Functional Characterization of the Bovine Conglutinin Promoter: Presence of a Novel Element for Transcriptional Regulation of a C-Type Mammalian Lectin Containing a Collagen-Like Domain

Abstract

Bovine conglutinin is a Ca²⁺-dependent, serum lectin that is specific for N-acetylglucosamine and a member of the collectin (collagen-like lectin) family. Here we report the identification of the cis-acting elements involved in regulating expression of the conglutinin gene. The 5'-flanking region of the conglutinin gene was cloned and sequenced by gene walking using vector (cassette)-ligation mediated PCR. A genomic fragment encompassing -741 to +50 by had significant promoter activity when linked to the luciferase reporter gene and transfected into the human hepatoma cell line HepG2. Transfection analysis using a series of luciferase vector/5'-stepwise deletion mutants of the promoter constructs indicated that the sequence of 7 base pairs at around -180 by from the transcription initiation site was necessary for the full expression of the conglutinin gene. The site-directed mutagenesis in the AP-1 (Activator Protein-1) sequence, immediately downstream of the positively controlling cis-element at around -180 bp, resulted in a marked loss of the promoter activity. The novel positively controlling cis-element and the AP-1 sequence regulated synergistically the expression of the conglutinin gene. Gel retardation assay and DNase I footprint analysis demonstrated the presence of the nuclear proteins that bind to these two cis-elements.