PCGF1 encodes one of six human Polycomb RING finger homologs that are linked to transcriptional repression and developmental gene regulation. Individual PCGF proteins define discrete Polycomb Repressor Complex 1 (PRC1) multi-protein complexes with diverse subunit composition whose functions are incompletely understood. PCGF1 is a component of a variant PRC1 complex that also contains the BCL6 co-repressor BCOR and the histone demethylase KDM2B. To further investigate the role of PCGF1, we mapped the physical interactions of the protein under endogenous conditions in a cell model of neuronal differentiation. Using stringent statistical cut-offs, 83 highly enriched interacting proteins were identified, including all previously reported members of the variant PRC1 complex containing PCGF1, as well as proteins linked to diverse cellular pathways such as chromatin and cell cycle regulation. Notably, a sub-network of proteins associated with the establishment and maintenance of pluripotency (NANOG, OCT4, PATZ1, and the developmental regulator DPPA4) were found to independently interact with PCGF1 in a subsequent round of physical interaction mapping experiments. Furthermore, knockdown of PCGF1 results in reduced expression of DPPA4 and other subunits of the variant PRC1 complex at both mRNA and protein levels. Thus, PCGF1 represents a physical and functional link between Polycomb function and pluripotency.
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