acid-induced enhancement of cell differentiation (in subline HL60-G) initiated by 1alpha,25(OH)2D3, ATRA, or 12-O-tetradecanoylphorbol-13-acetate (TPA). METHODS: We evaluated monocytic differentiation markers (CD11b, CD14, and monocytic serine esterase), cell cycle parameters, and cell proliferation rates after treatment of cells with different agents with or without carnosic acid. We also assessed the abundance of the vitamin D receptor (VDR), retinoid X receptor (RXR)-alpha, retinoic acid receptor (RAR)-alpha, and cell cycle-associated proteins by immunoblot analysis (p27, early growth response gene [EGR]-1, and p35Nck5a), the expression of corresponding genes by reverse transcription-polymerase chain reaction (RT-PCR), and the activity of VDR by electrophoretic mobility shift analysis. The two-sided nonparametric Kruskal-Wallis one-way analysis-of-variance test with Dunn's adjustment was used for statistical analyses. RESULTS: Monocytic differentiation induced by low (1 nM) concentrations of 1alpha,25(OH)2D3, ATRA, or TPA was enhanced by carnosic acid (10 microM), as shown by the increased expression of monocytic serine esterase (P<.001, P<.001, and P =.043, respectively) and of CD11b (P =.008, P =.046, and P =.041, respectively). Increased expression of CD14 was seen only for 1alpha,25(OH)2D3 and ATRA (P =.009 and P =.048, respectively) and also for several cell cycle-associated proteins. Carnosic acid in combination with 1alpha,25(OH)2D3 and ATRA resulted in decreased cell proliferation and blocked the cell cycle transition from G1 to S phase (P<.05). Carnosic acid alone increased the expression of VDR and RXR-alpha, but the expression was greatly enhanced in the presence of 1alpha,25(OH)2D3 and ATRA. In combination with TPA, carnosic acid potentiated the expression of VDR and RAR-alpha. CONCLUSION: Carnosic acid enhances a program of gene expression consistent with 1alpha,25(OH)2D3-, ATRA-, or TPA-induced monocytic differentiation of HL60-G cells.

Lipopolysaccharide-induced switch between retinoid receptor (RXR) alpha and glucocorticoid attenuated response gene (GARG)-16 messenger RNAs in cultured rat microglia.

Glucocorticoid-attenuated response genes (GARG) belong to a recently described family of genes responsive to the action of dexamethasone. Full-length cDNA of one member of this family, GARG16, has been cloned from rat microglia and regulation of its mRNA expression has been studied. Moreover, regulation of retinoid/retinoic acid activated transcription factor (RXR/RAR) mRNAs in mixed astrocyte and in purified microglia cultures has been investigated. RARbeta mRNA was undetectable in microglia by RT-PCR, whereas clearly present in the mixed cultures. RXRalpha, RARgamma, and GARG16 mRNAs were found in both culture systems. RXRalpha mRNA was strongly expressed in control microglia but rapidly declined upon treatment with LPS. Conversely, GARG16 mRNA was almost untraceable in control microglia but rapidly increased by LPS. Time-course studies revealed an oscillating behavior of expression of both mRNAs during the first 6 hr, which receded to control levels (RXRalpha high, GARG16 low) at 72 hr of LPS-treatment. Additionally, p38 MAPK and SEK phosphorylations peaked at 1 hr followed by steady declines, whereas MEK and c-Jun showed double peaks at 1+4 hr and 1+6 hr, respectively, before subsiding to control levels. This behavior was not observed in comparative studies with TNF-alpha, interleukin-10 (IL-10), or interferon-gamma inducible protein 10 (IP-10). Finally, inhibitors of p38 MAPK, p42/p44 ERK, and PKCalpha as well as the use of dexamethasone revealed major influences of the p38 MAPK-c-Jun-AP-1 signaling pathway on RXRalpha and GARG16 mRNA expressions. The counter regulatory control of GARG16 and RXRalpha mRNA expression is believed to be an example of a fine-tuned cellular mechanism to react to inflammatory stimuli.

Cellular retinol-binding protein expression and breast cancer.

