Liver Receptor Homolog-1 Expression Research Articles

The nuclear receptor liver receptor homolog-1 is an estrogen receptor target gene.

Liver receptor homolog-1 (LRH-1) is a nuclear receptor previously known to have distinct functions during mouse development and essential roles in cholesterol homeostasis. Recently, a new role for LRH-1 has been discovered in tumor progression, giving LRH-1 potential transforming functions. In order to identify critical factors stimulating LRH-1 expression leading to deregulated cellular proliferation, we studied its expression and its regulation in several breast cancer cell lines. We observed that LRH-1 expression was increased in estrogen receptor (ER) alpha expressing cell lines, whereas weak-to-no expression was found in nonexpressing ERalpha cell lines. In MCF7, LRH-1 expression was highly induced after treatment with 17beta-estradiol (E2). This transcriptional regulation was the result of a direct binding of the ER to the LRH-1 promoter, as demonstrated by gelshift and chromatin immunoprecipitation assays. Interestingly, siRNA-mediated inactivation of LRH-1 decreased the E2-dependent proliferation of MCF7 cells. Finally, LRH-1 protein expression was detected by immunohistochemistry in tumor cells of human mammary ductal carcinomas. Altogether, these data demonstrate that LRH-1 is transcriptionally regulated by the ER alpha and reinforce the hypothesis that LRH-1 could exert potential oncogenic effects during breast cancer formation.

Temporal and spatial expression of liver receptor homologue‐1 (LRH‐1) during embryogenesis suggests a potential role in gonadal development

Liver receptor homologue-1 (LRH-1), an orphan member of the nuclear receptor family highly expressed in adult mouse ovary, is closely related to steroidogenic factor 1 (SF-1), known to be important in gonadal formation. To analyze the potential role of LRH-1 in gonadal differentiation, we compared LRH-1 and SF-1 expression during mouse embryonic and postnatal development. LRH-1 expression was first detected in the urogenital ridge before sexual determination, in primordial germ cells and surrounding somatic cells; expression persisted after differentiation into testes and ovaries. Of interest, LRH-1 expression declined in the developing ovary and testis at embryonic day 15.5 but increased again just after birth in the ovary in granulosa cells and transiently in oocytes of developing follicles. By comparing and contrasting LRH and SF-1 expression with the two tissue-specific steroidogenic markers, cytochromes P450 aromatase and P450 17alpha-hydroxylase/17,20 lyase, we provide evidence for a potential role for LRH-1 in gonadal development, the initiation of folliculogenesis and regulation of estrogen biosynthesis within the ovary.

The Orphan Nuclear Receptor, Liver Receptor Homolog-1, Regulates Cholesterol Side-Chain Cleavage Cytochrome P450 Enzyme in Human Granulosa Cells

After ovulation, there is a shift in ovarian steroidogenesis from an estrogen-producing ovarian follicle to a progesterone-producing corpus luteum. The first step in human ovarian steroidogenesis is catalyzed by cholesterol side-chain cleavage cytochrome P450 (CYP11A1) enzyme. Steroidogenic factor-1 is an orphan nuclear receptor that regulates several steroidogenic enzymes, including CYP11A1. Liver receptor homolog-1 (LRH-1) is another orphan nuclear receptor that is expressed in the human ovary. After ovulation there is a down-regulation in steroidogenic factor-1, which is associated with an up-regulation of LRH-1 expression. These changes coincide with increased level of CYP11A1 expression in human corpus luteum. In this study, we examined the role of LRH-1 in the regulation of human granulosa cell CYP11A1 expression. Cotransfection of human granulosa cell tumor cells with CYP11A1 promoter and LRH-1 expression vector resulted in a significant increase in CYP11A1 expression. Deletion analysis revealed two putative LRH-1 binding sites at -1580 and -40, which was confirmed by EMSA. Dosage-sensitive sex-reversal-adrenal hypoplasia congenita critical region on the X chromosome, gene-1 inhibited LRH-1 stimulated CYP11A1 expression, and that was not overcome by the presence of PKA agonist. We conclude that CYP11A1 expression in human granulosa cells is regulated by LRH-1. We propose that LRH-1 could be the major transcription factor for the post-ovulatory surge in human ovarian steroidogenesis.

Liver receptor homolog 1 contributes to intestinal tumor formation through effects on cell cycle and inflammation

Liver receptor homolog 1 (LRH-1) is an orphan nuclear receptor that synergizes with beta-catenin/T cell factor 4 signaling to stimulate intestinal crypt cell renewal. We evaluated here the impact of haploinsufficiency of LRH-1 on intestinal tumorigenesis by using two independent mouse models of human colon tumorigenesis. Haploinsufficiency of LRH-1 blunts intestinal tumorigenesis in the ApcMin/+ mice, a genetic model of intestinal cancer. Likewise, Lrh-1+/- mice are protected against the formation of aberrant crypt foci in the colon of mice exposed to the carcinogen azoxymethane. LRH-1 gene expression is reduced in tumors that express elevated levels of the proinflammatory cytokine TNF-alpha. Reciprocally, decreased LRH-1 expression in Lrh-1+/- mice attenuates TNF-alpha expression. Compared with normal human colon, expression and subcellular localization of LRH-1 is significantly altered in neoplastic colon. In combination, these data suggest a role of LRH-1 in the initiation of intestinal tumorigenesis both by affecting cell cycle control as well as through its impact on inflammatory pathways.

