CREG1 belongs to the CREG family. It is a adenovirus E1A protein which both activates and represses gene expression to promote cellular proliferation and inhibit differentiation. Thus it may contribute to the transcriptional control of cell growth and differentiation. The transcriptional control activity of cell growth requires interaction with IGF2R. CREG1 also antagonizes transcriptional activation and cellular transformation by E1A. It shares limited sequence similarity with E1A and binds both the general transcription factor TBP and the tumor suppressor pRb in vitro. CREG1 gene may contribute to the transcriptional control of cell growth and differentiation.