Biomedical subjects

V Pallet

Publications and source records attributed to V Pallet.

28 records · Page 2Linked to original sources

PubMed1996

Dexamethasone decreases the expression of retinoic acid receptors (RARs) in rat liver.

Although adrenalectomy was without effect on the expression of retinoic acid (RA) receptors (RARs), administration of the glucocorticoid analog dexamethasone (Dex) to both control and adrenalectomized rats reduced the expression of these receptors in rat liver. This effect can be mainly attributed to the action of Dex on 4-hydroxylation of RA. Dex, by enhancing 4-hydroxylation of RA, reduces its intracellular concentration thereby leading to a decreased expression of RARs, since RARbeta, the main type of RARs in liver, are known to be up-regulated by RA.

Adrenal Glands↗

PubMed1996

The influence of dietary vitamin A on triiodothyronine, retinoic acid, and glucocorticoid receptors in liver of hypothyroid rats.

The properties of nuclear receptors belonging to the superfamily of receptors acting as transcription factors are modulated by nutritional and hormonal conditions. We showed recently that retinoic acid (RA) restored to normal the expression of receptors attenuated by hypothyroidism. The present study was designed to find out whether dietary vitamin A (as retinol) had the same effect. Propylthiouracil in drinking water induced both hypothyroidism and a vitamin A-deficient status in rats. The maximum binding capacity (Cmax) of triiodothyronine nuclear receptors (TR) was unchanged, while that of nuclear RA receptors (RAR) and nuclear glucocorticoid hormone receptors (GRn) was reduced in the liver of these hypothyroid rats. The reduced Cmax of RAR stemmed from a lower level of RAR mRNA, while the reduced Cmax of GRn was assumed to be due to reduced translocation of the receptor from the cytosol to the nucleus. Feeding the hypothyroid rats with a vitamin A-rich diet did not restore the Cmax of either RAR or GRn to normal. The lack of effect of dietary retinol on RAR expression may be attributed to either genomic (unoccupied TR block the expression of RAR genes) and/or extragenomic (hypothyroidism decreases the availability of retinol and/or its metabolism to RA) mechanisms. Triiodothyronine is thought to favour the translocation of glucocorticoid hormone receptors from cytosol to nucleus. These findings provide more information on the relationship between vitamin A and hormonal status, showing that a vitamin A-rich diet is without apparent effect on the expression of nuclear receptors in hypothyroid rats.

Actins↗

PubMed1995

Retinoids modulate the binding capacity of the glucocorticoid receptor and its translocation from cytosol to nucleus in liver cells.

The binding capacity (Cmax) of the glucocorticoid hormone receptor (GR) was affected by vitamin A status in rat liver. In rats fed on a vitamin A-overloaded diet as well as in rats administered with retinoic acid (RA) there was an increased ratio Cmax of nuclear GR (expressed as fmol/mg liver): Cmax of cytosolic GR (expressed as fmol/mg liver) while in rats fed on a vitamin A-deficient diet this ratio was decreased. These results suggested that an increased amount of RA, resulting from either metabolization of an increased amount of dietary retinol or RA administration, enhanced the translocation of GR from the cytosolic compartment to the nuclear compartment. Moreover such an increased amount of RA could also induce the observed decreased Cmax of the total GR that we observed. These observations were similar to the well known effects of dexamethasone administration on the properties of GR. It is probable that RA, similarly to dexamethasone treatment, induces a dissociation of the tetrameric form of the cytosolic GR and thus enhances translocation of the monomeric form from cytosol to nucleus and also resulting in an increased proteolytic degradation of the receptor.

Animals↗

PubMed1994

Retinoic acid differentially modulates triiodothyronine and retinoic acid receptors in rat liver according to thyroid status.

Triiodothyronine (T3) receptors (TRs) and retinoic acid (RA) receptors (RARs) exert their effects on growth, differentiation and cellular homeostasis by acting as transcription factors. The binding characteristics of these receptors have been studied in liver of hypothyroid and hyperthyroid rats, with or without treatment with T3, RA or T3 + RA together. The changes in binding induced by RA treatment depended on the hormonal status of the rat. In hypothyroid rats the T3 binding capacity was unaltered by administration of T3 or RA alone but increased by 48% after treatment with T3 and RA together. In these rats administration of RA, T3 or T3 + RA increased the RAR binding capacity by 45, 79 and 112%, respectively. In hyperthyroid rats the administration of RA reduced the TR and RAR binding capacities by 22 and 37%, respectively. We found also that the affinity constants of TRs and RARs were reduced in hypothyroid rats after treatment with T3 or T3 + RA. It is suggested that this change of the properties of receptors is related to a ligand-dependent conformational change in these receptors.

Animals↗

PubMed1993

Chronic ethanol administration enhances retinoic acid and triiodothyronine receptor expression in mouse liver.

