Role of c-Myb during prolactin-induced signal transducer and activator of transcription 5a signaling in breast cancer cells

G-quadruplexes in cancer-related gene promoters: from identification to therapeutic targeting

INTRODUCTION

Guanine-rich DNA sequences can fold into four-stranded noncanonical secondary structures called G-quadruplexes (G4s) which are widely distributed in functional regions of the human genome, such as telomeres and gene promoter regions. Compelling evidence suggests their involvement in key genome functions such as gene expression and genome stability. Notably, the abundance of G4-forming sequences near transcription start sites suggests their potential involvement in regulating oncogenes.

AREAS COVERED

This review provides an overview of current knowledge on G4s in human oncogene promoters. The most representative G4-binding ligands have also been documented. The objective of this work is to present a comprehensive overview of the most promising targets for the development of novel and highly specific anticancer drugs capable of selectively impacting the expression of individual or a limited number of genes.

EXPERT OPINION

Modulation of G4 formation by specific ligands has been proposed as a powerful new tool to treat cancer through the control of oncogene expression. Actually, most of G4-binding small molecules seem to simultaneously target a range of gene promoter G4s, potentially influencing several critical driver genes in cancer, thus producing significant therapeutic benefits.

Breast Cancer and Prolactin - New Mechanisms and Models

The pathogenesis of breast cancer is driven by multiple hormones and growth factors. One of these, prolactin (PRL), contributes to both mammary differentiation and oncogenesis, and yet the basis for these disparate effects has remained unclear. The focus of this review is to examine and place into context 2 recent studies that have provided insight into the roles of PRL receptors and PRL in tumorigenesis and tumor progression. One study provides novel evidence for opposing actions of PRL in the breast being mediated in part by differential PRL receptor (PRLr) isoform utilization. Briefly, homomeric complexes of the long isoform of the PRLr (PRLrL-PRLrL) promotes mammary differentiation, while heteromeric complexes of the intermediate and long PRLr (PRLrI-PRLrL) isoforms trigger mammary oncogenesis. Another study describes an immunodeficient, prolactin-humanized mouse model, NSG-Pro, that facilitates growth of PRL receptor-expressing patient-derived breast cancer xenografts. Evidence obtained with this model supports the interactions of physiological levels of PRL with estrogen and ERBB2 gene networks, the modulatory effects of PRL on drug responsiveness, and the pro-metastatic effects of PRL on breast cancer. This recent progress provides novel concepts, mechanisms and experimental models expected to renew interest in harnessing/exploiting PRLr signaling for therapeutic effects in breast cancer.

Alpha7 Nicotinic Acetylcholine Receptor Antagonists Prevent Meningitic Escherichia coli-Induced Blood–Brain Barrier Disruptions by Targeting the CISH/JAK2/STAT5b Axis

Despite the availability of antibiotics over the last several decades, excessive antibiotic treatments for bacterial sepsis and meningitis (BSM) in children may result in several adverse outcomes. Hematogenous pathogens may directly induce permeability increases in human brain microvascular endothelial cells (HBMECs) and blood–brain barrier (BBB) dysfunctions. Our preliminary studies demonstrated that the alpha7 nicotinic acetylcholine receptor (α7nAChR) played an important role in the pathogenesis of BSM, accompanied by increasing cytokine-inducible SH2-containing protein (CISH) at the transcriptome level, but it has remained unclear how α7nAChR-CISH works mechanistically. The study aims to explore the underlying mechanism of α7nAChR and CISH during E. coli-induced BSM in vitro (HBMECs) and in vivo (α7nAChR-KO mouse). We found that in the stage of E. coli K1-induced BBB disruptions, α7nAChR functioned as the key regulator that affects the integrity of HBMECs by activating the JAK2–STAT5 signaling pathway, while CISH inhibited JAK2–STAT5 activation and exhibited protective effects against E. coli infection. Notably, we first validated that the expression of CISH could be regulated by α7nAChR in HBMECs. In addition, we determined the protective effects of MLA (methyllycaconitine citrate) and MEM (memantine hydrochloride) (functioning as α7nAChR antagonists) on infected HBMECs and suggested that the α7nAChR–CISH axis could explain the protective effects of the two small-molecule compounds on E. coli-induced HBMECs injuries and BBB disruptions. In conclusion, we dissected the α7nAChR/CISH/JAK2/STAT5 axis as critical for the pathogenesis of E. coli-induced brain microvascular leakage and BBB disruptions and provided novel evidence for the development of α7nAChR antagonists in the prevention of pediatric E. coli BSM.

Serine residues 726 and 780 have nonredundant roles regulating STAT5a activity in luminal breast cancer

In breast cancer, prolactin-induced activation of the transcription factor STAT5a results from the phosphorylation of STAT5a tyrosine residue 694. However, its role in mammary oncogenesis remains an unsettled debate as STAT5a exhibits functional dichotomy with both pro-differentiative and pro-proliferative target genes. Phosphorylation of STAT5a serine residues, S726 and S780, may regulate STAT5a in such a way to underlie this duality. Given hematopoiesis studies showing phospho-serine STAT5a as necessary for transformation, we hypothesized that serine phosphorylation regulates STAT5a activity to contribute to its role in mammary oncogenesis, specifically in luminal breast cancer. Here, phosphorylation of S726-, S780-, and Y694-STAT5a in response to prolactin in MCF7 luminal breast cancer cells was investigated with STAT5a knockdown and rescue with Y694F-, S726A-, or S780A-STAT5a, where the phospho-sites were mutated. RNA-sequencing and subsequent Ingenuity Pathway Analysis predicted that loss of each phospho-site differentially affected both prolactin-induced gene expression as well as functional pathways of breast cancer (e.g. cell survival, proliferation, and colony formation). In vitro studies of anchorage-independent growth and proliferation confirmed distinct phenotypes: whereas S780A-STAT5a decreased clonogenicity, S726A-STAT5a decreased proliferation in response to prolactin compared to wild type STAT5a. Collectively, these studies provide novel insights into STAT5a activation in breast cancer pathogenesis.

