GATA-6 is expressed in the human adrenal and regulates transcription of genes required for adrenal androgen biosynthesis

GATA-6 and GATA-4 are members of a family of transcription factors (GATA 1-6) that share conserved zinc-finger DNA binding domains. Using semiquantitative RT-PCR, we found that the human adrenal expresses mRNA for GATA-6 but not GATA-4. A recent study showed GATA-6 expression in the adrenal reticularis, the source of adrenal androgens. To investigate the role of GATA-6 in regulation of adrenal cell steroidogenesis, luciferase reporter constructs containing the 5'-flanking DNA from steroidogenic acute regulatory protein, cholesterol side-chain cleavage (CYP11A), 17alpha-hydroxylase (CYP17), and dehydroepiandrosterone-sulfotransferase (SULT2A1) were cotransfected with an expression vector containing GATA-6 into adrenal NCI-H295R cells and nonsteroidogenic HEK293 cells. All promoter/reporter constructs were increased by GATA-6 in the adrenal model. However, in the HEK293 cells only SULT2A1 reporter activity was increased by GATA-6. One key difference between H295R and HEK293 cell lines is the differential expression of steroidogenic factor 1 (SF1). Transfection of HEK293 cells with both GATA-6 and SF1 significantly increased transcriptional activation of all reporter constructs above the effect of GATA-6 or SF1 alone. To determine whether the action of GATA-6 required SF1, we transfected HEK293 cells with each promoter construct plus and minus GATA-6, SF1, and/or the orphan nuclear repressor DAX1. DAX1 opposed SF1-activated transcription of many genes and abolished the GATA-6/SF1 ability to increase reporter activity. These results suggest that the adrenal uses GATA-6 to enhance transcription of steroid-metabolizing enzymes needed to produce dehydroepiandrosterone sulfate. Additionally, GATA-6 works in synergy with SF1 to maximally increase expression of enzymes needed to produce adrenal androgens.

Lymphocyte accumulation in the spleen of retinoic acid receptor-related orphan receptor gamma-deficient mice

The hormone nuclear receptor retinoic acid receptor-related orphan receptor gamma (RORgamma) plays important roles in thymocyte development and lymphoid organogenesis. RORgamma and its thymus-specific isoform RORgammat are expressed in the thymus, but not in the spleen and bone marrow (BM). However, RORgamma(-/-) mice have 2- to 3-fold more splenocytes than wild-type controls due to an accumulation of conventional resting B lymphocytes. The increase in B lymphocytes in RORgamma(-/-) mice is caused neither by abnormal B cell development in the BM nor by an obvious defect in the peripheral T cell compartment. Furthermore, analyses of BM chimeras using either RORgamma(-/-) or recombinase-activating gene-2(-/-) mice as recipients and wild-type or RORgamma(-/-) mice as donors, respectively, demonstrate that the splenic microenvironment of RORgamma(-/-) mice is defective, since wild-type T and B lymphocytes accumulated in these chimeric mice. In addition, T lymphocyte homeostasis was altered due to a lowered thymic output in RORgamma(-/-) mice. Collectively, these results suggest that RORgamma regulates lymphocyte homeostasis at multiple levels.

