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G C Mueller

Publications and source records attributed to G C Mueller.

At least 55 records · Page 3Linked to original sources
PubMed1982

Rapid acceleration of deoxyglucose transport by phorbol esters in bovine lymphocytes.

12-O-Tetradecanoylphorbol-13-acetate (TPA), a highly active tumor-promoting agent, rapidly accelerates deoxyglucose transport in bovine lymphocytes. This acceleration in rate is dose-dependent and proceeds without evidence of a lag period to achieve a maximal response within 10 min. Structure-activity studies showed that the activity of various phorbol derivatives for the stimulation of glucose transport closely parallels their potency as comitogens and stimulators of phosphatidyl choline synthesis in bovine lymphocytes and as tumor promoters on carcinogen-initiated mouse skin. The acceleration of glucose transport by TPA proceeds in the absence of oxygen and in the presence of retinoic acid and 5,8,11,14-eicosatetraynoic acid (ETYA). This situation is in contrast to the TPA stimulation of choline phospholipid synthesis and amino acid transport which exhibits a lag and a sensitivity to anaerobiosis, retinoic acid, and ETYA. These results suggest that the stimulation of glucose transport by TPA is an oxygen-independent early event resulting from a direct action of the tumor promoter on the cell membrane of the lymphocyte; this action of TPA appears antecedent to the oxygen-dependent/retinoid-sensitive events.

Anaerobiosis↗
PubMed1982

Influence of tetracaine on the structure and function of estrogen receptors.

The local anesthetic agent tetracaine has been shown to relax the affinity of estrogen receptors for estradiol and unidentified ligands in uterine cytosols. This effect is dependent on both the temperature of the exchange reaction and the concentration of tetracaine. Increasing the concentration of tetracaine in the system from 0 to 6 mM while keeping the temperature at 10 C results in a stepwise increase in the fractions of receptors that engage in a rapid exchange. Increasing the temperature of the exchange reaction from 0 to 17 C in the presence of 4 mM tetracaine similarly results in a stepwise increase in the fraction of receptors exhibiting the rapid exchange. The combination of 4 mM tetracaine and 10 C achieves the displacement of [3H]estradiol by unlabeled estradiol from the majority of the receptors in 30 min. In addition, tetracaine appears to relax the specificity of the receptors so as to facilitate the displacement of [3H]estradiol from the receptor by otherwise low affinity ligands, such as tamoxifen, nafoxidine, and 17 alpha-(2',3'-dihydroxypropyl)17 beta-estradiol. Tetracaine also dissociates estrogen receptors from other macromolecules in the cytosol, so that the receptors sediment in low salt sucrose gradients an 4S complexes. The data support the view that estrogen receptors of uterine cytosols are functionally microheterogeneous, possibly by virtue of their interactions with other components of the cytosol, and that set fractions of receptors are transformed to a state with a lower affinity for estradiol by specific concentrations of tetracaine at a given temperature. A concept of receptor action is discussed in which the ability of receptors to mediate the interaction of macromolecules may regulate the activity of multienzyme systems or the function of specific chromatin complexes.

Animals↗
PubMed1982

Antagonism of concanavalin A capping in phorbol ester-activated lymphocytes by calmodulin inhibitors and certain amino acid esters.

12-O-Tetradecanoylphorbol-13-acetate (TPA), an effective tumor promoter in mouse skin and comitogen in bovine lymphocytes, rapidly stimulates concanavalin A-mediated cap formation in the latter cells. The ability of different phorbol derivatives to facilitate the capping reaction correlates well with their potencies as lymphocyte comitogens and as tumor-promoting agents. This effect of TPA on capping in bovine lymphocytes, which is apparent within min, is neither mimicked nor altered by dibutyryl cyclic adenosine 3':5'-monophosphate or cyclic guanosine 3':5'-monophosphate. Cytochalasin D, a microfilament-disrupting agent, inhibits cap formation, thereby suggesting the participation of microfilaments in the response. Benzoyl tyrosine ethyl ester selectively inhibits the TPA-stimulated cap formation, whereas benzoyl tyrosinamide is inactive. A comparison of related amino acid derivatives reveals that their activities are dependent on the nature of both the amino acid side chain and the carboxyl end blocking group. Trifluoperazine and N-(6-aminohexyl)-5-chloronaphthalenesulfonamide, known inhibitors of the calmodulin-dependent processes, also selectively block the TPA-stimulated cap formation, whereas trifluoperazine sulfoxide, a less effective calmodulin antagonist, is relatively inactive. These data suggest that the stimulation of capping by TPA involves the activation of a calmodulin-dependent process which may also be regulated by the function of an esterase.

