Inhibition of Bcl3 gene expression mediates the anti-proliferative action of estrogen in pituitary lactotrophs in primary culture

Multifaceted roles for BCL3 in cancer: a proto-oncogene comes of age

In the early 1990's a group of unrelated genes were identified from the sites of recurring translocations in B-cell lymphomas. Despite sharing the nomenclature 'Bcl', and an association with blood-borne cancer, these genes have unrelated functions. Of these genes, BCL2 is best known as a key cancer target involved in the regulation of caspases and other cell viability mechanisms. BCL3 on the other hand was originally identified as a non-canonical regulator of NF-kB transcription factor pathways - a signaling mechanism associated with important cell outcomes including many of the hallmarks of cancer. Most of the early investigations into BCL3 function have since focused on its role in NF-kB mediated cell proliferation, inflammation/immunity and cancer. However, recent evidence is coming to light that this protein directly interacts with and modulates a number of other signaling pathways including DNA damage repair, WNT/β-catenin, AKT, TGFβ/SMAD3 and STAT3 - all of which have key roles in cancer development, metastatic progression and treatment of solid tumours. Here we review the direct evidence demonstrating BCL3's central role in a transcriptional network of signaling pathways that modulate cancer biology and treatment response in a range of solid tumour types and propose common mechanisms of action of BCL3 which may be exploited in the future to target its oncogenic effects for patient benefit.

Rasd1 is an estrogen-responsive immediate early gene and modulates expression of late genes in rat anterior pituitary cells

Dexamethasone-induced Ras-related protein 1 (Rasd1) is a member of the Ras superfamily of monomeric G proteins that have a regulatory function in signal transduction. Here we investigated the role of Rasd1 in regulating estrogen-induced gene expression in primary cultures of rat anterior pituitary cells. Rasd1 mRNA expression in anterior pituitary cells decreased after treatment with forskolin or serum and increased after treatment with 17β-estradiol (E2). Increases in Rasd1 mRNA expression occurred as early as 0.5 h after E2 treatment, peaked at 1 h and were sustained for as long as 96 h. This rapid and profound increase in Rasd1 mRNA expression induced by E2 was also seen in GH4C1 cells, an estrogen receptor-positive somatolactotroph cell line. Among pituitary estrogen-responsive late genes studied, basal mRNA expression of Pim3 and Igf1 genes was decreased by RNA interference-mediated knockdown of Rasd1 expression, whereas basal expression of the Giot1 gene was increased. Moreover, Rasd1 knockdown enhanced stimulation of Pim3 mRNA expression and attenuated inhibition of Fosl1 mRNA expression 24 h after E2 treatment. These changes in mRNA expression were accompanied by enhanced activity of promoters containing CRE, AP-1 and SRE binding sequences. These results suggest that Rasd1 is an estrogen-responsive immediate early gene and modulates E2 induction of at least several late genes in anterior pituitary cells.

Activation of G protein-coupled estrogen receptor 1 mimics, but does not mediate, the anti-proliferative action of estradiol on pituitary lactotrophs in primary culture

Estrogen binds to nuclear estrogen receptors (ERs) to modulate transcription of target genes in estrogen-responsive cells. However, recent studies have shown that estrogen also binds to cytoplasmic membrane ERs to modulate protein kinase signaling cascades, leading to non-genomic actions. We investigated whether either nuclear or membrane ERs, including G protein-coupled estrogen receptor 1 (Gper1), mediate the inhibitory action of estrogen on insulin-like growth factor-1 (IGF-1)-induced proliferation of pituitary lactotrophs in primary culture. The cytoplasmic membrane-impermeable bovine serum albumin-conjugated estradiol (BSA-E2) at 1 nM, an equimolar concentration at which 17β-estradiol (E2) exerts anti-proliferative effects, did not inhibit IGF-1-induced lactotroph proliferation. In contrast, diethylstilbestrol, which is known to selectively activate nuclear ERs but not membrane ERs, inhibited IGF-1-induced proliferation and modulated mRNA expression of estrogen-responsive genes to a similar degree as E2. Activation of Gper1 by its agonist G-1 inhibited IGF-1-induced proliferation in a dose-dependent manner, but it had little effect on modulation of mRNA expression of estrogen-responsive genes. However, blockade of Gper1 by its antagonist G-15 did not affect the inhibitory action of E2 on IGF-1-induced proliferation. Here, we demonstrate that E2 inhibition of lactotroph proliferation is due to nuclear ER-mediated genomic action. Our results suggest that activation of Gper1 mimics, but does not mediate, the anti-proliferative action of E2 on lactotrophs.

