E2F1 and rheumatoid arthritis: To further show the role of E2F1 in TREX1 expression, E2F1 was overexpressed dose-dependently in RA-FLSs, and the transcript levels of TREX1 and DP-1 (an important activator of the E2F transcription factor) were found to be significantly and gradually increased (Fig. 6A).