Nox4 Mediates Renal Cell Carcinoma Cell Invasion through Hypoxia-Induced Interleukin 6- and 8- Production

Abstract

BackgroundInflammatory cytokines are detected in the plasma of patients with renal cell carcinoma (RCC) and are associated with poor prognosis. However, the primary cell type involved in producing inflammatory cytokines and the biological significance in RCC remain unknown. Inflammation is associated with oxidative stress, upregulation of hypoxia inducible factor 1-alpha, and production of pro-inflammatory gene products. Solid tumors are often heterogeneous in oxygen tension together suggesting that hypoxia may play a role in inflammatory processes in RCC. Epithelial cells have been implicated in cytokine release, although the stimuli to release and molecular mechanisms by which they are released remain unclear. AMP-activated protein kinase (AMPK) is a highly conserved sensor of cellular energy status and a role for AMPK in the regulation of cell inflammatory processes has recently been demonstrated.Methods and Principal FindingsWe have identified for the first time that interleukin-6 and interleukin-8 (IL-6 and IL-8) are secreted solely from RCC cells exposed to hypoxia. Furthermore, we demonstrate that the NADPH oxidase isoform, Nox4, play a key role in hypoxia-induced IL-6 and IL-8 production in RCC. Finally, we have characterized that enhanced levels of IL-6 and IL-8 result in RCC cell invasion and that activation of AMPK reduces Nox4 expression, IL-6 and IL-8 production, and RCC cell invasion.Conclusions/SignificanceTogether, our data identify novel mechanisms by which AMPK and Nox4 may be linked to inflammation-induced RCC metastasis and that pharmacological activation of AMPK and/or antioxidants targeting Nox4 may represent a relevant therapeutic intervention to reduce IL-6- and IL-8-induced inflammation and cell invasion in RCC.

Quinone compounds regulate the level of ROS production by the NADPH oxidase Nox4

“…Primary discovered in kidney tissue [13], Nox4 appears to be ubiquitously distributed. Its dysfunction has been linked to several pathologies including hypertension [14], diabetes [15], atherosclerosis [16], cancer [17], osteoarthritis [18] and inflammation [19], and Nox4 represent a potential therapeutic target [20]. Despite its wide distribution, its activation mechanisms at the molecular level are unclear.…”

Renal Carcinogenesis, Tumor Heterogeneity, and Reactive Oxygen Species: Tactics Evolved

“…The significance of this is that IL-6 stimulates cell migration and invasion in VHL-deficient cells (44). Notably, neither normal proximal tubular epithelial cells that are exposed to hypoxia nor VHL-deficient RCC cells that are exposed to normoxia secrete IL-6 or IL-8 (44). TGF-beta is a pleiotropic cytokine exerting positive and negative biological outcomes (cell proliferation, epithelial-mesenchymal transition (EMT), migration, invasion, and drug resistance) during carcinogenesis, and this is known as the TGF-beta paradox (154).…”

“…Silencing or inhibition of NOX1, but not NOX4, inhibits NF-kappaB (NF-jB)-dependent endothelial cell migration in vitro and impairs angiogenesis through peroxisome proliferator-activated receptor-alpha (PPARa) in vivo (48,102). Interestingly, VHL-deficient cells that are exposed to hypoxia induce interleukin (IL)-6 and IL-8 production in an NOX4-dependent manner (44). The significance of this is that IL-6 stimulates cell migration and invasion in VHL-deficient cells (44).…”

“…Interestingly, VHL-deficient cells that are exposed to hypoxia induce interleukin (IL)-6 and IL-8 production in an NOX4-dependent manner (44). The significance of this is that IL-6 stimulates cell migration and invasion in VHL-deficient cells (44). Notably, neither normal proximal tubular epithelial cells that are exposed to hypoxia nor VHL-deficient RCC cells that are exposed to normoxia secrete IL-6 or IL-8 (44).…”

“…Exogenous inflammatory cytokines can induce NOX4-derived ROS, cell migration, and metastasis in VHL-deficient renal cancer cells (44). Interestingly, the obesity paradox in renal cancer describes an inverse relationship between body mass index (BMI) and survival in advanced-stage RCC (24,76).…”