THYROID-HORMONE INFLUENCES BETA-MYOSIN HEAVY-CHAIN (BETA-MHC) EXPRESSION

3,5,3'-Triiodo-L-thyronine (T3) regulation of beta-MHC expression was studied in rat fetal heart cells using deletion mutants of both the ra t and human promoter regions fused to a CAT expression vector. T3 inhi bited the expression of human and rat beta-MHC constructs with an IC50 of about 1nM, which was similar to the EC50 for betaMHC-mRNA observed in cardiomyocytes. Deletion analysis of betaMHC promoter constructs s uggested that a T3 response element (TRE) is located near the start of transcription. Possibly, T3-receptor binding at this site interferes with formation of the transcriptional initiation complex. (C) 1994 Aca demic Press, Inc.