Mouse strain susceptibility to gonadectomy-induced adrenocortical tumor formation correlates with the expression of GATA-4 and luteinizing hormone receptor

Dlk1 is a novel adrenocortical stem/progenitor cell marker that predicts malignancy in adrenocortical carcinoma

Disruption of processes involved in tissue development and homeostatic self-renewal is increasingly implicated in cancer initiation, progression, and recurrence. The adrenal cortex is a dynamic tissue that undergoes life-long turnover. Here, using genetic fate mapping and murine adrenocortical carcinoma (ACC) models, we have identified a population of adrenocortical stem cells that express delta-like non-canonical Notch ligand 1 (DLK1). These cells are active during development, near dormant postnatally but are re-expressed in ACC. In a study of over 200 human ACC samples, we have shown DLK1 expression is ubiquitous and is an independent prognostic marker of recurrence-free survival. Paradoxically, despite its progenitor role, spatial transcriptomic analysis has identified DLK1 expressing cell populations to have increased steroidogenic potential in human ACC, a finding also observed in four human and one murine ACC cell lines. Finally, the cleavable DLK1 ectodomain is measurable in patients' serum and can discriminate between ACC and other adrenal pathologies with high sensitivity and specificity to aid in diagnosis and follow-up of ACC patients. These data demonstrate a prognostic role for DLK1 in ACC, detail its hierarchical expression in homeostasis and oncogenic transformation and propose a role for its use as a biomarker in this malignancy.

Adrenal gland responses surgical castration and immunocastration by different compensatory manners to increase DHEA secretion

Androgen from the testis and weak androgens from the adrenal cortex may interact with each other and affect their synthesis and secretion due to their similar functions. The purpose of this study was to investigate the compensatory effect of adrenal in rats after immunocastration and surgical castration, and the interaction between the hypothalamic-pituitary-testis (HPT) axis and the hypothalamic-pituitary-adrenal (HPA) axis. 24 male SD rats aged 8 weeks were randomly divided into three groups and accepted treatments: surgical castration group, immunocastration group and control group. In both surgical castration and immunocastration groups, the secretion of adrenocorticotropic hormone (ACTH) and dehydroepiandrosterone (DHEA) hormones was significantly increased compared with the control group (p < 0.05). In the HPT axis of the immunocastration group, the KISS1 expression was up-regulated, whereas GPR54, LH and LHR expression were down-regulated (p < 0.05). The expression levels of CRH, POMC and MC2R genes were also significantly up-regulated (p < 0.05). In addition, in the immunocastration group, the expression of adrenal LHR mRNA expression was decreased (p < 0.05). The expression of HPT axis genes and adrenal LHR were up-regulated in the surgical castration group (p < 0.05). These results show that in both immunocastration and surgical castration, adrenal androgen is increased, suggesting that the adrenal gland plays a compensatory role. Moreover, it also shows that different castration treatments have effects on adrenal steroid secretion through different mechanisms.

Pregnancy in patients with adrenocortical carcinoma: a case-based discussion

Although adrenocortical carcinoma (ACC) during pregnancy is rare, a retrospective review of a case series at our hospital revealed that almost one third of our patients were women in childbearing age. Given that the age of maternity is increasing, dealing with a tumor diagnosis during pregnancy and the need for fertility planning in cancer survivors is likely to become more frequent.We thus carried out a case-based discussion regarding: i) diagnosing and treating an ACC during pregnancy; ii) patients conceiving while on mitotane; iii) ACC survivors with a maternal desire.In each of these cases, it is important to provide patients with sufficient information, to offer medical advice and psychological support, to personalize treatments in accordance with the wishes of the patient and her relatives, and to collaborate with other specialists since a multidisciplinary expert team is required to manage each case individually.

Transgenic Mouse Models to Study the Development and Maintenance of the Adrenal Cortex

The cortex of the adrenal gland is organized into concentric zones that produce distinct steroid hormones essential for body homeostasis in mammals. Mechanisms leading to the development, zonation and maintenance of the adrenal cortex are complex and have been studied since the 1800s. However, the advent of genetic manipulation and transgenic mouse models over the past 30 years has revolutionized our understanding of these mechanisms. This review lists and details the distinct Cre recombinase mouse strains available to study the adrenal cortex, and the remarkable progress total and conditional knockout mouse models have enabled us to make in our understanding of the molecular mechanisms regulating the development and maintenance of the adrenal cortex.

Excess dietary zinc drives a Cushing's-like syndrome in ovariectomized mice - Implications for postmenopausal obesity

Postmenopausal women have an increased risk of obesity, but the underlying cause is not clear. We unexpectedly found that excess dietary zinc induced severe obesity and a Cushing's-like syndrome without increased food intake in ovariectomized (Ovx) but not in sham-operated mice. Zinc accumulated in the adrenal glands and inhibited adrenal 17,20-lyase activity and steroid synthesis. As adrenal steroids are the only source of estrogen in Ovx mice, estrogen deficiency induced adrenal hyperplasia, glucocorticoid overproduction, and consequent development of a Cushing's-like syndrome. Adrenal steroid supplementation prevented the effects of zinc. Plasma zinc was positively correlated with cortisol level and negatively correlated with the levels of adrenal steroids and estrogen in obese postmenopausal women. The finding of a link between dietary zinc, estrogen deficiency, and postmenopausal obesity, implies that postmenopausal obesity might be prevented by supplementation with a adrenal steroid and avoiding excess dietary zinc.

Stem cell function and plasticity in the normal physiology of the adrenal cortex

The adrenal cortex functions to produce steroid hormones necessary for life. To maintain its functional capacity throughout life, the adrenal cortex must be continually replenished and rapidly repaired following injury. Moreover, the adrenal responds to endocrine-mediated organismal needs, which are highly dynamic and necessitate a precise steroidogenic response. To meet these diverse needs, the adrenal employs multiple cell populations with stem cell function. Here, we discuss the literature on adrenocortical stem cells using hematopoietic stem cells as a benchmark to examine the functional capacity of particular cell populations, including those located in the capsule and peripheral cortex. These populations are coordinately regulated by paracrine and endocrine signaling mechanisms, and display remarkable plasticity to adapt to different physiological and pathological conditions. Some populations also exhibit sex-specific activity, which contributes to highly divergent proliferation rates between sexes. Understanding mechanisms that govern adrenocortical renewal has broad implications for both regenerative medicine and cancer.

DLK1/PREF1 marks a novel cell population in the human adrenal cortex

The adrenal cortex governs fundamental metabolic processes though synthesis of glucocorticoid, mineralocorticoids and androgens. Studies in rodents have demonstrated that the cortex undergoes a self-renewal process and that capsular/subcapsular stem/progenitor cell pools differentiate towards functional steroidogenic cells supporting the dynamic centripetal streaming of adrenocortical cells throughout life. We previously demonstrated that the Notch atypical ligand Delta-like homologue 1 (DLK1)/preadipocyte factor 1 (PREF1) is expressed in subcapsular Sf1 and Shh-positive, CYP11B1-negative and CYP11B2-partially positive cortical progenitor cells in rat adrenals, and that secreted DLK1 can modulate GLI1 expression in H295R cells. Here we show that the human adrenal cortex remodels with age to generate clusters of relatively undifferentiated cells expressing DLK1. These clusters (named DLK1-expressing cell clusters or DCCs) increased with age in size and were found to be different entities to aldosterone-producing cell clusters, another well-characterized and age-dependent cluster structure. DLK1 was markedly overexpressed in adrenocortical carcinomas but not in aldosterone-producing adenomas. Thus, this data identifies a novel cell population in the human adrenal cortex and might suggest a yet-to be identified role of DLK1 in the pathogenesis of adrenocortical carcinoma in humans.

