Pituitary Tumor Cell Growth Research Articles

7559 TRIM21 Regulates Activation of ERK1/2 to Promote Growth and Drug Resistance in Pituitary Neuroendocrine Tumors

Abstract Disclosure: Y. Liu: None. F. Liu: None. C. Li: None. T. Zhang: None. L. Xue: None. Z. Wu: None. Objective: To investigate the role of the TRIM family genes in pituitary neuroendocrine tumors (PitNETs) and provide new targets and strategies for the clinical treatment of these tumors. Methods: A CRISPR screening system targeting the TRIM family was constructed and validated using next-generation sequencing. Stable cell lines overexpressing or knocking out TRIM21 were generated, and functional validation was performed using assays such as CCK-8, colony formation, and xenograft tumor growth in nude mice. RNA-seq, mass spectrometry, immunohistochemistry, and immunoblotting were employed to explore the signaling pathways and mechanisms underlying TRIM21's actions. Immunoprecipitation, immunofluorescence, GST-pulldown, NanoBiT assays, and ubiquitination experiments were conducted to investigate the effects of TRIM21 on ERK1/2. Immunohistochemistry and immunoblotting were used to explore the role of TRIM21 in drug- resistant prolactinomas and the correlation between TRIM21 and p-ERK. Results: Through screening the proliferative and drug-resistant effects of the TRIM family in MMQ and GH3 cells, we found that knocking out TRIM21 may inhibit cell growth and enhance drug sensitivity. Subsequently, stable cell lines overexpressing or knocking out TRIM21 were generated in MMQ and GH3 cells, revealing that TRIM21 overexpression promotes pituitary tumor cell growth and resistance to drug treatment, while TRIM21 knockout inhibits cell growth and enhances drug sensitivity. Cell-derived xenograft models showed that TRIM21 overexpression promoted growth of GH3 cells in vivo and resistance to cabergoline (CAB), while TRIM21 knockout suppressed growth of MMQ cells in vivo. Further exploration of the signaling pathways influenced by TRIM21 revealed that TRIM21 knockout downregulates the MAPK signaling pathway, while TRIM21 overexpression upregulates it. TRIM21 overexpression upregulates p-ERK1/2 in the MAPK pathway, while TRIM21 knockout decreases p-ERK. However, there is no significant influence on ERK1/2, JNK, p-JNK, p38, or p-p38. Mechanically, TRIM21 interacted with ERK1/2, enhancing the K27-linked ubiquitination of ERK1/2 and promoting their interaction with MEK1/2. In addition, the TRIM21 with D-docking mutant or ERK1/2 with CD-domain mutant resulted in the loss of their interaction. Furthermore, TRIM21 and p-ERK levels were significantly elevated in drug-resistant prolactinomas and immunohistochemical semi-quantitative analysis demonstrated a positive correlation between TRIM21 and p-ERK. Conclusion: The ubiquitin ligase TRIM21 catalyzes K27-linked ubiquitination of ERK1/2, enhancing its interaction with MEK1/2 and activation, thereby promoting growth and drug resistance in pituitary neuroendocrine tumors. TRIM21 may serve as a potential target for the treatment of pituitary neuroendocrine tumors. Presentation: 6/3/2024

Evaluating the expression pattern of the opioid receptor in pituitary neuroendocrine tumors (PitNET) and the role of morphine and naloxone in the regulation of pituitary cell line growth and apoptosis

PurposeThe expression pattern of the opioid receptor (MOR) in pituitary neuroendocrine tumors (PitNET) and the possible effect of morphine and naloxone on GH3 cell growth and apoptosis were evaluated. MethodsThe 114 pituitary tissues including non-functioning, GH-producing and ACTH-producing PitNET and healthy cadaver pituitary tissues were included. The expression level of the MOR gene and protein was assessed using real-time PCR and Western blot. The association with patient demographic characteristics was assessed. Morphine and naloxone were applied to assess their possible pharmacological role in GH3 pituitary adenoma cell death. The cytotoxic effect, the apoptosis rate, the cell cycle distribution, the content of reactive oxygen species and the caspase 3 activity were measured. ResultsMOR gene levels increased significantly in pituitary neuroendocrine tumors (PitNET) compared to the healthy pituitary samples. The increased level of MOR gene expression was prominent in invasive functional and non-functional pituitary tumors. A consistent expression pattern was demonstrated for MOR protein levels in PitNET samples. A dose- and time-dependent reduction in the rate of GH3 pituitary cells was observed after morphine treatment with an IC50 of 483 µM after 24 h of incubation. Morphine induced early apoptosis, accumulation of cells in sub-G1 phase, increase in cellular ROS levels and caspase-3 activity. The observed effects of morphine were reversed after MOR blockade using 10 and 25 µM naloxone. ConclusionThe possible contributing role of the MOR in pituitary tumor cell growth and the putative pharmaceutical effect of morphine in pituitary neuroendocrine tumor cell death (PitNET) is illustrated

LBODP078 Role Of Ire1a-xbp1 Pathway In Rodent Functional Pituitary Tumor Cells.

