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Biomedical subjects

F Bayard

Publications and source records attributed to F Bayard.

At least 109 records · Page 6Linked to original sources
PubMed1986

Phorbol esters induce both intracellular translocation and down-regulation of protein kinase C in MCF-7 cells.

Exposure of MCF-7 human breast cancer cells to phorbol ester 12-O-tetradecanoyl-13-acetate (TPA) results in a complete inhibition of cell proliferation. We investigated the effects of TPA on protein kinase C activity when cells were exposed to phorbol ester for various lengths of time. TPA induces within 5 min a drastic dose-dependent decrease of the cytosolic protein kinase C activity. The enzyme apparently lost at the cytosolic level was only partially recovered in the particulate fraction. The apparent down-regulation of the translocated enzyme which was only 34% after 1 min reached 72% and 84% after respectively 10 min and 15 min. Moreover, when cells are treated with TPA for longer periods of time, the particulate protein kinase C activity continues to decrease, dropping below control after 1 hour. This progressive decline leads to an almost complete disappearance of protein kinase C activity in MCF-7 cells after 45 hours of TPA treatment. The apparent loss of protein kinase C activity upon short- as well as long-exposure of cells to TPA was not accompanied by a concomitant increase of Ca, PL-independent protein kinase activity. We discuss the implication of these biochemical events in the inhibition of cell proliferation with regard to the respective short- and long-term effects of TPA on protein kinase C activity.

Biological Transport↗
PubMed1986

Possible role of protein phosphorylation in the mitogenic effect of high density lipoproteins on cultured vascular endothelial cells.

The implication of protein phosphorylation in the mitogenic action of high density lipoproteins (HDL) on bovine vascular endothelial cells was investigated by incubating endothelial cell cultures in the presence of 32P-labeled phosphoric acid. The incorporation of 32P into proteins was measured after fractionation by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and autoradiography of the gel. In endothelial cells seeded at low density and made quiescent by serum starvation, HDL markedly and consistently enhanced the degree of phosphorylation of a Mr 27,000 protein in a time- and dose-dependent manner. Using 500 micrograms/ml HDL, 32P labeling of the 27-kDa protein was already measurable after 10 min of incubation and reached a maximum at 20-30 min. Minimal effective dose of HDL during a 30-min incubation period was in the range of 5-10 micrograms/ml. While the apolipoprotein moiety of HDL was able to mimic the effect of total HDL, the lipid part of HDL was not. Furthermore, fibroblast growth factor appeared to potentiate the effect of HDL on 27-kDa protein phosphorylation, in agreement with the synergism observed between fibroblast growth factor and HDL on endothelial cell proliferation. Two activators of protein kinase C, 12-O-tetradecanoylphorbol 13-acetate and 1-oleoyl-2-acetylglycerol also induced the phosphorylation of the 27-kDa protein. These results suggest that the 27-kDa protein may be a physiological substrate for protein kinase C and that HDL could exert their mitogenic effect on endothelial cells through activation of protein kinase C and subsequent protein phosphorylation.

Amino Acids↗
PubMed1986

Activation by phorbol esters of protein kinase C in MCF-7 human breast cancer cells.

Exposure of MCF-7 human breast cancer cells to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) leads to the inhibition of cell proliferation. We investigate here the short-term effects of TPA on subcellular distribution of protein kinase C, and on protein phosphorylation in cultured MCF-7 cells. We report a rapid and dramatic decrease in cytosolic protein kinase C activity after TPA treatment. Only 30% of the enzymatic activity lost in the cytosol was recovered in the particulate fraction. These data suggest that subcellular translocation of protein kinase C is accompanied by a rapid down-regulation of the enzyme (70%). Furthermore, TPA and other protein kinase C activators rapidly induce the phosphorylation of a 28 kDa protein in intact MCF-7 cells. Phorbol esters devoid of tumor-promoting activity are ineffective both for inducing these early biochemical events and for inhibiting cell proliferation.

Breast Neoplasms↗
PubMed1986

Different interaction of estradiol and antiestrogens with the estrogen receptor of rat uterus.

