Severe Obesity Associated With Pituitary Corticotroph Hyperplasia and Neoplasia.

OBJECTIVE: To investigate the incidence of corticotroph hyperplasia (CH) or lymphocyte infiltration in the pituitary of patients with obesity. METHODS: The pituitary and adrenal glands from 161 adult autopsies performed between 2010 and 2019 at our institution were reviewed. The clinical history, body mass index (BMI), and cause of death were recorded. Routine hematoxylin and eosin staining, reticulin staining, and immunohistochemical staining for adrenocorticotropic hormone, CD3, and CD20 were performed. The results were analyzed using the Fisher and chi-square statistics. Decedents were separated into 4 groups based on BMI (kg/m2): (1) lean (BMI, <25.0), (2) overweight (BMI, 25.0-29.9), (3) obesity class I (BMI, 30.0-34.9), and (4) obesity classes II to III (BMI, >34.9). RESULTS: CH/neoplasia was identified in 44 of 161 pituitary glands. Four (9.1%) of 53 lean patients had pituitary lesions, whereas 27.3% (12) of overweight, 22.7% (10) of obesity class I, and 40.9% (18) of obesity class II patients had hyperplasia (P < .0001). Small corticotroph tumors were identified in 15 patients; only 1 was a lean patient, and the tumor was associated with the Crooke hyaline change of nontumorous corticotrophs. The presence of CH and neoplasia was associated with adrenal cortical hyperplasia and lipid depletion. Microscopic foci of T and B lymphocytes were identified in the pituitaries of patients in each weight category; no independent association between BMI and lymphocyte inflammation was found. CONCLUSION: Our data indicate an association between CH/neoplasia and obesity. It remains unclear whether obesity is the cause or effect of adrenocorticotropic hormone and cortisol excess.

Protein kinase C delta mediates Pasireotide effects in an ACTH-secreting pituitary tumor cell line.

PURPOSE: Clinical control of corticotroph tumors is difficult to achieve since they usually persist or relapse after surgery. Pasireotide is approved to treat patients with Cushing's disease for whom surgical therapy is not an option. However, Pasireotide seems to be effective only in a sub-set of patients, highlighting the importance to find a response marker to this approach. Recent studies demonstrated that the delta isoform of protein kinase C (PRKCD) controls viability and cell cycle progression of an in vitro model of ACTH-secreting pituitary tumor, the AtT-20/D16v-F2 cells. This study aims at exploring the possible PRKCD role in mediating Pasireotide effects. METHODS: It was assessed cell viability, POMC expression and ACTH secretion in AtT20/D16v-F2 cells over- or under-expressing PRKCD. RESULTS: We found that Pasireotide significantly reduces AtT20/D16v-F2 cell viability, POMC expression and ACTH secretion. In addition, Pasireotide reduces miR-26a expression. PRKCD silencing decreases AtT20/D16v-F2 cell sensitivity to Pasireotide treatment; on the contrary, PRKCD overexpression increases the inhibitory effects of Pasireotide on cell viability and ACTH secretion. CONCLUSION: Our results provide new insights into potential PRKCD contribution in Pasireotide mechanism of action and suggest that PRKCD might be a possible marker of therapeutic response in ACTH-secreting pituitary tumors.

Chronic stress facilitates bursting electrical activity in pituitary corticotrophs.

