The transcriptional repression of equilibrative nucleoside transporter 1 by D-glucose rfsponses to transcription factor Sp1 and ZBP-89 in human foetal endothelium
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2008
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Abstract
Objectives: Adenosine is a vasodilator in most vascular beds, an effect depending on its extracellular concentration. Uptake of this nucleoside in human umbilical vein endothelial cells (HUVEC) is mainly mediated by human equilibrative nucleoside transporters 1 (hENT1). hENT1 expression and transport activity are reduced in HUVEC exposed to high D-glucose. Since specific mechanisms for these effects of D-glucose are unknown, we examined the role of Sp1 and BP-89 transcription factors on SLC29A1 (for hENT1) promoter activity in response to D-glucose. Methods: HUVEC from normal pregnancies were isolated and exposed (24 h) to 5 mM (normal) or 25 mM (high) D-glucose. Sp1 protein levels were evaluated by western blot in nuclear fractions. Reporter activity of plasmid constructs containing a wild type promoter region of SLC29A1 (-1114 bp to ATG, pGL3-hENT1-1114), or mutations (by PCR) for Sp1 (-815/-801 bp, pGL3-hENT1-1114mutSp1) or ZBP-89 (-992/-969 bp, pGL3-hENT1-1114mutZBP) or both (-1114 bp, pGL3-hENT1-1114mutSp1/ZBP) binding sites were assayed in cells over-expressing Sp1 (using pCGN-Sp1 vector). Results: Nuclear Sp1 abundance was increased, but pGL3-hENT1-1114 transcriptional activity was reduced by high D-glucose. Sp1 over-expression reduced pGL3-hENT1-1114 transcriptional activity in normal or high D-glucose. The effect of high D-glucose or Sp1 over-expression was absent in pGL3-hENT1-1114mutSp1, pGL3-hENT1-1114mutZBP and pGL3-hENT1-1114mutSp1/ZBP cells. Conclusion: A repression of the SLC29A1 promoter activity by Sp1 and ZBP-89 could explain the reduced hENT1 expression and activity exhibited by HUVEC in high extracellular D-glucose. FONDECYT 1070865/1080534/7070249 (Chile), AECI A/5484/06 (Spain). C Puebla andJL Vega hold CONICYT fellowships. M Farías holds CONICYT and PUC-School of Medicine PhD fellowships.