PRC2 facilitates PARP1 silencing by associating with RB1-E2F1-HDAC1-BRM/BRG1 repressor complex in G1 arrested cells. Epigenetic modifications (a,b and d), recruitment of HDAC1 (c), EZH2 (e), BRM (g), BRG1 (h) to PARP1 promoter and the density of histone H3 (f) were compared by ChIP between proliferating cells and cells arrested in G1 phase by their treatment with mimosine (Mim, 200 μM) for 48 h. Composition of PARP1 repressive complex in G1-arrested cells was determined by pulling down HDAC1 and followed by WB detection of RB1, E2F1, EZH2, BRM and BRG1 (j). The expression of PARP1 in HSPC supplemented with mimosine (50 µ) and additionally with 5 mM iHDAC, 125 nM iEZH2 and the mixture of 5 mM iHDAC and 125 nM and iEZH2 for 24 h was analyzed with western blot (k) and real-time PCR (l). Expression of PARP1 in G1-arrested cells treated with BRM/BRG1 inhibitor (iBRM/iBRG1 - PFI-3 – 1 μM) was determined with real-time PCR (n). Changes in epigenetic marks and in protein composition in PARP1 promoter upon THP-1 cells treatment with iHDAC/iEZH2/Mim versus Mim alone were monitored with ChIP (n–t).