Interactions between Prostaglandin E2, Liver Receptor Homologue-1, and Aromatase in Breast Cancer

Abstract Local synthesis of estrogens within breast adipose tissue by cytochrome P450 aromatase contributes to the growth of postmenopausal breast cancers. One of the major stimulators of aromatase expression in breast is prostaglandin E2 (PGE2) derived from tumorous epithelium and/or infiltrating macrophages. Recently, the orphan nuclear receptor, liver receptor homologue-1 (LRH-1), has also been shown to regulate aromatase expression in breast adipose tissue. We therefore examined the expression of, and correlations between, aromatase and LRH-1 mRNA in a panel of breast carcinoma tissues and adjacent adipose tissue. LRH-1 mRNA expression was low in normal breast tissue but markedly elevated in both breast carcinoma tissue and adipose tissue surrounding the tumor invasion (thereby paralleling aromatase expression). Laser capture microdissection localized the site of LRH-1 expression to tumor epithelial cells but not to intratumoral stromal cells. A strong correlation between LRH-1 and aromatase mRNA levels was observed in tumor-containing adipose tissue but not in tumor tissue. Ectopic expression of LRH-1 in primary human adipose stromal cells strongly activated endogenous aromatase mRNA expression and enzyme activity. Finally, treatment of adipose stromal cells with PGE2 induced expression of both LRH-1 and aromatase. We suggest that PGE2 derived from breast tumor tissue may increase aromatase expression in the surrounding adipose stroma in part by inducing LRH-1 in these cells. The roles of LRH-1 in breast cancer proliferation merit further study.

Liver receptor homolog-1 stimulates the progesterone biosynthetic pathway during follicle-stimulating hormone-induced granulosa cell differentiation.

FSH-stimulated granulosa cell differentiation is associated with the induction of the LH receptor (LHr) as well as induction of the estrogen and progesterone biosynthetic pathways. Although activation of the cAMP-protein kinase A pathway is sufficient to stimulate progesterone production, additional pathways are required for the induction of the LHr and p450 aromatase. The orphan nuclear receptor, liver receptor homolog-1 (LRH-1), is expressed in granulosa cells and has been shown to synergize with the cAMP signaling system to regulate the gonadal type II aromatase promoter in transient transfection assays. To determine whether LRH-1 can interact with the cAMP pathway in the induction of aromatase and the LHr, we examined the effects of an adenoviral vector that directs the expression of human LRH-1 (Ad-LRH-1) on FSH-stimulated granulosa cell differentiation. Infection of undifferentiated granulosa cells with LRH-1 alone had no effect on estrogen production, progesterone production, or the expression of the LHr. However, combination of FSH stimulation and Ad-LRH-1 infection led to significantly greater progesterone production and increases in mRNA for p450 side-chain cleavage and 3beta-hydroxysteroid dehydrogenase than granulosa cells stimulated by FSH alone. However, infection with Ad-LRH-1 did not stimulate estradiol production or increases in mRNA for p450 aromatase or the LHr above that seen with FSH treatment alone. Moreover, infection with Ad-LRH-1 was able to overcome H-89 inhibition of FSH-stimulated progesterone but not estrogen production. Collectively, these observations support a direct role for LRH-1 in the induction of the progesterone but not the estrogen biosynthetic pathway during granulosa cell differentiation.

Differential expression of steroidogenic factor-1/adrenal 4 binding protein and liver receptor homolog-1 (LRH-1)/fetoprotein transcription factor in the rat testis: LRH-1 as a potential regulator of testicular aromatase expression.

Aromatase converts testicular androgens to estrogens, which are essential for male fertility. Aromatase expression in testis occurs via transcription from promoter II, and requires the presence of a nuclear receptor half-site that binds the orphan receptor steroidogenic factor-1 [SF-1 (nuclear receptor 5A1)] to mediate basal and (in part) cAMP-induced transcription. We hypothesized that liver receptor homolog-1 (LRH-1) (nuclear receptor 5A2), a receptor closely related to SF-1, could also play a role in regulating aromatase expression in the testis. We demonstrate expression of LRH-1 in adult rat and immature mouse Leydig cells (LHR-1 > SF-1) as well as in pachytene spermatocytes and round spermatids but not in Sertoli cells, which in contrast, express high levels of SF-1. In transient transfection assays using TM3 Leydig cells and TM4 Sertoli cells, a rat promoter II luciferase reporter construct was stimulated by cotransfection of LRH-1 expression vector. Mutation analysis showed that induction by LRH-1 in TM3 and TM4 cells requires an AGGTCA motif at position -90, to which LRH-1 bound in gel shift analysis. We therefore provide evidence that LRH-1 plays an important role in the regulation of aromatase expression in Leydig cells. The colocalization of LRH-1 and aromatase to multiple testis cell types suggests that LRH-1 may have important effects on estrogen production, testis development, spermatogenesis, and testicular carcinogenesis.

