Interplay between PML NBs and HIRA for H3.3 dynamics following type I interferon stimulus

Promyelocytic Leukemia Nuclear Bodies (PML NBs) are nuclear membrane-less organelles physically associated with chromatin underscoring their crucial role in genome function. The H3.3 histone chaperone complex HIRA accumulates in PML NBs upon senescence, viral infection or IFN-I treatment in primary cells. Yet, the molecular mechanisms of this partitioning and its function in regulating histone dynamics have remained elusive. By using specific approaches, we identify intermolecular SUMO-SIM interactions as an essential mechanism for HIRA recruitment in PML NBs. Upon IFN-I stimulation, PML is required for interferon-stimulated genes (ISGs) transcription and PML NBs become juxtaposed to ISGs loci at late time points of IFN-I treatment. HIRA and PML are necessary for the prolonged H3.3 deposition at the transcriptional end sites of ISGs, well beyond the peak of transcription. Though, HIRA accumulation in PML NBs is dispensable for H3.3 deposition on ISGs. Hence, we describe an independent role of PML NBs as nuclear depot centers to regulate HIRA distribution in the nucleus, as a consequence of the availability of the pool of H3.3-H4 dimers or chromatin compaction. We thus uncover a dual function for PML/PML NBs in regulating ISGs transcription and H3.3 deposition at ISGs, and in modulating the nuclear distribution of HIRA upon inflammatory response.