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M Pons

Publications and source records attributed to M Pons.

At least 91 records · Page 5Linked to original sources
PubMed1994

Antiestrogenic effects of all-trans-retinoic acid and 1,25-dihydroxyvitamin D3 in breast cancer cells occur at the estrogen response element level but through different molecular mechanisms.

Most breast tumors show estrogen-dependent growth and are thus susceptible to antiestrogenic therapy. MCF-7 cells, obtained from a human estrogen-dependent breast carcinoma, are widely used for studying the modulation of estrogenic responses by different effectors. All-trans-retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (Vit D3) inhibited estrogen-induced growth of MCF-7 cells and their effect was potentiated by the classical antiestrogen, hydroxytamoxifen. In MCF-7 cells, we found that RA and Vit D3 also inhibited estrogen-induced transcription; this was shown both for an endogenous gene (pS2) and for various exogenous transfected genes. Their inhibitory effect could not be reversed by increasing estradiol concentrations, showing that contrary to classical antiestrogens, they did not compete with estradiol to bind the estrogen receptor (ER). Analysis of the inhibitory mechanisms indicates that RA and Vit D3 receptors can directly or indirectly impair the binding of ER to the estrogen responsive element. The antagonist effect of RA would be found especially at DNA level since it seems to essentially involve an estrogen responsive element. The antagonist effect of Vit D3 would be found especially at the ER level since it seems to concern estrogen binding and dimerization domains of ER. We conclude that the antiestrogenic effects of RA and Vit D3 are similar since they can, via their receptors, interfere with estrogenic action at the estrogen responsive element level but that they are not identical since different molecular mechanisms are involved.

Breast Neoplasms↗
PubMed1994

Effect of succinylation on the membrane activity and conformation of a short cecropin A-melittin hybrid peptide.

A 15-residue hybrid peptide (KWKLFKKIGAVLKVL-amide) incorporating partial sequences of cecropin A and melittin causes the release of carboxyfluoresceine encapsulated in phosphatidylcholine liposomes. Succinylation of the amino groups in the N-terminus and lysine side chains inhibits the effect of this peptide on liposome permeability. Conformational analysis of the parent peptide and its succinyl derivative by CD and nmr indicates that both peptides form amphipathic alpha-helices in the presence of hexafluoro-2-propanol, but only the unmodified peptide acquires a relevant level of alpha-helical conformation in the presence of liposomes.

Amino Acid Sequence↗
PubMed1994

Agonist-antagonist activity of anti-estrogens in the human breast cancer cell line MCF-7: an hypothesis for the interaction with a site distinct from the estrogen binding site.

Non-steroidal anti-estrogens exhibit an extremely complex pharmacology because of their estrogenic and anti-estrogenic effects in different species. Recently, we have reported evidence for an immunochemical difference in the estrogen receptor (ER) when it is occupied with anti-estrogens as compared to estrogens (Martin et al., 1988). In this study, we have compared immunoreactivity of MCF-7 cell estrogen receptor when bound to anti-estrogen versus estrogen. We show that the occupation of ER with antiproliferative concentrations of various anti-estrogens leads to the appearance of additional antigenic determinants for the H222 monoclonal anti-estrogen receptor antibody. When performing ER immunoassay after sedimentation of estrogen receptors on sucrose gradients, we show that exposure of new epitopes induced by anti-estrogens can occur on a 4 s molecular form related to the 66 kDa monomeric estrogen receptor. Also, when ER are previously occupied by estradiol, the addition of low anti-estrogen concentrations, which are unable to displace estradiol from the estrogen receptor, leads to a significant increase of H222 epitopes. Our results led us to propose a molecular model for anti-estrogen-receptor interaction in which their dual agonist/antagonist activity may be due to the occupation of distinct binding sites on the estrogen receptor.

Binding, Competitive↗
PubMed1994

Development of specific bioluminescent in vitro assays for selecting potential antimineralocorticoids.

Efficient antimineralocorticoid selection requires a reliable, discriminating and easy assay for monitoring biological activity of not only the specific receptor, but also closely related receptors such as glucocorticoid and progestin. These related activities should be as low as possible to obtain specific antimineralocorticoid compounds. In this paper, we describe two cellular models used for easy and specific measurement of mineralocorticoid and progestin activities. These models involve the induction of firefly luciferase under hormonal control mediated by a chimeric receptor. The first model comprises transiently transfected MCF-7 cells, whereas the second uses stably transfected HeLa cells. Glucocorticoid activity was assayed with the classic tyrosine-aminotransferase induction method in HTC cells. Six compounds of a new family of 11 beta-substituted-17-spirolactone steroids were thus studied and compared to control compounds. Five of them showed antimineralocorticoid activity and one was active at a concentration lower than that of mespirenone.