Prolactin Drives a Dynamic STAT5A/HDAC6/HMGN2 Cis-Regulatory Landscape Exploitable in ER+ Breast Cancer

The hormone prolactin has been implicated in breast cancer pathogenesis and regulates chromatin engagement by the transcription factor, STAT5A. STAT5A is known to inducibly bind promoters and cis-regulatory elements genome-wide, though the mechanisms by which it exerts specificity and regulation of target gene expression remain enigmatic. We previously identified HDAC6 and HMGN2 as cofactors that facilitate prolactin-induced, STAT5A-mediated gene expression. Here, multicondition STAT5A, HDAC6, and HMGN2 chromatin immunoprecipitation and sequencing with parallel condition RNA-seq are utilized to reveal the cis-regulatory landscape and cofactor dynamics underlying prolactin-stimulated gene expression in breast cancer. We find that prolactin-regulated genes are significantly enriched for cis-regulatory elements bound by HDAC6 and HMGN2, and that inducible STAT5A binding at enhancers, rather than promoters, conveys specificity for prolactin-regulated genes. The selective HDAC6 inhibitor, ACY-241, blocks prolactin-induced STAT5A chromatin engagement at cis-regulatory elements as well as a significant proportion of prolactin-stimulated gene expression. We identify functional pathways known to contribute to the development and/or progression of breast cancer that are activated by prolactin and inhibited by ACY-241. Additionally, we find that the DNA sequences underlying shared STAT5A and HDAC6 binding sites at enhancers are differentially enriched for estrogen response elements (ESR1 and ESR2 motifs) relative to enhancers bound by STAT5A alone. Gene set enrichment analysis identifies significant overlap of ERα-regulated genes with genes regulated by prolactin, particularly prolactin-regulated genes with promoters or enhancers co-occupied by both STAT5A and HDAC6. Lastly, the therapeutic efficacy of ACY-241 is demonstrated in in vitro and in vivo breast cancer models, where we identify synergistic ACY-241 drug combinations and observe differential sensitivity of ER+ models relative to ER- models.

Inhibition of the Activity of Cyclophilin A Impedes Prolactin Receptor-Mediated Signaling, Mammary Tumorigenesis, and Metastases

Prolactin (PRL) and its receptor (PRLr) play important roles in the pathogenesis of breast cancer. Cyclophilin A (CypA) is a cis-trans peptidyl-prolyl isomerase (PPI) that is constitutively associated with the PRLr and facilitates the activation of the tyrosine kinase Jak2. Treatment with the non-immunosuppressive prolyl isomerase inhibitor NIM811 or CypA short hairpin RNA inhibited PRL-stimulated signaling, breast cancer cell growth, and migration. Transcriptomic analysis revealed that NIM811 inhibited two-thirds of the top 50 PRL-induced genes and a reduction in gene pathways associated with cancer cell signaling. In vivo treatment of NIM811 in a TNBC xenograft lessened primary tumor growth and induced central tumor necrosis. Deletion of CypA in the MMTV-PyMT mouse model demonstrated inhibition of tumorigenesis with significant reduction in lung and lymph node metastasis. The regulation of PRLr/Jak2-mediated biology by NIM811 demonstrates that a non-immunosuppressive prolyl isomerase inhibitor can function as a potential breast cancer therapeutic.

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CypA inhibition or knockdown blocks breast cancer cell signaling, growth, and migration

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NIM811 inhibited PRL-induced genes and gene pathways relevant to cancer signaling

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Deletion of CypA has shown reduction in tumorigenesis and metastasis in mice

A serine/threonine protein PIM kinase as a biomarker of cancer and a target for anti-tumor therapy

The PIM Kinases belong to the family of a proto-oncogene that essentially phosphorylates the serine/threonine residues of the target proteins. They are primarily categorized into three types PIM-1, PIM-2, PIM-3 which plays an indispensable regulatory role in signal transduction cascades, by promoting cell survival, proliferation, and drug resistance. These kinases are overexpressed in several solid as well as hematopoietic tumors which supports in vitro and in vivo malignant cell growth along with survival by regulating cell cycle and inhibiting apoptosis. They lack regulatory domain which makes them constitutively active once transcribed. PIM kinases usually appear to be important downstream effectors of oncoproteins which overexpresses and helps in mediating drug resistance to available agents, such as rapamycin. Structural studies of PIM kinases revealed that they have unique hinge regions where two Proline resides and makes ATP binding unique, by offering a target for an increasing number of potent PIM kinase inhibitors. Preclinical studies of those inhibitory compounds in various cancers indicate that these novel agents show promising activity and some of them currently being under examination. In this review, we have outlined PIM kinases molecular mechanism and signaling pathways along with matriculation in various cancer and list of inhibitors often used.

