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Biomedical subjects

G C Mueller

Publications and source records attributed to G C Mueller.

At least 73 records · Page 4Linked to original sources
PubMed1978

Inhibition of the mixed lymphocyte proliferative response by phorbol esters.

The phorbol diester, 12-O-tetradecanoyl-phorbol-13-acetate, a potent cocarcinogen in mice, blocks the induction of DNA synthesis in lymphocytes undergoing the mixed lymphocyte response. At 10(-7) M diester, the induced DNA synthesis is inhibited almost completely (99%). This action of the diester affects some early step in the response which is necessary for the triggering of cell replication; on-going DNA replication is not significantly affected. Phorbol 12,13-diacetate, a less potent analogue in tumor promotion in vivo, is also a less potent inhibitor of the mixed lymphocyte response (75% inhibition at 10(-6) M). Phorbol, the parent alcohol, is not effective in either system. The use of phorbol diesters in the molecular dissection of mixed lymphocyte responses is discussed.

Animals↗
PubMed1978

Control of globin gene expression by steroid hormones in differentiating Friend leukemia cells.

Low levels of dexamethasone and related glucocorticoid hormones suppress the expression of globin genes during the DMSO-induced differentiation of Friend leukemia cells. In this response, the glucocorticoids appear to act at both the transcriptional and post-transcriptional levels in that 10(-8) M dexamethasone prevents the accumulation of both globin mRNA and globin protein, whereas 10(-9) M dexamethasone allows the accumulation of normal levels of hybridizable globin mRNA but prevents the accumulation of globin protein. This suppressive action of dexamethasone is more effective with DMSO as the inducer of globin gene expression than with hemin as the inducer. In contrast to the situation with glucocorticoids, certain sex steroids (etiocholanolone, testosterone and estradiol) facilitate the expression of globin genes in DMSO-treated Friend leukemia cells. The modulation of globin gene expression by steroid hormones is achieved in DMSO-treated cells without altering the growth and morphological changes which characteristically attend the differentiation of these cells.

Cell Differentiation↗
PubMed1978

Displacement of estradiol from estrogen receptors by simple alkyl phenols.

Simple alkyl phenols have been tested for their ability to prevent the binding of [3H]estradiol and to displace the prebound hormone from estrogen receptors of uterine cytosols. Tetrahydronaphthol, an analog of the A and B rings of estradiol, is highly effective in preventing the forward bindng of estradiol. p-sec-Amyl phenol (pSAP) with a flexible alkyl chain corresponding to the B ring of estradiol is highly effective at 0 C in displacing estradiol which had been prebound by the receptor. Both compounds were more effective at 0 C than at 23 C. The data are discussed in terms of sequential conformational changes which might be required for the binding and release of the natural hormones and their possible relevance to receptor action.

Animals↗
PubMed1978

Retinoic acid inhibition of the comitogenic action of mezerein and phorbol esters in bovine lymphocytes.

12-O-Tetradecanoylphorbol-13-acetate (TPA) is an effective comitogen in phytohemagglutinin-treated bovine lymphocytes. Concurrent addition of 10(-8) M TPA gives a greater than 6-fold increase in DNA synthesis over cultures treated with the lectin alone. The delayed addition of phorbol ester, relative to the start of the lectin treatment, eliminates this synergistic action. Structure-function studies show that the comitogenic activity of different phorbol diesters runs parallel to their tumor-promoting activity. A nontoxic level (50 micronM) of retinoic acid selectively antagonizes this synergistic effect of phorbol ester. This inhibitory action requires the near-concurrent addition of retinoic acid with TPA. In contrast, the TPA-mediated induction of RNA and protein synthesis is unaffected by retinolic acid. A number of natural and synthetic retinoids were evaluated; none were as inhibitory as was retinoic acid. Lymphocyte cultures appear to provide a useful system for exploring the mechanisms of action of both TPA and retinoic acid.

