Specificity of transcription enhancement via the STAT responsive element in the serine protease inhibitor 2.1 promoter

Section: Methodsmentioning

confidence: 99%

Identification of a Distal STAT5-binding DNA Region That May Mediate Growth Hormone Regulation of Insulin-like Growth Factor-I Gene Expression

Wang

Jiang

2005

“…To test the transcriptional activity of STAT5b mutants, we used the MEFs from STAT5a/5b knockout mice and the Spi 2.1-containing reporter plasmid that is specific for STAT5 (21) and kindly provided by Timothy J. J. Wood (Dept.…”

Section: Methodsmentioning

confidence: 99%

Novel Activation of STAT5b in Response to Epidermal Growth Factor

Kloth¹,

Catling²,

Silva³

2002

Of the seven signal transducers and activators of transcription that have been identified, STATs 1, 3, and 5a/5b can be activated not only by a multitude of cytokines but also by some growth factors. The data presented here demonstrate that, in contrast to activation by the cytokine, growth hormone (GH), the activation of STAT5b by the growth factor, epidermal growth factor (EGF), requires overexpression of the EGF receptor (EGFR The signal transducers and activators of transcription (STATs) 1 transmit signals from cytokine receptors at the membrane of the cell to the nucleus. Seven STAT proteins have been cloned and four of these (STATs 1, 3, 5a, and 5b) can be activated by a number of different cytokines (1-3). Similar to growth factor receptors, cytokine receptors are single transmembrane receptors that are activated by ligand-induced dimerization. However, the cytokine receptors do not contain a tyrosine kinase activity; rather they recruit one or more of a family of intracellular tyrosine kinases known as JAK kinases (JAKs 1, 2, 3, and tyk2) to the cytokine receptor complex. Activation of these kinases results in the tyrosine phosphorylation of one or more of the recruited STAT proteins (2). Some growth factor receptors have also been shown to activate the tyrosine phosphorylation of STAT proteins (4). Platelet-derived growth factor treatment results in the activation of STAT1 and STAT3, and EGF can activate STATs 1, 3, and 5 (5-8). Although JAK kinases are activated after growth factor stimulation, they are not required for growth factorstimulated tyrosine phosphorylation of STAT1 or STAT3 (4). In response to cytokine treatment, STAT proteins are activated by the phosphorylation of a single tyrosine residue at the C terminus of the molecule. Tyrosine phosphorylation of the STATs results in STAT dimerization through phosphotyrosine-SH2 domain interactions. Dimerization leads to nuclear translocation and binding of STAT dimers to consensus elements upstream of regulated genes. There is evidence that STATs 1, 3, and 5 are also serine-phosphorylated in their C-terminal transactivation domain resulting in maximal transcriptional activation (9). The importance of this C-terminal domain is evidenced by the fact that its truncation results in dominant negative STAT proteins that are able to inhibit the transcriptional activity of the wild type STAT proteins (2). Therefore, these C-terminal truncated proteins provide a direct means of inhibiting the biological function of wild type STATs at the cellular level. The biological actions of STAT proteins are diverse and involve a number of cellular processes, including proliferation, differentiation, and apoptosis (10).In our previous work on growth hormone (GH) receptor signaling, a member of the cytokine receptor superfamily, we identified and cloned the human forms of STAT5a and STAT5b, encoded by two separate genes that result in two highly homologous proteins (94% homology at the amino acid level) (11). Cytokine activation results in the phosphorylation of tyrosi...

“…11). Human GH is also a ligand for the PRL receptor (44), and therefore an activation of the PRL receptor and a STAT5-mediated transcriptional response to hGH via the PRL receptor can be expected (27). STAT5-mediated transcription, stimulated specifically through the PRL receptor either with hGH or with ovine PRL, was also enhanced in the presence of NLS-GHBP to a similar extent as the enhancement of STAT5-mediated transcription by NLS-GHBP through the GH receptor.…”

Section: Nls-ghbp Enhances Stat5-mediated Transcription Stimulated Bymentioning

confidence: 93%

“…The ECL kit was obtained from Amersham Biosciences. The GH, PRL, and EPO receptor cDNAs used here were as described previously (27). Transfection reagent DOTAP, poly(dI/dC) and the DNA 3Ј-end labeling kit were purchased from Roche Diagnostics.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

The Growth Hormone-binding Protein Is a Location-dependent Cytokine Receptor Transcriptional Enhancer

Graichen

Sandstedt²,

Goh

et al. 2003

In the rat, a growth hormone-binding protein (GHBP) exists that is derived from the growth hormone (GH) receptor gene by an alternative mRNA splicing mechanism such that the transmembrane and intracellular domains of the GH receptor are replaced by a hydrophilic carboxyl terminus. In isolation, the GHBP is inactive, although it does compete with the receptor for ligand binding in the extracellular space and therefore inhibits the cellular response to GH. The GHBP is also located intracellularly and is translocated to the nucleus upon ligand stimulation. We show here that endogenously produced GHBP, in contrast to exogenous GHBP, was able to enhance the STAT5-mediated transcriptional response to GH. Interestingly, when the GHBP was targeted constitutively to the nucleus by the addition of the nuclear localization sequence of the SV40 large T antigen, greater enhancement of STAT5-mediated transcription was obtained. The transcriptional enhancement did not require GH per se and was not specific to the GH receptor, since similar enhancement of STAT5-mediated transcription by nuclear localized GHBP was obtained with specific ligand stimulation of both prolactin and erythropoietin receptors. Thus, the GHBP exerts divergent effects on STAT5-mediated transcription depending on its cellular location. The use of a soluble cytokine receptor as a location-dependent transcriptional enhancer and the ligand-independent involvement of the extracellular domain of a polypeptide ligand receptor in intracellular signal transduction provide additional novel mechanisms of transcriptional control. Growth hormone (GH)1 is the major regulator of postnatal body growth and initiates its biological actions, including the induction of a number of RNA species in mammalian tissues, by interaction with a specific membrane-bound receptor (1, 2).The GH receptor was the first cloned member of the now extensive cytokine receptor superfamily, which includes the receptors for prolactin (PRL), erythropoietin (EPO), granulocyte colony-stimulating factor, granulocyte-macrophage colony stimulating factor, ciliary neutrophic factor, thrombopoietin, leptin, cardiotrophin I, and the ␤-chain of interleukin (IL)-2 through IL-7, IL-9, and IL-11 to IL-13 (3). Most receptors of the cytokine receptor superfamily exist in a soluble and transmembrane form (4 -7). The function of the transmembrane forms is well documented and includes signal transduction predominantly but not exclusively through the JAK-STAT pathway, resulting in gene transcription (8, 9). The role of the soluble cytokine receptors, with the notable exception of the soluble forms of the IL-6 and ciliary neurotropitir factor (CNTF) receptors (10, 11), appears confined to ligand sequestration in the extracellular space with a consequent impairment of the cellular response to exogenous ligand (4).A soluble rat growth hormone-binding protein (GHBP) exists that is derived from the GH receptor gene by an alternative mRNA splicing mechanism such that the transmembrane and intracellular domains of the GH r...