Stat transcription factors in mammary gland development and tumorigenesis

Methods for investigating STAT3 regulation of lysosomal function in mammary epithelial cells

The transcription factor STAT3 is activated by multiple cytokines and other extrinsic factors. It plays a key role in immune and inflammatory responses and, when dysregulated, in tumourigenesis. STAT3 is also an indispensable mediator of the cell death process that occurs during post-lactational regression of the mammary gland, one of the most dramatic examples of physiological cell death in adult mammals. During this involution of the gland, STAT3 powerfully enhances the lysosomal system to efficiently remove superfluous milk-producing mammary epithelial cells via a lysosomal-mediated programmed cell death pathway. The lysosome is a membrane-enclosed  cytoplasmic organelle that digests and recycles cellular waste, with an important role as a signalling centre that monitors cellular metabolism. Here, we describe key strategies for investigating the role of STAT3 in regulating lysosomal function using a mammary epithelial cell culture model system. These include protocols for lysosome enrichment and enzyme activity assays, in addition to microscopic analyses of the vesicular compartment in cell lines. Collectively, these approaches provide the tools to investigate multiple aspects of lysosome biogenesis and function, and to define both direct and indirect roles for STAT3.

A common regulatory haplotype doubles lactoferrin concentration in milk

BACKGROUND

Bovine lactoferrin (Lf) is an iron absorbing whey protein with antibacterial, antiviral, and antifungal activity. Lactoferrin is economically valuable and has an extremely variable concentration in milk, partly driven by environmental influences such as milking frequency, involution, or mastitis. A significant genetic influence has also been previously observed to regulate lactoferrin content in milk. Here, we conducted genetic mapping of lactoferrin protein concentration in conjunction with RNA-seq, ChIP-seq, and ATAC-seq data to pinpoint candidate causative variants that regulate lactoferrin concentrations in milk.

RESULTS

We identified a highly-significant lactoferrin protein quantitative trait locus (pQTL), as well as a cis lactotransferrin (LTF) expression QTL (cis-eQTL) mapping to the LTF locus. Using ChIP-seq and ATAC-seq datasets representing lactating mammary tissue samples, we also report a number of regions where the openness of chromatin is under genetic influence. Several of these also show highly significant QTL with genetic signatures similar to those highlighted through pQTL and eQTL analysis. By performing correlation analysis between these QTL, we revealed an ATAC-seq peak in the putative promotor region of LTF, that highlights a set of 115 high-frequency variants that are potentially responsible for these effects. One of the 115 variants (rs110000337), which maps within the ATAC-seq peak, was predicted to alter binding sites of transcription factors known to be involved in lactation-related pathways.

CONCLUSIONS

Here, we report a regulatory haplotype of 115 variants with conspicuously large impacts on milk lactoferrin concentration. These findings could enable the selection of animals for high-producing specialist herds.

Notch3 restricts metastasis of breast cancers through regulation of the JAK/STAT5A signaling pathway

PURPOSE

To explore the potential role of signal transducer and activator of transcription 5A (STAT5A) in the metastasis of breast cancer, and its mechanism of regulation underlying.

METHODS AND RESULTS

TCGA datasets were used to evaluate the expression of STAT5A in normal and different cancerous tissues through TIMER2.0, indicating that STAT5A level was decreased in breast cancer tissues compared with normal ones. Gene Set Enrichment Analysis predicted that STAT5A was associated with the activation of immune cells and cell cycle process. We further demonstrated that the infiltration of immune cells was positively associated with STAT5A level. Influorescence staining revealed the expression and distribution of F-actin was regulated by STAT5A, while colony formation assay, wound healing and transwell assays predicted the inhibitory role of STAT5A in the colony formation, migratory and invasive abilities in breast cancer cells. In addition, overexpression of the Notch3 intracellular domain (N3ICD), the active form of Notch3, resulted in the increased expression of STAT5A. Conversely, silencing of Notch3 expression by siNotch3 decreased STAT5A expression, supporting that STAT5A expression is positively associated with Notch3 in human breast cancer cell lines and breast cancer tissues. Mechanistically, chromatin immunoprecipitation showed that Notch3 was directly bound to the STAT5A promoter and induced the expression of STAT5A. Moreover, overexpressing STAT5A partially reversed the enhanced mobility of breast cancer cells following Notch3 silencing. Low expression of Notch3 and STAT5A predicted poorer prognosis of patients with breast cancer.

CONCLUSION

The present study demonstrates that Notch3 inhibits metastasis in breast cancer through inducing transcriptionally STAT5A, which was associated with tumor-infiltrating immune cells, providing a novel strategy to treat breast cancer.

Two novel SNPs identified in STAT1 gene adjoining a QTL for milk production in Holstein Friesian crossbreds of Kerala

We analyzed the effect of a single nucleotide polymorphism, g. C3141T in the 3' UTR of Signal transducer and activator of transcription-1 gene (STAT1) on milk production traits in the Holstein Friesian crossbred cattle of Kerala (n = 144) by association analysis and expression study. The population was genotyped by restriction fragment length polymorphism using Pag1. Association study using the General Linear Model-Analysis of Variance revealed that none of the yield or composition traits analyzed were significantly differed. The expression profile of STAT1 gene in leucocytes of animals bearing homozygous genotypes was compared by quantitative real time PCR using SYBR green chemistry with and relative expression was not found to be significantly differed. The second stage of the study, the STAT1 mRNA spanning 3213 bp was amplified from leucocytes and sequenced (GenBank: MT459802.1). Two novel SNPs were identified; one synonymous mutation in the coding region (g.A1212G) and the other in the 3'UTR (g.T3042C). The novel SNPs might contribute to STAT1 gene regulation mediated by alternate spicing or binding sites for regulatory molecules. The results reiterate the importance of extensive studies of STAT1 gene variants to substantiate the presence of a quantitative trait loci for dairy traits in the vicinity of STAT1 gene.

Lachnochromonin, a fungal metabolite from Lachnum virgineum, inhibits cell growth and promotes apoptosis in tumor cells through JAK/STAT3 signaling

Natural compounds that interfere with tumor cell growth have potential to be used as therapeutic agents to treat cancers. Lachnochromonin (p71) is a small molecule isolated from Lachnum virgineum. Here, we reported the effect of p71 on human tumor cells, especially on breast cancer MCF-7 cells. We found that p71 significantly suppresses cell growth and induces apoptosis. The luciferase results demonstrated that p71 specifically attenuates the activation of JAK/STAT3 signaling. Biochemical analysis revealed that p71 blocks the phosphorylation of STAT3 tyrosine 705 and serine 727, resulting in down-regulation of c-Myc and Cyclin D1 expression level. Importantly, p71 inhibited cell growth, colony-formation, and migration through affecting STAT3 activity. These results implied that p71 may be used as a therapeutic agent against breast cancer.

Aberrant RET expression impacts on normal mammary gland post-lactation transition enhancing cancer potential

RET is a receptor tyrosine kinase with oncogenic potential in the mammary epithelium. Several receptors with oncogenic activity in the breast are known to participate in specific developmental stages. We found that RET is differentially expressed during mouse mammary gland development: RET is present in lactation and its expression dramatically decreases in involution, the period during which the lactating gland returns to a quiescent state after weaning. Based on epidemiological and pre-clinical findings, involution has been described as tumor promoting. Using the Ret/MTB doxycycline-inducible mouse transgenic system, we show that sustained expression of RET in the mammary epithelium during the post-lactation transition to involution is accompanied by alterations in tissue remodeling and an enhancement of cancer potential. Following constitutive Ret expression, we observed a significant increase in neoplastic lesions in the post-involuting versus the virgin mammary gland. Furthermore, we show that abnormal RET overexpression during lactation promotes factors that prime involution, including premature activation of Stat3 signaling and, using RNA sequencing, an acute-phase inflammatory signature. Our results demonstrate that RET overexpression negatively affects the normal post-lactation transition.

