PML modulates epigenetic composition of chromatin to regulate expression of pro-metastatic genes in triple-negative breast cancer [ChIP-seq]

The promyelocytic leukemia (PML) protein organizes nuclear aggregates known as PML nuclear bodies (PML-NBs), where many transcription factors and transcriptional regulators converge to be regulated. Specific associations of PML and PML-NBs with chromatin are described in different cell types, further implicating PML in transcriptional regulation. However, a complete understanding of the functional consequences of PML association to DNA in a cellular context where it regulates relevant phenotypes is still lacking.We examined the role of PML in chromatin association and transcription in triple-negative breast cancer (TNBC), a pathological condition where PML exerts important oncogenic functions. We find that PML associates discontinuously with large heterochromatic PML-associated domains (PADs) that contain gene-rich euchromatic sub-domains locally depleted of PML. PML promotes heterochromatic organization in PADs and expression of pro-metastatic genes embedded in these sub-domains. Importantly, this occurs outside PML-NBs, suggesting that nucleoplasmic PML exerts a cell type-relevant function of transcriptional regulation. PML also plays an indirect regulatory function in TBNC cells by promoting the expression of pro-metastatic genes outside PADs.Our findings demonstrate that PML is an important transcriptional regulator of metastasis and pro-oncogenic metagenes in TNBC cells, via distinct molecular activities that include indirect transcriptional regulation and direct epigenetic organization of heterochromatin domains that embed regions of localized transcriptional activity. Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for PML, LMNB1, H3K9me3, H3K27me3, H3K4me3 and H3K27ac in MDA-MB-231 cells.