Identification of an epidermal growth factor receptor transcriptional repressor

Identification of the factors controlling transcription of the epidermal growth factor (EGF) receptor gene is essential for understanding regulation of the EGF receptor and its overexpression in human carcinomas. In this study, we have identified a 60-base pair (bp) region (-919 to -860) relative to the AUG translation initiation codon in the EGF receptor 5' promoter that functions as a cis-acting EGF receptor transcriptional repressor (ETR). This fragment also acted as a repressor when linked to the thymidine kinase promoter. Gel mobility shift assays demonstrated that trans-acting factors bind to 60- and 19-bp fragments. Competition and chloramphenicol acetyltransferase assays with oligonucleotides containing mutations and deletions in this region indicate that the TTCGAGGG sequence (-877 to -870) is required for binding as well as repressor activity. While the ETR-protected region contains consensus sequences for the E2F binding site, no competition was observed with an E2F binding fragment. However, DNA-protein blot analysis indicates that both the 60- and 19-bp fragments specifically bind a 128-kDa polypeptide in extracts from HeLa or A431 human epidermoid carcinoma cells. These results suggest that a novel transcription factor(s) negatively regulates EGF receptor gene expression through binding to the ETR element.