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

The number and coupling efficiency of beta-adrenoceptors in liver membranes and intact hepatocytes of lactating and non-lactating female rats were compared to assess whether or not alterations in this signalling system could contribute towards the changed pattern of hepatic metabolism during lactation. In view of the different adaptations of hepatic metabolism to lactation in ruminants, the adrenergic receptor profile of sheep liver membranes was also determined. Post-receptor responses at two stages 'down-stream' of cyclic AMP generation were also evaluated in rat hepatocytes in response to the beta-adrenergic agonist isoprenaline. No changes in the number of affinity of hepatic beta-adrenoceptors were found in sheep or rats when lactating and non-lactating individuals were compared. Sheep liver was found to have a much greater concentration of beta-adrenoceptors than rat liver, and a much higher ratio of beta:alpha 1. The sensitivity and responsiveness of cyclic AMP generation in response to isoprenaline were similar in hepatocytes prepared from lactating and non-lactating rats, although the response to saturating concentrations of glucagon was diminished in hepatocytes from lactating rats. The activity ratio of cyclic AMP-dependent protein kinase (PK-A) also reacted similarly (in respect of both responsiveness and sensitivity) to isoprenaline in these two groups of hepatocytes. Contrastingly, the sensitivity of rat hepatocyte phosphorylase activity to beta-adrenergic stimulation was greatly diminished during lactation.
Mol Cell Biochem 1992 Nov 04
PMID:Effects of lactation on the regulation of hepatic metabolism in the rat and sheep: adrenergic receptors and cyclic AMP responses. 133 22

Pituitary lactotroph cell function and PRL gene expression are highly regulated by the cAMP-protein kinase-A (PKA) pathway. To further our understanding of the molecular mechanisms by which cAMP/PKA regulates rat (r) PRL promoter activity and to determine whether cAMP regulation is cell type specific, we 1) transected intact (-425), internal and 5'-deletion, and site-specific mutants of the rPRL promoter ligated to the firefly luciferase reporter gene into both pituitary and nonpituitary cell lines; and 2) assessed the role of the cAMP-cAMP response element-binding protein (CREB) pathway in GH4 rat pituitary cells. The data show that deleting the rPRL promoter from -425 to -116 did not abolish cAMP regulation, implying that proximal elements, such as the basal transcription element (-112/-80) or the pituitary-specific footprint (FP) I (-67/-45), mediate the cAMP response. However, nucleotide changes within FP I or FP II (-130/-120) did not alter the rPRL promoter response to 1 microM forskolin (FSK), despite the 77% and 26% reductions in basal rPRL promoter activity caused by these mutations, respectively. Furthermore, internal deletion of either the basal transcription element of FP I element also failed to affect cAMP regulation of the rPRL promoter, again despite the 90% and 93% reductions in basal promoter activity by these deletions, respectively. Since these internal deletion constructs otherwise contain rPRL promoter sequences from -425 to +73, including the up-stream pituitary-specific FPs III and IV, the data suggest that any one of these cell-specific elements is capable of imparting cAMP regulation to the proximal rPRL promoter. To directly test the implication that the cAMP response of the rPRL promoter is restricted to the pituitary-specific cell type, we took advantage of a 5'-deletion mutant truncated at position -116 and a FP II site-specific mutant, since constructs containing these rPRL promoters are active in nonpituitary cells. Despite the 6.6- and 18.5-fold stimulations over wild-type rPRL promoter activity in nonpituitary cells, respectively, these mutations remained completely unresponsive to FSK treatment. To document that the cAMP-CREB pathway was functional in GC/GH4 rat pituitary cells, CREB was affinity purified from GC rat pituitary cells, and DNase-I protection studies showed that it does not bind to the proximal rPRL promoter. Also, the human glycoprotein alpha-subunit promoter was induced 10-fold by FSK in GH4 rat pituitary cells.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Endocrinol 1992 Dec
PMID:Cyclic adenosine 3',5'-monophosphate activation of the rat prolactin promoter is restricted to the pituitary-specific cell type. 133 42

We have used myelin basic protein immobilized in sodium dodecyl sulfate-polyacrylamide gels to identify protein kinases after gel electrophoresis, followed by protein kinase reactions. This technique has permitted us to detect three protein kinases in serum-deprived cells transformed by p60src. On induction of cellular transformation by a temperature-sensitive v-src, a p87 protein kinase is activated within 30 min and remains activated in fully transformed cells. The p63 protein kinase is not fully activated until 24 h but remains activated in transformed cells. The commonly studied p42MBPK is rapidly activated within 30 min, and its kinase activity decreases significantly by 24 h, when the p63 enzyme is fully activated. The p42MBPK, as well as the p63 and p87 enzymes, are stimulated by transforming p60c-src mutants but not normal c-src or nonmyristylated p60c-src. In addition, the kinase activity of p63 enzyme, but not of p42MBPK, can be induced in okadaic acid-treated chicken embryo fibroblasts, indicating that phosphatase 2A and/or phosphatase 1 may be involved in the regulation of its activity. Additional data indicate that either p42MBPK or p63 activity correlates with the stimulation of the protein kinase p90RSK. Thus, there may be two independent pathways leading to the activation of the RSK gene product.
Mol Biol Cell 1992 Dec
PMID:Activation of protein serine/threonine kinases p42, p63, and p87 in Rous sarcoma virus-transformed cells: signal transduction/transformation-dependent MBP kinases. 133 88

