Augmentation of the erythropoietin enhancer-mediated hypoxia inducible gene expression by co-transfection with the plasmid encoding hypoxia inducible factor 1a

Abstract

Therapeutic angiogenesis with gene encoding vascular endothelial growth factor (VEGF) has been investigated as a potential treatment for many disorders and injuries with ischemia. However, unregulated VEGF expression has the potential to promote tumor growth, accelerate diabetic proliferative retinopathy and promote rupture of atherosclerotic plaque. Therefore, the expression of VEGF should be tightly regulated to avoid the unfavorable side effects. Our group developed the erythropoietin (Epo) enhancer-SV40 promoter system for a hypoxia-inducible gene expression. Similarly, the hypoxia-response elements (HREs) and SV40 promoter system induced the gene expression in ischemic myocardium. The activity of the hypoxia specific promoter was further enhanced by using a two-step transcription amplification system (TSTA). Indeed, the TSTA system could increase the overall promoter activity. However, this system compromised the hypoxia specificity, which is not desirable. Hypoxia inducible gene expressions are mediated by hypoxia inducible factor 1 (HIF-1 ). In normal tissues, HIF-1 is rapidly degraded via ubiquitin-dependent proteolysis pathway. However, in ischemic tissue, HIF-1 is stabilized and induces the gene expression. In the present study, we developed a hypoxia specific gene expression system, in which the promoter activity of the Epo enhancer and SV40 promoter system was further enhanced without compromise of the specificity by the co-transfection of the HIF-1 gene.