Two Estrogen Response Element Sequences Near the PCNA Gene Are Not Responsible for Its Estrogen-Enhanced Expression in MCF7 Cells
The proliferating cell nuclear antigen (PCNA) is an adenovirus E1A-inducible factor that is intimately linked to the processes of DNA replication and cell cycle regulation. Previously, we defined a novel cis-acting element, the PCNA E1A-responsive element (PERE), that confers induction by the E1A 243R oncoprotein upon the human PCNA promoter. To better understand the regulation of PCNA expression by E1A 243R, we have identified cellular transcription factors that associate with the PERE. In electrophoretic mobility shift assays, the PERE formed three major complexes (P1, P2 and P3) with proteins in nuclear extracts from HeLa or 293 cells. Formation of complexes P2 and P3, which correlates with PCNA promoter activity in vivo, requires the activating transcription factor (ATF) binding site found within the PERE [Labrie et al. (1993) Mol. Cell. Biol., 13, 1697-1707]. Antibody interference experiments and mobility shift assays performed with in vitro-synthesized protein indicated that the transcription factor ATF-1 is a major component of these complexes. Similar assays demonstrated that the hepatitis B virus enhancer-associated protein RFX1 constitutes a major component of the P1 complex. In addition, we examined the binding of proteins to the minimal E1A-responsive promoter to identify other factors important for transcription from the PCNA promoter. Mobility shift assays revealed that a fragment encompassing the region from -87 to +62 relative to the transcription initiation site forms at least five complexes, EH1-EH5, with HeLa cell nuclear extracts. The transcription factor YY1 associates with the initiator element of the PCNA promoter. The identification of these transcription factors will allow their roles in the activation of PCNA by E1A to be evaluated.