Bottardi Stefania, Mavoungou Lionel, Pak Helen, Daou Salima, Bourgoin Vincent, Lakehal Yahia A, Affar El Bachir, Milot Eric
Maisonneuve Rosemont Hospital Research Center, Maisonneuve-Rosemont Hospital and Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada.
PLoS Genet. 2014 Dec 4;10(12):e1004827. doi: 10.1371/journal.pgen.1004827. eCollection 2014 Dec.
IKAROS is a critical regulator of hematopoietic cell fate and its dynamic expression pattern is required for proper hematopoiesis. In collaboration with the Nucleosome Remodeling and Deacetylase (NuRD) complex, it promotes gene repression and activation. It remains to be clarified how IKAROS can support transcription activation while being associated with the HDAC-containing complex NuRD. IKAROS also binds to the Positive-Transcription Elongation Factor b (P-TEFb) at gene promoters. Here, we demonstrate that NuRD and P-TEFb are assembled in a complex that can be recruited to specific genes by IKAROS. The expression level of IKAROS influences the recruitment of the NuRD-P-TEFb complex to gene regulatory regions and facilitates transcription elongation by transferring the Protein Phosphatase 1α (PP1α), an IKAROS-binding protein and P-TEFb activator, to CDK9. We show that an IKAROS mutant that is unable to bind PP1α cannot sustain gene expression and impedes normal differentiation of Ik(NULL) hematopoietic progenitors. Finally, the knock-down of the NuRD subunit Mi2 reveals that the occupancy of the NuRD complex at transcribed regions of genes favors the relief of POL II promoter-proximal pausing and thereby, promotes transcription elongation.
IKAROS是造血细胞命运的关键调节因子，其动态表达模式对于正常造血过程是必需的。它与核小体重塑和去乙酰化酶（NuRD）复合物协同作用，促进基因的抑制和激活。IKAROS在与含HDAC的复合物NuRD相关联的情况下如何支持转录激活仍有待阐明。IKAROS还在基因启动子处与正转录延伸因子b（P-TEFb）结合。在此，我们证明NuRD和P-TEFb组装成一个复合物，该复合物可被IKAROS招募到特定基因。IKAROS的表达水平影响NuRD-P-TEFb复合物向基因调控区域的募集，并通过将IKAROS结合蛋白和P-TEFb激活剂蛋白磷酸酶1α（PP1α）转移到CDK9来促进转录延伸。我们表明，无法结合PP1α的IKAROS突变体不能维持基因表达，并阻碍Ik（NULL）造血祖细胞的正常分化。最后，NuRD亚基Mi2的敲低表明，NuRD复合物在基因转录区域的占据有利于缓解POL II启动子近端的暂停，从而促进转录延伸。
