Concurrent IgG4-related hypophysitis and clinically nonfunctioning gonadotroph pituitary neuroendocrine tumor.

BACKGROUND: Some patients develop immunoglobulin G4 (IgG4)-related hypophysitis associated with systemic diseases. More than 30 cases of IgG4-related hypophysitis have been reported. However, biopsy has rarely been performed in these patients, and none have had an associated pituitary neuroendocrine tumor (PitNET). We present a case of concurrent IgG4-related hypophysitis and PitNET. CASE PRESENTATION: A 56-year-old Japanese man arrived at the hospital with visual impairment, bitemporal hemianopia, and right abducens nerve palsy. Magnetic resonance imaging revealed pituitary body and stalk swelling as well as a small poorly enhanced right anterior lobe mass. Laboratory and loading test results suggested hypopituitarism. Because IgG4 level was elevated, a systemic examination was performed; multiple nodules were found in both lung fields. The diagnosis was based on an endoscopic transnasal biopsy of the pituitary gland. A histopathological examination revealed a marked infiltration of plasma cells into the pituitary gland, which was strongly positive for IgG4. The histological features of the resected tumor were consistent with those of gonadotroph PitNET, which was immunohistochemically positive for follicle-stimulating hormone-ß and steroidogenic factor-1, and no plasma cell infiltration was observed. Based on the histopathological examination results, steroid therapy was initiated, which reduced pituitary gland size and serum IgG4 levels. DISCUSSION AND CONCLUSIONS: This is the first reported case of IgG4-related hypophysitis with PitNET. Although no pathological findings indicating a relationship between the two conditions were found, we were able to preoperatively differentiate multiple lesions via detailed diagnostic imaging.

Functioning gonadotroph adenomas in premenopausal women: clinical and molecular characterization and review of the literature.

PURPOSE: To summary the clinical features of premenopausal women with functioning gonadotroph adenomas (FGAs) and preliminarily explore their molecular characterization. METHODS: 12 premenopausal females with FGAs in our center were retrospectively analyzed. Previously reported cases were also summarized. The patients were clinically divided into FSH- or LH-predominant types according to their preoperative serum FSH/LH ratio. The expressions of related genes in the tumor tissues of female FGAs, non-functioning gonadotroph adenomas (NFGAs), and silent corticotropin adenomas were evaluated by RT-qPCR. RESULTS: Of all the 12 patients with FGAs from our center, 11 (91.7%) were diagnosed as FSH-predominant type, and they all had menstrual disorders, including 9 with spontaneous ovarian hyperstimulation syndrome (sOHSS). Their hormonal profiles showed non-suppressed FSH (12.45 ± 7.34 IU/L) with hyperestrogenemia [median estradiol level 1353.0 pg/mL (636.0, 3535.0)]. The other patient (8.3%) with LH-predominant type mainly manifested with infertility and sustained elevated serum LH without FSH or estradiol increasing. 65 premenopausal FGAs patients were systematic reviewed. 60 patients (92.3%) were FSH-predominant type, including 86.7% presented with menstrual disorders, 16.7% reported infertility, and 98.2% (55/56) showed sOHSS. No sOHSS or hyperestrogenemia were found in the 5 patients (7.7%) with LH-predominant type. Pituitary imaging data revealed macroadenomas and microadenomas accounted for 89.2% and 10.8%, respectively. Of 63 patients (96.9%) who underwent pituitary adenoma resection, 77.8% had complete tumor resection and no recurrence at the last follow-up. The relative expressions of KISS1 mRNA were significantly higher in FGA group than in NFGA group (p = 0.018), and significantly positively correlated with the preoperative serum estradiol levels (p = 0.004). CONCLUSIONS: Different clinical features were observed in premenopausal women with FGAs of FSH- or LH-predominant types. The elevated KISS1 expression in tumor tissues might involve in the secretion function of FGAs.

Pituitary apoplexy secondary to metastatic breast carcinoma into a gonadotroph cell adenoma of the pituitary.