Coordination of an appropriate stress response is dependent upon anterior pituitary corticotroph excitability in response to hypothalamic secretagogues and glucocorticoid negative feedback. A key determinant of corticotroph excitability is large conductance calcium- and voltage-activated (BK) potassium channels that are critical for promoting corticotrophin-releasing hormone (CRH)-induced bursting that enhances adrenocorticotrophic hormone secretion. Previous studies revealed hypothalamic-pituitary-adrenal axis hyperexcitability following chronic stress (CS) is partly a function of increased corticotroph output. Thus, we hypothesise that chronic stress promotes corticotroph excitability through a BK-dependent mechanism. Corticotrophs from CS mice displayed significant increase in spontaneous bursting, which was suppressed by the BK blocker paxilline. Mathematical modelling reveals that the time constant of BK channel activation, plus properties and proportion of BK channels functionally coupled to L-type Ca2+ channels determines bursting activity. Surprisingly, CS corticotrophs (but not unstressed) display CRH-induced bursting even when the majority of BK channels are inhibited by paxilline, which modelling suggests is a consequence of the stochastic behaviour of a small number of BK channels coupled to L-type Ca2+ channels. Our data reveal that changes in the stochastic behaviour of a small number of BK channels can finely tune corticotroph excitability through stress-induced changes in BK channel properties. Importantly, regulation of BK channel function is highly context dependent allowing dynamic control of corticotroph excitability over a large range of time domains and physiological challenges in health and disease. This is likely to occur in other BK-expressing endocrine cells, with important implications for the physiological processes they regulate and the potential for therapy. KEY POINTS: Chronic stress (CS) is predicted to modify the electrical excitability of anterior pituitary corticotrophs. Electrophysiological recordings from isolated corticotrophs from CS male mice display spontaneous electrical bursting behaviour compared to the tonic spiking behaviour of unstressed corticotrophs. The increased spontaneous bursting from CS corticotrophs is BK-dependent and mathematical modelling reveals that the time constant of activation, properties and proportion of BK channels functionally coupled to L-type calcium channels determines the promotion of bursting activity. CS (but not unstressed) corticotrophs display corticotrophin-releasing hormone-induced bursting even when the majority of BK channels are pharmacologically inhibited, which can be explained by the stochastic behaviour of a small number of BK channels with distinct properties. Corticotroph excitability can be finely tuned by the stochastic behaviour of a small number of BK channels dependent on their properties and functional co-localisation with L-type calcium channels to control corticotroph excitability over diverse time domains and physiological challenges.

Pituitary corticotroph tumour with adrenocortical cells: A distinct clinicopathologic entity with unique morphology and methylation profile.

We describe a rare TPIT-positive corticotroph PitNET that is admixed with SF1-positive adrenocortical cells. This dimorphous population of cells showed no colocalisation between TPIT and SF1 by immunofluorescence, and an adrenocortical choristoma was favoured. Methylation array analysis revealed a novel methylation profile in relation to other pituitary neoplasms.

PI3K inhibition by BKM120 results in anti-proliferative effects on corticotroph tumor cells.

PURPOSE: Cushing's disease is associated with significant morbidity; thus, additional tumor-directed drugs with the potential to exert antineoplastic effects on corticotroph adenoma cells are desired. The phosphoinositide-3-kinase (PI3K)/protein kinase B (AKT) pathway, which plays regulatory role in cell survival and proliferation, is activated in pituitary adenomas. The present study evaluated the effects of BKM120 (Buparlisib), an oral PI3K inhibitor, on cell viability, apoptosis, cell cycle phase distribution, and ACTH production in mouse corticotroph tumor cells. METHODS: AtT-20/D16v-F2 mouse pituitary corticotroph tumor cells were treated with increasing concentrations of BKM120 or vehicle. Cell viability was measured using an MTS-based assay. Apoptosis was evaluated by Annexin V staining. Cell cycle analysis was performed by propidium iodide DNA staining and flow cytometry. Gene expression of cell cycle regulators (Cdkn1b, Ccnd1, Ccne1, Cdk2, Cdk4, Myc, and Rb1) was assessed by qPCR. Protein expression of p27, total and phosphorylated Akt was assessed by Western blot. ACTH levels were measured in the culture supernatants by chemiluminescent immunometric assay. RESULTS: Treatment with BKM120 decreased AtT-20/D16v-F2 cell viability, induced a G0/G1 cell cycle arrest, reduced the phosphorylation of Akt at Serine 473, and increased p27 expression. Furthermore, BKM120 treatment diminished ACTH levels in the cell culture supernatants. CONCLUSION: In vitro inhibition of PI3K/AKT pathway by BKM120 resulted in anti-proliferative effects on corticotroph tumor cells, decreasing cell viability and ACTH production. These encouraging findings shape the path for further experiments with the inhibition of PI3K/AKT pathway in Cushing's disease.

