Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.11 (AMPK)
12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The antiproliferative effect of glucocorticoid hormones on lymphoid tissue serves as the basis for their use in chemotherapy of lymphomas and leukemias. The effectiveness of the steroid-mediated response is potentially contingent upon a variety of factors, including the cellular level of glucocorticoid receptors. This report demonstrates that differences in the expression of the glucocorticoid receptor gene can modulate steroid sensitivity of individuals within a population of lymphoma cells. We have also found that loss of cAMP-dependent protein kinase activity caused a measurable decrease of steroid sensitivity in the murine T-lymphoma WEHI-7 without producing a significant change in steroid binding capacity. However, the extent of this change in sensitivity was dependent upon the level of glucocorticoid receptor expression. Lymphoma cells containing few spare steroid receptors became significantly resistant to glucocorticoids through loss of cAMP-dependent kinase function. On the other hand, elevated levels of cAMP were found to cause an increase in glucocorticoid receptor mRNA concentrations. Thus, cAMP-dependent protein kinase activity has the potential to modulate a lymphoma cell's steroid sensitivity by affecting the level of glucocorticoid receptor expression as well as the receptor's efficiency in producing a cytolytic response.
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PMID:Cyclic AMP-dependent protein kinase modulation of the glucocorticoid-induced cytolytic response in murine T-lymphoma cells. 262 44

The expression of the tyrosine aminotransferase (TAT) gene of the rat was analyzed in primary hepatocytes. The TAT gene remains active in primary cultured cells at a level similar to that in liver cells. Expression can be induced by glucocorticoids and cAMP, glucocorticoids lead to a 8-10-fold increase in TAT mRNA level, cAMP to a 20-30-fold increase. The elevation of the TAT mRNA is preceeded by a rise in the relative rate of transcription of the gene. Surprisingly transcription of the albumin gene, which steadily declines with the age of the culture, can also strongly be stimulated by glucocorticoids in primary hepatocytes. cAMP antagonists, which act as competitive inhibitors of the cAMP-dependent protein kinase, prevent induction of transcription of the tyrosine aminotransferase gene by cAMP suggesting that the effect of cAMP on expression of the tyrosine aminotransferase gene is mediated by a cAMP-dependent protein kinase. The cAMP antagonist does not interfere with induction by glucocorticoids which suggests that phosphorylation of the glucocorticoid receptor by the cAMP-dependent protein kinase is not required for its function. We thus conclude that the two inducers affect transcription by independent mechanisms.
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PMID:Transcription activation of the tyrosine aminotransferase gene by glucocorticoids and cAMP in primary hepatocytes. 288 94

In this report we demonstrate glucocorticoid receptors in seminiferous tubules of the rat testis, and that these receptors are localized in Sertoli cells and peritubular cells. The receptors had high affinity for [3H]dexamethasone (Kd = 0.5 - 1 x 10(-9) M), and similar Kd values were calculated from equilibrium analysis and from rate studies (k1 = 1.5 x 10(6) M-1 min-1 and k-1 = 1.4 x 10(-3) min-1, O C). Binding specificity was typical for glucocorticoid receptors (affinity: dexamethasone greater than corticosterone greater than cortisol approximately R5020 approximately progesterone greater than aldosterone = R1881 greater than 17 beta-estradiol approximately cortisone approximately testosterone greater than 5 alpha-dihydrotestosterone). The concentration of glucocorticoid receptors in rat seminiferous tubules revealed an age-dependent decrease, coinciding with the increase in the number of germ cells. Glucocorticoid receptor levels were higher in Sertoli cells from immature rats than in cells from adult rats. Cultured peritubular cells from immature rats contained levels of glucocorticoid receptors similar to cultured Sertoli cells from rats of the same age. With a nick-translated human glucocorticoid receptor complementary DNA probe, a messenger RNA (mRNA) species of approximately 7 kilobase was clearly detected in both Sertoli cells and peritubular cells. In peritubular cells, a smaller mRNA species (5 kilobase) was also clearly detectable. In mRNA from whole testis tissue, a similar developmental pattern as for dexamethasone binding was found. Dexamethasone caused a concentration-dependent stimulation of mRNA levels for androgen binding protein and for the cAMP-dependent protein kinase regulatory subunit type II beta in cultured immature rat Sertoli cells. On the other hand, mRNA levels for glucocorticoid receptor decreased, whereas mRNA levels for beta-actin remained constant. This report documents for the first time the presence of glucocorticoid receptors and glucocorticoid effects in rat Sertoli cells, and is also the first demonstration of glucocorticoid receptors in peritubular cells of the rat testis.
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PMID:Glucocorticoid receptors and glucocorticoid effects in rat Sertoli cells. 290 75