Summary: We show that RET activation stimulates Stat3 signaling in mammary epithelial cell culture and in vivo during post-lactation transition, demonstrating that the RET receptor participates in the post-lactation transition priming tumorigenesis.

STAT3 polymorphisms in North Africa and its implication in breast cancer

BACKGROUND

Only a few studies have investigated the association of single nucleotide polymorphisms in STAT3 gene with the susceptibility to cancer and response to chemotherapy. Our aim was to determine the allele frequencies of rs3869550, rs957971, and rs7211777 at the STAT3 gene in North African populations and compare them to 1000 genomes populations, and to investigate their relation with cancer.

METHODS

The targeted SNPs have been analyzed in six Tunisian populations and a sample of Libyans using TaqMan® Assay. The results were compared to 1000 Genomes Project population samples. Targeting of the regions encompassing the three SNPs by micro-ARN was assessed using miR databases.

RESULTS

The analysis of the 3 SNPs showed that North African populations were close to South Asians. As expected, African populations presented a significant frequency of the ancestral CCG haplotype in contrast to other populations where the fully derived TGA haplotype was more frequent. The presence and diversity of rare haplotypes at STAT3 in North African populations could have been generated by recombination between the two major haplotypes. A screening of the micro-RNA databases showed that the STAT3 region with the mutated allele of rs7211777 (G>A) could be targeted by miR hsa-miR-3606-5p, which also targets genes involved in breast cancer.

Role of the JAK-STAT Pathway in Bovine Mastitis and Milk Production

Simple Summary

The cytokine-activated Janus kinase (JAK)—signal transducer and activator of transcription (STAT) pathway has an important role in the regulation of immunity and inflammation. In addition, the signaling of this pathway has been reported to be associated with mammary gland development and milk production. Because of such important functions, the JAK-STAT pathway has been widely targeted in both human and animal diseases as a therapeutic agent. Recently, the JAK2, STATs, and inhibitors of the JAK-STAT pathway, especially cytokine signaling suppressors (SOCSs), have been reported to be associated with milk production and mastitis-resistance phenotypic traits in dairy cattle. Thus, in the current review, we attempt to overview the development of the JAK-STAT pathway role in bovine mastitis and milk production.

Abstract

The cytokine-activated Janus kinase (JAK)—signal transducer and activator of transcription (STAT) pathway is a sequence of communications between proteins in a cell, and it is associated with various processes such as cell division, apoptosis, mammary gland development, lactation, anti-inflammation, and immunity. The pathway is involved in transferring information from receptors on the cell surface to the cell nucleus, resulting in the regulation of genes through transcription. The Janus kinase 2 (JAK2), signal transducer and activator of transcription A and B (STAT5 A & B), STAT1, and cytokine signaling suppressor 3 (SOCS3) are the key members of the JAK-STAT pathway. Interestingly, prolactin (Prl) also uses the JAK-STAT pathway to regulate milk production traits in dairy cattle. The activation of JAK2 and STATs genes has a critical role in milk production and mastitis resistance. The upregulation of SOCS3 in bovine mammary epithelial cells inhibits the activation of JAK2 and STATs genes, which promotes mastitis development and reduces the lactational performance of dairy cattle. In the current review, we highlight the recent development in the knowledge of JAK-STAT, which will enhance our ability to devise therapeutic strategies for bovine mastitis control. Furthermore, the review also explores the role of the JAK-STAT pathway in the regulation of milk production in dairy cattle.

Potential candidate gene markers for milk fat in bovines: A review

In dairy animals, the principal goal of selection is to improve quality and quantity of milk. Genetic information inferred from single nucleotide polymorphism (SNP) primarily linked to Quantitative Trait Loci (QTL) can be used to improve selection for milk and milk constituent traits in bovines. Selection for a marker allele known to be associated with a beneficial QTL increases the frequency of that allele and hence, dairy performance can be enhanced. One of the potential benefit of selection based on molecular marker is that the marker genotypes can be determined in a dairy animal just after birth. Thus, marker information can be used to predict an animal's genotype before its actual performance recording for a trait is available, which considerably reduces generation interval and thus improves genetic gain in a herd for milk and its constituent traits. This review article is an attempt to comprehend the idea behind marker based selection for milk fat and genes regulating milk fat with significant effects that can be targeted specifically in selection of superior dairy animals. Once an association is established, itcan be utilized in a marker assisted breeding program for improvement of bovines.

Meta-analysis of mammary RNA seq datasets reveals the molecular understanding of bovine lactation biology

A better understanding of the biology of lactation, both in terms of gene expression and the identification of candidate genes for the production of milk and its components, is made possible by recent advances in RNA seq technology. The purpose of this study was to understand the synthesis of milk components and the molecular pathways involved, as well as to identify candidate genes for milk production traits within whole mammary transcriptomic datasets. We performed a meta-analysis of publically available RNA seq transcriptome datasets of mammary tissue/milk somatic cells. In total, 11 562 genes were commonly identified from all RNA seq based mammary gland transcriptomes. Functional annotation of commonly expressed genes revealed the molecular processes that contribute to the synthesis of fats, proteins, and lactose in mammary secretory cells and the molecular pathways responsible for milk synthesis. In addition, we identified several candidate genes responsible for milk production traits and constructed a gene regulatory network for RNA seq data. In conclusion, this study provides a basic understanding of the lactation biology of cows at the gene expression level.

MicroRNA-135a induces prostate cancer cell apoptosis via inhibition of STAT6

Clinical management of metastatic prostate cancer remains a challenge. Activation of apoptosis signaling pathways via signal transducer and activator of transcription 6 (STAT6) has been hypothesized to be a therapeutic strategy for patients with metastatic prostate cancer. The ONCOMINE^® prostate cancer database and two Gene Expression Omnibus datasets (Gene Series 40026 and 21032) were re-analyzed to determine the expression levels of STAT6 and microRNA (miR)-135a in prostate cancer. The current study investigated the induced overexpression of miR-135a in prostate cancer cell lines to detect its function in prostate cell apoptosis using Hoechst staining and fluorescence-activated cell sorting and examined the expression levels of STAT6 and its DNA binding ability using western blotting and an electrophoretic mobility shift assay. In analysis of the ONCOMINE^® database, STAT6 expression levels in prostate cancer tissue were higher compared with those in normal prostate gland tissue and were associated with the overall survival rate and biochemical relapse rate following radical prostatectomy. Additionally, there was an inverse correlation between miR-135a and STAT6 expression levels in prostate cancer cell lines. miR-135a was able to induce prostate cancer cell apoptosis via targeting STAT6 mRNA and subsequently repressing protein expression and phosphorylation, which also altered the transcriptional factor function of STAT6 through its DNA-binding capabilities. In conclusion, miR-135a may function as a tumor-suppressing miRNA in prostate cancer and its anti-oncogenic activity may involve the direct targeting and inhibition of STAT6.

MiR-141-3p suppresses gastric cancer induced transition of normal fibroblast and BMSC to cancer-associated fibroblasts via targeting STAT4

BACKGROUND

Cancer associated fibroblasts (CAFs) are known to be crucial constituents of cancer microenvironment (CME) and play an important role in initiation, progression and metastasis of various types of cancer, such as oral cancer, pancreatic cancer, and gastric cancer. CAFs are usually derived from normal fibroblasts (NFs), but the mechanism of the transition in gastric cancer has not yet been fully elucidated.

METHODS

qRT-PCR and western blot were employed to investigate differences of miR-141 and STAT4 expression respectively. The CAF-like features and wnt/β-catenin pathway related proteins in NF or BMSC were assessed by qRT-PCR or western blot after treated with the conditioned medium from different indicated groups of gastric cancer cells. The invasion and migration ability of AGS cells after transfection were analyzed by Transwell assay and wound healing assay. Dual-luciferase report assay was employed to determine the direct binding of miR-141 to STAT4 3' UTR.

