Kim Kyunghwan, Choi Jongkyu, Heo Kyu, Kim Hyunjung, Levens David, Kohno Kimitoshi, Johnson Edward M, Brock Hugh W, An Woojin
Department of Biochemistry and Molecular Biology, University of Southern California Keck School of Medicine, Los Angeles, CA 90089, USA.
J Biol Chem. 2008 Apr 4;283(14):9113-26. doi: 10.1074/jbc.M708205200. Epub 2008 Feb 7.
Linker histone H1 has been generally viewed as a global repressor of transcription by preventing the access of transcription factors to sites in chromatin. However, recent studies suggest that H1 can interact with other regulatory factors for its action as a negative modulator of specific genes. To investigate these aspects, we established a human cell line expressing H1.2, one of the H1 subtypes, for the purification of H1-interacting proteins. Our results showed that H1.2 can stably associate with sets of cofactors and ribosomal proteins that can significantly repress p53-dependent, p300-mediated chromatin transcription. This repressive action of H1.2 complex involves direct interaction of H1.2 with p53, which in turn blocks p300-mediated acetylation of chromatin. YB1 and PURalpha, two factors present in the H1.2 complex, together with H1.2 can closely recapitulate the repressive action of the entire H1.2 complex in transcription. Chromatin immunoprecipitation and RNA interference analyses further confirmed that the recruitment of YB1, PURalpha, and H1.2 to the p53 target gene Bax is required for repression of p53-induced transcription. Therefore, these results reveal a previously unrecognized function of H1 as a transcriptional repressor as well as the underlying mechanism involving specific sets of factors in this repression process.
连接组蛋白H1通常被视为转录的全局抑制因子，它通过阻止转录因子接近染色质中的位点来发挥作用。然而，最近的研究表明，H1可以与其他调节因子相互作用，作为特定基因的负调节因子发挥作用。为了研究这些方面，我们建立了一种表达H1.2（H1亚型之一）的人类细胞系，用于纯化与H1相互作用的蛋白质。我们的结果表明，H1.2可以与一组辅因子和核糖体蛋白稳定结合，这些蛋白可以显著抑制p53依赖的、p300介导的染色质转录。H1.2复合物的这种抑制作用涉及H1.2与p53的直接相互作用，这反过来又阻断了p300介导的染色质乙酰化。H1.2复合物中的两个因子YB1和PURalpha，与H1.2一起可以在转录过程中紧密重现整个H1.2复合物的抑制作用。染色质免疫沉淀和RNA干扰分析进一步证实，将YB1、PURalpha和H1.2募集到p53靶基因Bax上是抑制p53诱导转录所必需的。因此，这些结果揭示了H1作为转录抑制因子的一种先前未被认识的功能，以及在这一抑制过程中涉及特定因子组的潜在机制。
