In situ hybridization analysis of Pit-1 mRNA and hormonal production in human pituitary adenomas

Clinicopathological Features of Growth Hormone-Producing Pituitary Adenomas in 242 Acromegaly Patients: Classification according to Hormone Production and Cytokeratin Distribution

The aim of this study was to clarify the relationship between the histological features of GH-producing adenomas surgically resected at the Toranomon Hospital and the clinical features of the patients. Histological examinations, including immunohistochemistry for anterior pituitary hormones and cytokeratin (CK), were performed on 242 consecutively excised GH-producing pituitary adenomas. Immunohistochemistry showed 45% of the adenomas to be monohormonal and 55% to be plurihormonal, producing GH-PRL (77%), GH-TSH (13%), and GH-PRL-TSH (10%). One-fourth of the monohormonal GH adenomas had a dot-like pattern of CK immunoreactivity in the majority of the tumor cells (>80%); they were significantly more common in female or younger patients and usually tended to be larger and more invasive than monohormonal GH adenomas with perinuclear CK. Interestingly, CK-immunonegative adenomas were found in only 5% of the patients; they also showed a tendency to be larger, suggesting that they are a distinct type of GH adenoma with clinically aggressive features. Serum hormone levels correlated well with tumor size only in GH-producing adenomas with a perinuclear pattern of CK immunoreactivity. Each histological subtype of adenoma, classified according to the pattern of CK immunoreactivity, was associated with distinct clinical characteristics. This information is useful for understanding the pathophysiology of acromegaly-causing GH-producing adenomas.

Expression of FOXL2 in human normal pituitaries and pituitary adenomas

Many transcription factors have important roles in the function and differentiation of the human pituitary adenomas. Forkhead box gene transcription factor L2, Foxl2, is expressed during mouse pituitary development and co-localizes with the expression of α-glycoprotein hormone subunit (αGSU). In addition, Foxl2 regulates expression of the αGSU gene (Cga) in cell culture. To elucidate the functional role of FOXL2 in the human pituitary, we examined the expression and localization of FOXL2 in normal human pituitaries and various types of pituitary adenomas. Human pituitary adenomas were obtained by trans-sphenoidal surgery from 67 patients. Three normal adult pituitaries were obtained from autopsies of non-endocrine cases. The localization of FOXL2 and pituitary hormones in these pituitary patients was examined by immunohistochemical staining and RT-PCR. Quantitative analysis of FOXL2 protein was performed by immunoblotting. FOXL2 was localized in the nuclei of ∼20% of normal pituitary cells that also co-expressed gonadotropins including follicule-stimulating hormone β (FSHβ), luteinizing hormone β (LHβ), and αGSU, whereas it was observed in minor proportion of thyroid-stimulating hormone (TSH)-producing cells, prolactin (PRL)-producing cells, and precursor of adrenocorticotropic hormone (ACTH)-producing cells. FOXL2 immunoreactivity was not detected in growth hormone (GH)-producing cells or S100-positive folliculo-stellate cells. In human pituitary adenomas, FOXL2 was expressed in the nuclei of the adenoma cells. FOXL2 was detected in 13 of 15 gonadotropin-subunit-producing adenoma (Gn-oma) cases and 8 of 11 null cell adenoma cases, but its incidence was reduced or not detected in the other types of adenomas. The results of this study suggest that FOXL2 contributes to the human-specific functional expression and the differentiation of gonadotroph cells and adenomas.

ACTH and alpha-subunit are co-expressed in rare human pituitary corticotroph cell adenomas proposed to originate from ACTH-committed early pituitary progenitor cells

