FUNCTIONAL EVIDENCE FOR LIGAND-DEPENDENT DISSOCIATION OF THYROID-HORMONE AND RETINOIC ACID RECEPTORS FROM AN INHIBITORY CELLULAR FACTOR
FUNCTIONAL EVIDENCE FOR LIGAND-DEPENDENT DISSOCIATION OF THYROID-HORMONE AND RETINOIC ACID RECEPTORS FROM AN INHIBITORY CELLULAR FACTOR
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DOI：
10.1128/mcb.14.9.5756
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发表时间：
1994-09-01
影响因子：
5.3
通讯作者：
SAMUELS, HH
中科院分区：
文献类型：
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作者：
CASANOVA, J;HELMER, E;SAMUELS, HH
甲状腺激素（L-三碘甲状腺原氨酸[T3]）受体（T3 R）、全反式视黄酸（RA）受体（RAR）和9-顺式RA受体（RAR和RXR）的配体结合结构域包含一系列被认为对二聚体相互作用很重要的七肽基序。使用嵌合体含有氨基酸120至392的鸡T3 R α（cT 3R α）之间的酵母GAL 4蛋白的DNA结合域和有效的90个氨基酸的反式激活结构域的单纯疱疹病毒VP 16蛋白（GAL-T3 R-VP 16），我们提供的功能证据，结合配体释放T3 R和RAR从抑制性细胞因子。GAL 4-T3 R-VP 16不结合T3，并且当单独表达时不激活来自GAL 4报告基因的转录，但当与未配体的T3 R或RAR共表达时能够激活转录。这种激活被T3或RA逆转，表明这些受体与GAL 4-T3 R-VP 16竞争细胞抑制剂，并且配体通过使T3 R或R3 UI与抑制剂解离来逆转这种作用。含有与VP 16连接的cT 3R α（氨基酸120至408）的整个配体结合结构域的嵌合体[G; AL 4-T3 R（JOS）-VP 16]被非配体受体以及T3激活。相反，含有氨基酸120至408配体结合区而没有VP 16结构域的GAL 4-T3 R仅被T3激活。高度保守的第九个七肽，这是参与异源二聚体，似乎参与受体-抑制剂的相互作用，这表明抑制剂是受体基因家族的相关成员。与T3 R和RAR形成鲜明对比的是，RXR仅用其配体9-顺式Ri激活GAL 4-T3 R-VP 16，但未配体的RXR似乎不是这些研究所建议的抑制剂。孤儿受体可能是抑制剂的进一步证据来自我们的发现，COUP-TF抑制GAL 4-T3 R-VP 16被未配体的T3 R激活和GAL 4-T3 R被T3激活。这些和其他结果表明，抑制因子抑制T3 R和RAR的反式激活，而这些受体结合到DNA和配体的作用，部分地，通过灭活或促进受体-抑制剂复合物的解离。
The ligand-binding domains of thyroid hormone (L-triiodothyronine [T3]) receptors (T3Rs), all-trans retinoic acid (RA) receptors (RARs), and 9-cis RA receptors (RARs and RXRs) contain a series of heptad motifs thought to be important for dimeric interactions. Using a chimera containing amino acids 120 to 392 of chicken T3R alpha (cT3R alpha) positioned between the DNA-binding domain of the yeast GAL4 protein and the potent 90-amino-acid transactivating domain of the herpes simplex,virus VP16 protein (GAL-T3R-VP16), we provide functional evidence that binding of ligand releases T3Rs and RARs from an inhibitory cellular factor. GAL4-T3R-VP16 does not bind T3 and does not activate transcription from a GAL4 reporter when expressed alone but is able to activate transcription when coexpressed with unliganded T3R or RAR. This activation is reversed by T3 or RA, suggesting that these receptors compete with GAL4-T3R-VP16 for a cellular inhibitor and that ligand reverses this effect by dissociating T3R or R;UI from the inhibitor. A chimera containing the entire ligand-binding domain of cT3R alpha (amino acids 120 to 408) linked to VP16 [G;AL4-T3R(JOS)-VP16] is activated by unliganded receptor as well as by T3. In contrast, GAL4-T3R containing the amino acid 120 to 408 ligand-binding region without the VP16 domain is activated only by T3. The highly conserved ninth heptad, which is involved in heterodimerization, appears to participate in the receptor-inhibitor interaction, suggesting that the inhibitor is a related member of the receptor gene family. In striking contrast to T3R and RAR, RXR activates GAL4-T3R-VP16 only with its ligand, 9-cis Ri, but unliganded RXR does not appear to be the inhibitor suggested by these studies. Further evidence that an orphan receptor may be the inhibitor comes from our finding that COUP-TF inhibits activation of GAL4-T3R-VP16 by unliganded T3R and the activation of GAL4-T3R by T3. These and other results suggest that an inhibitory factor suppresses transactivation by the T3Rs and RARs while these receptors are bound to DNA and that ligands act, in part, by inactivating or promoting dissociation of a receptor-inhibitor complex.