At the Crossroads of Fate-Somatic Cell Lineage Specification in the Fetal Gonad

The reproductive endocrine systems are vastly different between males and females. This sexual dimorphism of the endocrine milieu originates from sex-specific differentiation of the somatic cells in the gonads during fetal life. Most gonadal somatic cells arise from the adrenogonadal primordium. After separation of the adrenal and gonadal primordia, the gonadal somatic cells initiate sex-specific differentiation during gonadal sex determination with the specification of the supporting cell lineages: Sertoli cells in the testis vs granulosa cells in the ovary. The supporting cell lineages then facilitate the differentiation of the steroidogenic cell lineages, Leydig cells in the testis and theca cells in the ovary. Proper differentiation of these cell types defines the somatic cell environment that is essential for germ cell development, hormone production, and establishment of the reproductive tracts. Impairment of lineage specification and function of gonadal somatic cells can lead to disorders of sexual development (DSDs) in humans. Human DSDs and processes for gonadal development have been successfully modeled using genetically modified mouse models. In this review, we focus on the fate decision processes from the initial stage of formation of the adrenogonadal primordium in the embryo to the maintenance of the somatic cell identities in the gonads when they become fully differentiated in adulthood.

Novel genes involved in pathophysiology of gonadotropin-dependent adrenal tumors in mice

Specific inbred strains and transgenic inhibin-α Simian Virus 40 T antigen (inhα/Tag) mice are genetically susceptible to gonadectomy-induced adrenocortical neoplasias. We identified altered gene expression in prepubertally gonadectomized (GDX) inhα/Tag and wild-type (WT) mice. Besides earlier reported Gata4 and Lhcgr, we found up-regulated Esr1, Prlr-rs1, and down-regulated Grb10, Mmp24, Sgcd, Rerg, Gnas, Nfatc2, Gnrhr, Igf2 in inhα/Tag adrenal tumors. Sex-steroidogenic enzyme genes expression (Srd5a1, Cyp19a1) was up-regulated in tumors, but adrenal-specific steroidogenic enzyme (Cyp21a1, Cyp11b1, Cyp11b2) down-regulated. We localized novel Lhcgr transcripts in adrenal cortex parenchyma and in non-steroidogenic A cells, in GDX WT and in intact WT mice. We identified up-regulated Esr1 as a potential novel biomarker of gonadectomy-induced adrenocortical tumors in inhα/Tag mice presenting with an inverted adrenal-to-gonadal steroidogenic gene expression profile. A putative normal adrenal remodeling or tumor suppressor role of the down-regulated genes (e.g. Grb10, Rerg, Gnas, and Nfatc2) in the tumors remains to be addressed.

GLI1+ progenitor cells in the adrenal capsule of the adult mouse give rise to heterotopic gonadal-like tissue

As certain strains of mice age, hyperplastic lesions resembling gonadal tissue accumulate beneath the adrenal capsule. Gonadectomy (GDX) accelerates this heterotopic differentiation, resulting in the formation of wedge-shaped adrenocortical neoplasms that produce sex steroids. Stem/progenitor cells that reside in the adrenal capsule and retain properties of the adrenogonadal primordium are thought to be the source of this heterotopic tissue. Here, we demonstrate that GLI1⁺ progenitors in the adrenal capsule give rise to gonadal-like cells that accumulate in the subcapsular region. A tamoxifen-inducible Cre driver (Gli1-creER^T2) and two reporters (R26R-lacZ, R26R-confetti) were used to track the fate of GLI1⁺ cells in the adrenal glands of B6D2F2 mice, a strain that develops both GDX-induced adrenocortical neoplasms and age-dependent subcapsular cell hyperplasia. In gonadectomized B6D2F2 mice GLI1⁺ progenitors contributed to long-lived adrenal capsule cells and to adrenocortical neoplasms that expressed Gata4 and Foxl2, two prototypical gonadal markers. Pdgfra, a gene expressed in adrenocortical stromal cells, was upregulated in the GDX-induced neoplasms. In aged non-gonadectomized B6D2F2 mice GLI1⁺ progenitors gave rise to patches of subcapsular cell hyperplasia. Treatment with GANT61, a small-molecule GLI antagonist, attenuated the upregulation of gonadal-like markers (Gata4, Amhr2, Foxl2) in response to GDX. These findings support the premise that GLI1⁺ progenitor cells in the adrenal capsule of the adult mouse give rise to heterotopic tissue.

[Adrenocortical carcinoma and pregnancy]

Adrenocortical carcinoma is a rare cancer with a poor but heterogeneous prognosis. These tumours are more frequently encountered in women, sometimes very young and may be diagnosed in women in their child bearing years or already pregnant. Several clinical data have indicated that the secretion and or proliferation of adrenocortical tumors may be affected by the hormonal context of pregnancy. In this review, we will examine the link between ACC and pregnancy in two main aspects. We will first consider the situation of a pregnant woman with a clinical suspicion of adrenocortical carcinoma: which diagnostic procedures will be useful and safe for the foetus? What are the therapeutic options? What is the prognosis if the diagnosis is confirmed? In a second part, we will examine the possible risk of mothering a child in a patient previously treated for an ACC. The data shown here were obtained from studies carried out in a tertiary reference medical centre in Paris (Hôpital Cochin) and from the European Network for the Study of Adrenal Tumor (ENS@T) database of adrenocortical carcinoma.

Mouse models of adrenocortical tumors

The molecular basis of the organogenesis, homeostasis, and tumorigenesis of the adrenal cortex has been the subject of intense study for many decades. Specifically, characterization of tumor predisposition syndromes with adrenocortical manifestations and molecular profiling of sporadic adrenocortical tumors have led to the discovery of key molecular pathways that promote pathological adrenal growth. However, given the observational nature of such studies, several important questions regarding the molecular pathogenesis of adrenocortical tumors have remained. This review will summarize naturally occurring and genetically engineered mouse models that have provided novel tools to explore the molecular and cellular underpinnings of adrenocortical tumors. New paradigms of cancer initiation, maintenance, and progression that have emerged from this work will be discussed.

Pregnancy in Women Previously Treated for an Adrenocortical Carcinoma

CONTEXT

Adrenocortical carcinomas (ACCs) are rare, aggressive tumors, of which some express receptors for estradiol, progesterone, and/or human chorionic gonadotoropin. Because this disease is encountered frequently in young women, pregnancy is a relevant issue.

OBJECTIVE

to evaluate the impact of pregnancy on outcome of patients previously treated for ACC.

DESIGN/SETTING

retrospective observational multicenter study of the European Network for the Study of Adrenal Tumors.

PATIENTS

Seventeen ACC patients (21 pregnancies), becoming pregnant at least 3 months after the initial treatment, were compared with 247 nonpregnant ACC patients less than 47 years old. A control group of 34 patients matched for age, sex, and tumor stage was used for survival analysis.

MAIN OUTCOME MEASURE(S)

Overall survival, tumors characteristics at diagnosis, pregnancy outcome.

RESULTS

All 17 patients with pregnancies had localized ACC. The median time between surgery and conception was 4 years (0.3-12 y). Two pregnancies were terminated at 8 weeks. Sixteen women gave birth to 19 live infants. With exception of 1 (presumably unrelated) cardiac malformation, no severe fetal or maternal complication was observed. After a median follow-up time of 8.36 years and 5.26 years after the first conception, 1 of the 17 patients had died and 5 had experienced a recurrence, among whom 3 occurred before conception. Overall survival was not significantly different between the "pregnancy group" and the matched controls.

CONCLUSION

Pregnancy in patients previously treated for ACC seems to not be associated with worse clinical outcome, although a "healthy mother effect" cannot be excluded.

