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Proteasomes and Proteasome Activator 200 kDa (PA200) Accumulate on Chromatin in Response to Ionizing Radiation

Jennifer Blickwedehl, Sarah McEvoy, Irene Wong, Philaretos Kousis, James Clements, Rosemary Elliott, Peter Cresswell, Ping Liang and Naveen Bangia
Radiation Research
Vol. 167, No. 6 (Jun., 2007), pp. 663-674
Stable URL: http://www.jstor.org/stable/4138657
Page Count: 12
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Proteasomes and Proteasome Activator 200 kDa (PA200) Accumulate on Chromatin in Response to Ionizing Radiation
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Abstract

Proteasome activator 200 kDa (PA200) forms nuclear foci after exposure of cells to ionizing radiation and enhances proteasome activity in vitro. Within cells, it is unclear whether PA200 responds to radiation alone or in association with proteasomes. In the present study, we identified three forms of cellular PA200 (termed PA200i, ii and iii) at the mRNA and protein levels. Neither PA200ii nor PA200iii appears to associate with proteasomes. All detectable PA200i is associated with proteasomes, which indicates that PA200i and proteasomes function together within the cell. Consistent with this idea, we find that exposure of cells to radiation leads to an equivalent accumulation of both PA200i and core proteasomes on chromatin. This increase in PA200 and proteasomes on chromatin is not specific to the stage of cell cycle arrest since it occurs in cells that arrest in G₂/M and cells that arrest in G₁/S after exposure to radiation. These data provide evidence that PA200 and proteasomes function together within cells and respond to a specific radiation-induced damage independent of the stage of cell cycle arrest.

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