Involvement of the Dysregulation of miR-23b-3p, miR-195-5p, miR-656-5p, and miR-340-5p in Trastuzumab Resistance of HER2-Positive Breast Cancer Cells and System Biology Approach to Predict Their Targets Involved in Resistance

Resistance to trastuzumab has become a limiting factor for therapeutic efficacy of human epidermal growth factor 2 (HER2)-positive breast cancer. Different expression levels of miRNAs in cancer cells have been associated with poor prognosis and response to chemotherapy. The aim of this study was to evaluate miRNAs that were thought to be associated with HER2-positive breast cancer chemoresistance. In this study, the relative expression of candidate miRNAs to U6 RNA was evaluated in trastuzumab-resistant and trastuzumab-sensitive cells using relative real-time PCR. Our results demonstrated that miR-23b-3p, miR-195-5p, miR-656-5p, and miR-340-5p were significantly dysregulated. For the first time in this study, these miRNAs were identified to be involved in trastuzumab resistance. TargetScan and miRDB were then used for predicting the potential targets of the candidate miRNAs. Our results also revealed that the predicted potential targets of these miRNAs were strongly associated with drug resistance pathways. As a relative expression of candidate miRNAs was statistically different in trastuzumab-resistant and trastuzumab-sensitive cells, their potential targets were involved in drug resistance pathways. We strongly hypothesized the dysregulation of miRNAs as a possible mechanism of trastuzumab resistance. We also assumed that the strategic manipulation of these regulatory networks might be a possible therapeutic strategy to improve the results of chemotherapy for this resistance. However, more research is needed to evaluate the role of these miRNAs in the acquisition of trastuzumab resistance.

Exploration of G-quadruplex function in c-Myb gene and its transcriptional regulation by topotecan

Our bioinformatics research shows that there are four G-rich sequences (S1-S4) in the upstream region of the transcription start site of c-Myb gene, and we have proved that these sequences have the ability to form G-quadruplex structures. This work mainly focuses on G-quadruplex function, recognition and transcription regulation in c-Myb gene, revealing a novel regulatory element in c-Myb proximal promoter region, and its transcription regulation by G-quadruplex binder. The research has identified that the enhancer effect in c-Myb transcription was primarily affected by the G-quadruplex formed by S1 sequence, and the up-regulation effect may due to the removal of repressive progress of MZF-1 by stabilizing G-quadruplex. Attentions were being paid to the development of G-quadruplex binders for selective recognition, and topotecan was found to have high binding affinity in vitro and could effectively affect the c-Myb transcription activities in cells. The regulation of G-quadruplex with binders in transcriptional, translational levels by Q-RT-PCR and western blot was in expectation of providing a strategy for gene expression modulation. In conclusion, our study revealed a G-quadruplex structure in c-Myb proximal promoter region, which was of great importance in the regulation of c-Myb function.

MiR-15a suppresses hepatocarcinoma cell migration and invasion by directly targeting cMyb

PURPOSE

This study aimed to determine the function of miR-15a in HCC, and identify cMyb as a target of miR-15a.

METHODS

RNA expression was evaluated by quantitative real-time PCR (qRT-PCR). The effects of miR-15a or cMyb on HCC cells were evaluated by transwell migration assay and western blot analysis. CMyb, the predicted target, has been frequently verified by luciferase assay.

RESULTS

MiR-15a was markedly downregulated in sphere culture HCC cells by qRT-PCR. CMyb was predicted to be a potential target of miR-15a using bioinformatics analysis. This prediction has been frequently verified by luciferase assay and western blot. A positive correlation between cMyb and the migration ability of HCC cells was demonstrated by transwell assays. MiR-15a mimic suppressed cMyb expression to weaken HCC cell migration ability. On the other hand, miR-15a inhibitor upregulated cMyb and induced HCC cell migration.

CONCLUSION

MiR-15a could suppress HCC progression through the repression of cMyb, making miR-15a a potential therapeutic target.

c-Myb knockdown increases the neomycin-induced damage to hair-cell-like HEI-OC1 cells in vitro

c-Myb is a transcription factor that plays a key role in cell proliferation, differentiation, and apoptosis. It has been reported that c-Myb is expressed within the chicken otic placode, but whether c-Myb exists in the mammalian cochlea, and how it exerts its effects, has not been explored yet. Here, we investigated the expression of c-Myb in the postnatal mouse cochlea and HEI-OC1 cells and found that c-Myb was expressed in the hair cells (HCs) of mouse cochlea as well as in cultured HEI-OC1 cells. Next, we demonstrated that c-Myb expression was decreased in response to neomycin treatment in both cochlear HCs and HEI-OC1 cells, suggesting an otoprotective role for c-Myb. We then knocked down c-Myb expression with shRNA transfection in HEI-OC1 cells and found that c-Myb knockdown decreased cell viability, increased expression of pro-apoptotic factors, and enhanced cell apoptosis after neomycin insult. Mechanistic studies revealed that c-Myb knockdown increased cellular levels of reactive oxygen species and decreased Bcl-2 expression, both of which are likely to be responsible for the increased sensitivity of c-Myb knockdown cells to neomycin. This study provides evidence that c-Myb might serve as a new target for the prevention of aminoglycoside-induced HC loss.

The transcriptional responsiveness of LKB1 to STAT-mediated signaling is differentially modulated by prolactin in human breast cancer cells

Background

Liver kinase 1 (LKB1) is an important multi-tasking protein linked with metabolic signaling, also controlling polarity and cytoskeletal rearrangements in diverse cell types including cancer cells. Prolactin (PRL) and Signal transducer and activator of transcription (STAT) proteins have been associated with breast cancer progression. The current investigation examines the effect of PRL and STAT-mediated signaling on the transcriptional regulation of LKB1 expression in human breast cancer cells.