RESULTS

For the first time, the present study found that STAT4 over-expression in gastric cancer cells induced NFs to obtain CAF-like features via activating wnt/β-catenin pathway. Further gain-of-function and loss-of-function analysis revealed that miR-141 not only limited the migration and invasion of the gastric cancer cells, but also inhibited the transition of NFs and BMSC to CAFs. The luciferase assay indicated that miR-141 directly targeted the 3'-UTR predictive sequence of STAT4.

CONCLUSION

Our data showed that miR-141 inhibited migration and invasion of gastric cancer cells and inhibited transition from NFs to CAFs via targeting STAT4/wnt/β-catenin pathway.

Rare Variants in the ABCG2 Promoter Modulate In Vivo Activity

ABCG2 encodes the breast cancer resistance protein (BCRP), an efflux membrane transporter important in the detoxification of xenobiotics. In the present study, the basal activity of the ABCG2 promoter in liver, kidney, intestine, and breast cell lines was examined using luciferase reporter assays. The promoter activities of reference and variant ABCG2 sequences were compared in human hepatocellular carcinoma cell (HepG2), human embryonic kidney cell (HEK293T), human colorectal carcinoma cell (HCT116), and human breast adenocarcinoma cell (MCF-7) lines. The ABCG2 promoter activity was strongest in the kidney and intestine cell lines. Four variants in the basal ABCG2 promoter (rs76656413, rs66664036, rs139256004, and rs59370292) decreased the promoter activity by 25%-50% in at least three of the four cell lines. The activity of these four variants was also examined in vivo using the hydrodynamic tail vein assay, and two single nucleotide polymorphisms (rs76656413 and rs59370292) significantly decreased in vivo liver promoter activity by 50%-80%. Electrophoretic mobility shift assays confirmed a reduction in nuclear protein binding to the rs59370292 variant probe, whereas the rs76656413 probe had a shift in transcription factor binding specificity. Although both rs59370292 and rs76656413 are rare variants in all populations, they could contribute to patient-level variation in ABCG2 expression in the kidney, liver, and intestine.

STAT3 Knockdown Induces Tumor Formation by MDA-MB-231 Cells

STAT3 plays a central role in oncogenesis by mediating cell survival, growth, and differentiation. It is constitutively activated in breast cancer. We investigated the role of STAT3 in tumor development by knocking down STAT3 levels in MDA-MB-231 triple negative breast cancer cells using short hairpin RNA. The tumor forming potential of these STAT3-depleted cells was assessed by xenografts in immunocompromised NOD SCID mice. Contrary to its accepted tumor promoting role, we found STAT3 to be a negative regulator of growth in MDA-MB-231- derived tumors. Although similar observations have been made in thyroid carcinoma and lung adenocarcinoma xenograft studies, our novel results showed for the first time that the role of STAT3 in promoting tumorigenesis may be context-specific, and that STAT3 may actually be a negative regulator of certain breast-cancer types. Studies to identify the mechanisms of STAT3's negative regulatory role may be useful in developing STAT3-based therapeutics.

The nuclear receptor ERβ engages AGO2 in regulation of gene transcription, RNA splicing and RISC loading

BACKGROUND

The RNA-binding protein Argonaute 2 (AGO2) is a key effector of RNA-silencing pathways It exerts a pivotal role in microRNA maturation and activity and can modulate chromatin remodeling, transcriptional gene regulation and RNA splicing. Estrogen receptor beta (ERβ) is endowed with oncosuppressive activities, antagonizing hormone-induced carcinogenesis and inhibiting growth and oncogenic functions in luminal-like breast cancers (BCs), where its expression correlates with a better prognosis of the disease.

RESULTS

Applying interaction proteomics coupled to mass spectrometry to characterize nuclear factors cooperating with ERβ in gene regulation, we identify AGO2 as a novel partner of ERβ in human BC cells. ERβ-AGO2 association was confirmed in vitro and in vivo in both the nucleus and cytoplasm and is shown to be RNA-mediated. ChIP-Seq demonstrates AGO2 association with a large number of ERβ binding sites, and total and nascent RNA-Seq in ERβ + vs ERβ - cells, and before and after AGO2 knock-down in ERβ + cells, reveals a widespread involvement of this factor in ERβ-mediated regulation of gene transcription rate and RNA splicing. Moreover, isolation and sequencing by RIP-Seq of ERβ-associated long and small RNAs in the cytoplasm suggests involvement of the nuclear receptor in RISC loading, indicating that it may also be able to directly control mRNA translation efficiency and stability.

CONCLUSIONS

These results demonstrate that AGO2 can act as a pleiotropic functional partner of ERβ, indicating that both factors are endowed with multiple roles in the control of key cellular functions.

The Role of CSF-1 in Normal Physiology of Mammary Gland and Breast Cancer: An Update

Colony stimulating factor (CSF-1) and its receptor (CSF-1R, product of c-fms proto-oncogene) were initially implicated as essential for normal monocyte development as well as for trophoblastic implantation. However, studies have demonstrated that CSF-1 and CSF-1R have additional roles in mammary gland development during pregnancy and lactation. This apparent role for CSF-1/CSF-1R in normal mammary gland development is very intriguing because this receptor/ligand pair has also been found to be important in the biology of breast cancer in which abnormal expression of CSF-1 and its receptor correlates with tumor cell invasiveness and adverse clinical prognosis. Recent findings also implicate tumor-produced CSF-1 in promotion of bone metastasis in breast cancer, and a certain membrane-associated form of CSF-1 appears to induce immunity against tumors. This review aims to summarize recent findings on the role of CSF-1 and its receptor in normal and neoplastic mammary development that may elucidate potential relationships of growth factor–induced biological changes in the breast during pregnancy and tumor progression.

Global Gene Expression Profiling of Chemically Induced Rat Mammary Gland Carcinomas and Adenomas

Chemical carcinogens induce both benign and malignant mammary gland tumors in female Sprague-Dawley rats. To identify gene expression profiles associated with malignancy, cDNA microarray analysis was used to compare gene expression profiles in rat mammary gland carcinomas, adenomas, and normal mammary gland. Tumors were induced with various chemical carcinogens including 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5- f]quinoxaline (MeIQx), 7-12-dimethylbenz[ a]anthracene (DMBA), N-nitrosomethylurea (NMU), and 4-aminobiphenyl. The global gene expression profiles in carcinomas and adenomas were distinguishable by hierarchical clustering and multi-dimensional scaling analyses. Permutation analysis revealed 110 clones statistically differentially expressed between benign and malignant tumors ( p < 0.0005). Carcinomas showed relatively high expression of several genes associated with mammary epithelial cell growth and proliferation (e.g., cyclin D1, PDGFα) and relatively low expression of differentiation marker genes (e.g., β-casein, whey acidic protein, transferrin). Other categories of genes showing differential expression between carcinomas and adenomas were associated with protein homeostasis, cytoskeleton, extracellular matrix, and cell metabolism (fatty acid metabolism, oxidative phosphorylation, and glycolysis). Major gene families implicated in malignancy by over-expression in carcinomas included the annexins (annexin A1 and A4) and Stat family of transcription factors (Stat3 and Stat5a). The elevated expression of the prolactin receptor in carcinomas concomitant with several components of the mitogenic prolactin signaling pathway implicated prolactin/prolactin receptor/Stat5a/cyclin D1 in rat mammary gland malignancy.

