Effects of estrogen and epidermal growth factor on prolactin and Pit-1 mRNA in GH3 cells

Prolactinoma ErbB receptor expression and targeted therapy for aggressive tumors

As ErbB signaling is a determinant of prolactin synthesis, role of ErbB receptors was tested for prolactinoma outcomes and therapy. The objective of this study was to characterize ErbB receptor expression in prolactinomas and then perform a pilot study treating resistant prolactinomas with a targeted tyrosine kinase inhibitor (TKI). Retrospective analysis of prolactinomas and pilot study for dopamine agonist resistant prolactinomas in tertiary referral center. We performed immunofluorescent staining of a tissue array of 29 resected prolactinoma tissues for EGFR, ErbB2, ErbB3, and ErbB4 correlated with clinical features. Two patients with aggressive resistant prolactinomas enrolled and completed trial. They received lapatinib 1,250 mg daily for 6 months with tumor and hormone assessments. Main outcome measures were positive tumor staining of respective ErbB receptors, therapeutic reduction of prolactin levels and tumor shrinkage. Treated PRL levels and tumor volumes were suppressed in both subjects treated with TKI. EGFR expression was positive in 82 % of adenomas, ErbB2 in 92 %, ErbB3 in 25 %, and ErbB4 in 71 %, with ErbB2 score > EGFR > ErbB4 > ErbB3. Higher ErbB3 expression was associated with optic chiasm compression (p = 0.03), suprasellar extension (p = 0.04), and carotid artery encasement (p = 0.01). Higher DA response rates were observed in tumors with higher ErbB3 expression. Prolactinoma expression of specific ErbB receptors is associated with tumor invasion, symptoms, and response to dopamine agonists. Targeting ErbB receptors may be effective therapy in patients with resistant prolactinomas.

Expression and function of ErbB receptors and ligands in the pituitary

The role of ErbB family in discreet pituitary functions is reviewed. Several ErbB receptor ligands, EGF, TGFα, and heregulin are differentially expressed in normal gonadotroph and lacto-somatotroph lineages, and other elements of the anterior pituitary. ErbB receptors, i.e. EGFR and ErbB2, are also localized to the anterior pituitary with preferential EGFR lactosomatotroph expression. EGF regulates CRH and ACTH secretion and corticotroph proliferation as well as exhibiting autocrine and paracrine effects on gonadotrophs and on lactosomatotroph proliferation, gene and protein expression, and hormonal secretion. EGF and EGFR are expressed in both functioning and non-functioning pituitary adenomas, with higher expression in more aggressive tumor subtypes. ErbB2 receptor is detected in all tumor subtypes, particularly in invasive tumors. ErbB tyrosine kinase inhibitors regulate hormonal secretion, cell morphology, and proliferation in lacto-somatotroph tumors, reflecting the emerging application of targeted pituitary therapeutics.

Melatonin-induced calbindin-D9k expression reduces hydrogen peroxide-mediated cell death in rat pituitary GH3 cells

In this study, we investigated whether calbindin-D9k (CaBP-9k) expression was regulated by melatonin during hydrogen peroxide (H(2)O(2))-induced cell death in rat pituitary GH3 cells. CaBP-9k expression was increased by melatonin in a dose- and time-dependent manner, indicating that CaBP-9k expression is regulated by melatonin. Cell survival was increased approximately 27-30% where H(2)O(2)-treated cells (0.25 or 0.5 mm) were also incubated with 1 mm melatonin, when compared with H(2)O(2) alone or H(2)O(2) plus 0.5 mm melatonin. This result was consistent with 4,6-diamidino-2-phenylindole staining. CaBP-9k expression was also augmented by co-treatment with H(2)O(2) and 1 mm melatonin, suggesting a functional relationship between increased cell death and melatonin-induced CaBP-9k expression during H(2)O(2)-mediated apoptosis. Bcl-2-associated protein expression increased following treatment with H(2)O(2) alone, whereas Bcl-2 expression was elevated following treatment with melatonin alone, or H(2)O(2) plus melatonin. The expression of p53 was depressed by treatment with melatonin alone, or co-treatment with H(2)O(2) plus melatonin. These results correlated with CaBP-9k expression levels and activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase signaling pathway. Knockdown of CaBP-9k expression using a small inhibitory RNA resulted in an elevation of H(2)O(2)-induced cell death, whereas cell survival was increased in cells that overexpressed CaBP-9k, providing additional evidence that the induction of CaBP-9k expression may be associated with survival signaling during H(2)O(2)-mediated oxidative cell death. CaBP-9k appears to interact with p53, suggesting a possible role for this interaction in cell proliferation and cell cycle progression.

