Transactivation of the human cdc2 promoter by adenovirus E1A in cycling cells is mediated by induction of a 110-kDa CCAAT-box-binding factor

Cyclin-dependent protein kinases (Cdks) are key regulatory proteins of the eukaryotic cell cycle. Cdc2 is expressed in late G1/S phase and functions in the G2 to M phase transition. Adenovirus E1A proteins are known to induce the expression of p34cdc2 and DNA synthesis in normal quiescent cells. In this study, mutational analysis of the human cdc2 promoter revealed that transactivation of the promoter by the E1A proteins in cycling cells is mediated through the two CCAAT box binding motifs. A 110-kDa protein (CBF/cdc2) was identified in nuclear extracts from monkey kidney (CV-1) cells stably expressing E1A as well as from adenovirus-transformed human 293 cells. Further, we show that this E1A-inducible CBF/cdc2 is related to the CBF which was shown to activate the heat shock protein 70 promoter. Analyses of the functional domain(s) of E1A required for the induction of the CBF and transactivation of the cdc2 promoter in these conditions revealed that E1A mutants which were defective in binding the pRB family of proteins or the cellular p300 protein were still active in assays measuring the induction of the CBF and transactivation of the cdc2 promoter, albeit with reduced efficiencies. But the E1A mutant which lost both functional domains was inactive in these assays. These results suggest that E1A has redundant functional domains for the induction of the 110-kDa CBF and activation of human cdc2 gene expression.