Abstract Introduction Pituitary tumors (PTs) occur in almost 17% of the population and they represent about 10% of all intracranial tumors. At present, many patients with pituitary tumors suffer from symptoms and complications caused by abnormal hormone production and/or mass effects due to limited treatment options. Therefore, the development of novel therapies is an urgent issue. The inositol requiring enzyme 1a (IRE1a)-X-box binding protein 1 (XBP1) pathway is an important component for the endoplasmic reticulum (ER) stress response. This pathway is activated by immature protein overload in the ER and elimination or repair of such protein can reduce ER stress. This pathway has been reported to regulate cancer cell growth and secretory protein production. The detection of potential XBP1 binding sites in the promoter region of rat GH and mouse POMC similar to those of human genes suggests the involvement of the IRE1a-XBP1 pathway in the production of these hormones and pituitary tumor cell growth. In this study, we aimed to clarify the role of the IRE1a-XBP1 pathway in functional pituitary tumor cells. Methods and Results We conducted in vitro experiments by using rat GH-producing pituitary GH4 cells and mouse ACTH-producing AtT-20 cells as the models of GH- and ACTH-producing pituitary adenomas, respectively. Cell proliferation was measured by WST-8 assay, gene expression levels by qPCR, and protein expression by western blotting, respectively. In GH4 cells, STF08310 (40µM), an IRE1a inhibitor, reduced levels of GH and XBP1 spliced form (XBP1s) mRNA and GH protein with suppressed cell proliferation. In AtT-20 cells, STF08310 (40µM) also suppressed protein expression of proopiomelanocortin (POMC) and cell proliferation. Gene suppression of IRE1a by siRNA and over-expression of XBP1s showed marked reduction and increase of POMC protein, respectively. Conclusion Our findings suggest that the IRE1a-XBP1s pathway would be a possible therapeutic target that has both anti-tumoral and hormone control effects against functional pituitary tumor. Presentation: No date and time listed

DRD2 Agonist Cabergoline Abolished the Escape Mechanism Induced by mTOR Inhibitor Everolimus in Tumoral Pituitary Cells.

The mammalian target of rapamycin (mTOR) inhibitor everolimus has been shown to display antiproliferative effects on a wide spectrum of tumors. In vitro studies demonstrated that everolimus inhibited pituitary neuroendocrine tumor (PitNET) cell growth in a subset of patients. Sensitivity to everolimus is reduced by an escape mechanism that increases AKT phosphorylation (p-AKT), leading to pro-survival pathway activation. Dopamine receptor type 2 (DRD2) mediates a reduction of p-AKT in a subgroup of non-functioning PitNETs (NF-PitNETs) and in prolactin-secreting tumor cells (MMQ cells) through a β-arrestin 2-dependent mechanism. The aim of this study was to investigate the efficacy of everolimus combined with DRD2 agonist cabergoline in reducing NF-PitNET primary cells and MMQ cell proliferation and to evaluate AKT phosphorylation and a possible role of β-arrestin 2. We found that 9 out of 14 NF-PitNETs were resistant to everolimus, but the combined treatment with cabergoline inhibited cell proliferation in 7 out of 9 tumors (-31.4 ± 9.9%, p < 0.001 vs. basal) and reduced cyclin D3 expression. In the everolimus-unresponsive NF-PitNET group, everolimus determined a significant increase of p-AKT/total-AKT ratio (2.1-fold, p < 0.01, vs. basal) that was reverted by cabergoline cotreatment. To investigate the molecular mechanism involved, we used MMQ cells as a model of everolimus escape mechanism. Indeed everolimus did not affect MMQ cell proliferation and increased the p-AKT/total-AKT ratio (+1.53 ± 0.24-fold, p < 0.001 vs. basal), whereas cabergoline significantly reduced cell proliferation (-22.8 ± 6.8%, p < 0.001 vs. basal) and p-AKT. The combined treatment of everolimus and cabergoline induced a reduction of both cell proliferation (-34.8 ± 18%, p < 0.001 vs. basal and p < 0.05 vs. cabergoline alone) and p-AKT/total-AKT ratio (-34.5 ± 14%, p < 0.001 vs. basal and p < 0.05 vs. cabergoline alone). To test β-arrestin 2 involvement, silencing experiments were performed in MMQ cells. Our data showed that the lack of β-arrestin 2 prevented the everolimus and cabergoline cotreatment inhibitory effects on both p-AKT and cell proliferation. In conclusion, this study revealed that cabergoline might overcome the everolimus escape mechanism in NF-PitNETs and tumoral lactotrophs by inhibiting upstream AKT activation. The co-administration of cabergoline might improve mTOR inhibitor antitumoral activity, paving the way for a potential combined therapy in β-arrestin 2-expressing NF-PitNETs or other PitNETs resistant to conventional treatments.

