Basic fibroblastic growth factor stimulates prolactin secretion from human anterior pituitary adenomas without affecting adenoma cell proliferation

Breaking the Backbone: Central Arginine Residues Induce Membrane Exit and Helix Distortions within a Dynamic Membrane Peptide

Transmembrane domains of membrane proteins sometimes contain conserved charged or ionizable residues which may be essential for protein function and regulation. This work examines the molecular interactions of single Arg residues within a highly dynamic transmembrane peptide helix. To this end, we have modified the GW^4,20ALP23 (acetyl-GGAW⁴(AL)₇AW²⁰AGA-amide) model peptide framework to incorporate Arg residues near the center of the peptide. Peptide helix formation, orientation and dynamics were analyzed by means of solid-state NMR spectroscopy to monitor specific ²H- or ¹⁵N-labeled residues. GW^4,20ALP23 itself adopts a tilted orientation within lipid bilayer membranes. Nevertheless, the GW^4,20ALP23 helix exhibits moderate to high dynamic averaging of NMR observables, such as ²H quadrupolar splittings or ¹⁵N-¹H dipolar couplings, due to competition between the interfacial Trp residues on opposing helix faces. Here we examine how the helix dynamics are impacted by the introduction of a single Arg residue at position 12 or 14. Residue R14 restricts the helix to low dynamic averaging and a well-defined tilt that varies inversely with the lipid bilayer thickness. To compensate for the dominance of R14, the competing Trp residues cause partial unwinding of the helix at the C-terminal. By contrast, R¹²GW^4,20ALP23 exits the DOPC bilayer to an interfacial surface-bound location. Interestingly, multiple orientations are exhibited by a single residue, Ala-9. Quadrupolar splittings generated by ²H-labeled residues A3, A5, A7, and A9 do not fit to the α-helical quadrupolar wave plot defined by residues A11, A13, A15, A17, A19, and A21. The discontinuity at residue A9 implicates a helical swivel distortion and an apparent 3₁₀-helix involving the N-terminal residues preceding A11. These molecular features suggest that, while arginine residues are prominent factors controlling transmembrane helix dynamics, the influence of interfacial tryptophan residues cannot be ignored.

Antibody array strategy for human growth factor secretome profiling of GH-secreting adenomas

PURPOSES

To test if the antibody array strategy could be utilized to simultaneously detect the secretion of multiple growth factors by human pituitary GH-adenomas and to measure octreotide-induced alterations.

METHODS

Specimens of human pituitary adenomas were cultured and incubated with or without octreotide for 24 h. Conditional media were analyzed by human growth factor antibody array and VEGF concentrations were measured by ELISA. Media were also analyzed for GH concentrations. p21 expression levels were examined by Western blot of the specimens lysates.

RESULTS

The antibody arrays successfully identified growth factors secreted by GH-adenomas in vitro. Octreotide treatment induced both elevations and reductions in growth factors secretion. GH response to octreotide was measured, and in this small-sized study resistant and sensitive GH-adenomas presented with no unique secretome pattern of each of the groups. Octreotide-induced VEGF alterations analyzed by the antibody array and by ELISA were not fully matched.

CONCLUSIONS

This study suggests that the broad proteomic strategy of antibody arrays may be utilized to study the growth factors secretion pattern of GH-adenomas and its regulation by somatostatin analogs or other compounds.

Identification of Important Invasion-Related Genes in Non-functional Pituitary Adenomas

Non-functioning pituitary adenomas (NFPAs) are locally invasive with high morbidity. The objective of this study was to diagnose important genes and pathways related to the invasiveness of NFPAs and gain more insights into the underlying molecular mechanisms of NFPAs. The gene expression profiles of GSE51618 were downloaded from the Gene Expression Omnibus database with 4 non-invasive NFPA samples, 3 invasive NFPA samples, and 3 normal pituitary gland samples. Differentially expressed genes (DEGs) are screened between invasive NFPA samples and normal pituitary gland samples, followed by pathway and ontology (GO) enrichment analyses. Subsequently, a protein-protein interaction (PPI) network was constructed and analyzed for these DEGs, and module analysis was performed. In addition, a target gene-miRNA network and target gene-TF (transcription factor) network were analyzed for these DEGs. A total of 879 DEGs were obtained. Among them, 439 genes were upregulated and 440 genes were downregulated. Pathway enrichment analysis indicated that the upregulated genes were significantly enriched in cysteine biosynthesis/homocysteine degradation (trans-sulfuration) and PI3K-Akt signaling pathway, while the downregulated genes were mainly associated with docosahexaenoate biosynthesis III (mammals) and chemokine signaling pathway. GO enrichment analysis indicated that the upregulated genes were significantly enriched in animal organ morphogenesis, extracellular matrix, and hormone activity, while the downregulated genes were mainly associated with leukocyte chemotaxis, dendrites, and RAGE receptor binding. Subsequently, ESR1, SOX2, TTN, GFAP, WIF1, TTR, XIST, SPAG5, PPBP, AR, IL1R2, and HIST1H1C were diagnosed as the top hub genes in the upregulated and downregulated PPI networks and modules. In addition, HS3ST1, GPC4, CCND2, and SCD were diagnosed as the top hub genes in the upregulated and downregulated target gene-miRNA networks, while CISH, ISLR, UBE2E3, and CCNG2 were diagnosed as the top hub genes in the upregulated and downregulated target gene-TF networks. The new important DEGs and pathways diagnosed in this study may serve key roles in the invasiveness of NFPAs and indicate more molecular targets for the treatment of NFPAs.

