Wong J, Patterton D, Imhof A, Guschin D, Shi Y B, Wolffe A P
Laboratory of Molecular Embryology, National Institute of Child Health and Human Development, Bethesda, MD 20892-5431, USA.
EMBO J. 1998 Jan 15;17(2):520-34. doi: 10.1093/emboj/17.2.520.
Histone deacetylase and chromatin assembly contribute to the control of transcription of the Xenopus TRbetaA gene promoter by the heterodimer of Xenopus thyroid hormone receptor and 9-cis retinoic acid receptor (TR-RXR). Addition of the histone deacetylase inhibitor Trichostatin A (TSA) relieves repression of transcription due to chromatin assembly following microinjection of templates into Xenopus oocyte nuclei, and eliminates regulation of transcription by TR-RXR. Expression of Xenopus RPD3p, the catalytic subunit of histone deacetylase, represses the TRbetaA promoter, but only after efficient assembly of the template into nucleosomes. In contrast, the unliganded TR-RXR represses templates only partially assembled into nucleosomes; addition of TSA also relieves this transcriptional repression. This result indicates the distinct requirements for chromatin assembly in mediating transcriptional repression by the deacetylase alone, compared with those needed in the presence of unliganded TR-RXR. In addition, whereas hormone-bound TR-RXR targets chromatin disruption as assayed through changes in minichromosome topology and loss of a regular nucleosomal ladder on micrococcal nuclease digestion, addition of TSA relieves transcriptional repression but does not disrupt chromatin. Thus, TR-RXR can facilitate transcriptional repression in the absence of hormone through mechanisms in addition to recruitment of deacetylase, and disrupts chromatin structure through mechanisms in addition to the inhibition or release of deacetylase.
组蛋白去乙酰化酶和染色质组装参与非洲爪蟾甲状腺激素受体（TR）和9-顺式视黄酸受体（RXR）异二聚体对非洲爪蟾TRbetaA基因启动子转录的调控。在将模板显微注射到非洲爪蟾卵母细胞核后，添加组蛋白去乙酰化酶抑制剂曲古抑菌素A（TSA）可缓解由于染色质组装导致的转录抑制，并消除TR-RXR对转录的调控。非洲爪蟾组蛋白去乙酰化酶的催化亚基RPD3p的表达可抑制TRbetaA启动子，但仅在模板有效组装成核小体后才会出现这种情况。相比之下，未结合配体的TR-RXR仅对部分组装成核小体的模板有抑制作用；添加TSA也可缓解这种转录抑制。这一结果表明，与未结合配体的TR-RXR存在时相比，单独由去乙酰化酶介导转录抑制时，染色质组装的要求不同。此外，通过微小染色体拓扑结构的变化以及微球菌核酸酶消化后常规核小体梯带的消失来检测，激素结合的TR-RXR靶向染色质破坏，而添加TSA可缓解转录抑制但不会破坏染色质。因此，TR-RXR可以通过除募集去乙酰化酶之外的机制在无激素情况下促进转录抑制，并通过除抑制或释放去乙酰化酶之外的机制破坏染色质结构。