Evaluation of the expression of necroptosis pathway mediators and its association with tumor characteristics in functional and non-functional pituitary adenomas

BackgroundPituitary adenomas impose a burden of morbidity on patients and characterizing the molecular mechanisms underlying its pathogenesis received remarkable attention. Despite the appealing role of necroptosis as an alternative cell death pathway in cancer pathogenesis, its relevance to pituitary adenoma pathogenesis has yet to be determined that is perused in the current study.MethodsThe total number of 109 specimens including pituitary adenomas and cadaveric healthy pituitary tissues were enrolled in the current study. Tumor and healthy pituitary tissues were subjected to RNA extraction and gene analysis using Real-Time PCR. The expression levels of necroptosis markers (RIP1K, RIP3K and, MLKL) and their association with the patient’s demographic features were evaluated, also the protein level of MLKL was assessed using immunohistochemistry in tissues.ResultsBased on our data, the remarkable reduction in RIP3K and MLKL expression were detected in nonfunctional and GH-secreting pituitary tumors compared to pituitary normal tissues. Invasive tumors revealed lower expression of RIP3K and MLKL compared to non-invasive tumors, also the attenuated level of MLKL was associated with the tumor size in invasive NFPA. The simultaneous down-regulation of MLKL protein in pituitary adenoma tissues was observed which was in line with its gene expression. While, RIP1K over-expressed significantly in both types of pituitary tumors which showed no significant correlation with patient’s age, gender and tumor size in GHPPA and NFPA group. Notably, MLKL and RIP3K gene expression was significantly correlated in the GHPPA group.ConclusionsAccording to our data, the reduced expression of necroptosis mediators (RIP3K, MLKL) in pituitary adenoma reinforces the hypothesis that the necroptosis pathway can be effective in regulating the proliferation and growth of pituitary tumor cells and tumor recurrence.

MicroRNA-30d target TIMP3 induces pituitary tumor cell growth and invasion.

As one of the most common intracranial tumors, pituitary adenomas, especially the Cushing's disease subtype, have been studied for many years. However, at present, effective methods for the early diagnosis of pituitary adenomas are very limited, especially for subtypes such as Cushing's disease. Therefore, it is of urgent importance to find effective molecular targets to develop new diagnostic and therapeutic methods for pituitary adenomas. We showed the abnormally high expression of miR-30d in pituitary adenomas by analyzing data in the Gene Expression Omnibus (GEO) database and revealed a novel molecular mechanism of miR-30d in regulating the proliferation and invasion of a pituitary adenoma cell line (AtT-20). Cell culture and transfection, and RNA interference (RNAi) were used to treat AtT-20 cells to test the effects of miR-30d and TIMP3 on cells. Quantitative polymerase chain reaction (qPCR) was used to determine the messenger RNA (mRNA) expressions. We used 3-(4,5-diphenyltetrazolium bromide) (MTT) to determine cell viabilities. An invasion assay was performed using Transwell chambers. Luciferase activity was tested with a dual-luciferase assay. We found that the expression of miR-30d in pituitary adenoma was higher than that in normal pituitary tissues. It was revealed that miR-30d promoted the proliferation and invasion of AtT-20 cells by inhibiting the expression of TIMP3. In the above process, miR-30d could bind to the 3'-untranslated region (3'-UTR) of TIMP3 mRNA. The mir-30d/TIMP3 signaling pathway plays an important regulatory role in pituitary adenomas. These new discoveries may reveal more functions of miR-30d and lay the foundation for future clinical development of new drug targets.

