Identification of a novel promoter and exons of the c-ERBB-2 gene

The c-ERBB-2 gene is frequently amplified in various cancers. During the course of studies on the structural characterization of the amplification units, we isolated four cDNA clones, A39, GRB7, C51 and CAB1 with corresponding genes localized on the c-ERBB-2 locus. A tentative gene, C51, was located at about 12 kb upstream of the c-ERBB-2 gene. By molecular cloning of a full-length cDNA clone of C51 and the reverse transcription PCR (RT-PCR) method, we identified a novel transcript of c-ERBB-2 containing new 5' sequences including the C51 sequence, demonstrating that the c-ERBB-2 gene has a novel promoter and new exons. The structural organization of the novel promoter and exons of c-ERBB-2 was revealed by complete sequence analysis of a total size of about 20 kb of genomic DNA clones containing the 5'-flanking region of the previously described c-ERBB-2 gene. Transient expression of the newly identified promoter-reporter gene constructs in breast cancer cell line MCF-7 showed that the elements responsible for promoter activity were contained in a 697 bp region upstream of the transcriptional start site. The new transcript may encode a protein different in the portion of the extracellular domain. Although the presence of the predicted protein product was not examined, this report is important in that it provides a new aspect of the c-ERBB-2 protooncogene products.