EGF modulates expression of STAT5 in mammary epithelial cells

Peg1/Mest, an imprinted gene, is involved in mammary gland maturation

Imprinted genes, which are specific to mammals, play important roles in cell proliferation, differentiation, ontogeny, and other phenomena. Moreover, these genes are considered crucial in the research of mammalian evolution. In the current study, we investigated the association between the expression of paternally imprinted gene paternally expressed 1/mesoderm-specific transcript (Peg1/Mest) and the maturation of the mammary gland. Quantitative real-time polymerase chain reaction analysis of Peg1/Mest gene expression at different stages of mouse mammary gland maturation revealed that its expression increased during gestation but decreased during lactation. Immunohistochemical staining demonstrated that Peg1/Mest was expressed in mammary epithelial cells. We measured expression levels of Peg1/Mest and E-cadherin during mammary alveoli formation using immunofluorescence staining a cell model for mammary alveoli formation in a 3D culture system. We found that the onset of E-cadherin expression roughly coincided with the peak of Peg1/Mest expression. Moreover, we discovered that the formation and proliferation of alveoli were suppressed in Peg1/Mest knockdown mammary epithelial cells. These results suggest that Peg1/Mest plays a certain role in mammary alveoli formation. To clarify the role of Peg1/Mest in the lactogenic differentiation of mammary epithelial cells, we examined the lactogenic differentiation capability of Peg1/Mest-overexpressing HC11 cells. Application of a differentiation-inducing stimulus did not increase β-casein expression in Peg1/Mest-overexpressing HC11 cells. The current study for the first time reports the involvement of an imprinted gene in mammary gland maturation.

Conversion of non-adipogenic fibroblasts into adipocytes by a defined hormone mixture

Non-adipogenic fibroblasts were induced into adipocytes by treatment with a defined hormone mixture including epidermal growth factor, hepatocyte growth factor, dexamethasone and insulin. Non-adipogenic fibroblasts were directly converted into adipocytes without a pre-adipocyte stage.

Replacement of E-cadherin by N-cadherin in the mammary gland leads to fibrocystic changes and tumor formation

Introduction

E-cadherin (E-cad; cadherin 1) and N-cadherin (N-cad; cadherin 2) are the most prominent members of the cadherin family of cell adhesion molecules. Although they share many structural and functional features, they are expressed in an almost mutually exclusive manner in vivo.

Methods

To explore functional differences between the two cadherins in vivo, we recently generated a knock-in line in which N-cad is expressed from the E-cad locus. In combination with a conditional gene inactivation approach, we expressed N-cad in the absence of E-cad (referred to as Ncadk.i.) in alveolar epithelial cells of the mammary gland starting in late pregnancy.

Results

We found that the sole presence of N-cad induces constitutively active fibroblast growth factor (Fgf) signaling and a precocious involution resulting in massive apoptosis of alveolar cells. To block apoptosis, we conditionally deleted one allele of p53 in Ncadk.i. mice and observed a temporal rescue of alveolar morphology and function. However, an accumulation of fibrotic tissue and cysts with increasing age and lactation cycles was observed. This phenotype closely resembled fibrocystic mastopathy (FM), a common disorder in humans, which is thought to precede breast cancer. Concordantly, 55% of Ncadk.i. mice harboring a heterozygous p53 deletion developed malignant and invasive tumors.

Conclusions

Our results demonstrate a possible role for N-cad in the formation of fibrosis and cysts in the mammary gland. Moreover, we show that these lesions precede the development of malignant tumors. Thus, we provide a new mouse model to investigate the molecular mechanisms of fibrocystic mastopathy and the transition from benign to malignant tumors.

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.

Gene expression in murine mammary epithelial stem cell-like cells shows similarities to human breast cancer gene expression

Introduction

Mammary stem cells are bipotential and suggested to be the origin of breast cancer development, but are elusive and vaguely characterized. Breast tumors can be divided into subgroups, each one requiring specific treatment. To determine a possible association between mammary stem cells and breast cancer, a detailed characterization of the transcriptome in mammary stem cells is essential.

Methods

We have used a murine mammary epithelial stem-like cell line (HC11) and made a thorough investigation of global gene-expression changes during stepwise differentiation using dual-color comparative microarray technique. Subsequently, we have performed a cross-species comparison to reveal conserved gene expression between stem cells and subtype-specific and prognosis gene signatures, and correlated gene expression to in vivo mammary gland development.

