Jj. Breen et al., THE RAT TSH-BETA GENE CONTAINS DISTINCT RESPONSE ELEMENTS FOR REGULATION BY RETINOIDS AND THYROID-HORMONE, Molecular and cellular endocrinology, 131(2), 1997, pp. 137-146
We have previously shown that thyroid stimulating hormone-beta (TSH be
ta) mRNA levels are modulated by vitamin A status in vivo and using tr
ansient transfection, that suppression of rat TSH beta gene promoter a
ctivity by all-traits retinoic acid (RA) requires RA receptor (RAR) an
d retinoid X receptor (RXR). In this paper we have used deletion analy
sis to delineate the sequences of the rTSH beta gene involved in RA re
gulation, their relationship to the rTSH beta gene negative thyroid ho
rmone response elements and the retinoid receptor species that interac
t with these sequences. Using transient transfection in CV-1 cells, we
found that the -204/+9 region of the rat TSH beta gene, when fused to
a luciferase reporter, was sufficient for suppression by all-trans-RA
in the presence of RAR/RXR. Thus, regulation by RA did not involve th
e major rTSH beta negative TRE located between +15 and +43. Mutational
analysis also showed that the minor rTSH beta negative TRE between -1
1 and +5 was not required by suppression by RA. However, in a heterolo
gous promoter this sequence element acted as a strong positive RARE, T
he combination of RA and T3 treatment caused synergistic inhibition of
rat TSH beta gene expression in the presence of RAR/RXR and TR. EMSA
analysis demonstrated that the -204/-79 sequence binds RAR/RXR heterod
imer. Therefore, we conclude that there are separate response elements
for RA and T3 on the rat TSH beta gene, that the RARE binds RAR/RXR h
eterodimer and that RA and T3 interact functionally via these elements
in the negative regulation of rat TSH beta gene expression. (C) 1997
Elsevier Science Ireland Ltd.