Deregulation of cytokine and growth factor signaling due to an altered expression of endogenous regulators is well recognized in prostate cancer (PCa) and other cancers. Suppressor of cytokine signaling 2 (SOCS2) is a key regulator of the GH, IGF, and prolactin signaling pathways that have been implicated in carcinogenesis. In this study, we evaluated the expression patterns and functional significance of SOCS2 in PCa. Protein expression analysis employing tissue microarrays from two independent patient cohorts revealed a significantly enhanced expression in tumor tissue compared with benign tissue as well as association with Gleason score and disease progression. In vitro and in vivo assays uncovered the involvement of SOCS2 in the regulation of cell growth and apoptosis. Functionally, SOCS2 knockdown inhibited PCa cell proliferation and xenograft growth in a CAM assay. Decreased cell growth after SOCS2 downregulation was associated with cell-cycle arrest and apoptosis. In addition, we proved that SOCS2 expression is significantly elevated upon androgenic stimulation in androgen receptor (AR)-positive cell lines, providing a possible mechanistic explanation for high SOCS2 levels in PCa tissue. Consequently, SOCS2 expression correlated with AR expression in the malignant tissue of patients. On the whole, our study linked increased SOCS2 expression in PCa with a pro-proliferative role in vitro and in vivo.
Julia Hoefer, Johann Kern, Philipp Ofer, Iris E Eder, Georg Schäfer, Dimo Dietrich, Glen Kristiansen, Stephan Geley, Johannes Rainer, Eberhard Gunsilius, Helmut Klocker, Zoran Culig, and Martin Puhr
C Schaaf, B Shan, M Buchfelder, M Losa, J Kreutzer, W Rachinger, G K Stalla, T Schilling, E Arzt, M J Perone, and U Renner
Curcumin (diferuloylmethane) is the active ingredient of the spice plant Curcuma longa and has been shown to act anti-tumorigenic in different types of tumours. Therefore, we have studied its effect in pituitary tumour cell lines and adenomas. Proliferation of lactosomatotroph GH3 and somatotroph MtT/S rat pituitary cells as well as of corticotroph AtT20 mouse pituitary cells was inhibited by curcumin in monolayer cell culture and in colony formation assay in soft agar. Fluorescence-activated cell sorting (FACS) analysis demonstrated curcumin-induced cell cycle arrest at G2/M. Analysis of cell cycle proteins by immunoblotting showed reduction in cyclin D1, cyclin-dependent kinase 4 and no change in p27kip. FACS analysis with Annexin V-FITC/7-aminoactinomycin D staining demonstrated curcumin-induced early apoptosis after 3, 6, 12 and 24 h treatment and nearly no necrosis. Induction of DNA fragmentation, reduction of Bcl-2 and enhancement of cleaved caspase-3 further confirmed induction of apoptosis by curcumin. Growth of GH3 tumours in athymic nude mice was suppressed by curcumin in vivo. In endocrine pituitary tumour cell lines, GH, ACTH and prolactin production were inhibited by curcumin. Studies in 25 human pituitary adenoma cell cultures have confirmed the anti-tumorigenic and hormone-suppressive effects of curcumin. Altogether, the results described in this report suggest this natural compound as a good candidate for therapeutic use on pituitary tumours.
B K Vonderhaar
Normal development and differentiation of the mammary gland are profoundly influenced by prolactin (PRL). In rodent mammary cancer PRL plays a well defined role, but its role, in human breast cancer has not been appreciated until recently. It is now clear that breast tissue, both normal and malignant, is a significant source of extrapituitary PRL. Thus an autocrine/paracrine role of PRL in human breast cancer may be invoked. Both PRL and PRL receptor mRNA are expressed in the vast majority of breast cancer biopsies independent of estrogen and progesterone receptor status. An autocrine/paracrine PRL acting in human breast cancer requires that this hormone's action be blocked at the cellular level, as opposed to suppressing the synthesis and secretion of pituitary PRL. Mutants of PRL or human growth hormone are being explored which act as selective PRL antagonists. In addition, tamoxifen has been shown to act locally at the target tissue by binding directly to the PRL receptor and thus inhibiting PRL's action. These strategies may have clinical relevance in treating PRL-responsive human breast cancer.