BIMMER: a novel algorithm for detecting differential DNA methylation regions from MBDCap-seq data

DNA methylation is a common epigenetic marker that regulates gene expression. A robust and cost-effective way for measuring whole genome methylation is Methyl-CpG binding domain-based capture followed by sequencing (MBDCap-seq). In this study, we proposed BIMMER, a Hidden Markov Model (HMM) for differential Methylation Regions (DMRs) identification, where HMMs were proposed to model the methylation status in normal and cancer samples in the first layer and another HMM was introduced to model the relationship between differential methylation and methylation statuses in normal and cancer samples. To carry out the prediction for BIMMER, an Expectation-Maximization algorithm was derived. BIMMER was validated on the simulated data and applied to real MBDCap-seq data of normal and cancer samples. BIMMER revealed that 8.83% of the breast cancer genome are differentially methylated and the majority are hypo-methylated in breast cancer.

Activation of D2 dopamine receptors inhibits estrogen response element-mediated estrogen receptor transactivation in rat pituitary lactotrophs

Estrogen and dopamine are major opposing regulators of the endocrine functions of pituitary lactotrophs. Dopamine inhibits estrogen-induced changes in the synthesis and secretion of prolactin, and lactotroph proliferation. We studied the mechanism of the inhibitory effects of dopaminergic stimulation on estrogen-induced functional changes of rat lactotrophs in primary culture. The dopaminergic agonist, bromocriptine (BC), suppressed 17β-estradiol-stimulated lactotroph proliferation, prolactin promoter activity, and mRNA expression of some estrogen-responsive genes. In lactotroph-enriched pituitary cells, BC treatment inhibited the estrogen response element (ERE) DNA sequence-mediated estrogen receptor (ER) transcriptional activity. Using a lactotroph-specific ERE transcriptional assay, we found that BC inhibition of the ERE-mediated ER transcriptional activity partly involved D2 dopamine receptor-mediated, pertussis toxin-sensitive G protein-coupled, cAMP/protein kinase A-dependent signaling. BC treatment had no effect on the cellular concentration of ERα or its phosphorylation status at Ser-118. Similar transcriptional inhibition by BC was also found in GH4ZR7 cells, a D2 dopamine receptor-expressing somatomammotrophic cell line. These results suggest that activation of the D2 dopamine receptors inhibits estrogen-dependent lactotroph functions in part via attenuation of ERE-mediated ER transactivation.

Differences between rat strains in the development of PRL-secreting pituitary tumors with long-term estrogen treatment: In vitro insulin-like growth factor-1-induced lactotroph proliferation and gene expression are affected in Wistar-Kyoto rats with low estrogen-susceptibility

There are differences in the susceptibility of rat strains to pituitary growth and lactotroph proliferation caused by long-term treatment with estrogens. To investigate the pituitary mechanism for this strain difference in estrogen-induced lactotroph proliferation, we compared the abilities of 17-β estradiol (E2) and insulin-like growth factor-1 (IGF-1) to modulate lactotroph proliferation and gene expression in vitro in Wistar and Wistar-Kyoto (WKY) rats. These two strains of rats have a high and very low susceptibility to estrogen, respectively. Long-term in vivo treatment with E2 was confirmed to markedly increase pituitary weight and lactotroph proliferation in ovariectomized Wistar, but not in WKY rats. Pituitary lactotrophs in primary cultures showed similar proliferative responsiveness to the culture condition-dependent, stimulatory and inhibitory actions of E2 in both strains. The only difference in lactotroph proliferation in vitro was a lower response to IGF-1 in WKY cells compared with Wistar cells. This difference in proliferation was associated with strain differences in IGF-1-induced gene expression in Wistar and WKY cultured cells. Of the genes tested, IGF-1-induced expression of the Wnt4, Stc1, Mybl1, and Myc genes was attenuated or abolished in WKY cells. These results suggest that the proliferative response to estrogen in lactotrophs in primary culture does not reflect the proliferative response to long-term estrogen treatment observed in vivo in Wistar and WKY rats. The strain difference in proliferation and gene expression to IGF-1 may be implicated in the variable degree of susceptibility for lactotroph proliferation observed in different strains of rats following long-term estrogen treatment.