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Biomedical subjects

M Atger

Publications and source records attributed to M Atger.

At least 55 records · Page 3Linked to original sources
PubMed1980

[Uteroglobin].

Uteroglobin has been studied under two aspects: 1) as a model of specific interaction between a protein and a steroid hormone: crystals were obtained and analyzed by X-ray diffraction; 2) as a marker of progesterone action in the endometrium: messenger RNA was translated, purified and transcribed into complementary DNA.

Animals↗
PubMed1979

N-terminal sequences of uteroglobin and its precursor.

Translation of uteroglobin mRNA in wheat-germ extract has yielded a precursor protein (pre-uteroglobin) containing an N-terminal extension of 21 amino acid residues. The sequence of this extension and that of the 50 N-terminal amino acid residues of uteroglobin have been determined.

Amino Acid Sequence↗
PubMed1976

Interaction of rat-liver glucocorticoid receptor with DNA.

The complex of [3H]dexamethasone and rat liver receptor binds to rat liver DNA. This interaction takes place only in the presence of hormone and is enhanced by 'activation'. No evidence of saturatability can be obtained with concentrations of steroid-receptor complexes corresponding to those observed physiologically in the intact liver cell. The binding is inhibited by high ionic strength and by millimolar concentrations of divalent cations. No species specificity has been observed: the complex binds equally well to prokaryotic and eukaryotic DNA'S. There was no difference between binding to native and denatured DNA. In comparable conditions twice as much [3H]dexamethasone-receptor complexes were bound by DNA than by rat liver nuclei. Thus, the interaction of steroid-receptor complexes with DNA probably does not correspond to the recognition of a few very specific sequences. It is however possible that this interaction is actually operating in vivo in the intact cell.

Animals↗
PubMed1976

Chromatographic separation on phosphocellulose of activated and nonactivated forms of steroid-receptor complex. Purification of the activated complex.

Steroid-receptor complexes formed at low temperature and ionic strength are unable to bind to target cell nuclei. After a temporary exposure to high ionic strength and/or temperature they become activated (i.e., able to bind to nuclei). However, there exists an equilibrium between activated and nonactivated complexes; thus, mixtures of both populations are obtained. In this paper it is shown that activated [3H]triamcinolone acetonide-rat liver receptor complexes bind strongly to phosphocellulose, whereas nonactivated complexes do not. Thus, it is chromatographically possible to isolate these two populations of complexes. The experimental conditions of the separation have been established. The most important feature is that upon prolonged exposure to phosphocellulose, nonactivated complexes become progressively activated. The separation on phosphocellulose has at least three potential applications. A first application is the possibility of measuring the concentration of activated complexes in incubates. However, when activated complexes were titrated with rat liver nuclei in excess or assayed through binding to phosphocellulose, slightly different results were obtained. This discrepancy was due on one hand to the difficulty of obtaining binding of all the activated complexes and on the other hand to the second activation of some of the complexes during their exposure to phosphocellulose. A second application was the possibility of obtaining a homogeneous population of activated complexes. This was actually achieved, since the complexes eluted from phosphocellulose were demonstrated to be 90--100% activated. The use of such homogeneous preparations simplifies considerably studies on binding of steroid-receptor complexes to nuclear acceptors (nuclei, chromatin, DNA). A third application is the use of phosphocellulose for the purification of receptor. Cytosol containing nonactivated complexes was filtered through phosphocellulose the complexes present in the breakthrough of the column were then activated and bound to phosphocellulose in a second chromatography. Advantage was also taken of the "amphoteric" behavior of the receptor that binds to both anionic (phosphocellulose) and cationic (diethylaminoethylcellulose) resins. Purification (940fold) with 24% yield could be obtained in preparations taking less than 2 days. The partially purified receptor was a heavy aggregate (greater than 12 S) that could be dissociated into 4S subunits by exposure to 0.3 M K C1. It has kept its property of interacting with nuclear acceptor. Preliminary experiments have shown that this technique could be of general application for steroid hormone receptors: activation enhanced binding to phosphocellulose of progesterone, aldosterone, and estradiol receptors.

Animals↗
PubMed1976

Mechanism and kinetics of the thermal activation of glucocorticoid hormone receptor complex.

Steroid-receptor complexes formed at low temperature and ionic strength do not bind to nuclei or chromatin. After a temporary exposure to high temperature, or ionic strength, or both, a fraction of them becomes activated (able to bind to nuclei). An assay of the activated form of the complex based upon titration with nuclei in excess was established. This assay was used to perform kinetic and equilibrium studies of the thermal activation of glucocorticoid-receptor complex in order to elucidate its mechanism. It was found that the reaction is of apparent first order and yields a monomolecular product. It thus probably consists of a conformational change in the steroid-receptor complex. The rate of activation is 1.37 +/- 0.06 X 10(-3) S-1 at 25 degrees. The free energy of thermodynamic activation (The word activation is used here in its usual thermodynamic meaning and not in the sense of receptor modification) of this reaction is greater than G = 21.3 Kcal. The corresponding enthalpy and entropy are respectively greater than H = 31.4 kcal and greater than S = 4 cal/degree. These positive and high values of greater than H and greater than S are very similar to those described for denaturation reactions of proteins suggesting that breakage of some noncovalent bonds could take place during activation. The reaction proceeds until approximately 60% of the complexes are activated. It was shown that this corresponds to an equilibrium between activated and nonactivated forms and not to the presence of a population of complexes unable to undergo activation. This equilibrium is not modified by temperature variations between 10 degrees and 30 degrees. It is possible to activate over 80% of the complexes when the activation is performed in the presence of excess acceptor, thus shifting the equilibrium. A similar situation is probably observed in situ in cells since 90% of the complexes are found in the nuclei when liver slices are incubated with hormone.

Animals↗