FIG. 4.

Synergistic activation of CRE-dependent transcription by calcium and cGMP is prevented by dominant negative CREB and C/EBP constructs but not by a dominant negative Fos. (A and B) UMR106 cells were transfected with pCRE-Luc, pRSV-βGal, or G-kinase II vector as described in the legend to Fig. 3; some cells were cotransfected with 40 ng of expression vector encoding the dominant negative A-CREB, A-C/EBP, A-Fos, or empty vector. Cells were treated for 8 h with 0.3 μM A23187 (Ca⁺⁺), 250 μM CPT-cGMP (cGMP), or both (A), or cells were treated with 100 μM CPT-cAMP (B), as indicated. The ratio of luciferase to β-galactosidase activity was normalized as described in the legend to Fig. 3. (C) Cells were transfected with pSRE-Luc, pRSV-βGal, and G-kinase II and cotransfected with empty vector (solid bars) or C/EBP-β (20 ng; open bars); some cells also received vector encoding A-C/EBP (40 ng) as indicated. (D) Cells were transfected with pAP1-Luc, pRSV-βGal, and G-kinase II and cotransfected with empty vector (solid bars) or JunB (20 ng; open bars); some cells also received vector encoding A-Fos (40 ng) as indicated.