Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rhodamine 123 is a lipophilic cationic fluorescent dye that localizes in mitochondria. We found that 17 beta-estradiol changes the ability of GH4C1 cells, clonal rat pituitary tumor cells, to retain rhodamine 123. Cells incubated with 10 micrograms/ml rhodamine 123 for 30 min at 37 C took up about equal amounts of rhodamine 123, as determined by fluorescence microscopy, regardless of whether they had been treated with estradiol. After three 5-min washes at 37 C, cells treated with 1 nM estradiol for 7 days before incubation with rhodamine 123 had lost more fluorescence than untreated cells. We further characterized the effect by flow cytometry. The difference in fluorescence between control and treated cells ranged from 50- to 500-fold. The effect of estradiol was maximal at 10(-10) M and took a week to develop fully. The effect is specific for estradiol, because estradiol and diethylstilbestrol reduced retention of rhodamine 123 fluorescence at 10(-10) M, but the same concentrations of dihydrotestosterone, progesterone, dexamethasone, and cholesterol did not. To test if the effect on rhodamine 123 fluorescence was caused by activation of the multidrug resistance transport system, we examined the effect of estradiol on the retention of daunomycin, a known substrate of the transport system. Estradiol treatment caused a 3-fold decrease in daunomycin fluorescence. We isolated clones resistant to estradiol-induced loss of rhodamine 123 fluorescence by flow cytometry and found that two clones still showed an estradiol-induced decrease in daunomycin fluorescence equivalent to that of the parent line.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1990 Jan
PMID:Estradiol decreases retention of rhodamine 123 fluorescence in GH4C1 pituitary tumor cells. 232 64

The report that ANF inhibits basal and CRF-stimulated adenylate cyclase activity in anterior pituitary homogenates suggested that the atrial peptide could inhibit ACTH secretion. This possibility was investigated in the ACTH-secreting AtT-20 mouse pituitary tumor cell line as well as homogenates or primary cell cultures from rat anterior hypophysis. ANF (up to 5 X 10(-7) M) was found to be completely ineffective in stimulating basal, CRF- and/or forskolin-stimulated adenylate cyclase activity, cAMP accumulation and ACTH secretion. Similarly, ANF had no effect on spontaneous or GRF-induced GH release from cells in primary culture. ANF receptors, however, are present in AtT-20 cells and anterior pituitary cells as evidenced by the ability of the peptide to stimulate intracellular cGMP accumulation. The data, therefore, suggests that ANF does not have a negative modulatory action on the secretory function of anterior pituitary. The role of cGMP in any other action(s) of ANF remains unknown.
Mol Cell Endocrinol 1986 Feb
PMID:Atrial natriuretic factor does not affect basal, forskolin- and CRF-stimulated adenylate cyclase activity, cAMP formation or ACTH secretion, but does stimulate cGMP synthesis in anterior pituitary. 241 82

HeLA H23 cells are a mutant female human tumor cell line harboring defective hypoxanthine phosphoribosyltransferase (HPRT; IMP-pyrophosphate phosphoribosyltransferase, EC 2.4.2.8) as a result of a mutation that alters the isoelectric point of the enzyme (G. Milman, E. Lee, G. S. Changas, J. R. McLaughlin, and J. George, Jr., Proc. Natl. Acad. Sci. USA 73:4589-4592, 1976). As shown by Milman et al. and confirmed by us here, rare HAT+ revertants arise spontaneously at 1.9 X 10(-8) frequency and express both mutant and wild-type polypeptides. Thus, the H23 mutant also carries a silent wild-type HPRT allele that is activated in revertants. To test whether the silent allele was activated via hypomethylation of genomic DNA, H23 cells were treated with inhibitors of DNA methylation, and revertants were scored by HAT or azaserine selection. At an optimal dose of 5 microM 5-azacytidine, the reversion frequency was increased about 50-fold when assayed by HAT selection and over 1,000-fold when assayed by azaserine selection. HAT+ and azaserine revertants were heterozygous for HPRT, expressing both wild-type and mutant HPRT polypeptides. Like spontaneous revertants, they contained active HPRT enzyme and were genetically unstable, reverting at about 10(-4) frequency. Similar results were found after treatment with N-methyl-N'-nitro-N-nitrosoguanidine, a DNA-alkylating agent and potent inhibitor of mammalian DNA methylation. By contrast, the DNA-ethylating agent, ethyl methanesulfonate (EMS), did not increase the HAT+ reversion frequency; it did, however, increase the frequency by which H23 revertants heterozygous for HPRT reverted to 6-thioguanine resistance. Of nine EMS revertants, seven lacked HPRT activity and had a substantially reduced expression of the wild-type polypeptide. These observations support the hypothesis that DNA methylation plays an important role in human X-chromosome inactivation and that EMS can inactivate gene expression by promoting enzymatic methylation of genomic DNA as found previously for the prolactin gene in GH3 rat pituitary tumor cells (R. D. Ivarie and J. A. Morris, Proc. Natl. Acad. Sci. USA 79:2967-2970, 1982; R. D. Ivarie, J. A. Morris, and J. A. Martial, Mol. Cell. Biol. 2:179-189, 1982).
Mol Cell Biol 1986 Jan
PMID:Activation of a nonexpressed hypoxanthine phosphoribosyltransferase allele in mutant H23 HeLa cells by agents that inhibit DNA methylation. 243 Dec 68