In vitro modulation of prolactin mRNA by toxaphene and 3,3',4,4'-tetrachlorobiphenyl

It is now well recognized that many environmental contaminants are capable of disrupting endocrine processes in a variety of species, including birds, mammals, reptiles, and fish. Among these contaminants are toxaphene and polychlorinated biphenyls (PCBs), two of the most prevalent contaminants present in aquatic food chains of the Great Lakes and the Canadian Arctic region. We set out to investigate the possible endocrine-modulating activities of toxaphene, the PCB congener 3,3',4,4'-tetrachlorobiphenyl (TeCB), an equimolar mixture of both compounds (toxaphene/TeCB), and estradiol (E(2)) (E(2)/toxaphene, E(2)/TeCB) on prolactin (PRL) mRNA expression. Concentrations ranging from 10(-7) to 10(-11)M for both toxaphene and TeCB were assayed but only toxaphene modulated PRL mRNA levels, as determined by relative quantitative reverse transcriptase-polymerase chain reaction. Maximal induction by toxaphene was seen at 10(-7)M, resulting in a fourfold increase in PRL mRNA levels. No interactions were observed for combinations of the test substances. Our study demonstrates that toxaphene may exhibit estrogen-like activity by modulating PRL mRNA levels in GH(3) cells.

Combined effect of xenoestrogens and growth factors in two estrogen-responsive cell lines

It is now well recognized that estrogenic signaling mechanisms are far more complex than once thought. Several crosstalks between the estrogen receptor and other signaling pathways may influence the estrogenic stimulation of cell growth. Thus, the estrogenic effects of several environmental contaminants, now suspected to act as endocrine disrupters, may be influenced by a simultaneous stimulation of other signaling pathways. The aim of this study was to investigate whether the growth response of two estrogen-responsive cell lines, MCF-7 and GH3, treated with xenoestrogens might be affected by the addition of growth factors to their culture medium. Cells were treated with two known xenoestrogens, endosulfan and chlordane, alone or in the presence of insulin-like growth factor-1 and epidermal growth factor, respectively, and their growth was measured using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxyanilide proliferation assay. Our results show that treatment with endosulfan or chlordane as well as treatment with growth factors increased cell growth, while the administration of xenoestrogens together with growth factors triggered a partly additive response with no antagonist or synergistic effect. These results sustain a role for xenoestrogens in cellular growth.

Restoration of growth hormone-releasing hormone (GHRH) responsiveness in pituitary GH3 cells by adenovirus-directed expression of the human GHRH receptor

GH-secreting GH3 cells lack GH-releasing hormone (GHRH) receptors. In this study we used adenoviral vectors to transfer the human GHRH receptor to GH3 cells in an effort to restore GHRH responsiveness. A replication-deficient recombinant adenovirus (AdGHRH-R) was designed to allow cytomegalovirus promoter-driven expression of the GHRH receptor messenger RNA. COS-7 cells and GH-producing GH3 cells infected with AdGHRH-R showed GHRH receptor expression on their membranes and exhibited specific GHRH binding. The addition of GHRH to GH3 cells infected with AdGHRH-R increased cAMP levels, induced cAMP response element-binding protein phosphorylation and restored GH secretory responsiveness. GHRH treatment also caused activation of mitogen-activated-protein kinase, induction of c-fos, stimulation of GH promotor activity, and increased cellular proliferation. These findings indicate that adenoviral vectors carrying human GHRH receptor are useful for in vitro studies of GHRH receptor biology and represent a first step toward the development of gene therapy for dwarfism caused by GHRH receptor mutations.

