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

---

Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr-1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RI alpha decreased within 24 h of 8-Cl-cAMP treatment, that RII beta increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.
...
PMID:Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells. 754 90

The somatic Sertoli cells of the testis are major targets for FSH and are important for the regulation of spermatogenesis. The binding of FSH to Sertoli cells activates the cAMP-dependent protein kinase A signaling pathway, resulting in phosphorylation of the cAMP response element-binding protein (CREB), which is required to transactivate genes containing cAMP response elements (CREs). Here we show that the addition of forskolin to cultured primary Sertoli cells results in the phosphorylation of CREB within 2-5 min. Phospho-CREB levels remain elevated with continued forskolin stimulation, but fall by 60% within 5 min after the removal of forskolin. In addition, we found that 8-bromo-cAMP induces CREB RNA accumulation in the Sertoli cells. Transient transfections of primary Sertoli cells with CREB promoter-chloramphenicol acetyltransferase reporter plasmids define a conserved 300-base pair region of the CREB promoter surrounding the transcription start site that is required for both basal and cAMP-inducible expression of the CREB gene. This region of the promoter contains three Sp1-binding sites flanking the transcription initiation site and two CREs located 65 and 85 base pairs downstream of the transcription initiation site. We show that the Sp1 motifs bind Sp1 in Sertoli extracts and contribute to basal promoter activity, and that the CREs bind CREB and are essential for cAMP induction of CREB gene transcription. These findings support the model of FSH- and cAMP-mediated CREB autoregulation of its own promoter and may explain the dramatic stage-specific oscillations in Sertoli cells of CREB messenger RNA levels during the 12-day cycles of spermatogenesis in rat seminiferous tubules.
...
PMID:Expression of the gene encoding transcription factor cyclic adenosine 3',5'-monophosphate (cAMP) response element-binding protein (CREB): regulation by follicle-stimulating hormone-induced cAMP signaling in primary rat Sertoli cells. 762 90

Somatostatin (SS) and neuropeptide Y (NPY) are coproduced in a subpopulation of neurons that are selectively resistant to NMDA neurotoxicity. We have previously reported that quinolinic acid (QUIN), an NMDA receptor agonist, augments SS mRNA in cultured fetal rat cortical neurons. This study examines coregulation of SS and NPY by QUIN and NMDA in cultured cortical neurons and compares the effects of these agents with those of forskolin and phorbol 12-myristate 13-acetate (PMA), known to activate SS and NPY gene transcription by protein kinase A- and protein kinase C-dependent mechanisms. In addition, transcriptional regulation of the SS gene was investigated by acute transfection of cortical cultures with an SS promoter-chloramphenicol acetyltransferase (CAT) construct. QUIN and NMDA displayed dose-dependent fourfold augmentation of levels of mRNA for SS but not for NPY. In contrast, forskolin and PMA increased both SS and NPY mRNA levels. QUIN- and NMDA-mediated induction of SS mRNA was blocked by the NMDA receptor antagonist (-)-2-amino-5-phosphonovaleric acid and displayed regional brain specificity because it was not observed in fetal hypothalamic cell cultures. In time course studies, the effects of QUIN/NMDA on SS mRNA occurred after a latency of 8 h, indicating a delayed effect. Cortical cells transfected with pSS-750 CAT showed three- to fourfold stimulation of CAT activity with forskolin but not by QUIN or NMDA. These data reveal a dose-dependent, tissue-specific, NMDA receptor-mediated stimulation of SS but not NPY mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Differential stimulation of somatostatin but not neuropeptide Y gene expression by quinolinic acid in cultured cortical neurons. 764 30

