IN VITRODEMONSTRATION OF SPECIFIC TRIIODOTHYRONINE BINDING SITES IN RAT LIVER NUCLEI12

A B S T R A C T We have investigated the relationship between the administration of triiodothyronine (T3) and a high carbohydrate (CHO) fat-free diet in the induction of lipogenic enzymes in two rat tissues, liver, and fat. Male thyroidectomized rats were treated with graded daily doses of T3 and either supplemented with a high CHO diet or left on a regular diet. Enzymes studied included malic enzyme (ME), fatty acid synthetase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase. In the liver, all four lipogenic enzymes showed a synergistic response between T3 administration and high CHO feeding. In fat, ME also responded synergistically. The interaction was reflected in ani increased sensitivity to T3. The dose of T3 required to achieve 50% Y maximal response was reduced three-to seven-fold by the high CHO diet. This phenomenon could not be attributed to a dietary-induced alteration either in T3 metabolism or in number or affinity of the T3-nuclear receptors. Moreover, studies of the relative rate of synthesis of ME suggested a simultaneous time of onset in the induction of ME, within 2 h after the application of either T3 or CHO. Thus, it is unlikely that either stimulus is secondary to the other. Since parallel experiments from this laboratory (Towle, Mariash, and Oppenheimer. 1980. Changes in hepatic levels of messenger ribonucleic acid for malic enzylme during induction by thyroid hormone or diet. show that ME induction both by CHO and T3 is mediated by an increase in specific messenger RNA for ME, the interaction of T3 and the dietary factor occurs at a pretranslational level.Dr.

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“…Since (T3N) = 0.5 in the euthyroid animal (24), and if ii = 3, then it follows that the amplification factor (16 = (1)4/(0.5)4)…”

Section: Resultsmentioning

confidence: 99%

“…Isolation of liver nuclei and determination of the nuclear T3 receptor content and affinity were carried out as previously described (24). Similarly, the ratio of isotopically labeled T3 in nuclei and plasma was determined according to methods previously described (25).…”

Section: Methodsmentioning

confidence: 99%

Synergism of thyroid hormone and high carbohydrate diet in the induction of lipogenic enzymes in the rat. Mechanisms and implications.

Mariash¹,

Kaiser²,

Schwartz³

et al. 1980

J. Clin. Invest.

150

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“…This is based primarily on the good agreement between the relative affinity of thyroid hormone analogues for isolated liver nuclei in vitro and their reported in vivo biologic effects in terms of anti-goiter activity and 02 consumption (14)(15)(16)(17)(18)(19), and induction of a-glycerophosphate dehydrogenase in rat liver (20). Two hormonal analogues which show a higher affinity for the receptor, using isolated nuclei in vitro (21)(22)(23)) as compared with their in vivo biological activity, are triiodothyroacetic acid (triac) and D-triiodothyronine (D-T3). It has been argued that this discrepancy indicates that the cell nucleus is not the only site of action of thyroid hormone in the cell (24).…”

Section: Introductionmentioning

confidence: 93%

“…Studies with isolated liver nuclei by Koemer et al (21) and DeGroot and Torresani (23) have demonstrated that triac has a 164 (21) to 400% (23) greater affinity than L-T3, whereas the relative affinity of D-T3 was equal to (23) or 60% (21) of that of L-T3. These results differ significantly from the relative affinity determined in intact cells with 10% hypothyroid calf serum medium in which triac had an affinity which was slightly less then L-T3, and D-T3 had only 5.8% of the affinity as compared with L-T3.…”

Section: Introductionmentioning

confidence: 99%

Relationship of receptor affinity to the modulation of thyroid hormone nuclear receptor levels and growth hormone synthesis by L-triiodothyronine and iodothyronine analogues in cultured GH1 cells.