Results

Our analysis of mammary stem-like and stepwise cell differentiation, and an in-depth description of our findings in a breast cancer perspective provide a unique map of the transcriptomic changes and a number of novel mammary stem cell markers. We correlate the alterations to in vivo mammary gland differentiation, and describe novel changes in nuclear receptor gene expression. Interestingly, our comparisons show that specific subtypes of breast cancers with poor prognosis and metastasizing capabilities show resemblance to stem-like gene expression.

Conclusions

The transcriptional characterization of these mammary stem-like cells and their differentiation-induced gene expression patterns is here made widely accessible and provides a basis for research on mammary stem-like cells. Our comparisons suggest that some tumors are more stem-like than others, with a corresponding worse prognosis. This information would, if established, be important for treatment decisions. We also suggest several marker candidates valuable to investigate further.

Global expression profiling reveals regulation of CTGF/CCN2 during lactogenic differentiation

Mammary epithelial cells go through a series of developmental changes during pregnancy and lactation including proliferation, differentiation, secretion and apoptosis. HC11 mouse mammary epithelial cells, which undergo lactogen-induced differentiation in cell culture, were used to follow the changes in gene expression during this process. The expression profiles of over 20,000 genes were compared in HC11 cells undergoing lactogenic differentiation to non-differentiated cells using DNA microarray analysis. Greater than two fold changes were detected in 998 genes in the differentiated cells versus growth controls. Several genes including CTGF/CCN2 exhibited greater than five-fold increase. Validation of the gene expression pattern for more than twenty genes was performed. The results indicate the involvement of numerous genes and pathways in the differentiation of mouse mammary epithelial cells in culture and they identify genetic pathways associated with specific transcriptional regulation. In addition, the expression of a subset of genes regulated by lactogenic differentiation in HC11 cells, including CTGF/CCN2 and osteopontin, was examined in mouse mammary glands revealing expression during pregnancy and lactation that declined during involution of the glands. To probe the mechanism by which epidermal growth factor (EGF), a known inhibitor of lactogenic differentiation in HC11 cells, blocks lactogenesis, the HC11 cells stimulated with lactogenic hormone in the presence of EGF were profiled. This data revealed EGF regulation of a specific subset of genes including important cell cycle regulators. The studies confirm the value of expression profiling in defining gene transcription associated with differentiation of mammary epithelial cells.

In vivo identification of novel STAT5 target genes

STAT5A and STAT5B proteins belong to the family of signal transducers and activators of transcription. They are encoded by two separate genes with 91% identity in their amino acid sequences. Despite their high degree of conservation, STAT5A and STAT5B exert non-redundant functions, resulting at least in part from differences in target gene activation. To better characterize the differential contribution of STAT5A and STAT5B in gene regulation, we performed single or double knockdown of STAT5A and STAT5B using small interfering RNA. Subsequent gene expression profiling and RT-qPCR analyses of IL-3-stimulated Ba/F3-β cells led to the identification of putative novel STAT5 target genes. Chromatin immunoprecipitation assays analyzing the corresponding gene loci identified unusual STAT5 binding sites compared to conventional STAT5 responsive elements. Some of the STAT5 targets identified are upregulated in several human cancers, suggesting that they might represent potential oncogenes in STAT5-associated malignancies.

EGF-induced activation of Akt results in mTOR-dependent p70S6 kinase phosphorylation and inhibition of HC11 cell lactogenic differentiation

BACKGROUND

HC11 mouse mammary epithelial cells differentiate in response to lactogenic hormone resulting in expression of milk proteins including beta-casein. Previous studies have shown that epidermal growth factor (EGF) blocks differentiation not only through activation of the Ras/Mek/Erk pathway but also implicated phosphatidylinositol-3-kinase (PI-3-kinase) signaling. The current study analyzes the mechanism of the PI-3-kinase pathway in an EGF-induced block of HC11 lactogenic differentiation.

