Cezanne Regulates Inflammatory Responses to Hypoxia in Endothelial Cells by Targeting TRAF6 for Deubiquitination
Rationale: Hypoxia followed by reoxygenation promotes inflammation by activating NF-κB transcription factors in endothelial cells (EC). This process involves modification of the signalling intermediary TRAF6 with polyubiquitin chains. Thus cellular mechanisms that suppress TRAF6 ubiquitination are potential therapeutic targets to reduce inflammation in hypoxic tissues.
Objective: In this study, we tested the hypothesis that endothelial activation in response to hypoxia-reoxygenation can be influenced by Cezanne, a deubiquitinating enzyme that cleaves ubiquitin from specific modified proteins.
Methods and Results: Studies of cultured endothelial cells (EC) demonstrated that hypoxia (1% oxygen) induced Cezanne via p38 MAP kinase-dependent transcriptional and post-transcriptional mechanisms. Hypoxia-reoxygenation had minimal effects on pro-inflammatory signalling in unmanipulated EC but significantly enhanced Lys-63 polyubiquitination of TRAF6, activation of NF-κB and expression of inflammatory genes following silencing of Cezanne. Thus although hypoxia primed cells for inflammatory activation it simultaneously induced Cezanne which impeded signalling to NF-κB by suppressing TRAF6 ubiquitination. Similarly, ischemia induced Cezanne in the murine kidney in vascular EC, glomerular EC, podocytes and epithelial cells, and genetic deletion of Cezanne enhanced renal inflammation and injury in murine kidneys exposed to ischemia followed by reperfusion.
Conclusions: We conclude that inflammatory responses to ischemia are controlled by a balance between ubiquitination and deubiquitination and that Cezanne is a key regulator of this process. Our observations have important implications for therapeutic targeting of inflammation and injury during ischemia-reperfusion.
- Received September 18, 2012.
- Revision received April 5, 2013.
- Accepted April 5, 2013.