The functional differentiation of pituitary cells and adenomas follows the combination of transcription factors and co-factors in three cell lineages [growth hormone-prolactin-thyroid-stimulating hormone lineage, adrenocorticotrophic hormone (ACTH)/pro-opiomelanocortin (POMC) lineage, and follicular stimulating hormone (FSH)/luteinizing hormone (LH) lineage], which include Pit-1, GATA-2, SF-1, NeuroD1/beta2, Tpit, ERalpha, and others. Only rarely are hormones from different lineages co-expressed in the same adenoma cells. Most corticotroph cell adenomas belonging to the ACTH/POMC lineage are mono-hormonal. In our study of 89 corticotroph cell adenomas, 5 cases expressed both ACTH and alpha-subunit; these adenomas did not express any other anterior pituitary hormones or subunits. To clarify the mechanism involved, we studied the transcription factors that regulate pituitary cell differentiation. NeuroD1 and T-pit, markers of the ACTH/POMC lineage, and SF-1 and DAX-1, related to the LH/FSH cell lineage were expressed in all cases. GATA2, a synergistic factor in the gonadotroph cell lineage with SF-1, was also expressed in three of five cases. As ACTH and alpha-subunit are the earliest hormones to appear during development, we speculate that these particular adenomas are derived from committed ACTH progenitor cells. The molecular process governing functional differentiation of these adenomas requires further investigation.

Induction of GH, PRL, and TSHβ mRNA by transfection of Pit-1 in a human pituitary adenoma-derived cell line

The functional development of pituitary cells depends on the expression of a combination of transcription factors and co-factors. Pituitary-specific transcription factor-1 (Pit-1) is required for the expression of growth hormone (GH), prolactin (PRL), and the thyroid-stimulating hormone beta subunit (TSH beta) and acts synergistically with the estrogen receptor (ER) and GATA-binding protein 2 (GATA-2) to induce PRL and TSH beta expression, respectively. The glycoprotein hormone alpha subunit (alpha SU) is the first hormone to be expressed during pituitary development. In addition to being expressed in follicle-stimulating hormone, luteinizing hormone (LH), and TSH cells, alpha SU is reported to co-localize with GH in pituitary cells. These findings have led to the suggestion that the expression of Pit-1 in cells of the alpha SU-based gonadotropin cell lineage might also lead to the expression of GH. In this study, we transfected HP 75 cells (derived from a human non-functioning pituitary adenoma that expressed alpha SU and LH beta) with Pit-1 by using an adenovirus FLAG-Pit-1 construct. Most of the transfected cells expressed GH mRNA, with fewer cells expressing PRL and TSH beta mRNA. The HP 75 cells expressed the genes for ER and GATA-2, thus allowing their expression of GH, PRL, and TSH beta mRNA in response to Pit-1. These results support the hypothesis that GH can be induced in cells that possess an active alpha SU gene and shed light on the basic molecular mechanism that drives the development of GH, PRL, and TSH beta expression in the alpha SU-based gonadotroph lineage.

Dietary Soybean Enhances Pit-1 Dependent Pituitary Hormone Production in Iodine Deficient Rats

Reports have shown that soybeans are goitrogenic. In the present study, we investigated the effects of a high soybean diet in rats that were fed normal or iodine-deficient chow on the regulation of anterior pituitary hormone production. Iodine deficiency alone resulted in thyroid hyperplasia, reduced serum thyroxine levels, and a tendency towards an increase in serum thyroid stimulating hormone (TSH). The combination of a high soybean and low iodine diet (ID + DS) acted synergistically to induce thyroid hypertrophy, reduce serum thyroxine and tri-iodothyronine, and markedly increase serum TSH. Immunohistochemical analysis revealed that rats fed the ID + DS diet exhibited a marked increase in their number of pituitary TSH, prolactin (PRL), and growth hormone (GH) producing cells. Pituitary transcription factor-1 (Pit-1) which is involved in the expression of the TSH, PRL, and GH genes was also increased in ID + DS fed rats. These results suggest that a diet high in soybean products modulates anterior pituitary hormone production by regulating Pit-1 induction, in iodine-deficient animals.

Cytochemical and molecular biological aspects of the pituitary and pituitary adenomas--cell differentiation and transcription factors

The anterior pituitary is composed of several cell types, each responsible for the production of specific hormones. Each hormone secreting cells is defined by the activation of its respective hormone genes in a temporally and spatially regulated manner. Recent development in cytochemistry and molecular biology have provided various aspects of human pituitary adenomas, i.e., functional differentiation and classification. The molecular factors that determine hormone production have now been identified as transcription factors. Many novel transcription factors that play a role in anterior pituitary development are implicated. In this review, we focus on the transcriptional factors roles on functional differentiation of the pituitary cells and adenomas and the contribution of cytochemistry and recent development in molecular biological techniques.