A 65 year-old lady with metastatic breast cancer presented with pituitary apoplexy. Following surgery, histopathology confirmed metastatic breast carcinoma into a gonadotroph cell adenoma of the pituitary. Tumours that metastasise to a normal pituitary gland are unusual. More so, such neoplasm-to-neoplasm metastasis is extremely rare. This is, as far as we are aware, the first description of a metastasis into a gonadotroph cell pituitary adenoma presenting as apoplexy.

Functional pituitary gonadotroph adenoma in male patients: Case report.

Pituitary gonadotroph adenomas are common but very rarely do they secrete biologically active luteinizing hormone (LH) and follicle-stimulating hormone (FSH). There have been case studies reporting high sex hormones (testosterone/estrogen) in the presence of high or normal LH and FSH. Here we report two cases (with their consent) who presented with visual disturbance and headache at a tertiary care hospital (Aga Khan university hospital) Karachi, Pakistan. Brain imaging revealed a pituitary macroadenoma. Further workup was consistent with pituitary gonadotroph adenoma with high FSH (case 1) and normal LH/FSH (case 2) and elevated serum testosterone in both cases. Transsphenoidal resection was performed and the tissue sample histopathology confirmed pituitary adenoma. Postoperatively, improvement in hormonal profile was observed along with a resolution of visual disturbances and headaches. Thus, functional gonadotroph adenoma should be considered in the presence of elevated testosterone/estrogen and normal or elevated follicle-stimulating hormone (FSH)/ luteinizing hormone (LH). Early diagnosis leads to a better outcome.

Updating the Landscape for Functioning Gonadotroph Tumors.

Functioning gonadotroph adenomas (FGAs) are rare tumors, as the overwhelming majority of gonadotroph tumors are clinically silent. Literature is based on case reports and small case series. Gonadotroph tumors are poorly differentiated and produce and secrete hormones inefficiently, but in exceptional cases, they cause clinical syndromes due to hypersecretion of intact gonadotropins. The clinical spectrum of endocrine dysfunction includes an exaggerated response of ovaries characterized as ovarian hyperstimulation syndrome (OHSS) in premenopausal females and adolescent girls, testicular enlargement in males, and isosexual precocious puberty in children. Transsphenoidal surgery and removal of tumor reduces hormonal hypersecretion, improves endocrine dysfunction, and provides tissue for further analysis. Medical therapies (somatostatin analogues, dopamine agonists, GnRH agonists/antagonists) are partially or totally ineffective in many cases, especially with respect to antitumor effect. This review aims to update recent literature on these rare functioning tumors and highlight their therapeutic management.

Clinical characteristics and outcomes of null-cell versus silent gonadotroph adenomas in a series of 1166 pituitary adenomas from a single institution.

OBJECTIVE: Nonfunctioning pituitary adenomas present without biochemical or clinical signs of hormone excess and are the second most common type of pituitary adenomas. The 2017 WHO classification scheme of pituitary adenomas differentiates null-cell adenomas (NCAs) and silent gonadotroph adenomas (SGAs). The present study sought to highlight the differences in patient characteristics and clinical outcomes between NCAs and SGAs. METHODS: The records of 1166 patients who underwent transsphenoidal surgery for pituitary adenoma between 2012 and 2019 at a single institution were retrospectively reviewed. Patient demographics and clinical outcomes were collected. RESULTS: Of the overall pituitary adenoma cohort, 12.8% (n = 149) were SGAs and 9.2% (n = 107) NCAs. NCAs were significantly more common in female patients than SGAs (61.7% vs 26.8%, p < 0.001). There were no differences in patient demographics, initial tumor size, or perioperative and short-term clinical outcomes. There was no significant difference in the amount of follow-up between patients with NCAs and those with SGAs (33.8 months vs 29.1 months, p = 0.237). Patients with NCAs had significantly higher recurrence (p = 0.021), adjuvant radiation therapy usage (p = 0.002), and postoperative diabetes insipidus (p = 0.028). NCA pathology was independently associated with tumor recurrence (HR 3.64, 95% CI 1.07-12.30; p = 0.038), as were cavernous sinus invasion (HR 3.97, 95% CI 1.04-15.14; p = 0.043) and anteroposterior dimension of the tumor (HR 2.23, 95% CI 1.09-4.59; p = 0.030). CONCLUSIONS: This study supports the definition of NCAs and SGAs as separate subgroups of nonfunctioning pituitary adenomas, and it highlights significant differences in long-term clinical outcomes, including tumor recurrence and the associated need for adjuvant radiation therapy, as well as postoperative diabetes insipidus. The authors also provide insight into independent risk factors for these outcomes in the adenoma population studied, providing clinicians with additional predictors of patient outcomes. Follow-up studies will hopefully uncover mechanisms of biological aggressiveness in NCAs and associated molecular targets.