Continuous loss of oocytes throughout meiotic prophase in the normal mouse ovary

The number of germ cells reaches the maximum just prior to entry into meiosis, yet decreases dramatically by a few days after birth in the female mouse, rat, and human. Previous studies have reported a major loss at the pachytene stage of meiotic prophase during fetal development, leading to the hypothesis that chromosomal pairing abnormalities may be a signal for oocyte death. However, the identification as well as the quantification of germ cells in these studies have been questioned. A recent study using Mouse Vasa Homologue (MVH) as a germ cell marker reached a contradictory conclusion claiming that oocyte loss occurs in the mouse only after birth. In the present study, we established a new method to quantify murine germ cells by using Germ Cell Nuclear Antigen-1 (GCNA-1) as a germ cell marker. Comparison of GCNA-1 and MVH immunolabeling revealed that the two markers identify the same population of germ cells. However, nuclear labeling of GCNA-1 was better suited for counting germ cells in histological sections as well as for double labeling with the antibody against synaptonemal complex (SC) proteins in chromosome spreading preparations. The latter experiment demonstrated that the majority of GCNA-1-labeled cells entered and progressed through meiotic prophase during fetal development. The number of GCNA-1-positive cells in the ovary was estimated by counting the labeled cells retained in chromosome spreading preparations and also in histological sections by using the ratio estimation method. Both methods demonstrated a continuous decline in the number of GCNA-1-labeled cells during fetal development when the oocytes progress through meiotic prophase. These observations suggest that multiple causes are responsible for oocyte elimination.

Retinoid X receptor alpha represses GATA-4-mediated transcription via a retinoid-dependent interaction with the cardiac-enriched repressor FOG-2

Dietary vitamin A and its derivatives, retinoids, regulate cardiac growth and development. To delineate mechanisms involved in retinoid-mediated control of cardiac gene expression, the regulatory effects of the retinoid X receptor alpha (RXR alpha) on atrial naturietic factor (ANF) gene transcription was investigated. The transcriptional activity of an ANF promoter-reporter in rat neonatal ventricular myocytes was repressed by RXR alpha in the presence of 9-cis-RA and by the constitutively active mutant RXR alpha F318A indicating that liganded RXR confers the regulatory effect. The RXR alpha-mediated repression mapped to the proximal 147 bp of the rat ANF promoter, a region lacking a consensus retinoid response element but containing several known cardiogenic cis elements including a well characterized GATA response element. Glutathione S-transferase "pull-down" assays revealed that RXR alpha interacts directly with GATA-4, in a ligand-independent manner, via the DNA binding domain of RXR alpha and the second zinc finger of GATA-4. Liganded RXR alpha repressed the activity of a heterologous promoter-reporter construct containing GATA-response element recognition sites in cardiac myocytes but not in several other cell types, suggesting that additional cardiac-enriched factors participate in the repression complex. Co-transfection of liganded RXR alpha and the known cardiac-enriched GATA-4 repressor, FOG-2, resulted in additive repression of GATA-4 activity in ventricular myocytes. In addition, RXR alpha was found to bind FOG-2, in a 9-cis-RA-dependent manner. These data reveal a novel mechanism by which retinoids regulate cardiogenic gene expression through direct interaction with GATA-4 and its co-repressor, FOG-2.

Lipopolysaccharide represses cholesterol 7-alpha hydroxylase and induces binding activity to the bile acid response element II

BACKGROUND

Inflammatory states such as hepatitis and sepsis are frequently associated with alterations of bile acid synthesis. These conditions are mediated by bacterial wall products like lipopolysaccharide (LPS). Cholesterol 7-alpha hydroxylase is the rate-limiting enzyme of bile acid synthesis. Hydrophobic bile acids repress cholesterol 7-alpha hydroxylase transcription via binding to the farnesoid X receptor and interaction with the bile acid response element II in the cholesterol 7-alpha hydroxylase promoter.

METHODS

We tested the effect of LPS on hepatic expression of cholesterol 7-alpha hydroxylase in C57BL/6 mice and Wistar rats. Further, we analyzed the binding activity of hepatic nuclear extracts to the bile acid response element II and the binding site for farnesoid X receptor heterodimers (ecdysone response element).

RESULT

Lipopolysaccharide caused a 100-fold reduction of cholesterol 7-alpha hydroxylase mRNA levels in mice and a 10-fold reduction in rats. Protein levels of cholesterol 7-alpha hydroxylase also decreased in both species. These changes inversely correlated with the increased binding activity of nuclear proteins to the bile acid response element II and the ecdysone response element.