Exploiting D2 receptor β-arrestin2-biased signalling to suppress tumour growth of pituitary adenomas.

Dopamine agonists targeting D2 receptor have been used for decades in treating pituitary adenomas. There has been little clear evidence implicating the canonical G protein signalling as the mechanism by which D2 receptor suppresses the growth of pituitary tumours. We hypothesize that β-arrestin2-dependent signalling is the molecular mechanism dictating D2 receptor inhibitory effects on pituitary tumour growth. The involvement of G protein and β-arrestin2 in bromocriptine-mediated growth suppression in rat MMQ and GH3 tumour cells was assessed. The anti-growth effect of a β-arrestin2-biased agonist, UNC9994, was tested in cultured cells, tumour-bearing nude mice and primary cultured human pituitary adenomas. The effect of G protein signalling on tumour growth was also analysed by using a G protein-biased agonist, MLS1547, and a Gβγ inhibitor, gallein, in vitro. β-arrestin2 signalling but not G protein pathways mediated the suppressive effect of bromocriptine on pituitary tumour growth. UNC9994 inhibited pituitary tumour cell growth in vitro and in vivo. The suppressive function of UNC9994 was obtained by inducing intracellular reactive oxygen species generation through downregulating mitochondrial complex I subunit NDUFA1. The effects of Gαi/o signalling and Gβγ signalling via D2 receptor on pituitary tumour growth were cell-type-dependent. Given the very low expression of Gαi/o proteins in pituitary tumours and the complexity of the responses of pituitary tumours to G protein signalling pathways, our study reveals D2 receptor β-arrestin2-biased ligand may be a more promising choice to treat pituitary tumours with improved therapeutic selectivity.

AFAP1-AS1 Promotes Proliferation of Pituitary Adenoma Cells through miR-103a-3p to Activate PI3K/AKT Signaling Pathway

We previously found that AFAP1-AS1 regulates the cell growth of pituitary tumor cells; however, the mechanism still remains unclear. Here, we investigated whether AFAP1-AS1 acts as a competing endogenous RNA of miR-103a-3p to regulate pituitary adenoma growth via the PI3K/AKT pathway. The bind between AFAP1-AS1 and rno-miR-103a-3p was measured by luciferase reporter assay, and rno-miR-103a-3p expression was measured by quantitative reverse transcription polymerase chain reaction. Proliferation, cell cycle, and apoptosis were measured by cell counting kit 8 and flow cytometry. Rat growth hormone (GH) and prolactin (PRL) levels in culture supernatant of GH3 and MMQ cells were measured by enzyme-linked immunosorbent assay. AFAP1-AS1 binds to rno-miR-103a-3p in rat pituitary adenoma cells. Additionally, rno-miR-103a-3p overexpression suppressed rat pituitary adenoma cell proliferation, induced cell apoptosis, arrested cell cycle in the G/S phase, reduced GH and PLR secretion, and inhibited the PI3K/AKT signaling pathway. Activated PI3K/AKT signaling pathway revised the effect of rno-miR-103a-3p overexpression on proliferation and GH and PLR secretion. Coexpression of both si-AFAP1-AS1 and rno-miR-103a-3p inhibitor promoted cell proliferation and cell cycle progression, reduced cell apoptosis, enhanced GH and PLR secretion, and activated thePI3K/AKT signaling pathway in rat pituitary adenoma cells. We found that AFAP1-AS1 and miR-103a-3p could be a potential therapeutic target for pituitary adenoma.

Downregulation of glucose‑6‑phosphate dehydrogenase by microRNA‑1 inhibits the growth of pituitary tumor cells.

