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A Sotiropoulos

Publications and source records attributed to A Sotiropoulos.

At least 19 recordsLinked to original sources
PubMed1996

Deletion of the carboxyl-terminal transactivation domain of MGF-Stat5 results in sustained DNA binding and a dominant negative phenotype.

The Stat (signal transducer and activator of transcription) factors transmit cytokine, growth factor, and hormone responses. Seven members of the Stat gene family are known. MGF-Stat5a has been discovered as a mediator of the prolactin response in mammary epithelial cells. Two closely related variants of Stat5, Stat5a and Stat5b, are encoded by distinct genes. We examined the functional properties of the carboxyl termini of these molecules. Wild-type Stat5a (794 amino acids) and the carboxyl-terminal deletion mutant Stat5a delta 772 supported prolactin-induced transcription of a beta-casein promoter-reporter construct in COS7 cells; Stat5a delta 750 did not. Upon prolactin activation, tyrosine phosphorylation and the specificity of DNA binding were indistinguishable among the three Stat5a variants. Tyrosine dephosphorylation and the downregulation of the DNA-binding activity were delayed in the Stat5a delta 750 mutant. The carboxyl-terminal transactivation domain of Stat5a, amino acids 722 to 794, can be conferred to the DNA-binding domain of the yeast transcription factor GAL4. Coexpression of Stat5a or Stat5b and of the carboxyl-terminal deletion mutants resulted in the suppression of transcriptional induction in COS or Ba/F3 cells. We propose that Stat5a delta 750 and Stat5b delta 754 are lacking functional transactivation domains and exert their dominant negative effects by blocking the DNA-binding site in Stat5-responsive gene promoters.

Amino Acid Sequence↗
PubMed1996

A novel growth hormone response element unrelated to STAT (signal transducer and activator of transcription)-binding sites is a bifunctional enhancer.

Regulation of gene expression by GH has so far been shown to be mediated by a few cis-acting elements, most of which are signal transducer and activator of transcription (STAT)-binding sites. Here we have characterized a novel GH-response element present in the promoter of rat serine protease inhibitor (spi) genes. It consists of a 13 nucleotide-long GAGA box containing two GAGGAG repeats separated by a G, structurally unrelated to STAT-binding sites. In hepatocytes, the spi GAGA box behaves as a position-dependent bifunctional enhancer controlling basal and GH-dependent transcription. In addition, spi GAGA box oligonucleotides inhibit cell-free transcription driven by GAGA box-containing as well as GAGA box-less promoters, suggesting that the spi GAGA box interacts directly or indirectly with component(s) of the basic transcriptional machinery. Mobility shift assays showed that this GAGA box is specifically recognized by nuclear factors that are unrelated to previously characterized proteins binding to purine-rich elements or to GH-activated STATs. Finally, experiments performed with cells expressing wild type, truncated, or mutated forms of the GH receptor indicate that protein kinase Janus kinase 2 is involved in the GH-dependent activation of the spi GAGA box. These studies reveal the existence of an as yet unidentified Janus kinase-2-dependent, STAT-independent pathway in GH activation of gene expression.

Animals↗
PubMed1996

Differential activation of Stat3 and Stat5 by distinct regions of the growth hormone receptor.

The GH receptor (GHR) is a member of the cytokine receptor superfamily; its signaling involves the activation of Janus tyrosine kinases (JAK2) and Stat (signal transducers and activators of transcription) transcription factors. Using truncated and tyrosine mutants of the receptor, we show that different receptor domains are essential for the activation of Stat3 and Stat5. GH-dependent phosphorylation of JAK2, Stat3, and Stat5, as well as transactivation studies with reporter genes containing Stat3 and Stat5 DNA-binding elements, was performed in cells expressing the various GHR mutants. The membrane-proximal region of the receptor necessary for JAK2 activation is sufficient for Stat3 activation. In contrast, C-terminal tyrosine residues of GHR are absolutely required for Stat5 activation. The same residues are also involved in the regulation of JAK2 dephosphorylation, possibly through the activation of a phosphatase. Using in vitro experiments with glutathione-S-transferase fusion proteins, we demonstrate that the SH2 domain of Stat5 binds to the carboxy-terminal tyrosine-phosphorylated residues of GHR. Our results show that a cytokine receptor can mediate differently the activation of distinct Stat proteins that could be involved in cytokine-specific effects.

Animals↗
PubMed1995

The membrane proximal region of the cytoplasmic domain of the growth hormone receptor is involved in the activation of Stat 3.

