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Dra. Gisele Giannocco
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.
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