RESULTS

HC11 and HC11-luci cells, which contain luciferase gene under the control of a beta-casein promotor, were treated with specific chemical inhibitors of signal transduction pathways or transiently infected/transfected with vectors encoding dominant negative-Akt (DN-Akt) or conditionally active-Akt (CA-Akt). The expression of CA-Akt inhibited lactogenic differentiation of HC11 cells, and the infection with DN-Akt adenovirus enhanced beta-casein transcription and rescued beta-casein promotor-regulated luciferase activity in the presence of EGF. Treatment of cells with Rapamycin, an inhibitor of mTOR, blocked the effects of EGF on beta-casein promotor driven luciferase activity as effectively as PI-3-kinase inhibitors. While expression of CA-Akt caused a constitutive activation of p70S6 kinase (p70S6K) in HC11 cells, the inhibition of either PI-3-kinase or mTOR abolished the activation of p70S6K by EGF. The activation of p70S6K by insulin or EGF resulted in the phosphorylation of ribosomal protein S6 (RPS6), elongation initiation factor 4E (elF4E) and 4E binding protein1 (4E-BP1). But lower levels of PI-3-K and mTOR inhibitors were required to block insulin-induced phosphorylation of RPS6 than EGF-induced phosphorylation, and insulin-induced phosphorylation of elF4E and 4E-BP1 was not completely mTOR dependent suggesting some diversity of signaling for EGF and insulin. In HC11 cells undergoing lactogenic differentiation the phosphorylation of p70S6K completely diminished by 12 hours, and this was partly attributable to dexamethasone, a component of lactogenic hormone mix. However, p70S6K phosphorylation persisted in the presence of lactogenic hormone and EGF, but the activation could be blocked by a PI-3-kinase inhibitor.

CONCLUSION

PI-3-kinase signaling contributes to the EGF block of lactogenic differentiation via Akt and p70S6K. The EGF-induced activation of PI-3-kinase-Akt-mTOR regulates phosphorylation of molecules including ribosomal protein S6, eIF4E and 4E-BP1 that influence translational control in HC11 cells undergoing lactogenic differentiation.

Epidermal growth factor reduces hepatic sequelae in experimental necrotizing enterocolitis

BACKGROUND AND AIM

Neonatal necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We recently demonstrated that the gut/liver axis plays an important role in the pathophysiology of NEC through the release of inflammatory mediators into the intestinal lumen. We have also shown that supplementation of formula with epidermal growth factor (EGF) dramatically decreases ileal pathology associated with experimental NEC. In this study, we examined the effects of EGF on the liver portion of the gut/liver axis in the neonatal rat model of NEC.

METHODS

Newborn rats were divided into three experimental groups, NEC, hand-fed with growth-factor free formula; NEC + EGF, hand-fed with formula supplemented with 500 ng/ml rat EGF; or DF, dam fed. All animals were exposed to asphyxia and cold stress twice daily for 4 days to develop NEC.

RESULTS

EGF receptor expression was significantly (p <or= 0.01) decreased in the NEC+EGF group compared to the NEC group. EGF supplementation significantly decreased Kupffer cell numbers (p <or= 0.01) as well as hepatic tumor necrosis factor (TNF)-alpha and interleukin-18 production (p <or= 0.05). Further, TNF-alpha in the intestinal luminal contents of the NEC+EGF group were normalized to levels observed in DF controls compared to the NEC group (p <or= 0.05). Activated nuclear factor-kappaB was also substantially decreased in the NEC+EGF group versus the NEC group.

CONCLUSION

The results of this study indicate that EGF normalizes cytokine overproduction in the liver of neonatal rats with NEC, which contributes to diminished intestinal damage during the development of experimental NEC. These data suggest that supplementation of formula with EGF can have beneficial effects on the gut/liver axis during NEC pathogenesis.

Estrogen receptors alfa (ERalpha) and beta (ERbeta) differentially regulate proliferation and apoptosis of the normal murine mammary epithelial cell line HC11

The mitogenic effect of 17beta-estradiol (E2) on the breast is mediated by estrogen receptor alfa (ERalpha), hence ERalpha antagonists are effective in the treatment of breast cancer. The possible use of estrogen receptor beta (ERbeta) as a target in treatment of breast cancer is under investigation. The mouse mammary cell line HC11 expresses both ERs and was used to study the role of the two receptors in proliferation. E2 had no effect on proliferation. The ERalpha-selective agonist 4,4',4''-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) stimulated proliferation. The ERbeta-selective agonist 2,3-bis(4-hydroxy-phenyl)-propionitrile (DPN) inhibited cell growth and induced apoptosis. PPT upregulated while DPN downregulated cyclin D1 and proliferating cell nuclear antigen (PCNA). Upon inhibition of ERalpha expression with RNA interference, E2 caused a decrease in cyclin D1 and PCNA, and increased apoptosis. When ERbeta expression was blocked, E2 induced proliferation and cells gained the capacity to grow in soft agar. In summary, in HC11 mammary epithelial cells, ERalpha drives proliferation in response to E2 while ERbeta is growth inhibitory. The lack of effect of E2 on HC11 cell growth is the result of the combined actions of ERalpha (proliferation) and ERbeta (apoptosis). We suggest that use of ERbeta agonists will be a useful addition in treatment of breast cancer, which, at present, is only aimed at inhibition of ERalpha.