We have examined the involvement of tyrosine residues 333 and 338 of the growth hormone (GH) receptor in the cellular response to GH. Stable Chinese hamster ovary (CHO) cell clones expressing a receptor with tyrosine residues at position 333 and 338 of the receptor substituted for phenylalanine (CHO-GHR1-638 Y333F, Y338F) were generated by cDNA transfection. Compared with the wild type receptor the Y333F,Y338F mutant possessed normal high affinity ligand binding, hormone internalization, and ligand-induced receptor down-regulation. GH activation of mitogen-associated protein kinase was also similar in CHO clones expressing similar wild type and Y333F,Y338F receptor number. However, two GH-regulated cellular events (lipogenesis, and protein synthesis) were deficient in the tyrosine substituted receptor. In contrast, transcriptional regulation by GH (as evidenced by chloramphenicol acetyltransferase cDNA expression driven by the GH-responsive region of the SPI 2.1 gene) was not affected by Y333F,Y338F substitution. Thus we provide the first experimental evidence that specific tyrosine residues of the GH receptor are required for selected cellular responses to GH.
...
PMID:Requirement of tyrosine residues 333 and 338 of the growth hormone (GH) receptor for selected GH-stimulated function. 766 93

ATP-citrate lyase (CL) catalyzes the conversion of citrate and CoA to oxaloacetate (OA) and acetyl-CoA. As the coupled malic dehydrogenase (MDH) assay is not able either to study the effect of oxaloacetate (OA) on CL activity or to measure accurately CL activity in biological samples, a new assay was developed. The CL-citrate coupled CAT assay measures the amount of acetyl-CoA formed by transferring radiolabeled acetyl-CoA synthesized from [14C]citrate to chloramphenicol with chloramphenicol acetyltransferase (CAT). Employing this assay, the rate of increase in acetyl-CoA synthesis from citrate is linear with respect to added CL. Kinetic values for ATP, CoA and citrate are similar to those obtained using the MDH assay. The effect of CL phosphorylation on enzyme activity was determined. CL phosphorylated by cAMP-dependent protein kinase or by this kinase and glycogen synthase kinase-3 (GSK-3) decreases the apparent Vmax without changing the apparent Km. The effect of OA, a product of the enzyme reaction, on CL activity was also determined. Computational analysis of the data obtained without added OA and at three concentrations of OA indicate that the apparent Km for the substrate is not altered even though the apparent Vmax is decreased. The effect of OA on the activity of phosphorylated enzyme was also determined. OA decreases the apparent Vmax of the phosphorylated enzyme to the same extent as in control CL. This assay is able to measure CL activity in cytosol from 3T3-L1 adipocytes.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Effect of oxaloacetate and phosphorylation on ATP-citrate lyase activity. 766 53

Since we have observed effects of growth factors and cAMP as well as estradiol (E2) on regulation of expression of some genes stimulated by the estrogen receptor (ER), we have undertaken studies to examine directly whether activators of protein kinases can modulate transcriptional activity of the ER. We find that activators of protein kinase-A [cholera toxin plus 3-isobutyl-1-methylxanthine (CT+IBMX)] and protein kinase-C [12-O-tetradecanoylphorbol-13-acetate (TPA)] markedly synergize with E2 in ER-mediated transcriptional activation. When a reporter plasmid [with a minimal promoter containing a TATA region and estrogen-responsive elements (ERE) linked to a chloramphenicol acetyltransferase (CAT) reporter gene] was transfected into MCF-7 human breast cancer cells, which contain endogenous ER, E2 evoked a dose-dependent increase in CAT activity. While treatment with protein kinase-A or -C activator alone evoked only very low CAT activity, the maximal (approximately 25-fold) CAT activity stimulated by E2 alone was increased 2- to 3-fold (to approximately 60 times the control value) upon cotreatment with either of the protein kinase activators. Interestingly, antiestrogen abolished all of the CAT activity induced by E2 and protein kinase activators. Immunoblots showed that TPA reduced ER levels to 30% of control values after 24 h, while CT+IBMX increased levels about 1.5-fold. Scatchard binding analysis revealed no change in the binding affinity of E2 to ER by these agents. Gel mobility shift competition assays with extracts prepared from cells that had been treated with E2 and protein kinase activators did not reveal any quantitative or qualitative changes in the binding of ER to the ERE in vitro. In ER-deficient Chinese hamster ovary (CHO) cells transfected with the reporter gene and varying amounts of an ER expression vector, the level of CAT activity obtained by cotreatment with E2 and CT+IMBX was 3-fold higher than that observed with E2 alone over the range of different ER amounts tested. This ER-mediated synergism was still retained in an amino-terminal A/B-domain-deleted ER mutant lacking the hormone-independent transcriptional activation function (TAF-1), but was greatly reduced in two hormone-binding domain (region E) mutants that exhibit significantly diminished ligand-dependent transcriptional activation. TPA did not show any synergistic activation with E2 in CHO cells, indicating differences in responses between cell types.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Synergistic activation of estrogen receptor-mediated transcription by estradiol and protein kinase activators. 768 75