Chronic alcoholism induces perturbations of storage and metabolization of retinol and related compounds. After 6 months of ethanol consumption we have observed in mouse liver an increased expression of Tri-iodothyronine receptors (TR) while the expression of retinoic acid (RA) receptors (RAR) was unaffected. After 10 months of alcoholization the TR expression was strongly increased and the RAR expression was also increased. At this time the activity of aldehyde dehydrogenase and that of alcohol dehydrogenase, two enzymes involved in biosynthesis of RA from retinol, were similar in the liver of alcoholized and pair-fed mice. Thus it can be hypothesized that (i) the change of RAR expression was, at least in part, the result of a change of TR expression (result in agreement with previous data), (ii) the increased expression of RAR could induce apoptosis and subsequently liver necrosis.

Alcohol Dehydrogenase↗

PubMed1993

Dietary vitamin A modulates the properties of retinoic acid and glucocorticoid receptors in rat liver.

Properties of retinoic acid receptors and glucocorticoid receptors of rat liver were influenced by retinol status in a nonsimilar manner. The binding of the retinoic acid receptors which was lowered in vitamin A--deficient animals relative to controls was restored by a single dose (100 micrograms) of retinoic acid; in vitamin A--overloaded animals (40-fold the control intake) the binding was greater than in controls. The binding of the glucocorticoid receptor was higher in vitamin A--deficient rats than in controls and restored by retinoic acid supplementation, but did not differ from controls in the vitamin A--overloaded rats. The cellular actions of glucocorticoid hormone and retinoic acid were investigated by assaying the activity of some related enzymes. The activity of tyrosine aminotransferase reflected glucocorticoid receptor binding in vitamin A--deficient and vitamin A--restored rats. The decreased tyrosine amino transferase activity observed in vitamin A--overloaded rats could be related to the inhibition of expression of tyrosine amino transferase gene by retinoic acid. Alcohol dehydrogenase activity was unaffected or only slightly affected by vitamin A status. The known existence of glucocorticoid hormone- and retinoic acid--sensitive elements in the alcohol dehydrogenase gene could explain such observations. Furthermore, the changes in the binding of retinoic acid receptors and glucocorticoid receptors were often in opposite directions. These results provide new evidence for the mechanisms by which the amount of dietary vitamin A modulates hormonal status.

Administration, Oral↗

PubMed1992

Retinoic acid decreases retinoic acid and triiodothyronine nuclear receptor expression in the liver of hyperthyroidic rats.

Retinoic acid (RA) and triiodothyronine (T3) exert many of their actions by binding to specific nuclear receptors (respectively, RA receptor (RAR) and T3) receptor (TR) belonging to a 'superfamily' of receptors. Some heterologous regulation of these receptors has been shown, and in particular regulation of the maximum binding capacity of TR by either retinol or RA. Now, using hyperthyroidic rats as a model, the effect of RA on binding capacity and on the mRNA levels of TR and RAR was investigated. The results show that the benefit of vitamin A treatment for the hyperthyroidic state, which has been described for a long time, could be the result of a down-heteroregulation of TR by RA, the active metabolite of retinol.

Animals↗

PubMed1991

Calpain 1-protein kinase C complex: effect of calpain inhibitors after dissociation.

A calpain 1-protein kinase C (PKC) complex was isolated from rabbit skeletal muscle by hydrophobic interaction chromatography on phenyl-sepharose and by strong anion exchange chromatography on Q-Sepharose. Calpain 1 and kinase activities were then dissociated on a phenyl-Sepharose matrix using gradients of decreasing ionic strength. The purified PKC obtained corresponded to conventional PKC and was recognized by a monoclonal antibody specific for alpha and beta isotypes. Leupeptin, calpain inhibitor II, and the more selective calpain inhibitors calpeptin and MDL 28170 did not block the activation of the purified PKC by Ca2+ and phosphatidylserine.

Amino Acid Sequence↗

PubMed1988

[Calpains, protein kinase c and development of muscle tissue].

Calpains are Ca2+ -dependent thiol proteases which have been identified in various tissues of eucaryotes, but their physiological function in the cell is uncertain. In the muscle fiber, two types of calpains are present which differ by their calcium sensitivity: calpain 1 and calpain 2, which require for their activity micro and millimolar concentrations of calcium respectively. These calpains are associated with protein kinase C activities in the differentiated fiber. The multinucleate myotube is formed by fusion of mononucleated precursor cells, myoblasts. Calpains have been reported to appear in myoblasts at around the time of fusion. Moreover, an apparent synthesis of 1,2 diacylglycerol, an activator of protein kinase C, was observed during fusion of myoblasts. However, more information is required to incriminate totally protein kinase C and calpains in the mechanism of myoblast fusion.

Animals↗

PubMed1987

Association of calpains 1 and 2 with protein kinase C activities.

Calpains 1 and 2 co-eluted with protein kinase C activities after hydrophobic (phenyl-Sepharose) and anion-exchange (Mono Q) chromatographies of a 100,000 X g supernatant which was defined as cytosol. After centrifugation of the cytosol at 200,000 X g for 16 h, the major part of calpain 1 and of its associated protein kinase C activity was recovered in the pellet, when the major part of calpain 2, also associated to a protein kinase C activity, was present in the resulting supernatant. Polyacrylamide gel electrophoresis of the fractions eluted from the Mono Q column, which contained calpains 1 or 2 and their associated protein kinase C activities, revealed two main bands with a molecular mass of 80 and 28 kDa.

Animals↗