Acetylation of nuclear hormone receptor superfamily members: Thyroid hormone causes acetylation of its own receptor by a mitogen-activated protein kinase-dependent mechanism

Abstract

Because the androgen and estrogen nuclear hormone receptors are subject to acetylation, we speculated that the nuclear thyroid hormone receptor-β1 (TRβ1), another superfamily member, was also subject to this posttranslational modification. Treatment of 293T cells that contain TRβ1 wt with l-thyroxine (T 4)(10 −7 M, total concentration) resulted in the accumulation of acetylated TR in nuclear fractions at 30–45 min and a decrease in signal by 60 min. A similar time course characterized recruitment by TR of p300, a coactivator protein with intrinsic transacetylase activity. Recruitment by the receptor of SRC-1, a TR coactivator that also acetylates nucleoproteins, was also demonstrated. Inhibition of the MAPK (ERK1/2) signal transduction cascade by PD 98059 blocked the acetylation of TR caused by T 4. Tetraiodothyroacetic acid (tetrac) decreased T 4-induced acetylation of TR. At 10 −7 M, 3,5,3′-triiodo- l-thyronine (T 3) was comparably effective to T 4 in causing acetylation of TR. We studied acetylation in TR that contained mutations in the DNA-binding domain (DBD) (residues 128–142) that are known to be relevant to recruitment of coactivators and to include the MAPK docking site. In response to T 4 treatment, the K128A TR mutant transfected into CV-1 cells recruited p300, but not SRC-1, and was subject to acetylation. R132A complexed with SRC-1, but not p300; it was acetylated equally well in both the absence and presence of T 4. S142E was acetylated in the absence and presence of T 4 and bound SRC-1 under both conditions; this mutant was also capable of binding p300 in the presence of T 4. There was no serine phosphorylation of TR in any of these mutants. We conclude that (1) TRβ1, like AR and ER, is subject to acetylation; (2) the process of acetylation of TR requires thyroid hormone-directed MAPK activity, but not serine phosphorylation of TR by MAPK, suggesting that the contribution of MAPK is upstream in the activation of the acetylase; (3) the amino acid residue 128–142 region of the DBD of TR is important to thyroid hormone-associated recruitment of p300 and SRC-1; (4) acetylation of TR DBD mutants that is directed by T 4 appears to be associated with recruitment of p300.