Animals↗
PubMed1978

Effects of retinoic acid and juvenile hormone on the induction of ornithine decarboxylase activity by 12-O-tetradecanoylphorbol-13-acetate.

The tumor-promoting agent 12-O-tetradecanoylphorbol-13-acetate (TPA), a highly active comitogen in phytohemagglutinin-treated bovine lymphocytes, induces an 11-fold increase in ornithine decarboxylase activity over cultures treated with the lectin alone. This synergistic action of TPA could be antagonized by the simultaneous addition of the acyclic sesquiterpene, insect juvenile hormone III. Retinoic acid (vitamin A acid), an inhibitor of the tumor-promoting action of TPA in mice, was also an effective antagonist but required administration to lectin-activated lymphocytes 1 hr prior to TPA. These data suggest that metabolic activation of retinoic acid is required in order to exert its antagonistic action. Comparison of the responses in the lymphocytes and mouse skin suggests that the lymphocytes provide an excellent system for studying the molecular processes through which phorbol esters and retinoids influence the growth and differentiation of both normal and premalignant cells.

Animals↗
PubMed1978

Proposed coupling of chromatin replication, hormone action, and cell differentiation.

DNA replication in isolated nuclei is highly dependent on the availability of soluble proteins from the cell cytoplasm. Activity is distributed nonrandomly among the different proteins, and the range of proteins that are required for optimal DNA replication varies with the fractions of DNA being replicated. Support of DNA replication has been correlated with the uptake of these proteins by nuclei and their integration into an immature form of the newly replicated chromatin; the latter has been shown by density analysis to be richer in protein content than the bulk of nonreplicating chromatin. Pulse labeling of DNA in living cells has revealed that a similar protein-rich chromatin is formed as an intermediate in chromatin replication in vivo; however, this form rapidly matures by the exclusion of proteins. The dependency of DNA replication on the presence of soluble cytoplasmic proteins and the physical association of these entities with newly replicated chromatin prompt the proposal that availability of specific proteins may play an important role in determining the ultimate genetic expressability of the matured chromatin and thus the cell phenotype. The finding that dexamethasone, a steroid that regulates the expression of several genes and directs the differentiation of certain cells, can modify the uptake of proteins in isolated nuclei is in accord with this hypothesis.

Cell Differentiation↗
PubMed1977

Deoxyribonucleic acid chain growth and organization of replicating units in HeLa cells.

A method for studying DNA chain growth and chromosomal organization of replicons in HeLa cells has been developed. DNA replication is initiated with bromodeoxyuridine followed by pulse labeling of active replicons with [3H]thymidine and growth of chains for finite intervals in unlabeled thymidine. Photolysis of the bromodeoxyuridine-DNA leader with 313-nm light releases the newly replicated chains that are then analyzed by sedimentation in alkaline sucrose gradients. This method of analysis provides data on the rate of chain growth, the bidirectionality of replication, and the distribution of the active replicons at specific intervals in the S period. Applying this method to cells caused to synthesize DNA at a lowered temperature (27 degrees C) or with protein synthesis restricted by cycloheximide revealed that the immediate reduction in the rate of DNA replication in both instances was due to a decreased rate of chain growth without derangement of the overall process.

Bromodeoxyuridine↗
PubMed1976

Dissociation and reconstitution of the DNA replicase system of HeLa cell nuclei.

The DNA replication system of S-phase HeLa nuclei has been dissociated by cautious extraction at 0 degrees C with 0.25 M NaCl. Replicase activity has been reestablished by recombination of the fractions and reduction of the salt concentration. The reconstituted system, like the starting nuclei, depended on ATP, 4dNTP, MgCl2, the proper ionic strength and the soluble cytoplasmic protein fraction. The activity of the nuclear extract showed a cell cycle dependency and was elevated in the nuclei of cells at the G1 leads to S boundary. In the presence of Mg2+ the major activity of the nuclear extract precipitated during dialysis to reduce the salt concentration; this precipitate exhibited DNA polymerase alpha activity. Chromatography of the active extracts over phosphocellulose separated the replicase supporting factors into three fractions. The major activity eluted in the fraction containing the DNA polymerase alpha activity; the other two active fractions were devoid of polymerase activity. The fraction containing DNA polymerase alpha from the nuclear extracts supported DNA replicase activity in salt-extracted nuclei whereas an equivalent level of DNA polymerase alpha from the cytoplasm was not effective. The data suggest that the DNA polymerase alpha of the salt extracts of S-phase nuclei is either different than the cytoplasmic enzyme or is associated with some essential replicase-supporting factor.

