Regulation of FGF2-induced proliferation by inhibitory GPCR in normal pituitary cells.

Introduction: Intracellular communication is essential for the maintenance of the anterior pituitary gland plasticity. The aim of this study was to evaluate whether GPCR-Gαi modulates basic fibroblast growth factor (FGF2)-induced proliferative activity in normal pituitary cell populations. Methods: Anterior pituitary primary cell cultures from Wistar female rats were treated with FGF2 (10ng/mL) or somatostatin analog (SSTa, 100nM) alone or co-incubated with or without the inhibitors of GPCR-Gαi, pertussis toxin (PTX, 500nM), MEK inhibitor (U0126, 100µM) or PI3K inhibitor (LY 294002, 10 µM). Results: FGF2 increased and SSTa decreased the lactotroph and somatotroph BrdU uptak2e (p<0.05) whereas the FGF2-induced S-phase entry was prevented by SSTa co-incubation in both cell types, with these effects being reverted by PTX, U0126 or LY294002 pre-incubation. The inhibition of lactotroph and somatotroph mitosis was associated with a downregulation of c-Jun expression, a decrease of phosphorylated (p) ERK and pAKT. Furthermore, SSTa was observed to inhibit the S-phase entry induced by FGF2, resulting in a further increase in the number of cells in the G1 phase and a concomitant reduction in the number of cells in the S phases (p< 0.05), effects related to a decrease of cyclin D1 expression and an increase in the expression of the cell cycle inhibitors p27 and p21. Discussion: In summary, the GPCR-Gαi activated by SSTa blocked the pro-proliferative effect of FGF2 in normal pituitary cells via a MEK-dependent mechanism, which acts as a mediator of both anti and pro-mitogenic signals, that may regulate the principal effectors of the G1 to S-phase transition.

Ultrastructural and Molecular Evidence of Macroautophagy in Functioning PitNETs and Experimental Pituitary Tumors.

INTRODUCTION: Macroautophagy is a lysosome-mediated degradation process that controls the quality of cytoplasmic components and organelles, with its regulation depending on autophagy-related proteins (Atg) and with Beclin1/Atg6 and microtubule-associated protein light chain 3 (LC3/Atg8) being key players in the mammalian autophagy. As reports on this mechanism in the field of pituitary neuropathology and neuroendocrinology are scarce, our study analyzed the ultrastructural signs of macroautophagy and the expression of Beclin1 and LC3 proteins in human functioning PitNETs and in experimental pituitary tumors. METHODS: A group of humans functioning PitNETs and an experimental lactotroph model in rats of the F344 strain stimulated with estradiol benzoate (BE) were used. Ultrastructural and molecular evidence of the macroautophagic process was evaluated using different techniques. RESULTS: In functioning PitNETs cohort, 60% exhibited evidence of macroautophagy, with a significant difference found for Beclin1 and LC3 between macro- and micro-PitNETs (p < 0.05). In the experimental model, the expression of both Beclin1 and LC3 proteins was immunopositive in normal and tumoral glands when analyzed by immunofluorescence, Western blot, and immunohistochemistry. In the experimental model, protein expression was associated with increased glandular size and weight. CONCLUSIONS: Our study revealed evidence of macroautophagy at the pituitary level and the important role of Beclin1 and LC3 in the progression of functioning PitNETs, implying that this mechanism participate in regulating pituitary cell growth.

Perinatal DEHP exposure modulates pituitary estrogen receptor α and ß expression altering lactotroph and somatotroph cell growth in prepuberal and adult male rats.

Phthalates are synthetic chemicals widely used to make polyvinylchloride (PVC) soft and flexible. Of these, Di-(2-ethylhexyl) phthalate (DEHP) is the most commonly used, with high human exposure occurring as early as the fetal developmental stage and affecting the endocrine system. We focused on the perinatal DEHP effects on pituitary estrogen receptor (ER) expression in male rats, explored their impact on lactotroph and somatotroph cell growth, and evaluated the direct effects of this phthalate on pituitary cell cultures. Our results showed that DEHP perinatal exposure was unable to modify the ERα+ pituitary cell number from prepuberal rats, but increased ERß+ cells. In adulthood, the pituitary ERα+ cells underwent a slight decrease with ERß showing the greatest changes, and with a significant increase observed in somatotroph cells. Also, in vitro, DEHP reduced the ERα+ cells, increased the percentage of ERß+ pituitary cells and modified the Ki67 index, as well as decreasing the lactotrophs and increasing the somatotroph cells. In conclusion, the present study showed that DEHP induced ER expression changes in normal pituitary glands from male rats in in vivo and in vitro conditions, suggesting that DEHP could differentially modulate lactotroph and somatotroph cell growth, possibly as a consequence of ER imbalance.

TGF-ß1/Smad2/3 signaling pathway modulates octreotide antisecretory and antiproliferative effects in pituitary somatotroph tumor cells.

