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S Jaken

Publications and source records attributed to S Jaken.

85 records · Page 5Linked to original sources
PubMed1983

Association of phorbol ester receptor down modulation with a cryptic receptor state.

Sustained exposure of GH4C1 rat pituitary cells to phorbol esters or the hypothalamic tripeptide thyrotropin-releasing hormone decreases the number of phorbol ester binding sites without changing affinity (down modulation; Jaken, S., Tashjian, A. H., Jr., and Blumberg, P. M. Cancer Res., 41: 2175-2181, 1981). In untreated control cultures, the concentration of receptors in lysates was not significantly different from the concentration in intact cells. In contrast, in down-modulated cultures, the concentration of receptors in lysates was greater than the concentration in the corresponding intact cells and instead was equal to the concentration in lysates of control cultures. Therefore, the processes of both homologous (phorbol ester-induced) and heterologous (thyrotropin-releasing hormone-induced) phorbol ester receptor down modulation involves the generation of a cryptic receptor state that is revealed upon cell lysis. Furthermore, comparison of receptor properties in cells and lysates revealed that the affinity of the receptor for phorbol dibutyrate was decreased from a Kd of 11.1 +/- 0.6 nM (S.D.) in intact cells to 40 +/- 10 nM in cell lysates. Binding of the receptor for the structurally related diterpene, mezerein, fit a one-component model in intact cells, but was better fit to a two-component model in cell lysates. That is, the apparently homogeneous phorbol 12,13-dibutyrate receptor population in cell lysates appeared heterologous with respect to mezerein binding. This is not due to a preferential recovery of a subset of receptors in the lysates, because no substantial loss of receptor number was associated with cell lysis. Instead, these results suggest that the affinity and ligand specificity of the phorbol ester receptor may depend on its cellular environment.

Animals↗
PubMed1983

Relationship between mezerein-mediated biological responses and phorbol ester receptor occupancy.

The phorbol ester analog, mezerein, is a weak complete and Stage 1 tumor promoter; however, it is as potent as the most active phorbol esters as a second stage promoter and inflammatory agent. Therefore, mezerein is a useful compound for studying responses associated with Stage 1 or Stage 2 promotion. In this paper, we show that in G-292 osteosarcoma cells in culture, mezerein is 25-fold more potent in causing a decrease in binding of epidermal growth factor to its specific cellular receptor than in inducing prostaglandin E2 production. This differential potency for these two actions was not noted for other phorbol esters. Our findings indicate that mezerein interacts with the major phorbol dibutyrate receptor to increase prostaglandin E2 production and also either with a distinct cellular target with a higher affinity or the same target with increased efficacy to cause a decrease in the binding of epidermal growth factor. These human osteosarcoma cells thus provide a model system to facilitate analysis of phorbol ester receptor heterogeneity.

Binding, Competitive↗
PubMed1982

Specific binding of phorbol ester tumor promoters to mouse tissues and cultured cells.

Phorbol esters bind to mouse tissues and chick embryo fibroblasts in a specific, saturable, and reversible fashion. The binding site, located in the membrane fraction, is heat and protease sensitive. Binding can be measured most readily with [3H]PDBu. Binding of [3H]PDBu is of high affinity and is inhibited competitively by nonradioactive phorbol esters; the dissociation constants of the phorbol esters correspond quantitatively to their respective biological and tumor-promoting activities. Of particular significance, highly inflammatory but weakly promoting or nonpromoting diterpene esters are much less potent than PMA. Binding of [3H]PMA has been measured directly. The results confirm that PMA and PDBu interact at the same major high-affinity binding site. [3H]PDBu binding is entropy driven. The equilibrium dissociation constant is independent of temperature, whereas the off-rate is highly temperature dependent. In vivo, specific binding activity increases during embryonic development. It also shows considerable variation among tissues. In the mouse, highest binding activity, 28 pmole/mg, is in the brain (skin, for example, binds 3.9 pmole/mg). Between regions of he brain, 10-fold differences in binding activity are found. The high level of phorbol ester binding in brain suggests that the phorbol ester receptor plays a functional rather than an exclusively information-transducing role in the cell. Growth of cells in the presence of PDBu causes marked down-modulation of phorbol ester receptors. In the GH4C1 rat pituitary cell line, receptor number is decreased by 80% in 24 hr. In membrane preparations, the phorbol ester binding affinity is calcium sensitive. It has been speculated that endogenous ligands interacting at the phorbol ester receptor may exist. The finding that the supernatant fraction from boiled or acidified brain inhibits [3H]PDBu binding is therefore exciting.