Expression of Pit-1 and growth hormone-releasing hormone receptor mRNA in human pituitary adenomas: difference among functioning, silent, and other nonfunctioning adenomas

We analyzed the expression of Pit-1 and growth hormone-releasing hormone receptor (GHRH-R) mRNA in various types of functioning and nonfunctioning adenomas using a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) method. Among clinically nonfunctioning adenomas, tumors considered as silent adenomas were reclassified on a pathologic basis. Competitive RT-PCR showed that the levels of Pit-1 and GHRH-R mRNA expression in silent somatotroph adenomas and silent prolactinomas were similar to those in the corresponding functioning adenomas. In silent thyrotroph adenomas, both mRNAs showed high levels of expression that were similar to those in functioning and silent somatotroph adenomas. The results suggest that the cause of the silence in these tumors seems to be in the downstream to transcription of Pit-1 gene in the signaling pathway leading to hormone secretion. Competitive RT-PCR assay could distinguish silent adenomas of the Pit-1 group from the other nonfunctioning adenomas in the expression levels of Pit-1 and GHRH-R mRNAs. In the future, precise diagnosis of various adenomas may become possible by assaying transcription factors such as steroidogenic factor-1 and thyrotroph embryonic factor, which are thought to be related to adenohypophyseal cytodifferentiation.

Thyrotropin-secreting pituitary adenomas. Clinical and biological heterogeneity and current treatment

Thyrotropin (TSH)-secreting pituitary adenomas represent about 1-2% of all pituitary adenomas and cause secondary or central hyperthyroidism. TSH-secreting adenomas are part of the syndrome of 'inappropriate secretion of TSH' (SITSH). The hormonal profile is characterized by nonsuppressed TSH in the presence of high levels of free thyroid hormones (FT3 and FT4). Previous reports have described the surgical cure of TSH adenoma to be more difficult than other functional adenomas because of large and invasive features. However, with the current introduction of ultrasensitive immunometric assays, TSH-secreting adenomas are more often recognized. Early diagnosis of TSH-secreting adenomas leads to a high rate of remission of hyperthyroidism after surgery. However, some of those type of adenomas have clinical heterogeneity, and subsequently cannot be cured by surgery alone. We present our experiences and review reported cases of TSH-secreting adenomas to direct current management.

Expression of neuro D1 in human normal pituitaries and pituitary adenomas

Neuro D1 is a basic helix-loop-helix transcription factor expressed in the endocrine cells of pancreas and in a subset of neurons as they undergo terminal differentiation. In the adult pituitary gland, Neuro D1 is expressed in corticotroph cells and contributes to the corticotroph-specific pro-opiomelanocortin (POMC) transcription by interacting with Pituitary homeobox 1 (Ptx 1) transcription factor. In the present study, we investigated the expression of Neuro D1 in human normal pituitaries and different types of human pituitary adenomas using the RT-PCR and immunohistochemical techniques. Using RT-PCR, Neuro D1 mRNA was found to be expressed in ACTH-secreting adenomas (n = 3) and 6 of 8 non-functioning adenomas. On the other hand, GH-secreting adenomas (n = 5) and PRL-secreting adenomas (n = 3) were completely negative for Neuro D1 mRNA. Immunohistochemically, Neuro D1 was expressed in all ACTH-secreting adenomas (n = 10), and in 14 of 20 nonfunctioning adenomas. In contrast, 3 of 10 PRL-secreting adenomas and 2 of 10 GH-secreting adenomas showed positive Neuro D1 staining in the nuclei. The above results suggest that Neuro D1 contribute to the functional expression and the differentiation of ACTH-secreting adenomas. It also appears from our study that Neuro D1 might play a role in the differentiation of non-functioning adenomas, the mechanism of which remains to be further investigated. This is the first study on Neuro D1 in case of human pituitary adenomas.