Methods

MDA-MB-231, MCF-7, and T47D human breast cancer cells, and CHO-K1 cells transiently expressing the PRL receptor (long form), were treated with 100 ng/ml of PRL for 24 hours. A LKB1 promoter-luciferase construct and its truncations were used to assess transcriptional changes in response to specific siRNAs or inhibitors targeting Janus activated kinase 2 (JAK2), STAT3, and STAT5A. Real-time PCR and Western blotting were applied to quantify changes in mRNA and protein levels. Electrophoretic mobility shift (EMSA) and chromatin immunoprecipitation (ChIP) assays were used to examine STAT3 and STAT5A binding to the LKB1 promoter.

Results

Consistent with increases in mRNA, the LKB1 promoter was up-regulated by PRL in MDA-MB-231 cells, a response that was lost upon distal promoter truncation. A putative GAS element that could provide a STAT binding site mapped to this region, and its mutation decreased PRL-responsiveness. PRL-mediated increases in promoter activity required signaling through STAT3 and STAT5A, also involving JAK2. Both STATs imparted basally repressive effects in MDA-MB-231 cells. PRL increased in vivo binding of STAT3, and more definitively, STAT5A, to the LKB1 promoter region containing the GAS site. In T47D cells, PRL down-regulated LKB1 transcriptional activity, an effect that was reversed upon culture in phenol red-free media. Interleukin 6, a cytokine activating STAT signaling in diverse cell types, also increased LKB1 mRNA levels and promoter activity in MDA-MB-231 cells.

Conclusions

LKB1 is differentially regulated by PRL at the level of transcription in representative human breast cancer cells. Its promoter is targeted by STAT proteins, and the cellular estrogen receptor status may affect PRL-responsiveness. The hormonal and possibly cytokine-mediated control of LKB1 expression is particularly relevant in aggressive breast cancer cells, potentially promoting survival under energetically unfavorable conditions.

MicroRNA-195 inhibits non-small cell lung cancer cell proliferation, migration and invasion by targeting MYB

MicroRNA-195 (miR-195) has been implicated in several other cancers; however, its role in non-small cell lung cancer (NSCLC) remains unclear. In this study, we demonstrated that miR-195 was significantly down-regulated in NSCLC samples and cell lines compared with corresponding normal counterparts. In vitro and in vivo functional assays demonstrated that modulation of miR-195 expression affected NSCLC cell proliferation, migration and invasion. Using miRNA target prediction algorithms and reporter assays, we demonstrated that miR-195 suppressed the expression of MYB both at the mRNA and protein level, and was directly bound to the 3'untranslated region of MYB mRNA. Overexpression of MYB in NSCLC cells using an ectopic expression vector restored the decreased cell proliferation, migration and invasion effects induced by miR-195. Finally, we observed an inverse correlation between MYB and miR-195 in NSCLC. Taken together, our findings indicated that miR-195 functions as tumour suppressor in NSCLC, and the miR-195/MYB axis might represent a potential therapeutic target for NSCLC intervention.

Genetic interaction between mutations in c-Myb and the KIX domains of CBP and p300 affects multiple blood cell lineages and influences both gene activation and repression

Adult blood cell production or definitive hematopoiesis requires the transcription factor c-Myb. The closely related KAT3 histone acetyltransferases CBP (CREBBP) and p300 (EP300) bind c-Myb through their KIX domains and mice homozygous for a p300 KIX domain mutation exhibit multiple blood defects. Perplexingly, mice homozygous for the same KIX domain mutation in CBP have normal blood. Here we test the hypothesis that the CBP KIX domain contributes subordinately to hematopoiesis via a genetic interaction with c-Myb. We assessed hematopoiesis in mice bearing compound mutations of c-Myb and/or the KIX domains of CBP and p300, and measured the effect of KIX domain mutations on c-Myb-dependent gene expression. We found that in the context of a p300 KIX mutation, the CBP KIX domain mutation affects platelets, B cells, T cells, and red cells. Gene interaction (epistasis) analysis provides mechanistic evidence that blood defects in KIX mutant mice are consistent with reduced c-Myb and KIX interaction. Lastly, we demonstrated that the CBP and p300 KIX domains contribute to both c-Myb-dependent gene activation and repression. Together these results suggest that the KIX domains of CBP, and especially p300, are principal mediators of c-Myb-dependent gene activation and repression that is required for definitive hematopoiesis.

Nemo-like kinase associated with proliferation and apoptosis by c-Myb degradation in breast cancer

Nemo-like kinase (NLK), a mediator of the Wnt signaling pathway, binds directly to c-Myb, leading to its phosphorylation, ubiquitination and proteasome-dependent degradation. NLK was significantly downregulated in the breast cancer tissues compared to corresponding normal tissues. NLK expression was negatively correlated with c-Myb expression. NLK suppressed proliferation, induced apoptosis and mediated c-Myb degradation in MCF-7 cells via a mechanism that seems to involve c-myc and Bcl2. These findings might provide a novel target for therapeutic intervention in patients with breast cancer.