Sarah A Dabydeen and Priscilla A Furth
The majority of human breast cancers are estrogen receptor-positive (ER+), but this has proven challenging to model in genetically engineered mice. This review summarizes information on 21 mouse models that develop ER+ mammary cancer. Where available, information on cancer pathology and gene expression profiles is referenced to assist in understanding which histological subtype of ER+ human cancer each model might represent. ESR1, CCDN1, prolactin, TGFα, AIB1, ESPL1, and WNT1 overexpression, PIK3CA gain of function, as well as loss of P53 (Trp53) or STAT1 are associated with ER+ mammary cancer. Treatment with the PPARγ agonist efatutazone in a mouse with Brca1 and p53 deficiency and 7,12-dimethylbenz(a)anthracene exposure in combination with an activated myristoylated form of AKT1 also induce ER+ mammary cancer. A spontaneous mutant in nude mice that develops metastatic ER+ mammary cancer is included. Age of cancer development ranges from 3 to 26 months and the percentage of cancers that are ER+ vary from 21 to 100%. Not all models are characterized as to their estrogen dependency and/or response to anti-hormonal therapy. Strain backgrounds include C57Bl/6, FVB, BALB/c, 129S6/SvEv, CB6F1, and NIH nude. Most models have only been studied on one strain background. In summary, while a range of models are available for studies of pathogenesis and therapy of ER+ breast cancers, many could benefit from further characterization, and opportunity for development of new models remains.
Louise Maymann Rasmussen, Klaus Stensgaard Frederiksen, Nanni Din, Elisabeth Galsgaard, Leif Christensen, Martin Werner Berchtold, and Svetlana Panina
The pituitary hormone prolactin (PRL) plays an important role in mammary gland development. It was also suggested to contribute to breast cancer progression. In vivo data strongly supported a crucial role of PRL in promoting tumour growth; however, PRL demonstrated only a weak, if any, pro-proliferative effect on cancer cells in vitro. Several recent studies indicated that PRL action in vivo may be influenced by the hormonal milieu, e.g. other growth factors such as 17β-oestradiol (E2). Here, we explored the potential interplay between PRL and E2 in regulation of gene expression and cell growth. PRL alone induced either a weak or no proliferative response of T47D and BT-483 cells respectively, while it drastically enhanced cell proliferation in E2-stimulated cultures. Affymetrix microarray analysis revealed 12 genes to be regulated by E2, while 57 genes were regulated by PRL in T47D cells. Most of the PRL-regulated genes (42/57) were not previously described as PRL target genes, e.g. WT1 and IER3. One hundred and five genes were found to be regulated upon PRL/E2 co-treatment: highest up-regulation was found for EGR3, RUNX2, EGR1, MAFF, GLIPR1, IER3, SOCS3, WT1 and AREG. PRL and E2 synergised to regulate EGR3, while multiple genes were regulated additively. These data show a novel interplay between PRL and E2 to modulate gene regulation in breast cancer cells.
Thomas Cuny, Caroline Zeiller, Martin Bidlingmaier, Céline Défilles, Catherine Roche, Marie-Pierre Blanchard, Marily Theodoropoulou, Thomas Graillon, Morgane Pertuit, Dominique Figarella-Branger, Alain Enjalbert, Thierry Brue, and Anne Barlier
Pegvisomant (PEG), an antagonist of growth hormone (GH)-receptor (GHR), normalizes insulin-like growth factor 1 (IGF1) oversecretion in most acromegalic patients unresponsive to somatostatin analogs (SSAs) and/or uncontrolled by transsphenoidal surgery. The residual GH-secreting tumor is therefore exposed to the action of circulating PEG. However, the biological effect of PEG at the pituitary level remains unknown. To assess the impact of PEG in vitro on the hormonal secretion (GH and prolactin (PRL)), proliferation and cellular viability of eight human GH-secreting tumors in primary cultures and of the rat somatolactotroph cell line GH4C1. We found that the mRNA expression levels of GHR were characterized in 31 human GH-secreting adenomas (0.086 copy/copy β-Gus) and the GHR was identified by immunocytochemistry staining. In 5/8 adenomas, a dose-dependent inhibition of GH secretion was observed under PEG with a maximum of 38.2±17% at 1μg/mL (P<0.0001 vs control). A dose-dependent inhibition of PRL secretion occurred in three mixed GH/PRL adenomas under PEG with a maximum of 52.8±11.5% at 10μg/mL (P<0.0001 vs control). No impact on proliferation of either human primary tumors or GH4C1 cell line was observed. We conclude that PEG inhibits the secretion of GH and PRL in primary cultures of human GH(/PRL)-secreting pituitary adenomas without effect on cell viability or cell proliferation.
