Department of Bioscience, Faculty of Applied Bioscience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
Mol Brain. 2009 Nov 19;2:34. doi: 10.1186/1756-6606-2-34.
Previous studies have demonstrated tissue-specific regulation of the rhythm of circadian transcription, suggesting that transcription factor complex CLOCK/BMAL1, essential for maintaining circadian rhythm, regulates transcription in a tissue-specific manner. To further elucidate the mechanism of the cell type-specific regulation of transcription by CLOCK/BMAL1 at the molecular level, we investigated roles of CBP/p300 and tissue-specific cofactors in CLOCK/BMAL1-mediated transcription.
As shown previously, CBP/p300 stimulates CLOCK/BMAL1-mediated transcription in COS-1 cells. However, CBP/p300 repressed CLOCK/BMAL1-mediated transcription in NIH3T3 cells and knockdown of CBP or p300 expression by siRNA enhanced this transcription. Studies using GAL4-fusion proteins suggested that CBP represses CLOCK/BMAL1-mediated transcription by targeting CLOCK. We further investigated mechanisms of this cell type-specific modulation of CLOCK/BMAL1-mediated transcription by CBP by examining roles of co-repressor HDAC3 and co-activator pCAF, which are highly expressed in NIH3T3 and COS cells, respectively. CBP repressed CLOCK/BMAL1-mediated transcription in COS-1 cells when HDAC3 was overexpressed, but activated it in NIH3T3 cells when pCAF was overexpressed. CBP forms a complex with CLOCK by interacting with HDAC3 or pCAF; however, direct interaction of CBP with CLOCK was not observed.
Our findings indicate possible mechanisms by which CBP/p300 tissue-specifically acts cooperatively with pCAF and HDAC3 either as a co-activator or co-repressor, respectively, for CLOCK/BMAL1.
先前的研究表明，生物钟转录的节律受到组织特异性调控，这表明生物钟转录所必需的转录因子复合物 CLOCK/BMAL1 以组织特异性方式调节转录。为了在分子水平上进一步阐明 CLOCK/BMAL1 对转录的细胞类型特异性调控机制，我们研究了 CBP/p300 和组织特异性共因子在 CLOCK/BMAL1 介导的转录中的作用。
如前所述，CBP/p300 在 COS-1 细胞中刺激 CLOCK/BMAL1 介导的转录。然而，CBP/p300 在 NIH3T3 细胞中抑制 CLOCK/BMAL1 介导的转录，并且通过 siRNA 敲低 CBP 或 p300 的表达增强了这种转录。使用 GAL4 融合蛋白的研究表明，CBP 通过靶向 CLOCK 来抑制 CLOCK/BMAL1 介导的转录。我们通过研究在 NIH3T3 和 COS 细胞中高度表达的共抑制子 HDAC3 和共激活子 pCAF 在 CBP 对 CLOCK/BMAL1 介导的转录的这种细胞类型特异性调节中的作用，进一步探讨了这种调节的机制。当 HDAC3 过表达时，CBP 抑制了 COS-1 细胞中 CLOCK/BMAL1 介导的转录，但当 pCAF 过表达时，它激活了 NIH3T3 细胞中的转录。CBP 通过与 HDAC3 或 pCAF 相互作用与 CLOCK 形成复合物；然而，没有观察到 CBP 与 CLOCK 之间的直接相互作用。
我们的研究结果表明，CBP/p300 可能通过与 HDAC3 或 pCAF 相互作用形成复合物，分别作为 CLOCK/BMAL1 的共激活子或共抑制子，以组织特异性的方式发挥作用的机制。
