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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mammary gland development involves complex cycles of proliferation, differentiation, and morphogenesis, regulated by hormones including estrogens, prolactin (PRL), and epidermal growth factor (EGF). The mouse mammary epithelial cell line HC11 has been shown to be valuable for investigations of differentiation of mammary gland. In this study, we show that HC11 cells express estrogen receptor (ER)alpha and ER beta proteins at all developmental stages. We have established two different stable HC11 cell lines; H-estrogen response element (ERE) containing an ERE-reporter and H-Bc containing a beta-casein reporter. Transcription of the ERE-reporter was activated only in proliferating cells in the presence of EGF. When the cells entered the differentiation program, in the absence of EGF, estradiol-induced transcription of the ERE reporter was repressed, and similar results were obtained when MAPK signaling was inhibited in proliferating cells. We propose that these findings are related to changes in ER corepressor levels, regulated by EGF. We also report that the beta-casein reporter was activated in terminally differentiated cells and that this induction was effectively repressed by estradiol treatment. Finally, we show a physical interaction between endogenous ER alpha and signal transducer and activator of transcription 5 in differentiated HC11 cells. In summary, our results show that ER functional activity changes during differentiation of HC11 cells.
Mol Endocrinol 2004 Feb
PMID:Estrogen receptor functional activity changes during differentiation of mammary epithelial cells. 1460 98

STATs (signal transducers and activators of transcription) are proteins with dual functions: signal transducers in the cytoplasm and transcriptional activators in the nucleus. STAT proteins act as transcription factors activated by phosphorylation on its tyrosine residues upon stimulation by various cytokines. The phosphorylated STAT molecules then form homo- or heterodimers through SH2-mediated interaction and translocate into the nucleus to activate the transcription of various target genes. STAT5 recognizes the interferon-gamma activated site TTCNNNGAA (GAS sequence) in the promoter region of the beta-casein gene. Except for prolactin-dependent beta-casein production in mammary gland cells, the biological consequences of STAT5a activation in various systems are not clear. Here we showed that STAT5a was phosphorylated 10 min after desferrioxamine (DFO) treatment, and reached a maximum induction at 4 h in mammary epithelial cells (HC11) and transfected COS-7 cells. Under hypoxic conditions (2% O2), a maximal phosphorylation of STAT5a was observed within 6 h. EMSA (electrophoretic mobility shift assay) showed that DFO or hypoxia enhanced the binding activities of STAT5a DNA to beta-casein gene promoter in mammary epithelial cells (HC11) and transfected COS-7 cells. These results showed that DFO or hypoxia induces tyrosine phosphorylation of STAT5a and also increases the binding activity of STAT5a DNA in mammary epithelial cells. Our data suggest that the STAT5 may act as a mediator in hypoxia-mediated gene expression.
Exp Mol Med 2003 Oct 31
PMID:Hypoxia activates signal transducers and activators of transcription 5 (STAT5) and increases its binding activity to the GAS element in mammary epithelial cells. 1464 87

Notch signaling plays an important role in the regulation of self-renewal and differentiation of hematopoietic cells. Human monoblastic U937 cells undergo differentiation into macrophage-like cells, growth suppression, and apoptosis following stimulation with GM-CSF. We examined the effects of Notch activation induced by Notch ligands on GM-CSF-induced differentiation and apoptosis in U937 cells. Furthermore, the molecular mechanism of the effects was investigated. A recombinant Notch ligand, Delta-1 protein did not affect the growth of U937 cells by itself. GM-CSF-induced growth suppression and apoptosis of U937 cells were partially rescued by incubation with Delta-1. Delta-1 also reduced the GM-CSF-induced differentiation. Incubation with Delta-1 did not affect the expression of GM-CSF receptor. GM-CSF stimulation induced the phosphorylation of ERK1/2 and STAT5 and the cleavage of caspase-8, which were not affected by Delta-1 incubation, either. GM-CSF stimulation induced the cleavage of PARP, which is the key molecule for differentiation and apoptosis. We found that incubation with Delta-1 significantly suppressed the GM-CSF-induced cleavage of PARP. Taken together, we found that Notch activation induced by Delta-1 partially inhibited GM-CSF-induced differentiation, growth suppression, and apoptosis, along with reducing the GM-CSF-induced cleavage of PARP. These findings suggest one of the mechanisms by which Notch activation inhibits differentiation and apoptosis.
Int J Mol Med 2004 Mar
PMID:The Notch ligand, Delta-1, partially inhibits GM-CSF-induced differentiation and apoptosis along with reducing the cleavage of PARP in U937 cells. 1476 73

