PARENT SESSION
1:30 PM to 3:30 PM
Monday, April 22, 2002
Poster Session 10 Cell Cycle Effects
Room: Nevada Exhibition Center
(P15-144) IR-induced dephosphorylation of PP1 is controlled by ATM.
Larner, James*,1, Brautigan, David2, Guo, Chang1, 1 Dept. of Radiation Oncology, Charlottesville, Va2 Center for Cell Signaling, Charlottesville, Va
ABSTRACT-
Protein phosphatase 1 (PP1) is a serine/threonine protein phosphatase that controls diverse cellular processes including cell cycle progression and histone H3 dephosphorylation in yeast. We therefore asked if PP1 was a target of an IR-activated damage-sensing pathway. To explore the possibility that IR altered the phosphorylation status of PP1, Jurkat cells were subjected to irradiation or sham radiation followed by 32p labeling. Extracts were then subjected to microcystin affinity chromatography followed by a 2D-gel analysis. Several microcystin associated proteins dramatically changed in 32p intensity following IR. Sequencing revealed that the proteins which demonstrated the greatest change in 32p intensity following IR were PP1 C (isoforms alpha and delta). Extracts were also subjected to immunoprecipitation with antibodies to various isoforms of PP1 and analyzed by immunoblot analysis with a phospho-threonine-proline monoclonal antibody against a C-terminal Thr-Pro-Pro-Arg motif which is known to be a preferred sequence for CDK phosphorylation. In Jurkat cells and ATM cells transfected with full length ATM, IR resulted in dephosphorylation of the threoine- proline motif of PP1c. However, in AT cells IR failed to induce dephosphorylation of this site. Since dephosphorylation of this motif has been associated with activation of PP1, IR- induced PP1 activation may be critical component in an ATM mediated pathway controlling checkpoint activation.
KEYWORDS: ATM, phosphatase, cell cycle, checkpoint