Related Experiment Video
Updated: Jun 14, 2026
Assessing Cellular Target Engagement by SHP2 (PTPN11) Phosphatase Inhibitors
Published on: July 17, 2020
The NADPH oxidase subunit p22phox inhibits the function of the tumor suppressor protein tuberin
Karen Block1, Yves Gorin, David D New
1Department of Medicine, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA. block@uthscsa.edu
Abstract:
Mutations in the von Hippel-Lindau (VHL) gene give rise to renal cell carcinoma. Reactive oxygen species, generated by Nox oxidases, are involved in tumorigenesis. We have previously demonstrated that in VHL-deficient cells, p22(phox)-dependent Nox1 and Nox4 oxidases maintain hypoxia inducible factor-2alpha (HIF-2alpha) protein expression through an Akt-dependent translational pathway. Phosphorylation of tuberin, by Akt, results in its inactivation. Here we show that diphenyleneiodonium chloride, an inhibitor of Nox oxidases, and small-interfering RNA-mediated down-regulation of p22(phox) inhibit Akt-dependent phosphorylation of tuberin and stabilizes tuberin protein levels in VHL-deficient renal carcinoma cells. p22(phox)-mediated inactivation of tuberin is associated with an increase in ribosomal protein S6 kinase 1 and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1) phosphorylation as well as HIF-2alpha stabilization. Importantly, we find that marked up-regulation of p22(phox) in human renal cell carcinoma correlates with increased tuberin phosphorylation, decreased tuberin protein levels, and increased phosphorylation of 4E-BP1. Our data provide the first evidence that p22(phox)-based Nox oxidases maintain HIF-2alpha protein expression through inactivation of tuberin and downstream activation of ribosomal protein S6 kinase 1/4E-BP1 pathway.
Insights
In von Hippel-Lindau (VHL) disease, Nox oxidases and p22(phox) inactivate tuberin, stabilizing hypoxia-inducible factor-2alpha (HIF-2alpha) and promoting renal cell carcinoma growth.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Mutations in the von Hippel-Lindau (VHL) gene are a primary cause of renal cell carcinoma.
- Reactive oxygen species (ROS) produced by Nox oxidases play a role in cancer development.
- VHL-deficient cells utilize p22(phox)-dependent Nox1 and Nox4 to sustain hypoxia-inducible factor-2alpha (HIF-2alpha) via an Akt-dependent pathway.
Purpose of the Study:
- To investigate the role of p22(phox)-based Nox oxidases in regulating tuberin and HIF-2alpha in VHL-deficient renal carcinoma cells.
- To elucidate the molecular mechanisms linking Nox oxidase activity, tuberin phosphorylation, and HIF-2alpha stabilization.
Main Methods:
- Utilized diphenyleneiodonium chloride (Nox inhibitor) and small-interfering RNA (siRNA) targeting p22(phox) in VHL-deficient renal carcinoma cells.
- Assessed Akt-dependent phosphorylation of tuberin, tuberin protein levels, and phosphorylation of downstream targets like S6K1 and 4E-BP1.
- Correlated p22(phox) expression with tuberin and 4E-BP1 phosphorylation in human renal cell carcinoma samples.
Main Results:
- Inhibition of Nox oxidases or p22(phox) down-regulation reduced tuberin phosphorylation and increased tuberin stability.
- p22(phox)-mediated tuberin inactivation correlated with increased S6K1 and 4E-BP1 phosphorylation and HIF-2alpha stabilization.
- Human renal cell carcinoma exhibited elevated p22(phox) linked to increased tuberin phosphorylation, reduced tuberin levels, and heightened 4E-BP1 phosphorylation.
Conclusions:
- p22(phox)-based Nox oxidases are critical for maintaining HIF-2alpha protein expression by inactivating tuberin.
- This process involves the activation of the S6K1/4E-BP1 pathway downstream of tuberin.
- These findings reveal a novel mechanism in VHL-deficient renal cell carcinoma pathogenesis involving Nox oxidases and tuberin signaling.
Related Concept Videos
02:23Abnormal Proliferation
01:05Cancer-Critical Genes II: Tumor Suppressor Genes
When the function of certain critical genes, especially those involved in cell cycle regulation and cell growth signaling cascades, gets disrupted, it upsets the cell cycle progression. Such cells with unchecked cell cycles start proliferating uncontrollably and eventually develop into tumors.
Such genes that act...
01:05Cancer-Critical Genes II: Tumor Suppressor Genes
When the function of certain critical genes, especially those involved in cell cycle regulation and cell growth signaling cascades, gets disrupted, it upsets the cell cycle progression. Such cells with unchecked cell cycles start proliferating uncontrollably and eventually develop into tumors.
Such genes that act...
01:12Loss of Tumor Suppressor Gene Functions
When the tumor suppressor genes develop mutations or are lost, cells start growing out of control, leading to cancer. However, a single functional copy of the tumor suppressor gene is enough for the cells to maintain their normal functions and cell...
01:12Loss of Tumor Suppressor Gene Functions
When the tumor suppressor genes develop mutations or are lost, cells start growing out of control, leading to cancer. However, a single functional copy of the tumor suppressor gene is enough for the cells to maintain their normal functions and cell...
01:31The Intrinsic Apoptotic Pathway