Transcriptional Regulation of the AP-2α Promoter by BTEB-1 and AP-2rep, a Novel wt-1/egr-Related Zinc Finger Repressor

Abstract

AP-2 transcription factors have been suggested to exert key regulatory functions in vertebrate embryonic development, in tumorigenicity of various cancer cell types, and in controlling cell cycle and apoptotic effector genes. In this study, we investigated transcriptional regulation of the AP-2α gene promoter mediated by an autoregulatory element (referred to as A32) with a core consensus AP-2 binding site at position −336 relative to the mRNA initiation site. AP-2 and multiple different nuclear proteins in HeLa and Neuro2A cell extracts form specific bandshifts with the A32 element. By screening a mouse brain cDNA expression library, we isolated two different cDNAs encoding the transcription factor BTEB-1 and a novel zinc finger protein, AP-2rep. AP-2rep reveals a modular structure with homology to transcription factors of the wt-1/egr-1-family. AP-2rep, BTEB-1, and AP-2 interact in a mutually exclusive manner with overlapping binding sites in the A32 element. Transfection studies revealed that BTEB-1 is a strong activator of AP-2α promoter activity, whereas cotransfected AP-2α resulted in moderate autoactivation of promoter activity. In contrast, AP-2rep confers strong transcriptional repression to the AP-2α gene, and we observed an excellent correlation between induction of AP-2rep mRNA expression and downregulation of AP-2α mRNA during development of the kidney. In summary, we have identified multiple transcription factors and cloned from an expression library a novel zinc finger silencing factor, AP-2rep, mediating positive and negative regulation of AP-2α expression through a set of overlapping cis-regulatory promoter elements.

ACKNOWLEDGMENTS

This work was supported by grants from the DFG and the Wilhelm Sander-Stiftung to R.B. and represents a part of projects performed in the DFG-Forschergruppe “Molecular Mechanisms of Cell Death in Neuronal Systems.” A.I. was supported as a predoctoral fellow from the DFG.

A.I., M.S., and O.W. made equal contributions to this study.