Growth hormone receptor (GHR) signaling involves activation of the Janus Kinases (Jak) and of Stat proteins (signal transducers and activators of transcription). Growth hormone (GH) induces transcriptional activation of c-fos gene and the c-sis inducible element (SIE) of its promoter was shown to bind the Stat proteins. Using cells co-transfected with GHR and Stat 3 expression vectors, we directly demonstrate that GH induces tyrosine phosphorylation of Stat 3 and its binding to the SIE probe. We showed, using mutant forms of GHR, that only the cytoplasmic membrane proximal domain of the receptor, including a conserved proline rich region (box 1), is required for this effect.

Amino Acid Sequence↗
PubMed1995

[Growth hormone receptor. Structure and signal transduction].

The growth hormone receptor (GHR) belongs to the family of the prolactin and cytokine receptors. The full length receptor in a 620 amino acid protein with a unique transmembrane domain. The GH binding protein (GHBP) corresponds to the extracellular domain of the membrane GHR. In all human tissues tested, one form of 4.5 kb for the GHR mRNA was detected, suggesting that GHBP is generated through proteolytic cleavage of the membrane receptor. The three dimensional crystollographic structure of GHBP-hGH complex has identified a homodimer made of two receptor molecules and one molecule of hGH. Hormone-induced receptor dimerisation appears to be crucial for signal transduction. Functional tests using the GH effect on transcription of genes, such as SP12.1 and beta lactoglobulin, have been developed to define the sequences of the receptor which are important for signaling. A proline-rich juxtamembranous sequence, called Box 1, is important for GH effects on gene transcription, on MAP kinase activity, on cell proliferation, and on JAK2 activation. JAK2 has been identified to be a GHR-associated tyrosine kinase. The first 46 amino acids of the cytoplasmic domain are necessary for JAK2 and MAP kinase activation whereas a C-Ter sequence is necessary for the transcriptional effect. Substrates for JAK2, other than the receptor itself, have to be identified. Good candidates are the transcription factors STAT.

Humans↗
PubMed1994

The GH receptor and signal transduction.

The primary structure of the growth hormone (GH) receptor in rabbits and humans determined by complementary DNA cloning revealed a single membrane-spanning protein of approximately 620 amino acids. A binding protein (bp) specific for GH has been identified in the serum of a number of species. In rabbits and man, a single 4.5-kb transcript has been identified that encodes the full-length receptor. In rats and mice, however, a smaller transcript produced by alternative splicing has been reported which is specific for the GHbp. Recently, the X-ray crystallographic structure of GH and its receptor have clearly shown the formation of an unusual homodimer, consisting of one molecule of GH and two molecules of hGHbp. Formation of the GH dimer is a necessary prerequisite for biological activity. The transcriptional activity of wild-type and mutant forms of GH receptor has been determined by co-transfecting the promoter of a GH-responsive gene, coupled to CAT along with the receptor cDNA. A 25-amino acid region near the transmembrane domain has been shown to be important for functional activity, although 8 amino acids (known as Box 1), rich in prolines, is essential. Alanine scanning mutagenesis has revealed that individual substitution of each residue is without effect, while the replacement of the last 2 or all 4 of the prolines abolishes activity. Finally, GH has been shown to induce rapid tyrosine phosphorylation of several proteins in cells expressing the receptor, one of which has recently been identified as the kinase JAK2 and another as MAP kinase.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Distinct cytoplasmic regions of the growth hormone receptor are required for activation of JAK2, mitogen-activated protein kinase, and transcription.

The GH receptor (GHR) is a member of the cytokine/hematopoietic growth factor family, and protein tyrosine phosphorylation has been implicated in the signaling cascade of these receptors. It was recently shown that the tyrosine kinase JAK2 is associated with the GHR. GH induces the activation of JAK2, which phosphorylates itself and the receptor. Mitogen-activated protein (MAP) kinase activation and transcriptional stimulation of specific genes, such as Spi 2.1, have also been reported to be induced by GH. To identify functionally important regions in the cytoplasmic domain of the GHR, we compared the actions of the wild-type receptor, two truncated mutants, and one internal deletion mutant (similar to the intermediate Nb2 form of the PRL receptor) in transfectants of the Chinese hamster ovary cell line. A region of 46 amino acids adjacent to the membrane was found to be sufficient for activation of both JAK2 and MAP kinases. This region contains a proline-rich sequence (box 1) conserved in the cytokine receptor family that is important for signal transduction. For transcriptional activity, the C-terminal region of the GHR is required, and we found that the last 80 terminal residues contain sequences allowing activation of the Spi 2.1 promoter. Tyrosine phosphorylation of the receptor also requires the C-terminal portion of the GHR cytoplasmic domain, and we found that GHR tyrosine phosphorylation appears to be linked to activation of the Spi 2.1 transcription pathway. Thus, the GHR could be composed of at least 2 functional regions: the 46 proximal amino acids required for activation of JAK2 and sufficient to stimulate the MAP kinase pathway, and an additional carboxy-terminal region necessary for transcriptional activation.