Cytosoluble estradiol-receptor (ER) complexes obtained from uteri of castrated rats show a 4.3 S sedimentation coefficient when analysed by sucrose gradient in high salt buffer both in the absence and presence of 0.1 M ammonium thiocyanate. After incubation with nuclei, the complexes sediment at 4.3 S and at 3.2 S, in the absence and presence of 0.1 M ammonium thiocyanate respectively. This structural modification of ER is also confirmed by gel filtration analysis. In similar conditions hydroxytamoxifen-ER complexes apparently do not undergo such a modification. However, increasing the molarity of the chaotropic ion up to 0.5 M shows that, in fact, the modification occurs. Sodium dodecylsulfate-polyacrylamide gel electrophoresis analysis of covalently linked tamoxifen aziridine-ER 'complexes' confirms that the nuclear treatment reduces the apparent molecular weight of ER from 62 000 to 47 000. These data demonstrate that, in vitro, nuclear ER is cleaved into a smaller molecular form and that the receptor fragments can be held together by the triphenylethylene antiestrogen hydroxytamoxifen.

Animals↗
PubMed1986

Dissimilarities between the uterine estrogen receptor in cytosol of castrated and estradiol-treated rats.

The estrogen receptor (ER) in its native state appears oligomeric and can be dissociated by salt into a monomer with a mol wt of 50,000-80,000. Lower molecular weight fragments have also been observed but are considered to result from ER proteolysis by tissue proteases. Three-month-old Sprague-Dawley rats have been studied after castration, estradiol treatment (3 days at 25 micrograms/day), or during the normal estrus cycle. The uterine cytosol was labeled with [3H]estradiol, and the [3H]estradiol-receptor complexes were studied by sucrose gradient centrifugation, gel filtration, diethylaminoethyl (DEAE)-Trisacryl and phosphocellulose chromatography, and kinetic experiments. In low salt buffer in presence of molybdate (20 mM), uterine ER of castrated and treated rats could not be differentiated by sucrose gradient centrifugation (9.9S), gel filtration (7.7 nm), or DEAE-Trisacryl and phosphocellulose chromatography, but the dissociation rate at 23 C was lower for castrated than for treated rats (t1/2 = 45 and 27 min, respectively). In high salt buffer (0.4 M KCl) in presence of molybdate (20 mM), no difference was apparent by sucrose gradient centrifugation (3.7S) or gel filtration (3.4 nm), but again the dissociation rate at 23 C was lower for castrated than for treated rats (t1/2 = 102 and 45 min, respectively). In high salt buffer in presence of molybdate and ammonium thiocyanate (0.5 M), differences were observed by sucrose gradient centrifugation (3.6 and 3.2S), gel filtration (3.2 and 2.6 nm), and dissociation rate assays at 10 C (t1/2 = 24 and 12 min) for castrated and treated rats. The calculated wts were 50,000 and 35,000, respectively. Protection from limited proteolysis by molybdate, contained in all buffers used, plus various protease inhibitors, particularly leupeptin, as well as mixing tissues before homogenization, suggested that the 35,000-dalton monomer was not a product of protease action formed after cell breakage. ERs covalently labeled with [3H]tamoxifen aziridine also showed different entities of 62,000 and 47,000 mol wts, respectively, on denaturing polyacrylamide gels. In vitro activation and transformation were demonstrated for the two types of [3H]estradiol-receptor complexes by sucrose gradient centrifugation analysis and affinity for phosphocellulose and purified nuclei. Finally, it has been shown that both entities coexisted in different proportions during the diestrous (1:2) and proestrous (1:1) phases of the estrus cycle; only the low mol wt component was present during the estrous phase.

Animals↗
PubMed1985

Interaction of estradiol and high density lipoproteins on proliferation of the human breast cancer cell line MCF-7 adapted to grow in serum free conditions.