CONCLUSION

Lipopolysaccharide-induced repression of cholesterol 7-alpha hydroxylase occurs at the transcriptional level. The underlying mechanism involves an increased binding activity of nuclear proteins to the bile acid response element II and the ecdysone response element. In conclusion, the farnesoid and retinoid X receptors participate in LPS-induced cholesterol 7-alpha hydroxylase repression.

Orphan nuclear receptors in T lymphocyte development

Lymphocyte development is initiated from hematopoietic stem cells and can be divided into multiple phenotypically distinct stages. Transcription factors play important roles in programming the developmental process of lymphocytes. Recent studies have identified key roles of several orphan nuclear receptors in T lymphocyte development. The orphan nuclear receptor RORgamma has been shown to promote thymocyte survival by activating the expression of antiapoptotic protein Bcl-x(L). RORgamma is also required for the development of lymph nodes and Peyer's patches. The orphan receptors Nur77 and Nor1 are involved in TCR-mediated cell death and thymocyte-negative selection. These studies provide novel insights into the molecular mechanisms of T lymphocyte development.

Stereoselective synthesis of annular 9-cis-retinoids and binding characterization to the retinoid X receptor

Analogues of 9-cis-retinoic acid incorporating an alicyclic ring between the C19 and C10 positions have been synthesized and evaluated as ligands for the RXRalpha nuclear receptor. The stereocontrolled synthesis of these configurationally constrained retinoids combines a Stille cross-coupling and the Wittig reaction as key bond-forming steps. The palladium-catalyzed cross-coupling reaction of the beta-bromo-alpha,beta-unsaturated aldehydes 5 to dienylstannane 6 is very fast at room temperature, and takes place with preservation of the dienylstannane geometry. A highly stereoselective Wittig reaction afforded the C7-C8 bond connecting the hydrophobic ring to the retinoid side chain. The binding affinities of these compounds for the receptor were determined, and the structural and energetic rationale behind the affinity profile of the cyclic 9-cis-retinoic acid derivatives for the RXRalpha nuclear receptor was characterized by using Molecular Mechanics protocols.

Linkage between retinoid and fatty acid receptors: implications for breast cancer prevention

Certain dietary retinoids and polyunsaturated fatty acids (PUFAs) consistently inhibit progression of mammary carcinogenesis both in animal studies and cell culture, but clinically, their effect is inconsistent. New evidence of synergistic interaction between the nuclear receptors for the two groups of nutritional agents suggests that appropriate selective ligands from each group might be combined in breast cancer chemoprevention studies. Peroxisome proliferator-activated receptor (PPAR) gamma is a nuclear receptor that is activated by PUFAs, eicosanoids and antidiabetic agents such as troglitazone. Such activation can cause growth inhibition in human mammary cancer cells in culture and the effect is enhanced by ligands of retinoic acid receptor (RAR) and retinoid X receptor (RXR). In mouse mammary tissue in organ culture, an RXR-selective ligand has been shown to enhance the effect of troglitazone in suppressing carcinogen-induced pre-neoplastic changes. A PPAR/RXR heterodimer is involved in tumour growth inhibition and has been shown to bind directly to nuclear oestrogen response elements (ERE) independently of oestrogen receptor (ER) activity. A combination of an RXR-selective retinoid with either troglitazone or else a long-chain n-3 PUFA, is proposed for a short-term study in postmenopausal women after primary surgery for intraductal breast cancer. The resulting activation of PPAR/RXR expression may increase response to retinoid administration, especially in the presence of obesity and insulin resistance, because of the ability of PPAR gamma ligands to reduce insulin-like growth factor I (IGF-I) concentrations. Serial core biopsies of breast tissue over a short term are proposed to identify changes in phenotype, which may influence progression to invasiveness. In addition to cytomorphological criteria, expression of ER alpha and beta, RAR alpha and beta, and IGF-I receptor in the nucleus should be examined.