We have compared the properties of pp60c-src from the mouse pituitary tumor cell line, AtT20, and from mouse fibroblasts. In vitro, pp60c-src phosphotransferase activity from AtT20 cells is 2- to 3-fold that of mouse NIH 3T3 fibroblast pp60c-src. In analyzing the reason for this elevation in specific activity, we found that pp60c-src from AtT20 cells differs structurally in at least three ways from pp60c-src in fibroblasts. First, AtT20 cells and primary rat anterior pituitary cells express low levels of the neuronal form of pp60c-src. Second, pp60c-src from AtT20 cells is phosphorylated at two additional N-terminal serine residues. Last, AtT20 pp60c-src is phosphorylated to a lower overall stoichiometry.
Mol Endocrinol 1989 Jan
PMID:AtT20 cells express modified forms of pp60c-src. 246 57

Previous studies have demonstrated that the high basal level of transcription of the rat PRL gene in pituitary tumor GH3 cells is dependent on [CA2+]e. In the present study, we have extended these findings by examining the effects of the Ca2+ ionophores, A23187 and ionomycin, on [Ca2+]i, and on PRL mRNA levels and glucose-regulated protein (GRP) mRNA levels in GH3 cells cultured in a low Ca2+, serum-free medium (SFM). Using digital imaging microscopy of individual Fura 2-loaded GH3 cells in SFM plus 0.4 mM CaCl2, extranuclear and nuclear [Ca2+] were both about 70 nM. Addition of 600 nM ionomycin increased these levels by 10-fold within minutes, and by about 45-fold after 120 min. As previously published, addition of 0.4 mM CaCl2 to GH3 cells cultured in SFM significantly increased PRL mRNA, and had little or no effect on GRP78 and GRP94 mRNA after 16 h. Addition of 0.4 mM CaCl2 plus 100 nM A23187 significantly increased GRP78 and GRP94 mRNA. Surprisingly, the Ca2+ ionophore significantly inhibited PRL gene expression below that obtained in 0.4 mM CaCl2 without A23187. This same pattern of stimulation of GRP78 gene expression, but inhibition of PRL gene expression, was observed with 125 and 600 nM ionomycin. Both Ca2+ ionophores had no effect on histone 3 mRNA, and A23187 depressed PRL gene expression at a concentration (50 nM) that did not affect protein synthesis. Although A23187 reproducibly lowered PRL mRNA levels, it slightly inhibited its degradation in cells in which RNA synthesis was blocked by actinomycin D.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1989 Nov
PMID:Calcium regulation of prolactin gene expression: opposing effects of extracellular CaCl2 and Ca2+ ionophores. 251 48