Pituitary tumors are generally intracranial neoplasms with high incidence and mortality rates. The investigation of novel factors involved in the tumorigenesis of pituitary tumors and the characterization of the underlying molecular mechanisms is urgently required for the diagnosis and treatment of pituitary tumors. Accumulating evidence has indicated that microRNAs (miRs) serve important roles in the initiation and progression of cancer. The present study found that miR‑1 was significantly downregulated in pituitary tumor tissues upon reverse transcription‑quantitative polymerase chain reaction analysis. Decreased expression of miR‑1 was associated with the progression and worse prognosis of patients with pituitary tumors. The MTT assay showed that overexpression of miR‑1 significantly suppressed proliferation. Highly expressed miR‑1 promoted the apoptosis of pituitary tumor cells upon fluorescence‑activated cell sorting analysis. Further molecular study revealed that glucose‑6‑phosphate dehydrogenase (G6PD), the first and rate‑limiting enzyme of the pentose phosphate pathway (PPP), was one of the targets of miR‑1. Western blot assays showed that overexpression of miR‑1 significantly decreased the protein level of G6PD in pituitary tumor cells without changing the mRNA level of G6PD. Consequently, oxidative PPP flux analysis revealed that suppression of G6PD by miR‑1 decreased the production of nicotinamide adenine dinucleotide phosphate and the glycolysis of pituitary cancer cells. Restoration of the expression of G6PD significantly reversed the inhibitory effect of miR‑1 on the PPP and the growth of pituitary tumor cells. Collectively, the present results uncovered the critical involvement of miR‑1 in pituitary tumors, indicating that miR‑1 is a potential therapeutic target for the treatment of pituitary tumors.

Trastuzumab inhibits pituitary tumor cell growth modulating the TGFB/SMAD2/3 pathway.

In pituitary adenomas, early recurrences and resistance to conventional pharmacotherapies are common, but the mechanisms involved are still not understood. The high expression of epidermal growth factor receptor 2 (HER2)/extracellular signal-regulated kinase (ERK1/2) signal observed in human pituitary adenomas, together with the low levels of the antimitogenic transforming growth factor beta receptor 2 (TBR2), encouraged us to evaluate the effect of the specific HER2 inhibition with trastuzumab on experimental pituitary tumor cell growth and its effect on the antiproliferative response to TGFB1. Trastuzumab decreased the pituitary tumor growth as well as the expression of ERK1/2 and the cell cycle regulators CCND1 and CDK4. The HER2/ERK1/2 pathway is an attractive therapeutic target, but its intricate relations with other signaling modulators still need to be unraveled. Thus, we investigated possible cross-talk with TGFB signaling, which has not yet been studied in pituitary tumors. In tumoral GH3 cells, co-incubation with trastuzumab and TGFB1 significantly decreased cell proliferation, an effect accompanied by a reduction in ERK1/2 phosphorylation, an increase of SMAD2/3 activation. In addition, through immunoprecipitation assays, a diminution of SMAD2/3-ERK1/2 and an increase SMAD2/3-TGFBR1 interactions were observed when cells were co-incubated with trastuzumab and TGFB1. These findings indicate that blocking HER2 by trastuzumab inhibited pituitary tumor growth and modulated HER2/ERK1/2 signaling and consequently the anti-mitogenic TGFB1/TBRs/SMADs cascade. The imbalance between HER2 and TGFBRs expression observed in human adenomas and the response to trastuzumab on experimental tumor growth may make the HER2/ERK1/2 pathway an attractive target for future pituitary adenoma therapy.

Effects of metformin on cell growth and AMPK activity in pituitary adenoma cell cultures, focusing on the interaction with adenylyl cyclase activating signals.

For a few years we have been investigating AMP-activated protein kinase (AMPK) as a target for drug therapy of GH-secreting pituitary adenomas. Aim of this study was to investigate the direct effects of metformin, which causes AMPK activation in different cell types, on rat pituitary adenoma cell growth and on related cell signalling pathways. Our results suggest that metformin can exert a growth-inhibitory activity in rat pituitary tumor cells mediated by AMPK activation, although multiple mechanisms are most likely involved. Membrane proteins, including growth factor receptors, are valuable targets of AMPK. The inhibition of the mTOR-p70S6 kinase signalling pathway plays a role in the suppressive effect of metformin on pituitary tumor cell growth. Metformin did not affect the MTT reduction activity in energetic stress conditions. Finally, metformin was still able to induce AMPK activation and to inhibit cell growth in cells treated with forskolin and in transfected cells overexpressing GHRH-receptor and treated with GHRH. Hence, adenylyl cyclase over-activation does not account for the lack of response of some human pituitary tumors to AMPK-activating compounds invitro.

Pregnancy promotes pituitary tumors by increasing the rate of the cell cycle.