A case of functioning gonadotroph adenoma in a reproductive aged woman.

A 34-year-old woman presented our hospital with complaint of irregular menstruation and abnormal uterine bleeding lasting for a month. After her second parturition at the age of 27, her menstrual cycle had been regular, but it suddenly became irregular at the age of 30. Transvaginal ultrasound revealed the presence of ovarian mass, and the patient underwent diagnostic laparoscopic surgery. Bilateral ovaries temporally shrink after puncture but the size soon resumed. Gonadotropins were almost normal, but estradiol and PRL levels turned out to be elevated, and cabergoline treatment was initiated. After referral to our hospital, we found that the ovaries showed multifollicular appearance. Brain magnetic resonance imaging showed an 18-mm macroadenoma in the suprasellar area. To suppress the secretion of endogenous gonadotropins and estrogen, low-dose estrogen-progestin was prescribed. Surprisingly, the treatment temporarily reduced the size of the ovaries. The patient was referred to a neurosurgeon, and a functioning gonadotroph adenoma was suspected. After the resection of the pituitary tumor, her menstrual cycle became regular, and the size of bilateral ovaries became normal. We also noticed that her ovarian reserve judged by anti-Müllerian hormone had been almost diminished after the surgical treatment, probably reflecting the exhaustion of follicular pool. Women with multifollicular ovaries and elevated estradiol levels may have functioning gonadotroph adenomas, although the level of FSH is relatively normal, and ovarian reserve can be followed by measuring anti-Müllerian hormone.

Gonadotroph adenoma causing ovarian hyperstimulation syndrome in a premenopausal woman.

INTRODUCTION: Gonadotroph adenomas occur commonly in middle-aged adults without any specific endocrinological symptoms. To date, only 30 cases of gonadotropinoma causing ovarian hyperstimulation syndrome in pre-menopausal women have been reported. CASE REPORT: A 37-year old woman with pituitary macroadenoma and hyperprolactinaemia was admitted to the Department of Endocrinology, Diabetology and Isotope Therapy. She presented with recurrent ovarian cysts, menstrual disturbances, headaches, visual impairment and galactorrhea. Her endocrine profile showed normal values of FSH, elevated concentrations of estradiol and suppressed LH levels. Transsphenoidal resection of the tumor tissue resulted in normalization of the hormone values and improvement in the clinical picture. CONCLUSIONS: Gonadotroph adenomas should be considered in the differential diagnosis in premenopausal women with OHSS.

Acute spill-mimicking exposure effect of hexavalent chromium on the pituitary-ovarian axis of a teleost, Channa punctatus (Bloch).

Acute exposure to hexavalent chromium (as 10, 20, and 40 mg/L potassium dichromate for 96 h) adversely affected the pituitary-ovarian axis of a teleost Channa punctatus. The toxic impact of metal exposure on fish ovary was revealed in the form of increased percentage of atretic follicles, significantly in 20 mg/L and 40 mg/L exposure groups. The follicular atresia mostly occurred in vitellogenic (stage II and stage III) oocytes. Reduction of serum level of 17ß-estradiol was also significant in 20 mg/L and 40 mg/L exposure groups. The increase of LH-immunointensity of pituitary gonadotrophs (LHß-immunoreactive cells) and their hypertrophy was evident, significantly in fish of 40 mg/L exposed group. Thus, the present acute metal spill-mimicking laboratory study clearly demonstrated that short-term exposures to high doses of hexavalent chromium may disrupt reproduction of the fish and affect their population.

