CAMP-independent activation of the adenovirus type 12 E2 promoter correlates with the recruitment of CREB-1/ATF-1, E1A(12S), and CBP to the E2-CRE

Expression of the transcription unit early region 2 (E2) is of crucial impo rtance for adenoviruses because this region encodes proteins essential for viral replication. Here, we demonstrate that the E1A(12S) protein of the on cogenic adenovirus serotype 12 activates the E2 promoter in dependence of t he N terminus and the conserved region 1. Activation is mediated through a cAMP-response element that is bound by CREB-1 and ATF-1. Moreover, the Ad12 E2 promoter is inducible by protein kinase A and repressed by either a dom inant-negative cAMP-response element-binding protein (CREB) mutant or the h ighly specific protein kinase A inhibitor protein underscoring the particip ation of CREB-1/ATF-1 in promoter activation. E1A(12S) binds to CREB-1 and ATF-1 in dependence of the N terminus and CR1 and is recruited to the E2 cA MP-response element through both cellular transcription factors. Most inter estingly, point mutations revealed that E1A(12S) domains essential for bind ing to CREB-1/ATF-1 and for activation of the Ad12 E2 promoter are also ess ential for binding to the CREB-binding protein. Due to these data and resul ts obtained in DNA-dependent protein-protein interaction assays, we propose a model in which the cAMP-independent activation of the Ad12 E2 promoter i s mediated through a ternary complex consisting of CREB-1/ATF-1, E1A(12S) a nd CREB-binding protein, which assembles on the E2 cAMP-response element.