Regulation of elastin gene expression: evidence for functional promoter activity in the 5'-flanking region of the human gene.

Analysis of nucleotide sequences in the 5'-flanking region of the human elastin gene has revealed several unusual features, suggesting that regulation of elastin gene expression is complex. To identify any cis-acting regulatory promoter elements, a 35-kb fragment of DNA (CosE) was isolated from a human genomic cosmid library by hybridizations with a human elastin cDNA. Southern blots of EcoRI digests of CosE DNA, utilizing a 5'-end labeled 21-mer oligonucleotide corresponding to the signal sequence of elastin, revealed the presence of a single 7.8-kb genomic fragment. Partial dideoxynucleotide sequencing of this EcoRI genomic subclone revealed that it extended approximately 2.5 kb 3' of the translation initiation site (ATG), encompassing exon 1 and a portion of the first intron, while the remaining DNA encompassed the 5'-flanking region. Exonuclease III digestion (3'----5') was performed to remove sequences of the first intron and first exon, including the ATG site. One clone, approximately 5 kb in size, had the 3' end located 14 bp upstream of the ATG site. A 462-bp 3' portion of this 5-kb fragment was subcloned into a Bluescript/CAT chimeric plasmid (pBS0CAT) to generate an elastin gene promoter/CAT reporter gene construct (pEP6CAT). Transient transfection experiments with pEP6CAT using human skin fibroblasts, human HT-1080, mouse NIH-3T3, or freshly isolated neonatal rat aortic smooth muscle cells revealed significant CAT activity in each cell line. These results suggest that the 5'-flanking region of the elastin gene contains the cis-acting regulatory elements necessary for transcription. The chimeric plasmid pEP6CAT provides a means to study the transcriptional control of elastin gene expression by exogenous affector molecules, as well as in human dermatologic diseases.