Clinical and Molecular Characteristics of Gonadotroph Pituitary Tumors According to the WHO Classification.

Since 2017, hormone-negative pituitary neuroendocrine tumors expressing the steroidogenic factor SF1 have been recognized as gonadotroph tumors (GnPT) but have been poorly studied. To further characterize their bio-clinical spectrum, 54 GnPT defined by immunostaining for FSH and/or LH (group 1, n = 41) or SF1 only (group 2, n = 13) were compared and studied for SF1, ßFSH, ßLH, CCNA2, CCNB1, CCND1, caspase 3, D2R, and AIP gene expression by qRT-PCR. Immunohistochemistry for AIP and/or D2R was performed in representative cases. Overall, patients were significantly younger in group 1 (P = 0.040 vs group 2), with a similar trend excluding recurrent cases (P = 0.078), and no significant difference in gender, tumor size, invasion or Ki67. SF1 expression was similar in both groups but negatively correlated with the patient's age (P = 0.013) and positively correlated with ßLH (P < 0.001) expression. Beta-FSH and AIP were significantly higher in group 1 (P = 0.042 and P = 0.024, respectively). Ki67 was unrelated to gonadotroph markers but positively correlated with CCNB1 (P = 0.001) and negatively correlated with CCND1 (P = 0.008). D2R and AIP were strongly correlated with each other (P < 0.001), and both positively correlated with SF1, ßFSH, ßLH, and CCND1. AIP immunopositivity was frequently observed in both groups, with a similar median score, and unrelated to Ki67. D2R immunostaining was best detected with a polyclonal antibody and mostly cytoplasmic. This study indicates that hormone-negative GnPT tend to occur in older patients but do not significantly differ from other GnPT in terms of invasion or proliferation. It also points out the current limits of D2R immunostaining in such tumors.

A clone of elusive parents: gonadotroph adenoma-female type.

A 69-year-old woman presented with visual disturbance. Perimetry testing revealed a bitemporal hemianopia. Brain MRI demonstrated a 2.2-cm gadolinium-enhancing pituitary mass. Previously she had been treated for hypothyroidism, hypertension, and dyslipidemia. She had hyperprolactinemia. Endoscopic transsphenoidal debulking improved her visual field defects. Histology showed a chromophobic adenoma. Electron microscopy showed elongated, polar cells with long, slender processes. The small uniform secretory granules were peripherally disposed, collecting heavily within cell processes. Based on electron microscopical characteristics the tumor is consistent with an ACTH-negative female gonadotroph adenoma. The parent cell of this rare variant of a pituitary adenoma is yet unknown.

Intratumoural spatial distribution of S100B + folliculostellate cells is associated with proliferation and expression of FSH and ERα in gonadotroph tumours.

Folliculostellate cells are S100B-expressing cells with numerous functions in the normal anterior pituitary. These cells have also been identified in pituitary neuroendocrine tumours (PitNETs), where their precise role remains elusive. Here, we aimed to build a refined cartography of S100B-expressing cells to characterise their interpatient and intratumoural spatial distribution, and to start identifying their potential functions in PitNETs. High-throughput histological analysis of S100B-stained tumour sections of 54 PitNETs revealed a significant decrease in S100B + cells in PitNETs compared to the normal anterior pituitary. A Ki67 index ≥ 3, a mitosis count > 2/10 per high power fields, and a proliferative status, were all associated with fewer S100B + cells in gonadotroph tumours. Gonadotroph tumours also showed interpatient and intratumoural heterogeneity in the spatial distribution of S100B + cells. The existence of an intratumoural heterogeneity was further confirmed by the incorporation to our spatial analysis of additional markers: Ki67, FSH, LH, ERα and SSTR2. The tumour areas with fewer S100B + cells displayed a higher percentage of Ki67 + cells, whereas strong positive correlations were observed between S100B + , FSH + , and ERα + cells. Such spatial associations suggest that S100B + folliculostellate cells could play a role in gonadotroph tumorigenesis, and may contribute to the maintenance of tumour cells in a low proliferating, FSH + /ERα + differentiated state. Albeit, further in-depth functional studies are required to decipher the mechanisms underlying these spatial associations and to potentially identify a therapeutic use.