BACKGROUND: The biologic activity of vitamin A depends, in part, on its metabolism to active nuclear receptor ligands, chiefly retinoic acid. The cellular retinol-binding protein (CRBP) binds vitamin A with high affinity and is postulated to regulate its uptake and metabolism. In this report, we analyze the expression of CRBP in normal and malignant breast tissues. METHODS: We evaluated CRBP expression by in situ hybridization in six reduction mammoplasty specimens and 49 human breast carcinoma specimens by use of digoxigenin-labeled RNA probes and in nine cultured mammoplasty specimens by northern or western blot analysis. Statistical significance was evaluated with the chi(2) test or Fisher's exact test if the sample sizes were small. All P values are from two-sided tests. RESULTS: CRBP was expressed in all 15 mammoplasty specimens (normal breast tissue) and in 33 of 35 available specimens of normal tissue adjacent to carcinoma. In contrast, 12 (24%) of 49 carcinoma lesions were uniformly negative for CRBP (P =.023 for comparison with adjacent normal breast tissue). The loss of CRBP expression was as frequent in ductal carcinoma in situ (six [27%] of 22) as in invasive lesions (six [22%] of 27), suggesting that it is a relatively early event in carcinogenesis and not associated with patient age, tumor grade, and expression of steroid receptors or c-Myc. Preliminary experiments did not find an association between CRBP and retinoic acid receptor beta loss, but most (four of five) CRBP-negative tumors were also retinoic acid receptor beta negative. CONCLUSION: CRBP is underexpressed in 24% (95% confidence interval = 12.5%-36.5%) of human breast carcinomas, implying a link between cellular vitamin A homeostasis and breast cancer. We hypothesize that the loss of CRBP restricts the effects of endogenous vitamin A on breast epithelial cells.

Immunohistochemical study of the receptors for retinoic acid in prostatic adenocarcinoma.

BACKGROUND: Retinoids play an important role in regulating cellular proliferation and differentiation. Although their effects are mediated by retinoic acid receptors (RARs) and retinoid X receptors (RXRs), limited information is available about the expression of RARs and RXRs in prostatic adenocarcinoma. We intended in this study to elucidate further the participation of those receptors in tumor progression of human prostate. MATERIALS AND METHODS: The immunohistochemical expression of RARs and RXRs proteins was studied using paraffin-embedded archival tissues obtained from patients with and without neoadjuvant hormonal therapies for prostatic adenocarcinoma. RESULTS: The immunoreactivity against RAR-alpha, RAR-gamma, RXR-alpha and RXR-gamma were detected in many, if not all, prostatic adenocarcinoma cells of the cases without and with neoadjuvant hormonal therapy, whereas less expression of both RAR-beta and RXR-beta were identified. Positively stained adenocarcinoma cells with RAR-beta and RXR-beta were found to be decreased in the cases with neoadjuvant therapy. In addition, the specimens showing positive immunoreaction of RAR-beta were limited to the cases of moderately- and poorly-differentiated but not well-differentiated, adenocarcinomas. CONCLUSION: We first demonstrated the expression of RARs and RXRs proteins in prostatic adenocarcinoma using subtype-specific antibodies. Immunohistochemistry using those antibodies might give an indication of susceptibility of the patients to retinoid therapy as a possible treatment of prostatic adenocarcinoma.

Chronic alcohol intake reduces retinoic acid concentration and enhances AP-1 (c-Jun and c-Fos) expression in rat liver.

Chronic ethanol intake may interfere with retinoid signal transduction by inhibiting retinoic acid synthesis and by enhancing activator protein-1 (AP-1) (c-Jun and c-Fos) expression, thereby contributing to malignant transformation. To determine the effect of ethanol on hepatic retinoid levels, retinoic acid receptors (RARs) and AP-1 (c-Jun and c-Fos) gene expression, chronic ethanol (36% of total calorie intake) pair-feeding was conducted on rats for a 1-month period. Retinoic acid, retinol, and retinyl ester concentrations in both liver and plasma were examined by using high-performance liquid chromatography (HPLC). Both retinoic acid receptor (alpha, beta, gamma) and AP-1 (c-Jun and c-Fos) expression in the rat liver were examined by using Western blot analysis. Treatment with high-dose ethanol led to a significant reduction of retinoic acid concentration in both the liver and the plasma (11- and 8.5-fold reduction, respectively), as compared with animals pair-fed an isocaloric control diet containing the same amount of vitamin A. Similar to the retinoic acid reductions, both retinol and retinyl palmitate levels in the livers of the alcohol-fed group decreased significantly, but in smaller fold reduction (6.5- and 2.6-fold reduction, respectively). Ethanol did not modulate the expression of RARalpha, -beta, and -gamma genes in the liver. However, chronic alcohol feeding enhanced AP-1 (c-Jun and c-Fos) expression by 7- to 8-fold, as compared with the control group. These data suggest that functional downregulation of RARs by inhibiting biosynthesis of retinoic acid and up-regulation of AP-1 gene expression may be important mechanisms for causing malignant transformation by ethanol.