Samuels¹,

Stanley²,

Casanova³

1979

J. Clin. Invest.

122

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A B S T R A C T We have previously demonstrated that L-triiodothyronine (L-T3) induces an increase in growth hormone synthesis and messenger RNA in cultured GH1 cells, a rat pituitary cell line. In addition to regulating the growth hormone response, L-T3 elicits a time-and dose-dependent reduction in the level of its nuclear receptor, which is a direct function of the occupancy of the receptor binding site. In this study we have compared the relative affinity of L-T3, triiodothyroacetic acid, D-triiodothyronine (D-T3), and L-thyroxine (L-T4) for the receptor with the induction ofthe growth hormone synthesis and the ability of these compounds to elicit a reduction in thyroid hormone nuclear receptor levels. Triiodothyroacetic acid and D-T3 were specifically examined because the biologic effect of these compounds in the intact rat is significantly lower than predicted by their affinity for the receptor using isolated rat liver nuclei in vitro. In intact cells each compound demonstrated an excellent relationship between the relative receptor affinity, the induction of growth hormone production, and the concentration-dependent reduction in nuclear receptor levels. With the exception of D-T3, the relative affinity of iodothyronine was identical for the receptor using intact cells in serum-free media, or isolated GH, cell nuclei in vitro. The apparent receptor affinity of D-T3 with intact cells was 5.5-fold lower than with isolated nuclei, which suggests a decrease in cell entry of D-T3 relative

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“…Recently, high-affinity, limitedcapacity binding sites for triiodothyronine (T3), and thyroxine (T4), which appear to be receptors for these hormones, have been found in target cell nuclei (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). The concentrations of T3 or T4 required for binding to these receptors and for bioreactivity are similar (6), and there is a good correlation between the ability of thyroid hormone analogs to inhibit T3-receptor binding and to promote the biological effect (15).…”

mentioning

confidence: 99%

Nuclear receptors for thyroid hormone: evidence for nonrandom distribution within chromatin.

Charles¹,

Ryffel²,

Obinata³

et al. 1975

Proc. Natl. Acad. Sci. U.S.A.

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Chromatin receptor proteins appear to mediate some actions of thyroid hormone. In this study, sheared mammalian chromatin containing [125Itriiodo-thyronine (T3) bound by these receptors was separated using sucrose gradient velocity sedimentation. T3-receptor complexes were distributed throughout the chromatin fractions, but were enriched in the slowly sedimenting fractions. The latter contain most of the template capacity for RNA synthesis and most of the endogenous RNA polymerase activity but a minor portion of the total DNA. Formaldehyde treatment of chromatin containing receptor-bound [1261IT3 resulted in fixation of radioactivity, as evidenced by its migration with chromatin after equilibrium density gradient sedimentation in both cesium chloride and Conray. This fixation implies that the T3 receptor protein is closely associated with chromatin. These results suggest that proteins involved in the regulation of gene function may be nonrandomly distributed within chromatin subfractions, and are consistent with a direct role for thyroid hormone in regulating genetic expression.Thyroid hormones play a key role in vertebrate development and maintenance (1-3). Recently, high-affinity, limitedcapacity binding sites for triiodothyronine (T3), and thyroxine (T4), which appear to be receptors for these hormones, have been found in target cell nuclei (4-15). The concentrations of T3 or T4 required for binding to these receptors and for bioreactivity are similar (6), and there is a good correlation between the ability of thyroid hormone analogs to inhibit T3-receptor binding and to promote the biological effect (15). Studies of thyroid hormone analogs also suggest that T3 and T4 function through physical interactions, such as with receptors, rather than through chemical reactions involving iodine or quinones (16).The thyroid hormone receptors appear to be salt-extractable, acidic chromatin proteins (5,8,10,11). The possibility that thyroid hormones act at the chromatin level is also consistent with findings that these hormones influence RNA synthesis (3,17,18). Thus, the receptors may represent an identifiable acidic chromatin protein which possibly regulates the expression of specific genes. In the present studies, the T3 receptor association with chromatin and distribution within sheared chromatin subfractions (19,20)

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IN VITRODEMONSTRATION OF SPECIFIC TRIIODOTHYRONINE BINDING SITES IN RAT LIVER NUCLEI¹²

Cited by 88 publications

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Synergism of thyroid hormone and high carbohydrate diet in the induction of lipogenic enzymes in the rat. Mechanisms and implications.

Synergism of thyroid hormone and high carbohydrate diet in the induction of lipogenic enzymes in the rat. Mechanisms and implications.

Relationship of receptor affinity to the modulation of thyroid hormone nuclear receptor levels and growth hormone synthesis by L-triiodothyronine and iodothyronine analogues in cultured GH1 cells.

Nuclear receptors for thyroid hormone: evidence for nonrandom distribution within chromatin.

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