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 th e cell cycle, The expression of cyclin A is restrained during GO and G 1, but steeply induced at the G1/S boundary, Analysis of the rat cycli n A promoter elements with the 5' sequential deletion derivatives of t he promoter fused to the luciferase cDNA indicated that the ATF/CRE mo tif primarily determines the inducibility at G1/S. Gel shift analysis of the complex formed at the ATP/CRE site indicated that the complex w as not formed with the G0/G1 cell extract, but maximally formed with t he late-GI cell extract, The complex was supershifted by anti-JunD ant ibody, and Western blot analysis of the immune complexes prepared with anti-JunD antibody revealed the presence of ATF2, suggesting heterodi merization of JunD with ATF2. The cyclin A promoter in a reporter plas mid was activated by nearly 10-fold in quiescent rat 3Y1 cells by cotr ansfection with the expression plasmids encoding ATF2 and Jun family m embers, In contrast, cotransfection with the ATF4 expression plasmid s uppressed the promoter activation mediated by ATP2 and Jun family memb ers. The expression of Jun family members during G1 to S progression w as induced biphasically in early and late G1 and the level of JunD inc reased markedly at the G1/S, while that of ATP family members was grad ually increased along with the G1 to S progression. These results indi cate that the cyclin A promoter activity is regulated, at least in par t, by relative amounts of the ATF and Jun family members. (C) 1998 Aca demic Press.