Histopathological analyses of silent pituitary somatotroph adenomas using immunohistochemistry, in situ hybridization and confocal laser scanning microscopic observation

To characterize the morphological and functional aspects of silent somatotroph adenomas with paradoxical responses of GH in TRH or GnRH provocation tests, which are considered to be a useful strategy for endocrinological identification of silent somatotroph adenomas, we examined three silent somatotroph adenomas histopathologically. The adenomas were investigated by immunohistochemistry, including the highly sensitive catalyzed signal amplification system, the non-radioisotopic in situ hybridization method, and confocal laser scanning microscopy. GH production and GH-immunopositive secretory granules in the adenoma cells were demonstrated histopathologically, and the adenomas were interpreted as being densely granulated somatotroph adenomas. Endocrinological identification of silent somatotroph adenomas in combination with paradoxical responses of GH in TRH or GnRH provocation tests may elucidate the increasing number of silent somatotroph adenomas that have been regarded as mammotroph or clinically inactive adenomas. One should be aware of the differences between the previously reported silent somatotroph adenomas, most of which are sparsely granulated somatotroph adenomas, a somatotroph adenomas with paradoxical and the silent somatotroph adenomas, most of which are sparsely granulated somatotroph adenomas, and the silent somatotroph adenomas with paradoxical responses of GH in TRH or GnRH provocation tests, which are densely granulated somatotroph adenomas.

POU domain factors in the neuroendocrine system: lessons from developmental biology provide insights into human disease

POU domain factors are transcriptional regulators characterized by a highly conserved DNA-binding domain referred to as the POU domain. The structure of the POU domain has been solved, facilitating the understanding of how these proteins bind to DNA and regulate transcription via complex protein-protein interactions. Several members of the POU domain family have been implicated in the control of development and function of the neuroendocrine system. Such roles have been most clearly established for Pit-1, which is required for formation of somatotropes, lactotropes, and thyrotropes in the anterior pituitary gland, and for Brn-2, which is critical for formation of magnocellular and parvocellular neurons in the paraventricular and supraoptic nuclei of the hypothalamus. While genetic evidence is lacking, molecular biology experiments have implicated several other POU factors in the regulation of gene expression in the hypothalamus and pituitary gland. Pit-1 mutations in humans cause combined pituitary hormone deficiency similar to that found in mice deleted for the Pit-1 gene, providing a striking example of how basic developmental biology studies have provided important insights into human disease.

Expression of pituitary homeo box 1 (Ptx1) in human non-neoplastic pituitaries and pituitary adenomas

We investigated the localization of pituitary homeo box 1 (Ptx1) protein in five human non-neoplastic pituitaries and 73 of all types of pituitary adenomas using immunohistochemistry, and the expression of Ptx1 messenger RNA (mRNA) in 18 representative pituitary adenomas using the reverse transcriptase polymerase chain reaction (RT-PCR) technique. By immunohistochemical analysis, Ptx1 protein was extensively detected in the nuclei of normal human pituitary cells. Ptx1 was detected in 10/14 (71.4%) of growth hormone (GH)-secreting adenomas, 12/12 (100%) of prolactin (PRL)-secreting adenomas, 18/20 (90%) of adrenocorticotropic hormone (ACTH)-secreting adenomas, 6/7 (85.7%) of thyroid-stimulating hormone (TSH)-secreting adenomas, and 17/20 (85%) of clinically non-functioning adenomas, including 9/10 (90%) of gonadotropin-subunit-positive adenomas. Thus, there was no relationship between Ptx1 expression and a particular type of pituitary adenomas. By RT-PCR analysis, Ptx1 mRNA was expressed in all 18 cases of pituitary adenomas, including two cases negative for Ptx1 protein by immunohistochemistry. These results suggested that Ptx1 may be an universal transcription factor in both neoplastic and non-neoplastic conditions in human pituitaries. The synergistic action with other transcription factors may be speculated to determine the specific production of the anterior pituitary hormones.