Defective retinoic acid regulation of the Pit-1 gene enhancer: a novel mechanism of combined pituitary hormone deficiency

Pit-1 is a pituitary-specific transcription factor responsible for pituitary development and hormone expression in mammals. Pit-1 contains two protein domains, termed POU-specific and POU-homeo, which are both necessary for DNA binding and activation of the GH and PRL genes and regulation of the PRL, TSH-beta subunit (TSH-beta), and Pit-1 genes. Pit-1 is also necessary for retinoic acid induction of its own gene during development through a Pit-1-dependent enhancer. Combined pituitary hormone deficiency is caused by defective transactivation of target genes in the anterior pituitary. In the present report, we provide in vivo evidence that retinoic acid induction of the Pit-1 gene can be impaired by a Pit-1 gene mutation, suggesting a new molecular mechanism for combined pituitary hormone deficiency in man.

Effects of estrogen on cell growth and fibroblast growth factor receptor induction in MtT/Se cells

The effects of estradiol (E2) on cell growth and the expression of fibroblast growth factor receptor (FGFR) were investigated in a cultured rat anterior pituitary cell line (MtT/Se) established from an E2-induced mammotropic pituitary tumor. E2 stimulated cell growth 2-3 fold as compared to the control. Basic fibroblast growth factor (bFGF) stimulated cell growth in the presence of E2 (10(-9) M) but not in the absence of E2. Tamoxifen as an antiestrogen agent inhibited the proliferation of MtT/Se cells which had been treated with E2 or E2 and bFGF. Numbers of FGFR in E2-stimulated MtT/Se cells significantly exceeded those in cells not treated with E2. These observations indicate that E2 plays an important role in the regulation of FGFR induction in the anterior pituitary cells.

Expression and Regulation of Transforming Growth Factor B1 in Cultured Normal and Neoplastic Rat Pituitary Cells

Pituitary prolactin (PRL) cell gene expression and proliferation are regulated by hormones and growth factors. Transforming growth factor beta (TGFB) and blast growth factor (bFGF) have been implicated in the regulation of antenor pituitary function. To study the roles of TGFB and bFGF in anterior pituitary cell function, we analyzed normal and neoplastic pituitary cells in serum-free media. The various isoforms of TGFB and TGFB receptor types I, II, and III were also analyzed by reverse transcription-polymerase chain reaction (RT-PCR) in pituitary cells. Transforming growth factor beta 1 (TGFB1) stimulated PRL expression and PRL cell proliferation in normal pituitary. TGFB1 stimulated PRL expression, but inhibited proliferation in the growth hormone (GH) and PRL-producing GH(3) cells. Estradiol 17 B (E(2)) and bFGE stimulated PRL gene expression in normal pituitary and GH(3) cells, whereas E(2) inhibited and bFGF stimulated TGFB1 mRNA levels in normal pituitary PRL cells, but not in GH(3) cells. Both normal pituitary and GH(3) cells expressed the mRNAs for TGFB1, TGFB2, and TGFB3 isoforms and for TGFB receptors I, II, and III. These results indicate that there is a relative loss of regulatory control by growth factors in neoplastic GH(3) cells compared to normal pituitary PRL cells.