Animals↗
PubMed1994

Circadian rhythms of renal hemodynamics in unanesthetized, unrestrained rats.

Catheters were placed in the jugular vein and femoral artery of male Sprague-Dawley rats and connected to a specially designed perfusor for continuous constant infusion of 0.9% NaCl and a syringe to perform simultaneous and intermittent blood collections. This permitted continuous 24-h study of renal hemodynamics, estimated by inulin (Cin) and p-amino-hippuric acid (CPAH) clearances; Cin represents glomerular filtration rate and CPAH renal plasma flow. Animals were individually housed in metabolism cages in a controlled environment with light/dark 12:12 h. Urine was collected every 4 h (12:00, 16:00, 20:00, 24:00, 04:00, and 08:00) and blood sampled at the midpoint of urine collection periods. Urine and plasma sodium, potassium, inulin, and PAH were spectrophotometrically assessed. During continuous infusion of isotonic saline, Cin exhibited circadian changes with large decrease between 12:00 and 20:00 h (0.9 +/- 0.2 ml/min) and acrophase at 00:30 h. Rhythmicity in CPAH was similar with the minimum between 16:00 and 20:00 h (2.5 +/- 0.3 ml/min) and peak between 00:00 and 04:00 h (acrophase at 00:25 h). Water and electrolyte excretion were also circadian rhythmic with a similar nighttime enhancement and daytime minimum. Such circadian changes persisted during continuous 0.9% NaCl infusion for several consecutive days. The unanesthetized, unrestrained rat model enables investigations in renal chronopharmacology and chronotoxicology.

Animals↗
PubMed1994

[Hip prosthesis infection: diagnostic approach and treatment of 27 cases].

BACKGROUND: Preoperative diagnosis of hip prosthesis infection (HPI) is difficult. There is no therapeutic option which is completely effective and without risk. The aim of this study was to evaluate a diagnostic approach and therapeutic strategy in a group of patients with HPI. PATIENTS AND METHODS: A retrospective study of 27 episodes of HPI diagnosed by anatomopathologic and/or microbiologic examination of surgical samples was performed. RESULTS: Twenty-three patients with 27 episodes of HPI out of a total of 24 hip prosthesis (HP) were treated. The infection was early in 15 episodes. The etiologic agents were plasmocoagulase negative staphylococcus (NSP) in 11 cases, P. aeruginosa in 8, S. aureus in 5, Enterococcus sp. in 2 and miscellaneous in the remaining cases. In 2 cases the infection was polymycrobial. Following a mean follow period of 22.6 +/- 15.2 months, 13 out of the 14 patients in whom the prosthesis was withdrawn were cured (in 4 a second prosthesis was implanted), one out of 6 in those in whom the prosthesis remained in situ following debridement, and 2 out of 3 episodes in whom reimplantation was performed over time. The withdrawal of the prosthesis was significantly greater than debridement in the treatment of early infection (p < 0.001). The total mean length of postoperative antibiotherapy was 48.2 +/- 17 days. No differences were observed in the oral versus parenteral treatment (p = 0.22), and nor was prognosis worse in those treated for less than 42 days. CONCLUSIONS: The authors' experience suggests that attempts to save a hip prosthesis in early infection usually fail. In addition to prosthesis withdrawal or implantation of another prosthesis, six weeks of postoperative antibiotic therapy, which may be oral route, appear to be sufficient.

Aged↗
PubMed1993

CD of proline-rich polypeptides: application to the study of the repetitive domain of maize glutelin-2.

An overview of CD of proline-rich peptides is reported. First, structural characteristics, theoretical CD studies, and the biological relevance of polyproline II structure in such peptides are discussed. Second, a CD study of peptides belonging to the repetitive domain of maize glutelin-2, H-(Val-His-Leu-Pro-Pro-Pro)n-OH (n = 3, 5, 8), is described. This series of peptides displayed the CD features of polyproline II structure in water (5 degrees C, pH 5). Moreover, it was shown that the addition of increasing amounts of the polyanionic molecule heparin forced a displacement of the conformational equilibrium of those peptides toward higher proportions of the polyproline II structure. In contrast, when the temperature is raised such a structure gradually disappears, leading to more disordered conformations.