Analysis and prediction of pathways in HeLa cells by integrating biological levels of organization with systems-biology approaches

It has recently begun to be considered that cancer is a systemic disease and that it must be studied at every level of complexity using many of the currently available approaches, including high-throughput technologies and bioinformatics. To achieve such understanding in cervical cancer, we collected information on gene, protein and phosphoprotein expression of the HeLa cell line and performed a comprehensive analysis of the different signaling pathways, transcription networks and metabolic events in which they participate. A total expression analysis by RNA-Seq of the HeLa cell line showed that 19,974 genes were transcribed. Of these, 3,360 were over-expressed, and 2,129 under-expressed when compared to the NHEK cell line. A protein-protein interaction network was derived from the over-expressed genes and used to identify central elements and, together with the analysis of over-represented transcription factor motifs, to predict active signaling and regulatory pathways. This was further validated by Metal-Oxide Affinity Chromatography (MOAC) and Tandem Mass Spectrometry (MS/MS) assays which retrieved phosphorylated proteins. The 14-3-3 family members emerge as important regulators in carcinogenesis and as possible clinical targets. We observed that the different over- and under-regulated pathways in cervical cancer could be interrelated through elements that participate in crosstalks, therefore belong to what we term "meta-pathways". Additionally, we highlighted the relations of each one of the differentially represented pathways to one or more of the ten hallmarks of cancer. These features could be maintained in many other types of cancer, regardless of mutations or genomic rearrangements, and favor their robustness, adaptations and the evasion of tissue control. Probably, this could explain why cancer cells are not eliminated by selective pressure and why therapy trials directed against molecular targets are not as effective as expected.

β-arrestin-selective G protein-coupled receptor agonists engender unique biological efficacy in vivo

Biased G protein-coupled receptor agonists are orthosteric ligands that possess pathway-selective efficacy, activating or inhibiting only a subset of the signaling repertoire of their cognate receptors. In vitro, D-Trp(12),Tyr(34)-bPTH(7-34) [bPTH(7-34)], a biased agonist for the type 1 PTH receptor, antagonizes receptor-G protein coupling but activates arrestin-dependent signaling. In vivo, both bPTH(7-34) and the conventional agonist hPTH(1-34) stimulate anabolic bone formation. To understand how two PTH receptor ligands with markedly different in vitro efficacy could elicit similar in vivo responses, we analyzed transcriptional profiles from calvarial bone of mice treated for 8 wk with vehicle, bPTH(7-34) or hPTH(1-34). Treatment of wild-type mice with bPTH(7-34) primarily affected pathways that promote expansion of the osteoblast pool, notably cell cycle regulation, cell survival, and migration. These responses were absent in β-arrestin2-null mice, identifying them as downstream targets of β-arrestin2-mediated signaling. In contrast, hPTH(1-34) primarily affected pathways classically associated with enhanced bone formation, including collagen synthesis and matrix mineralization. hPTH(1-34) actions were less dependent on β-arrestin2, as might be expected of a ligand capable of G protein activation. In vitro, bPTH(7-34) slowed the rate of preosteoblast proliferation, enhanced osteoblast survival when exposed to an apoptotic stimulus, and stimulated cell migration in wild-type, but not β-arrestin2-null, calvarial osteoblasts. These results suggest that bPTH(7-34) and hPTH(1-34) affect bone mass in vivo through predominantly separate genomic mechanisms created by largely distinct receptor-signaling networks and demonstrate that functional selectivity can be exploited to change the quality of G protein-coupled receptor efficacy.

The prolactin receptor transactivation domain is associated with steroid hormone receptor expression and malignant progression of breast cancer

The polypeptide hormone prolactin (PRL) stimulates breast epithelial cell growth, differentiation, and motility through its cognate receptor, PRLr. PRLr is expressed in most breast cancers; however, its exact role remains elusive. Our laboratory previously described a novel mode of PRLr signaling in which Stat5a-mediated transcription is regulated through ligand-induced phosphorylation of the PRLr transactivation domain (TAD). Herein, we used a PRLr transactivation-deficient mutant (PRLrYDmut) to identify novel TAD-specific target genes. Microarray analysis identified 120 PRL-induced genes up-regulated by wild type but not PRLrYDmut. Compared with control, PRLr expression significantly induced expression of approximately 4700 PRL-induced genes, whereas PRLrYDmut ablated induction of all but 19 of these genes. Ingenuity pathway analysis found that the PRLr TAD most profoundly affected networks involving cancer and proliferation. In support of this, PRLrYDmut expression reduced anchorage-dependent and anchorage-independent growth. In addition, pathway analysis identified a link between the PRLr TAD and the estrogen and progesterone receptors (ERα/PR). Although neither ERα nor PR was identified as a PRL target gene, a TAD mutation significantly impaired ERα/PR expression and estrogen responsiveness. TMA analysis revealed a marked increase in nuclear, but not cytoplasmic, PRLr TAD phosphorylation as a function of neoplastic progression. We propose that PRLr TAD phosphorylation contributes to breast cancer pathogenesis, in part through regulation of ERα and PR, and has potential utility as a biomarker in this disease.

Induction of multidrug resistance transporter ABCG2 by prolactin in human breast cancer cells

The multidrug transporter, breast cancer resistance protein, ABCG2, is up-regulated in certain chemoresistant cancer cells and in the mammary gland during lactation. We investigated the role of the lactogenic hormone prolactin (PRL) in the regulation of ABCG2. PRL dose-dependently induced ABCG2 expression in T-47D human breast cancer cells. This induction was significantly reduced by short-interfering RNA-mediated knockdown of Janus kinase 2 (JAK2). Knockdown or pharmacologic inhibition of the down-stream signal transducer and activator of transcription-5 (STAT5) also blunted the induction of ABCG2 by PRL, suggesting a role for the JAK2/STAT5 pathway in PRL-induced ABCG2 expression. Corroborating these findings, we observed PRL-stimulated STAT5 recruitment to a region containing a putative γ-interferon activation sequence (GAS) element at -434 base pairs upstream of the ABCG2 transcription start site. Introduction of a single mutation to the -434 GAS element significantly attenuated PRL-stimulated activity of a luciferase reporter driven by the ABCG2 gene promoter and 5'-flanking region containing the -434 GAS motif. In addition, this GAS element showed strong copy number dependency in its response to PRL treatment. Interestingly, inhibitors against the mitogen-activated protein kinase and phosphoinositide-3-kinase signaling pathways significantly decreased the induction of ABCG2 by PRL without altering STAT5 recruitment to the GAS element. We conclude that the JAK2/STAT5 pathway is required but not sufficient for the induction of ABCG2 by PRL.