Regulation of the mouse cellular retinoic acid-binding protein-I gene by thyroid hormone and retinoids in transgenic mouse embryos and P19 cells.

The regulation of mouse cellular retinoic acid-binding protein-I (CRABP-I) gene expression by the retinoids and thyroid hormones was examined, by using a beta-galactosidase (lacZ) reporter gene and a CRABP-I specific antibody, in transgenic mouse embryos and a mouse embryonal carcinoma cell line P19. The CRABP-lacZ reporter gene expression recapitulated the expression pattern of endogenous CRABP-I in the developing central nervous system. In mid-gestation mouse embryos the expression of both the transgene and the endogenous protein was elevated under the condition of hypovitaminosis A, suggesting that depletion of retinoic acid (RA) induced CRABP-I expression in embryos. Consistently, this reporter was suppressed by RA in P19 cells. In co-transfection experiments it was demonstrated that the expression of RAR beta, RAR gamma or RXR alpha suppressed this reporter expression. In experiments designed to alter the thyroid hormone status in animals it was demonstrated that both the reporter gene and the endogenous CRABP-I expression were reduced by triiodothyronine injection and were elevated in a hypothyroidic condition induced by feeding with iodine-deficient diet supplemented with 6-propyl-2-thiouracil. In co-transfection experiments it was also demonstrated that the expression of T3R beta suppressed the reporter expression in P19 cells. It was concluded that RA had a suppressive effect on CRABP-I gene expression in embryos and P19 cells and the effect could be mediated through RAR beta, RAR gamma or RXR alpha. A role of thyroid hormones in CRABP-I gene expression and vitamin A metabolism in animals is discussed.

Two novel RXR alpha isoforms from mouse testis.

We report the isolation from mouse testis cDNA of two novel RXR alpha isoforms, mRXR alpha 2 and mRXR alpha 3, with distinct sequences upstream of exon 2. These two isoforms encode a similar protein (mRXR alpha 2/3) which lacks that 28 N-terminal amino acid residues of the major RXR alpha isoform, mRXR alpha 1. The N-terminal activation function (AF-1) of mRXR alpha 2/3 appears altered when compared to that of mRXR alpha 1. mRXR alpha 2 and mRXR alpha 3 are specifically expressed in the testis, and their expression is strongly upregulated in this tissue at puberty. These observations increase the molecular complexity of RXRs, and indicate that RXR alpha may play a specific function during spermatogenesis.

Temporal expression of retinoic acid receptors in hamster fetus during organogenesis and alteration by retinoic acid treatment.

Retinoic acid receptors alpha, beta and gamma (RAR alpha, beta, gamma) mRNAs from whole 8- to 15-day-old hamster fetuses were characterized and quantitated by Northern blots and solution hybridization using riboprobes from cloned hamster RAR cDNAs, derived from 12-day fetal hamster library. Two RAR alpha transcripts of approximately 3.1 and approximately 3.5 kb, one transcript of RAR beta approximately 2.8 kb and one transcript of RAR gamma approximately 3.1 kb were observed. The relative abundance levels of these transcripts were RAR gamma > beta > alpha. RAR beta and gamma levels peaked at day 11, increasing approximately 4-fold (beta) and approximately 2.5-fold (gamma) above their initial values at day 8. RAR alpha did not change appreciably and peaked on day 14 at 1.7 x of its lowest level at day 9. Regulation patterns of the three RARs diverged between days 8 and 9 and 13 and 14 postcoitum (p.c.) and coordinately increased between days 9 and 13 and decreased between days 14 and 15 p.c. In 12-day-old conceptuses exposed to all-trans-retinoic acid, RAR alpha did not increase significantly, but RAR beta increased 12-fold at 4 hr and RAR gamma 2-fold at 1 hr after the maternal treatments.

Sensitive and specific detection of retinoid receptor subtype proteins in cultured cell and tumor extracts.