Expression of LRH-1 and SF-1 in the mouse ovary: localization in different cell types correlates with differing function

Steroid biosynthesis in ovary is enhanced by the orphan nuclear receptor, steroidogenic factor-1 (SF-1); however, we reported that liver receptor homolog-1 (LRH-1), a closely related receptor to SF-1, is also expressed in mouse ovary. To further investigate the role of LRH-1 in mouse ovary, we used in situ hybridization to identify the cell types that express LRH-1 versus SF-1, and carried out functional studies to determine the role of LRH-1 in the regulation of the human ( h) ovary-specific CYP19 promoter. LRH-1 expression was found to be abundant and highly restricted to cells involved in estrogen biosynthesis-granulosa cells during the estrous cycle, and in corpora lutea (CL) of pregnancy. In contrast, SF-1 was expressed most highly in C 19-steroid-producing theca cells and interstitium, and at low levels in granulosa and luteal cells. Transfection studies using granulosa cells demonstrated that LRH-1 is a potent regulator of both basal and forskolin-induced transcription of the ovary-specific hCYP19 promoter. This activity was dependent upon two nuclear receptor half-sites within the proximal hCYP19 promoter. Based on these findings, we propose that LRH-1 plays an important role as a competence factor in regulating aromatase, and thus estrogen biosynthesis, in ovary.

Liver receptor homolog 1 controls the expression of the scavenger receptor class B type I.

The scavenger receptor class B type I (SR-BI), which mediates selective cellular cholesterol uptake from high-density lipoproteins (HDLs), plays a key role in reverse cholesterol transport. The orphan nuclear receptor liver receptor homolog 1 (LRH-1) and SR-BI are co-expressed in liver and ovary, suggesting that LRH-1 might control the expression of SR-BI in these tissues. LRH-1 induces human and mouse SR-BI promoter activity by binding to an LRH-1 response element in the promoter. Retroviral expression of LRH-1 robustly induces SR-BI, an effect associated with histone H3 acetylation on the SR-BI promoter. The decrease in SR-BI mRNA levels in livers of LRH-1(+/-) animals provides in vivo evidence that LRH-1 regulates SR-BI expression. Our data demonstrate that SR-BI is an LRH-1 target gene and underscore the pivotal role of LRH-1 in reverse cholesterol transport.

Liver Receptor Homologue-1 (LRH-1) Regulates Expression of Aromatase in Preadipocytes

Estrogen biosynthesis from C(19) steroids is catalyzed by aromatase cytochrome P450. Aromatase is expressed in breast adipose tissue through the use of a distal, cytokine-responsive promoter (promoter I.4). Breast tumors, however, secrete soluble factors that stimulate aromatase expression through an alternative proximal promoter, promoter II. In other estrogenic tissues such as ovaries, transcription from promoter II requires the presence of the Ftz-F1 homologue steroidogenic factor-1 (SF-1); adipose tissue, however, does not express SF-1. We have explored the hypothesis that in adipose tissue, an alternative Ftz-F1 family member, liver receptor homologue-1 (LRH-1), substitutes for SF-1 in driving transcription from promoter II. In transient transfection assays using 3T3-L1 preadipocytes, promoter II reporter constructs were modestly (2-3-fold) stimulated by either treatment with activators of protein kinases A or C (PKA/C) or by cotransfection with LRH-1. In combination, these treatments synergistically activated promoter II (>30-fold). Induction by LRH-1 (but not by PKA/C) required an AGGTCA motif at -130 base pairs, to which LRH-1 bound in gel shift assays. Activity of GAL4-LRH-1 fusion proteins was not altered by activators of PKA or PKC. Quantitative real-time PCR revealed that LRH-1 (but not SF-1) is expressed in the preadipocyte fraction of human adipose tissue at levels comparable with that of liver. Differentiation of cultured human preadipocytes into mature adipocytes was associated with a time-dependent induction of peroxisome proliferator-activated receptor-gamma (PPARgamma), and rapid loss of LRH-1 and aromatase expression. We conclude that LRH-1 is a preadipocyte-specific nuclear receptor that regulates expression of aromatase in adipose tissue. Alterations in LRH-1 expression and/or activity in adipose tissue could therefore have considerable effects on local estrogen production and breast cancer development.