Insulin promotes adipocyte differentiation via a complex signaling network involving multiple insulin receptor substrates (IRSs). In cultured brown preadipocytes, expression of IRS-1 and IRS-2 mRNAs and proteins was at relatively high levels before and after differentiation into mature fat cells, while IRS-3 transcript was not detectable in preadipocytes but increased during the course of differentiation, and IRS-4 mRNA was barely detected in both states. To determine more precisely the roles of various IRS proteins in adipogenesis, we established and characterized brown preadipocyte cell lines from wild-type and IRS knockout (KO) animals. While wild-type, IRS-2 KO, and IRS-4 KO cells fully differentiated into mature adipocytes, IRS-3 KO cells showed a moderate defect in differentiation and IRS-1 KO cells exhibited a severe defect in the process. Cells lacking both IRS-1 and IRS-3 completely failed to differentiate. Expression of the adipogenic markers peroxisome proliferator-activated receptor gamma (PPARgamma), CCAAT/enhancer-binding protein alpha, fatty acid synthase, glucose transporter 4, and the transcription factor signal transducer and activator of transcription 5, as well as the brown-fat-specific markers PPARgamma coactivator 1 alpha and uncoupling protein 1, mirrored the differentiation pattern. Reconstitution of the IRS-1 KO cells with IRS-1 and IRS-4, but not IRS-2 or IRS-3, compensated for the lack of differentiation in IRS-1 KO cells. A chimeric molecule containing the N terminus of IRS-1 and the C terminus of IRS-2, but not one with the N terminus of IRS-2 and the C terminus of IRS-1, also rescued differentiation. Expression of Wnt 10a, a molecule known to inhibit adipogenesis, was dramatically increased in the IRS-1 KO cells, and this could be reduced by overexpression of IRS-1 or IRS-4, which was correlated with restoration of differentiation. These data indicate that both IRS-1 and -3 play important roles in the differentiation of brown adipocytes and that the N terminus of IRS-1 is more important for this function of the molecule. Although IRS-4 is not essential for the process, overexpression of IRS-4 can compensate for the deficiency in differentiation in IRS-1 KO cells.
Mol Cell Biol 2004 Mar
PMID:Differential roles of insulin receptor substrates in brown adipocyte differentiation. 1496 73

An effective mechanism for interfering with prolactin signalling would provide a powerful tool for clarifying the importance of prolactin in breast cancer, as well as for investigating functions of prolactin in other tissues. Based on our previous identification of a dominant-negative mutation in the growth hormone receptor that causes familial short stature, we investigated the potential for using a similar truncated mutant of the prolactin receptor (PRLR1-242). Like the mutant growth hormone receptor, PRLR1-242 exerts an exceptionally powerful dominant-negative effect. A probable explanation for the strong dominant-negative activity of this class of mutation is that, lacking internalisation motifs, the truncated mutants accumulate at the cell surface and form non-functional heterodimers with wild-type receptors. In accordance with evidence for heterodimer formation between the two receptors, PRLR1-242 also blocks signalling by the growth hormone receptor. When expressed from an adenoviral vector, PRLR1-242 inhibits activation of STAT5 (signal transducer and activator of transcription 5) by prolactin in T47-D breast cancer cells, and blocks the ability of prolactin to induce proliferation in these cells. Thus PRLR1-242 provides an effective means of blocking the responsiveness of target tissues to human prolactin.
J Mol Endocrinol 2004 Apr
PMID:A mutant receptor with enhanced dominant-negative activity for the blockade of human prolactin signalling. 1507 46

