Volume 76, Issue 9, Pages 939-945 (November 2009) The role of VHL in clear-cell renal cell carcinoma and its relation to targeted therapy  Peter E. Clark  Kidney International  Volume 76, Issue 9, Pages 939-945 (November 2009) DOI: 10.1038/ki.2009.296 Copyright © 2009 International Society of Nephrology Terms and Conditions

Figure 1 VHL and HIFα. In the presence of normal tissue oxygenation levels (depicted to the left in figure), prolyl hydroxylases hydroxylate HIFα. Once hydroxylated, an E3 ligase complex binds HIFα in a process that is VHL dependent. This leads to ubiquitination (Ub) of HIFα, marking it for degradation by the proteasomal machinery of the cell. In the right of the figure is depicted the disruption of this normal regulatory process when VHL function is aberrant. In the absence of functional VHL, the E3 ligase complex cannot bind HIFα, irrespective of its hydroxylation status. This leads to accumulation of HIFα in the cell cytoplasm, allowing it to dimerize with the constitutively present HIFβ, translocate to the nucleus, bind to hypoxia response elements, and regulate gene transcription. HIFα, hypoxia-inducible factor alpha; HIFβ, hypoxia-inducible factor beta; HRE, hypoxia response element; Ub, ubiquitin; VHL, von Hippel–Lindau. Kidney International 2009 76, 939-945DOI: (10.1038/ki.2009.296) Copyright © 2009 International Society of Nephrology Terms and Conditions

Figure 2 Hypoxia responsive genes. Binding of the HIFα–HIFβ heterodimer to the HRE in the promoter region results in transcriptional upregulation of genes important to the cell's response to hypoxia. These include vascular endothelial growth factor (VEGF), platelet- derived growth factor (PDGF), transforming growth factor alpha (TGFα), carbonic anhydrase IX (CA-IX), erythropoietin (EPO), glucose transporter 1 (GLUT-1), and BCL2/adenovirus E1B 19kDa-interacting protein 3 (BNIP3). Binding of ligands, such as VEGF, to their respective cell surface receptors, such as VEGFR, leads to tyrosine phosphorylation of the receptor and subsequent downstream signaling through several kinase-dependent pathways, such as the PI3K–Akt–mTOR pathway and the RAS–RAF–MEK–ERK pathway. Note that mTOR leads to upregulation of basal levels of HIFα. Also shown within these pathways is a subset of the known therapeutic target sites for the monoclonal antibody to VEGF (bevacizumab), the tyrosine kinase inhibitors (sorafenib and sunitinib), and the mTOR inhibitors (temsirolimus and everolimus). AKT, protein kinase B; HIFα, hypoxia-inducible factor alpha; HIFβ, hypoxia-inducible factor beta; HRE, hypoxia response element; mTOR, mammalian target of rapamycin; PI3K, phosphatidylinositol-3 kinase. Kidney International 2009 76, 939-945DOI: (10.1038/ki.2009.296) Copyright © 2009 International Society of Nephrology Terms and Conditions