Oncotarget

Research Papers:

Targeting HIF2α Translation with Tempol in VHL-Deficient Clear Cell Renal Cell Carcinoma

Carole Sourbier, Gaurav Srivastava, Manik C. Ghosh, Sanchari Ghosh, Youfeng Yang, Gopal Gupta, William DeGraff, Murali C. Krishna, James B. Mitchell, Tracey A. Rouault and W. Marston Linehan _

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Oncotarget. 2012; 3:1472-1482. https://doi.org/10.18632/oncotarget.561

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Abstract

Carole Sourbier1,*, Gaurav Srivastava1,*, Manik C. Ghosh2, Sanchari Ghosh1, Youfeng Yang1, Gopal Gupta1, William DeGraff3, Murali C. Krishna3, James B. Mitchell3, Tracey A. Rouault2, W. Marston Linehan1

1 Urologic Oncology Branch, Center for Cancer Research, National Cancer Institute

2 National Institute of Child Health and Human Development

3 Radiation Biology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD

* Authors contributed equally to this work.

Correspondence:

W. Marston Linehan, email:

Keywords: HIF, Tempol, RCC, VHL, IRP1, iron metabolism

Received: July 19, 2012, Accepted: November 06, 2012, Published: November 08, 2012

Abstract

The tumor suppressor gene, Von Hippel-Lindau (VHL), is frequently mutated in the most common form of kidney cancer, clear cell renal cell carcinoma (CCRCC). In hypoxic conditions, or when there is a VHL mutation, the hypoxia inducible factors, HIF1α and HIF2α, are stabilized and transcribe a panel of genes associated with cancer such as vascular endothelial growth factor receptor (VEGFR), platelet derived growth factor (PDGF), and glucose transporter 1 (GLUT1). Recent studies in clear cell kidney cancer have suggested that HIF2α, but not HIF1α, is the critical oncoprotein in the VHL pathway. Therefore, targeting HIF2α could provide a potential therapeutic approach for patients with advanced CCRCC. Since iron regulatory protein 1 (IRP1) is known to inhibit the translation of HIF2α, we investigated whether Tempol, a stable nitroxide that activates IRP1 towards IRE-binding, might have a therapeutic effect on a panel of human CCRCC cells expressing both HIF1α and HIF2α. We first evaluated the protein expression of HIF1α and HIF2α in 15 different clear cell renal carcinoma cell lines established from patient tumors in our laboratory. Tempol decreased the expression of HIF2α, and its downstream targets in all the cell lines of the panel. This effect was attributed to a dramatic increase of IRE-binding activity of IRP1. Several cell lines were found to have an increased IRP1 basal activity at 20% O2 compared to 5% O2, which may lower HIF2α expression in some of the cell lines in a VHL-independent manner. Taken together our data identify Tempol as an agent with potential therapeutic activity targeting expression of HIF2α in VHL-deficient clear cell kidney cancer and illustrate the importance of studying biochemical processes at relevant physiological O2 levels.


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