Signal transducer and activator of transcription 5 as a key signaling pathway in normal mammary gland developmental biology and breast cancer

STAT5 consists of two proteins, STAT5A/B, that impact mammary cell differentiation, proliferation, and survival. In normal development, STAT5 expression and activity are regulated by prolactin signaling with JAK2/ELF5, EGF signaling networks that include c-Src, and growth hormone, insulin growth factor, estrogen, and progesterone signaling pathways. In cancer, erythropoietin signaling can also regulate STAT5. Activation levels are influenced by AKT, caveolin, PIKE-A, Pak1, c-Myb, Brk, beta-integrin, dystroglycan, other STATs, and STAT pathway molecules JAK1, Shp2, and SOCS. TGF-β and PTPN9 can downregulate prolactin- and EGF-mediated STAT5 activation, respectively. IGF, AKT, RANKL, cyclin D1, BCL6, and HSP90A lie downstream of STAT5.

Negative cross talk between NFAT1 and Stat5 signaling in breast cancer

The molecular mechanisms that modulate the activity of the signal transducers and activators of transcription 5 (Stat5) during the progression of breast cancer remain elusive. Here, we present evidence that the calcineurin/nuclear factor of activated T cells (NFAT) pathway negatively regulates the activation of Stat5, and vice versa in breast cancer. NFAT1 interacts with Stat5 in breast cancer cells, and their physical association is mediated by the DNA binding and transactivation domains of Stat5. Ectopically expressed NFAT1 is capable of inhibiting Stat5-dependent functions, including Stat5 transactivation, Stat5-mediated transcription of the downstream target gene expression, and binding of Stat5a to the Stat5 target promoter. By contrast, overexpression of a selective NFAT inhibitor VIVIT reversed NFAT1-mediated suppression of Stat5-dependent gene expression, whereas silencing of NFAT1 through RNA interference enhanced prolactin-induced, Stat5-mediated gene transcription, and breast cancer cell proliferation. A reciprocal inhibitory effect of Stat5 activity on NFAT1 signaling was also observed, implying these two signaling cascades antagonize each other in breast cancer. Importantly, analysis of a matched breast cancer progression tissue microarray revealed a negative correlation between levels of NFAT1 and Stat5 (pY694) during the progression of breast cancer. Taken together, these studies highlight a novel negative cross talk between the NFAT1- and Stat5-signaling cascades that may affect breast tumor formation, growth, and metastasis.

A cis-acting regulatory variation of the estrogen receptor α (ESR1) gene is associated with hepatitis B virus-related liver cirrhosis

The hepatic fibrogenesis and sexual dimorphism of hepatitis B virus-related liver cirrhosis (HBV-LC) are related to estrogen and its receptors. Abnormal expression of estrogen receptor α (ESR1) is implicated in the development of cirrhosis in both animal models and humans. Here, we examine whether the ESR1 polymorphisms are related to HBV-LC risk among chronic HBV carriers, and we investigate the functional significance of positively associated polymorphisms. A total of 2,404 unrelated Chinese HBV carriers were recruited to conduct the two-stage designed case-control study. Two ESR1 haplotype tagging polymorphisms, c.30T>C (rs2077647) and c.453-397T>C (rs2234693), were genotyped in 1,285 patients with HBV-LC and in 1,119 asymptomatic HBV carriers. We observed a significantly increased susceptibility to HBV-LC associated with the c.30C allele (P = 4.2 × 10(-8) ), c.453-397C allele (P = 2.0 × 10(-8) ), and [c.30C; c.453-397C] haplotype (Dominant model, P = 8.85 × 10(-10) , odds ratio = 1.50, 95% CI 1.32∼1.71) compared with the T alleles and (c.30T; c.453-397T) haplotype of c.30T>C and c.453-397T>C polymorphisms, respectively. Functional analyses were conducted to verify the biological functions of the associated genetic variations and showed that the c.453-397T>C polymorphism is a novel c.453-397C allele-specific and c-myb-dependent enhancer-like cis-acting regulatory variation and could be part of the genetic variations underlying the susceptibility of individuals to HBV-LC.

The early growth response gene Egr2 (Alias Krox20) is a novel transcriptional target of transforming growth factor-β that is up-regulated in systemic sclerosis and mediates profibrotic responses