Difference in miRNA Expression in Functioning and Silent Corticotroph Pituitary Adenomas Indicates the Role of miRNA in the Regulation of Corticosteroid Receptors.

Corticotroph pituitary adenomas commonly cause Cushing's disease (CD), but some of them are clinically silent. The reason why they do not cause endocrinological symptoms remains unclear. We used data from small RNA sequencing in adenomas causing CD (n = 28) and silent ones (n = 20) to explore the role of miRNA in hormone secretion and clinical status of the tumors. By comparing miRNA profiles, we identified 19 miRNAs differentially expressed in clinically functioning and silent corticotroph adenomas. The analysis of their putative target genes indicates a role of miRNAs in regulation of the corticosteroid receptors expression. Adenomas causing CD have higher expression of hsa-miR-124-3p and hsa-miR-135-5p and lower expression of their target genes NR3C1 and NR3C2. The role of hsa-miR-124-3p in the regulation of NR3C1 was further validated in vitro using AtT-20/D16v-F2 cells. The cells transfected with miR-124-3p mimics showed lower levels of glucocorticoid receptor expression than control cells while the interaction between miR-124-3p and NR3C1 3' UTR was confirmed using luciferase reporter assay. The results indicate a relatively small difference in miRNA expression between clinically functioning and silent corticotroph pituitary adenomas. High expression of hsa-miR-124-3p in adenomas causing CD plays a role in the regulation of glucocorticoid receptor level and probably in reducing the effect of negative feedback mediated by corticosteroids.

Differential effects of ß-arrestin1 and ß-arrestin2 on somatostatin receptors in murine AtT-20 corticotroph tumor cells.

Autonomous production of adrenocorticotropic hormone (ACTH) from pituitary corticotroph adenomas is the primary cause of Cushing's disease. Somatostatin receptor, a G protein-coupled receptor (GPCR), types 2 (SSTR2) and 5 (SSTR5) mRNA expression is greater than that of other SSTR subtypes in human corticotroph adenomas. Further, the multiligand SOM230 shows potent effects in decreasing ACTH plasma levels and urinary free cortisol levels in patients with Cushing's disease. We previously showed that both Sstr2 and Sstr5 mRNA levels were unaffected by SOM230 treatment, suggesting that both receptors might not be downregulated by the agonist. Intracellular molecules, such as ß-arrestins, modulate ligand activated-receptor responses. In the present study, we determined regulation of ß-arrestin1 and ß-arrestin2 by SOM230 and dexamethasone in murine AtT-20 corticotroph tumor cells. In addition, we examined the effects of ß-arrestin1 and ß-arrestin2 on Sstr mRNA and their protein levels. SOM230 treatment increased ß-arrestin1 mRNA levels and did not alter ß-arrestin2 mRNA levels. SOM230 treatment could induce ß-arrestin1 production in corticotroph tumor cells. Dexamethasone treatment decreased ß-arrestin2 mRNA levels. ß-arrestin2 knockdown increased proopiomelanocortin, and both Sstr2 and Sstr5 mRNA and their protein levels. The ß-arrestin2 knockdown-increased proopiomelanocortin mRNA levels were canceled by SOM230 treatment.

Differential Effects of Fkbp4 and Fkbp5 on Regulation of the Proopiomelanocortin Gene in Murine AtT-20 Corticotroph Cells.