Pituitary tumors may secrete hormones that affect pregnancy. Pregnancy also induces pituitary tumor growth; however, how pregnancy increases the growth of pituitary tumors remains unclear. The present study investigated pregnant female mice with subcutaneous pituitary tumors. The time of tumor occurrence and tumor weight were detected in pregnant and control mice. Tumor weights were measured at the end of the experiment. Blood was collected from pregnant and control mice. Brain-derived neurotrophic factor (BDNF) levels in the blood were detected using an ELISA kit. The in vitro effects of BDNF on pituitary tumor AtT-20 cell proliferation and cell cycle were investigated. It was revealed that pregnancy promoted the growth of pituitary tumors. In comparison to non-pregnant mice, the pregnant mice exhibited increased BDNF levels in the blood. In vitro BDNF treatment was able to increase the rate of proliferation of pituitary tumor cells. Additional cell cycle analysis revealed that BDNF was able to alter the cell cycle distribution of pituitary tumor cells. These results indicated that pregnancy was able to increase the BDNF level and promote the growth of pituitary tumor cells by increasing the rate of the cell cycle, leading to increased tumor growth rate in vivo. The present study provides insights into how pregnancy affects the growth of pituitary tumors. Therefore, it may be beneficial to perform pituitary tumor diagnosis or therapy on pregnant patients.

Structure-Based Screen Identification of a Mammalian Ste20-like Kinase 4 (MST4) Inhibitor with Therapeutic Potential for Pituitary Tumors.

Pituitary tumors of the gonadotrope lineage are often large and invasive, resulting in hypopituitarism. No medical treatments are currently available. Using a combined genetic and genomic screen of individual human gonadotrope pituitary tumor samples, we recently identified the mammalian sterile-20 like kinase 4 (MST4) as a protumorigenic effector, driving increased pituitary cell proliferation and survival in response to a hypoxic microenvironment. To identify novel inhibitors of the MST4 kinase for potential future clinical use, computational-based virtual library screening was used to dock the SelleckChem kinase inhibitor library into the ATP-binding site of the MST4 crystal structure. Several inhibitor candidates were identified with the potential to bind with high affinity. Using a TR-FRET in vitro recombinant kinase assay, hesperadin, initially described as an Aurora kinase inhibitor, exhibited potent inhibition of the MST4 kinase at nanomolar concentrations. The LβT2 gonadotrope pituitary cell hypoxic model was used to test the ability of this inhibitor to antagonize MST4 actions. Under short-term severe hypoxia (1% O2), MST4 protection from hypoxia-induced apoptosis was abrogated in the presence of hesperadin. Similarly, under chronic hypoxia (5%), hesperadin blocked the proliferative and colony-forming actions of MST4 as well as the ability to activate specific downstream signaling and hypoxia-inducible factor-1 effectors. Together, these data identify hesperadin as the first potent, selective inhibitor of the MST4 kinase with the capacity to block pituitary tumor cell growth in a hypoxic microenvironment.

Molecular Mechanisms Underlying Pituitary Pathogenesis

During the last years, progress has been made on the identification of mechanisms involved in anterior pituitary cell transformation and tumorigenesis. Oncogene activation, tumor suppressor gene inactivation, epigenetic changes, and microRNAs deregulation contribute to the initiation of pituitary tumors. Despite the high prevalence of pituitary adenomas, they are mostly benign, indicating that intrinsic mechanisms may regulate pituitary cell expansion. Senescence is characterized by an irreversible cell cycle arrest and represents an important protective mechanism against malignancy. Pituitary tumor transforming gene (PTTG) is an oncogene involved in early stages of pituitary tumor development, and also triggers a senescence response by activating DNA-damage signaling pathway. Cytokines, as well as many other factors, play an important role in pituitary physiology, affecting not only cell proliferation but also hormone secretion. Special interest is focused on interleukin-6 (IL-6) because its dual function of stimulating pituitary tumor cell growth but inhibiting normal pituitary cells proliferation. It has been demonstrated that IL-6 has a key role in promoting and maintenance of the senescence program in tumors. Senescence, triggered by PTTG activation and mediated by IL-6, may be a mechanism for explaining the benign nature of pituitary tumors.

Somatostatin system: molecular mechanisms regulating anterior pituitary hormones.

The somatostatin (SRIF) system, which includes the SRIF ligand and receptors, regulates anterior pituitary gland function, mainly inhibiting hormone secretion and to some extent pituitary tumor cell growth. SRIF-14 via its cognate G-protein-coupled receptors (subtypes 1-5) activates multiple cellular signaling pathways including adenylate cyclase/cAMP, MAPK, ion channel-dependent pathways, and others. In addition, recent data have suggested SRIF-independent constitutive SRIF receptor activity responsible for GH and ACTH inhibition in vitro. This review summarizes current knowledge on ligand-dependent and independent SRIF receptor molecular and functional effects on hormone-secreting cells in the anterior pituitary gland.

