Joint study for the thyroid hormone receptor phosphorylation

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 08044231
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Joint Research
• Research Institution: Tohoku University
• Principal Investigator: SUGAWARA Akira Tohoku University The 2nd Dept, of Int. Med. Josyu, 医学部・附属病院, 助手 (90270834)
• Co-Investigator(Kenkyū-buntansha): YEN Panl M. ; SACKS David B. ; CHIN Willoam W. Harvard Medical School Dept. of Med. Professor
• Project Period (FY): 1996
• Keywords: Thyroid Hormine / Receptor / Phosphorylation

Research Abstract

Bacterially-expressed human thyroid hormone receptor β-1(hTRβ1) recently has been shown to be phosphorylated in vitro by HeLa cytosolic extract. In the present study, we first demonstrated that hTRβ1 also could be phosphorylated in vitro by purified casein kinase II(CKII). Phosphoamino acid analysis revealed that hTRβ1 was phosphorylated on both serine and threonine residues. In vitro CKII phosphorylation of glutathione S-transferase (GST)hTRβ1 fusion proteins whose predicted CKII phosphorylation sites were mutated demonstrated that a threonine residue located in the hinge region (Tht-210) could be phosphorylated by CKII. In order to elucidate the functional significance of CKII phosphorylation of Thr-210 in hTRβ1, we next performed transient transfection studies using either wild type or Thr-210 mutated hTRβ1. Interestingly, the basal repression level in the absence of ligand was attenuated significantly when Thr-210 mutated hTRβ1 was used. Since Thr-210 is located within the interacting domain with nuclear receptor co-repressor (N-CoR), we next performed electrophoretic mobility shift assay (EMSA) to examine the interaction between amino terminal-truncated N-CoR (NCoRI) and wild type or Thr-210 mutated hTRβ1. Interestingly, in contrast to retinoid X receptor β(RXRβ) which equally formed heterodimers with both types of hTRβ1, NCoRI preferentially formed heterodimers with wild type hTRβ1 than Thr-210 mutated hTRβ1. Taken together, we speculate that CKII phosphorylation of Thr-210 in hTRβ1 might modulate interaction with N-CoR, and contribute to mediate basal repression in the absence of ligand.