J Biol Chem, Vol. 274, Issue 50, 35475-35482, December 10, 1999

Synergistic Transcriptional Activation by hGABP and Select Members of the Activation Transcription Factor/cAMP Response Element-binding Protein Family^*

Jun-ichi Sawada, Noriaki Simizu, Fumihiko Suzuki, Chika Sawa, Masahide Goto^§, Makoto Hasegawa, Takeshi Imai, Hajime Watanabe, and Hiroshi Handa^¶

From the Research Function for Biotechnology, Frontier Collaborative Research Center, and  Molecular Medical Engineering, Department of Biological Information, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan

The Ets-related DNA-binding protein human GA-binding protein (hGABP)  interacts with the four ankyrin-type repeats of hGABP to form an hGABP tetrameric complex that stimulates transcription through the adenovirus early 4 (E4) promoter. Using co-transfection assays, this study demonstrated that the hGABP complex mediated efficient activation of transcription from E4 promoter synergistically with activating transcription factor (ATF) 1 or cAMP response element-binding protein (CREB), but not ATF2/CRE-BP1. This synergy also partially occurred when hGABP was used alone in place of the combination of hGABP and hGABP. hGABP activated an artificial promoter containing only ATF/CREB-binding sites under coexistence of ATF1 or CREB. Consistent with these results, physical interactions of hGABP with ATF1 or CREB were observed in vitro. Functional domain analyses of the physical interactions revealed that the amino-terminal region of hGABP bound to the DNA-binding domain of ATF1, which resulted in the formation of ternary complexes composed of ATF1, hGABP, and hGABP. In contrast to hGABP, hGABP did not significantly interact with ATF1 and CREB. Taken together, these results indicate that hGABP functionally interacts with selective members of the ATF/CREB family, and also suggest that synergy results from multiple interactions which mediate stabilization of large complexes within the regulatory elements of the promoter region, including DNA-binding and non-DNA-binding factors.