The phosphoenolpyruvate carboxykinase (PEPCK) gene is highly expressed in cultured rat hepatoma cells, but extinguished in hepatoma x fibroblast hybrids. Extinction of PEPCK gene expression in hybrids is a polygenic process that involves several fibroblast loci, only one of which (tissue-specific extinguisher-1, TSE1) has been characterized to date. To identify sequence elements of the PEPCK gene that are involved both in TSE1-mediated extinction and in TSE1-independent processes, we assayed expression of chimeric PEPCK transgenes in transiently and stably transfected hybrid cells. We report that TSE1 responsiveness mapped to the PEPCK CRE (cAMP response element), as shown previously for the tyrosine aminotransferase gene. This was expected from the recent identification of the TSE1 gene product as a regulatory subunit of protein kinase A. However, none of the transgenes we assayed were responsive to TSE1-independent extinction mechanisms, suggesting that these controls require DNA sequences and/or chromatin structures that were not present in the transfected reporters. The implications of these findings are discussed.
Somat Cell Mol Genet 1992 Nov
PMID:Multiple elements regulate phosphoenolpyruvate carboxykinase gene expression in hepatoma hybrid cells. 133 26

Transcription of the rat serine dehydratase (SDH) gene is induced by glucagon, mediated by the action of cAMP. To identify the nucleotide sequences in the SDH gene responsible for this regulation, we constructed chimeric genes containing different portions of the 5' flanking region of the rat SDH gene fused to the structural sequence encoding the bacterial reporter enzyme, chloramphenicol acetyltransferase (CAT). The transcriptional activities of the fusion genes introduced into the rat hepatoma cell line 7AD-7 were assayed by measuring CAT activity in the cell lysates. Chlorophenylthio-cyclic AMP (CPT-cAMP), a potent protein kinase A activating agent, stimulated the expression of SDH-CAT fusion genes, and these inductions could be enhanced further by the addition of dexamethasone, although the glucocorticoid alone had no effect on CAT activity. Deletion analysis demonstrated that an 80 bp region located approximately 3.5 kb upstream from the transcription initiation site of the rat SDH gene was responsible for stimulation of transcription by CPT-cAMP, whereas the 120 bp region immediately upstream of the cAMP responsive element (CRE)-containing sequences is essential for the enhancement of CPT-cAMP induction by the glucocorticoid.
Mol Cell Endocrinol 1992 Dec
PMID:Identification of regions in the rat serine dehydratase gene responsible for regulation by cyclic AMP alone and in the presence of glucocorticoids. 133 28

The cyclic AMP (cAMP) response elements (CREs) of the somatostatin and vasoactive intestinal peptide (VIP) promoters contain binding sites for CRE-binding protein (CREB) that are essential for cAMP-regulated transcription. Using F9 embryonal carcinoma cells, we show that the somatostatin and VIP promoters exhibit a differentiation-dependent cAMP response, demonstrating that these promoters are regulated by transcription factors that become active during differentiation. Lack of cAMP responsiveness of the somatostatin promoter in undifferentiated cells is not due to the absence of known positive-acting factors (the catalytic subunit of protein kinase A [cPKA] and CREB) or a general inhibition of protein kinase A activity. Since overexpression of exogenous cPKA and CREB is sufficient to activate the somatostatin promoter in undifferentiated cells, these findings suggest that a negative factor(s) represses endogenous cPKA and CREB. In contrast to their effects on somatostatin, exogenous CREB and cPKA do not activate the VIP promoter. Thus, despite coregulation during differentiation and the ability to bind CREB, the somatostatin and VIP promoters are not coordinately activated by CREB in undifferentiated F9 cells.
Mol Cell Biol 1992 Mar
PMID:Cyclic AMP response element-binding protein and the catalytic subunit of protein kinase A are present in F9 embryonal carcinoma cells but are unable to activate the somatostatin promoter. 134 42

We have studied the requirement for an intact cAMP-dependent protein kinase (PKA) system to regulate cAMP-mediated gene transcription in Chinese hamster ovary (CHO) cells. Wild-type CHO cells and mutant CHO cell lines selected for their resistance to the growth inhibitory effect of 8-Br-cAMP and defective in their PKA system were transiently transfected with reporter plasmids containing 2.5 and 3.0 kb of the 5'-flanking sequence of the rat tyrosine aminotransferase (TAT) gene promoter. This segment of DNA contains no CRE-like sequences, yet wild-type transfectants exhibited a specific increase in TAT promoter activity following growth in medium containing 8-Br-cAMP. In CHO cell lines defective in their PKA, the transfected TAT promoter failed to respond to cAMP treatment. We conclude that an intact PKA system is necessary for the cAMP-mediated increase in TAT promoter activity in CHO cells and that there is no requirement for a CRE to see this effect.
Somat Cell Mol Genet 1992 Mar
PMID:Ablation of stimulation of a cAMP-responsive promoter in CHO cell lines defective in their cAMP-dependent protein kinase system. 134 45