An invertebrate signal transducer and activator of transcription 5 (STAT5) ortholog from the disk abalone, Haliotis discus discus: Genomic structure, early developmental expression, and immune responses to bacterial and viral stresses

Signal transducer and activator of transcription (STAT) family members are key signaling molecules that transduce cellular responses from the cell membrane to the nucleus upon Janus kinase (JAK) activation. Although seven STAT members have been reported in mammals, very limited information on STAT genes in molluscans is available. In this study, we identified and characterized a STAT paralog that is homologous to STAT5 from the disk abalone, Haliotis discus discus, and designated as AbSTAT5. Comparison of the deduced amino acid sequence for AbSTAT5 (790 amino acids) with other counterparts revealed conserved residues important for functions and typical domain regions, including the N-terminal domain, coiled-coil domain, DNA-binding domain, linker domain, and Src homology 2 (SH2) domains as mammalian counterparts. Analysis of STAT phylogeny revealed that AbSTAT5 was clustered with the molluscan subgroup in STAT5 clade with distinct evolution. According to the genomic structure of AbSTAT5, the coding sequence was distributed into 20 exons with 19 introns. Immunologically essential transcription factor-binding sites, such as GATA-1, HNF, SP1, C/EBP, Oct-1, AP1, c-Jun, and Sox-2, were predicted at the 5'-proximal region of AbSTAT5. Expression of AbSTAT5 mRNA was detected in different stages of embryonic development and observed at considerably higher levels in the morula and late veliger stages. Tissue-specific expressional studies revealed that the highest level of AbSTAT5 transcripts was detected in hemocytes, followed by gill tissues. Temporal expressions of AbSTAT5 were analyzed upon live bacterial (Vibrio parahemolyticus and Listeria monocytogenes), viral (viral hemorrhagic septicemia virus), and pathogen-associated molecular pattern (lipopolysaccharides and Poly I:C) stimulations, and significant elevations indicated immune modulation. These results suggest that AbSTAT5 may be involved in maintaining innate immune responses from developmental to adult stages in the disk abalone. Further, this study provides a basis for structural and functional exploration of STAT members in the invertebrate JAK/STAT signaling pathway.

Genetic effects of single nucleotide polymorphisms in JAK2 and STAT5A genes on susceptibility of Chinese Holsteins to mastitis

The JAK-STAT pathway plays a key role in host immunity. The present study was designed to evaluate the effects of single nucleotide polymorphisms (SNPs) in STAT5A and JAK2 genes on some serum cytokines, mastitis and milk production traits. Two SNPs (SNP1 43046497A/C and SNP2 43047829G/A) in STAT5A, and four SNPs in JAK2 (SNP3 39652267A/G, SNP4 39630048C/T, SNP5 39631044G/A, and SNP6 39631175T/C) were revealed and genotyped in 268 Chinese Holstein cattle. Fixed model was used to analyze the association of SNPs with phenotypes by general linear model procedure of SAS 9.1. SNP1 and SNP4 were significantly associated with IL-6 and IL-17 (P < 0.05), respectively. In JAK2 gene, SNP3 was highly significant (P < 0.01) and SNP5 was significant (P < 0.05) in association with SCC, whereas, the association of SNP6 was found significant (P < 0.05) with both SCC and SCS. Combination genotype analysis revealed that SNPs in JAK2 gene significantly associated with SCC and SCS were associated significantly with the corresponding phenotypes in combinations as well. The GG genotype of SNP3 individually and in any combination genotypes showed lowest SCC. The dominant effect of SNP1, SNP5 and SNP6 was found highly significant (P < 0.01) on the corresponding phenotypes (IL-6, SCC and SCS). As for haplotype analysis, two haplotypes were revealed between the two SNPs of STAT5A gene and four haplotypes amongst four SNPs in JAK2 gene; strong linkage disequilibrium (D' > 0.9) was observed between all these haplotypes. The results imply that the identified SNPs could be powerful markers to select dairy cattle with improved genetic resistance against mastitis.

The tumor suppressor function of STAT1 in breast cancer

The anti-tumor function of STAT1 through its capacity to control the immune system and promote tumor immune surveillance has been well understood. However, little is known about cell autonomous (i.e., tumor cell-specific) functions of STAT1 in tumor formation. Recent studies have provided strong evidence that STAT1 suppresses mouse mammary gland tumorigenesis by both, immune regulatory and tumor cell-specific functions of STAT1. Specifically, STAT1 deficiency in the mouse mammary gland inhibits ErbB2/Neu-mediated tumorigenesis and contributes to spontaneous formation of estrogen receptor α (ER α)-positive as well as ER α-negative tumors closely resembling human disease. Herein, we review the anti-tumor functions of STAT1 revealed from investigations of murine breast cancer models and from characterization of the signaling properties of STAT1 in human breast tumor cells. The significance of STAT1 in breast cancer is underscored by studies proposing a prognostic value for the expression and/or phosphorylation of STAT1 for specific molecular types of breast cancer. Furthermore, STAT1 dependent transcription is proposed to contribute to therapeutic responses by modulating the efficacy of chemotherapeutic drugs and the development of drug resistance.

STAT signaling in mammary gland differentiation, cell survival and tumorigenesis

The mammary gland is a unique organ that undergoes extensive and profound changes during puberty, menstruation, pregnancy, lactation and involution. The changes that take place during puberty involve large-scale proliferation and invasion of the fat-pad. During pregnancy and lactation, the mammary cells are exposed to signaling pathways that inhibit apoptosis, induce proliferation and invoke terminal differentiation. Finally, during involution the mammary gland is exposed to milk stasis, programmed cell death and stromal reorganization to clear the differentiated milk-producing cells. Not surprisingly, the signaling pathways responsible for bringing about these changes in breast cells are often subverted during the process of tumorigenesis. The STAT family of proteins is involved in every stage of mammary gland development, and is also frequently implicated in breast tumorigenesis. While the roles of STAT3 and STAT5 during mammary gland development and tumorigenesis are well studied, others members, e.g. STAT1 and STAT6, have only recently been observed to play a role in mammary gland biology. Continued investigation into the STAT protein network in the mammary gland will likely yield new biomarkers and risk factors for breast cancer, and may also lead to novel prophylactic or therapeutic strategies against breast cancer.

A 3-D in vitro co-culture model of mammary gland involution

An in vitro model of mammary gland supporting 3D cell–cell and cell–matrix interactions demonstrates complete in vivo-like neo-tissue formation and remodelling processes (involution) under hormonal control.

Mechanism and preclinical prevention of increased breast cancer risk caused by pregnancy

While a first pregnancy before age 22 lowers breast cancer risk, a pregnancy after age 35 significantly increases life-long breast cancer risk. Pregnancy causes several changes to the normal breast that raise barriers to transformation, but how pregnancy can also increase cancer risk remains unclear. We show in mice that pregnancy has different effects on the few early lesions that have already developed in the otherwise normal breast—it causes apoptosis evasion and accelerated progression to cancer. The apoptosis evasion is due to the normally tightly controlled STAT5 signaling going astray—these precancerous cells activate STAT5 in response to pregnancy/lactation hormones and maintain STAT5 activation even during involution, thus preventing the apoptosis normally initiated by oncoprotein and involution. Short-term anti-STAT5 treatment of lactation-completed mice bearing early lesions eliminates the increased risk after a pregnancy. This chemoprevention strategy has important implications for preventing increased human breast cancer risk caused by pregnancy.

DOI:http://dx.doi.org/10.7554/eLife.00996.001

Pregnancy changes the probability that a woman will later develop breast cancer. If a woman’s first pregnancy occurs before her 22^nd birthday, the chances of developing breast cancer are reduced. However, if the first pregnancy occurs after her 35^th birthday, there is an increased risk of breast cancer. It is not clear why this age-related difference exists, but as more women wait until their 30s to start a family, there is greater urgency to understand this difference.

Breasts undergo extensive changes during pregnancy. This remodeling makes their cells less likely to multiply, and also less likely to develop tumors, which could explain the protective effect of pregnancy for younger women. But why would older women not reap the same benefits? One hypothesis is that older first-time mothers are more likely than younger first-time mothers to already have breast tissue with cells carrying cancer-causing mutations, or to have clusters of abnormal precancerous cells.