The hypothalamic-pituitary-adrenal axis is stimulated in response to stress. When activated, it is suppressed by the negative feedback effect of glucocorticoids. Glucocorticoids directly inhibit proopiomelanocortin (Pomc) gene expression in the pituitary. Glucocorticoid signaling is mediated via glucocorticoid receptors, 11ß-hydroxysteroid dehydrogenases, and the FK506-binding immunophilins, Fkbp4 and Fkbp5. Fkbp4 and Fkbp5 differentially regulate dynein interaction and nuclear translocation of the glucocorticoid receptor, resulting in modulation of the glucocorticoid action. Here, we explored the regulation of Fkbp4 and Fkbp5 genes and their proteins with dexamethasone, a major synthetic glucocorticoid drug, in murine AtT-20 corticotroph cells. To elucidate further roles of Fkbp4 and Fkbp5, we examined their effects on Pomc mRNA levels in corticotroph cells. Dexamethasone decreased Pomc mRNA levels as well as Fkpb4 mRNA levels in mouse corticotroph cells. Dexamethasone tended to decrease Fkbp4 protein levels, while it increased Fkpb5 mRNA and its protein levels. The dexamethasone-induced decreases in Pomc mRNA levels were partially canceled by Fkbp4 knockdown. Alternatively, Pomc mRNA levels were further decreased by Fkbp5 knockdown. Thus, Fkbp4 contributes to the negative feedback of glucocorticoids, and Fkbp5 reduces the efficiency of the glucocorticoid effect on Pomc gene expression in pituitary corticotroph cells.

Orexin A Enhances Pro-Opiomelanocortin Transcription Regulated by BMP-4 in Mouse Corticotrope AtT20 Cells.

Orexin is expressed mainly in the hypothalamus and is known to activate the hypothalamic-pituitary-adrenal (HPA) axis that is involved in various stress responses and its resilience. However, the effects of orexin on the endocrine function of pituitary corticotrope cells remain unclear. In this study, we investigated the roles of orexin A in pro-opiomelanocortin (POMC) transcription using mouse corticotrope AtT20 cells, focusing on the bone morphogenetic protein (BMP) system expressed in the pituitary. Regarding the receptors for orexin, type 2 (OXR2) rather than type 1 (OX1R) receptor mRNA was predominantly expressed in AtT20 cells. It was found that orexin A treatment enhanced POMC expression, induced by corticotropin-releasing hormone (CRH) stimulation through upregulation of CRH receptor type-1 (CRHR1). Orexin A had no direct effect on the POMC transcription suppressed by BMP-4 treatment, whereas it suppressed Smad1/5/9 phosphorylation and Id-1 mRNA expression induced by BMP-4. It was further revealed that orexin A had no significant effect on the expression levels of type I and II BMP receptors but upregulated inhibitory Smad6/7 mRNA and protein levels in AtT20 cells. The results demonstrated that orexin A upregulated CRHR signaling and downregulated BMP-Smad signaling, leading to an enhancement of POMC transcription by corticotrope cells.

SOX2 is sequentially required for progenitor proliferation and lineage specification in the developing pituitary.

Sox2 mutations are associated with pituitary hormone deficiencies and the protein is required for pituitary progenitor proliferation, but its function has not been well characterized in this context. SOX2 is known to activate expression of Six6, encoding a homeodomain transcription factor, in the ventral diencephalon. Here, we find that the same relationship likely exists in the pituitary. Moreover, because Six6 deletion is associated with a similar phenotype as described here for loss of Sox2, Six6 appears to be an essential downstream target of SOX2 in the gland. We also uncover a second role for SOX2. Whereas cell differentiation is reduced in Sox2 mutants, some endocrine cells are generated, such as POMC-positive cells in the intermediate lobe. However, loss of SOX2 here results in complete downregulation of the melanotroph pioneer factor PAX7, and subsequently a switch of identity from melanotrophs to ectopic corticotrophs. Rescuing proliferation by ablating the cell cycle negative regulator p27 (also known as Cdkn1b) in Sox2 mutants does not restore melanotroph emergence. Therefore, SOX2 has two independent roles during pituitary morphogenesis; firstly, promotion of progenitor proliferation, and subsequently, acquisition of melanotroph identity.

