Serum responsiveness of the rat PCNA promoter involves the proximal ATF and AP-1 sites.

We have previously shown that the rat PCNA (proliferating cell nuclear antigen) gene promoter is responsive to serum stimulation. In this study, the sequence of the promoter responsive to serum stimulation has been localized in the region between nucleotides -70 and +125 relative to the transcription initiation site. This region contains an ATF site (nucleotides -51 to -44) and an AP-1 site (nucleotides -64 to -58). Mutation at either the ATF or the AP-1 site reduced the serum responsiveness of the promoter. In gel mobility shift assays, nuclear extracts from serum stimulated cells, compared to those from quiescent cells, exhibit an increasing binding activity toward a promoter related oligonucleotide (-70 to -42) which includes the ATF site and the AP-1 site. Formation of the DNA:protein complexes requires the simultaneous involvement of ATF and AP-1 sites as either element can abrogate the complexes in the competition experiment. Both the distance and sequence are essential to complex formation. Moreover, ATF-1 but not ATF-2 (or CREB) has been identified as a major component of the complexes in the antibody supershift or interference experiment. The results of this study suggest that ATF-1 in association with other factors is involved in regulating the serum stimulation of the rat PCNA promoter activity via the proximal ATF and AP-1 sites.