Relationship: 974



reduced dimerization, ARNT/HIF1-alpha leads to reduced production, VEGF

Upstream event


reduced dimerization, ARNT/HIF1-alpha

Downstream event


reduced production, VEGF

Key Event Relationship Overview


AOPs Referencing Relationship


AOP Name Directness Weight of Evidence Quantitative Understanding
Aryl hydrocarbon receptor activation leading to embryolethality via cardiotoxicty directly leads to Moderate Moderate

Taxonomic Applicability


Term Scientific Term Evidence Link
chicken Gallus gallus Strong NCBI

Sex Applicability


Sex Evidence
Unspecific Strong

Life Stage Applicability


Term Evidence
Embryo Strong
During development and at adulthood Strong

How Does This Key Event Relationship Work


Dimerization between AHR nuclear translocator (ARNT) and hypoxia inducible factor 1 alpha (HIF-1α) forms a transcription factor complex (HIF-1) that binds to hypoxia response enhancer sequences on DNA to activate the expression of angiogenic factors including vascular endothelial growth factor (VEGF) (Fong 2009). The HIF-1 complex binds to the VEGF gene promoter, then recruits additional transcriptional factors such as P-CREB and P-STAT3, to the promoter and initiates VEGF transcription (Ahluwalia and Tarnawski 2012).  In the absence of HIF-1, VEGF expression and secretion is diminished.

Weight of Evidence


Biological Plausibility


The transcriptional control of VEGF by HIF-1 is well understood (Ahluwalia and Tarnawski 2012; Fong 2009)

Empirical Support for Linkage


Include consideration of temporal concordance here

  • In chick embryo development, the oxygen gradient within myocardium induces VEGF mRNA in cardiac myocytes (Cheung 1997).
  • ARNT- and HIF-1α- null mice cannot survive gestation due to defects in vasculature development (Iyer et al. 1998; Maltepe et al. 1997)
  • Hypoxia increased VEGF expression in AHR+/+ aortic endothelial cells (MAECs) but not in AHR-/- MAECs, suggesting that HIF-1α modulates endothelial VEGF expression in an AHR-dependent manner (Roman et al. 2009)
  • HIF-1α protein degradation by 2-methoxyestradio blocked hypoxia induced VEGF expression in AHR+/+ but not AHR-/- MAECs (Roman et al. 2009)
  • Exogenous hypoxia significantly increased cardiac VEGF-A mRNA expression and expanded its spatial expression in the myocardium of developing chicks; in contrast, AHR activation (which competes with HIF1α for ARNT) tended to limit the spatial expression of VEGF-A to ventricular trabeculae (Ivnitski-Steele et al. 2004)
  • AHR activation reduced myocardial VEGF-A expression in chick embryos and reduced explant VEGF-A secretion (Ivnitski-Steele et al. 2005)


Uncertainties or Inconsistencies


  • ARNT knock-out in mice (effectively null for HIF-1) show disrupted angiogenesis and reduced VEGF expression (Maltepe et al. 1997); however, HIF-1α null mice (also effectively null for HIF-1) show disrupted angiogenesis with a slight increase in VEGF expression (Compernolle et al. 2003).  This may indicate that alternate, compensatory mechanisms for transcriptional regulation of VEGF exist, which are HIF-1α-independent but ARNT dependent.
  • There is also the ptential for HIF-1-independent regulation of VEGF, as illustrated in an ARNT-deficient mutant cell line (Hepa1 C4) in which VEGF expression was only partially abrogated (Gassmann et al. 1997).
  • It has been reported that the AHR/ARNT heterodimer binds to estrogen response elements, with mediation of the estrogen receptor (ER), and activates transcription of VEGF-A (Ohtake et al. 2003). The potential involvement of AHR in opposing regulatory cascades (directly inducing VEGF through ER and indirectly suppressing it by ARNT sequestration) also helps explain conflicting results found in the literature.

Quantitative Understanding of the Linkage


Although the mechanism of control is well understood, a quantitative relationship has not yet been described.

