The epidermal growth factor receptor (EGFR) is overexpressed in many human cancers and cancer cell lines due to gene amplification and/or increased gene transcription. We have identified transcription factors that regulate EGFR expression and cloned a skeletal muscle form of a novel transcription repressor, GCF2. EGFR gene expression is upregulated by interferons. We have determined that this induction of the EGFR gene is mediated via interferon regulated factor 1 (IRF-1). Transient transfection assays with an IRF-1 expression plasmid and an EGFR promoter reporter construct resulted in an increase of promoter activity up to 200-fold. This induction was partially inhibited by interferon regulated factor 2 (IRF-2) which is known to bind and compete for the same DNA element as IRF-1. Using deletion mutants of the EGFR promoter, the IRF-1 induction was shown to require the -1104 to -911 region. DNA sequences in this region were capable of binding IRF-1 in gel mobility shift assays. Also, the IRF-1 expression construct was able to induce the endogenous EGFR level approximately ten-fold in transient transfection assays. These results indicate that IRF-1 may be an important modulator of EGFR gene expression. We have shown that activator protein 1 (AP1) binds to four sites in the EGFR promoter and that an AP1 expression construct is able to induce EGFR promoter activity 3-5 fold in transient transfection assays. We have examined cell lines overexpressing AP1 or containing a dominant negative AP1 for changes in EGFR levels. We found no direct correlation of AP1 expression level and EGFR level in these cell lines. We have recently identified a transcription factor termed GCF2 which has been shown to bind to the EGFR promoter and repress transcription of the gene. GCF2 mRNA is expressed as a 4.2 kilobase mRNA in most cell lines and tissues but is expressed as a 2.7 kilobase mRNA in heart and skeletal muscle tissue. We have cloned and sequenced a cDNA of 2770 base pairs corresponding to this mRNA. The open reading frame encodes 625 amino acids and has 66% similarity to the previously identified GCF2.
