Book of Abstracts: Albany 2007
June 19-23 2007
Gene Transactivation by Z-DNA Binding Proteins
Left-handed Z-DNA is transiently stabilized in the promoter region of many genes when they are expressed. In several cases it has been demonstrated that Z-DNA is necessary for the activation of the gene. A series of proteins have been identified that include a domain with high affinity for Z-DNA. When a Z-DNA binding domain is expressed in a cell, it binds to promoter regions that form Z-DNA and stabilize the left-handed form. This up regulates expression of the genes to which the protein binds. This transactivation involves a number of different genes and profoundly affects the host cell.
DNA binding domains have been studied from the editing enzyme double-stranded RNA adenosine deaminase (ADAR-1), Z-DNA binding protein 1 (ZBP-1) and the virulence factor E3L of vaccinia poxvirus. The structure of several of these protein domains has been determined co crystallized with Z-DNA. The Z-DNA binding domains of these proteins share a similar helix-turn-helix with a beta-sheet architecture, and they interact with five successive phosphate groups in the zig-zag Z-DNA backbone. The structural similarity of these domains is complemented by common functional properties. When these domains are expressed in a HeLa cell, the cell converts to an anti-apoptotic state, a feature necessary for virulence of poxvirus. A number of genes are found to be up-regulated, while some are down-regulated. Estaban and colleagues have found that HeLa cells expressing E3L grow faster than control cells and form solid tumors when injected into nude mice. We have discovered that these properties are associated with up-regulation of c-myc. After transfection with E3L or its Z-DNA binding domain, HeLa cells have increased levels of c-myc mRNA. The c-myc gene is pulled down by an antibody against E3L in a chromatin immune precipitation analysis. Since ADAR-1 and ZBP-1, which also contain Z-DNA binding domains, are proteins found in normal human cells, the question arises whether these genes become up-regulated in human diseases such as cancer.
Department of Biology