Now, Haricharan et al. have tested this hypothesis by inserting two cancer-causing genes into female mice. Half of the mice were then made pregnant and allowed to nurse their young, whilst the other half were never mated. Although, both groups of mice later developed tumors, the mice that had been pregnant developed more tumors and did so faster.

The increased cancer levels in the mice that had been pregnant were not due to them having more precancerous cells at the early stages of pregnancy than the unmated mice of the same age. Further, the precancerous cells in the impregnated mice did not proliferate faster than those in the mice that were never pregnant. Instead, pregnancy weakened the protective process that culls pre-existing precancerous cells. These cells evaded destruction by activating a signaling pathway called the STAT5 pathway in response to pregnancy hormones.

Haricharan et al. also examined tissue samples from women with a very early form of breast cancer and found elevated levels of STAT5 in tumors from women who had been pregnant compared to those who had not been pregnant.

The good news is that precancerous cells do not always become cancerous. However, for those women with a high risk of developing breast cancer, Haricharan et al. suggest that temporarily reducing STAT5 activity after pregnancy with medication might reduce this risk. Treating mice with anti-STAT5 drugs for a few weeks after they finished nursing their young lessened the elevated cancer risk, and so the next challenge is to see if this approach will also be effective in human clinical trials.

DOI:http://dx.doi.org/10.7554/eLife.00996.002

Cucurbitacin I inhibits Rac1 activation in breast cancer cells by a reactive oxygen species-mediated mechanism and independently of Janus tyrosine kinase 2 and P-Rex1

The small GTPase Rac1 has been widely implicated in mammary tumorigenesis and metastasis. Previous studies established that stimulation of ErbB receptors in breast cancer cells activates Rac1 and enhances motility via the Rac-guanine nucleotide exchange factor P-Rex1. As the Janus tyrosine kinase 2 (Jak2)/signal transducer and activator of transcription 3 (Stat3) pathway has been shown to be functionally associated with ErbB receptors, we asked if this pathway could mediate P-Rex1/Rac1 activation in response to ErbB ligands. Here we found that the anticancer agent cucurbitacin I, a Jak2 inhibitor, reduced the activation of Rac1 and motility in response to the ErbB3 ligand heregulin in breast cancer cells. However, Rac1 activation was not affected by Jak2 or Stat3 RNA interference, suggesting that the effect of cucurbitacin I occurs through a Jak2-independent mechanism. Cucurbitacin I also failed to affect the activation of P-Rex1 by heregulin. Subsequent analysis revealed that cucurbitacin I strongly activates RhoA and the Rho effector Rho kinase (ROCK) in breast cancer cells and induces the formation of stress fibers. Interestingly, disruption of the RhoA-ROCK pathway prevented the inhibitory effect of cucurbitacin I on Rac1 activation by heregulin. Lastly, we found that RhoA activation by cucurbitacin I is mediated by reactive oxygen species (ROS). The ROS scavenger N-acetyl L-cysteine and the mitochondrial antioxidant Mito-TEMPO rescued the inhibitory effect of cucurbitacin I on Rac1 activation. In conclusion, these results indicate that ErbB-driven Rac1 activation in breast cancer cells proceeds independently of the Jak2 pathway. Moreover, they established that the inhibitory effect of cucurbitacin I on Rac1 activity involves the alteration of the balance between Rho and Rac.

Effects of 5-fluorouracil and gemcitabine on a breast cancer cell line (MCF-7) via the JAK/STAT pathway

Aberrant activation of the JAK/STAT pathway may predispose to malignancy as a consequence of the deregulation of cell proliferation, differentiation or apoptosis such as in cancer of the blood, head and neck, and breast. In our study we aimed to investigate the effects of 5-fluorouracil (5-FU) and gemcitabine on a breast cancer cell line (MCF-7 cells) via the JAK/STAT pathway. Distribution of JAK1, JAK2, JAK3 and STAT2, STAT3, STAT4, STAT5 were evaluated on MCF-7 cells following gemcitabine and 5-FU treatment and in the absence of drug treatment by an indirect immunohistochemical method. It was observed that JAK1, JAK3, STAT5 and particularly STAT2 activation were more effective than the other JAK/STATs in breast cancer progression. Following treatment with 5-FU, JAK1 and STAT5 immunoreactivities were decreased in MCF-7 cells in comparison with both gemcitabine-treated and non-treated groups. These results suggest that the JAK/STAT pathway plays an important role in breast cancer pathogenesis and may be more affected after 5-FU treatment rather than gemcitabine. Drugs which block STAT5 may provide a novel therapeutic approach for the treatment of breast cancer.

MUC16 induced rapid G2/M transition via interactions with JAK2 for increased proliferation and anti-apoptosis in breast cancer cells

MUC16/CA125 is a tumor marker currently used in clinics for the follow-up of patients with ovarian cancer. However, MUC16 expression is not entirely restricted to ovarian malignancies and has been reported in other cancers including breast cancer. Although it is well established as a biomarker, function of MUC16 in cancer remains to be elucidated. In the present study, we investigated the role of MUC16 in breast cancer and its underlying mechanisms. Interestingly, our results showed that MUC16 is overexpressed in breast cancer tissues whereas not expressed in non-neoplastic ducts. Further, stable knockdown of MUC16 in breast cancer cells (MDA MB 231 and HBL100) resulted in significant decrease in the rate of cell growth, tumorigenicity and increased apoptosis. In search of a mechanism for breast cancer cell proliferation we found that MUC16 interacts with the ezrin/radixin/moesin domain-containing protein of Janus kinase (JAK2) as demonstrated by the reciprocal immunoprecipitation method. These interactions mediate phosphorylation of STAT3 (Tyr705), which might be a potential mechanism for MUC16-induced proliferation of breast cancer cells by a subsequent co-transactivation of transcription factor c-Jun. Furthermore, silencing of MUC16 induced G2/M arrest in breast cancer cells through downregulation of Cyclin B1 and decreased phosphorylation of Aurora kinase A. This in turn led to enhanced apoptosis in the MUC16-knockdown breast cancer cells through Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated extrinsic apoptotic pathway with the help of c-Jun N-terminal kinase signaling. Collectively, our results suggest that MUC16 has a dual role in breast cancer cell proliferation by interacting with JAK2 and by inhibiting the apoptotic process through downregulation of TRAIL.

Loss of protein kinase C delta alters mammary gland development and apoptosis

As apoptotic pathways are commonly deregulated in breast cancer, exploring how mammary gland cell death is regulated is critical for understanding human disease. We show that primary mammary epithelial cells from protein kinase C delta (PKCδ) −/− mice have a suppressed response to apoptotic agents in vitro. In the mammary gland in vivo, apoptosis is critical for ductal morphogenesis during puberty and involution following lactation. We have explored mammary gland development in the PKCδ −/− mouse during these two critical windows. Branching morphogenesis was altered in 4- to 6-week-old PKCδ −/− mice as indicated by reduced ductal branching; however, apoptosis and proliferation in the terminal end buds was unaltered. Conversely, activation of caspase-3 during involution was delayed in PKCδ −/− mice, but involution proceeded normally. The thymus also undergoes apoptosis in response to physiological signals. A dramatic suppression of caspase-3 activation was observed in the thymus of PKCδ −/− mice treated with irradiation, but not mice treated with dexamethasone, suggesting that there are both target- and tissue-dependent differences in the execution of apoptotic pathways in vivo. These findings highlight a role for PKCδ in both apoptotic and nonapoptotic processes in the mammary gland and underscore the redundancy of apoptotic pathways in vivo.

