Cardiac Myocyte Differentiation Induced by 3,5,3′-Triiodo-L-Thyronine (T3) in P19-Teratocarcinoma Cells Is Accompanied by Preferential Binding of RGG(T/A)CA Direct Repeats Spaced by Four Base Pairs in the DNA

Abstract When treated with T 3 , P19 cells differentiate into ultrastructurally proven cardiac myocytes and express the cardiac ventricular specific marker ventricular myosin light chain 2V. This differentiation is irreversibly induced in culture during the first 48 hrs of exposure to T 3 . We studied the binding of P19-indigenous transcription factors of the Steroid-Thyroid-Retinoic superfamily of nuclear receptors to oligonucleotide response elements bearing direct, inverted and palindromic repeats of the consensus sequence RGG(T/A)CA. Electrophoretic mobility shift assays showed a preference in T 3 -treated P19 cells for binding RGG(T/A)CA "half sites" in direct repeat orientation separated by 4 base pairs. The specificity of binding was confirmed in competition experiments. This finding suggests that target genes bearing thyroid response elements spaced by 4 base pairs in their promoter regions play an important role in the cardiac differentiation induced by T 3 in P19 teratocarcinoma cells.