Interaction of Retinoblastoma Gene Product with Transcription Factors ATFa and ATF2

Two highly related transcription factors, activating transcription factors a and 2 (ATFa and ATF2) are able to activate expression in CHO cells of a reporter gene driven by the human transforming growth factor β2 gene promoter. This action is dependent on the intact motif CGTCA which is found as part of the cAMP responsive element in a number of promoters and to which both factors can bind in vitro. The retinoblastoma gene product also weakly stimulates expression of this reporter gene but, in combination with the factors, it exhibits a differential action: additive or greater stimulatory effects with ATF2 but strong inhibition of the actions of ATFa. Thus, although both of these two related factors are able to exert the same apparent effect on this promoter, coexpression of the retinoblastoma gene product reveals at least one significant difference in their actions.