The chromatin remodeling protein INO80 contributes to the removal of H2A.Z at the p53-binding site of the p21 gene in response to doxorubicin.

Transcriptional activation of p21 (cyclin-dependent kinase inhibitor 1A) due to DNA damage often alters the distribution of histone variant H2A.Z at the p21 gene. However, whether the human INO80 complex regulates changes in H2A.Z at the p21 promoter is unclear. We show here that activation of p21 expression by doxorubicin (Doxo) in U2OS cells is required for removal of H2A.Z by INO80 at the p53-binding site proximal region (-2.2 kb) of the p21 promoter. A purified INO80 complex, but not the INO80E653Q mutant-complex, which lost DNA-sliding activity, is mainly responsible for removing H2A.Z from reconstituted nucleosomes in vitro. This activity was enhanced with MOF-mediated histone acetylation, suggesting that INO80 more readily removes H2A.Z from loosened nucleosomes. Also, co-occupancy of INO80 and H2A.Z -2.2 kb upstream of the p21 transcriptional start site (TSS) was observed. H2A.Z at this region was removed in a short time after Doxo treatment and activated p21 expression. However, p21 induction was inhibited by INO80 knockdown by delaying H2A.Z removal, indicating the need for INO80. Moreover, shMOF-mediated histone acetylation reduced recruitment of INO80 -2.2 kb upstream of p21 TSS and inhibited the removal of H2A.Z in Doxo-treated cells. These data provide new insights into the transcriptional regulation of p21 by the INO80 complex.