Activation of the rat cyclin A promoter by ATF2 and Jun family members and its suppression by ATF4.

Cyclin A plays an essential role in the G1 to S phase transition in the cell cycle. The expression of cyclin A is restrained during G0 and G1, but steeply induced at the G1/S boundary. Analysis of the rat cyclin A promoter elements with the 5' sequential deletion derivatives of the promoter fused to the luciferase cDNA indicated that the ATF/CRE motif primarily determines the inducibility at G1/S. Gel shift analysis of the complex formed at the ATF/CRE site indicated that the complex was not formed with the G0/G1 cell extract, but maximally formed with the late-G1 cell extract. The complex was supershifted by anti-JunD antibody, and Western blot analysis of the immune complexes prepared with anti-JunD antibody revealed the presence of ATF2, suggesting heterodimerization of JunD with ATF2. The cyclin A promoter in a reporter plasmid was activated by nearly 10-fold in quiescent rat 3Y1 cells by cotransfection with the expression of plasmids encoding ATF2 and Jun family members. In contrast, cotransfection with the ATF4 expression plasmid suppressed the promoter activation mediated by ATF2 and Jun family members. The expression of Jun family members during G1 to S progression was induced biphasically in early and late G1 and the level of JunD increased markedly at the G1/S, while that of ATF family members was gradually increased along with the G1 to S progression. These results indicate that the cyclin A promoter activity is regulated, at least in part, by relative amounts of the ATF and Jun family members.