Amino Acids↗
PubMed1981

Role of dexamethasone in globin gene expression in differentiating Friend cells.

The expression of the globin genes which accompanies the chemically induced differentiation of Friend erythroleukemia cells is subject to inhibition by glucocorticoid hormones. The present study inquires into the possible mechanisms for this suppression. It is shown that the synthetic glucocorticoid, dexamethasone, can both prevent the initial appearance of beta-globin mRNA during the induction of differentiation and inhibit the ongoing production of this RNA in induced cells. Isolated nuclei from dexamethasone-treated cells also exhibited a depressed ability to synthesize beta-globin mRNA. These effects were achieved without altering the turnover rate of the mature messenger RNA. Electrophoretic analysis of pulse-labeled transcripts before and after a chase interval indicated that large Mr beta-globin precursor molecules were processed normally to mature nuclear beta-globin mRNA in cells treated with dexamethasone. S1 nuclease protection experiments showed further that dexamethasone treatment of induced cells uniquely depressed the amount of precursor-specific beta-globin sequences contained in unlabeled nuclear RNA preparations. The data support the view that dexamethasone regulates globin gene expression at or very close to the transcriptional level.

Animals↗
PubMed1981

Role of cytosol proteins in DNA chain growth and chromatin replication in Friend erythroleukemia cell nuclei.

The influence of cytosol proteins on the replication of DNA and chromatin in isolated nuclei from Friend erythroleukemia cells has been investigated. The overall process has been clearly shown to proceed stepwise. In the absence of cytosol proteins DNA chain growth tends to stop after the addition of approximately 200 nucleotides to the ends of growing chains. In the presence of cytosol proteins these sections grow to approximately 250 nucleotides, and participate in the stepwise extension of the replication process through adjacent nucleosomal sections of the template. Immediately following pulse labeling, the newly replicated DNA resides in a chromatin form which appears to be relatively resistant to digestion by micrococcal nuclease. During a chase interval, the association of the pulse-labeled DNA with nuclear proteins matures to a form which yields lengths of DNA upon digestion with micrococcal nuclease that correspond to mono-, di-, tri- and polynucleosomal units of chromatin. In the absence of cytosol proteins the nuclease resistant state of the labeled DNA tends to predominate and persist. The data support the view that DNA replication in a chromosomal setting proceeds stepwise over successive nucleosomal sections of template made accessible by the interaction of the cytosol proteins at or near the replication fork.

Animals↗
PubMed1981

Analogues of the cytostatic cyclic tetrapeptide chlamydocin. Synthesis of N beta-(N-maleoylglycyl) and N beta-(tert-butyloxycarbonyl) derivatives of cyclo(Gly-L-Phe-D-Pro-L-Dap).

The synthesis of analogues of the cytostatic cyclic tetrapeptide chlamydocin is described. cyclo(Gly-L-Phe-D-Pro-N beta-Boc-L-Dap) (4) was prepared from N beta-(tert-butyloxycarbonyl)-L-diaminopropionic acid methyl ester (Dap) and Cbz-Gly-L-Phe-D-Pro using DCC/HOBt as the coupling reagent. The methyl ester was saponified to the acid, which was converted to the 2,4,5-trichlorophenyl (Tcp) ester by reaction with trichlorophenol and DCC. The N-(benzyloxycarbonyl) group was removed by hydrogenolysis and the amine active ester cyclized at 95 degrees C in pyridine. The Boc-protected cyclic tetrapeptide 4 was isolated in 14% yield. Cyclic tetrapeptide 4 was converted to cyclo-[Gly-L-Phe-D-Pro-N beta-(N-maleoylglycyl)-L-Dap] (5) to test for a possible sulfhydryl group at the chlamydocin receptor. Removal of the tert-butyloxycarbonyl group, followed by reaction with N-maleoylglycine and DCC/HOBt in methylene chloride, gave cyclic tetrapeptide 5 in 68% yield. The maleoyl cyclic tetrapeptide 5 did not inhibit [3H]thymidine incorporation into calf thymus lymphocytes at concentrations 1000-fold higher than the IC50 for chlamydocin (6 nM).