The importance of prolactin (PRL) in physiological proliferation and differentiation of the mammary gland, together with high levels of PRL receptors in breast tumors, the association of circulating PRL with incidence of breast cancer, and the recognition of locally produced PRL, point to the need for greater understanding of PRL actions in mammary disease. Although PRL has been shown to activate multiple kinase cascades in various target cells, relatively little is known of its signaling pathways in the mammary gland apart from the Janus kinase 2/ signal transducer and activator of transcription 5 pathway, particularly in tumor cells. Another potential effector is activating protein-1 (AP-1), a transcription complex that regulates processes essential for neoplastic progression, including proliferation, survival and invasion. We demonstrate that PRL activates AP-1 in MCF-7 cells, detectable at 4 h and sustained for at least 24 h. Although Janus kinase 2 and ERK1/2 are the primary mediators of PRL-induced signals, c-Src, phosphatidylinositol 3'-kinase, protein kinase C, and other MAPKs contribute to maximal activity. PRL activation of these pathways leads to increased c-Jun protein and phosphorylation, JunB protein, and phosphorylation of c-Fos, elevating the levels of AP-1 complexes able to bind DNA. These active AP-1 dimers may direct expression of multiple target genes, mediating some of PRL's actions in mammary disease.
Mol Endocrinol 2004 Dec
PMID:Multiple kinase cascades mediate prolactin signals to activating protein-1 in breast cancer cells. 1531 52

The GH receptor (GHR) mediates metabolic and somatogenic actions of GH. Its extracellular domain (ECD; residues 1-246) has two subdomains, each with seven beta strands organized into two antiparallel beta sheets, connected by a short hinge region. Most of the ECD residues involved in GH binding reside in subdomain 1, whereas subdomain 2 harbors a dimerization interface between GHR dimers that alters conformation in response to GH. A regulated GHR metalloprotease cleavage site is in the membrane-proximal stem region of subdomain 2. We have identified a monoclonal anti-ECD antibody, anti-GHR(ext-mAb), which recognizes the rabbit and human GHRs by immunoprecipitation, but less so after GH treatment. By immunoblotting and immunoprecipitation, anti-GHR(ext-mAb) recognized a glutathione-S-transferase (GST) fusion incorporating subdomain 2, but not one including subdomain 1. In transient transfection experiments, anti-GHR(ext-mAb) failed to recognize by immunoprecipitation a previously characterized dimerization interface mutant GHR that is incompetent for signaling. In signaling experiments, brief pretreatment of GH-responsive human fibrosarcoma cells with anti-GHR(ext-mAb) dramatically inhibited GH-induced Janus kinase 2 and signal transducer and activator of transcription 5 tyrosine phosphorylation and prevented GH-induced GHR disulfide linkage (a reflection of GH-induced conformational changes). In contrast, anti-GHR(ext-mAb) only partially inhibited radiolabeled GH binding, suggesting its effects on signaling were not simply via inhibition of binding. Furthermore, anti-GHR(ext-mAb) prevented phorbol ester-stimulated GHR proteolysis, but GHR cleavage site mutants were normally recognized by the antibody, indicating that the stem region cleavage site is not a direct epitope. A Fab fragment of anti-GHR(ext-mAb) inhibited GH-induced GHR disulfide linkage and signaling, as well as phorbol ester-induced GHR proteolysis, in a fashion similar to the intact antibody. Thus, our findings suggest that anti-GHR(ext-mAb) has promise as a GH antagonist and as a tool in studies of conformational changes required for GHR activation.
Mol Endocrinol 2004 Dec
PMID:A conformationally sensitive GHR [growth hormone (GH) receptor] antibody: impact on GH signaling and GHR proteolysis. 1534 46