Amino Acid Sequence↗
PubMed1993

Relative involvement of protein kinase C and of the estrogen receptor in the cytotoxic action of a population of triphenylethylenes on MCF7 cells as revealed by correspondence factorial (CF) analysis.

A multivariate statistical method, correspondence factorial (CF) analysis, was used to examine the correlations among the protein binding and cell proliferation effects of a series of 36 di- and triphenylethylenes (DPEs and TPEs). The analysis was applied to a study which measured their competition for estradiol binding to cytosol estrogen receptor (ER), their influence on protein kinase C (PKC) activity under different conditions of enzyme activation, their ability to promote the growth of a breast cancer cell line and to inhibit growth at high concentrations (cytotoxicity). The CF analysis revealed several levels of correlation. First, it distinguished those molecules within the population that stimulated rather than inhibited PKC activity. Second, it made apparent a strong correlation between cytotoxicity and inhibition of Ca++ and phosphatidylserine-dependent PKC activity, which was most marked when the enzyme had been activated by diacylglycerol indicating that PKC inhibition under physiological conditions might contribute to the overall cytotoxicity of these compounds. Third, a lower level of correlation was established between competition for ER binding and cytotoxicity. Taken together, the results suggest that MCF7 cells might be most sensitive to a cytotoxic effect of TPEs (via PKC and other targets) when they at the same time decrease estrogen-stimulated proliferation via an ER-mediated antiestrogenic effect.

Animals↗
PubMed1993

MVLN cells: a bioluminescent MCE-7-derived cell line to study the modulation of estrogenic activity.

We previously established a stable expression system in MCF-7 cells for the detection of (anti)estrogenic activity by assaying the reporter enzyme activity of firefly luciferase. In this cell line (called MVLN), the bioluminescent response can be measured either in the cellular homogenate, or in intact living cells. Here we present various potential experimental uses of this cellular model. First, we used this cell line to screen natural or synthetic molecules classified as full or partial (anti)estrogens and observed that their behavior towards our model was identical to that expected. Moreover, the bioluminescent response was in agreement with the natural responses like cellular proliferation or stimulation of the progesterone receptor. We then demonstrated the inhibitory effects of retinoic acid and 1,25 dihydroxyvitamin D3, two molecules which do not compete with estradiol for its receptor. We thus deduced that with this cell line an "antiestrogenic" effect which occurred at any step of the estrogenic action, might be detected. Finally, we showed that detection of luciferase activity in intact living cells was particularly helpful for investigating the evolution of estrogenic activity. For instance, we observed that long-term treatment of MVLN cells with an antiestrogen irreversibly decreased the bioluminescent response by more than 90%. This phenomenon affected all cells equally and could not be reversed, even by long-term estradiol treatment. We therefore conclude that this chimeric response faithfully reflects estrogenic action in the cell and can be used to develop different aspects of the endocrine research.

Calcitriol↗
PubMed1992

Study of an antiestrogenic effect of retinoic acid in MCF-7 cells.

We recently developed the cellular model MVLN-15 in which estrogenic action can be detected by bioluminescence. Using this cellular model, we characterized the inhibitory effect of retinoic acid on the estrogen-dependent induction of luciferase transcription. We present evidence that i) the inhibitory effect of retinoic acid is not due to a simple competition between retinoic acid and estradiol for binding to the estrogen receptor, ii) a DNA sequence restricted to an estrogen-responsive element (ERE) was sufficient for the antiestrogenic effect of retinoic acid, and iii) retinoic acid does not act via a cryptic AP-1 binding site associated with this ERE. Therefore, we conclude that the antiestrogenic effect of retinoic acid is due to an inhibition of estrogen receptor activity, for example by altering the amount of estrogen receptor protein bound to the ERE or affecting the transcriptional efficiency of this complex.

Breast Neoplasms↗
PubMed1992

Multivariate analysis by the minimum spanning tree method of the structural determinants of diphenylethylenes and triphenylacrylonitriles implicated in estrogen receptor binding, protein kinase C activity, and MCF7 cell proliferation.