The orphan nuclear receptor REV-ERBalpha controls circadian transcription within the positive limb of the mammalian circadian oscillator

Mammalian circadian rhythms are generated by a feedback loop in which BMAL1 and CLOCK, players of the positive limb, activate transcription of the cryptochrome and period genes, components of the negative limb. Bmal1 and Per transcription cycles display nearly opposite phases and are thus governed by different mechanisms. Here, we identify the orphan nuclear receptor REV-ERBalpha as the major regulator of cyclic Bmal1 transcription. Circadian Rev-erbalpha expression is controlled by components of the general feedback loop. Thus, REV-ERBalpha constitutes a molecular link through which components of the negative limb drive antiphasic expression of components of the positive limb. While REV-ERBalpha influences the period length and affects the phase-shifting properties of the clock, it is not required for circadian rhythm generation.

Regulation of the TCRalpha repertoire by the survival window of CD4(+)CD8(+) thymocytes

T cell receptor (TCR) alpha alleles undergo primary and secondary rearrangement in double-positive (DP) thymocytes. By analyzing TCRalpha rearrangement in orphan nuclear receptor RORgamma-deficient mice, in which the DP lifespan is shorter, and in Bcl-x(L)-transgenic mice, in which the DP lifespan is extended, we show that the progression of secondary V(alpha) to J(alpha) rearrangements is controlled by DP thymocyte survival. In addition, because Bcl-x(L) induces a bias towards 3' J(alpha) usage in peripheral T cells, we conclude that the programmed cell death of DP thymocytes is not simply a consequence of failed positive selection. Rather, it limits the progression of rearrangement along the J(alpha) locus and the opportunities for positive selection, thereby regulating the TCRalpha repertoire.

Nuclear hormone receptors in T lymphocytes

Among the numerous steroid and orphan nuclear receptors encoded within mammalian genomes, several are involved in regulating immune system functions. We review here recent studies on the glucocorticoid receptor and the orphan receptors Nur77 and RORgamma. These molecules play key roles in the development and the effector functions of T lymphocytes.

The retinoid-inducible gene I: effect on apoptosis and mitogen-activated kinase signal pathways

BACKGROUND

The retinoid-inducible gene I (RIG1), belonging to the family of type II tumor suppressor genes, was isolated from human gastric cancer cells treated with all-trans retinoic acid. The activity of the RIG1 gene was investigated in this study.

MATERIALS AND METHODS

HtTA cervical and TSGH9201 gastric cancer cells were transiently transfected with expression vectors that synthesized RIG1-myc or RIG1-EGFP fusion protein. Cell growth was analyzed by measuring the incorporation of bromodeoxyuridine. Apoptosis was evaluated by the formation of in situ DNA breakage. The activities of mitogen-activated kinase signal pathways were analyzed using signal pathway trans-reporting systems.

RESULTS

Expression of the RIG1-myc fusion protein resulted in decreased cell growth. Both RIG1-EGFP and RIG1-myc fusion proteins induced cellular apoptosis that was characterized by the presence of apoptotic bodies and in situ DNA breakage. The transactivation activities of Elk1, c-Jun and CHOP proteins were suppressed by 80, 50 and 88%, respectively, in HtTA cells expressing the RIG1-myc fusion protein for two days. Similarly, the transactivation activities of the CHOP protein was suppressed in TSGH9201 and HtTA cells transiently expressing RIG1-myc and RIG1-EGFP, respectively.

CONCLUSION

The RIG1 fusion proteins exhibited growth suppressive and apoptosis-inducing activity. The protein negatively-regulated signal pathways of extracellular signal-regulated kinase, c-Jun N-terminal kinase and p38 mitogen-activated kinase.