Dominant negative Ras enhances lactogenic hormone-induced differentiation by blocking activation of the Raf-Mek-Erk signal transduction pathway

Epidermal growth factor (EGF) and Ras mitogenic signal transduction pathways are frequently activated in breast carcinoma and inhibit mammary differentiation and apoptosis. HC11 mouse mammary epithelial cells, which differentiate and synthesize beta-casein following growth to confluency and stimulation with lactogenic hormones, were used to study EGF-dependent signaling during differentiation. Blocking Mek-Erk or phosphotidylinositol-3-kinase (PI-3 kinase) signaling with specific chemical inhibitors enhanced beta-casein promotor-driven luciferase activity. Because EGF stimulation of HC11 cells resulted in the activation of Ras, the effect of activated Ras (RasV12) or dominant negative (DNRasN17) on lactogen induced differentiation was examined. HC11 cell lines expressing RasV12 or DNRasN17 under the control of a tetracycline (tet)-responsive promotor were constructed. Activated RasV12 expression resulted in reduced tyrosine phosphorylation of Stat5 and a delay in beta-casein expression in response to prolactin. However, the expression of tet-regulated DNRasN17 and adenovirus-encoded DNRasN17 enhanced Stat5 tyrosine phosphorylation, Stat5 DNA binding, and beta-casein transcription. The expression of DNRasN17 blocked the activation of the Mek-Erk pathway by EGF but did not prevent the phosphorylation of AKT, a measure of activation of the PI-3-kinase pathway. Moreover, the expression of DNRasN17 prevented the block to lactogenic differentiation induced by EGF. Stimulation of HC11 cells with prolactin resulted in the association of the SHP2 phosphatase with Stat5, and this association was prevented by DNRasN17 expression. These results demonstrate that in HC11 cells DNRas inhibits the Mek-Erk pathway and enhances lactogenic hormone-induced differentiation. This occurs, in part, by inhibiting the association of the SHP2 phosphatase with Stat5.

PEA3 transactivates the Muc4/sialomucin complex promoter in mammary epithelial and tumor cells

Sialomucin complex (SMC, rat Muc4) is a heterodimeric glycoprotein composed of two subunits, the mucin component ascites sialoglycoprotein ASGP-1 and the transmembrane subunit ASGP-2, which is aberrantly expressed on the surfaces of a variety of tumor cells. Up-regulation of the Muc4/SMC gene in the 13762 sublines of the rat mammary adenocarcinoma correlates with the overexpression of transcription factor PEA3 and the receptor tyrosine kinase ErbB2. Here we report that PEA3 is capable of transactivating the Muc4/SMC promoter in a dose-dependent manner via direct attachment to a PEA3 binding site. ERM and ER81, the other two members of the PEA3 subfamily of transcription factors, could not transactivate the Muc4/SMC promoter. Transcriptional activation of Muc4/SMC by PEA3 is potentiated by Ras and MEKK1 kinases. These data suggest that expression of PEA3 in mammary tumors leads to up-regulation of Muc4/SMC transcription, the gene product of which may contribute to the metastatic potential of mammary tumors.

Constitutive activation of STAT3 and STAT5 is present in the majority of nasopharyngeal carcinoma and correlates with better prognosis

Constitutively activated signal transducers and activators of transcription (STAT) factors, in particular STAT1, STAT3 and STAT5, have been demonstrated in a variety of human tumours and cancer cell lines. However, data on the expression of these STATs in nasopharyngeal carcinoma (NPC) are limited. In this study, the expression patterns of STAT1, STAT3 and STAT5 were immunohistochemically examined on the archival specimens from 61 patients with NPC. Staining results of each STATs were then correlated with the clinical parameters and prognosis of these patients. The results showed that constitutive activation of STAT3 and STAT5 was detected in the majority, 70.5 and 62.3%, respectively, of the 61 tumour specimens. Furthermore, coexpression of activated STAT3 and STAT5 was found in 54.1% of the specimens. In contrast, constitutive activated STAT1 could only be detected in 8 (13.1%) cases. Surprisingly, following radiotherapy, patients with constitutive STAT5 activation, or activation of both STAT3 and STAT5, had better disease-free survival and overall survival than those without activated STAT5. To our knowledge, this is the first report providing the overall expression patterns and prognostic significance of specific STATs in NPC.