Activation of Toll-like receptor 5 on breast cancer cells by flagellin suppresses cell proliferation and tumor growth

Increasing evidence showed that Toll-like receptors (TLR), key receptors in innate immunity, play a role in cancer progression and development but activation of different TLRs might exhibit the exact opposite outcome, antitumor or protumor effects. TLR function has been extensively studied in innate immune cells, so we investigated the role of TLR signaling in breast cancer epithelial cells. We found that TLR5 was highly expressed in breast carcinomas and that TLR5 signaling pathway is overly responsive in breast cancer cells. Interestingly, flagellin/TLR5 signaling in breast cancer cells inhibits cell proliferation and an anchorage-independent growth, a hallmark of tumorigenic transformation. In addition, the secretion of soluble factors induced by flagellin contributed to the growth-inhibitory activity in an autocrine fashion. The inhibitory activity was further confirmed in mouse xenografts of human breast cancer cells. These findings indicate that TLR5 activation by flagellin mediates innate immune response to elicit potent antitumor activity in breast cancer cells themselves, which may serve as a novel therapeutic target for human breast cancer therapy.

Singleminded-2s (Sim2s) promotes delayed involution of the mouse mammary gland through suppression of Stat3 and NFκB

Postlactational involution of the mammary gland provides a unique model to study breast cancer susceptibility and metastasis. We have shown that the short isoform of Singleminded-2s (Sim2s), a basic helix loop helix/PAS transcription factor, plays a role in promoting lactogenic differentiation, as well as maintaining mammary epithelial differentiation and malignancy. Sim2s is dynamically expressed during mammary gland development, with expression peaking during lactation, and decreasing in early involution. To determine the role of SIM2S in involution, we used transgenic mice expressing SIM2S under the mouse mammary tumor virus-Sim2s promoter. Overexpression of Sim2s in the mouse mammary gland resulted in delayed involution, indicated by a lower proportion of cleaved caspase-3-positive cells and slower reestablishment of the mammary fat pad. Immunohistochemical and quantitative RNA analysis showed a decrease in apoptotic markers and inflammatory response genes, and an increase in antiapoptotic genes, which were accompanied by inhibition of signal transducer and activator of transcription 3 activity. Microarray analysis confirmed that genes in the signal transducer and activator of transcription 3 signaling pathway were repressed by SIM2S expression, along with nuclear factor-κB and other key pathways involved in mammary gland development. Multiparous mouse mammary tumor virus-Sim2s females displayed a more differentiated phenotype compared with wild-type controls, characterized by enhanced β-casein expression and alveolar structures. Together, these results suggest a role for SIM2S in the normal involuting gland and identify potential downstream pathways regulated by SIM2S.

STAT1 activation regulates proliferation and differentiation of renal progenitors

We have shown previously that activation of STAT1 contributes to the pathogenesis of Wilms tumor. This neoplasm caricatures metanephric development and is believed to originate from embryonic renal mesenchymal progenitors that lose their ability to undergo mesenchymal-epithelial transition (MET). Therefore, we hypothesized that STAT1 is also activated and functional during metanephric development. Here we have demonstrated that both STAT1 and STAT3 are activated during normal development of the embryonic kidney. Furthermore, activation of STAT1 stimulated the proliferation of metanephric mesenchymal cells, but it prevented MET and tubulogenesis induced by leukemia inhibitory factor, which preferentially activates STAT3. Consistent with its negative regulation of metanephric mesenchymal differentiation, inhibition of STAT1 activation with protein kinase CK2 inhibitor TBB or RNAi-mediated knockdown of STAT1 promoted differentiation of metanephric progenitors and abolished the effect of cytokine-induced STAT1 activation in these cells. Additionally, a cell-permeable peptide that inhibits STAT1-mediated transactivation by targeting the STAT1 N-domain also blocked cytokine-induced STAT1-dependent proliferation in metanephric progenitors and promoted LIF-induced MET and tubulogenesis. Finally, the STAT1 peptide inhibitor caused the down regulation of survival/anti-apoptotic factors, Mcl-1 and Hsp-27, and induced apoptosis in renal tumor cells with constitutively active STAT1, indicating that STAT1 is required for these cells to survive. These findings show that both metanephric progenitors and renal tumor cells utilize a STAT1-dependent mechanism for growth or survival.

Repression of Lim only protein 4-activated transcription inhibits proliferation and induces apoptosis of normal mammary epithelial cells and breast cancer cells

Lim only protein (LMO) 4 acts as a transcriptional adapter and modulates mammary gland morphogenesis as well as breast oncogenesis in transgenic mice. Yet, the molecular and cellular mechanisms of these effects remain to be fully elucidated. Engrailed LMO4 fusion protein is a powerful dominant repressor of LMO4 activated transcription that was successfully used to discover the role of LMO4 as a transcriptional activator in mammary gland development in our previous studies using mouse models. In this manuscript, we investigated the cellular effects of LMO4 in human normal mammary epithelial cells (HMECs) and breast cancer cell lines using the Engrailed-LMO4 fusion protein. HMEC cell growth was inhibited by the expression of the Engrailed-LMO4 fusion protein. The decrease in cell number was due to both decreased cell proliferation and enhanced apoptosis, suggesting that LMO4 promotes proliferation and survival of normal mammary epithelial cells. The expression of the Engrailed-LMO4 fusion protein also suppressed cell growth, and induced apoptosis in two breast cancer cell lines, MDA-MB-231 and T47D, suggesting that LMO4 contributes to oncogenesis by similar mechanisms of enhanced cell survival and proliferation. Taken together, our data indicate that LMO4 has similar cellular effects in normal mammary epithelial cells and breast cancer cells, and also provide direct evidence for the idea that normal development and carcinogenesis share conserved molecular mechanisms.

Tumor Necrosis Factor alpha (TNFalpha) regulates CD40 expression through SMAR1 phosphorylation

CD40 plays an important role in mediating inflammatory response and is mainly induced by JAK/STAT phosphorylation cascade. TNFalpha is the key cytokine that activates CD40 during inflammation and tumorigenesis. We have earlier shown that SMAR1 can repress the transcription of Cyclin D1 promoter by forming a HDAC1 dependent repressor complex. In this study, we show that SMAR1 regulates the transcription of NF-kappaB target gene CD40. SMAR1 recruits HDAC1 and forms a repressor complex on CD40 promoter and keeps its basal transcription in check. Further, we show that TNFalpha stimulation induces SMAR1 phosphorylation at Ser-347 and promotes its cytoplasmic translocation, thus releasing its negative effect. Concomitantly, TNFalpha induced phosphorylation of STAT1 at Tyr-701 by JAK1 facilitates its nuclear translocation and activation of CD40 through p300 recruitment and core Histone-3 acetylation. Thus, TNFalpha mediated regulation of CD40 expression occurs by dual phosphorylation of SMAR1 and STAT1.

Impaired lactation in mice expressing dominant-negative FADD in mammary epithelium

The Fas-associated death domain (FADD/Mort1) adaptor protein was originally identified as a key mediator of apoptosis, although pleiotropic functions for FADD have also been reported. FADD-mediated tumoricidal effects have been described in breast cancer cells; however, its physiological role in normal mammary gland epithelium is not well understood. To determine the role of FADD signaling during mammary gland development, we generated transgenic mice overexpressing dominant-negative FADD (DN-FADD) in mammary epithelium, using the steroid responsive mouse mammary tumor virus promoter. Transgenic mice exhibited a perturbation in lactation resulting in impaired milk production and pup growth retardation. Reduced expansion of alveoli was evident during early lactation with extensive shedding of luminal alveolar cells. Significantly more TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling)-positive cells were present at this time point and a subsequent increase in bromodeoxyuridine-positive cells was observed. These findings suggest a role for FADD in maintaining the survival of mammary secretory alveolar cells after the establishment of lactation.

