Selective Inhibition of the Human tie-1 Promoter with Triplex-Forming Oligonucleotides Targeted to Ets Binding Sites

Abstract

The Tie receptors (Tie-1 and Tie-2/Tek) are essential for angiogenesis and vascular remodeling/integrity. Tie receptors are upregulated in tumor-associated endothelium, and their inhibition disrupts angiogenesis and can prevent tumor growth as a consequence. To investigate the potential of anti-gene approaches to inhibit tie gene expression for anti-angiogenic therapy, we have examined triple-helical (triplex) DNA formation at 2 tandem Ets transcription factor binding motifs (designated E-1 and E-2) in the human tie-1 promoter. Various tie-1 promoter deletion/mutation luciferase reporter constructs were generated and transfected into endothelial cells to examine the relative activities of E-1 and E-2. The binding of antiparallel and parallel (control) purine motif oligonucleotides (21-22 bp) targeted to E-1 and E-2 was assessed by plasmid DNA fragment binding and electrophoretic mobility shift assays. Triplex-forming oligonucleotides were incubated with tie-1 reporter constructs and transfected into endothelial cells to determine their activity. The Ets binding motifs in the E-1 sequence were essential for human tie-1 promoter activity in endothelial cells, whereas the deletion of E-2 had no effect. Antiparallel purine motif oligonucleotides targeted at E-1 or E-2 selectively formed strong triplex DNA (K d~1 0 -7 M) at 37 °C. Transfection of tie-1 reporter constructs with triplex DNA at E-1, but not E-2, specifically inhibited tie-1 promoter activity by up to 75% compared with control oligonucleotides in endothelial cells. As similar multiple Ets binding sites are important for the regulation of several endothelial-restricted genes, this approach may have broad therapeutic potential for cancer and other pathologies involving endothelial proliferation/dysfunction.

Identification and characterization of a novel porcine endothelial cell‐specific Tie1 promoter

“…3B). This finding is consistent with another study that found that mutation of Ets sites in the human Tie1 promoter also had an immense effect on its activity [14]. Therefore, Ets-binding sites should be conserved in endothelium-specific gene expression, and it is necessary for a promoter or an enhancer to improve transcription.…”

“…The activity and specificity of the mouse Tie1 promoter have been confirmed and used to study vascular development . Several putative transcription‐factor‐binding sites in endothelial cell‐specific promoters have been identified, including AP2, GATA, Ets, and Oct1, which regulate specific gene expression in endothelial cells . However, the porcine Tie1 promoter has not been identified and used for genetic modification.…”

The triple helix: 50 years later, the outcome

“…TFOs have been shown in vitro to alter gene expression during the transcription process (Figure 5A and B), by interfering either with the binding of transcription factors (94,95) or with the formation of the initiation complex (96). It can also arrest transcription elongation by binding to the transcribed position of the targeted gene (97).…”

“…A recent example of inhibition of transcription by triplex strategy has been reported on tie-1 promoter, where the formation of a stable triplex prevents the binding of Ets transcription factors that are essential for the promoter activity (94). In this case, PS TFOs inhibit promoter activity and tie1 expression in vitro and in endothelial cells.…”

Delivery, Effect on Cell Viability, and Plasticity of Modified Aptamer Constructs

“…Triplex forming ONs (TFOs) can bind to the major groove of the DNA double helix, which has been explored in different applications, such as transcriptional activation (72), blocking of transcription (73)(74)(75)(76), recruitment of transcription factors (77,78), fluorescent in situ hybridization of repetitive chromosomal regions (79) and TFO-padlock mediated tagging of DNA fragments (80). TFOs can even bind to DNA at transcriptionally silent loci, however, binding was dramatically increased upon targeting actively transcribed genes (81,82).…”