High incidence of T-cell lymphomas in mice deficient in the retinoid-related orphan receptor RORgamma

Nuclear receptors are critical regulators of many physiological processes and have been shown to be involved in a variety of disease processes, including malignant neoplasms. Our laboratory is investigating the function of the retinoid-related orphan receptor gamma (RORgamma) and its possible role in disease. Studies of mice deficient in the expression of RORgamma demonstrated that this receptor plays a crucial role in the regulation of thymopoiesis and lymph node organogenesis. In this study, we show that changes in homeostasis in the thymus of RORgamma-/- mice are associated with a high incidence of T-cell lymphomas. Over 50% of the deficient mice of mixed genetic background die within the first 4 months as a result of thymic lymphomas. A high incidence of lymphomas was also observed in RORgamma-/- 129/SvEv mice. The lymphoblastic cells metastasized frequently to spleen and liver. No other tumor types were detected in any of RORgamma-/- mice that died during the course of the experiment, and none of the heterozygous mice developed thymic lymphomas. Lymphoma formation was associated with increased cellular proliferation and an increase in the number of apoptotic cells. When placed in culture, the RORgamma-/- lymphoblastic cells underwent accelerated "spontaneous" apoptosis at a rate similar to that of RORgamma-/- thymocytes. Upon prolonged culture, several lymphoblastic cell lines could be established. Analysis of the immunophenotype of the lymphoblastic cells showed that the CD4 and CD8 subpopulations varied substantially among different lymphomas. The established cell lines consisted mostly of CD44-CD25+CD4-CD8- cells. Our studies indicate that loss of RORgamma disturbs homeostasis in the thymus by enhancing apoptosis and cellular proliferation. The latter may enhance the probability of individual cells to acquire genetic alterations that make them escape negative selection and normal differentiation programs and as a consequence lead to increased susceptibility to the development of T-cell lymphoma.

The ROR nuclear orphan receptor subfamily: critical regulators of multiple biological processes

The nuclear receptor superfamily, a group of structurally related, ligand-dependent transcription factors, includes a large number of orphan receptors for which no ligand has yet been identified. These proteins function as key regulators of many physiological processes that occur during embryonic development and in the adult. The retinoid-related orphan receptors (RORs) alpha, beta, and gamma comprise one nuclear orphan receptor gene subfamily. RORs exhibit a modular structure that is characteristic for nuclear receptors; the DNA-binding domain is highly conserved and the ligand-binding domain is moderately conserved among RORs. By a combination of alternative promoter usage and exon splicing, each ROR gene generates several isoforms that differ only in their amino terminus. RORs bind as monomers to specific ROR response elements (ROREs) consisting of the consensus core motif AGGTCA preceded by a 5-bp A/T-rich sequence. RORE-dependent transcriptional activation by RORs is cell type-specific and mediated through interactions with nuclear cofactors. RORs have been shown to interact with certain corepressors as well as coactivators, suggesting that RORs are not constitutively active but that their activity is under some regulatory control. RORs likely can assume at least two different conformations: a repressive state, which allows interaction with corepressor complexes, and an active state, which promotes binding of coactivator complexes. Whether the transition between these two states is regulated by ligand binding and/or by phosphorylation remains to be determined. Ca2+/calmodulin-dependent kinase IV (CaMKIV) can dramatically enhance ROR-mediated transcriptional activation. This stimulation involves CaMKIV-mediated phosphorylation not of RORs, but likely of specific nuclear cofactors that interact with RORs. RORalpha is widely expressed. In the cerebellum, its expression is limited to the Purkinje cells. RORalpha-/- mice and the natural RORalpha-deficient staggerer mice exhibit severe cerebellar ataxia due to a defect in Purkinje cell development. In addition, these mice have thin long bones, suggesting a role for RORalpha in bone metabolism, and develop severe atherosclerosis when placed on a high-fat diet. Expression of RORbeta is very restricted. RORbeta is highly expressed in different parts of the neurophotoendocrine system, the pineal gland, the retina, and suprachiasmatic nuclei, suggesting a role in the control of circadian rhythm. This is supported by observations showing alterations in circadian behavior in RORbeta-/- mice. RORgamma, which is most highly expressed in the thymus, plays an important role in thymopoiesis. Thymocytes from RORgamma-/- mice undergo accelerated apoptosis. The induction of apoptosis is, at least in part, due to a down-regulation of the expression of the antiapoptotic gene Bcl-XL. In addition to the thynic phenotype, RORgamma-/- mice lack lymph nodes, indicating that RORgamma is essential for lymph node organogenesis. Overexpression of RORgamma has been shown to inhibit T cell receptor-mediated apoptosis in T cell hybridomas and to repress the induction of Fas-ligand and interleukin 2. These studies demonstrate that RORs play critical roles in the regulation of a variety of physiological processes. Further characterization of the mechanisms of action of RORs will not only lead to the identification of ROR target genes and provide additional insight into their normal physiological functions, but will also determine their roles in disease.