Salivary-specific and cAMP-inducible expression of the rat proline-rich protein gene RP4 is dependent on a 28-base pair sequence of a salivary-specific cAMP response element (SCRE) (Lin, H. H., and Ann, D. K. (1992) Gene Expression 2, 365-377). To unravel its trans-acting factor(s), we used double-stranded oligoprobes corresponding to the SCRE to screen a randomly primed lambda gt11 cDNA expression library made from RNA of rat salivary cells. In this report, we describe the cDNA cloning of these helix-loop-helix SCRE-binding proteins (SCBPs) and demonstrate that there are at least three isoforms in salivary cells, namely SCBP alpha, SCBP beta, and SCBP gamma. RNA polymerase chain reaction and sequence analyses further confirmed the existence of these three different SCBP isoforms, which code for putative proteins of 707, 706, and 682 amino acids, respectively. Expression of the cloned SCBP cDNAs in salivary cells stimulates the expression of a cotransfected reporter construct containing multicopies of the SCRE cloned upstream of the thymidine kinase promoter and the chloramphenicol acetyltransferase structural gene. This stimulation is much more pronounced in transfections in which SCBP alpha and SCBP beta are cotransfected than when they are transfected individually. Furthermore, when low concentrations of SCBP alpha and SCBP beta are cotransfected with the SCRE reporter gene, coexpression of the catalytic subunit of protein kinase A is required to efficiently activate the expression of the reporter gene. These results strongly suggest that the observed stimulation of the SCRE is achieved through the coordinated expression of the SCBP alpha, SCBP beta, and protein kinase A activities, perhaps via a direct association of the two SCBPs and their phosphorylation by protein kinase A. We conclude that the isolated SCBP alpha and SCBP beta cDNAs encode transcription activators that participate in the control of the inducible RP4 gene expression in salivary cells.
...
PMID:The helix-loop-helix proteins (salivary-specific cAMP response element-binding proteins) can modulate cAMP-inducible RP4 gene expression in salivary cells. 768 70

All-trans-retinoic acid (RA) and retinoids induce synthesis of tissue-type plasminogen activator (t-PA) in endothelial and neuroblastoma cells in vitro and in rats in vivo. In HT1080 fibrosarcoma cells, induction of t-PA-related antigen secretion and t-PA mRNA steady state levels by RA were found to depend on de novo protein and mRNA synthesis. Fragments derived from the 5'-flanking region of the t-PA gene (+197 to -9578 base pairs (bp)) were linked to the chloramphenicol acetyltransferase gene. Transfection studies demonstrated that the region spanning bp -7145 to -9578 mediated induction by RA. A functional retinoic acid response element (RARE), consisting of a direct repeat of the GGGTCA motif spaced by 5 nucleotides (t-PA/DR5), was localized at -7.3 kilobases. The t-PA/DR5 element interacted with the heterodimer composed of retinoic acid receptor alpha and retinoid X receptor alpha in vitro, whereas its mutation abolished induction by RA in transient expression. In human EA.hy926 hybrid endothelial and in SK-N-SH neuroblastoma cells, the activity of t-PA/DR5 was found to be independent of the intervening sequence (-632 to -7144 bp) and of its distance from the transcription initiation site. Staurosporine, an inhibitor of protein kinase activity, inhibited induction by RA, suggesting that it required protein phosphorylation.
...
PMID:Retinoic acid induction of human tissue-type plasminogen activator gene expression via a direct repeat element (DR5) located at -7 kilobases. 770 55

Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the rate-limiting step in hepatic gluconeogenesis. Glucagon (via the second messenger cAMP) and glucocorticoids stimulate the transcription of the PEPCK gene, whereas insulin and phorbol esters inhibit, in a dominant fashion, these effects. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase, prevents the stimulation of glycogen synthesis, glucose transport, mitogen-activated protein kinase, and p70/p85 ribosomal S6 protein kinase by insulin. We now show that wortmannin can also block the inhibition of glucocorticoid- and cAMP-stimulated PEPCK gene expression by insulin. PEPCK-chloramphenicol acetyltransferase fusion gene experiments demonstrate that wortmannin blocks an activity that is required for insulin signaling to elements within the PEPCK promoter. Phorbol esters mimic the action of insulin on the regulation of PEPCK gene expression, but wortmannin does not block the effect of these agents. Thus, phosphatidylinositol 3-kinase is required for the regulation of PEPCK gene expression by insulin, but not by phorbol esters. The immunosuppressant rapamycin, a potent inhibitor of insulin or phorbol ester stimulation of p70/p85 ribosomal S6 protein kinase, has no significant effect on the regulation of PEPCK gene expression by insulin or phorbol esters. Thus, p70/p85 ribosomal S6 protein kinase does not have a role in signaling to the PEPCK promoter by insulin or phorbol esters.
...
PMID:Phosphatidylinositol 3-kinase, but not p70/p85 ribosomal S6 protein kinase, is required for the regulation of phosphoenolpyruvate carboxykinase (PEPCK) gene expression by insulin. Dissociation of signaling pathways for insulin and phorbol ester regulation of PEPCK gene expression. 779 43

Transcription factor CREB regulates cyclic AMP (cAMP)-dependent gene expression by binding to and activating transcription from cAMP response elements (CREs) in the promoters of target genes. The transcriptional transactivation functions of CREB are activated by its phosphorylation by cAMP-dependent protein kinase A (PKA). In studies of many different phenotypically distinct cells, the CRE of the somatostatin gene promoter is a prototype of a highly cAMP-responsive element regulated by CREB. We now report on a somatostatin-producing rat insulinoma cell line, RIN-1027-B2, in which transcription from the somatostatin gene promoter is paradoxically repressed by CREB. We find that CREB fails to transactivate a CRE-containing somatostatin-chloramphenicol acetyltransferase reporter even when coexpressed with the catalytic subunit of PKA. CAAT box/enhancer-binding protein beta (C/EBP beta) and C/EBP-related activating transcription factor bind to the CRE in the promoter of the somatostatin gene and transactivate transcription. CREB binds competitively with C/EBP beta to the somatostatin CRE in vitro and represses C/EBP beta-induced transcription of the CRE-containing somatostatin-chloramphenicol acetyltransferase reporter. The lack of CREB-mediated transcriptional stimulation is due to the presence of a heat-stable inhibitor of PKA that prevents activation of PKA and subsequent CREB phosphorylation in the nucleus. These findings indicate that dephosphorylated CREB is a negative regulator of C/EBP-activated transcription of the somatostatin gene promoter in RIN-1027-B2 cells.
...
PMID:Impaired cyclic AMP-dependent phosphorylation renders CREB a repressor of C/EBP-induced transcription of the somatostatin gene in an insulinoma cell line. 779 50


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---