Small interfering RNA silencing pituitary tumor transforming gene inhibits growth of human prolactin pituitary tumor cells

Objective To observe the effect of small interfering RNA (siRNA) silencing pituitary tumor transforming gene (PTTG) on the growth of primary cultured human prolactin pituitary adenoma cells (HPAs).Methods After the HPAs were primary cultured and steadily subcultured,the cells were divided into three groups:the blank control group,the negative control group and the siRNA-PTTG transfection group.After 48 h of infection,proliferation rate of HPAs was measured by using cell counting kit-8 (CCK-8).Transfection efficiency and the apoptosis rate were tested by using flow cytometry.The expression of PTTG mRNA and protein were detected by using reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting respectively.Caspase-3 activity was measured by Caspase activity assay kit.Prolactin changes in cell supernatants were measured by radioimmunoassay.Results Compared to the blank cotnrol group and the negative control group,the transcription of PTTG mRNA and the expression of PTTG protein were significantly down-regulated in the siRNA-PTTG transfection group,and the proliferation was suppressed [the inhibition rate in the negative control group and the siRNA-PTTG transfection group was (3.02 ± 1.77) ％ and (25.38 ± 0.11) ％ respectively (P ＜ 0.05),while the apoptosis was significantly increased [the apoptosis rate in the blank control group,negative control group and siRNA-PTTG transfection group was (6.21 ± 2.36) ％,(7.23 ± 3.56) ％ and (32.33 ± 5.69) ％ respectively (P ＜ 0.05).The activity of Caspase-3 was increased (P ＜ 0.05),and the radioimmunoassay revealed that the prolactin level in the cell supernatants was significantly decreased in the siRNA-PTTG transfection group,32.9％ of the blank control group (P ＜ 0.05).Conclusion Down-regulation of PTTG expression can suppress the proliferation and induce apoptosis of HPAs,which results in the reduction of prolactin secretion. Key words: Pituitary tumor transforming gene; RNA interference; Human prolactin pituitary gland tumor; Apoptosis

Interplay between the intracellular energy sensor AMP-activated protein kinase (AMPK) and the estrogen receptor activities in regulating rat pituitary tumor cell (GH3) growth in vitro

Estrogen receptor α has a role in regulating rat somatolactotroph tumor cell growth (GH3 cells). AMP-activated protein kinase (AMPK) is a metabolic checkpoint which is able to negatively regulate intracellular signaling downstream of growth factors receptors in conditions increasing cellular AMP levels. We have recently reported on the role of AMPK activation in affecting viability and proliferation of GH3 cells. In the present study, we investigated the interplay between ER- and AMPK-pathways. Results can be regarded as relevant to the development of novel multi-targeted pharmacological therapies against pituitary tumors. We confirmed that estradiol (E2) and the ER antagonist fulvestrant exert stimulatory and inhibitory effects, respectively on GH3 cell growth in a competitive manner. The upstream kinase LKB1 is known to phosphorylate and activate AMPK. Here we showed that neither E2 nor fulvestrant caused a downregulation of LKB1 expression and phospho-AMPK levels in GH3 cells. Actually, fulvestrant strongly reduced the phosphorylation of ACC, which is a direct target of AMPK and a known index of AMPK activity. 2-deoxyglucose, a compound reducing glucose utilization, caused an increase in AMPK activity vs baseline and was able to hinder the stimulatory effect of E2 on cell viability, confirming that the exposure of GH3 cells to estrogens does not prevent them from being responsive to the inhibitory activity of compounds activating AMPK. Finally, the AMPK activator AICAR (AMP analog) did not cause further decrease in cell viability in the course of co-treatments with fulvestrant versus fulvestrant alone, in agreement with impaired phospho-AMPK activity in the presence of the anti-estrogen.

