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Nuclear thyroid hormone receptors in cultured bone cells
Metabolism: Clinical and Experimental
|January 1, 1986
Summary
This study demonstrates that triiodothyronine (T3) directly binds to nuclear receptors in rat osteosarcoma cells, influencing bone Gla protein secretion. This finding suggests a direct role for thyroid hormones in bone cell metabolism.
Area of Science:
- Endocrinology
- Bone Biology
- Cellular Metabolism
Background:
- Thyroid hormones are known to affect bone metabolism.
- However, direct evidence of triiodothyronine (T3) interaction with nuclear receptors in bone cells was lacking.
Purpose of the Study:
- To investigate the binding of 125I-T3 to nuclei from rat osteosarcoma cells (ROS 17/2.8).
- To determine if T3 nuclear receptors in bone cells are functionally coupled to a biological response.
Main Methods:
- Isolated nuclei from ROS 17/2.8 cells were used for 125I-T3 binding assays.
- Competition assays were performed using unlabeled T3, thyroxine, and 3,3',5'-triiodothyronine.
- Bone Gla protein (BGP) secretion was measured following T3 treatment.
Main Results:
- Saturable binding of 125I-T3 to isolated nuclei was observed, reaching equilibrium within 30 minutes at 37°C.
- T3 exhibited higher affinity for nuclear binding sites compared to thyroxine and 3,3',5'-triiodothyronine.
- Analysis revealed a single class of binding sites with a specific association constant and nuclear binding capacity.
- T3 treatment resulted in a twofold increase in bone Gla protein (BGP) secretion.
Conclusions:
- Direct binding of triiodothyronine (T3) to nuclear receptors in osteoblast-like cells (ROS 17/2.8) was confirmed.
- These T3 nuclear receptors are functionally coupled to the regulation of bone Gla protein (BGP) secretion, indicating a direct role in bone cell function.