The human hepatocyte growth factor receptor gene: complete structural organization and promoter characterization

The hepatocyte growth factor (HGF) receptor is a tyrosine kinase transmembrane protein encoded by the c-met proto-oncogene. Here, we have isolated and characterized human genomic DNA clones containing the entire coding sequence of the HGF receptor. The gene spans approx. 120kb in length and consists of 21 exons interrupted by 20 introns. Two alternative splice sites corresponding to known mRNA transcripts are located at exon 10 and exon 14, respectively. Structural analysis of the 5'-regulatory region reveals that the c-met promoter lacks TATA or CAAT elements but has an extremely high G-C content and multiple Sp1 binding sites. By transfection of a series of chimeric reporter constructs containing a variable region of the c-met promoter and the coding region for chloramphenicol acetyltransferase, we have identified two positive, and one negative regulatory elements that dictate c-met transcription in renal epithelial mIMCD-3 cells at nucleotide positions -2615 to -1621, -223 to -68, and -1621 to -1093, respectively. Moreover, deletion and mutation of the multiple Sp1 sites in the c-met promoter region markedly reduced c-met promoter activity in mIMCD-3 cells, suggesting that the Sp1 sites are essential for establishing the constitutive expression of the c-met gene. These data provide fundamental information on HGF receptor gene organization, as well as on the genomic origin of different receptor isoforms, and should facilitate further studies on the transcriptional regulation of its expression.