Molecular Network Basis of Invasive Pituitary Adenoma: A Review

Cases with pituitary adenoma comprise 10-25% of intracranial neoplasm, being the third most common intracranial tumor, most of the adenomas are considered to be benign. About 35% of pituitary adenomas are invasive. This review summarized the known molecular basis of the invasiveness of pituitary adenomas. The study pointed out that hypoxia-inducible factor-1α, pituitary tumor transforming gene, vascular endothelial growth factor, fibroblast growth factor-2, and matrix metalloproteinases (MMPs, mainly MMP-2, and MMP-9) are core molecules responsible for the invasiveness of pituitary adenomas. The reason is that these molecules have the ability to directly or indirectly induce cell proliferation, epithelial-to-mesenchymal transition, angiogenesis, degradation, and remodeling of extracellular matrix. HIF-1α induced by hypoxia or apoplexy inside the adenoma might be the initiating factor of invasive transformation, followed with angiogenesis for overexpressed VEGF, EMT for overexpressed PTTG, degradation of ECM for overexpressed MMPs, creating a suitable microenvironment within the tumor. Together, they form a complex interactive network. More investigations are required to further elucidate the mechanisms underlying the invasiveness of pituitary adenomas.

Expression of estrogen receptor α and growth factors in human prolactinoma and its correlation with clinical features and gender

BACKGROUND

Many studies demonstrate that growth factors play an important role in the pathogenesis of prolactinoma induced by estrogen. The effects of estrogen are mainly mediated through its nuclear receptor (ERα); however, expression of ERα and growth factors in prolactinoma and healthy pituitary and their relationship remain obscure.

AIM

To obtain new insights regarding the expression differences of these factors and their relationship and to investigate the correlation between gender and clinical features in patients with prolactinoma.

SUBJECTS AND METHODS

A total of 21 human prolactinomas and 6 healthy human pituitaries were examined for mRNA expression of ERα, basic fibroblast growth factor (bFGF), transforming growth factor α (TGFα), TGFβ1, TGFβ3, and TGFβ receptor type II (TGFβRII) by means of real-time PCR. Patient clinical data was also analyzed.

RESULTS

Both PRL level and tumor volume of the male patient group were higher than that of the female patient group. There was a significant correlation between PRL level and tumor volume in the total patient group. Expression of ERα, bFGF, TGFα, and TGFβ3 mRNA levels of the patient group were significantly different from that of the control group. A significant correlation between ERα mRNA levels and PRL levels, tumor volume, TGFβ1 mRNA levels in the total patient group were found.

CONCLUSIONS

PRL level and tumor volume have a significant difference between genders in prolactinoma patients. ERα and some growth factors may be involved in the tumorigenesis of prolactinoma. ERα could potentially be an effective therapy target for treating prolactinoma.

Fibroblast growth factor-2 and epidermal growth factor modulate prolactin responses to TRH and dopamine in primary cultures

Fibroblast growth factor-2 (FGF-2) and epidermal growth factor (EGF) are expressed in most tissues of the organism including pituitary. FGF-2 increases PRL levels and PRL mRNA in GH3 cells and primary cultures, and it has been involved in the lactotroph proliferation and hyperplasia. EGF also increases PRL levels in vitro. However, the effects of these two factors in the responses of lactotroph cells to TRH and dopamine (DA) remain to be clarified. In the present work we have studied the modulator activity of FGF-2 and EGF on in vitro PRL in responses to TRH and DA in primary cultures from in vivo vehicle- or estrogen (E2)-treated rats. We have found that FGF-2 (2 x 10(-11) M) prevents the EGF-induced dose-dependent increase in PRL levels in control cells, and reversed the EGF-stimulating effects in cells from E2-treated rats. Both FGF-2 (2 x 10(-11) M) and EGF (6.6 x 10(-9) M) significantly increase (>30% and >120%, respectively) the PRL levels in response to TRH (10(-6), 10(-5) M). FGF-2 blocked the inhibitory effects of low doses of DA (10(-9) M). EGF was unable to do so, although markedly increased (>200%) the post-DA PRL rebound. In cells from in vivo E2-treated rats, FGF-2 increased (>50%) the PRL secretion in response to TRH, while EGF reduced responses to high doses of TRH (10(-6), 10(-5) M). In addition, FGF-2 reversed and EGF increased the inhibitory effects of DA. Both FGF-2 and EGF completely blocked the post-DA PRL rebound, in these cells. Taken together our data suggest that FGF-2 and EGF are important regulators of lactotroph responsiveness to TRH and DA in vitro, although their actions are highly dependent on estrogenic milieu.