Measurement of a Comprehensive Sex Steroid Profile in Rodent Serum by High-Sensitive Gas Chromatography-Tandem Mass Spectrometry

Accurate measurement of sex steroid concentrations in rodent serum is essential to evaluate mouse and rat models for sex steroid-related disorders. The aim of the present study was to develop a sensitive and specific gas chromatography-tandem mass spectrometry (GC-MS/MS) method to assess a comprehensive sex steroid profile in rodent serum. A major effort was invested in reaching an exceptionally high sensitivity for measuring serum estradiol concentrations. We established a GC-MS/MS assay with a lower limit of detection for estradiol, estrone, T, DHT, progesterone, androstenedione, and dehydroepiandrosterone of 0.3, 0.5, 4.0, 1.6, 8, 4.0, and 50 pg/mL, respectively, whereas the corresponding values for the lower limit of quantification were 0.5, 0.5, 8, 2.5, 74, 12, and 400 pg/mL, respectively. Calibration curves were linear, intra- and interassay coefficients of variation were low, and accuracy was excellent for all analytes. The established assay was used to accurately measure a comprehensive sex steroid profile in female rats and mice according to estrous cycle phase. In addition, we characterized the impact of age, sex, gonadectomy, and estradiol treatment on serum concentrations of these sex hormones in mice. In conclusion, we have established a highly sensitive and specific GC-MS/MS method to assess a comprehensive sex steroid profile in rodent serum in a single run. This GC-MS/MS assay has, to the best of our knowledge, the best detectability reported for estradiol. Our method therefore represents an ideal tool to characterize sex steroid metabolism in a variety of sex steroid-related rodent models and in human samples with low estradiol levels.

Steroidogenic organ development and homeostasis: A WT1-centric view

Adrenal and gonads are the main steroidogenic organs and are central to regulate body homeostasis in the vertebrate organism. Although adrenals and gonads are physically separated in the adult organism, both organs share a common developmental origin, the adrenogonadal primordium. One of the key genes involved in the development of both organs is the Wilms' tumor suppressor WT1, which encodes a zinc finger protein that has fascinated the scientific community for more than two decades. This review will provide an overview of the processes leading to the development of these unique organs with a particular focus on the multiple functions WT1 serves during adrenogonadal development. In addition, we will highlight some recent findings and open questions on how maintenance of steroidogenic organs is achieved in the adult organism.

Novel markers of gonadectomy-induced adrenocortical neoplasia in the mouse and ferret

Gonadectomy (GDX) induces sex steroid-producing adrenocortical tumors in certain mouse strains and in the domestic ferret. Transcriptome analysis and DNA methylation mapping were used to identify novel genetic and epigenetic markers of GDX-induced adrenocortical neoplasia in female DBA/2J mice. Markers were validated using a combination of laser capture microdissection, quantitative RT-PCR, in situ hybridization, and immunohistochemistry. Microarray expression profiling of whole adrenal mRNA from ovariectomized vs. intact mice demonstrated selective upregulation of gonadal-like genes including Spinlw1 and Insl3 in GDX-induced adrenocortical tumors of the mouse. A complementary candidate gene approach identified Foxl2 as another gonadal-like marker expressed in GDX-induced neoplasms of the mouse and ferret. That both "male-specific" (Spinlw1) and "female-specific" (Foxl2) markers were identified is noteworthy and implies that the neoplasms exhibit mixed characteristics of male and female gonadal somatic cells. Genome-wide methylation analysis showed that two genes with hypomethylated promoters, Igfbp6 and Foxs1, are upregulated in GDX-induced adrenocortical neoplasms. These new genetic and epigenetic markers may prove useful for studies of steroidogenic cell development and for diagnostic testing.

WT1 maintains adrenal-gonadal primordium identity and marks a population of AGP-like progenitors within the adrenal gland

Adrenal glands and gonads share a common primordium (AGP), but the molecular events driving differentiation are poorly understood. Here we demonstrate that the Wilms tumor suppressor WT1 is a key factor defining AGP identity by inhibiting the steroidogenic differentiation process. Indeed, ectopic expression of WT1 precludes differentiation into adrenocortical steroidogenic cells by locking them into a progenitor state. Chromatin immunoprecipitation experiments identify Tcf21 and Gli1 as direct targets of WT1. Moreover, cell lineage tracing analyses identify a long-living progenitor population within the adrenal gland, characterized by the expression of WT1, GATA4, GLI1, and TCF21, that can generate steroidogenic cells in vivo. Strikingly, gonadectomy dramatically activates these WT1(+) cells and leads to their differentiation into gonadal steroidogenic tissue. Thus, our data describe a mechanism of response to organ loss by recreating hormone-producing cells at a heterotopic site.

The permissive role of prolactin as a regulator of luteinizing hormone action in the female mouse ovary and extragonadal tumorigenesis

Transgenic female mice overexpressing the hCGβ subunit (hCGβ(+)) and producing elevated levels of luteinizing hormone (LH)/hCG bioactivity present as young adults with enhanced ovarian steroidogenesis, precocious puberty, and infertility. They subsequently develop pituitary prolactinomas, high circulating prolactin (PRL) levels, and marked mammary gland lobuloalveolar development followed by adenocarcinomas. None of these phenotypes appear in gonadectomized mice, indicating that the hCG-induced aberrations of ovarian function are responsible for the extragonadal phenotypes. PRL receptor-deficient (PRLR(-/-)) female mice are sterile, despite ovulating, due to a failure of embryo implantation, as a consequence of decreased ovarian LH receptor (Lhcgr) expression and inadequate corpus luteum formation and progesterone production. To study further the presumed permissive role of PRL in the maintenance of gonadal responsiveness to LH/hCG stimulation, we crossed the hCGβ(+) and PRLR(-/-) mice. The double-mutant hCGβ(+)/PRLR(-/-) females remained sterile with an ovarian phenotype similar to PRLR(-/-) mice, indicating that LH action, Lhcgr expression, and consequent luteinization are not possible without simultaneous PRL signaling. The high frequency of pituitary prolactinomas in PRLR(-/-) mice was not affected by transgenic hCGβ expression. In contrast, none of the hCGβ(+)/PRLR(-/-) females showed either mammary gland lobuloalveolar development or tumors, and the increased mammary gland Wnt-5b expression, possibly responsible for the tumorigenesis in hCGβ(+) mice, was absent in double-mutant mice. Hence, high LH/hCG stimulation is unable to compensate for missing PRL signaling in the maintenance of luteal function. PRL thus appears to be a major permissive regulator of LH action in the ovary and of its secondary extragonadal effects.

A case of metastatic adrenocortical carcinoma diagnosed with steroidogenic factor-1 in a sprague-dawley rat

This report describes the morphological and immunohistochemical characteristics of an adrenocortical carcinoma with distant metastasis in a Sprague-Dawley rat. Macroscopically, a single large mass was observed in the adrenal gland, and multiple nodules were noted in the lung, liver and thyroid. Histologically, the adrenal tumor consisted of a solid growth of eosinophilic round cells with nuclear atypia. Vascular invasion was present, and multiple metastatic lesions were also observed in the lungs, liver, and mediastinal lymph nodes. Immunohistochemically, the nuclei of these tumor cells were positive for Steroidogenic Factor-1 (SF-1). In the thyroid, tumor cells histologically resembling adrenal cells were immunohistochemically negative for SF-1 but positive for calcitonin; thus the lesion was diagnosed as thyroid C-cell carcinoma. From these results, the present case was diagnosed as adrenocortical carcinoma with distant metastases. SF-1 could be a valuable marker for the differential diagnosis of adrenocortical tumors versus other endocrine tumors such as C-cell carcinoma.