Evidence Supporting Taxonomic Applicability


Transcriptional regulation of VEGF by the HIF-1 complex has been demonstrated in chicken embryos (Cheung 1997; Ivnitski-Steele et al. 2004) fish (Vuori et al. 2004) and mammals (Maltepe et al. 1997; Levy et al.1995)



1. Ahluwalia, A., and Tarnawski, A. S. (2012). Critical role of hypoxia sensor--HIF-1alpha in VEGF gene activation. Implications for angiogenesis and tissue injury healing. Curr. Med. Chem 19(1), 90-97.

2. Cheung, C. Y. (1997). Vascular endothelial growth factor: possible role in fetal development and placental function. J Soc. Gynecol. Investig. 4(4), 169-177.

3. Fong, G. H. (2009). Regulation of angiogenesis by oxygen sensing mechanisms. J Mol. Med. (Berl) 87(6), 549-560.

4. Ivnitski-Steele, I. D., Friggens, M., Chavez, M., and Walker, M. K. (2005). 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibition of coronary vasculogenesis is mediated, in part, by reduced responsiveness to endogenous angiogenic stimuli, including vascular endothelial growth factor A (VEGF-A). Birth Defects Res. A Clin Mol. Teratol. 73(6), 440-446.

5. Ivnitski-Steele, I. D., Sanchez, A., and Walker, M. K. (2004). 2,3,7,8-tetrachlorodibenzo-p-dioxin reduces myocardial hypoxia and vascular endothelial growth factor expression during chick embryo development. Birth Defects Res. A Clin. Mol. Teratol. 70(2), 51-58.

6. Iyer, N. V., Kotch, L. E., Agani, F., Leung, S. W., Laughner, E., Wenger, R. H., Gassmann, M., Gearhart, J. D., Lawler, A. M., Yu, A. Y., and Semenza, G. L. (1998). Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1 alpha. Genes Dev. 12(2), 149-162.

7. Maltepe, E., Schmidt, J. V., Baunoch, D., Bradfield, C. A., and Simon, M. C. (1997). Abnormal angiogenesis and responses to glucose and oxygen deprivation in mice lacking the protein ARNT. Nature 386(6623), 403-407.

8. Roman, A. C., Carvajal-Gonzalez, J. M., Rico-Leo, E. M., and Fernandez-Salguero, P. M. (2009). Dioxin receptor deficiency impairs angiogenesis by a mechanism involving VEGF-A depletion in the endothelium and transforming growth factor-beta overexpression in the stroma. J Biol. Chem 284(37), 25135-25148.

9. Vuori, K.A.M., Soitamo, A., Vuorinen, P.J., and Nikinmaa, M. (2004) Baltic salmon (Salmo salar) yolk-sac fry mortality is associated with disturbances in the function of hypoxia-inducible transcription factor (HIF-1α) and consecutive gene expression. Aquatic Toxicology 68: 301–313

10. Maltepe, E., Achmidt, J.V., Baunoch, D, Bradfield, C.A., ad Simon, M.C. (1997) Abnormal angiogenesis and responses to glucose and oxygen deprivation in mice lacking the protein ARNT. Nature 386 (6623). p.403 - 407.

11. Levy, A. P., Levy, N. S., Wegner, S., and Goldberg, M. A. (1995). Transcriptional regulation of the rat vascular endothelial growth factor gene by hypoxia. J. Biol. Chem. 270(22), 13333-13340.

12. Compernolle, V., Brusselmans, K., Franco, D., Moorman, A., Dewerchin, M., Collen, D., and Carmeliet, P. (2003). Cardia bifida, defective heart development and abnormal neural crest migration in embryos lacking hypoxia-inducible factor-1alpha. Cardiovasc. Res. 60(3), 569-579.

13. Gassmann, M., Kvietikova, I., Rolfs, A., and Wenger, R. H. (1997). Oxygen- and dioxin-regulated gene expression in mouse hepatoma cells. Kidney Int. 51(2), 567-574.

14. Ohtake, F., Takeyama, K., Matsumoto, T., Kitagawa, H., Yamamoto, Y., Nohara, K., Tohyama, C., Krust, A., Mimura, J., Chambon, P., Yanagisawa, J., Fujii-Kuriyama, Y., and Kato, S. (2003). Modulation of oestrogen receptor signalling by association with the activated dioxin receptor. Nature 423(6939), 545-550.