Cell cycle arrest by FoxO transcription factors involves transcriptional repression of cyclin D, although the exact mechanism remains unclear. In this study, we used the BCR-ABL-expressing cell line BV173 as a model system to investigate the mechanisms whereby FoxO3a regulates cyclin D2 expression. Inhibition of BCR-ABL by STI571 results in down-regulation of cyclin D2 expression, activation of FoxO3a activity, and up-regulation of BCL6 expression. Using reporter gene assays, we demonstrate that STI571, FoxO3a, and BCL6 can repress cyclin D2 transcription through a STAT5/BCL6 site located within the cyclin D2 promoter. We propose that BCR-ABL inhibition leads to FoxO3a activation, which in turn induces the expression of BCL6, culminating in the repression of cyclin D2 transcription through this STAT5/BCL6 site. This process was verified by mobility shift and chromatin immunoprecipitation analyses. We find that conditional activation of FoxO3a leads to accumulation of BCL6 and down-regulation of cyclin D2 at protein and mRNA levels. Furthermore, silencing of FoxO3a and BCL6 in BCR-ABL-expressing cells abolishes STI571-mediated effects on cyclin D2. This report establishes the signaling events whereby BCR-ABL signals are relayed to cyclin D2 to mediate cell cycle progression and defines a potential mechanism by which FoxO proteins regulate cyclin D2 expression.
Mol Cell Biol 2004 Nov
PMID:FoxO3a and BCR-ABL regulate cyclin D2 transcription through a STAT5/BCL6-dependent mechanism. 1550 6

Here we examined the role of interferon (IFN)-gamma in regulating the Sonic hedgehog (Shh) pathway and cerebellar development in bigenic mice with temporal control of IFN-gamma gene expression driven by a tetracycline-controllable promoter. In IFN-gamma-expressing but not age-matched non-IFN-gamma-expressing bigenic or control mice, development of the cerebellum was severely affected with the persistence and extensive proliferation of the external granule neuron layer (EGL) and infiltration with modest numbers of T-lymphocytes. Following induction of IFN-gamma transgene expression, both total and tyrosine-phosphorylated signal transducer and activator of transcription (STAT)1 (the major transcriptional factor for IFN-gamma), phosphorylated STAT3 and STAT5, and expression of a number of IFN-gamma-regulated genes were significantly increased in cerebellum. In the cerebellum from IFN-gamma-expressing but not age-matched non-IFN-gamma-expressing mice, the level of Shh and Gli-1 but not Patched (Ptch) 1 RNA was increased as was the 19-kDa signaling product of the Shh precursor protein. In situ localization studies revealed ectopic expression of the Shh gene by the granule neurons. We conclude that IFN-gamma directly affects the proliferation and fate of EGL neurons in the cerebellum by activating the Shh pathway and stimulating an autocrine growth response by these cells.
Mol Cell Neurosci 2004 Dec
PMID:Inducible production of interferon-gamma in the developing brain causes cerebellar dysplasia with activation of the Sonic hedgehog pathway. 1555 26

The growth hormone receptor (GHR) is a critical regulator of postnatal growth and metabolism. However, the GHR signaling domains and pathways that regulate these processes in vivo are not defined. We report the first knock-in mouse models with deletions of specific domains of the receptor that are required for its in vivo actions. Mice expressing truncations at residue m569 (plus Y539/545-F) and at residue m391 displayed a progressive impairment of postnatal growth with receptor truncation. Moreover, after 4 months of age, marked male obesity was observed in both mutant 569 and mutant 391 and was associated with hyperglycemia. Both mutants activated hepatic JAK2 and ERK2, whereas STAT5 phosphorylation was substantially decreased for mutant 569 and absent from mutant 391, correlating with loss of IGF-1 expression and reduction in growth. Microarray analysis of these and GHR(-/-) mice demonstrated that particular signaling domains are responsible for the regulation of different target genes and revealed novel actions of growth hormone. These mice represent the first step in delineating the domains of the GHR regulating body growth and composition and the transcripts associated with these domains.
Mol Cell Biol 2005 Jan
PMID:In vivo analysis of growth hormone receptor signaling domains and their associated transcripts. 1560 31


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