I Ben-Batalla, S Seoane, M Macia, T Garcia-Caballero, L O Gonzalez, F Vizoso, and R Perez-Fernandez
The transcription factor Pit-1/Pou1f1 regulates GH and prolactin (PRL) secretion in the pituitary gland. Pit-1 expression and GH regulation by Pit-1 have also been demonstrated in mammary gland. However, no data are available on the role of Pit-1 on breast PRL. To evaluate this role, several human breast cancer cell lines were transfected with either the Pit-1 expression vector or a Pit-1 small interference RNA construct, followed by PRL mRNA and protein evaluation. In addition, transient transfection of MCF-7 cells by a reporter construct containing the proximal PRL promoter, and ChIP assays were performed. Our data indicate that Pit-1 regulates mammary PRL at transcriptional level by binding to the proximal PRL promoter. We also found that Pit-1 raises cyclin D1 expression before increasing PRL levels, suggesting a PRL-independent effect of Pit-1 on cell proliferation. By using immunohistochemistry, we found a significant correlation between Pit-1 and PRL expression in 94 human breast invasive ductal carcinomas. Considering the possible role of PRL in breast cancer disorders, the function of Pit-1 in breast should be the focus of further research.
Petteri Ahtiainen, Victoria Sharp, Susana B Rulli, Adolfo Rivero-Müller, Veronika Mamaeva, Matias Röyttä, and Ilpo Huhtaniemi
The etiology of pituitary adenomas remains largely unknown, with the exception of involvement of estrogens in the formation of prolactinomas. We have examined the molecular pathogenesis of prolactin-producing pituitary adenomas in transgenic female mice expressing the human choriongonadotropin (hCG) β-subunit. The LH/CG bioactivity is elevated in the mice, with consequent highly stimulated ovarian progesterone (P4) production, in the face of normal estrogen secretion. Curiously, despite normal estrogen levels, large prolactinomas developed in these mice, and we provide here several lines of evidence that the elevated P4 levels are involved in the growth of these estrogen-dependent tumors. The antiprogestin mifepristone inhibited tumor growth, and combined postgonadectomy estradiol/P4 treatment was more effective than estrogen alone in inducing tumor growth. Evidence for direct growth-promoting effect of P4 was obtained from cultures of primary mouse pituitary cells and rat somatomammotroph GH3 cells. The mouse tumors and cultured cells revealed stimulation of the cyclin D1/cyclin-dependent kinase 4/retinoblastoma protein/transcription factor E2F1 pathway in the growth response to P4. If extrapolated to humans, and given the importance of endogenous P4 and synthetic progestins in female reproductive functions and their pharmacotherapy, it is relevant to revisit the potential role of these hormones in the origin and growth of prolactinomas.
Frauke Döll, Josef Pfeilschifter, and Andrea Huwiler
Sphingosine kinases (SK) catalyze the formation of sphingosine-1-phosphate (S1P) which plays a crucial role in cell growth and survival. Here, we show that prolactin (PRL) biphasically activates the SK-1, but not the SK-2 subtype, in the breast adenocarcinoma cell-line MCF7. A first peak occurs after minutes of stimulation and is followed by a second delayed activation after hours of stimulation. A similar biphasic effect on SK-1 activity is seen for 17β-estradiol (E2). The delayed activation of SK-1 derives from an upregulated mRNA and protein expression and is due to increased SK-1 promoter activity and mechanistically involves STAT5 activation as well as protein kinase C and the classical mitogen-activated protein kinases. Furthermore, glucocorticoids also block both hormone-induced SK-1 expression and activity. Functionally, long-term stimulation of MCF7 cells with PRL or E2 is well known to trigger increased cell proliferation and migration. Both hormone-induced cell responses critically involve SK-1 activation since the depletion of SK-1, but not SK-2, by siRNA transfection abolishes the hormone-induced cell proliferation and migration. In summary, our data show that PRL and E2 cause a pronounced delayed SK-1 activation which is due to increased gene transcription, and critically determines the capability of cells to grow and move. Thus, the SK-1 may represent a novel attractive target for anti-tumor therapy.
Elizabeth W LaPensee and Nira Ben-Jonathan
Resistance to chemotherapy is a major complication in the treatment of advanced breast cancer. Estrogens and prolactin (PRL) are implicated in the pathogenesis of breast cancer but their roles in chemoresistance have been overlooked. A common feature to the two hormones is activation of their receptors by diverse compounds, which mimic or antagonize their actions. The PRL receptor is activated by lactogens (PRL, GH, or placental lactogen) originating from the pituitary, breast, adipose tissue, or the placenta. Estrogen receptors exist in multiple membrane-associated and cytoplasmic forms that can be activated by endogenous estrogens, man-made chemicals, and phytoestrogens. Here, we review evidence that low doses of PRL, estradiol (E2), and bisphenol A (BPA) antagonize multiple anticancer drugs that induce cell death by different mechanisms. Focusing on cisplatin, a DNA-damaging drug which is effective in the treatment of many cancer types but not breast cancer, we compare the abilities of PRL, E2, and BPA to antagonize its cytotoxicity. Whereas PRL acts by activating the glutathione-S-transferase detoxification enzyme, E2 and BPA act by inducing the antiapoptotic protein Bcl-2. The implications of these findings to patients undergoing chemotherapy are discussed.