Contributions of immunohistochemistry and in situ hybridization to the functional analysis of pituitary adenomas

Immunohistochemistry (IHC) and recently in situ hybridization (ISH) have elucidated various aspects of human pituitary adenomas, i.e., functional differentiation and classification, transcription factors and mechanism of hormone production, regulation of hormone secretion, and processing of prohormones. Recently, the use of tyramide (catalyzed signal amplification; TSA or CSA) and RT-PCR has been effective for detection of trivial amount of proteins (peptides) and mRNA, respectively. Immunomolecular histochemistry is expected to further clarify the function and biology of human pituitary adenomas.

Reverse transcription polymerase chain reaction analysis of pituitary hormone, Pit-1 and steroidogenic factor-1 messenger RNA expression in pituitary tumors

Pit-1 is a transcription factor that appears early in embryonic pituitary gland formation and is necessary for the development of somatotropes, lactotropes and thyrotropes. Steroidogenic factor-1 (SF-1) is another early appearing transcription factor that is involved in the development of gonadotropes. In this study we have compared RT-PCR analysis of hormone mRNA with traditional IHC for classification of 27 pituitary tumors and have evaluated the correlation of Pit-1 and SF-1 mRNA with hormone mRNA. RT-PCR detected concordant hormone mRNA in 100% of GH IHC positive, 100% of PRL IHC positive, 33% of TSH IHC positive, and 93% of gonadotropin IHC positive tumors. IHC, however, was concordant in only 71% of GH mRNA positive, 78% of PRL mRNA positive, 17% of TSH beta mRNA positive, and 76% of FSH beta mRNA positive tumors. Pit-1 mRNA was positive in 87% of tumors in which mRNA for GH, PRL or TSH beta was detected and in only 17% of GH, PRL and TSH beta mRNA negative tumors. SF-1 mRNA was positive in 94% of tumors in which mRNA for FSH beta was present and in no FSH beta mRNA negative tumors. We conclude that RT-PCR analysis of hormone mRNA may be more sensitive than traditional hormone IHC for classification of pituitary tumors. Furthermore, tumor Pit-1 mRNA positively correlates with GH, PRL and TSH beta mRNA while tumor SF-1 mRNA correlates well with FSH beta mRNA. Combined analysis of hormone and transcription factor mRNA in pituitary tumor tissue may therefore be a more meaningful approach to pituitary tumor characterization.

Target cells of gamma3-melanocyte-stimulating hormone detected through intracellular Ca2+ responses in immature rat pituitary constitute a fraction of all main pituitary cell types, but mostly express multiple hormone phenotypes at the messenger ribonucleic acid level. Refractoriness to melanocortin-3 receptor blockade in the lacto-somatotroph lineage

