Wiśnik Ewelina, Płoszaj Tomasz, Robaszkiewicz Agnieszka
Department of Biophysics of Environmental Pollution, Institute of Biophysics, University of Lodz, Pomorska 141/143, 90-236, Lodz, Poland.
Department of Molecular Biology, Medical University of Lodz, Narutowicza 60, 90-136, Lodz, Poland.
Sci Rep. 2017 Aug 25;7(1):9483. doi: 10.1038/s41598-017-10307-z.
Differentiation of certain cell types is followed by a downregulation of PARP1 expression. We show that the reduction in the abundance of PARP1 in hematopoietic progenitor cells and monocytes is tightly controlled by the cell cycle. The differentiation-associated cell cycle exit induces E2F1 replacement with E2F4 at the PARP1 promoter and the assembly of an E2F4-RBL2-HDAC1-BRM(SWI/SNF) repressor complex which deacetylates nucleosomes and compacts chromatin. In G1 arrested cells, PARP1 transcription is reduced by the recruitment of E2F1-RB1-HDAC1-EZH2(PRC2)-BRM/BRG1(SWI/SNF), which additionally trimethylates H3K27 and causes an even higher increase in nucleosome density. The re-establishment of an active chromatin structure by treating post-mitotic monocytes with the HDAC inhibitor and G1 arrested cells with a combination of HDAC and EZH2 inhibitors restores PARP1 expression completely but does not affect the interaction between the components of the repressor complex with chromatin. This suggests that RB1 and RBL2, as well as PRC2, SWI/SNF and HDAC1, do not interfere with the transcription machinery. Interestingly, reinstatement of PARP1 expression by the silencing of RBL2 or by the inhibition of HDACs in monocytes and by transfection with the PARP1 expression vector in differentiated THP-1 cells substantially increased transcription of pluripotency stem cell factors such as POU5F1, SOX2 and NANOG.
某些细胞类型的分化伴随着PARP1表达的下调。我们发现造血祖细胞和单核细胞中PARP1丰度的降低受到细胞周期的严格控制。与分化相关的细胞周期退出诱导PARP1启动子处E2F1被E2F4取代，并组装成E2F4-RBL2-HDAC1-BRM（SWI/SNF）阻遏复合物，该复合物使核小体去乙酰化并压缩染色质。在G1期停滞的细胞中，PARP1转录通过募集E2F1-RB1-HDAC1-EZH2（PRC2）-BRM/BRG1（SWI/SNF）而降低，该复合物还会使H3K27三甲基化，并导致核小体密度进一步升高。用HDAC抑制剂处理有丝分裂后单核细胞，并用HDAC和EZH2抑制剂组合处理G1期停滞细胞，重新建立活跃的染色质结构，可完全恢复PARP1表达，但不影响阻遏复合物各组分与染色质之间的相互作用。这表明RB1和RBL2以及PRC2、SWI/SNF和HDAC1不会干扰转录机制。有趣的是，通过沉默RBL2或抑制单核细胞中的HDAC，以及在分化的THP-1细胞中用PARP1表达载体转染来恢复PARP1表达，可显著增加多能干细胞因子如POU5F1、SOX2和NANOG的转录。