Conditional mutagenesis of Gata6 in SF1-positive cells causes gonadal-like differentiation in the adrenal cortex of mice

Transcription factor GATA6 is expressed in the fetal and adult adrenal cortex and has been implicated in steroidogenesis. To characterize the role of transcription factor GATA6 in adrenocortical development and function, we generated mice in which Gata6 was conditionally deleted using Cre-LoxP recombination with Sf1-cre. The adrenal glands of adult Gata6 conditional knockout (cKO) mice were small and had a thin cortex. Cytomegalic changes were evident in fetal and adult cKO adrenal glands, and chromaffin cells were ectopically located at the periphery of the glands. Corticosterone secretion in response to exogenous ACTH was blunted in cKO mice. Spindle-shaped cells expressing Gata4, a marker of gonadal stroma, accumulated in the adrenal subcapsule of Gata6 cKO mice. RNA analysis demonstrated the concomitant upregulation of other gonadal-like markers, including Amhr2, in the cKO adrenal glands, suggesting that GATA6 inhibits the spontaneous differentiation of adrenocortical stem/progenitor cells into gonadal-like cells. Lhcgr and Cyp17 were overexpressed in the adrenal glands of gonadectomized cKO vs control mice, implying that GATA6 also limits sex steroidogenic cell differentiation in response to the hormonal changes that accompany gonadectomy. Nulliparous female and orchiectomized male Gata6 cKO mice lacked an adrenal X-zone. Microarray hybridization identified Pik3c2g as a novel X-zone marker that is downregulated in the adrenal glands of these mice. Our findings offer genetic proof that GATA6 regulates the differentiation of steroidogenic progenitors into adrenocortical cells.

Laser capture microdissection-reduced representation bisulfite sequencing (LCM-RRBS) maps changes in DNA methylation associated with gonadectomy-induced adrenocortical neoplasia in the mouse

DNA methylation is a mechanism for long-term transcriptional regulation and is required for normal cellular differentiation. Failure to properly establish or maintain DNA methylation patterns leads to cell dysfunction and diseases such as cancer. Identifying DNA methylation signatures in complex tissues can be challenging owing to inaccurate cell enrichment methods and low DNA yields. We have developed a technique called laser capture microdissection-reduced representation bisulfite sequencing (LCM-RRBS) for the multiplexed interrogation of the DNA methylation status of cytosine–guanine dinucleotide islands and promoters. LCM-RRBS accurately and reproducibly profiles genome-wide methylation of DNA extracted from microdissected fresh frozen or formalin-fixed paraffin-embedded tissue samples. To demonstrate the utility of LCM-RRBS, we characterized changes in DNA methylation associated with gonadectomy-induced adrenocortical neoplasia in the mouse. Compared with adjacent normal tissue, the adrenocortical tumors showed reproducible gains and losses of DNA methylation at genes involved in cell differentiation and organ development. LCM-RRBS is a rapid, cost-effective, and sensitive technique for analyzing DNA methylation in heterogeneous tissues and will facilitate the investigation of DNA methylation in cancer and organ development.

Transgenic GATA-4 expression induces adrenocortical tumorigenesis in C57Bl/6 mice

A link between elevated luteinizing hormone (LH) levels, GATA-4 and LH receptor (LHCGR) expression and gonadotropin-dependent adrenocortical tumorigenesis in humans and mice has been shown. To assess the mechanistic tumorigenic interrelationships between these factors, we transgenically expressed Gata4 under the 21-hydroxylase promoter (Cyp21a1, 21-OH) in C57Bl/6N mice. There was a gradual age-dependent increase of GATA-4 expression only in 21-OH-GATA-4 (TG) female adrenals, in association with slowly progressing neoplasia of non-steroidogenic spindle-shaped A cells in the subcapsular cortex. Gonadectomy (GDX), apparently through direct action of elevated serum LH, markedly enhanced the adrenocortical neoplasia, which now also appeared in GDX TG males. The neoplastic areas of the post-GDX TG adrenals contained, besides A cells, larger lipid-laden, steroidogenically active and LHCGR-positive B cells. Prolonged (>10 months) exposure to elevated post-GDX LH levels resulted in formation of adrenocortical adenomas in the TG mice. Intact and GDX TG mouse adrenals displayed elevated FOG-2 and decreased GATA-6 expression. Additionally, increased expression/activation of components of the Inhbb-Acvr2a-Acvr1c-Smad2/3 signaling system was observed in 12-month-old GDX TG adrenals. Our findings show that two distinct GATA-4-dependent populations of neoplastic adrenocortical cells form: non-steroidogenic LH-independent A cells and steroidogenic LH-dependent B cells.

GATA4 is a critical regulator of gonadectomy-induced adrenocortical tumorigenesis in mice

In response to gonadectomy certain inbred mouse strains develop sex steroidogenic adrenocortical neoplasms. One of the hallmarks of neoplastic transformation is expression of GATA4, a transcription factor normally present in gonadal but not adrenal steroidogenic cells of the adult mouse. To show that GATA4 directly modulates adrenocortical tumorigenesis and is not merely a marker of gonadal-like differentiation in the neoplasms, we studied mice with germline or conditional loss-of-function mutations in the Gata4 gene. Germline Gata4 haploinsufficiency was associated with attenuated tumor growth and reduced expression of sex steroidogenic genes in the adrenal glands of ovariectomized B6D2F1 and B6AF1 mice. At 12 months after ovariectomy, wild-type B6D2F1 mice had biochemical and histological evidence of adrenocortical estrogen production, whereas Gata4(+/-) B6D2F1 mice did not. Germline Gata4 haploinsufficiency exacerbated the secondary phenotype of postovariectomy obesity in B6D2F1 mice, presumably by limiting ectopic estrogen production in the adrenal glands. Amhr2-cre-mediated deletion of floxed Gata4 (Gata4(F)) in nascent adrenocortical neoplasms of ovariectomized B6.129 mice reduced tumor growth and the expression of gonadal-like markers in a Gata4(F) dose-dependent manner. We conclude that GATA4 is a key modifier of gonadectomy-induced adrenocortical neoplasia, postovariectomy obesity, and sex steroidogenic cell differentiation.

Luteinizing hormone receptor deficiency increases the susceptibility to alkylating agent-induced lymphomagenesis in mice

Previous studies have revealed a close link between luteinizing hormone (LH)/human chorionic gonadotropin (hCG) signaling and oncogenesis in gonadal and nongonadal tissues. To investigate whether genetic ablation of LH receptor (Lhr) affects the animal's oncogenic susceptibility, adult female wild-type (wt), heterozygous, and homozygous Lhr knockout (LhrKO) mice were intraperitoneally injected with an alkylating agent, N-methyl-N-nitrosourea (MNU, 50 mg/kg of body weight). The mice were sacrificed when they were short of breath or 10 months after the injection. The results showed that MNU induced non-Hodgkin's thymic and lymphonodus lymphomas in 70.6% and 100% of heterozygous and homozygous animals, respectively, compared with 35.7% in wt siblings. The tumor development was rapid; they were more aggressive and metastasized to the spleen, liver, and kidney in Lhr-deficient mice compared to wt siblings. All tumors were immunostained-positive for a T-cell specific marker, CD3, but not for a B-cell marker, CD22, suggesting that all the lymphomas arose from T-cells, which are known to be LH/hCG receptor-positive. There was no rearrangement of the Lhr gene locus or differences in thymic cell proliferation among the genotypes. However, apoptosis was lower in the Lhr-deficient thymuses. The thymic Bcl-2 levels were elevated and caspase-3 activation was reduced in Lhr heterozygous and homozygous animals. In conclusion, MNU induced a higher incidence and an earlier onset of aggressive lymphomas in LhrKO animals, which may be associated with a reduction in apoptosis of thymocytes.