The responsiveness of the human mammary carcinoma cell line MCF-7 to estradiol and tamoxifen treatment has been studied in different culture conditions. Cells from exponentially growing cultures were compared with cells in their initial cycles after replating from confluent cultures ("confluent-log" cells). It has been observed that estradiol stimulation of tritiated thymidine incorporation decreases with cell density and that "confluent-log" cells are estrogen unresponsive for a period of four cell cycles in serum-free medium conditions. On the other hand, growth of cells replated from exponentially growing, as well as from confluent cultures, can be inhibited by tamoxifen or a combined treatment with tamoxifen and the progestin levonorgestrel. This growth inhibitory effect can be rescued by estradiol when cells are replated from exponentially growing cultures. The growth inhibitory effect cannot be rescued by estradiol alone (10(-10) to 10(-8) M) when cells are replated from confluent cultures. In this condition, the addition of steroid depleted serum is necessary to reverse the state of estradiol unresponsiveness. Serum can be replaced by high density lipoproteins but not by low density lipoproteins or lipoprotein deficient serum. The present data show that estradiol and HDL interact in the control of MCF-7 cell proliferation.

Breast Neoplasms↗
PubMed1984

Rapid purification and activity of apolipoprotein C1 on the proliferation of bovine vascular endothelial cells in vitro.

The growth-promoting activity of human high-density lipoproteins (HDL) and of their apolipoprotein components on bovine vascular endothelial cells in vitro has been compared. When maintained on plastic culture dishes and exposed to medium containing lipoprotein-deficient serum and fibroblast growth factor, these cells do not proliferate. Addition of either HDL or the total HDL apolipoproteins induces significant cell proliferation. Apolipoprotein C1, purified by chromatography on the ion-exchanger resin Polybuffer exchanger 94, has an effect on the cell growth similar to that of the total apolipoproteins of HDL.

Animals↗
PubMed1983

Physicochemical and genetic evidence for specific antiestrogen binding sites.

In rat uterus and human breast cancer MCF-7 cell cytosol, the antiestrogens tamoxifen (Tam) and 4-hydroxytamoxifen (OH-Tam) bind to "antiestrogen binding sites" (ABS), which do not bind estradiol (E). Demonstrated in total cytosol by binding studies with radioactive antiestrogens in the presence of a large concentration of E, ABS can be physically separated from E-binding estrogen receptor (ER) by removing the latter with an E-containing bioaffinity adsorbent or with heparin-Sepharose gel. ABS concentration is 10-20% of that of ER; the Kd for Tam and OH-Tam is 1-2 x 10(-9) M, whereas the Kd of OH-Tam binding by ER (approximately equal to 1 x 10(-10) M) is approximately equal to 1/50 that of Tam. Other triphenylethylene antiestrogens compete against Tam for binding to ABS, contrary to steroid hormones. Sucrose gradient ultracentrifugation analyses of total cytosol and of affinity gel effluents show a heterogenous pattern of ABS from 10 to 40 S, unchanged by 0.4 M KCl and limited trypsinization (which however provoke transitions of ER from 8S to 4S forms) and by 20 mM molybdate (which stabilizes the 8S form of ER and prevents large aggregates). Preliminary results suggest that ABS may be associated with particulate components of the cell. RTx6 cells of a clone selected from MCF-7 cells for resistance to the antigrowth effect of Tam have ER in the same concentration and have similar affinity for E and antiestrogens as do unselected MCF-7 cells. However, RTx6 cells have virtually no ABS detectable by binding and gradient ultracentrifugation studies. It is proposed that the double binding of Tam and OH-Tam to ER and ABS in estrogen target cells may be related to the complex double series of estrogenic and "antiestrogenic" activities displayed by nonsteroidal triphenylethylene derivatives.

Animals↗
PubMed1981

[Mechanism of action of a triphenylethylene type antiestrogen on growth of the human breast cancer cell line. MCF-7 in culture].

The antiestrogen of the triphenylethylene type, Taxomifen (Tx), exerts its inhibitory action on cell multiplication of the human breast cancer cell line MCF-7 in the complete absence of estrogens in the culture medium. These cells contain saturable, high affinity (KA = 7 x 10(8) LM(-1)) binding sites for Tx and specific for antiestrogens (12,000 sites/cell). The concentration of these sites is significantly decreased in Tx-resistant variants of this cell line (2,700 sites/cell). In contrast, the concentration of estrogen receptors is similar in this population of variants and in the wild population (43,000 and 48,000 sites/cell respectively). These data support the concept of a role of these antiestrogen binding sites in the molecular mechanism controlling the multiplication of these breast cancer cells.

