Distal regulatory element of the STAT1 gene potentially mediates positive feedback control of STAT1 expression

We previously identified a distal regulatory element located approximately 5.5‐kb upstream of the signal transducer and activator of transcription 1 ( STAT 1 ) gene, thereafter designating it as 5.5‐kb upstream regulatory region (5.5 URR ). In this study, we investigated the functional roles of 5.5 URR in the transcriptional regulation of STAT 1 gene. A chromosome conformation capture assay indicated physical interaction of 5.5 URR with the STAT 1 core promoter. In luciferase reporter assays, 5.5 URR ‐combined STAT 1 core promoter exhibited significant increase in reporter activity enhanced by forced STAT 1 expression or interferon ( IFN ) treatment, but STAT 1 core promoter alone did not. The 5.5 URR contained IFN‐stimulated response element and GAS sites, which bound STAT 1 complexes in electrophoretic mobility shift assays. Consistently, chromatin immunoprecipitation (Ch IP ) assays of HEK 293 cells with Halo‐tagged STAT 1 expression indicated the association of Halo‐tagged STAT 1 with 5.5 URR . Ch IP assays with IFN treatment demonstrated that IFN s promoted the recruitment of Halo‐tagged STAT 1 to 5.5 URR . Forced STAT 1 expression or IFN treatment increased the expression of endogenous STAT 1 and other IFN signaling pathway components, such as STAT 2, IRF 9 and IRF 1, besides IFN ‐responsive genes. Collectively, the results suggest that 5.5 URR may provide a regulatory platform for positive feedback control of STAT 1 expression possibly to amplify or sustain the intracellular IFN signals.