The role of orphan nuclear receptor in thymocyte differentiation and lymphoid organ development

T lymphocytes differentiate in the thymus through several phenotypically distinct stages that are tightly regulated by multiple nuclear transcription factors. Immature CD4+CD8+ double positive (DP) thymocytes make up a majority of the population in the thymus, and exhibit several phenotypic features distinct from mature T cells. DP thymocytes express only about 10% of surface TCR that are found on mature T cells and do not proliferate and produce IL-2 in response to stimulation. Several critical events of T lymphocyte maturation such as TCRalpha gene recombination, positive and negative selection, and CD4/CD8 lineage commitment occur around the DP stage. Recent studies from our group and others on the orphan nuclear receptor RORgamma and its thymus-specific isoform RORgammat support a critical role for this nuclear receptor in the regulation of DP thymocyte function. In addition, RORgamma is required for the development of lymph nodes and Peyer's patches.

A novel inducible expression system to study transdominant mutants of HIV-1 Vpr

In this study, an episomal system for ecdysone-inducible gene expression was developed. Human embryonic kidney 293 cells (293VE) expressing a heterodimer of modified ecdysone and retinoid X receptors and the Epstein-Barr nuclear antigen-1 were screened. Plasmids containing the EBV replication origin, oriP, and the ecdysone-response element could replicate and persist in 293VE cells to inducibly express luciferase or Vpr. The induction level, tested with luciferase reporter plasmid, varied among cell lines from 254- to 2056-fold. In one highly inducible cell line, HIV-1 Vpr was expressed well and caused G2 cell cycle arrest in the presence of the inducer, while in the absence of the inducer, no Vpr protein or cell cycle arrest could be detected. Using different selection markers, HIV-1 Vpr was coexpressed with Vpr mutants defective in phosphorylation at Ser79 and G2 cell cycle arrest activity. These Vpr mutants were transdominant to wild-type Vpr for G2 cell cycle arrest activity, but did not alter wild-type Vpr phosphorylation. It is likely that the transdominant mutants and wild-type Vpr compete for a downstream target(s) of G2 cell cycle arrest.

TNF-alpha inhibits 3T3-L1 adipocyte differentiation without downregulating the expression of C/EBPbeta and delta

Tumor necrosis factor-alpha (TNF-alpha) has been reported to inhibit adipocyte differentiation in which multiple transcription factors including CCAAT enhancer binding proteins (C/EBPs) and peroxisome proliferator-activated receptor (PPAR) gamma play an important role. Induction of C/EBPalpha and PPARgamma, which regulate the expression of many adipocyte-related genes, is dependent on the expression of C/EBPbeta and C/EBPdelta at the early phase of adipocyte differentiation. To elucidate the mechanism by which TNF-alpha inhibits adipocyte differentiation, we examined the effect of TNF-alpha on the expression of these transcription factors in mouse 3T3-L1 preadipocytes. TNF-alpha did not abrogate the induction of C/EBPbeta and C/EBPdelta in response to differentiation stimuli. In fully differentiated adipocytes, TNF-alpha rapidly induced C/EBPbeta and C/EBPdelta, whereas it downregulated the expression of C/EBPalpha and PPARgamma. Our results suggest that TNF-alpha inhibits adipocyte differentiation independently of the downregulation of C/EBPbeta and C/EBPdelta.

