INVESTIGADORES
SUSPERREGUY Sebastian
congresos y reuniones científicas
Título:
HORMONE RECEPTOR B1 (TRb1) GENE TRANSCRIPTION IS INCREASED BY DEXAMETHASONE (DEX) IN RAT LIVER. EVIDENCE FOR THE GLUCOCORTICOID RECEPTOR (GR) INVOLVMENT
Autor/es:
MONTESINOS M; PELLIZAS C; VÉLEZ M; SUSPERREGUY S; MASINI-REPISO A; COLEONI A
Lugar:
Octubre 30-Noviembre 4, 2005- Bs As. Argentina.
Reunión:
Congreso; 13 th Internacional Thyroid Congress; 2005
Resumen:
Glucocorticoids (GC) enhance T3-dependent specific
metabolic actions. We demonstrated that Dex increased TRß1 protein, mRNA and
the transcriptional rate of TR gene in rat liver. Herein, we further explored
the mechanism of the Dex-induced increase of TRß1. We evaluated: a) the effect
of Dex on in vitro TRß1 promoter gene transcriptional activity. COS-7 cells
were transfected with a Luc-plasmid containing TRß1 promoter (-1325bp to
+44bp), GR and TRß1 expression vectors. Cells were treated or not with T3 and
Dex for 12 or 24 h. b) the interaction of proteins from liver nuclear extracts
from control and Dex-treated rats to sequences in the TRß1 promoter by EMSA.
Results: a) Dex-treated COS-7 cells for 12 h increased TRß1 transcriptional
activity only in the presence of T3. Dex for 24 h augmented TRß1 promoter
activity in the absence or presence of T3. b) Sequence analysis of TRß1
promoter revealed a consensus sequence for GR-binding (GRE:-840/-835bp). EMSA
using an oligonucleotide comprising the GRE conserving the flanking nucleotides
of TRß1 promoter (-850/-824) formed two additional complexes with liver nuclear
extracts from Dex-treated vs control rats. Both complexes decreased markedly
after preincubation with anti-GR Ab. Protein extracts from COS-7 cells
overexpressing GR with the oligonucleotide, formed the same complexes observed
with nuclear extracts from Dex-treated rats, revealing the involvement of GR.
TRß1-850/-824 and mutated GRE as competitors reduced such complexes; however
mutations of GRE and the 5
and 3
flanking nucleotides close to GRE abolished the capacity to compete with the
labeled oligonucleotide.
The mechanism of the enhanced T3-dependent
metabolic actions induced by Dex involves an increase of the transcriptional
activity of the TRß1 promoter at least in part, through an interaction of GR
and other transacting factors bound to sequences flanking the GRE in the TRß1
promoter.
The results are of importance considering the impact of GC effect on the
peripheral thyroid hormone metabolic action.