The role of Stat5 in estrogen receptor-positive breast cancer

Estrogen receptor (ER) has been a successful target for effective prevention and treatment strategies in breast cancer, whereas growth factors and their signaling molecules are proving to be effective treatment targets as well. Understanding the interaction between ER and growth factor signaling pathways should provide clues to optimal treatment approaches and new strategies to overcome and prevent endocrine resistance. Cross-talk between ER and signal transducer and activator of transcription 5 (Stat5) has also been reported. Stat5 regulates growth, differentiation, and survival of mammary and hematopoietic cells. The role of Stat5 in breast cancer has not been established, although Stat5 is critical for some hematopoietic malignancies. We have analyzed the role of Stat5 in the progression of ER-positive breast cancer cells such as T47D and MCF7 in which Stat5b is constitutively activated. Adenoviral-mediated dominant-negative Stat5 induced apoptosis in T47D cells but not in caspase-3 negative MCF7 cells. Our study indicates that targeting Stat5 may represent a new strategy to suppress estrogen receptor activity and induce apoptosis in Stat5-activated, ER-positive breast cancer.

Naturally occurring dominant-negative Stat5 suppresses transcriptional activity of estrogen receptors and induces apoptosis in T47D breast cancer cells

Signal transducer and activator of transcription (Stat) 5 regulates growth, differentiation, and survival of mammary and hematopoietic cells. The role of Stat5 in breast cancer has not been established, although Stat5 is critical for some hematopoietic malignancies. We detected for the first time that Stat5b is constitutively activated in human breast cancer cell lines, and analysed the role of Stat5 in estrogen receptor(ER)-positive breast cancer cell lines using dominant-negative variants of Stat5. Two distinct carboxyl-truncated Stat5a derivatives were generated. Stat5aDelta740 corresponded to a naturally occurring alternative splice variant, and Stat5aDelta713 was analogous to an 80 kDa Stat5a product of a nuclear protease. Stat5aDelta740 and Stat5aDelta713 displayed comparable dominant-negative properties and suppressed transcriptional activity of wild-type Stat5a and Stat5b equally well. Cotransfection experiments revealed that Stat5aDelta740 completely blocked transcriptional activity of endogenous estrogen receptor in T47D and MCF7 cells, and of both ER alpha and ER beta in COS-7 cells. Stat5aDelta740 was selected for adenoviral delivery, and high-efficiency expression of tyrosine phosphorylated Stat5aDelta740 was achieved in infected cells. Adenoviral-mediated Stat5aDelta740 induced apoptosis in T47D cells but not in caspase-3-negative MCF7 cells. The present study indicates that overexpression of a dominant-negative variant of Stat5 suppresses ER transcriptional activity and induces apoptosis in estrogen-responsive breast cancer tissue culture cells.

Ileal cytokine dysregulation in experimental necrotizing enterocolitis is reduced by epidermal growth factor

BACKGROUND

Necrotizing enterocolitis (NEC) is the most common gastrointestinal disease of premature infants. We have shown in previous studies that proinflammatory interleukin-18 and interleukin-12 are up-regulated in the ileum of rats with experimental NEC and that epidermal growth factor (EGF) reduces the development of disease. Here we investigated whether the protective effects of EGF are a result of changes in ileal interleukin-18, interleukin-12 and/or antiinflammatory interleukin-10.

METHODS

Newborn rats were artificially fed with either growth-factor-free rat milk substitute (RMS) or RMS supplemented with 500 ng/mL EGF (RMS + EGF) and NEC was induced via exposure to asphyxia and cold stress. Cytokine expression and localization were assessed using reverse-transcription real-time polymerase chain reaction and immunohistology/confocal microscopy.

RESULTS

Enteral administration of EGF (RMS + EGF) decreased overproduction of interleukin-18 and increased interleukin-10 production in the ileum. Furthermore, increased interleukin-10 production was associated with up-regulation of the transcription factor Sp1 in RMS + EGF rats.

CONCLUSIONS

These data suggest that EGF may reduce NEC via increased interleukin-10 and decreased interleukin-18 and that EGF-mediated up-regulation of Sp1 may account for the increased interleukin-10.