Murine lymphoma cell lines such as WEHI-7 exhibit a cytolytic response to both cAMP and glucocorticoids. We have exploited this behavior to ask if cyclic AMP-dependent protein kinase plays a role in regulating glucocorticoid receptor function. We have found that cAMP-resistant cell lines containing a defective cAMP-dependent protein kinase activity give rise to spontaneous steroid-resistant variants at a high frequency (approximately 10(-7)) relative to wild type cells (less than 10(-10)). Unlike previous results with wild type cells, nearly complete loss of glucocorticoid receptor function was observed in a single selection using unmutagenized cAMPr derivatives of WEHI-7. Thus, the initial selection of the cAMPr phenotype serves as a permissive step toward the acquisition of glucocorticoid resistance in WEHI-7. In addition, cAMP was found to increase the levels of steroid binding in these cell lines, and the dose response was dependent upon the phenotype of the cyclic AMP-dependent protein kinase. The results demonstrate an important role for cAMP in regulating glucocorticoid receptor activity and strongly suggest that this novel two-step selection scheme leads to the isolation of new forms of glucocorticoid resistance.
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PMID:Cyclic AMP-dependent protein kinase promotes glucocorticoid receptor function. 300 79

We have developed a sequential selection procedure for the isolation of novel steroid-resistant variants of the murine thymoma WEHI-7. The first step involves the isolation of cell lines with an altered cAMP-dependent protein kinase (cAPK) activity by selection for resistance to dibutyryl cAMP (dbcAMP). The second step involves the selection for resistance to dexamethasone (dex) which results in the isolation of variants with decreased receptor function and a cAMPrdexr phenotype. The initial selection, to cAMPr, serves as a permissive step since isolation of spontaneous glucocorticoid resistance from wild-type WEHI-7 does not occur at a measurable frequency. The results demonstrate a potential role for cAPK in regulating the functional levels of glucocorticoid receptor and suggest that mutations in other cellular functions that affect receptor activity could lead to steroid resistance in lymphoid cells.
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PMID:Isolation of new types of dexamethasone-resistant variants from a cAMP-resistant lymphoma. 300 78

The biological effects of pituitary adenylate cyclase-activating peptide (PACAP) 27 and 38 on peptide secretion and gene regulation were studied in the mouse corticotrope-derived cell line AtT20. Treatment of these cells with PACAP 27/38 led to a dose-dependent increase in cAMP content and ACTH accumulation in the medium with an apparent ED50 value close to 10(-9) M. The genomic effects of PACAP were first investigated by using a reporter gene containing a cAMP responsive element (CRE: TGACGTCA) PACAP 27/38 stimulate transcription from this construction and the effect is further increased when cells are cotreated with the phosphodiesterase inhibitor rolipram. Furthermore, we show by measuring nuclear heterologous proopiomelanocortin (POMC) RNA levels or by using a reporter gene containing the POMC promoter region, that PACAP stimulates POMC transcription. This transcriptional stimulation is mediated by the cAMP-dependent protein kinase (PKA) since genetic inactivation of PKA by a dominant inhibitory mutant of this enzyme completely abolished the effect of PACAP on POMC transcription. Finally, we show that the transcriptional stimulation of POMC by PACAP is repressed by the glucocorticoid receptor agonist dexamethasone. Taken together, these data suggest that PACAP is a hypophysiotropic hormone that exert similar if not identical functions as corticotropin-releasing hormone (CRH) on corticotrope cells.
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PMID:Pituitary adenyl cyclase-activating peptide: a hypophysiotropic factor that stimulates proopiomelanocortin gene transcription, and proopiomelanocortin-derived peptide secretion in corticotropic cells. 784 39

Genomic sequences flanking the 5' end of the cDNA encoding isoform C beta 2 of the catalytic subunit of bovine cAMP-dependent protein kinase were cloned, sequenced and analyzed for promoter activity and transcription initiation sites. A region of 913 bp upstream the translation initiator ATG was amplified from genomic DNA by vectorette polymerase chain reaction. In primer extension reactions and RNase protection assays, residues C (at position -91), T (-71) and G (-70) were found to serve as transcription initiation sites of the gene. Amplification products and sub-fragments thereof were ligated upstream of the reporter gene chloramphenicol acetyltransferase to test for promoter activity. Constructs were transiently transfected into a Chinese hamster ovary cell line which was shown to express endogenous C beta 2 mRNA. The genomic sequence upstream the C beta 2 cDNA does have promoter activity. The region from position -51 to -292 proved sufficient to drive efficient transcription of the reporter gene. The promoter is AT rich (68%), does not contain a TATA box within 50 bp upstream of the first initiation site and possesses putative binding sites for several transcription factors such as PEA-3 and a glucocorticoid receptor.
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PMID:Promoter of the gene encoding the bovine catalytic subunit of cAMP-dependent protein kinase isoform C beta 2. 898 58

