Background
Polycomb group (PcG) proteins play a crucial role in cellular senescence as key transcriptional regulators of the Ink4a/Arf tumor suppressor gene locus. However, how PcG complexes target and contribute to stable gene silencing of the Ink4a/Arf locus remains little understood. Methodology/principal findings: We examined the function of Zinc finger domain-containing protein 277 (Zfp277), a novel zinc finger protein that interacts with the PcG protein Bmi1. Zfp277 binds to the Ink4a/Arf locus in a Bmi1-independent manner and interacts with polycomb repressor complex (PRC) 1 through direct interaction with Bmi1. Loss of Zfp277 in mouse embryonic fibroblasts (MEFs) caused dissociation of PcG proteins from the Ink4a/Arf locus, resulting in premature senescence associated with derepressed p16(Ink4a) and p19(Arf) expression. Levels of both Zfp277 and PcG proteins inversely correlated with those of reactive oxygen species (ROS) in senescing MEFs, but the treatment of Zfp277(-/-) MEFs with an antioxidant restored the binding of PRC2 but not PRC1 to the Ink4a/Arf locus. Notably, forced expression of Bmi1 in Zfp277(-/-) MEFs did not restore the binding of Bmi1 to the Ink4a/Arf locus and failed to bypass cellular senescence. A Zfp277 mutant that could not bind Bmi1 did not rescue Zfp277(-/-) MEFs from premature senescence. Conclusions/significance: Our findings implicate Zfp277 in the transcriptional regulation of the Ink4a/Arf locus and suggest that the interaction of Zfp277 with Bmi1 is essential for the recruitment of PRC1 to the Ink4a/Arf locus. Our findings also highlight dynamic regulation of both Zfp277 and PcG proteins by the oxidative stress pathways.
Significance
Our findings implicate Zfp277 in the transcriptional regulation of the Ink4a/Arf locus and suggest that the interaction of Zfp277 with Bmi1 is essential for the recruitment of PRC1 to the Ink4a/Arf locus. Our findings also highlight dynamic regulation of both Zfp277 and PcG proteins by the oxidative stress pathways.