Evidence for a local effect of leptin in bovine mammary gland

On average, high-energy diets promoting body growth rates above 1 kg/d before puberty impair mammary development by 15 to 20% in cattle. We hypothesized that leptin, a protein produced by adipocytes, mediates the inhibitory effect of high-energy diets on mammary development. Therefore, our objectives were to determine the effect of leptin on mammary epithelial cell proliferation, and the distribution of mRNA for two leptin receptor isoforms in prepubertal bovine mammary glands and other peripheral tissues. Addition of leptin to culture media containing either 5 ng/ml of insulin-like growth factor-I (IGF-I) or 1% fetal bovine serum decreased DNA synthesis of a bovine mammary epithelial cell line (MAC-T) in a dose-dependent manner. The minimal doses of leptin that decreased IGF-I- and fetal bovine serum-stimulated cell proliferation were 64 and 1 ng/ml, respectively. In addition, we determined that MAC-T cells and isolated bovine mammary epithelial cells express the long form of leptin receptor (Ob-Rb) mRNA. Ob-Rb mRNA was detected in all bovine tissues examined. In contrast with reports on other species, mRNA expression of the short form of leptin receptor (Ob-Ra) was detected only in bovine liver, pituitary body, and spleen. These results support the concept that leptin mediates the inhibitory effect of high-energy diets on mammary development.

Effects of hyperactive Janus kinase 2 signaling in mammary epithelial cells

Prolactin, the Janus kinase 2 (JAK2) and the signal transducer and activator of transcription 5 (STAT5) are important for mammary gland development and have also been implicated in development and growth of breast tumors. In the present study we have investigated the role for JAK2 in proliferation, differentiation, and apoptosis of the mammary epithelial cell line HC11 by stably overexpressing two hyperactive JAK2 mutants. Cells expressing a JAK2 mutant consisting of only the kinase domain had high amount of nuclear STAT5 protein with low DNA-binding activity, which was rapidly induced to a DNA-binding state by prolactin treatment. Cells expressing JAK2 deleted of the kinase-like domain showed increased sensitivity to prolactin treatment compared to wild type cells. Proliferation was not affected by any of the mutants whereas the ability to undergo apoptosis was decreased implicating a transforming potential of the JAK2 mutants.

Regulated expression of signal transducer and activator of transcription, Stat5, and its enhancement of PRL expression in human endometrial stromal cells in vitro

Differentiation of human endometrium during the secretory phase of the menstrual cycle is characterized by expression of a variety of genes implicated in the establishment and maintenance of pregnancy. An increased abundance of signal transducers and activators of transcription (Stats) in the secretory phase suggests Stat5 as a component of the differentiation of endometrium in response to ovarian hormone stimulation in vivo. Decidualization is initiated in a subset of endometrial stromal cells (ESC) in vivo during the secretory phase, but it is unclear whether regulated expression of Stat5 is a feature of these cells. Here, therefore, the abundance and subcellular distribution of Stat5 in ESC after a decidualization stimulus of cAMP plus medroxyprogesterone acetate (MPA) has been investigated in vitro. Western blotting revealed an increase in the apparent abundance of Stat5a and Stat5b, in the cytosolic and nuclear fractions, at 2, 3, and 4 d after stimulation. The potential functional relevance of this increase in Stat5 is suggested by the ability of transiently transfected Stat5a or Stat5b to significantly enhance the response of the decidual PRL promoter to cAMP/MPA and attenuation of the response to cAMP/MPA by dominant negative Stat5. Recent evidence suggests endometrial differentiation, including PRL production, as a possible target of antiphospholipid antibodies (aPL) prevalent in recurrent miscarriage. Monoclonal antibody, ID2, which has similar reactivity as human aPL, significantly decreased the apparent abundance of nuclear Stat5b in response to cAMP/MPA and was associated with decreased decidual PRL promoter activation and PRL secretion. Regulated expression of Stat5 is therefore a component of decidual differentiation of human ESC and contributes significantly to activation of the decidual PRL promoter. Alteration of this process by an aPL component suggests decidual differentiation as a potential clinical target in recurrent early miscarriages.