Effects of remoxipride and raclopride on prolactin release from clonal pituitary tumour cells

The dopamine D2 receptor antagonist remoxipride (30 microM) stimulated prolactin release from the prolactin-producing rat pituitary tumour cell strains GH3 and GH4C1 as well as from transfected GH4C1 cells expressing the short isoform of the rat D2 receptor (GH4ZR7). The effect of remoxipride on prolactin release is probably not due to an interaction with D2 receptors since GH4C1 cells, in contrast to GH3 and GH4ZR7 cells, are completely devoid of D2 receptors; in contrast, we have previously shown that the D2 antagonist haloperidol causes prolactin release from D2 receptor-expressing cells, only. Exposure of GH3 cells to the inhibitor of intracellular Ca2+ mobilization, 8-(diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8) prevented the prolactin-releasing effect of remoxipride whereas pretreatment with the membrane Ca2+ channel antagonist nimodipine did not influence the response. The D2 receptor antagonist raclopride counteracted the reduction of VIP-stimulated prolactin release induced by the D2 agonist quinpirole but caused no prolactin release per se.

DNA measurement, proliferation markers, and other factors in pituitary adenomas

To assess the proliferative activity of pituitary adenomas, 36 surgically removed adenomas were studied by light microscopical parameters; mitotic count; expression of PCNA, Ki-67, cathepsin D, and EGF; and image cytometry. Three adenomas (9%) showed high, 11 (34%) medium, 17 (53%) moderate, and 1 (3%) low structural differentiation. In 10 adenomas (31%), no mitosis was observed. The average was 2.4 mitoses/100 HPF; the highest count was 7.1 mitoses/100 HPF. Eleven adenomas (33.3%) were PCNA-negative; in 20 adenomas (60.6%), between 0.05 and 3.9, and in 2 adenomas (6.0%), between 10.5 and 16.4 PCNA-positive nuclei were observed. Only a recurrent null-cell adenoma (9%) was Ki-67-negative. Three adenomas (9.1%) were EGF-negative, 28 (84.8%) showed up to 10% positive cells, and 2 (6.1 %) showed between 10 and 30% positive cells; 19 adenomas (68%) were cathepsin D-negative, including all endocrine-inactive adenomas. Half the adenomas had an euploid DMA stem line. Endocrine-inactive adenomas displayed a higher rate of euploid DNA stem lines than endocrine-active adenomas. The S-phase fraction varied between 2.97 and 28%, with a mean value of 14.4%. Half the adenomas showed an S-phase fraction of 11.65% or lower.

Pit-1/ghf-1 transcription factor expression in rodent pituitaries

The Pit-1/GHF-1 (Pit-1) transcription factor is important for the development of anterior pituitary cells that produce GH and PRL. We examined the expression of Pit-1 mRNA in pituitary tissues from rats and mice. Analysis of pituitaries from normal and GHRH transgenic mice showed that Pit-1 transcripts were readily detected in normal, hyperplastic, and neoplastic pituitaries. A cell line (GHRH-CL1) established from a GhRH transgenic mouse pituitary tumor in our laboratory also expressed Pit-1 mRNA. Normal rat pituitaries and those with estrogen-induced PRL cell hyperplasia expressed Pit-1 mRNA. There was a decrease in Pit-1 mRNA in hyperplastic rat pituitaries concomitant with a decrease In GH mRNA amounts and an increase in PRL mRNA amounts after estrogen treatment. Similarly, analysis of GH₃ cells in vitro showed that estrogen and bFGF modulated PRL but not Pit-1 mRNA levels. Pit-1 mRNA was localized by combined in situ hybridization and immunohistochemistry to predominantly GH and PRL cells, although some TSH and LH cells in the rat pituitary also expressed Pit-1 mRNA, indicating wide distribution of the mRNA for this transcription factor in various anterior pituitary cell types. Analysis of cell proliferation in normal rat pituitary and GH₃ cells revealed that estrogen and bFGF stimulated cell proliferation in normal pituitaries but inhibited proliferation in GH₃ cells, whereas Pit-1 transcripts remained unchanged in both groups of cultured cells. These results indicate that Pit-1 mRNA is readily detected in normal, hyperplastic, and neoplastic rodent pituitaries. Changes in Pit-1 mRNA amounts appear to correlate more closely with changes in GH than PRL mRNA levels in cultured pituitary cells.Endocr Pathol 4:146-154, 1993.