Protein Inhibitor of Activated STAT1 (PIAS1) is a Functional Cell Specific Co-activator for CP2 Mediated α-globin Gene Expression

Abstract

CP2 activates the transcription of α-globin gene in red blood cells. Previously we identified three CP2 isoforms (CP2a/b/c) that interact each other. The maximal transcriptional activity was obtained in CP2b/c dimerization and observed in K562 cells, but not in 293T cells suggesting differential modifications of CP2 isoforms in these cells or other cell type-specific factors modulating the interaction between CP2 isoforms. We identified PIAS1 as a potential factor that regulates CP2 activity. PIAS1 interacts most strongly with CP2b among isoforms. Deletion mutation studies demonstrated that the enhanced interaction between PIAS1 and CP2b is due to the specific domain in CP2b. The endogenous level of PIAS1 in K562 cells is much higher than that in 293T cells. Cotransfection of PIAS1 with CP2b/c showed the enhanced CP2-mediated transcriptional activation in both K562 and 293T cells suggesting that PIAS1 is a key player for enhanced α-globin gene expression. Furthermore this expression was significantly reduced in RNAi-mediated knockdown of PIAS1 or CP2c in K562 cells strongly indicating that PIAS1 acts as a cell specific co-activator for CP2 mediated α-globin gene expression.