Selenoprotein T is a novel OST subunit that regulates UPR signaling and hormone secretion.

Selenoprotein T (SelT) is a recently characterized thioredoxin-like protein whose expression is very high during development, but is confined to endocrine tissues in adulthood where its function is unknown. We report here that SelT is required for adaptation to the stressful conditions of high hormone level production in endocrine cells. Using immunofluorescence and TEM immunogold approaches, we find that SelT is expressed at the endoplasmic reticulum membrane in all hormone-producing pituitary cell types. SelT knockdown in corticotrope cells promotes unfolded protein response (UPR) and ER stress and lowers endoplasmic reticulum-associated protein degradation (ERAD) and hormone production. Using a screen in yeast for SelT-membrane protein interactions, we sort keratinocyte-associated protein 2 (KCP2), a subunit of the protein complex oligosaccharyltransferase (OST). In fact, SelT interacts not only with KCP2 but also with other subunits of the A-type OST complex which are depleted after SelT knockdown leading to POMC N-glycosylation defects. This study identifies SelT as a novel subunit of the A-type OST complex, indispensable for its integrity and for ER homeostasis, and exerting a pivotal adaptive function that allows endocrine cells to properly achieve the maturation and secretion of hormones.

Cell specific interaction of pasireotide: review of preclinical studies in somatotroph and corticotroph pituitary cells.

BACKGROUND: Pasireotide is a second-generation somatostatin (SRIF) receptor ligand (SRL), approved for medical treatment of acromegaly and Cushing's disease (CD). The molecule is a stable cyclohexapeptide synthetized based on SRIF structure. Differently from first-generation SRLs (e.g. octreotide), preferentially binding somatostatin receptor (SST) subtype 2 (SST2), pasireotide has high affinity for multiple SSTs (SST5 > SST2 > SST3 > SST1). Interestingly, early preclinical studies demonstrated that pasireotide shows distinct functional properties compared to SRIF and first-generation SRLs when binding SSTs. METHODS: We aimed to highlight the differential receptor-targeted action of pasireotide in the treatment of somatotroph and corticotroph adenomas, throughout the critical revision of preclinical studies carried out on acromegaly and CD models. RESULTS: Different authors demonstrated that the antisecretory effect of pasireotide in somatotroph adenoma cell cultures is comparable to that of the SST2-preferential agonist octreotide. Some reports even show a direct correlation between SST2 mRNA expression and GH reduction after pasireotide treatment, thus laying for a predominant role of SST2 in driving pasireotide efficacy in somatotropinomas in vitro. On the other hand, the inhibitory effect of pasireotide on ACTH secretion in corticotropinoma cells seems to be mainly mediated by SST5. Indeed, most reports show a higher potency and efficacy of pasireotide compared to SST2 preferential agonists, while functional studies confirm the pivotal role of SST5 targeting in corticotroph cells. CONCLUSIONS: The analysis of preclinical studies carried out in somatotroph and corticoph adenomas points out that pasireotide shows a cell-specific activity, exerting its biological effects via different SSTs in the different adenoma histotypes.

Lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells.