In vivo function of a differentiation inhibitor, Id2

Cell differentiation is an essential process for the development of various cell types that constitute multicellular organisms. During development, the large family of factors bearing a helix-loop-helix (HLH) motif participates profoundly in this process and these factors serve as good experimental tools for investigating mechanisms underlying tissue-specific differentiation. The HLH family includes both positive and negative regulators of cell differentiation: basic HLH (bHLH)-type transcription factors and Id proteins, respectively. Following an exciting decade focusing on bHLH factors, advances achieved in studies of the inhibitory factors in the last couple of years have placed them in the front line of the research on differentiation and proliferation control. Here, we present and discuss recent results obtained using Id2-deficient mice, which manifest intriguing phenotypes in various systems.

The retinoids and cancer prevention mechanisms

Carcinogenesis is a multistep process that converts normal cells into malignant cells. Once transformed, malignant cells acquire the ability to invade and metastasize, leading to clinically evident disease. During this continuum from normal to metastatic cells, carcinogenic steps can be arrested or reversed through pharmacological treatments, known as cancer chemoprevention. Chemoprevention strategies represent therapeutic interventions at early stages of carcinogenesis, before the onset of invasive cancer. Effective chemoprevention should reduce or avoid the clinical consequences of overt malignancies by treating early neoplastic lesions before development of clinically apparent signs or symptoms. Preclinical, clinical, and epidemiological data provide considerable support for cancer chemoprevention as an attractive therapeutic strategy. This clinical approach was validated in the recent tamoxifen randomized trial, demonstrating that a selective estrogen receptor modulator reduces the risk of breast cancer in women at high risk for this malignancy. Derivatives of vitamin A, the retinoids, have reported activity in treating specific premalignant lesions and reducing incidence of second primary tumors in patients with prior head and neck, lung or liver cancers. Whether the retinoids will prevent primary cancers at these sites is not yet known. Notably, a carotenoid (beta-carotene) was shown as inactive in primary prevention of lung cancers in high-risk individuals. This underscores the need for relevant in vitro models to identify pathways signaling chemopreventive effects. These models should assess the activity of candidate chemoprevention agents before the conduct of large and costly prevention trials. An improved understanding of cancer prevention mechanisms should aid in the discovery of new therapeutic targets and chemoprevention agents. Ideally, these agents should have tolerable clinical toxicities suitable for chronic administration to individuals at high risk for developing primary or second cancers. This article reviews what is now known from clinical and preclinical studies about the retinoids as cancer prevention agents.

Impaired distribution of retinoic acid receptors in the hindgut-tailgut region of murine embryos with anorectal malformations

BACKGROUND/PURPOSE

Retinoid-mediated signal transduction plays a crucial role in the organogenesis of various organs. To investigate the pathogenesis of anorectal malformations (ARM), the authors studied the distribution pattern of retinoic acid receptors (RARs) in ARM murine embryos induced by overdose of all-trans retinoic acid (ATRA).

METHODS

Pregnant mice were gavage-fed 100 mg/kg of ATRA on the ninth gestational day (E9.0). Embryos were obtained between E11.0 and E14.0 and were fixed immediately in a 4% paraformaldehyde solution. Frozen sections were prepared for immunohistochemistry using antibodies specifically raised against RAR-alpha, RAR-beta, and RAR-gamma.

RESULTS

Over 98% of the embryos administered ATRA had ARM; rectoprostatic urethral and rectocloacal fistulas were the most frequent anomalies. The immunoreactivity of RAR-alpha was found equally in the epithelium of hindgut-tailgut in normal embryos on E11.5. However, it was absent in the hindgut in the treated embryos. The immunoreactivities of RAR-beta and RAR-gamma showed no difference in the distal hindgut.