The IKK-related kinases: from innate immunity to oncogenesis

Over the past four years, the field of the innate immune response has been highly influenced by the discovery of the IkappaB kinase (IKK)-related kinases, TANK Binding Kinase 1 (TBK1) and IKKi, which regulate the activity of interferon regulatory factor (IRF)-3/IRF-7 and NF-kappaB transcription factors. More recently, additional essential components of the signaling pathways that activate these IKK homologues have been discovered. These include the RNA helicases RIGi and MDA5, and the downstream mitochondrial effector known as CARDIF/MAVS/VISA/IPS-1. In addition to their essential functions in controlling the innate immune response, recent studies have highlighted a role of these kinases in cell proliferation and oncogenesis. The canonical IKKs are well recognized to be a bridge linking chronic inflammation to cancer. New findings now suggest that the IKK-related kinases TBK1 and IKKi also participate in signaling pathways that impact on cell transformation and tumor progression. This review will therefore summarize and discuss the role of TBK1 and IKKi in cellular transformation and oncogenesis by focusing on their regulation and substrate specificity.

A microRNA, miR-101a, controls mammary gland development by regulating cyclooxygenase-2 expression

Mammary glands exhibit a series of developmental states that are typified by proliferation, differentiation, and involution. Here, we demonstrate that a microRNA (miRNA), miR-101a, plays an important role in the process of mammary gland development. We used miRNA microarray analysis to show that some miRNAs exhibit changes in their expression during mouse mammary gland epithelial cell (HC11) differentiation, which corresponds to the time when these cells acquire the milk-producing phenotype. In particular, we observed an increase of miR-101a expression throughout differentiation and involution in mammary gland tissue, as well as in HC11 cells. Overexpression experiments revealed that miR-101a suppressed the expression of beta-casein mRNA, a milk protein, and marker of cell differentiation, but its suppression was not mediated by transcriptional or direct post-transcriptional regulation of beta-casein mRNA. Overexpression of miR-101a also inhibited HC11 cell proliferation that could influence the differentiation state of the mammary gland. We speculate that a direct target of miR-101a is cyclooxygenase-2 (Cox-2) mRNA because there was an inverse relationship between these two genes during mammary gland development. Indeed, Cox-2 protein expression was suppressed by the overexpression of miR-101a, and the luciferase activity of reporter constructs containing the Cox-2 3'UTR was also suppressed by miR-101a overexpression. As Cox-2 has been shown to mediate cell proliferation, it is possible that the inhibition of HC11 cell proliferation by miR-101a might be mediated by Cox-2. Taken together, these results suggest that miR-101a regulates cell proliferation via altering Cox-2 expression, which is critical for controlling mammary gland development.

Mutations in the STAT5A gene are associated with embryonic survival and milk composition in cattle

The objective of this study was to investigate the association of the signal transducer and activator of transcription 5A (STAT5A) gene with fertilization rate, embryonic survival, and milk production and composition in cattle. The STAT proteins are transcription factors that are specifically activated to regulate gene transcription when cells encounter cytokines and growth factors. The STAT5A gene is a member of the interferon-tau (IFN-tau) and placental lactogen (PL) signaling pathway, which is involved in both milk production and initiation of pregnancy. Using the DNA-pooling sequencing approach, a total of 12 single nucleotide polymorphisms (SNP) were identified, 1 exonic and 11 intronic. For the study of association of these SNP with embryonic survival, 1,551 embryos were produced in vitro from 160 cows and 3 sires. Significant associations with embryonic survival were found for 7, 5, and 2 SNP for embryos produced from sires 1, 2, and 3 respectively. The association of fertilization rate with STAT5A polymorphisms was evaluated in more than 2,300 oocytes. Significant associations were found for 6, 2, and 2 SNP for sires 1, 2, and 3 respectively. For sire 1, 5 SNP showed significant associations with both embryonic survival and fertilization rate compared with 1 SNP for sires 2 and 3. To determine if embryonic losses had occurred before the blastocyst stage, 145 of the surviving embryos were harvested at d 7 of development and genotyped for the single exonic SNP12195. A significant segregation distortion was observed between oocytes produced from 2 sires carrying the same genotype. Thus, it is most likely that STAT5A is associated with 2 mechanisms of embryo death. One is a prefertilization mechanism involving sperm factors that cause low fertilization rate. The second is a postfertilization mechanism that causes incompatibility between the male pronucleus and the oocyte, which in turn leads to death of the embryo before the blastocyst stage. Association testing of SNP12195 (exon 8) and SNP14217 (intron 9) with milk composition revealed that allele G of SNP12195 was associated with a decrease in both protein and fat percentages. However, SNP14217 in intron 9 showed no significant association with milk production or health traits. The G allele of SNP12195 was also associated with low embryonic survival, making this SNP an attractive candidate for progeny testing programs in dairy cattle.

Iron homeostasis and erythropoiesis

Erythrocytes require iron to perform their duty as oxygen carriers. Mammals have evolved a mechanism to maintain systemic iron within an optimal range that fosters erythroid development and function while satisfying other body iron needs. This chapter reviews erythroid iron uptake and utilization as well as systemic factors that influence iron availability. One of these factors is hepcidin, a circulating peptide hormone that maintains iron homeostasis. Elevated levels of hepcidin in the bloodstream effectively shut off iron absorption by disabling the iron exporter ferroportin. Conversely, low levels of circulating hepcidin allow ferroportin to export iron into the bloodstream. Aberrations in hepcidin expression or responsiveness to hepcidin result in disorders of iron deficiency and iron overload. It is clear that erythroid precursors communicate their iron needs to the liver to influence the production of hepcidin and thus the amount of iron available for use. However, the mechanism by which erythroid cells accomplish this remains unclear and is an area of active investigation.

Characterization of the SOCS3 promoter response to prostaglandin E2 in T47D cells

Suppressor of cytokine signaling 3 (SOCS3), a negative regulator of cytokine signaling, is expressed in breast cancer cells where it can modify sensitivity and responsiveness to cytokine signaling through the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways. Although it is widely accepted that SOCS3 expression is in itself regulated by STATs, we and others have shown that prostaglandins can also up-regulate SOCS3 expression. Here we used T47D breast cancer cells treated with prostaglandin E2 (PGE2) to examine this pathway. T47D cells responded to PGE2 stimulation with a significant increase in SOCS3 mRNA that was independent of de novo protein synthesis. PGE2 stimulation resulted in STAT3 serine and tyrosine phosphorylation, although mutation of either of the two previously characterized STAT response elements on the SOCS3 promoter did not affect SOCS3 promoter activation by PGE2. In addition, overexpression of STAT3 wild-type, constitutively active or dominant-negative constructs did not affect PGE2-induced SOCS3 promoter activation, indicating that STATs are unlikely mediators of this pathway in these cells. PGE2 is a known activator of the cAMP/protein kinase A (PKA) pathway, and in T47D cells, up-regulation of SOCS3 mRNA by PGE2 was abolished by pretreatment with H89, a PKA inhibitor and increased by cAMP and forskolin treatment. Consistent with this, PGE2 treatment increased cAMP response element (CRE)-binding protein serine phosphorylation. However, mutation of the activator protein 1/CRE on the promoter did not affect basal or PGE2-stimulated activation, suggesting a role for cAMP/PKA that is independent of CRE-binding protein binding. Mutation of the GC-rich region of the SOCS3 promoter, a putative Sp1/Sp3 binding site, abolished both basal and PGE2-stimulated activation. Gel-shift assays showed increased complex formation after treatment, and this was inhibited by the addition of an Sp1 antibody or pretreatment with PKA inhibitor. Chromatin immunoprecipitation assay verified Sp1 binding to the promoter in response to PGE2. Sp1 overexpression increased SOCS3 promoter activation, and both basal and PGE2-induced SOCS3 mRNA expression was prevented by mithramycin, an inhibitor of Sp1 DNA binding. Finally, a physiological role for PGE2 was demonstrated with PGE2 pretreatment reducing lipopolysaccharide-induced STAT3 activation. Collectively, this study details a novel mechanism of SOCS3 up-regulation by PGE2 in breast cancer cells that appears to be STAT independent and involve Sp1 binding to the promoter. This process has possible implications for cytokine responsiveness and tumor progression.

