Research on the Mechanism of thyroid hormone action

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1. Production of an antibody against c-erb A/nuclear T_3 receptor proteins and analysis of nuclear T_3 receptorsIt has been reported that c-erb A encodes nuclear T_3 receptors (NT_3R). Based on the sequence of c-erb A cDNA, we synthesized a polypeptide consisting of 15 amino acids, the sequence of which has high homology between c-erb A _1, and , and raised an anti c-erb A antibody. We have studied the interaction between NT_3R and the anti c-erb A antibody and obtained the following results.(1) The antibody immunoprecipitated NT_3R prepared from rat liver, kidney, brain and human kidney similarly.(2) The antibody specifically inhibited T_3-binding to NT_3R in a competitive manner. It decreased the value for T3-binding association constant dose dependently, while maximal binding capacity was not influenced.(3) No effect of the antibody was detected on T_3-binding to rat liver cytosolic binding proteins or human serum TBG, suggesting that the protein conformation of the T_3-binding region of these proteins might be different from that of NT_3R.(4) The immunoabsorption study revealed that reverse T_3 binding protein was not the same as NT_3R.(5)The antibody immunoprecipitated the in vitro transcription/translation products of c-erb A _1 and .2. Nuclear T_3 receptors in thyroid cells.We have found that nuclear T_3 receptor proteins exist in porcine thyroid cells and cultured rat thyroid cell line, FRTL-5 cells, and that TSH significantly decreases NT_3R level in FRTL-5 cells. The results may suggest the existence of another control system of the hypothalamic-pituitary-thyroid axis via modulation of the hormone receptor levels.