Atypical pituitary adenoma with malignant features.

Pituitary carcinoma is characterized by the presence of systemic or central nervous system metastases rather than malignant histological features, making it an anomaly amongst carcinomas. In contrast, aggressive or atypical pituitary adenomas often have a relatively bland histological appearance despite their malignant growth patterns. We now report a case of a 67-years-old male with a giant pituitary tumor with overt pathologic and phenotypic features of malignancy, but the absence of metastases, that evolved from a benign non-functioning gonadotroph macroadenoma treated 10 years earlier. This case represents the first report of a pituitary adenoma with overt malignant histology that does not meet criteria for classification as pituitary carcinoma, helping to complete the pathological spectrum of disease observed with pituitary tumors.

Sellar collision tumor involving pituitary gonadotroph adenoma and chondroma: a potential clinical diagnosis.

We report on a 74-year-old male patient who presented with progressive neuroophthalmologic symptoms soon after the administration of a long-acting gonadotropin-releasing hormone agonist for treatment of a prostate cancer. Imaging revealed a destructively growing and extensively calcified sellar mass inconsistent with a pituitary adenoma. A transseptal transsphenoidal tumor mass reduction yielded a histological diagnosis of a collision tumor comprised of a gonadotroph adenoma intermingled with osteochondroma. We discuss a potential causal relationship between the administration of the long-acting gonadotropin-releasing hormone agonist and the sudden appearance of the previously unsuspected sellar lesion. Although the association of these two tumors is very likely coincidental, the possibility of causal relationship is addressed.

[Hypoplasia adrenal congenita of anencephalic type: two cases with pituitary abnormalities and review of literature]. / L'hypoplasie surrénale congénitale de type anencéphalique: deux cas avec anomalies hypophysaires, sans mutation de DAX-1 et SF-1 et revue de la littérature.

Hypoplasia adrenal congenita is an extremely uncommon disease of early onset. This condition can be lethal in the absence of treatment. Some forms are due to the congenital adrenal hypoplasia of anencephalic type whose origin is even unknown. Here, we present two cases of congenital adrenal hypoplasia of anencephalic type with pituitary abnormalities. The two male newborns died because adrenal insufficiency in the neonatal period. The adrenal glands were hypoplastic with a histological structure of anencephalic type Immunocytochemical study of the pituitary revealed an absence of the gonadotrophs. No mutation of DAX 1 and SF-1 was found.

Immune Landscape of Pituitary Tumors Reveals Association Between Macrophages and Gonadotroph Tumor Invasion.

PURPOSE: Pituitary neuroendocrine tumors (PitNETs) are frequent intracranial neoplasms that present heterogenic characteristics. Little is known about the immune cell network that exists in PitNETs and its contribution to their aggressive behavior. METHODS: Here we combined flow cytometry, t-SNE analysis, and histological approaches to define the immune landscape of surgically resected PitNETs. Xenografts of rodent pituitary tumor cells and resected PitNETs were performed in Rag2KO mice, in combination with in vitro analysis aimed at dissecting the role of pituitary tumor-cells in monocyte recruitment. RESULTS: We report that gonadotroph PitNETs present an increased CD68+ macrophage signature compared to somatotroph, lactotroph, and corticotroph PitNETs. Transcriptomic and histological characterizations confirmed gonadotroph infiltrating macrophages expressed CD163, MRC-1, ARG1, and CSF1R M2 macrophage markers. Use of growth hormone (GH)3/GH4 somatotroph and LßT2/αT3.1 gonadotroph cells drove THP1 macrophage migration through respective expression of CCL5 or CSF1. Although both LßT2 and GH3 cells recruited F4/80 macrophages following their engraftment in mice, only LßT2 gonadotroph cells showed a capacity for M2-like polarization. Similar observations were performed on patient-derived xenografts from somatotroph and gonadotroph tumors. Analysis of clinical data further demonstrated a significant correlation between the percentage of CD68+ and CD163+ infiltrating macrophages and the invasive character of gonadotroph tumors. CONCLUSIONS: Gonadotroph tumor drive the recruitment of macrophages and their subsequent polarization to an M2-like phenotype. More importantly, the association between infiltrating CD68+/CD163+ macrophages and the invasiveness of gonadotroph tumors points to macrophage-targeted immunotherapies being a potent strategy to limit the progression of gonadotroph PitNETs.

