Essential Role Of Tea Domain Transcription Factors In The Negative Regulation Of The Myh 7 Gene By Thyroid Hormone And Its Receptors

MYH7 (also referred to as cardiac myosin heavy chain beta) gene expression is known to be repressed by thyroid hormone (T3). However, the molecular mechanism by which T3 inhibits the transcription of its target genes (negative regulation) remains to be clarified, whereas those of transcriptional activation by T3 (positive regulation) have been elucidated in detail. Two MCAT (muscle C, A, and T) sites and an A/T-rich region in the MYH7 gene have been shown to play a critical role in the expression of this gene and are known to be recognized by the TEAD/TEF family of transcription factors (TEADs). Using a reconstitution system with CV-1 cells, which has been utilized in the analysis of positive as well as negative regulation, we demonstrate that both T3 receptor (TR) beta 1 and alpha 1 inhibit TEAD-dependent activation of the MYH7 promoter in a T3 dose-dependent manner. TR beta 1 bound with GC-1, a TR beta-selective T3 analog, also repressed TEAD-induced activity. Although T3-dependent inhibition required the DNA-binding domain (DBD) of TR beta 1, it remained after the putative negative T3-responsive elements were mutated. A co-immunoprecipitation study demonstrated the in vivo association of TRb1 with TEAD-1, and the interaction surfaces were mapped to the DBD of the TR beta 1 and TEA domains of TEAD-1, both of which are highly conserved among TRs and TEADs, respectively. The importance of TEADs in MYH7 expression was also validated with RNA interference using rat embryonic cardiomyocyte H9c2 cells. These results indicate that T3-bound TRs interfere with transactivation by TEADs via protein-protein interactions, resulting in the negative regulation of MYH7 promoter activity.