MicroRNA expression in ACTH-producing pituitary tumors: up-regulation of microRNA-122 and -493 in pituitary carcinomas

MicroRNAs (miRNAs) are involved in cell proliferation, differentiation, and apoptosis, and can function as tumor suppressor genes or oncogenes. The expression of miRNAs in pituitary carcinomas has not been previously examined. We used miRNA profiling with 1,145 probes to study miRNA expression in normal anterior pituitary (6 cases), adrenocorticotropin (ACTH)-producing adenomas (8 cases), and ACTH-producing pituitary carcinomas (two cases). Real-time RT-PCR and in situ hybridization were used to confirm and independently validate miRNAs that were significantly up-regulated or down-regulated between the pituitary tissues. There were more miRNAs up- (188) or down-regulated (160) between adenomas and normal pituitaries compared to carcinomas and normal pituitaries (92 up- and 91 down-regulated) or between carcinomas and adenomas (46 up- and 52 down-regulated). Both real-time RT-PCR and in situ hybridization showed significant up-regulation of miRNA-122 between pituitary carcinomas and adenomas. MiRNA-493 was also up-regulated in carcinomas compared to ACTH adenomas. Analysis of genes that miRNA-493 interacts with included LGALS3 and RUNX2 ( http://microrna.sanger.ac.uk ) both of which have been shown to have roles in pituitary tumor cell growth. These results provide information about marker miRNAs that may lead to further insights into the regulation of pituitary tumor growth and development.

Impact of curcumin on growth and apoptosis of pituitary tumor cells

Curcumin (Diferuloylmethan) is the active ingredient in the traditional herbal remedy and dietary spice turmeric (Curcuma Longa). Curcumin has a wide range of beneficial properties, including anti-inflammatory, antioxidant, chemopreventive and chemotherapeutic activity. The pleiotropic activities of curcumin derive from its ability to influence multiple signalling pathways. We have investigated in vitro effects of curcumin in lactosomatotroph GH3 and somatotroph MtT/S rat pituitary cells, in corticotroph AtT20 mouse pituitary cells and in folliculostellate TtT/GF mouse pituitary cells. Curcumin inhibited growth of all cell lines in monolayer cell culture and suppressed colony formation in soft agar (IC50: 19µM). At least for GH3 cells it could be shown, that GH3 cell tumor formation was reduced by curcumin in nude mice. FACS analysis with Annexin-V-FITC/7AAD-staining demonstrated curcumin-induced early apoptosis after 12 and 24h treatment and nearly no necrosis. In endocrine cell types, hormone production was inhibited by curcumin. Angiogenic components (VEGF, VEGF receptor type 2, HIF-1alpha) and immunomodulatory factors (IL-6, TLr4) were all suppressed by curcumin in pituitary cells. Regarding the mechanism of action, results indicate that curcumin suppresses the PI3 kinase/Akt pathway and inhibits CDK4. Reduction of Bcl-2 and enhancement of cleaved caspase 9 suggest induction of apoptosis by curcumin, which was confirmed by cell death ELISA. In summary, curcumin shows clear anti-tumorigenic properties and its effects on human pituitary tumors will be tested in future studies.

INHIBITION OF NFκB REDUCES CELLULAR VIABILITY IN GH3 PITUITARY ADENOMA CELLS

Adenomas of the pituitary gland are among the most common types of tumors of the adult brain. Although adenomas are histologically benign, they may be associated with significant morbidity and mortality, mostly because of their invasive growth pattern and hormone hypersecretion. Current medical therapies are suppressive, acting at a receptor level. Thus, there is a need to identify novel cellular and molecular targets for pituitary tumors. We investigated the possible role of the NFkappaB transcription factor in pituitary tumor cell growth. The effect of NFkappaB pathway inhibition on cellular viability was studied in the GH3 pituitary adenoma cell line, a well-characterized rat cell line that secretes growth hormone and prolactin. Cells were treated with mechanistically diverse pharmacological NFkappaB pathway inhibitors or with molecular inhibitors that were overexpressed in tumor cells before the assessment of cellular viability. NFkappaB activity was also assessed in GH3 cells using deoxyribonucleic acid binding assays. GH3 cells exhibited constitutive NFkappaB activity, which contributed to increased cellular proliferation. Treatment with wedelolactone, an IkappaB kinase inhibitor, or overexpression of an IkappaB super-repressor reduced cell viability, further implicating NFkappaB in pituitary tumor cell growth. Pharmacological or molecular inhibition of Akt similarly reduced GH3 viability and NFkappaB binding, suggesting that constitutive activation of NFkappaB may be, at least in part, mediated by Akt. Directed targeting of the Akt and NFkappaB signaling pathways may be a useful adjunct in the clinical management of pituitary tumors. Further elucidation of this pathway may yield novel information regarding the behavior of pituitary tumors in humans.