Treatment Options for Gonadotroph Tumors: Current State and Perspectives.

CONTEXT: Gonadotroph tumors represent approximatively one-third of anterior pituitary tumors, but despite their frequency, no medical treatment is currently recommended for them. This would be greatly needed because following surgery, which is the first-line treatment, a significant percentage of gonadotroph tumors regrow. EVIDENCE ACQUISITION: We performed PubMed searches in March 2020 using the term "gonadotroph" in combination with 36 different keywords related to dopamine type 2 receptor agonists, somatostatin receptor (SST) ligands, temozolomide, peptide receptor radionuclide therapy (PRRT), immunotherapy, vascular endothelial growth factor receptor (VEGFR)-targeted therapy, mammalian target of rapamycin (mTOR) inhibitors, and tyrosine kinase inhibitors. Articles resulting from these searches, as well as relevant references cited by these articles were reviewed. EVIDENCE SYNTHESIS: SST2 analogs have demonstrated only very limited antitumor effect, while high-dose cabergoline has been more effective in preventing tumor regrowth, but still in only a minority of cases. In the setting of an aggressive gonadotroph tumor, temozolomide is the recommended medical treatment, but has demonstrated also only limited efficacy. Still, its efficacy has been so far better than that of PRRT. No case of a gonadotroph tumor treated with pasireotide, VEGFR-targeted therapy, mTOR inhibitors, tyrosine kinase inhibitors, or immune checkpoint inhibitors is reported in literature. CONCLUSIONS: Gonadotroph tumors need better phenotyping in terms of both tumor cells and associated tumor microenvironment to improve their treatment. Until formal recommendations will be available, we provide the readers with our suggested approach for the management of gonadotroph tumors, management that should be discussed within multidisciplinary teams.

Plurihormonal gonadotroph cell pituitary adenoma: report of a unique case.

OBJECTIVE AND IMPORTANCE: Pituitary adenomas producing primarily FSH and to a lesser extent GH, LH, alpha-subunit, TSH and PRL without clinical or laboratory evidence of increased hormone release have not previously been reported. Our aim was to obtain some insight into the possible cytogenesis of this unusual tumor. CLINICAL PRESENTATION: A 65-year-old woman presented with headaches. Magnetic resonance imaging (MRI) demonstrated a sellar mass. Pituitary hormone assays showed normal blood levels. The tumor was removed by the transsphenoidal approach. RESULT: By light microscopy, the adenoma was chromophobic, weakly PAS-positive, and immunoreactive mainly for FSH (85%) and to a lesser extent for GH (30%), LH (15%), alpha-subunit (3%), TSH (2%), and PRL (1%). Although double immunostaining showed hormone reactivities to be localized largely in separate distinct cells, the tumor was ultrastructurally monomorphous, i.e., consisted of a single-cell type, resembling gonadotrophs. CONCLUSION: The cytogenesis of plurihormonal pituitary adenomas is not fully understood. Further investigations are required to clarify the basis for their plurihormonality despite an ultrastructural gonadotroph phenotype.

Functioning gonadotroph adenoma with severe ovarian hyperstimulation syndrome: A new emergency in pituitary adenoma surgery? Surgical considerations and literature review.

