Protein Inhibitor of Activated STAT1 (PIAS1) Enhances the Transcriptional Activity of CP2 Isoforms by a Specific Interaction with CP2 Isoforms

초록

The transcription factor CP2 was initially identified to bind to activate the promoter of the murine ?-globin gene. Previously, we identified three CP2 isoforms, CP2a, CP2b, and CP2c, in which original CP2 corresponds to CP2c. CP2b has a strong transcriptional activation domain and a dimerization domain, but lacks a DNA binding domain. When tested transcriptional activities, CP2c shows strong transcriptional activity whereas those of CP2a and CP2b are weak or negligible. Interestingly, CP2b suppresses the transcriptional activity of CP2c in 293T cells, whereas it augmented CP2c activity in K562 cells. It suggests that there are differential modifications of CP2 isoforms in these cells or that there exist other cell type-specific factors modulating the interaction between CP2 isoforms. As one of factors that interact or modulate CP2 activity, we identified PIAS1 by screening a phage display library. PIAS1 more strongly interacted with CP2b than CP2c in vivo and in vitro, and derepressed the CP2b effect on the DNA binding of CP2c in EMSA. In addition, when cotransfected with CP2b and CP2c, PIAS1 showed maximal synergy in CP2-mediated transcriptional activation in both K562 and 293T cells. Our results suggest that PIAS1 quenches the transcriptional repression activity of CP2b against CP2c through protein-protein interaction with CP2b.