Cells, Cultured↗
PubMed1981

Role of nonhemoglobin heme accumulation in the terminal differentiation of Friend erythroleukemia cells.

The differentiation of murine erythroleukemia cells (T3C12 Friend cells) on treatment with dimethyl sulfoxide (DMSO) has been correlated with an early and extended overproduction of heme. The cessation of cell replication and the development of nuclear condensation, changes which are associated with the terminal differentiation of these cells, occur when the level of heme rises 0.1 nmol/10(6) cells over that amount which can be complexed by globin protein. A significant fraction of the excess heme is localized in the nuclei of the DMSO-treated cells. The addition of exogenous hemin facilitates the onset of terminal differentiation in the DMSO-treated T3C12 cells, whereas only the induction of globin gene expression is observed in the absence of DMSO. To study the role of heme in erythroid differentiation, a Friend cell variant (R10) has been isolated whose synthesis and accumulation of heme in response to DMSO is deficient. This variant grows logarithmically in the presence of DMSO and fails to terminally differentiate. When exogenous hemin is added, the DMSO-treated R10 cells stop replicating. In the absence of DMSO, however, hemin-treated R10 cells continue to grow and express their globin genes without exhibiting other signs of terminal differentiation. The combined results support the conclusion that both the DMSO treatment and the accumulation of excess heme are required to bring about the terminal differentiation of Friend erythroleukemia cells. Preliminary evidence is presented which suggests that in addition to the induction of heme and globin synthesis, DMSO also induces a heme activation process which is required for differentiation. The possible relationship of this process to the terminal differentiation of erythroid cells is discussed.

Animals↗
PubMed1980

Localization of globin gene replication in Friend Leukemia cells to a specific interval of the S phase.

Murine erythroblastic leukemia cells, infected with Friend leukemia virus, were grown and synchronized in suspension culture by a double-block procedure involving medium depletion and treatment with excess thymidine. Replicating cultures were then caused to synthesize DNA during the early, middle, or late third of the S period with bromodeoxyuridine as a precursor. The bromodeoxyuridine density-labeled DNA and normal DNA were isolated by sedimentation in a cesium chloride density gradient and analyzed for the level of globin-specific DNA by hybridization with radioactive cDNA of the globin messenger RNA. Globin genes were found to be replicated near the end of the middle third of the S phase. The incorporation of bromodeoxyuridine into DNA also resulted in a lowered induction of hemoglobin synthesis in dimethyl sulfoxide-treated cells. In this case, the sensitivity was correlated with the introduction of bromodeoxyuridine into DNA replicated in early S phase. The possibility that this fraction of DNA, which is low in globin gene content, carries genes regulating the erythroid differentiation or the expression of globin genes is discussed.

Animals↗
PubMed1980

Inhibition of 12-O-tetradecanoylphorbol-13-acetate-accelerated phospholipid metabolism by 5,8,11,14-eicosatetraynoic acid.

The tumor-promoting agent, 12-O-tetradecanoylphorbol-13-acetate (TPA), accelerates choline phospholipid synthesis in bovine lymphocytes by an oxygen-dependent mechanism. This action is prevented by high concentrations of the cyclooxygenase inhibitor, indomethacin (1 to 3 mM), suggesting a possible involvement of lipid oxidation in the response. The acetylenic analog of arachidonic acid, 5,8,11,14-eicosatetraynoic acid (ETYA), at concentrations in the 10 to 50 microM range also prevents the acceleration of the incorporation of [methyl-3H]choline hydrochloride into choline phospholipids, and it appears more selective in its action. This antagonistic effect of ETYA, an agent which inhibits both the cyclooxygenase and lipoxygenase routes of arachidonic acid oxidation, can be precluded by arachidonic acid but not by other unsaturated or saturated fatty acids. If ETYA is added to lymphocyte cultures after 1 hr of TPA treatment, the established rate of [methyl-3H]choline hydrochloride incorporation is unaffected, but further acceleration is blocked. The inhibition by ETYA cannot be counteracted by any of the prostaglandins, Types A, B, D, E, or F alpha, or by the prostacyclin compounds, PGI1 and 6,9-thia-PGI2. The thromboxane pathway also appears not to be involved since 9,11-azoprosta-5,13-dienoic acid (Azo I), a selective inhibitor of thromboxane synthetase, does not affect the TPA response. These results suggest that TPS may activate the lipoxygenase rather than the cyclooxygenase pathway for lipid oxidation and that an arachidonic acid hydroperoxide or a subsequent metabolite plays a key role in the stimulation of choline phospholipid synthesis by the tumor-promoting phorbol ester, TPA.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1980

Inhibition of skin tumor promotion by retinoic acid and its metabolite 5,6-epoxyretinoic acid.