Cushing's disease is almost always caused by hypersecretion of adrenocorticotropic hormone (ACTH) from a pituitary adenoma. A mutation in the deubiquitinase gene USP8 has been found in human ACTH-producing pituitary adenoma cells. This mutational hotspot hyperactivates USP8, rescuing epidermal growth factor receptor (EGFR) from lysosomal degradation and ensuring its sustained signaling in Cushing's disease. An EGFR inhibitor would be an effective anti-tumor agent in EGFR-related tumors. We investigated the effect of a potent dual tyrosine kinase inhibitor, lapatinib, on ACTH production and cell proliferation in AtT-20 mouse corticotroph tumor cells. Lapatinib decreased proopiomelanocortin (Pomc) mRNA levels and ACTH levels in AtT-20 cells and also inhibited cell proliferation, induced apoptosis, and decreased pituitary tumor-transforming gene 1 (Pttg1), a hallmark of pituitary tumors, mRNA levels. KSN/Slc nude mice were subcutaneously inoculated with AtT-20 cells. After 1 week, the mice were randomized either to control or lapatinib groups. The inhibitor decreased the tumor weight of AtT-20 allografts in vivo versus control mice. Lapatinib also significantly decreased Pomc and Pttg1 mRNA levels in the tumor and plasma ACTH and corticosterone levels in vivo. Thus, lapatinib decreases the ACTH production and proliferation of corticotroph tumor cells. An EGFR-targeting therapy could be an important treatment for Cushing's disease.

Clock genes alterations and endocrine disorders.

BACKGROUND: Various endocrine signals oscillate over the 24-hour period and so does the responsiveness of target tissues. These daily oscillations do not occur solely in response to external stimuli but are also under the control of an intrinsic circadian clock. DESIGN: We searched the PubMed database to identify studies describing the associations of clock genes with endocrine diseases. RESULTS: Various human single nucleotide polymorphisms of brain and muscle ARNT-like 1 (BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK) genes exhibited significant associations with type 2 diabetes mellitus. ARNTL2 gene expression and upregulation of BMAL1 and PER1 were associated with the development of type 1 diabetes mellitus. Thyroid hormones modulated PER2 expression in a tissue-specific way, whereas BMAL1 regulated the expression of type 2 iodothyronine deiodinase in specific tissues. Adrenal gland and adrenal adenoma expressed PER1, PER2, CRY2, CLOCK and BMAL1 genes. Adrenal sensitivity to adrenocorticotrophin was also affected by circadian oscillations. A significant correlation between the expression of propio-melanocorticotrophin and PER 2, as well as between prolactin and CLOCK, was found in corticotroph and lactosomatotroph cells, respectively, in the pituitary. Clock genes and especially BMAL1 showed an important role in fertility, whereas oestradiol and androgens exhibited tissue-specific effects on clock gene expression. Metabolic disorders were also associated with circadian dysregulation according to studies in shift workers. CONCLUSIONS: Clock genes are associated with various endocrine disorders through complex mechanisms. However, data on humans are scarce. Moreover, clock genes exhibit a tissue-specific expression representing an additional level of regulation. Their specific role in endocrine disorders and their potential implications remain to be further clarified.

Pregnancy-associated Cushing's disease? An exploratory retrospective study.

PURPOSE: In most clinical series of Cushing's disease (CD), over 80% of patients are women, many of whom are of reproductive age. The year following pregnancy may be a common time to develop CD. We sought to establish the incidence of CD onset associated with pregnancy. METHODS: A retrospective review was conducted for patients with biochemically-proven CD. Demographics, clinical history, biochemistry, imaging, pathology, and outcomes were reviewed. Pregnancy-associated CD was defined as symptom onset within 1 year of childbirth. RESULTS: Over 10 years, 77 patients including 64 women (84%), with CD underwent endonasal surgery. Of the 64 women, 64% were of reproductive age (15-45 years) at the time of diagnosis, and 11 (27%) met criteria for pregnancy-associated CD. Of these 11 women, median number of pregnancies prior to onset of CD was 2 (range 1-4) compared to zero (range 0-7) for 30 other women with CD onset during reproductive age (p = 0.0024). With an average follow-up of 47 ± 34 months, sustained surgical remission rates for woman with pregnancy-associated CD, other women of reproductive age, and women not of reproductive age were 91%, 80% and 83%, respectively. The average lag-time from symptom onset to diagnosis for women with pregnancy-associated CD was 4 ± 2 years. CONCLUSIONS: In this exploratory study, over one quarter of women of reproductive age with CD appeared to have symptomatic disease onset within 1 year of childbirth. This relatively high rate of pregnancy-associated CD suggests a possible causal relationship related to the stress of pregnancy and pituitary corticotroph hyperactivity in the peripartum period. This possible association suggests a heightened degree of clinical suspicion and biochemical testing for CD may be warranted after childbirth. Further study of this possible link between pregnancy and CD is warranted.

