Analysis of cis-acting elements present in the CD20/B1 antigen promoter.

A genomic clone spanning a large portion of the 5' untranscribed region of the CD20 gene was isolated. Deletion analysis of subcloned fragments identified several regulatory elements. A major positive cis-acting element was localized between base pairs -290/-186. A second positive regulatory element was localized between -454/-280 and negative regulatory elements were present in the region between bp -828/-454. The sequence -280/-186 conferred B cell-specific expression on a heterologous, TATA box containing c-fos promoter. Electrophoretic mobility shift assays with overlapping oligonucleotide probes spanning -280/-186 revealed that a 25-bp probe (-225/-201) bound a nuclear protein present in B cell lines expressing the CD20/B1 antigen but not in Jurkat (T cell), U937 (promonocytic), U251 (glioma), or HeLa cells. To confirm the functional significance of this sequence, a trimer of this region was subcloned into the c-fos promoter containing CAT plasmid. Expression was observed only in BJA-B and HS-Sultan cells but not in CD20/B1- cell lines. This sequence element is also important in phorbol ester-induced CD20 expression in the pre-B cell line BP-697. These results partially characterize several regulatory elements present in the CD20 promoter that are likely important in the B cell-specific expression of the CD20 gene.     

Transcriptional control of the mouse prealbumin (transthyretin) gene: both promoter sequences and a distinct enhancer are cell specific.

The mouse genomic clone for the prealbumin (transthyretin) gene was cloned, and its upstream regulatory regions were analyzed. The 200 nucleotides 5' to the cap site when placed within a recombinant plasmid were sufficient to direct transient expression in HepG2 (human hepatoma) cells, but this DNA region did not support expression in HeLa cells. The sequence of the 200-nucleotide region is highly conserved between mouse and human DNA and can be considered a cell-specific promoter. Deletions of this promoter region identified a crucial element for cell-specific expression between 151 and 110 nucleotides 5' to the RNA start site. A region situated at about 1.6 to 2.15 kilobases upstream of the RNA start site was found to stimulate expression 10-fold in HepG2 cells but not in HeLa cells. This far upstream element was invertible and increased expression from the beta-globin promoter in HepG2 cells. Unlike the simian virus 40 enhancer, the prealbumin enhancer would not stimulate beta-globin synthesis in HeLa cells, and even the simian virus 40 enhancer did not stimulate the prealbumin promoter in HeLa cells. Thus, we identified in the prealbumin gene two DNA elements that respond in a cell-specific manner: a proximal promoter including a crucial sequence between -108 and -151 nucleotides and a distant enhancer element located between 1.6 and 2.15 kilobases upstream.