The ability of an upstream element of the rat PRL gene to permit transcriptional regulation in response to several different hormones has been examined. To test the ability of specific DNA sequences to mediate hormone responsiveness, DNA fragments were subcloned upstream of a thymidine kinase-chloramphenicol acetyltransferase fusion gene and transferred into GH3 pituitary tumor cells. Initially, fragments representing a distal enhancer element (positions -1713 to -1495) and a more proximal element (positions -292 to -38) were tested. The results demonstrate that the distal enhancer permits cAMP, TRH, epidermal growth factor (EGF), and estradiol to stimulate expression of the thymidine kinase-chloramphenicol acetyltransferase gene. The proximal element permitted fusion gene regulation in response to cAMP, TRH, EGF, and phorbol esters. For the cAMP, TRH, and EGF responses, the distal element permitted responses approximately equal to or greater than responses conferred by the proximal PRL gene fragment. The response of the distal element to cAMP and TRH was more than additive with the response to estradiol, suggesting that the estrogen response element is distinct but may interact cooperatively with the other hormone response elements. Mutation of the estrogen-responsive element abolished both the response to estrogen and the cooperative response with cAMP, but not the response to cAMP itself. Mutation of a sequence involved in basal enhancer activity of the distal element reduced both basal transcription and the response to cAMP. These results suggest that the distal enhancer sequence of the PRL gene contains, in addition to an estrogen response element, elements that confer responsiveness to cAMP, TRH, and EGF.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1989 Jan
PMID:The distal enhancer region of the rat prolactin gene contains elements conferring response to multiple hormones. 253 91

Thyrotropin-releasing hormone (TRH) receptors were solubilized from a rat pituitary tumor cell line, GH4C1, with digitonin. Convenient assays were developed based on the ability of hydroxylapatite and polyethyleneimine-soaked glass fiber filters to adsorb the solubilized [3H]methyl-TRH-receptor complex but not free [3H]methyl-TRH. The kinetics of [3H]methyl-TRH binding to solubilized receptors were extremely temperature dependent. Binding reached equilibrium at 10-20 nM [3H]methyl-TRH in 30 min at 23 degrees and 6 hr at 0 degree. The half-times for dissociation were less than 5 min at 23 degrees and 7.6 hr at 0 degree. Equilibrium binding experiments yielded linear Scatchard plots at 0 degree with Kd = 3 nM, whereas the Kd was greater than 20 nM at 23 degrees. A series of TRH congeners displaced [3H]methyl-TRH with the rank order reported for membrane receptors, N3-methyl-HisTRH greater than or equal to TRH greater than pGlu-N3-methyl-HisProNH(CH2)6NH2 greater than or equal to pGluHisProNH(CH2)6NH2 greater than pGluHisTyrNH2 much greater than TRH free acid. The antagonist chlordiazepoxide exhibited an IC50 of 10 microM. [3H]methyl-TRH binding to solubilized receptors displayed a broad pH optimum, from 6.5 to 7.5. The solubilized receptor could be obtained from cultured GH4C1 cells and in much larger quantities from GH4C1 tumors. Tumors from 12 rats yielded greater than 700 pmol of specific soluble TRH binding activity (1 g of protein). The solubilized receptor could be purified 10-20-fold by chromatography on wheat germ agglutinin columns and could be concentrated by adsorption on either DEAE-Sephadex or hydroxylapatite. The procedures outlined allow the solubilization of pituitary TRH receptors from a rich and abundant source, the rapid and reproducible assay of [3H]methyl-TRH binding, and substantial enrichment of receptor activity. These findings should be valuable for the purification and identification of the TRH receptor protein.
Mol Pharmacol 1989 Apr
PMID:Solubilization and characterization of pituitary thyrotropin-releasing hormone receptors. 253 60