The ability of 5,6-epoxyretinoic acid, a biologically active metabolites of retinoic acid, to inhibit both the induction of ornithine decarboxylase (ODC) activity and skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) was evaluated. Application of 5,6-epoxyretinoic acid either concurrently with or 1 hr after each application of TPA to the initiated mouse skin inhibited the formation of skin tumors as effectively as did retinoic acid. 5,6-Dihydroretinoic acid, which is a poor substrate for epoxidation, also inhibited skin tumor promotion. 5,6-Epoxyretinoic acid, 5,6-dihydroretinoic acid, and retinoic acid were equally effective in inhibiting the induction of ODC activity by TPA. Insect juvenile hormones inhibited neither the induction of ODC activity nor skin tumor promotion by TPA. These results indicate that (a) epoxidation of retinoic acid at the 5,6-position is not a rate-limiting modification for the anti-promoting activity of retinoic acid and that (b) inhibition of the induction by TPA of mouse epidermal ODC activity may be a simple test for screening the potential prophylactic activities of new retinoids.

Animals↗
PubMed1979

Effects of hexachlorocyclohexane isomers on concanavalin A 'capping' in bovine lymphocytes.

The effects of alpha, beta, gamma, and delta isomers of hexachlorocyclohexane on concanavalin A 'capping' in bovine lymphocytes were evaluated, gamma and delta hexochlorocyclohexane inhibited 'capping' whereas the alpha and beta isomers were without effect. In addition, gamma-hexachlorocyclohexane has been shown to antagonize the maintenance of preformed 'caps' and cause the rapid dispersal of the concanavalin A-receptor complexes over the surface of cells by a temperature-dependent mechanism. The possible role of a gamma-hexachlorocyclohexane-sensitive process in the organization of microflow patterns in the lectin-activated lymphocyte membrane is discussed.

Animals↗
PubMed1979

Inhibition of phorbol ester-accelerated amino acid transport in bovine lymphocytes.

12-O-Tetradecanoylphorbol-13-acetate, a highly active tumor-promoting agent and lymphocyte comitogen, rapidly accelerates the transport of alpha-aminoisobutyric acid in cultured bovine lymphocytes. Structure-activity studies show that the ability of phorbol diesters to accelerate alpha-aminoisobutyric acid uptake runs parallel to their potency as lymphocyte comitogens and as tumor promoters in mouse skin. This phorbol ester-accelerated, amino acid transport is largely insensitive to the inhibition of RNA and protein synthesis by actinomycin D and cycloheximide, respectively, and is insensitive to the inhibition of membrane movement by cytochalasin B and colchicine. Retinoic acid, an antagonist of the tumor-promoting and comitogenic actions of phorbol esters also inhibits the acceleration of amino acid uptake by 12-O-tetradecanoylphorbol-13-acetate; however, the epoxy derivatives of retinoic acid and structurally related analogs, which are potent antagonists of the other aspects of phorbol ester activation of lymphocytes, are inactive in blocking amino acid uptake. Comparative studies in lymphocytes show that this phorbol ester elicits a number of metabolic responses which appear to originate at the cell membrane and that these are differentially antagonized by retinoic acid, the 5,6-epoxide of retinoic acid, and related retinoid analogs.

Aminoisobutyric Acids↗
PubMed1979

Possible role of glucocorticoid receptors in globin gene expression in differentiating Friend cells.

Previous studies from this laboratory have shown that the expression of globin genes during the dimethyl sulfoxide-induced differentiation of T3C12 Friend erythroleukemia cells in inhibited by dexamethasone and related glucocorticoids. The present report shows that dexamethasone exerts a similar effect on the accumulation of globin mRNA and hemoglobin in differentiating GM86 Friend cells, but that these cells are less sensitive to this hormone. The higher sensitivity of T3C12 cells has been correlated with the presence of 6 times as many cytoplasmic glucocorticoid receptors as in the GM86 cells. The receptors of T3C12 cells have been shown to have properties in common with glucocorticoid receptors found in other tissues. It is proposed that these receptors may be responsible for the steroid control of the globin genes in Friend cells.

Animals↗