Animals↗
PubMed1981

Correlation between a specific molecular weight form of plasminogen activator and metabolic activity of 3T3 cells.

In quiescent cultures of 3T3 cells, plasminogen activator (PA) is found predominantly as a 75,000 dalton species. When quiescent cells are exposed to mitogenic agents such as phorbol myristate acetate, Ca++, or 25% serum, the absolute levels of PA in cell lysates may either increase or decrease. However, a consistent observation is that in the stimulated cultures PA is found predominantly as a 49,000 dalton species. This also is the predominant form of PA in growing and transformed cells. Concomitant with the mitogen-induced stimulation of the 49,000 dalton PA in quiescent cultures is a change in morphology to one that is characteristic of growing and transformed cells. The data suggest that PA is not operative in causing the morphological change that occurs with activation; however, the 49,000 dalton PA in particular is closely related to the pleiotypic response accompanying growth stimulation and transformation.

Animals↗
PubMed1981

Regulation of plasminogen activator in 3T3 cells: effect of phorbol myristate acetate on subcellular distribution and molecular weight.

The tumor promoter, phorbol myristate acetate (PMA), stimulates plasminogen activator production and extracellular release in confluent Swiss 3T3 cells. Coordinated with the increased extracellular release is a redistribution of the activity into plasma membrane-enriched fractions and a shift in the predominant molecular weight species from 75,000 to 49,000 daltons. The evidence suggests that PMA induces the formation of the 49,000 dalton species which is preferentially located in plasma membrane-enriched fractions.

Animals↗
PubMed1981

Relationship between biological responsiveness to phorbol esters and receptor levels in GH4C1 rat pituitary cells.

During a 24-hr incubation of GH4C1 cells with phorbol esters or thyrotropin-releasing hormone, there is a decrease in the number of phorbol esters receptors (down-modulation). The purpose of this study was to investigate whether this decrease in receptor number attenuated cellular responsiveness to subsequent challenge with phorbol esters. Accordingly, cellular sensitivity to a phorbol ester-mediated biological response, namely the decrease in binding of epidermal growth factor, was compared in control and down-modulated cells. This phorbol ester-mediated event is closely associated with phorbol ester receptor occupancy, and it is therefore an effect for which altered dose-response characteristics correlating with alterations in the number of phorbol ester receptors could be anticipated. In fact, during a 48-hr exposure to phorbol esters, GH4C1 cells become refractory to the effect on epidermal growth factor binding. This time course is similar to that for the loss of phorbol ester receptors. However, when cells are down modulated by pretreatment with phorbol ester or thyrotropin-releasing hormone and then (re)challenged with phorbol ester, no differences in dose-response characteristics were observed between control and down-modulated cells. We therefore conclude that phorbol ester receptor down-modulation does not affect cellular responsiveness to phorbol esters, at least when decreased epidermal growth factor binding is used as the marker for the phorbol ester-mediated event.

Animals↗
PubMed1981

Characterization of phorbol ester receptors and their down-modulation in GH4C1 rat pituitary cells.

Phorbol ester binding to intact GH4C1 cells, a continuous strain of rat pituitary cells, was measured using [3H]phorbol 12,13-dibutyrate. The binding was saturable; Scatchard analysis indicated one class of high-affinity binding sites (Kd, 11 nM) with 6.4 pmol [3H]phorbol 12,13-dibutyrate bound per mg cell protein at saturation. The relative binding affinities for other phorbol esters and analogs were similar to those demonstrated for binding to homogenates of chick embryo fibroblasts and mouse skin, as well as for tumor promotion in vivo. A close correlation was shown to exist between the binding affinities of these derivatives and their potencies for inducing biological responses in GH4C1 cells, such as decreases in binding of epidermal growth factor and thyrotropin-releasing hormone. A distinctive new finding is the down modulation of phorbol ester binding sites on GH4C1 cells by both homologous and heterologous ligands. Prolonged exposure to phorbol esters or thyrotropin-releasing hormone produced a loss of available [3H]phorbol 12,13-dibutyrate binding sites with a maximal decrease to about 20% of control after 24 hr of treatment. Scatchard analysis indicated that the decrease in binding was due to a loss of receptors with no change in affinity. The biological significance of phorbol ester receptor down modulation is not yet known; however, it may represent a mechanism for attenuating cellular responsiveness to phorbol esters in their continued presence.

