Barrier-to-Autointegration Factor Proteome Reveals Chromatin-Regulatory PartnersReport as inadecuate

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Nuclear lamin filaments and associated proteins form a nucleoskeletal -lamina- network required for transcription, replication, chromatin organization and epigenetic regulation in metazoans. Lamina defects cause human disease -laminopathies- and are linked to aging. Barrier-to-autointegration factor BAF is a mobile and essential component of the nuclear lamina that binds directly to histones, lamins and LEM-domain proteins, including the inner nuclear membrane protein emerin, and has roles in chromatin structure, mitosis and gene regulation. To understand BAF-s mechanisms of action, BAF associated proteins were affinity-purified from HeLa cell nuclear lysates using BAF-conjugated beads, and identified by tandem mass spectrometry or independently identified and quantified using the iTRAQ method. We recovered A- and B-type lamins and core histones, all known to bind BAF directly, plus four human transcription factors Requiem, NonO, p15, LEDGF, disease-linked proteins e.g., Huntingtin, Treacle and several proteins and enzymes that regulate chromatin. Association with endogenous BAF was independently validated by co-immunoprecipitation from HeLa cells for seven candidates including Requiem, polyADP-ribose polymerase 1 PARP1, retinoblastoma binding protein 4 RBBP4, damage-specific DNA binding protein 1 DDB1 and DDB2. Interestingly, endogenous BAF and emerin each associated with DDB2 and CUL4A in a UV- and time-dependent manner, suggesting BAF and emerin have dynamic roles in genome integrity and might help couple DNA damage responses to the nuclear lamina network. We conclude this proteome is a rich source of candidate partners for BAF and potentially also A- and B-type lamins, which may reveal how chromatin regulation and genome integrity are linked to nuclear structure.

Author: Rocío Montes de Oca, Christopher J. Shoemaker, Marjan Gucek, Robert N. Cole, Katherine L. Wilson



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