Mouse models of adrenal tumorigenesis

Adrenocortical carcinomas (ACCs) are heterogeneous tumors with a poor prognosis. The rarity of this disorder causes a lack of treatment experience and material availability which is necessary to optimize existing treatments and to develop novel therapeutic strategies. Although surgery is still the treatment of choice, adjuvant therapies are urgently needed as the rate of recurrence for these tumors is high. In recent years molecular characterization of surgical tumor specimen has aided in the understanding of disease mechanisms and definition of therapeutic targets also in adrenocortical carcinoma. However, most of the functional properties of potential target molecules are still unpredictable from pure expression and sequence analysis. For functional studies of gene products, mouse models remain to be intensively utilized as an experimental system due to the similarity to humans with respect to genome organization, development and physiology. Here we give an overview on rodent models that have been described to either have adrenocortical tumors as part of their phenotype or have been utilized for therapeutic screens as adrenocortical tumor models.

Neural tube defects in mice with reduced levels of inositol 1,3,4-trisphosphate 5/6-kinase

Inositol 1,3,4-trisphosphate 5/6-kinase (ITPK1) is a key regulatory enzyme at the branch point for the synthesis of inositol hexakisphosphate (IP(6)), an intracellular signaling molecule implicated in the regulation of ion channels, endocytosis, exocytosis, transcription, DNA repair, and RNA export from the nucleus. IP(6) also has been shown to be an integral structural component of several proteins. We have generated a mouse strain harboring a beta-galactosidase (betagal) gene trap cassette in the second intron of the Itpk1 gene. Animals homozygous for this gene trap are viable, fertile, and produce less ITPK1 protein than wild-type and heterozygous animals. Thus, the gene trap represents a hypomorphic rather than a null allele. Using a combination of immunohistochemistry, in situ hybridization, and betagal staining of mice heterozygous for the hypomorphic allele, we found high expression of Itpk1 in the developing central and peripheral nervous systems and in the paraxial mesoderm. Examination of embryos resulting from homozygous matings uncovered neural tube defects (NTDs) in some animals and axial skeletal defects or growth retardation in others. On a C57BL/6 x 129(P2)Ola background, 12% of mid-gestation embryos had spina bifida and/or exencephaly, whereas wild-type animals of the same genetic background had no NTDs. We conclude that ITPK1 is required for proper development of the neural tube and axial mesoderm.

Transplantation of adrenal cortical progenitor cells enriched by Nile red

BACKGROUND

The adrenal cortex may contain progenitor cells useful for tissue regeneration. Currently there are no established methods to isolate these cells.

MATERIAL AND METHODS

Murine adrenal cells were sorted into a Nile-red-bright (NR(bright)) and a Nile-red-dim (NR(dim)) population of cells according to their degree of cholesterol content revealed by Nile red fluorescence. The cells were transplanted under the renal capsule to determine their ability for regeneration.

RESULTS

The NR(bright) cells contained an abundance of lipid droplets, whereas the NR(dim) cells contained little. The NR(bright) cells expressed Sf1 and the more differentiated adrenal cortical genes, including Cyp11a1, Cyp11b1, and Cyp11b2, whereas the NR(dim) cells expressed Sf1 but not the more differentiated adrenal cortical genes. After 56 d of implantation in unilateral adrenalectomized mice, the NR(dim) cells expressed Sf1 and the more differentiated adrenal cortical genes, whereas the NR(bright) cells ceased to express Sf1 as well as the more differentiated adrenal cortical genes. NR(dim) cells also proliferated in the presence of basic fibroblast growth factor.

CONCLUSIONS

The population of NR(dim) cells contained adrenal cortical progenitor cells that can proliferate and give rise to differentiated daughter cells. These cells may be useful for adrenal cortical regeneration.

In search of adrenocortical stem and progenitor cells

Scientists have long hypothesized the existence of tissue-specific (somatic) stem cells and have searched for their location in different organs. The theory that adrenocortical organ homeostasis is maintained by undifferentiated stem or progenitor cells can be traced back nearly a century. Similar to other organ systems, it is widely believed that these rare cells of the adrenal cortex remain relatively undifferentiated and quiescent until needed to replenish the organ, at which time they undergo proliferation and terminal differentiation. Historical studies examining cell cycle activation by label retention assays and regenerative potential by organ transplantation experiments suggested that the adrenocortical progenitors reside in the outer periphery of the adrenal gland. Over the past decade, the Hammer laboratory, building on this hypothesis and these observations, has endeavored to understand the mechanisms of adrenocortical development and organ maintenance. In this review, we summarize the current knowledge of adrenal organogenesis. We present evidence for the existence and location of adrenocortical stem/progenitor cells and their potential contribution to adrenocortical carcinomas. Data described herein come primarily from studies conducted in the Hammer laboratory with incorporation of important related studies from other investigators. Together, the work provides a framework for the emerging somatic stem cell field as it relates to the adrenal gland.

Adrenal hyperplasia and tumours in mice in connection with aberrant pituitary-gonadal function

Gonadectomy induces in certain inbred stains of mice adrenal hyperplasia and tumorigenesis, originating from the putative subcapsular stem/progenitor cell layer. This response is apparently triggered by the elevated post-gonadectomy levels of luteinising hormone (LH), followed by ectopic upregulation of adrenal LH/chorionic gonadotrophin (CG) receptors (Lhcgr). The clear strain dependence of this adrenal response to gonadectomy prompted us to study its genetic basis. Tumorigenic DBA/2J and non-tumorigenic C57BL/6J mice, as well as their F2 and backcrosses, were studied by whole genome linkage analysis. Gonadectomy induced similar upregulation of adrenal Lhcgr in both parental strains and their crosses, irrespective of the tumour status, indicating that ectopic expression of this receptor is not the immediate cause of tumours. Linkage analysis revealed one major significant quantitative trait locus (QTL) for the tumorigenesis on chromosome 8, modulated by epistasis with another QTL on chromosome 18. Hence, post-gonadectomy adrenal tumorigenesis in DBA/2J mice is a dominant trait, not a direct consequence of adrenal Lhcgr expression, and is driven by a complex genetic architecture. A promising candidate gene in the tumorigenesis linkage region is Sfrp1 (secreted frizzled-related protein 1), a tumour suppressor gene, which was down-regulated in the neoplastic tissue. Our findings may have relevance to the human pathogenesis of macronodular adrenal hyperplasia and postmenopausal adrenocortical tumours. A distinctly different adrenal response was observed in TG mice overexpressing LH or CG, or a constitutively activated form of the follicle-stimulating hormone receptor (Fshr). These mice developed perimedullary hyperlasia of foamy multinucleated cells, reminding of macrophages and filled with lipofuscin. Similar response was observed in TG mice overexpressing aromatase (CYP19). The cause of this response is not related to direct LH/CG action, but merely to adrenal response to chronically elevated oestrogen levels. This phenotype is reminiscent of the rare 'black adenomas' of the human adrenal cortex.

Is the adrenal cortex a target for gonadotropins?

The human adrenal cortex expresses low levels of luteinizing hormone/chorionic gonadotropin receptors (LHCGR), a characteristic gonad-specific G-protein coupled receptor (GPCR). LHCGR levels increase in the adrenal cortex after exposure to chronically elevated gonadotropins (e.g. after gonadectomy). In fact, heightened ectopic LHCGR levels are observed in a subclass of human adrenocortical tumors, and gonadotropin-responsive adrenocortical hyperplasia and tumors occur in several animal species. These findings suggest that adrenocortical responsiveness to LH/CG might be a physiological phenomenon that is amplified in the presence of elevated gonadotropin levels. Such increased gonadotropin action can induce pathologies ranging from adrenocorticotropic hormone (ACTH)-independent Cushing syndrome to malignant adrenal tumors. The authors review the current information on adrenocortical responses to gonadotropins in experimental animals and humans.