Gamma3-MSH has recently been shown to be a biologically active peptide in the rat anterior pituitary. It induces a sustained rise in intracellular free calcium levels ([Ca2+]i) in a relatively small population of immature pituitary cells. The present study was intended to identify the target cells of this peptide and to discern the signal-transducing melanocortin (MC) receptor. In dispersed pituitary cells from 14-day-old rats, increasing doses of gamma3-MSH (0.1, 1, and 10 nM) evoked a sustained oscillating [Ca2+]i rise in an increasing number of cells (up to 14.5%). Within the responsive cells, 53% showed GH immunoreactivity (-ir), 12% showed PRL-ir, 2% showed TSHbeta-ir, 5% showed LHbeta-ir, and 10% showed ACTH-ir, whereas 18% did not express any hormone-ir to a detectable level. As assessed by single cell RT-PCR for the presence of pituitary hormone messenger RNA (mRNA), 26% of the gamma3-MSH-responsive cells contained only GH mRNA, 5% contained only PRL mRNA, and 4% contained only TSHbeta mRNA. Twenty-two percent contained mRNA of GH, PRL, and TSHbeta in various dual or triple combinations. About 24% of the gamma3-MSH-responsive cells expressed POMC mRNA, mostly together with other mRNAs, i.e. with GH mRNA and/or PRL mRNA or with mRNA of GH, PRL, and TSHbeta. Eighteen percent of the responsive cells expressed LHbeta, all of them together with mRNA of GH, PRL, and TSHbeta in various combinations. The absence of hormone mRNA was found in less than 1% of the responsive cells. In cells chosen at random (representative of the total pituitary cell population), the proportion of cells expressing two or multiple hormone mRNAs was twice as low as that in the gamma3-MSH-responsive population, whereas the proportion of cells expressing a single hormone mRNA was twice as high (about two thirds of all cells). Moreover, unlike in the gamma3-MSH-responsive cell population, randomly chosen cells were found that coexpressed POMC mRNA with LHbeta mRNA. The effect of gamma3-MSH on [Ca2+]i was blocked by the MC-3 receptor antagonist SHU9119 (used up to a 1000-fold excess) in 46% or less of the responsive cells. SHU9119 failed to block the [Ca2+]i response to gamma3-MSH in PRL-, GH-, and TSHbeta-ir cells, but it did block the response in most ACTH-ir cells and in cells expressing no hormone to a detectable level. Single cell RT-PCR revealed that expression of MC-3 receptor mRNA was detected in only 16% of gamma3-MSH-responsive cells. The present data suggest that the target cells of gamma3-MSH in terms of [Ca2+]i responses in the immature rat pituitary constitute subpopulations of all main pituitary cell types, including nonhormonal (or low expression hormonal) cells. However, in contrast to the total pituitary cell population, most of these cells display multilineage gene activation at the mRNA level, i.e. express mRNA of GH, PRL, TSHbeta, POMC, and LHbeta in dual, triple, or quadruple combinations. Although gamma3-MSH may act through the MC-3 receptor in a portion of these cells, most of these cells (mainly in the lacto-somatotroph lineage) may transduce the signal through another receptor or through an MC-3 receptor with unconventional binding characteristics.

Expression of Ptx1 in the adult rat pituitary glands and pituitary cell lines: hormone-secreting cells and folliculo-stellate cells

The pituitary homeobox1 gene (Ptx1) was initially identified as encoding a pituitary-restricted transcription factor for the proopiomelanocortin (POMC) gene. In order to elucidate the expression pattern of the Ptx1 protein, we investigated the localization of the protein in adult rat pituitary gland and in various pituitary cell lines. We produced an antibody specific for Ptxl protein, and confirmed its specificity by Western blot analysis. Immunohistochemically, many nuclei in the anterior pituitary cells as well as in the intermediate cells were positive for Ptxl staining with this specific antibody. Immunohistochemical double staining revealed the presence of Ptx1 not only in all types of hormone-secreting cells but also in some folliculo-stellate (FS) cells. Furthermore, the expression of Ptx1 mRNA was confirmed in various pituitary cell lines and in the FS cell line by using the reverse transcriptase-polymerase chain reaction (RT-PCR) method. Our studies indicated that Ptxl may not only play a role as a basic transcriptional factor for production of various hormones, but may also play some important role(s) in FS cells. Possible synergistic actions with other factors remain to be investigated. The novel finding of Ptx1 in FS cells is of particular interest, and may suggest that FS cells and hormone-secreting cells are derived from a common cellular ancestor.

Pit-1 positive alpha-subunit positive nonfunctioning human pituitary adenomas: a dedifferentiated GH cell lineage?

Pit-1 is a transcription factor which has been reported to regulate differentiation toward GH, PRL and TSH in the anterior pituitary glands. In the human pituitary adenomas, Pit-1 is highly expressed in GH secreting and TSH secreting adenomas as it can well be anticipated. Interestingly, human non-functioning pituitary adenomas also express Pit-1, especially it was expressed in all alpha SU positive nonfunctioning adenomas. The human anterior pituitary cells are special in comparison with rodents in a finding that alpha SU is frequently colocalized with GH. As alpha SU is the first hormone appearing during fetal development in the rodent pituitary glands, it may be postulated that alpha SU Pit-1 positive cells undergo differentiation in the GH cell lineage. From this background, this paper proposes that "alpha SU positive Pit-1 Positive" cells are the ones in the GH cell lineage, more specifically a dedifferentiated cell lineage toward alpha SU/GH/Pit-1.