Animals↗
PubMed1994

Receptor domains involved in signal transduction of prolactin and growth hormone.

Prolactin (PRL) and growth hormone (GH) receptors are members of a superfamily that include receptors for a number of cytokines. GH and its receptor form an unusual homodimer consisting of one molecule of GH and two molecules of receptor. A similar homodimer of the PRL receptor is probably required for biological effects to be seen. Using specific assays to measure the functional activity of PRL and GH receptors, a 25 amino acid juxtamembrane region has been identified as essential but not sufficient for normal action. More detailed studies have limited the region to eight amino acids, rich in prolines, that is highly conserved in many members of the receptor superfamily. Finally, GH and PRL have been shown to induce the rapid tyrosine phosphorylation of an associated kinase, Janus kinase 2, and of the receptor itself.

Animals↗
PubMed1993

Emphysematous pyelonephritis: a case report and review of the literature.

Emphysematous pyelonephritis is a rare and life-threatening suppurative infection of renal parenchymal and perirenal tissues, characterized by spontaneous gas production. Although uncommon (76 cases in the literature), it occurs almost exclusively in diabetic patients (87% of the cases). We describe a recent case of a diabetic woman with emphysematous pyelonephritis due to E. coli, successfully managed with unilateral nephrectomy. Symptoms, diagnostic approach and management are discussed and related to the previously reported series.

Aged↗
PubMed1993

Evidence for generation of the growth hormone-binding protein through proteolysis of the growth hormone membrane receptor.

The growth hormone-binding protein (GHBP) which circulates in plasma is a soluble short form of the membrane growth hormone receptor (GHR). In rats and mice, GHR and GHBP originate from two alternatively spliced mRNAs (4.5 and 1.2 kb). In human and rabbit tissues, a single predominant mRNA of 4.5 kb was detected and it was hypothesized that GHBP could be produced by proteolytic cleavage of the GHR. Using gel filtration and HPLC, we have detected a high level of GH binding activity in media of cells transfected with rabbit GHR cDNA. The [125I]hGH-GHBP complex eluted at the same time as the plasma complex and both the binding affinity and specificity of the BP were comparable to that of rabbit plasma. Immunoprecipitation experiments and Western blots confirmed that GHBP in the media of transfected cells was a 55 kDa protein related to the extracellular domain of the GHR. In contrast, no BP was detected in the media of cells transfected with the cDNA encoding the rat GHR. These results strongly suggest that, in rabbit and probably in man, the GHBP could, at least in part, be produced by proteolytic cleavage of the GHR.

Animals↗
PubMed1976

Management of urinary incontinence with electronic stimulation: observations and results.

The evolution in the management of urinary incontinence with electronic stimulation of the pelvic floor is reviewed. The effect of stimulation is analyzed. Our methods of candidate screening and the contraindications to treatment are discussed. Forty patients were treated for 2 to 15 months. Sixteen patients were post-prostatectomy, 4 had stress incontinence, 4 had upper motor neuron lesions, 1 was incontinent after repair of a rectovesical fistula and 15 were post-bladder exstrophy closure. The success rate in the first group was 45.4 per cent, in the second group 100 per cent, in the third group 50 per cent, in the fourth group 100 per cent and in the fifth group 27.2 per cent. In view of the method having been tried on cases resistant to other forms of treatment the results were encouraging. The most satisfying results were in the post-exstrophy group in which no response was expected.

Adolescent↗
PubMed1976

Long-term assessment of genital reconstruction in female pseudohermaphrodites.

The cases involving 32 women who had undergone early revision of ambiguous genitalia were reviewed 5 to 22 years postoperatively. Seven clitoridectomies, 25 clitoral recessions, 17 Y-V introitoplasties and 10 midline episiotomies were performed. There were 16 patients available for followup. The results of clitoral recessions were cosmetically and functionally satisfactory. Introital revisions done before puberty all required further revision and suggested that vaginoplasty should be deferred until after puberty.

Adolescent↗