Adrenal gland tumorigenesis after gonadectomy in mice is a complex genetic trait driven by epistatic loci

Postgonadectomy adrenocortical tumorigenesis is a strain-specific phenomenon in inbred mice, assumed to be caused by elevated LH secretion and subsequent ectopic LH receptor (LHR) overexpression in adrenal gland. However, the molecular mechanisms of this cascade of events remain unknown. In this study, we took advantage of the mouse strain dependency of the phenotype to unravel its genetic basis. Our results present the first genome-wide screening related to this pathology in two independent F2 and backcross populations generated between the neoplastic DBA/2J and the nonsusceptible C57BL/6J strains. Surprisingly, the postgonadectomy elevation of serum LH was followed by similar up-regulation of adrenal LHR expression in both parental strains and their crosses, irrespective of their tumor status, indicating that it is not the immediate cause of the tumorigenesis. Linkage analysis revealed one major significant locus for the tumorigenesis on chromosome 8, modulated by epistasis with another quantitative trait locus on chromosome 18. Weight gain, a secondary phenotype after gonadectomy, showed a significant but separate quantitative trait locus on chromosome 7. Altogether, postgonadectomy adrenocortical tumorigenesis in DBA/2J mice is a dominant trait that is not a direct consequence of adrenal LHR expression but is driven by a complex genetic architecture. Analysis of candidate genes in the tumorigenesis linkage region showed that Sfrp1 (secreted frizzled-related protein 1), a tumor suppressor gene, is differentially expressed in the neoplastic areas. These findings may have relevance to the human pathogenesis of macronodular adrenal hyperplasia and adrenocortical tumors in postmenopausal women and why some of them develop obesity.

Role of the GATA family of transcription factors in endocrine development, function, and disease

The WGATAR motif is a common nucleotide sequence found in the transcriptional regulatory regions of numerous genes. In vertebrates, these motifs are bound by one of six factors (GATA1 to GATA6) that constitute the GATA family of transcriptional regulatory proteins. Although originally considered for their roles in hematopoietic cells and the heart, GATA factors are now known to be expressed in a wide variety of tissues where they act as critical regulators of cell-specific gene expression. This includes multiple endocrine organs such as the pituitary, pancreas, adrenals, and especially the gonads. Insights into the functional roles played by GATA factors in adult organ systems have been hampered by the early embryonic lethality associated with the different Gata-null mice. This is now being overcome with the generation of tissue-specific knockout models and other knockdown strategies. These approaches, together with the increasing number of human GATA-related pathologies have greatly broadened the scope of GATA-dependent genes and, importantly, have shown that GATA action is not necessarily limited to early development. This has been particularly evident in endocrine organs where GATA factors appear to contribute to the transcription of multiple hormone-encoding genes. This review provides an overview of the GATA family of transcription factors as they relate to endocrine function and disease.

Increased steroidogenic factor-1 dosage triggers adrenocortical cell proliferation and cancer

Steroidogenic factor-1 (SF-1/Ad4BP; NR5A1), a nuclear receptor transcription factor, has a pivotal role in adrenal and gonadal development in humans and mice. A frequent feature of childhood adrenocortical tumors is SF-1 amplification and overexpression. Here we show that an increased SF-1 dosage can by itself augment human adrenocortical cell proliferation through concerted actions on the cell cycle and apoptosis. This effect is dependent on an intact SF-1 transcriptional activity. Gene expression profiling showed that an increased SF-1 dosage regulates transcripts involved in steroid metabolism, the cell cycle, apoptosis, and cell adhesion to the extracellular matrix. Consistent with these results, increased SF-1 levels selectively modulate the steroid secretion profile of adrenocortical cells, reducing cortisol and aldosterone production and maintaining dehydroepiandrosterone sulfate secretion. As a model to understand the mechanisms of transcriptional regulation by increased SF-1 dosage, we studied FATE1, coding for a cancer-testis antigen implicated in the control of cell proliferation. Increased SF-1 levels increase its binding to a consensus site in FATE1 promoter and stimulate its activity through modulation of the recruitment of specific cofactors. On the other hand, sphingosine, which can compete with phospholipids for binding to SF-1, had no effect on the SF-1 dosage-dependent increase of adrenocortical cell proliferation and expression of the FATE1 promoter. In mice, increased Sf-1 dosage produces adrenocortical hyperplasia and formation of tumors expressing gonadal markers (Amh, Gata-4), which originate from the subcapsular region of the adrenal cortex. Gene expression profiling revealed that genes involved in cell adhesion and the immune response and transcription factor signal transducer and activator of transcription-3 (Stat3) are differentially expressed in Sf-1 transgenic mouse adrenals compared with wild-type adrenals. Our studies reveal a critical role for SF-1 dosage in adrenocortical tumorigenesis and constitute a rationale for the development of drugs targeting SF-1 transcriptional activity for adrenocortical tumor therapy.

Adrenocorticotropic hormone-independent Cushing's syndrome

PURPOSE OF REVIEW

Endogenous Cushing's syndrome is adrenocorticotropic hormone (or corticotropin)-independent in 15-20% of cases. Primary Cushing's syndrome is most often secondary to adrenocortical adenomas or carcinomas, and more rarely to bilateral adrenal hyperplasias. Corticotropin-independent cortisol-producing hyperplasia is caused by micronodular diseases, including primary pigmented nodular adrenocortical disease and nonpigmented micronodular hyperplasia and adrenocorticotropic hormone-independent macronodular adrenal hyperplasia. Primary pigmented nodular adrenocortical disease can be found either alone or in the context of Carney complex, a multiple endocrine neoplasia syndrome.

RECENT FINDINGS

In recent years, the pathophysiology of adrenocortical tumors and hyperplasias became better understood following the identification of genes responsible for syndromes associated with corticotropin-independent Cushing's syndrome and the demonstration of aberrant expression and function of various hormone receptors in adrenocortical adenomas and adrenocorticotropic hormone-independent macronodular adrenal hyperplasia. This article reviews findings on the molecular and genetic aspects of corticotropin-independent Cushing's syndrome including recent gene expression profiling studies of adrenocortical tumors and hyperplasias and animal models that provided clues on the pathogenesis of primary Cushing's syndrome.

SUMMARY

A better understanding of molecular mechanisms involved in adrenocortical tumors and hyperplasias may lead to improved diagnostic and prognostic markers and treatment strategies to assist clinicians in the management of corticotropin-independent Cushing's syndrome.

GATA-4 is required for sex steroidogenic cell development in the fetal mouse

The transcription factor GATA-4 is expressed in Sertoli cells, steroidogenic Leydig cells, and other testicular somatic cells. Previous studies have established that interaction between GATA-4 and its cofactor FOG-2 is necessary for proper Sry expression and all subsequent steps in testicular organogenesis, including testis cord formation and differentiation of both Sertoli and fetal Leydig cells. Since fetal Leydig cell differentiation depends on Sertoli cell-derived factors, it has remained unclear whether GATA-4 has a cell autonomous role in Leydig cell development. We used two experimental systems to explore the role of GATA-4 in the ontogeny of testicular steroidogenic cells. First, chimeric mice were generated by injection of Gata4-/- ES cells into Rosa26 blastocysts. Analysis of the resultant chimeras showed that in developing testis Gata4-/- cells can contribute to fetal germ cells and interstitial fibroblasts but not fetal Leydig cells. Second, wild-type or Gata4-/- ES cells were injected into the flanks of intact or gonadectomized nude mice and the resultant teratomas examined for expression of steroidogenic markers. Wild-type but not Gata4-/- ES cells were capable of differentiating into gonadal-type steroidogenic lineages in teratomas grown in gonadectomized mice. In chimeric teratomas derived from mixtures of GFP-tagged Gata4+/+ ES cells and unlabeled Gata4-/- ES cells, sex steroidogenic cell differentiation was restricted to GFP-expressing cells. Collectively these data suggest that GATA-4 plays an integral role in the development of testicular steroidogenic cells.

