UP-REGULATION OF MYOGLOBIN (MB) GENE EXPRESSION BY THYROID HORMONE (T3) IN RAT CARDIAC MUSCLE: POSSIBLE INVOLVEMENT OF E-BOX-ASSOCIATED PROTEINS. Gisele Giannocco., Rosangela A. Santos, Maria Tereza Nunes. Department of Physiology and Biophysics, ICB1, University of São Paulo, São Paulo, Brazil.
T3 markedly increases heart function. Considering that Mb gene is highly expressed in the heart, improving O2 diffusion and mitochondrial respiration, we investigated if T3 is involved in Mb gene expression and if DNA binding activity of nuclear proteins are altered by T3 using E- box consensus sequence as a probe. Time-course studies were performed in euthyroid and thyroidectomized (Tx) rats treated, or not, with 100 ug/100 g of T3, BW, iv, for 30, 60, 120 min, 6 and 24 h. Rats were killed by decapitation; nuclear and cytosolic protein from ventricular (V) muscle were isolated. The cytosolic protein was electrophoresed and the Mb abundance were determined by western blot, using a laser-scanning densitometer. Nuclear protein was used to perform the electrophoretic mobility shift assays (EMSA). It was shown that Mb expression is under T3 control in V muscle, as indicated by decreased Mb protein content in Tx rats. The time-course study showed a progressive increase in the Mb protein abundance, as early as 30 min, which exceeded the control levels at 24 h of the T3 treatment. EMSA showed an enhanced capacity of nuclear proteins to bind the E-box probe after T3 treatment while Tx rats displayed a diminished binding. The present results showed that (1) Mb protein and, as previously shown, mRNA content are influenced by T3 and (2) T3 enhanced the binding capacity of E-box- associated proteins in rat cardiac muscle.