The response profiles of 36 para-substituted diphenylethylenes (DPEs) and triphenylacrylonitriles (TPEs) have been compared by multivariate analysis. The responses measured were (a) relative binding affinity (RBA) for the cytosol estrogen receptor (ER), (b) ability to promote the growth of the human MCF7 breast cancer cell-line, (c) cytotoxicity in MCF7 cells, and (d) ability to stimulate or inhibit protein kinase C (PKC) III activity under three different conditions of enzyme activation. The prime object of the analysis was to observe the simultaneous influence of diverse combinations of substituents on all these in vitro responses. To do this, the minimum spanning tree (MST) method was used to organize the molecules into a network in which proximate molecules are closely related with regard to their responses whereas remote molecules are distinct. The MST of this population of molecules had four main branches. E2 and its TPE mime were located in a central position within the trunk whereas the tips of the branches tended toward molecules of different specificity, i.e., cytotoxic molecules that bind to ER and interfere with PKC, noncytotoxic molecules that also bind to ER and interfere with PKC but promote cell growth, molecules only active on PKC, and molecules active on all parameters except PKC stimulation. A parallel MST analysis of the relationships among the response parameters themselves confirmed previous conclusions: For this population of molecules, RBAs for ER are fairly closely related to ability to promote MCF7 cell growth and only little to cytotoxicity (Bignon et al. J. Med. Chem. 1989, 32, 2092). Cytotoxicity is much more clearly correlated with inhibition of diacylglycerol-stimulated PKC activity than with RBAs for ER. PKC inhibition differs substantially depending upon whether the substrate is H1 histone or protamine sulfate.

Acrylonitrile↗
PubMed1992

[Bioluminescence and creation of chimeric cellular models].

The response of a chimeric cellular model to a hormone has to be more specific, more sensitive, more easily measurable and quantifiable than the natural response. Hence, it can be used either in fundamental and applied studies, for example to analyse hormonal interactions, or to screen new hormone molecules. In the field of steroid hormones, we took benefit from the advantages of the firefly luciferase as receptor gene (simplicity and rapidity of the measurement, high sensitivity, handiness ...) to construct such chimaeric models. Such cell lines were obtained by developing another original use of this reporter gene based on an easy detection of the luciferase activity in intact living cells and using a photon counting camera. This was successfully adapted to obtain and to detect stable transfected cells.

Cell Line↗
PubMed1992

[Using examples of firefly luciferase gene for the study of biological activities (estrogens, retinoids, phorbol esters)].

Some possible applications of chimeric cellular models, specifically responding to an effector through firefly luciferase induction are presented with the help of examples in relation with the biological activity of estradiol or retinoic acid, or phorbol ester. A comparison of experiments on either chimeric or natural responses shows that: i) the responses of both type of cellular models are effector concentration-dependent; ii) these concentrations are in the same order of magnitude; partial agonist compounds and antagonist compounds; iv) potencies (EC50) of test-compounds are similarly classified. Moreover we show that a chimeric cellular model allows the observation of interactions between hormone or effector pathways: it allows readily performed kinetic studies and long-term experiments in intact cells that permit to investigate the effect of a given effector, its reversibility and time-dependent action. Therefore, various steps of a cellular signalling pathway involved in the action of an effector may be observed with such a valuable tool.

Cell Line↗
PubMed1991

Influence of di- and tri-phenylethylene estrogen/antiestrogen structure on the mechanisms of protein kinase C inhibition and activation as revealed by a multivariate analysis.

We have performed a systematic study of the interaction of 36 di- and tri-phenylethylene derivatives (DPEs and TPEs) with protein kinase C (PKC). The results were submitted to a multivariate analysis in order to identify the structural features that might be implicated in interference with the activity of three PKC subspecies under three enzyme activation conditions. Four groups of test-compounds, each with common chemical features, could be distinguished clearly. The first group comprised all TPEs substituted with at least one basic dialkylaminoethoxy side-chain. These inhibited type alpha, beta and gamma PKC subspecies activated by Ca2+ and phosphatidylserine (PS) with or without diolein (DO) at micromolar concentrations but did not inhibit protamine sulfate phosphorylation. The other effectors, which all possessed a 1,1-bis-(p-hydroxyphenyl) ethylene moiety, influenced PKC activity at high concentrations (30-200 microM) and could be divided into two groups. One group constituted PKC inhibitors in the TPE series and inhibited PKC activated by Ca2+, PS and DO, as well as protamine sulfate phosphorylation. The other group constituted dual-type inhibitors/activators in the DPE series and stimulated PKC in the presence of Ca2+ and low PS concentrations but inhibited the enzyme in the simultaneous presence of DO. The fourth group of compounds was inactive and had, for the most part, one or two substituents with weak steric hindrance. In agreement with previous data for six lead compounds, this study suggests that, in these chemical series, a basic amino side-chain leads to interaction with phospholipid and the regulatory domain of PKC, whereas a 1,1-bis-(p-hydroxyphenyl) ethylene moiety leads to interaction with the catalytic domain of the enzyme.

Animals↗