We have studied the effect of protein kinase-C activation on the regulation of CRH gene expression in the human hepatoma cell line NPLC/PRF/5 (NPLC), the only cell line known to express the endogenous CRH gene. Incubation of NPLC cells with 100 nM 12-O-tetradecanoyl phorbol 13-acetate (TPA), a phorbol ester that activates protein kinase-C, resulted in a rapid (1-h) and prolonged (72-h) increase in CRH mRNA levels, with the maximum increase of 16-fold observed at 24 h. In addition, TPA treatment increased the size of CRH mRNA by approximately 100 nucleotides. This size increase, which was blocked by protein synthesis inhibitors, occurred within 1 h of TPA addition and lasted at least 8 h, with a return toward the baseline size by 24 h. Structural analysis of CRH mRNA revealed two poly(A) addition sites and, as found in human placenta, multiple transcription start sites. The increase in CRH mRNA size was not due to changes in the sites of either transcription initiation or poly(A) addition, but, rather, to a 3-fold increase in the length of the poly(A) tail itself. The ability of TPA to increase CRH mRNA levels in NPLC cells suggests that the protein kinase-C second messenger pathway may be involved in the physiological regulation of CRH gene expression. Increases in CRH mRNA poly(A) tail length potentially may influence CRH mRNA stability or translatability and, thus, may represent a general mechanism by which the protein kinase-C pathway can influence gene expression.
Mol Endocrinol 1992 Mar
PMID:Protein kinase-C activation increases the quantity and poly(A) tail length of corticotropin-releasing hormone messenger RNA in NPLC cells. 135 54

The transactivation of genes through the cAMP-regulated enhancer (CRE) is proposed to occur by the binding and phosphorylation of the transcription factor CREB (CRE-binding protein). Originally believed to be a single protein, more than 10 different CREB proteins have been cloned. The contributions of each of these factors to gene regulation have yet to be determined unambiguously. We have isolated a CREB cDNA that contains a mutation of a single amino acid in the DNA-binding domain. In gel shift assays, this mutant, designated KCREB, is unable to bind to the somatostatin (SS) CRE. In addition, KCREB acts as a dominant repressor of the wild-type factor, blocking the ability of wild-type CREB to bind to the CRE when present as a KCREB:CREB heterodimer. The KCREB mutant also acts as a dominant repressor in vivo, completely blocking the ability of wild-type CREB to mediate induction by protein kinase-A of a SS CRE reporter gene in F9 teratocarcinoma cells. We have used this mutant to analyze the participation of CREB in the induction of the SS promoter in CA-77 cells, a medullary thyroid carcinoma cell line that produces high levels of SS. Although KCREB can block a portion of the cAMP induction of the SS promoter in CA-77 cells, approximately 45% of the induction remains insensitive to the mutant. These data support the paradigm that CREB is involved in the cAMP induction of SS in vivo. Furthermore, the inability of KCREB to completely block cAMP-mediated SS expression in CA-77 cells suggests that additional factors may contribute to the cAMP regulation of CRE function.
Mol Endocrinol 1992 Apr
PMID:A dominant repressor of cyclic adenosine 3',5'-monophosphate (cAMP)-regulated enhancer-binding protein activity inhibits the cAMP-mediated induction of the somatostatin promoter in vivo. 135 57

Type 1 protein phosphatases (PP-1) comprise a group of widely distributed enzymes that specifically dephosphorylate serine and threonine residues of certain phosphoproteins. They all contain an isoform of the same catalytic subunit, which has an extremely conserved primary structure. One of the properties of PP-1 that allows one to distinguish them from other serine/threonine protein phosphatases is their sensitivity to inhibition by two proteins, termed inhibitor 1 and inhibitor 2, or modulator. The latter protein can also form a 1:1 complex with the catalytic subunit that slowly inactivates upon incubation. This complex is reactivated in vitro by incubation with MgATP and protein kinase FA/GSK-3. In the cell the type 1 catalytic subunit is associated with noncatalytic subunits that determine the activity, the substrate specificity, and the subcellular location of the phosphatase. PP-1 plays an essential role in glycogen metabolism, calcium transport, muscle contraction, intracellular transport, protein synthesis, and cell division. The activity of PP-1 is regulated by hormones like insulin, glucagon, alpha- and beta-adrenergic agonists, glucocorticoids, and thyroid hormones.
Crit Rev Biochem Mol Biol 1992
PMID:The structure, role, and regulation of type 1 protein phosphatases. 135 Feb 40


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