Although the early growth response-2 (Egr-2, alias Krox20) protein shows structural and functional similarities to Egr-1, these two related early-immediate transcription factors are nonredundant. Egr-2 plays essential roles in peripheral nerve myelination, adipogenesis, and immune tolerance; however, its regulation and role in tissue repair and fibrosis remain poorly understood. We show herein that transforming growth factor (TGF)-β induced a Smad3-dependent sustained stimulation of Egr2 gene expression in normal fibroblasts. Overexpression of Egr-2 was sufficient to stimulate collagen gene expression and myofibroblast differentiation, whereas these profibrotic TGF-β responses were attenuated in Egr-2-depleted fibroblasts. Genomewide transcriptional profiling revealed that multiple genes associated with tissue remodeling and wound healing were up-regulated by Egr-2, but the Egr-2-regulated gene expression profile overlapped only partially with the Egr-1-regulated gene profile. Levels of Egr-2 were elevated in lesional tissue from mice with bleomycin-induced scleroderma. Moreover, elevated Egr-2 was noted in biopsy specimens of skin and lung from patients with systemic sclerosis. These results provide the first evidence that Egr-2 is a functionally distinct transcription factor that is both necessary and sufficient for TGF-β-induced profibrotic responses and is aberrantly expressed in lesional tissue in systemic sclerosis and in a murine model of scleroderma. Together, these findings suggest that Egr-2 plays an important nonredundant role in the pathogenesis of fibrosis. Targeting Egr-2 might represent a novel therapeutic strategy to control fibrosis.

HMGN2 inducibly binds a novel transactivation domain in nuclear PRLr to coordinate Stat5a-mediated transcription

The direct actions of transmembrane receptors within the nucleus remain enigmatic. In this report, we demonstrate that the prolactin receptor (PRLr) localizes to the nucleus where it functions as a coactivator through its interactions with the latent transcription factor signal transducer and activator of transcription 5a (Stat5a) and the high-mobility group N2 protein (HMGN2). We identify a novel transactivation domain within the PRLr that is activated by ligand-induced phosphorylation, an event coupled to HMGN2 binding. The association of the PRLr with HMGN2 enables Stat5a-responsive promoter binding, thus facilitating transcriptional activation and promoting anchorage-independent growth. We propose that HMGN2 serves as a critical regulatory factor in Stat5a-driven gene expression by facilitating the assembly of PRLr/Stat5a onto chromatin and that these events may serve to promote biological events that contribute to a tumorigenic phenotype. Our data imply that phosphorylation may be the molecular switch that activates a cell surface receptor transactivation domain, enabling it to tether chromatin-modifying factors, such as HMGN2, to target promoter regions in a sequence-specific manner.

Cancer classification from gene expression data by NPPC ensemble

The most important application of microarray in gene expression analysis is to classify the unknown tissue samples according to their gene expression levels with the help of known sample expression levels. In this paper, we present a nonparallel plane proximal classifier (NPPC) ensemble that ensures high classification accuracy of test samples in a computer-aided diagnosis (CAD) framework than that of a single NPPC model. For each data set only, a few genes are selected by using a mutual information criterion. Then a genetic algorithm-based simultaneous feature and model selection scheme is used to train a number of NPPC expert models in multiple subspaces by maximizing cross-validation accuracy. The members of the ensemble are selected by the performance of the trained models on a validation set. Besides the usual majority voting method, we have introduced minimum average proximity-based decision combiner for NPPC ensemble. The effectiveness of the NPPC ensemble and the proposed new approach of combining decisions for cancer diagnosis are studied and compared with support vector machine (SVM) classifier in a similar framework. Experimental results on cancer data sets show that the NPPC ensemble offers comparable testing accuracy to that of SVM ensemble with reduced training time on average.

Transcription factor c-Myb promotes the invasion of hepatocellular carcinoma cells via increasing osteopontin expression

Background

Specific gene expression is tightly regulated by various transcription factors. Osteopontin (OPN) is a phosphoprotein that mediates hepatocellular carcinoma (HCC) progression and metastasis. However, the mechanism of OPN up-regulation in HCC metastasis remains to be clarified.

Methods

Oligonucleotide array-based transcription factor assays were applied to compare different activities of transcription factors in two human HCC cell lines with different OPN expression levels. The effects of one selected transcription factor on OPN expression were further evaluated.

Results

Eleven transcription factors were over-expressed in metastatic HCC cell line HCCLM6 cells whereas twelve transcription factors were down-regulated. Electrophoretic mobility shift assays (EMSA) and reporter gene assays showed that one of up-regulated transcription factors c-Myb could bind the OPN promoter and increase its transcription activity. In addition, small interfering RNA targeting c-Myb could inhibit OPN expression and significantly decrease migration and invasion of HCCLM6 cells in vitro.

Conclusion

Our data first demonstrate that c-Myb has a functionally important role in the regulation of OPN expression in HCC cells, suggesting that c-Myb might be a new target to control HCC metastasis.

The chicken miR-150 targets the avian orthologue of the functional zebrafish MYB 3'UTR target site

BACKGROUND

The c-myb proto-oncogene is the founding member of a family of transcription factors involved principally in haematopoiesis, in diverse organisms, from zebrafish to mammals. Its deregulation has been implicated in human leukaemogenesis and other cancers. The expression of c-myb is tightly regulated by post-transcriptional mechanisms involving microRNAs. MicroRNAs are small, highly conserved non-coding RNAs that inhibit translation and decrease mRNA stability by binding to regulatory motifs mostly located in the 3'UTR of target mRNAs conserved throughout evolution. MYB is an evolutionarily conserved miR-150 target experimentally validated in mice, humans and zebrafish. However, the functional miR-150 sites of humans and mice are orthologous, whereas that of zebrafish is different.