Adrenocortical tumorigenesis, luteinizing hormone receptor and transcription factors GATA-4 and GATA-6

Luteinizing hormone (LH/hCG) responsiveness of normal and pathological human adrenal glands as well as the possibility of constitutive expressions of luteinizing hormone receptor (LHR) in adrenal cortex has been reported. Some recent studies showed a correlation between the LHR and abundant GATA-4 expression in both metastasizing and non-metastasizing human adrenocortical tumors, but not in normal adrenals, implicating the putative relevance of LHR and GATA-4 for adrenocortical pathophysiology. However, the physio- and pathophysiological significance of LHR and GATA-4 in the mechanism of adrenocortical tumorigenesis remains unclear. The paucity of suitable models for adrenal tumorigenesis makes the establishment of proper animal models highly important. LHR expression in the murine adrenal gland is an exception and not found in wild-type (WT) animal. We have previously shown that ectopic LHR expression in the murine adrenal gland can be induced by chronically elevated LH levels. We have generated a gonadotropin-responsive adrenal tumor model in gonadectomized transgenic (TG) mice expressing the inhibin alpha promoter/Simian Virus 40 T antigen transgene (inhalpha/Tag). Given the induction of expression and regulation of GATA-4 and GATA-6 zinc finger transcription factors in the gonads by gonadotropins, this review will explore their relationship to LHR expression and their role in adrenocortical tumorigenesis. A functional link between LHR and GATA-4 actions in the adrenal pathophysiology is proposed.

Human adrenal cortex hyperfunction due to LH/hCG

Adrenal cortex hyperfunction may occasionally be due to stimulation of steroid hormone production by LH/hCG. The recent demonstration of the LH/hCG receptor in a variety of normal and abnormal human adrenal tissues has provided a novel explanation for these clinical observations and offers the possibility of spontaneous remission (as in pregnancy-related hyperfunction) or effective treatment with GnRH-agonists (to down-regulate LH secretion in menopausal patients). Involvement of adrenal LH/hCG receptors should be considered in pregnant or post-menopausal patients with ACTH-independent Cushing's syndrome or androgen excess. Additional investigations are needed to better define the role of the LH/hCG receptor in the normal adult and fetal human adrenal and to understand how this system is excessively activated in rare cases of human disease.

Adrenocortical cells with stem/progenitor cell properties: recent advances

The existence and location of undifferentiated cells with the capability of maintaining the homeostasis of the adrenal cortex have long been sought. These cells are thought to remain mostly quiescent with a potential to commit to self-renewal processes or terminal differentiation to homeostatically repopulate the organ. In addition, in response to physiologic stress, the undifferentiated cells undergo rapid proliferation to accommodate organismic need. Sufficient adrenocortical proliferative capacity lasting the lifespan of the host has been demonstrated through cell transplantation and enucleation experiments. Labeling experiments with tritium, BrdU, or trypan blue, as well as transgenic assays support the clonogenic identity and location of these undefined cells within the gland periphery. We define undifferentiated adrenocortical cells as cells devoid of steroidogenic gene expression, and differentiated cells as cells with steroidogenic capacity. In this review, we discuss historic developmental studies together with recent molecular examinations that aim to characterize such populations of cells.

GATA transcription factors in adrenal development and tumors

Of the six GATA transcription factors, GATA-4 and GATA-6 are expressed in the mouse and human adrenal with distinct developmental profiles. GATA-4 is confined to the fetal cortex, i.e. to the less differentiated proliferating cells, while GATA-6 is expressed both in the fetal and adult adrenal. In vitro, GATA-4 regulates inhibin-alpha and steroidogenic factor-1 implicated in normal adrenal function. GATA-6 probably has roles in the development and differentiation of adrenocortical cells, and in the regulation of steroidogenesis. GATA-4 expression is dramatically upregulated and GATA-6 downregulated in gonadotropin dependent mouse adrenocortical tumors. This is accompanied by the appearance of luteinizing hormone receptor (LHR). In vitro, GATA-4 transactivates LHR promoter, and gonadotropins upregulate GATA-4 levels. Human adrenal tumors occasionally express GATA-4, whereas GATA-6 levels are usually lower than normal.

Adrenocortical Tumorigenesis

Through the widespread use of imaging techniques with great sensitivity adrenal tumors are often diagnosed as an incidental finding. Although the majority of these adrenal lesions are benign and without evidence of endocrine activity or malignancy, hormone hypersecretion needs to be ruled out by specific tests. In addition to the classical forms of overt adrenocortical hypersecretion, it has become evident over the recent years that modest adrenocortical steroid autonomy as present in normokalemic primary aldosteronism and subclinical Cushing's syndrome is also associated with a significant morbidity. However, detection and differential diagnosis of these subtle changes in adrenal steroidogenesis can pose a diagnostic challenge to the clinician and is dependent on tests with reliable sensitivity and specificity. Regulation of adrenocortical development and growth, which results in clinical symptoms if disrupted, is dependent upon the distinct spatiotemporal expression of a variety of transcription factors as well as stimulation by extra-adrenal peptide hormones. Contributions to the elucidation of growth regulation of the adrenal cortex come from rare familiar syndromes associated with adrenocortical tumors, expression studies of adrenal tumor samples, in vitro studies on adrenocortical tumor cell lines, and mouse models displaying adrenal growth defects. In this review, we will summarize the important molecular aspects of adrenal tumorigenesis and highlight some prospects for clinical applications.

Origin and Identity of Adrenocortical Tumors in Inhibin Knockout Mice: Implications for Cellular Plasticity in the Adrenal Cortex

Inhibin knockout (Inha−/−) mice develop gonadal sex-cord tumors and—when gonadectomized—adrenocortical tumors. Previous reports demonstrated that adrenocortical tumors from Inha−/− mice produce estrogen and depend on gonadotropin signaling for initiation. Here we show that, in addition to producing estrogen, the adrenocortical tumors display a global change in cellular identity, composed of two unique cell types expressing differing arrays of genes normally restricted to theca and granulosa cells of the ovary. Many of these genes are also induced in wild-type adrenals after gonadectomy or upon chronic gonadotropin stimulation, suggesting that the adrenal cortex normally contains a population of pluripotent cells that can be driven toward an adrenal or gonadal identity given the appropriate pituitary stimuli. A central feature of this altered cellular identity is the switch from predominant expression of Gata6 (endogenous to the adrenal cortex) to Gata4, which defines cellular identity in the ovary. We show that stable transfection of Gata4 in cultured adrenocortical cells is sufficient to activate ovarian-specific genes of both theca and granulose lineages. Spatial analysis of Gata4 expression reveals a distinct pattern of localization to the supcapsular region of the adrenal, which contains undifferentiated progenitor cells that continuously populate the adrenocortical zones. Although both wild-type and Inha−/− mice display this pattern, only Inha−/− mice produce tumors composed of these Gata4-positive cells. These data suggest that Inha−/− adrenocortical tumors cells are derived from pluripotent adrenocortical progenitor cells that adopt a gonadal fate due to the convergent loss of inhibin and chronic exposure to elevated gonadotropins.

GLP-1: a novel zinc finger protein required in somatic cells of the gonad for germ cell development

Mouse gonadal development is regulated by a variety of transcription factors. Here we report the identification and characterization of a novel nuclear zinc finger protein called GATA like protein-1 (GLP-1), which is expressed at high levels in the somatic cells of the developing gonads, including Leydig cells in the testes and granulosa cells in the ovaries. Biochemical analysis of GLP-1 shows that it acts as a transcriptional repressor of GATA factor function. To determine the necessity of GLP-1 in gonadal development, a null allele in mice was generated by replacing all of the coding exons with the bacterial lacZ gene. GLP-1(lacZ) null mice are viable with no detectable defects in visceral organ development; however, both males and females are completely infertile. Loss of GLP-1 leads to defective sperm development in males with a marked reduction in mature spermatids observed as early as postnatal week 1. In females, loss of GLP-1 leads to a severe block in germ cell development as early as E17.5. Together, these data identify GLP-1 as a critical nuclear repressor in somatic cells of the gonad that is required for germ cell development, and highlight the importance of somatic-germ cell interactions in the regulation of this critical process.