Modeling the diversity of spontaneous and agonist-induced electrical activity in anterior pituitary corticotrophs.

Pituitary corticotrophs fire action potentials spontaneously and in response to stimulation with corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and such electrical activity is critical for calcium signaling and calcium-dependent adrenocorticotropic hormone secretion. These cells typically fire tall, sharp action potentials when spontaneously active, but a variety of other spontaneous patterns have also been reported, including various modes of bursting. There is variability in reports of the fraction of corticotrophs that are electrically active, as well as their patterns of activity, and the sources of this variation are not well understood. The ionic mechanisms responsible for CRH- and AVP-triggered electrical activity in corticotrophs are also poorly characterized. We use electrophysiological measurements and mathematical modeling to investigate possible sources of variability in patterns of spontaneous and agonist-induced corticotroph electrical activity. In the model, variation in as few as two parameters can give rise to many of the types of patterns observed in electrophysiological recordings of corticotrophs. We compare the known mechanisms for CRH, AVP, and glucocorticoid actions and find that different ionic mechanisms can contribute in different but complementary ways to generate the complex time courses of CRH and AVP responses. In summary, our modeling suggests that corticotrophs have several mechanisms at their disposal to achieve their primary function of pacemaking depolarization and increased electrical activity in response to CRH and AVP.NEW & NOTEWORTHY We and others recently demonstrated that the electrical activity and calcium dynamics of corticotrophs are strikingly diverse, both spontaneously and in response to the agonists CRH and AVP. Here we demonstrate this diversity with electrophysiological measurements and use mathematical modeling to investigate its possible sources. We compare the known mechanisms of agonist-induced activity in the model, showing how the context of ionic conductances dictates the effects of agonists even when their target is fixed.

Adrenalectomy facilitates ATAT1 expression and α-tubulin acetylation in ACTH-producing corticotrophs.

Microtubules play an important role in the intracellular transport of secretory granules in endocrine cells and in mitosis and the maintenance of cell morphology and are composed of heterodimers of α- and ß-tubulin. α-Tubulin N-acetyltransferase 1 (ATAT1), which acetylates the lysine residue at position 40 of α-tubulin, functions not only in stabilizing microtubule structures and forming the primary cilium assembly but also in vesicular trafficking in neurons. However, the localization of ATAT1 and the role of α-tubulin acetylation in endocrine cells in the pituitary are still poorly understood. Corticotrophs in the anterior lobe of the pituitary produce and secrete adrenocorticotropin (ACTH). Although removal of the adrenal gland, a target organ of ACTH, is reported to promote the synthesis and secretion of ACTH in corticotrophs and to induce structural alterations in their organelles, uncertainty remains as to whether the acetylation of α-tubulin is involved in such intracellular events of corticotrophs. We investigate the expression and localization of ATAT1 and the acetylation of α-tubulin in the pituitary of normal and adrenalectomized rats. We find that ATAT1 is localized to the Golgi apparatus of endocrine cells in the anterior lobe of normal pituitary and that the expression levels of ATAT1 and acetylation levels of α-tubulin increase following adrenalectomy. These results agree with the hypothesis that the acetylation of α-tubulin by ATAT1 regulates the intracellular transport of secretory granules in corticotrophs.

Large conductance Ca²âº-activated K⁺ (BK) channels promote secretagogue-induced transition from spiking to bursting in murine anterior pituitary corticotrophs.