Animals↗
PubMed1981

Variation with embryonic development and regional localization of specific [3H]phorbol 12,13-dibutyrate binding to brain.

We have previously characterized specific binding of the phorbol ester tumor promoter [20-3H]phorbol 12,13-dibutyrate to several tissues, including mouse skin and brain. We report here that specific binding activity in chicken brain increases dramatically during development. In whole embryonic chicken brain, binding increased from 2.0 to 6.8 to 10.6 pmol/mg of protein at 7, 14, and 20 days, respectively. Adult chicken brain bound 15 pmol/mg of protein. In contrast to specific binding activity, binding affinity remained constant. Substantial regional localization of binding activity within the brain was found. For calf brain, representative values ranged from 4.6 pmol/mg for medulla to 38.1 pmol/mg for frontal lobe. Binding affinity did not vary. Inhibition of binding by postulated neurotransmitters and antagonists was examined. D-Propranolol and quinidine, membrane-stabilizing drugs, inhibited binding competitively, although at mM concentrations.

Animals↗
PubMed1979

Purification and comparison of several catalytic parameters of the gamma-glutamyltranspeptidase of rat mammary adenocarcinoma (13762) and of normal rat mammary gland.

A method for the purification of a membrane-bound glycoprotein, gamma-glutamyltranspeptidase ((gamma-glutamyl)-peptide:amino-acid gamma-glutamyltransferase, EC 2.3.2.2), from a transplantable rat mammary tumor (13762 MT) is described. The properties of the tumor enzyme were compared with those of gamma-glutamyltranspeptidase similarly isolated from mammary tissue of nonpregnant multiparous rats. Evidence has been presented elsewhere that the mammary and tumor enzymes exist as groups of species differing in isoelectric point and that the tumor enzyme contains more of the those species with lower isoelectric points. In this study the normal and tumor enzyme preparations are found to be identical or very similar in regards to the effect of papain on molecular size, the ratios of the enzymatic activities as measured with various amino acids, the Km for gamma-glutamyl-p-nitroanilide, and the Ki for inhibition by glutathione. Neuraminidase treatment had no effect on these catalytic properties. The properties observed were generally similar to those previously reported for highly purified rat kidney preparations.

Adenocarcinoma↗
PubMed1979

Differences in intracellular distribution of plasminogen activator in growing, confluent, and transformed 3T3 cells.

The intracellular distribution of plasminogen activator in growing, confluent, and transformed 3T3 cells was investigated by using sucrose density gradient centrifugation. In confluent cells, which do not release plasminogen activator extracellularly, most of the activity was found in a heavy membrane fraction. In growing and transformed 3T3 cells, which do release plasminogen activator extracellularly in large amounts, most of the activity was found in lighter, plasma membrane-enriched fractions. A correlation between its presence in the light membrane fractions and the ability of the cells to release the plasminogen activator extracellularly is made.

Cell Cycle↗
PubMed1978

Differences in the isoelectric focusing patterns of gamma-glutamyl transpeptidase from normal and cancerous rat mammary tissue.

Highly purified fractions of gamma-glutamyl transpeptidase [gamma-glutamyltrinsferase; (5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2] from normal and malignant rat mammary tissue were prepared. Analyses by isoelectric focusing indicate the existence of at least 12 enzymatically active species. The gamma-glutamyl transpeptidase from the tumor tissue had a greater proportion of the activity concentrated in the more negative species than the enzyme from normal tissue. Treatment of the two enzyme preparations with neuraminidase (acylneuraminyl hydrolase, EC 3.2.1.18) greatly reduced this difference. When whole tissue homogenates were treated with papain to solubilize the enzyme and then focused, the same relationship held. The neuraminidase activities in the two homogenates were similar, but the sialytransferase activity (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) of the tumor homogenate was 13 times that of the normal mammary homogenate. These observations suggest that the gamma-glutamyl transpeptidase of the tumor is more heavily sialylated than that from the normal tissue, possibly reflecting the greater sialyltransferase activity of the tumor.

Adenocarcinoma↗