Our laboratory has proposed that phenobarbital (PB), a typical lipophilic agent that induces some members of the supergene family of liver microsomal cytochromes P450 (e.g., CYP2B1/2 and CYP3A23), acts through a complex process inhibitable by the presence of growth hormone (GH), the absence of some components of the extracellular matrix, or a disrupted cytoskeleton. To verify that these manipulations of the culture environment block specific steps in the PB induction pathway rather than simply exerting nonspecific or toxic effects on CYP2B1/2 gene transcription, we have now examined PB induction of CYP3A23, a gene known to also be transcriptionally activated by dexamethasone (DEX) through a "nonclassical" pathway apparently involving the glucocorticoid receptor. We found that in primary cultures of adult rat hepatocytes treated with PB, induction of CYP3A23 mRNA, just as we reported for induction of CYP2B1/2 mRNA, required the use of Matrigel (a reconstituted basement membrane) and was blocked by the presence of cytoskeletal inhibitors (colchicine or cytochalasins) or of physiologic concentrations of GH in the culture medium. Moreover, PB induction of CYP3A23 and of CYP2B1/2 mRNAs was greatly diminished by inhibitors of cAMP-dependent protein kinase (PKA). In striking contrast, induction of CYP3A23 mRNA by DEX was unaffected by any of these alterations of the culture conditions that block its induction by PB. We conclude that the effects of extracellular matrix, GH, disruption of the cytoskeleton, and activation of cAMP-dependent protein kinase, pharmacologically define multiple, pretranscriptional steps in the pathway(s) for PB induction of liver cytochromes P450.
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PMID:Characterization of a pretranscriptional pathway for induction by phenobarbital of cytochrome P450 3A23 in primary cultures of adult rat hepatocytes. 918 22

Nuclear receptors and their coactivators are key regulators of numerous physiological functions. GRIP1 (glucocorticoid receptor-interacting protein) is a member of the steroid receptor coactivator family. Here, we show that GRIP1 is regulated by cAMP-dependent protein kinase (PKA) that induces its degradation through the ubiquitin-proteasome pathway. GRIP1 was down-regulated in transiently transfected COS-1 cells after treatment with 8-para-chlorophenylthio-cAMP or forskolin and 3-isobutyl-1-methylxanthine and in adrenocortical Y1 cells after incubation with adrenocorticotropic hormone. Pulse-chase experiments with transiently transfected COS-1 cells demonstrated that the half-life of GRIP1 was markedly reduced in cells overexpressing the PKA catalytic subunit, suggesting that activation of PKA increases the turnover of GRIP1 protein. The proteasome inhibitors MG132 and lactacystin abolished the PKA-mediated degradation of GRIP1. Using ts20 cells, a temperature-sensitive cell line that contains a thermolabile ubiquitin-activating E1 enzyme, it was confirmed that PKA-mediated degradation of GRIP1 is dependent upon the ubiquitin-proteasome pathway. Coimmunoprecipitation studies of COS-1 cells transfected with expression vectors encoding GRIP1 and ubiquitin using anti-GRIP1 and anti-ubiquitin antibodies showed that the ubiquitination of GRIP1 was increased by overexpression of PKA. Finally, we show that PKA regulates the intracellular distribution pattern of green fluorescent protein-GRIP1 and stimulates recruitment of GRIP1 to subnuclear foci that are colocalized with the proteasome. Taken together, these data demonstrate that GRIP1 is ubiquitinated and degraded through activation of the PKA pathway. This may represent a novel regulatory mechanism whereby hormones down-regulate a nuclear receptor coactivator.
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PMID:cAMP-dependent protein kinase regulates ubiquitin-proteasome-mediated degradation and subcellular localization of the nuclear receptor coactivator GRIP1. 1534 61

Glucocorticoid excess induces hyperglycemia, which may result in diabetes. The present experiments explored whether glucocorticoids trigger apoptosis in insulin-secreting cells. Treatment of mouse beta-cells or INS-1 cells with the glucocorticoid dexamethasone (0.1 micromol/l) over 4 days in cell culture increased the number of fractionated nuclei from 2 to 7 and 14%, respectively, an effect that was reversed by the glucocorticoid receptor antagonist RU486 (1 micromol/l). In INS-1 cells, dexamethasone increased the number of transferase-mediated dUTP nick-end labeling-staining positive cells, caspase-3 activity, and poly-(ADP-) ribose polymerase protein cleavage; decreased Bcl-2 transcript and protein abundance; dephosphorylated the proapoptotic protein of the Bcl-2 family (BAD) at serine155; and depolarized mitochondria. Dexamethasone increased PP-2B (calcineurin) activity, an effect abrogated by FK506. FK506 (0.1 micromol/l) and another calcineurin inhibitor, deltamethrin (1 micromol/l), attenuated dexamethasone-induced cell death. The stable glucagon-like peptide 1 analog, exendin-4 (10 nmol/l), inhibited dexamethasone-induced apoptosis in mouse beta-cells and INS-1 cells. The protective effect of exendin-4 was mimicked by forskolin (10 micromol/l) but not mimicked by guanine nucleotide exchange factor with the specific agonist 8CPT-Me-cAMP (50 micromol/l). Exendin-4 did not protect against cell death in the presence of cAMP-dependent protein kinase (PKA) inhibition by H89 (10 micromol/l) or KT5720 (5 micromol/l). In conclusion, glucocorticoid-induced apoptosis in insulin-secreting cells is accompanied by a downregulation of Bcl-2, activation of calcineurin with subsequent dephosphorylation of BAD, and mitochondrial depolarization. Exendin-4 protects against glucocorticoid-induced apoptosis, an effect mimicked by forskolin and reversed by PKA inhibitors.
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PMID:Dexamethasone induces cell death in insulin-secreting cells, an effect reversed by exendin-4. 1664 95


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