Human nidogen gene: structural and functional characterization of the 5'-flanking region

Nidogen is a sulfated multifunctional glycoprotein present in basement membranes. In this study, we have cloned the 5'-flanking region of the human nidogen gene. Initially, an approximately 35-kb DNA clone (NCos4) was isolated from a human cosmid genomic library. Southern hybridization of EcoRI-digested NCos4 allowed isolation of a 3.7-kb fragment, which was shown to contain a portion of intron 1, the entire exon 1, and approximately 0.9 kb of 5'-flanking sequences of the nidogen gene. Nucleotide sequencing of the 5'-flanking DNA revealed the presence of two canonic CCAAT consensus sequences in the antisense strand and a potential variant of the TATA motif, TATTT, in the sense strand. One putative AP-2 and six putative SP1 binding sites were also present. To test the functional promoter activity of the 5'-flanking genomic DNA, two nidogen promoter/CAT reporter gene constructs, with the promoter segment spanning from -864 to -1 and from -534 to -1, respectively, were developed and analyzed in transient transfections of human and mouse cell cultures. Both constructs showed clearly detectable promoter activity, and the activity of the larger construct could be up-regulated by 12-O-tetradecanoyl phorbol 13-acetate up to 2.5 times. The results indicate that the nidogen promoter/CAT gene constructs developed in this study provide a means to examine the transcriptional regulation of nidogen gene expression in human diseases of the basement membrane zone.