Identification and Characterization of a Novel Enhancer for the Rat neu Promoter

We used chloramphenicol acetyltransferase (CAT) assays to identify and characterize cis-acting elements responsible for rat neu promoter function. Deletion of a region of the neu promoter (-504 to-312) resulted in a marked decrease in CAT activity, indicating that this promoter region corresponds to a positive cis-acting element. Using band shift assays and methylation interference analyses, we further identified a specific protein-binding sequence, AAGATAAAACC (-466 to-456), that binds a specific trans-acting factor termed RVF (for EcoRV factor on the neu promoter). The RVF-binding site is required for maximum transcriptional activity of the rat neu promoter. This same sequence is also found in the corresponding regions of both human and mouse neu promoters. Furthermore, this sequence can enhance the CAT activity driven by a minimum promoter of the thymidine kinase gene in an orientation-independent manner, and thus it behaves as an enhancer. Our results demonstrate that RVF is the major DNA-binding protein contributing to enhancer activity. In addition, Southwestern (DNA-protein) blot analysis using the RVF-binding site as a probe points to a 60-kDa polypeptide as a potential candidate for RVF. The rat neu oncogene encodes a 185-kDa transmembrane protein (p185) (29, 32) that is structurally similar to the epidermal growth factor (EGF) receptor (2). Activation o