Subtype-specific antipeptide antibodies have been developed against each of the retinoic acid receptors (RARs alpha, beta, and gamma) and each of the retinoid X receptors (RXRs alpha, beta, and gamma). Each antibody reacts specifically with its respective recombinantly expressed protein but not with any of the other retinoid receptor subtypes, by both immunoblot and immunoprecipitation technology. We describe a sensitive and specific assay that combines the binding of cultured cell and tumor extracts to [3H]all-trans-retinoic acid or [3H]9-cis-retinoic acid with immunoprecipitation of the hormone-receptor complexes by the subtype-specific antibodies to determine the levels of functional retinoid receptor subtype proteins that are present. We also report the use of a hormone-binding assay that uses RAR- and RXR-selective compounds as competitors of the tritiated retinoids to ascertain the RAR and RXR subfamily profiles of these cells. HeLa cells contain all six retinoid receptor proteins ranging in concentration from 9 fmol/mg total protein for RAR beta and RXR gamma to 50 fmol/mg for RXR alpha. Hep G2 and HL60 cells express RAR alpha and RXR alpha proteins at approximately 20-60 fmol receptor/mg protein, and RAR beta is expressed at lower levels (approximately 5 fmol/mg) in Hep G2 cells. MCF-7 cells in culture express RAR alpha (approximately 32 fmol/mg), RAR gamma (approximately 35 fmol/mg), and RXR alpha (approximately 60 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Xenopus laevis cellular retinoic acid-binding protein: temporal and spatial expression pattern during early embryogenesis.

There is increasing evidence that retinoic acid (RA) has a role in establishing normal axial patterns during Xenopus laevis embryo-genesis. Several types of retinoid binding proteins are thought to mediate the effects of RA. We report the isolation of a cDNA, named xCRABP-b, which encodes a X. laevis cellular retinoic acid-binding protein (xCRABP). This cDNA hybridises to a transcript in gastrular stage embryos of approximately 3 kb, much larger than those CRABP transcripts expressed in mice. The expression of the xCRABP mRNA is generally restricted to tissues which are sensitive to the teratogenic effects of excess RA. It is likely, that during normal X. laevis embryogenesis, concentrations of RA in RA-responsive cells are modulated by the xCRABP gene product.

RZRs, a new family of retinoid-related orphan receptors that function as both monomers and homodimers.

Members of the superfamily of nuclear receptors share the greatest homology in their DNA-binding domains. We have used reverse transcription-polymerase chain reaction and highly degenerate primers based on the amino acid sequence of the zinc finger motif of known nuclear receptors to identify novel members of the family. Starting with rat brain RNA, we have isolated an orphan receptor that we call RZR beta. The sequence of its nearly full-length complementary DNA shows great similarity to RZR alpha, a receptor we recently identified from human umbilical vein endothelial cells. These RZR subtypes represent members of a new family of orphan nuclear receptors that most likely regulate specific gene expression. Sequence comparison with other known nuclear receptors reveals great similarity for both RZR subtypes to retinoic acid and retinoid-X receptors. By Northern blot analyses, we found RZR beta messenger RNA only in brain, whereas RZR alpha is expressed in many tissues. We show here that the RZRs bind as monomers to natural retinoid response elements formed by (A/G)GGTCA half-sites. However, a T-residue in the -1 position of this motif greatly enhances the DNA binding affinity of RZRs, whereas the -2 position has no influence. We show that RZRs can bind as homodimers on response elements formed by palindromes, inverted palindromes, or direct repeats of two TAGGTCA half-sites. Interestingly, these response elements display dramatically reduced affinity for retinoic acid receptor-retinoid-X receptor heterodimers. Thus, the 5'-flanking sequence of hexameric half-sites appears to be crucial to direct the activity of several nuclear receptors. On monomeric as well as dimeric binding sites, RZRs show constitutive transactivational activity that can be enhanced by unidentified components of fetal calf serum.

Fetal isoform of human retinoic acid receptor beta expressed in small cell lung cancer lines.

The retinoic acid receptor type beta (RAR beta) complementary DNA from a small cell tumor line was amplified, sequenced, and found to be homologous to the murine RAR beta 1. Seventeen lung tumor lines were analyzed. Five of seven small cell lung carcinoma lines expressed RAR beta 1, but only one other line (epidermoid) expressed the isoform, and this was at trace levels. Two other epidermoid lines, as well as three adenocarcinoma, two adenosquamous, and two large cell-derived lines did not express RAR beta 1. Nine adult human tissues, including lung, were analyzed, and in contrast to what has been reported for the mouse, undetectable or barely detectable levels were observed. On the other hand, a total of 13 different fetal tissues, at three different developmental stages, all expressed RAR beta 1. RAR beta 1 may be a master developmental gene in humans, and the remarkably specific association with small cell lung carcinoma suggests a molecular link between this type of cancer and development.