The authors reported 2 cases of functioning gonadotroph pituitary adenoma (FGPA) revealed by an ovarian hyperstimulation syndrome (OHSS) in young women. In the first case, OHSS was observed after GnRH analog injection. Pelvic echography revealed multiple voluminous ovarian cysts. Dopamine agonist posology failed in estradiol hypersecretion control, which necessitated endoscopic endonasal transsphenoidal surgery. The patient experienced improvement in pelvic pain as estradiol hypersecretion decreased during the first few postoperative days. Outcome was favorable, and her menstrual cycle was normal after two months. The second case was a young girl with spontaneous pelvic pain and elevated plasma FSH and estradiol levels. FGPA was confirmed on cerebral MRI. Dopamine agonists were introduced, and surgical removal of the pituitary tumor was scheduled for 7 days later. In the meantime, the patient was admitted and underwent surgery for bilateral adnexal torsion related to OHSS. The pituitary tumor was removed one week later. Outcome was favorable, and estradiol and FSH plasma levels were normal after 3 months. The ovarian cysts were no longer visible on echography after 3 months. Given the lack of efficacy of the current standard medical therapy, surgical removal of pituitary adenomas is the reference treatment for FGPA. The authors suggest that severe OHSS related to FGPA should be considered as a relative surgical emergency and that surgery should not be unduly delayed, given the unpredictable risk of adnexal torsion, particularly in case of voluminous ovarian cysts. The authors performed a literature review on this topic.

Protein kinase A serves as a primary pathway in activation of Nur77 expression by gonadotropin-releasing hormone in the LbetaT2 mouse pituitary gonadotroph tumor cell line.

Nur77 belongs to a subfamily of nuclear receptors that includes two other members, Nor-1 and Nurr1. It plays an important role in a number of biological processes, including regulation of signaling functions in the hypothalamo-pituitary-adrenal axis, regulation of thymocyte apoptosis, regulation of steroidogenesis and regulation of tumor cell proliferation and apoptosis. In previous studies, using DNA microarray analysis of the effects of the gonadotropin-releasing hormone (GnRH) on the mouse pituitary gonadotroph cell line LbetaT2, we identified Nur77 as one of the highly regulated immediate early genes involved in this response, with >40-fold upregulation after 1 h of treatment of the cells with the GnRH agonist [D-Ala6GnRH (GnRHA)]. GnRH is a hypothalamic decapeptide that stimulates the secretion and expression of gonadotropins (follicle stimulating hormone, FSH and luteinizing hormone releasing hormone, LH) from anterior pituitary through activation of high affinity receptors present on cell membrane of pituitary gonadotropes. In addition to pituitary, the presence of GnRH high affinity receptors has been reported in various cancers and cancer cell lines. In addition, GnRH and its analogs are clinically used in the treatment of prostate cancer. To elucidate the molecular mechanism involved in regulation of Nur77 by GnRH, we first confirmed upregulation of Nur77 in response to GnRH analog (GnRHA) in LbetaT2 cells. Nur77 mRNA was upregulated within 30 min of GnRHA treatment and returned to nearly basal level after 24 h of treatment. Nur77 protein expression was upregulated after 2 h of treatment and remained steady even after 12 h of treatment. The expression of Nur77 mRNA was induced by GnRHA in a dose-dependent manner. Induction of Nur77 expression was stimulated on treatment of cells with forskolin and 8-Br-cAMP, whereas H-89, a specific inhibitor of PKA pathway significantly inhibited GnRHA-induced Nur77 expression. Treatment of cells with both H-89 and EGTA completely blocked the GnRHA-induced expression of Nur77, indicating that both calcium and cAMP/PKA play an important role in regulation of Nur77 expression by GnRHA. Analysis of the protein kinase C (PKC) signaling pathway using specific inhibitors for PKC, Erk1/2, p38 and JNK demonstrated that these pathways are not involved in GnRHA-induced Nur77 expression. Based on our results, we conclude that activation of protein kinase A is the major mechanism regulating the expression of Nur77 by GnRH which may serve as a down-stream signaling gene to mediate the antitumor effects of GnRH.