Transcription Factors Zic1 and Zic2 Bind and Transactivate the Apolipoprotein E Gene Promoter

Abstract

We have used the yeast one-hybrid system to identify transcription factors that bind to specific sequences in proximal regions of the apolipoprotein E gene promoter. The sequence between ؊163 and ؊124, that has been previously defined as a functional promoter element, was used as a bait to screen a human brain cDNA library. Ten cDNA clones that encoded portions of the human Zic1 (five clones) and Zic2 (five clones) transcription factors were isolated. Electrophoretic mobility shift assays confirmed the presence of a binding site for Zic1 and Zic2 in the ؊136/؊125 region. Displacement of binding with oligonucleotides derived from adjacent sequences within the APOE promoter revealed the existence of two additional Zic-binding sequences in this promoter. These sequences were identified by electrophoretic mobility shift assays and mutational analysis in regions ؊65/؊54 and ؊185/؊174. Cotransfection of Zic1 and Zic2 expression vector and different APOE promoter-luciferase reporter constructs in U87 glioblastoma cell line showed that the three binding sites partially contributed to the trans-stimulation of the luciferase reporter. Ectopic expression of Zic1 and Zic2 in U87 cells also trans-stimulated the expression of the endogenous gene, increasing the amount of apolipoprotein E produced by glial cells. These data indicate that Zic proteins might contribute to the transcriptional activity of the apolipoprotein E gene and suggest that apolipoprotein E could mediate some of the developmental processes in which Zic proteins are involved.

Zic2 Regulates Retinal Ganglion Cell Axon Avoidance of ephrinB2 through Inducing Expression of the Guidance Receptor EphB1

“…The molecular mechanisms of Zic2 action during development remain unclear. Only a handful of direct targets for Zic2 have been identified (Yang et al, 2000;Salero et al, 2001;Sakurada et al, 2005), and an "optimal" consensus target binding sequence for Zic2 proteins is unknown. It has been suggested that its activation of target genes may be by unconventional means, such as recruitment of a DNA/RNA helicase, RHA (Ishiguro et al, 2007;Ishiguro and Aruga, 2008).…”

Emerging roles for zic genes in early development

“…Yeast one-hybrid assays have identified DNA binding sites for Zic proteins in the apolipoprotein E gene (three sites, each regulated by both Zic1 and Zic2), the dopamine receptor 1a gene (regulated by Zic2; the precise DNA binding sequence was not narrowed to less than 20 nucleotides), and the Math1 gene (regulated by Zic1) (Yang et al, 2000;Salero et al, 2001;Ebert et al, 2003). The Zic DNA binding sites in these genes are quite different, although all are GC-rich (Aruga, 2004; Table 1C).…”

Divergent Effects of Peroxisome Proliferator-activated Receptor γ Agonists and Tumor Necrosis Factor α on Adipocyte ApoE Expression

“…Multiple potential control elements for apoE gene expression have been described in its 5Ј proximal promoter (15)(16)(17)(18)(19). In addition, downstream control elements have been described that are required to direct specific expression of apoE in various tissues.…”