Anterior pituitary corticotroph cells are a central component of the hypothalamic-pituitary-adrenal (HPA) axis essential for the neuroendocrine response to stress. Corticotrophs are excitable cells that receive input from two hypothalamic secretagogues, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) to control the release of adrenocorticotrophic hormone (ACTH). Although corticotrophs are spontaneously active and increase in excitability in response to CRH and AVP the patterns of electrical excitability and underlying ionic conductances are poorly understood. In this study, we have used electrophysiological, pharmacological and genetic approaches coupled with mathematical modelling to investigate whether CRH and AVP promote distinct patterns of electrical excitability and to interrogate the role of large conductance calcium- and voltage-activated potassium (BK) channels in spontaneous and secretagogue-induced activity. We reveal that BK channels do not play a significant role in the generation of spontaneous activity but are critical for the transition to bursting in response to CRH. In contrast, AVP promotes an increase in single spike frequency, a mechanism independent of BK channels but dependent on background non-selective conductances. Co-stimulation with CRH and AVP results in complex patterns of excitability including increases in both single spike frequency and bursting. The ability of corticotroph excitability to be differentially regulated by hypothalamic secretagogues provides a mechanism for differential control of corticotroph excitability in response to different stressors.

Relevance of mutations in protein deubiquitinases genes and TP53 in corticotroph pituitary tumors.

Introduction: Corticotroph pituitary neuroendocrine tumors (PitNETs) develop from ACTH-producing cells. They commonly cause Cushing's disease (CD), however, some remain clinically silent. Recurrent USP8, USP48, BRAF and TP53 mutations occur in corticotroph PitNETs. The aim of our study was to determine frequency and relevance of these mutations in a possibly large series of corticotroph PitNETs. Methods: Study included 147 patients (100 CD and 47 silent tumors) that were screened for hot-spot mutations in USP8, USP48 and BRAF with Sanger sequencing, while 128 of these patients were screened for TP53 mutations with next generation sequencing and immunohistochemistry. Results: USP8 mutations were found in 41% CD and 8,5% silent tumors, while USP48 mutations were found in 6% CD patients only. Both were more prevalent in women. They were related to higher rate of biochemical remission, non-invasive tumor growth, its smaller size and densely granulated histology, suggesting that these mutation may be favorable clinical features. Multivariate survival analyses did not confirm possible prognostic value of mutation in protein deubiquitinases. No BRAF mutations were found. Four TP53 mutations were identified (2 in CD, 2 in silent tumors) in tumors with size >10mm including 3 invasive ones. They were found in Crooke's cell and sparsely granulated tumors. Tumors with missense TP53 mutations had higher TP53 immunoreactivity score than wild-type tumors. Tumor with frameshift TP53 variant had low protein expression. TP53 mutation was a poor prognostic factor in CD according to uni- and multivariate survival analyses in spite of low mutations frequency. Conclusions: We confirmed high prevalence of USP8 mutations and low incidence of USP48 and TP53 mutations. Changes in protein deubiquitinases genes appear to be favorable prognostic factors in CD. TP53 mutations are rare, occur in both functioning and silent tumors and are related to poor clinical outcome in CD.

Modified S/MAR episomal vectors for stably expressing fluorescent protein-tagged transgenes with small cell-to-cell fluctuations.

We modified and tested scaffold/matrix attachment region (S/MAR) episomal vectors. The new vectors would be useful in obtaining cells stably expressing fluorescent protein-tagged transgenes with small, mostly within 10-fold cell-to-cell fluctuations. In the vectors, the same transcript directs episomal replication and expression of transgene/antibiotic marker, and only antibiotic selection without any other extra steps was sufficient to obtain desired stable cells, including those expressing two different proteins simultaneously. Furthermore, the two test cases (expression of human growth hormone in AtT20 and four protein kinase C isoforms in HEK293) would prove to be useful in visualizing and analyzing regulatory processes involving these proteins.