Regulation of GH gene expression by GRF involves cAMP as a second messenger. We have demonstrated that a 500-basepair fragment of the human GH (hGH) gene 5' flanking region can confer cAMP inducibility upon the chloramphenicol acetyltransferase transcription unit in transient transfections of rat pituitary tumor cells treated with forskolin, an activator of adenyl cyclase. The same hGH construct is not induced by forskolin in nonpituitary-derived cells. Experiments with hGH deletion constructs reveal that binding sites for transcription factor AP-2 and the pituitary-specific factor GHF-1 are not required for forskolin stimulation, but that GHF-1 may potentiate the effect. RNA analyses reveal that forskolin also stimulates accumulation of transcripts initiated at the hGH promoter. Other agents that elevate cAMP levels also stimulate hGH expression. Since the hGH 5' flanking region contains no sequences homologous to the cAMP-responsive element of the somatostatin gene, and the AP-2 sites do not appear to be required for the forskolin response, these results suggest that a novel cAMP-responsive element exists within 82 basepairs upstream from the transcriptional start of the hGH gene and that hGH regulation by GRF may involve interaction between a tissue-specific element and a cAMP-inducible element.
Mol Endocrinol 1989 May
PMID:Induction of human growth hormone promoter activity by the adenosine 3',5'-monophosphate pathway involves a novel responsive element. 254 55

To determine the rat PRL (rPRL) promoter sequences that mediate pituitary-specific and cAMP-induced gene expression in vivo, various lengths of the rPRL promoter were ligated to the luciferase reporter gene and introduced into pituitary and non-pituitary cell lines. A 30-fold increase in rPRL promoter activity was observed in GH4 rat pituitary tumor cells compared to nonpituitary Rat2 fibroblast and HeLa cervical carcinoma cells. About 45% of this cell-specific promoter activity was competed by a plasmid containing the -67 to -45 rPRL promoter region, which is the most proximal binding site for a lactotroph-specific factor. Compared to a -425 rPRL construct, transfection with rPRL 5'-end points of -212, -178, and -127 contained 23%, 45%, and 1%, respectively, of luciferase activity. Forskolin stimulation resulted in a 10-fold induction of all the rPRL promoter fragments tested. Of note, a -127 deletion which was devoid of any basal promoter activity was also induced 10-fold by forskolin. The forskolin effect was abolished when GH4 rat pituitary cells were cotransfected with a plasmid encoding a protein kinase A inhibitor, indicating protein kinase A is involved in the activation mechanism. These data document that both positive and negative effectors influence basal rPRL promoter activity. Furthermore, the minimum sequences required for pituitary-specific rPRL promoter activity are altered by intracellular cAMP levels. Taken together, the data indicate that hormone-activated and cell-specific factors may interact to establish a particular setpoint for rPRL gene expression.
Mol Endocrinol 1989 May
PMID:Analysis of rat prolactin promoter sequences that mediate pituitary-specific and 3',5'-cyclic adenosine monophosphate-regulated gene expression in vivo. 254 56

Pharmacological agents are widely used to probe the mechanism of action of TRH. A number of these drugs behave as local anesthetics at high concentrations. The effect of local anesthetics on the binding of [3H]Me-TRH to specific receptors was studied using the GH4C1 line of rat pituitary tumor cells. [3H]Me-TRH binding was inhibited by classical local anesthetics with the order of potency (IC50 values): dibucaine (0.37 mM) greater than tetracaine (1.2 mM) greater than lidocaine (3.3 mM) greater than procaine and benzocaine (greater than 10 mM). IC50 values for other drugs with local anesthetic properties that inhibited [3H]Me-TRH were: 100 microM trifluoperazine, 100 microM imipramine, 170 microM chlorpromazine, 300 microM verapamil, and 700 microM propranolol. Inhibition by tetracaine and verapamil increased as the pH was raised from 6 to 8.5, indicating that the free base form of the amine drugs was the inhibitory species, and the local anesthetic effect was greater at 37 C than at 24 C or 0 C. [3H]Me-TRH binding to receptors in isolated membranes was inhibited to the same extent as binding to receptors on intact cells. Local anesthetics were 3- to 20-fold less potent at inhibiting [3H]Me-TRH to digitonin-solubilized receptors than binding to intact cells. In contrast, the potency of chlordiazepoxide, a putative TRH antagonist, to inhibit [3H]Me-TRH binding was equal using cells and solubilized receptors (IC50 = 10 microM). Local anesthetics inhibited TRH-stimulated PRL release and also inhibited basal PRL secretion and secretion stimulated by two nonhormonal secretagogues, (Bu)2cAMP and a phorbol ester.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1989 Sep
PMID:Pituitary thyrotropin-releasing hormone receptors: local anesthetic effects on binding and responses. 255 7


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