The effect of endocrine disrupting chemicals on thyroid hormone binding to Japanese quail transthyretin and thyroid hormone receptor

ABSTRACT An aqueous two-phase partitioning study of partially purified nuclear thyroid hormone receptor from rat liver was performed. Stability of 3,5,3′-tri-iodo-l-thyronine (T3)–receptor complex and T3-binding activity in the presence of dextran or polyethylene glycol were assessed in order to determine the amount of occupied or unoccupied receptors in each phase. Partition coefficients were calculated as the ratio of receptor concentration in the upper polyethylene glycol-rich phase H2O and that in the lower dextranrich phase H2O. The partition coefficient was a sensitive function of the salt at pH above 6·1 and below 5·1. The salt had no effect on the partition coefficient at pH around 5·6. These results suggest that the isoelectric point of the thyroid hormone receptor is about 5·6, confirming previous determinations using isoelectric focusing. The partition coefficient of the receptor decreased upon T3 binding, regardless of the salt composition. In contrast, the partition coefficient of thyroxine-binding globulin increased upon T3 binding. Free T3 preferentially partitioned into the upper polyethylene glycol-rich phase and gave a partition coefficient higher than 1·0. These results strongly suggest that the decrease in the partition coefficient of the receptor upon hormone binding reflects conformational changes or changes in electrostatic properties of the receptor upon hormone binding. Such an alteration may be involved in biological activation of the receptor upon hormone binding. J. Endocr. (1988) 119, 431–437

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Loss of thyroid hormone receptor activity in primary cultured rat hepatocytes is reversed by 2-mercaptoethanol

Biochemical Journal ◽

10.1042/bj2810669 ◽

1992 ◽

Vol 281 (3) ◽

pp. 669-673 ◽

Cited By ~ 7

Author(s):

N Yamamoto ◽

A Inoue ◽

K P Takahashi ◽

Q Li ◽

H Nakamura ◽

...

Keyword(s):

Thyroid Hormone ◽

Hormone Receptor ◽

Hormone Receptors ◽

Thyroid Hormone Receptor ◽

Primary Cultures ◽

Rat Hepatocytes ◽

Binding Activity ◽

Dependent Manner ◽

Hormone Binding ◽

Level Of Activity

In primary cultures of rat hepatocytes, specific thyroid-hormone-binding activity diminished with time and was hardly detectable at 24 h. In accordance with the loss of 3,5,3′-tri-iodothyronine (T3) binding, responses to the hormone disappeared, as indicated by low induction of the thyroid-hormone-responsive gene S14. In contrast, thyroid hormone receptor proteins were present, as determined by immunostaining with a specific antibody against the receptor. Thus the loss of T3 binding was due to receptor inactivation. After various attempts to restore the T3-binding activity, we found that 2-mercaptoethanol, a reducing agent, when added to the culture medium restored the hormone binding activity in a dose- and time-dependent manner. The observed kinetics and experiments using cycloheximide suggested that mercaptoethanol prevented inactivation of the newly synthesized receptors. Oxidoreductive conditions within cells may have a role in determining the level of activity of thyroid hormone receptors.

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