Cell Nucleus↗
PubMed1975

Dissociation of the DNA replicase system of bovine lymphocyte nuclei.

Exposure of S-phase nuclei or subnuclear preparations from phytohemagglutinin-stimulated bovine lymphocytes to 0.02 M ATP caused an immediate and almost total loss of their ability to replicate DNA in vitro. Other ribonucleoside and deoxyribonucleoside triphosphates caused a similar inhibition of DNA replication. Levels of ATP which inhibit replication cause the release of DNA polymerases alpha and beta and small pieces of DNA from these nuclei. This release occurs both at 4 and 37 degrees C. The data support the conclusion that high levels of ATP or other nucleoside triphosphates inhibit DNA replication in nuclei by dissolution of the DNA replication complex. The limited success in reconstitution of the DNA replicase complexes is discussed.

Adenosine Triphosphate↗
PubMed1975

A permeable cell system for studying DNA replication in synchronized HeLa cells.

Treatment of HeLa cells with a hypotonic buffer solution makes them permeable to nucleotides. Cells which are in S-phase at the time of treatment continue to synthesize DNA when supplied with the four deoxyriboside triphosphates, ATP, Mg2+, and the proper ionic environment. DNA replication extends from sites which were active in the cells prior to treatment. The product is confined to the nucleus and is sensitive to deoxyribonuclease. Under optimum conditions, up to 5% of the HeLa genome can be replicated from exogenous nucleotides. In synchronized cultures the level of DNA replicase activity, as measured in permeable cells at different points in the cell cycle, correlates with the rate of [14C] thymidine incorporation measured in the living, untreated cells.

Cell Division↗
PubMed1975

DNA replication in nuclei isolated from bovine lymphocytes.

DNA replication was studied in nuclei isolated from phytohemagglutin-stimulated bovine lymphocytes. The mitogen treatment induced more than 60% of these cells to engage in DNA synthesis with a peak of synthetic activity occurring about 48 h after the addition of phytohemagglutinin. Throughout this response the ability of isolated nuclei and nuclear sonicates to synthesize DNA in vitro was proportional to the synthetic ability of the intact cells of origin. The subcellular systems appear to continue synthesis at replicative sites which were active in vivo. The rate of in vitro synthesis by both nuclei and nuclear sonicates was about two-thirds that of intact cells. The one cytoplasmic and two nuclear DNA polymerase activities separated from these cells were found to have properties similar to those of other eucaryotic cells.

Animals↗
PubMed1975

A requirement for RNA, protein and DNA synthesis in the establishment of DNA replicase activity in synchronized HeLa cells.

DNA replicase activity of synchronized cultures of HeLa cells was assayed by a permeable cell technique during normal S-phase and under conditions of restricted RNA, protein, or DNA synthesis. Inhibition studies with puromycin, cycloheximide, actinomycin D, and 2-mercapto-1-(beta-4-pyridethyl)benzimidazole revealed that the establishment as well as the maintenance of DNA replicase activity in S-phase cells was dependent on the continued synthesis of both RNA and protein. Measurements during limitation of DNA replication by hydroxyurea, cytosine arabinoside, or restricted availability of thymidine indicate that a low level of DNA synthesis is required to activate or assemble some subunits of DNA replicase. Evidence for the existence of short-lived RNA and protein factors essential for DNA replicase activity is discussed.

Cell Division↗