Dysregulation of mammary Stats 1,3 and 5 and PRL receptors by overexpression of TGFalpha

Mammary TGFalpha overexpression results in delayed involution and eventually mammary cancer in transgenic mice. We hypothesized that STATs and PRL receptors (PRLR), critical regulators of mammary function, are altered in these animals and may contribute to this phenotype. We examined these factors late in the first pregnancy (d.18) and during normal involution (d.4 post-lactation) in WAP-TGFalpha transgenic mice and non-transgenic controls. Long form PRLR mRNA in WAP-TGFalpha glands at both pregnant d.18 and d.4 post-lactation was significantly reduced compared to controls, and PRLR-S3 failed to rise during involution. Total and pTyr STAT 1,3,5a and 5b also were altered. STAT 3 was higher at both times in WAP-TGFalpha glands. STAT 5a and 5b were lower at late pregnancy, but higher post-lactation; however, pTyr(694) STAT 5 was abnormally low at both times. Thus overexpression of TGFalpha has direct or indirect effects on both STATs and PRL responsiveness in vivo, which may reflect mechanisms of TGFalpha-induced mammary epithelial abnormalities.

Growth hormone-regulated intracellular signaling in UMR 106 osteosarcoma cells

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are important growth factors for postnatal longitudinal bone growth. Although many effects of GH on bone growth are mediated by IGF-1, GH can directly influence bone cells. Limited knowledge exists regarding specific intracellular signaling pathways and genes activated by GH in bone cells. GH is known to activate several intracellular signaling pathways, among them the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. GH mainly activates JAK2 and both isoforms of STAT5, A and B. STAT5 gene deletion experiments have shown the importance of these transcription factors for growth. To understand the molecular mechanism(s) behind this, different experimental models are needed. The UMR 106 cell line is a rat clonal osteosarcoma cell line with osteoblast-like phenotypic properties, one is the endogenous expression of GH receptor (GHR). The present study focused on whether these cells express a functional GH-responsive JAK2/STAT5 pathway. Analysis of cell extracts by immunoprecipitation and Western blot showed that physiological concentrations of GH activated JAK2. Western blot analysis of nuclear extracts from GH-stimulated UMR 106 cells showed that physiological concentrations of GH induced nuclear translocation of both STAT5 isoforms, but with STAT5A being predominant. Both isoforms displayed similar nuclear turnover after GH stimulation of cells. Gel electrophoretic mobility shift assay (GEMSA) of nuclear extract revealed that both STAT5A and STAT5B obtained DNA-binding capacity after GH stimulation. Thus, we have shown, for the first time, the expression and GH-induced activation of JAK2 and STAT5A/B in UMR 106 osteoblast-like cells. This study also shows that this cell line is a suitable experimental model to study unique GH effects in osteoblasts mediated by STAT5.

Signal transducer and activator of transcription 3 activates CCAAT enhancer-binding protein delta gene transcription in G0 growth-arrested mouse mammary epithelial cells and in involuting mouse mammary gland

The CCAAT enhancer-binding protein (C/EBP) family of transcription factors is implicated in the regulation of cell proliferation and differentiation in a variety of tissues. C/EBPdelta is involved in regulating G(0) growth arrest and apoptosis of mouse mammary epithelial cells. This study shows that activation of signal transducer and activator of transcription 3 (Stat3), but not activation of Stat1 or Stat5, occurs concurrently with G(0) growth arrest of HC11 mouse mammary epithelial cells, but not NIH 3T3 fibroblasts. Promoter analysis demonstrates that the C/EBPdelta promoter fragment involved in transcriptional activation during G(0) growth arrest contains a Stat3 binding site and that mutation of this site eliminates the G(0) growth arrest inducibility of the C/EBPdelta promoter. Overexpression of Stat3 increases C/EBPdelta promoter activity during G(0) growth arrest of HC11 cells, whereas dominant negative Stat3 decreases C/EBPdelta promoter activity under the same conditions. Neither Stat3 overexpression nor dominant negative Stat3 expression influences C/EBPdelta promoter activity in growing HC11 cells or G(0) growth-arrested NIH3T3 cells, demonstrating that the effect is specific to G(0) growth arrest of mammary epithelial cells. Band shift assays and antibody interference assays demonstrate specific binding of Stat3 to the acute phase response element in the C/EBPdelta promoter in G(0) growth-arrested HC11 cell extracts and 24 h involuting mouse mammary gland extracts. These data indicate that Stat3 activates C/EBPdelta transcription in G(0) growth-arrested mouse mammary epithelial cells and binds to the C/EBPdelta promoter during involution. An autocrine mechanism of Stat3 activation is proposed.