Octreotide (OCT) is used to inhibit hormone secretion and growth in somatotroph tumors, although a significant percentage of patients are resistant. It has also been tested in nonfunctioning (NF) tumors but with poor results, with these outcomes having been associated with SSTR2 levels and impaired signaling. We investigated whether OCT inhibitory effects can be improved by TGF-ß1 in functioning and nonfunctioning somatotroph tumor cells. OCT effects on hormone secretion and proliferation were analyzed in the presence of TGF-ß1 in WT and SSTR2-overexpressing secreting GH3 and silent somatotroph tumor cells. The mechanism underlying these effects was assessed by studying SSTR and TGFßR signaling pathways mediators. In addition, we analyzed the effects of OCT/TGF-ß1 treatment on tumor growth and cell proliferation in vivo. The inhibitory effects of OCT on GH- and PRL-secretion and proliferation were improved in the presence of TGF-ß1, as well as by SSTR2 overexpression. The OCT/TGF-ß1 treatment induced downregulation of pERK1/2 and pAkt, upregulation of pSmad3, and inhibition of cyclin D1. In vivo experiments showed that OCT in the presence of TGF-ß1 blocked tumor volume growth, decreased cell proliferation, and increased tumor necrosis. These results indicate that SSTR2 levels and the stimulation of TGF-ß1/TGFßR/Smad2/3 pathway are important for strengthening the antiproliferative and antisecretory effects of OCT.

TGFß1 regulates prolactin secretion during postnatal development: gender differences.

Serum prolactin levels gradually increase from birth to puberty in both male and female rats, with higher levels observed in female since the first days of life. The increase in lactotroph secretion was attributed to the maturation of prolactin-inhibiting and prolactin-releasing factors; however, those mechanisms could not fully explain the gender differences observed. Prolactin secretion from isolated lactotrophs, in the absence of hypothalamic control, also increases during the first weeks of life, suggesting the involvement of intra-pituitary factors. We postulate that pituitary transforming growth factor beta 1 (TGFß1) is involved in the regulation of prolactin secretion as well as in the gender differences observed at early postnatal age. Several components of the local TGFß1 system were evaluated during postnatal development (11, 23, and 45 days) in female and male Sprague-Dawley rats. In vivo assays were performed to study local TGFß1 activation and its impact on prolactin secretion. At day 11, female pituitaries present high levels of active TGFß1, concomitant with the highest expression of TGFß1 target genes and the phospho-Smad3 immunostaining in lactotrophs. The steady increase in prolactin secretion inversely correlates with active TGFß1 levels only in females. Dopamine and estradiol induce TGFß1 activation at day 11, in both genders, but its activation induces the inhibition of prolactin secretion only in females. Our findings demonstrate that: (1) TGFß1 activation is regulated by dopamine and estradiol; (2) the inhibitory regulation of local TGFß1 on prolactin secretion is gender specific; and (3) this mechanism is responsible, at least partially, for the gender differences observed being relevant during postnatal development.

The ERα membrane pool modulates the proliferation of pituitary tumours.

The molecular mechanisms underlying the ERα nuclear/cytoplasmic pool that modulates pituitary cell proliferation have been widely described, but it is still not clear how ERα is targeted to the plasma membrane. The aim of this study was to analyse ERα palmitoylation and the plasma membrane ERα (mERα) pool, and their participation in E2-triggered membrane-initiated signalling in normal and pituitary tumour cell growth. Cell cultures were prepared from anterior pituitaries of female Wistar rats and tumour GH3 cells, and treated with 10 nM of oestradiol (E2). The basal expression of ERα was higher in tumour GH3 than in normal pituitary cells. Full-length palmitoylated ERα was observed in normal and pituitary tumour cells, demonstrating that E2 stimulation increased both, ERα in plasma membrane and ERα and caveolin-1 interaction after short-term treatment. In addition, the Dhhc7 and Dhhc21 palmitoylases were negatively regulated after sustained stimulation of E2 for 3 h. Although the uptake of BrdU into the nucleus in normal pituitary cells was not modified by E2, a significant increase in the GH3 tumoural cell, as well as ERK1/2 activation, with this effect being mimicked by PPT, a selective antagonist of ERα. These proliferative effects were blocked by ICI 182780 and the global inhibitor of palmitoylation. These findings indicate that ERα palmitoylation modulated the mERα pool and consequently the ERK1/2 pathway, thereby contributing to pituitary tumour cell proliferation. These results suggest that the plasma membrane ERα pool might be related to the proliferative behaviour of prolactinoma and may be a marker of pituitary tumour growth.

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.

Estrogen receptor ß regulates the tumoral suppressor PTEN to modulate pituitary cell growth.

In this study, we focused on ERß regulation in the adenohypophysis under different estrogenic milieu, by analyzing whether ER modulates the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) expression and its subcellular localization on anterior pituitary glands from Wistar rats and GH3 lactosomatotroph cells that over-expressed ERß. ERß was regulated in a cyclic manner, and underwent dynamic changes throughout the estrous cycle, with decreased ERß+ cells in estrus and under E2 treatment, but increased in ovariectomized rats. In addition, the ERα/ß ratio increased in estrus and under E2 stimulation, but decreased in ovariectomized rats. Double immunofluorescence revealed that lactotroph and somatotroph ERß+ were significantly decreased in estrus. Also, variations in the PTEN expression was observed, which was diminished with high E2 conditions but augmented with low E2 milieu. The subcellular localization of this phosphatase was cell cycle-dependent, with remarkable changes in the immunostaining pattern: nuclear in arrested pituitary cells but cytoplasmic in stimulated cells, and responding differently to ER agonists, with only DPN being able to increase PTEN expression and retaining it in the nucleus. Finally, ERß over-expression increased PTEN with a noticeable subcellular redistribution, and with a significant nuclear signal increase in correlation with an increase of cells in G0/G1 phase. These results showed that E2 is able to inhibit ERß expression and suggests that the tumoral suppressor PTEN might be one of the signaling proteins by which E2, through ERß, acts to modulate pituitary cell proliferation, thereby adapting endocrine populations in relation with hormonal necessities.