Transactivation activity of thyroid hormone receptors in fish ( Conger myriaster) in response to thyroid hormones

Abstract

We previously isolated cDNAs encoding conger eel ( Conger myriaster) thyroid hormone (TH) receptors (TRs). In the present study, we investigated the transactivation activities of conger eel TRs treated with THs (3,3′,5-triiodo- l-thyronine [T 3], l-thyroxine [T 4], and 3,3′,5′-triiodo- l-thyronine [rT 3]), or ligands and activators of other nuclear receptors. Following transient transfection into the Japanese eel ( Anguilla japonica) hepatocyte cell line Hepa-E1, the conger eel TRs (cTRs) showed TH-dependent activation of transcription from a TH-responsive promoter. However, no transactivation activity of any of the four cTRs was observed with ligands or activators of other nuclear receptors. Although T 3 activation for cTRs is stronger than other THs (T 3 > T 4 > rT 3), the transactivation sensitivity was different from the activity of cTRs with THs, respectively. Therefore, we conclude that cTRs can act in concert with THs in fish metamorphosis.