CONCLUSIONS

Impaired distribution of RAR-alpha in the hindgut-tailgut on E11.5 resulted in the incomplete partitioning of the cloaca and the rectourethral or rectocloacal fistula on E14.0. These results suggest that overdose of ATRA affects the distal hindgut development by directly disrupting the retinoid-mediated signalling pathway.

SF-1 (steroidogenic factor-1), C/EBPbeta (CCAAT/enhancer binding protein), and ubiquitous transcription factors NF1 (nuclear factor 1) and Sp1 (selective promoter factor 1) are required for regulation of the mouse aldose reductase-like gene (AKR1B7) expression in adrenocortical cells

The MVDP (mouse vas deferens protein) gene encodes an aldose reductase-like protein (AKR1B7) that is responsible for detoxifying isocaproaldehyde generated by steroidogenesis. In adrenocortical cell cultures, hormonal regulation of MVDP gene occurs through the cAMP pathway. We show that in adrenals, the pituitary hormone ACTH regulates MVDP gene expression in a coordinate fashion with steroidogenic genes. Cell transfection and DNA-binding studies were used to investigate the molecular mechanisms underlying MVDP gene regulation in Y1 adrenocortical cells. Progressive deletions of upstream regulatory regions identified a -121/+41 fragment that was sufficient for basal and cAMP-mediated transcriptional activities. Gel shift assays showed that CTF1/nuclear factor 1 (NF1), CCAAT enhancer binding protein-ss (C/EBPss), and selective promoter factor 1 (Sp1) factors bound to cis-acting elements at positions -76, -61, and -52, respectively. We report that the cell-specific steroidogenic factor-1 (SF-1) interacts specifically with a novel regulatory element located in the downstream half-site of the proximal androgen response element (AREp) at position -102. Functional analysis of SF-1 and NF1 sites in the -121/+41 promoter showed that mutation of one of them decreases both constitutive and forskolin-stimulated promoter activity without affecting the fold induction (forskolin stimulated/basal). Individual mutations of C/EBP and Sp1 sites resulted in a loss of more than 50% of the cAMP-dependent induction. When both sites were mutated simultaneously, cAMP responsiveness was nearly abolished. Thus, in adrenocortical cells, both SF-1 and NF1 are required for high expression of the MVDP promoter while Sp1 and C/EBPss functionally interact in an additive manner to mediate cAMP-dependent regulation. Furthermore, we report that MVDP gene regulation is impaired in stably transfected Y1 clones expressing DAX-1. Taken together, our findings suggest that detoxifying enzymes of the aldose reductase family may constitute new potential targets for regulators of adrenal and gonadal differentiation and function, e.g. SF-1 and DAX-1.

Genomic structure of the gene for mouse germ-cell nuclear factor (GCNF). II. Comparison with the genomic structure of the human GCNF gene

BACKGROUND

Germ-cell nuclear factor (GCNF, NR6AI) is an orphan nuclear receptor. Its expression pattern suggests it functions during embryogenesis, in the placenta and in germ-cell development. Mouse GCNF cDNA codes for a protein of 495 amino acids, whereas the four reported human cDNA variants code for proteins of 454 to 480 amino acids. Apart from this size difference, there is sequence conservation of up to 98.7%. To elucidate the genomic structure that gives rise to the different human GCNF mRNAs, the sequence information of the human GCNF locus is compared to the previously reported structure of the mouse locus.

RESULTS

The genomic structures of the mouse and human GCNF genes are highly conserved. The comparison reveals that the shorter human protein results from skipping the 45 base-pair third exon. Three different human isoforms - GCNF-1, GCNF-2a and GCNF-2b - are generated by differential usage of alternative splice acceptor sites of the fourth and the seventh exon.

CONCLUSION

By homology with the mouse gene, 11 GCNF coding exons can be defined on human chromosome 9. All human GCNF cDNAs identified so far are, however, derived from mRNAs generated by splicing the fourth to the second exon. Although the genomic sequence is highly conserved, the analysis suggests that alternative splicing generates a higher complexity of human GCNF isoforms compared with the situation in the mouse.