Genesis of pituitary adenomas: state of the art

In recent years, remarkable progress has been made in the understanding of the pathogenesis of pituitary tumors. Pituitary tumors originate from the uncontrolled proliferation of a single transformed cell in which an initiating event has caused a gain of proliferative function. After the initiation, promoting factors cooperate in the clonal expansion. Common oncogenes, such as ras, are only exceptionally involved. The only activating mutations identified so far are gsp mutations causing the constitutive activation of cAMP pathway. However, gsp-positive adenomas are not associated to a more aggressive tumoral phenotype. The oncogenic potential of gsp mutations is limited by a more rapid degradation of the mutant Gs(alpha) with respect to the wild-type protein, and by a faster removal of cAMP due to increased phosphodiesterase activity. Estrogen-inducible gene sequences with transforming properties (pituitary tumor-transforming gene (PTTG)) have been identified in human pituitary tumors. Human pituitary tumor-transforming gene (hPTTG) is involved both in early pituitary tumorigenesis, as it causes in vitro and in vivo transformation acting as a transcription activator, and in tumor progression, as it regulates the production of basic fibroblast growth factor (bFGF), a potent activator of angiogenesis and mitogenesis. Moreover, a role of cyclin D1 in pituitary tumorigenesis is emerging. The allelic loss of loci for unknown oncosuppressor genes are currently under investigation, while an exceedingly limited role for menin gene and RB1 has been demonstrated for sporadic pituitary tumors. Abnormal methylation that predisposing toward genetic instability may favor the allelic loss or the reduced expression of oncosuppressor genes, is also an emerging field of investigation. Several promoting factors, including the excessive action of physiological stimulators, the defective action of inhibitors, the susceptibility to respond to inappropriate stimuli and the locally produced growth factors, help in tumor progression. The study of homeobox genes that intervene in pituitary cell differentiation may help in expanding our knowledge in pituitary tumor cell genealogy.

Genetic basis of pituitary adenoma invasiveness: a review

Compatible with contemporary paradigms of the role of genetic aberrations in the progression of human tumors, the growth of pituitary tumors into a state of invasiveness appears to be due to genetic alterations. Amplification of H-ras and c-myc oncogenes and mutations of p53, nm23 and Rb genes have been identified disproportionately more in aggressive tumors and, in the case of Rb gene, in pituitary carcinomas, providing evidence that amplification of these oncogenes (H-ras and c-myc) and inactivation of tumor suppressor genes (p53, nm23 and Rb) seem to be at least one mechanism by which pituitary tumors progress. The current level of management of invasive pituitary adenomas should become more comprehensive as the advances in our understanding of genetic basis of pituitary adenoma invasiveness becomes translated into development of novel chemotherapy or gene transfer technique.

Proliferation Markers and Their Uses in the Study of Endocrine Tumors

A growing body of literature supports the view that the proliferative activity (PA) of tumor cells is an important prognostic indicator for a variety of different tumors. We examined the role of PA in diagnosis and prediction or malignancy of endocrine tumors (ETs) of pituitary gland, pancreas, thyroid, parathyroid glands, adrenal glands, paraganglia, gastroenteric tract, and lung. The data in the literature indicate that the assessment of PA is not a diagnostic indicator of malignancy especially at the individual case level, whereas it can be useful for identifying subsets of malignant tumors with different aggressiveness potential, as well as for choosing therapeutic options in metatstatic lesions. We hope that, in the near future, multiparametric approaches including PA markers, cell growth and differentiation factors, and oncogenes will yield valuable information for diagnosis and prognosis of ETs also in individual cases.

Heparin-binding secretory transforming gene (hst) facilitates rat lactotrope cell tumorigenesis and induces prolactin gene transcription

We have shown previously that human prolactinomas express transforming sequences of the heparin-binding secretory transforming gene (hst) which encodes fibroblast growth factor-4 (FGF-4). To elucidate the role of hst in pituitary tumorigenesis we treated primary rat pituitary and pituitary tumor cell cultures with recombinant FGF-4 and also stably transfected pituitary cell lines with full-length human hst cDNA. Transfectants were screened for hst mRNA expression and FGF-4 production. FGF-4 (0.1-50 ng/ml) caused a dose-dependent 2.5-fold increase of prolactin (PRL) secretion (P < 0.001) in GH4 cells and up to 60% (P < 0.05) in primary cultures, while decreasing growth hormone release (P < 0.001). GH4 hst transfectants displayed markedly enhanced basal PRL secretion (threefold, P < 0.001) and also proliferated faster (P < 0.001). FGF-4 treatment of wild-type GH4 cells, transiently transfected with an expression construct (rPRL.luc) containing a luciferase reporter driven by the rPRL promoter, resulted in a dose-dependent increase of up to 3.3-fold in PRL transcriptional activity. Tumors derived from in vivo subcutaneous injection of GH4 hst-transfected cells strongly expressing FGF-4 grew more aggressively as assessed by histologic invasiveness and proliferating cell nuclear antigen staining (P < 0.01). The results indicate that hst overexpression mediates lactotrope tumor growth and potently stimulates PRL synthesis. Thus, hst may directly facilitate prolactinoma development via paracrine or autocrine action of its secreted protein, FGF-4.