Gonadectomy-induced adrenocortical neoplasia in the domestic ferret (Mustela putorius furo) and laboratory mouse

Sex steroid-producing adrenocortical adenomas and carcinomas occur frequently in neutered ferrets, but the molecular events underlying tumor development are not well understood. Prepubertal gonadectomy elicits similar tumors in certain inbred or genetically engineered strains of mice, and these mouse models shed light on tumorigenesis in ferrets. In mice and ferrets, the neoplastic adrenocortical cells, which functionally resemble gonadal steroidogenic cells, arise from progenitors in the subcapsular or juxtamedullary region. Tumorigenesis in mice is influenced by the inherent susceptibility of adrenal tissue to gonadectomy-induced hormonal changes. The chronic elevation in circulating luteinizing hormone that follows ovariectomy or orchiectomy is a prerequisite for neoplastic transformation. Gonadectomy alters the plasma or local concentrations of steroid hormones and other factors that affect adrenocortical tumor development, including inhibins, activins, and Müllerian inhibiting substance. GATA-4 immunoreactivity is a hallmark of neoplastic transformation, and this transcription factor might serve to integrate intracellular signals evoked by different hormones. Synergistic interactions among GATA-4, steroidogenic factor-1, and other transcription factors enhance expression of inhibin-alpha and genes critical for ectopic sex steroid production, such as cytochrome P450 17alpha-hydroxylase/17,20 lyase and aromatase. Cases of human adrenocortical neoplasia have been linked to precocious expression of hormone receptors and to mutations that alter the activity of G-proteins or downstream effectors. Whether such genetic changes contribute to tissue susceptibility to neoplasia in neutered ferrets and mice awaits further study.

GATA-4:FOG interactions regulate gastric epithelial development in the mouse

Transcription factor GATA-4 is a key participant in cytodifferentiation of the mouse hindstomach. Here we show that GATA-4 cooperates with a Friend-of-GATA (FOG) cofactor to direct gene expression in this segment of gut. Immunohistochemical staining revealed that GATA-4 and FOG-1 are co-expressed in hindstomach epithelial cells from embryonic days (E) 11.5 to 18.5. The other member of the mammalian FOG family, FOG-2, was not detected in gastric epithelium. To show that GATA-4:FOG interactions influence stomach development, we analyzed Gata4(ki/ki) mice, which express a mutant GATA-4 that cannot bind FOG cofactors. Sonic Hedgehog, an endoderm-derived signaling molecule normally down-regulated in the distal stomach, was over-expressed in hindstomach epithelium of E11.5 Gata4(ki/ki) mice, and there was a concomitant decrease in fibroblast growth factor-10 in adjacent mesenchyme. We conclude that functional interaction between GATA-4 and a member of the FOG family, presumably FOG-1, is required for proper epithelial-mesenchymal signaling in the developing stomach.

Gonadotropin-induced adrenocortical neoplasia in NU/J nude mice

In response to prepubertal gonadectomy certain inbred mouse strains, including DBA/2J, develop sex steroid-producing adrenocortical neoplasms. This phenomenon has been attributed to a lack of gonadal hormones or a compensatory increase in gonadotropins. To assess the relative importance of these mechanisms, we created a new inbred model of adrenocortical neoplasia using female NU/J nude mice. These mice developed adrenocortical neoplasms in response to either gonadectomy or gonadotropin elevation from xenografts of human chorionic gonadotropin (hCG)-secreting Chinese hamster ovary cells. In each instance the adrenal tumors resembled the neoplasms found in gonadectomized DBA/2J mice and were composed of spindle-shaped A cells and lipid-laden B cells. Both cell populations were defined by ectopic expression of GATA-4 and an absence of the adrenocortical markers melanocortin-2-receptor and steroid 21-hydroxylase, but only B cells expressed the gonadal steroidogenic markers inhibin-alpha, LH receptor, P450c17, and P450c19. Expression of sex steroidogenic markers was attenuated in the neoplastic adrenal cortex of hCG-treated vs. gonadectomized mice. Whereas neoplastic adrenals were an obvious source of estradiol in gonadectomized mice, ovaries appeared to be the major source of this hormone in hCG-treated mice. Gonadectomy and hCG treatment elicited comparable increases in serum estradiol, but testosterone levels increased significantly only in hCG-treated mice. We conclude that chronic gonadotropin elevation, caused by either gonadectomy or hCG administration, signals a population of cells in the adrenal subcapsular region of permissive mice to undergo differentiation along a gonadal rather than an adrenal lineage. Thus, NU/J nude mice can be used as a model to study both neoplasia and adrenogonadal lineage specification.

Nude mice as a model for gonadotropin-induced adrenocortical neoplasia

Certain inbred mice (e.g., DBA/2J, CE) develop sex steroid producing adrenocortical tumors following gonadectomy. This adrenal response is thought to result from an unopposed increase in circulating gonadotropins and/or a decrease in factor(s) of gonadal origin. To differentiate between these two possibilities, we utilized the NU/J strain of nude mice, which are immunologically compromised and therefore permissive to xenografts. One group of female nude mice was gonadectomized, while another group of females received xenografts of CHO cells stably transfected with human chorionic gonadotropin (hCG). After 1-2 months, subcapsular adrenocortical neoplasms containing sex steroid-producing cells were observed in both groups. We conclude that high levels of circulating gonadotropins are sufficient to induce adrenocortical tumorigenesis, even in the presence of intact gonads.

Transcription factors GATA-4 and GATA-6 in human adrenocortical tumors

Transcription factors GATA-4 and GATA-6 are expressed during normal adrenocortical development in mice and humans, and in vitro studies have linked them to adrenal steroidogenesis. GATA-4 is highly expressed in the adrenocortical tumors of gonadectomized mice, whereas GATA-6 is down-regulated in the tumor area. Based on these findings we studied GATA-4 and GATA-6 expression in 39 human adrenocortical tumors using RT-PCR, Northern analysis and immunohistochemistry. 6/18 adenomas and 4/11 carcinomas were positive for GATA-4 mRNA. GATA-6 mRNA was expressed in 19/19 adenomas and 9/10 carcinomas, and GATA-6 immunoreactivity was remarkably lower in adrenocortical carcinomas than in adenomas (p < 0.05). Some of the steroidogenically active human adrenocortical cells (NCI-H295R) were weakly positive for GATA-4, whereas steroidogenically inactive cells (ACT-1) were totally GATA-4 negative. In contrast, both cell lines expressed GATA-6. GATA expression patterns similar to the animal models can thus be observed in human adrenocortical tumors, but the pathophysiological significance of these findings remains to be elucidated.

Transcription factor GATA-4 is a marker of anaplasia in adrenocortical neoplasms of the domestic ferret (Mustela putorius furo)

Adrenocortical neoplasms are a common cause of morbidity in neutered ferrets. Recently we showed that gonadectomized DBA/2J mice develop adrenocortical tumors that express transcription factor GATA-4. Therefore, we screened archival specimens of adrenocortical neoplasms from neutered ferrets to determine whether GATA-4 could be used as a tumor marker in this species. Nuclear immunoreactivity for GATA-4 was evident in 19/22 (86%) of ferret adrenocortical carcinomas and was prominent in areas exhibiting myxoid differentiation. Normal adrenocortical cells lacked GATA-4 expression. Two other markers of adrenocortical tumors in gonadectomized mice, inhibin-alpha and luteinizing hormone receptor, were coexpressed with GATA-4 in some of the ferret tumors. No GATA-4 expression was observed in three cases of nodular hyperplasia, but patches of anaplastic cells expressing GATA-4 were evident in 7/14 (50%) of tumors classified as adenomas. We conclude that GATA-4 can function as a marker of anaplasia in ferret adrenocortical tumors.