Breast Neoplasms↗
PubMed1981

Different effects of oestradiol, oestriol, oestetrol and of oestrone on human breast cancer cells (MCF-7) in long term tissue culture.

The effects of oestradiol (Oe2), oestrone (Oe1), oestriol (Oe3), oestetrol (Oe4) on the induction of the progesterone receptor (PgR) and growth of MCF-7 cells are compared. All the four oestrogens increased cell PgR concentration. Analysis of the dose-response curves shows induction by Oe2 to be 10 times and 50 times greater than Oe3 and Oe4, respectively. Oe1 and Oe2 are equally effective, even with consideration of metabolic conversion of O31 into Oe2. When compared with untreated cells, Oe2, Oe3, and Oe4 do not influence significantly the plating efficiency but all 3 hormones increase thymidine incorporation of the cells in log phase growth. Oe2, Oe3 and Oe4 are able to rescue the growth inhibition induced by antioestrogens. The respective potency compared to Oe2 is again in the range of 10 and 50 times lower for Oe3 and Oe4, respectively. On the other hand Oe1 decreases plating efficiency, thymidine incorporation and does not rescue the growth inhibition induced by antioestrogens when the metabolic conversion of Oe1 into Oe2 is prevented. Thus, Oe3 and Oe4 behave like complete Oe2 agonists whereas Oe1 has dissociated effects, agonist on PgR induction and antagonist on cell growth.

Breast Neoplasms↗
PubMed1980

17 beta-Hydroxysteroid dehydrogenase in monkey endometrium during the menstrual cycle and at the time of implantation.

In order to furhter identify physiological similarities between 17 beta-hydroxysteroid dehydrogenase (HSD) in human and monkey endometrium and to evaluate the role of estradiol-17 beta (e2) oxidation to estrone (E1) during periimplantation events, 30 rhesus monkeys were studied at different intervals of the nonfertile menstrual cycle (days 8, 12, 15, 18 and 24). Also, five pregnant monkeys provided endometrial tissue on day 24 of the fertile menstrual cycle, near the expected time of implantation. HSD activity in endometrium was low at midfollicular phase (day 8), increased to maximal levels (8-fold) during the periovulatory span (days 12 and 15), and was intermediate in mid to late luteal phase (days 18 and 24) in non-fertile menstrual cycles. In the absence of ovulation, HSD was low throughout. These enzyme data fit with a pattern of daily peripheral serum levels of E2 and progesterone (P) and suggest that when the normal sequence of P follows elevated estrogens in late follicular phase, HSD activity is markedly enhanced in the early luteal phase. However, HSD activity in endometrium did not increase more in the fertile menstrual cycle, despite further elevations of serum P during rescue of the corpus luteum.

17-Hydroxysteroid Dehydrogenases↗
PubMed1980

Patterns of estrogen and progesterone receptors in monkey endometrium during the normal menstrual cycle.

Total concentrations of estradiol-17 beta (E2) and progesterone (P) receptors (R) were measured in the endometrium of rhesus monkeys (Macaca mulatta) during the normal menstrual cycle. The endometrium was collected at abdominal fundal hysterotomy on days 8, 12, 15, 18 and 24 of the menstrual cycle. Visual inspection of the ovaries and measurement of E2, P, follicle stimulating hormone (FSH) and luteinizing hormone (LH) provided assuredness of normal ovarian function. Exchange procedures were used in order to measure the total concentrations of E2R and PR in nuclear and cytosol fractions. The pattern of estrogen receptor showed a slight increase in the cytosol and nuclear concentrations at the preovulatory interval. Later, the total E2R concentration was decreased when P increased during the luteal phase. Cytosol PR synthesis was parallel to the serum E2 increase during the late follicular phase. Secretion of P by the corpus luteum was accompanied by a rapid nuclear translocation and concomitant decrease in cytoplasmic PR. Thereafter the total PR concentration declined during the second half of the luteal phase. These findings in monkey endometrium are similar to those reported for human endometrium during the normal menstrual cycle and further establish the utility of these surrogate primates in investigations indicative of human endometrial function.

Animals↗