RESULTS

We identified the avian mature miRNA-150-5P, Gallus gallus gga-miR-150 from chicken leukocyte small-RNA libraries and showed that, as expected, the gga-miR-150 sequence was highly conserved, including the seed region sequence present in the other miR-150 sequences listed in miRBase. Reporter assays showed that gga-miR-150 acted on the avian MYB 3'UTR and identified the avian MYB target site involved in gga-miR-150 binding. A comparative in silico analysis of the miR-150 target sites of MYB 3'UTRs from different species led to the identification of a single set of putative target sites in amphibians and zebrafish, whereas two sets of putative target sites were identified in chicken and mammals. However, only the target site present in the chicken MYB 3'UTR that was identical to that in zebrafish was functional, despite the additional presence of mammalian target sites in chicken. This specific miR-150 site usage was not cell-type specific and persisted when the chicken c-myb 3'UTR was used in the cell system to identify mammalian target sites, showing that this miR-150 target site usage was intrinsic to the chicken c-myb 3'UTR.

CONCLUSION

Our study of the avian MYB/gga-miR-150 interaction shows a conservation of miR-150 target site functionality between chicken and zebrafish that does not extend to mammals.

MYB suppresses differentiation and apoptosis of human breast cancer cells

INTRODUCTION

MYB is highly expressed in estrogen receptor positive (ER + ve) breast tumours and tumour cell lines. We recently demonstrated that MYB is essential for the proliferation of ER + ve breast cancer cells, and have now investigated its role in mammary epithelial differentiation.

METHODS

MCF-7 breast cancer cells were treated with sodium butyrate, vitamin E succinate or 12-O-tetradecanoylphorbol-13-acetate to induce differentiation as measured by Nile Red staining of lipid droplets and β-casein expression. The non-tumorigenic murine mammary epithelial cell (MEC) line, HC11, was induced to differentiate with lactogenic hormones. MYB levels were manipulated by inducible lentiviral shRNA-mediated knockdown and retroviral overexpression.

RESULTS

We found that MYB expression decreases following chemically-induced differentiation of the human breast cancer cell line MCF-7, and hormonally-induced differentiation of a non-tumorigenic murine mammary epithelial cell (MEC) line, HC11. We also found that shRNA-mediated MYB knockdown initiated differentiation of breast cancer cells, and greatly sensitised them to the differentiative and pro-apoptotic effects of differentiation-inducing agents (DIAs). Sensitisation to the pro-apoptotic effects DIAs is mediated by decreased expression of BCL2, which we show here is a direct MYB target in breast cancer cells. Conversely, enforced expression of MYB resulted in the cells remaining in an undifferentiated state, with concomitant suppression of apoptosis, in the presence of DIAs.

CONCLUSIONS

Taken together, these data imply that MYB function is critical in regulating the balance between proliferation, differentiation, and apoptosis in MECs. Moreover, our findings suggest MYB may be a viable therapeutic target in breast cancer and suggest specific approaches for exploiting this possibility.

Cyclophilin B as a co-regulator of prolactin-induced gene expression and function in breast cancer cells

The effects of prolactin (PRL) during the pathogenesis of breast cancer are mediated in part though Stat5 activity enhanced by its interaction with its transcriptional inducer, the prolyl isomerase cyclophilin B (CypB). We have demonstrated that knockdown of CypB decreases cell growth, proliferation, and migration, and CypB expression is associated with malignant progression of breast cancer. In this study, we examined the effect of CypB knockdown on PRL signaling in breast cancer cells. CypB knockdown with two independent siRNAs was shown to impair PRL-induced reporter expression in breast cancer cell line. cDNA microarray analysis was performed on these cells to assess the effect of CypB reduction, and revealed a significant decrease in PRL-induced endogenous gene expression in two breast cancer cell lines. Parallel functional assays revealed corresponding alterations of both anchorage-independent cell growth and cell motility of breast cancer cells. Our results demonstrate that CypB expression levels significantly modulate PRL-induced function in breast cancer cells ultimately resulting in enhanced levels of PRL-responsive gene expression, cell growth, and migration. Given the increasingly appreciated role of PRL in the pathogenesis of breast cancer, the actions of CypB detailed here are of biological significance.

Involvement of MyoD and c-myb in regulation of basal and estrogen-induced transcription activity of the BRCA1 gene

BRCA1 is closely related to the pathogenesis of breast cancer, BRCA1 mRNA is reduced in sporadic breast cancer cells despite the lack of mutations. In the present report, we find that MyoD expression and BRCA1 expression is correlated in sporadic breast tumors, overexpression of MyoD and c-myb stimulates BRCA1 expression, knockdown of MyoD and c-myb attenuates BRCA1 expression and attenuates the ability of BRCA1 to protect cells against hydrogen peroxide. MyoD and c-myb interact with p300 and PCAF, forming activating transcriptional complexes which bind to E-box and c-myb sites on the BRCA1 promoter and activate its transcription by inducing histone acetylation. Regulation of BRCA1 expression by MyoD and c-myb complexes may be part of an integral signaling pathway that determines and explains breast cancer susceptibility. Detection expression status of the various proteins in these complexes may predispose to the onset of sporadic breast cancer.

c-myb activates CXCL12 transcription in T47D and MCF7 breast cancer cells

Chemokine C-X-C motif ligand 12 (CXCL12) is a potent chemotactic and angiogenic factor that has been proposed to play a role in organ-specific metastasis and angiogenic activity in several malignancies. In this study, we found that the overexpression of c-myb could elevate CXCL12 mRNA level and CXCL12 promoter activity in human T47D and MCF-7 breast cancer cells. Chromatin immunoprecipitation assay demonstrated that c-myb could bind to the CXCL12 promoter in the cells transfected with cmyb expression vector. c-myb siRNA attenuated CXCL12 promoter activity and the binding of c-myb to the CXCL12 promoter in T47D and MCF-7 cells. These results indicated that c-myb could activate CXCL12 promoter transcription.