Exogenous prolactin stimulates mammary development and alters expression of prolactin-related genes in prepubertal gilts

The goal of this project was to determine whether recombinant porcine (rp) prolactin (PRL) can enhance mammary development when given to pre-pubertal gilts and/or modify the expression of PRL-related genes. Crossbred gilts were injected s.c. twice daily with saline (CTRL; n = 13), 2 mg of rpPRL (4PRL; n = 13), or 4 mg of rpPRL (8PRL; n = 13) in a 2.0-mL volume for a period of 29 d, starting at 75.1 +/- 0.5 kg BW. Jugular blood samples were collected before the first injection, as well as 14 and 28 d later, and were assayed for PRL, IGF-I, and leptin. Gilts were slaughtered on d 29 of treatment, and mammary glands were collected for dissection of parenchymal and extraparenchymal tissues, and for determination of parenchymal DNA, DM, protein, and fat contents. Levels of mRNA for PRL, PRL receptor (PRL-R), and signal transducers and activators of transcription (STAT5A and STAT5B) were determined via real-time PCR in the mammary parenchyma, as well as levels for PRL and PRL-R in the pituitaries. Treatments did not alter plasma (P = 0.48) IGF-I. Serum concentrations of PRL at slaughter were greater (P < 0.01) in both 4PRL and 8PRL compared with CTRL, whereas at mid-treatment, they were greater (P < 0.05) only in 8PRL gilts. Parenchymal tissue weight and parenchymal DNA concentrations increased with exogenous rpPRL (P < 0.001). The percentage of protein in parenchyma increased (P < 0.001), whereas that of DM (P < 0.001), fat (P < 0.001), and the protein:DNA ratio (P < 0.05) decreased with exogenous rpPRL. Treatment differences were always observed between the 4 mg dose and CTRL, and no further differences were noted when the dose was increased to 8 mg daily. Expression levels of PRL, but not PRL-R, were decreased (P < 0.05) in anterior pituitary glands and mammary glands of treated gilts. The mRNA levels of STAT5A and STAT5B increased (P < 0.05) with exogenous rpPRL. It is evident from these data that rpPRL can stimulate mammogenesis in prepubertal gilts through hyperplasia and increased expression of PRL-related genes.

Stat5 activation inhibits prolactin-induced AP-1 activity: distinct prolactin-initiated signals in tumorigenesis dependent on cell context

The essential role of prolactin (PRL) in normal mammary gland growth and differentiation has implicated this hormone in the development and progression of breast cancer. Although Stat5 is the best-characterized mediator of PRL signals, PRL also activates multiple other signals, whose roles in normal and pathologic processes are not well understood. We have shown that PRL stimulates activating protein-1 (AP-1) activity in breast cancer cells, and can cooperate with estradiol in this pathway. AP-1 modulates many processes critical for carcinogenesis, including cell proliferation, survival, transformation, invasion and angiogenesis, and is elevated in many neoplasms, including breast tumors. Here, we investigated the relationship between PRL signals to AP-1 and Stat5. We found that PRL activation of Stat5a and Stat5b, but not Stat1 or Stat3, reduced PRL signals to AP-1, without altering estradiol-induced AP-1 activity. The truncation mutant, Stat5/Delta53C, but not Stat5Y699F, was an effective inhibitor, consistent with a requirement for Stat5 dimerization and nuclear accumulation, but not its C-terminal transactivation activity. The association of Stat5 with AP-1 proteins suggests that this underlies the inhibition. Predictably, the ability of PRL to activate Stat5 and AP-1 was inversely related in mammary cell lines. Further, reduction of Stat5 protein with siRNA in T47D cells, which contain elevated Stat5, increased PRL-induced AP-1 signals, transcripts for the AP-1 target, matrix metalloproteinase-2 and associated invasive behavior. This study points to the importance of cell context in determining the spectrum of PRL-induced actions, which is critical for understanding the contributions of PRL to breast cancer.

Immunohistochemical evaluation of STAT3-p-tyr705 expression in feline mammary gland tumours and correlation with histologic grade

STAT3 (signal transducer and activator of transcription 3) is a cytoplasmic transcription factor that plays a role in the G1 to S phase cell-cycle transition and is induced by cytokines and growth factors. The expression of STAT3 phosphorylated on tyrosine 705 (STAT3-p-tyr705) in normal, hyperplastic and neoplastic feline mammary gland tissue was assessed by immunohistochemistry in 45 cats. The samples included 4 normal mammary non-lactating tissues, 9 hyperplastic tissues (5 fibroepithelial hyperplasia and 4 lobular epithelial hyperplasia), 2 benign tumours (1 complex adenoma, and 1 simple adenoma), and 30 carcinomas (18 simple tubular papillary, 6 simple tubular, 2 simple solid, 3 cribriform, and 1 adenosquamous carcinoma). For immunohistochemistry, tissue sections were incubated with an anti-STAT3-p-tyr705 monoclonal antibody and visualized with EnVision-DAB polymer. STAT3-p-tyr705 positivity was quantified in a semi-quantitative manner. All positive samples showed cytoplasmic and/or nuclear positivity. Normal non-lactating mammary tissue showed a low number of positive cells, similar to hyperplastic tissue. In neoplastic tissues, a high number of positive cells with a moderate to intense reaction was observed. Moreover, a correlation was observed between nuclear positivity for STAT3-p-tyr705 and histologic grade (P=0.013; r=0.447), tubular formation (P=0.043; r=0.820), and mitotic activity (P<0.0001; r=0.689). In contrast, no such correlations were observed for cytoplasmic reactivity of STAT3-p-tyr705. A significant difference was observed between malignant lesions and hyperplasia with regards to expression of STAT3-p-tyr 705 in the cytoplasm (P=0.008; U=59.00) and nuclei (P=0.002; U=47.00). These results confirm previous our data and reinforce the potential role of STAT3 in malignancy as reported for human breast cancer and other sporadic tumours.

STAT5 transcriptional activity is impaired by LIF in a mammary epithelial cell line

Gene regulation mediated by STAT factors has been implicated in cellular functions with relevance to a variety of processes. Particularly, STAT5 and STAT3 play a crucial role in mammary epithelium displaying reciprocal activation kinetics during pregnancy, lactation and involution. Here, we show that LIF treatment of mammary epithelial HC11 cells reduces the phosphorylation levels and transcriptional activity of p-STAT5 in correlation with STAT3 phosphorylation. We have also found that STAT5 activity is negatively modulated by this cytokine, both on a gene whose expression is induced, as well as on a promoter repressed by STAT5. Besides, our results show that lactogenic hormones increase LIF effect on gene induction without modifying STAT3 phosphorylation state. Our findings strongly suggest that there is crosstalk between STAT5 and STAT3 pathways that could modulate their ability to regulate gene expression.

Leptin enhances STAT-3 phosphorylation in HC11 cell line: effect on cell differentiation and cell viability

Leptin is produced in the mammary gland by the fat tissue or by the mammary epithelium. The aim of this study was to investigate the role of leptin on mammary epithelial cell differentiation and cell viability. This study was conducted using the mouse mammary epithelial cell line HC11. We show that leptin, synergizes with prolactin to increase beta-casein gene expression during mammary epithelial cell differentiation. This was correlated with increased phosphorylation of the signal transducer and activator of transcription 3 (STAT-3). Inactivating the function of STAT-3 by expression of a short hairpin RNA demonstrated that the effect of leptin on beta-casein expression is mediated by STAT-3. Secondly, cells in which STAT-3 had been inactivated showed increased cell viability compared to controls and were resistant to the negative effect mediated by leptin. Further, leptin triggers apoptosis in mammary epithelial cells cultivated in non-differentiating conditions. Taken together, these results suggest that leptin, by activating STAT-3, may act as a paracrine factor modulating mammary epithelial cell function.