Open Access Research

The proteases HtrA2/Omi and UCH-L1 regulate TNF-induced necroptosis

Justyna Sosna1, Susann Voigt1, Sabine Mathieu1, Dieter Kabelitz1, Ahmad Trad2, Ottmar Janssen1, Catherine Meyer-Schwesinger3, Stefan Schütze1 and Dieter Adam1*

Author Affiliations

1 Institut für Immunologie, Christian-Albrechts-Universität zu Kiel, Michaelisstr. 5, 24105 Kiel, Germany

2 Biochemisches Institut, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Germany

3 Zentrum für Innere Medizin, Nephrologie, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany

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Cell Communication and Signaling 2013, 11:76  doi:10.1186/1478-811X-11-76

Published: 3 October 2013

Abstract

Background

In apoptosis, proteolysis by caspases is the primary mechanism for both initiation and execution of programmed cell death (PCD). In contrast, the impact of proteolysis on the regulation and execution of caspase-independent forms of PCD (programmed necrosis, necroptosis) is only marginally understood. Likewise, the identity of the involved proteases has remained largely obscure. Here, we have investigated the impact of proteases in TNF-induced necroptosis.

Results

The serine protease inhibitor TPKC protected from TNF-induced necroptosis in multiple murine and human cells systems whereas inhibitors of metalloproteinases or calpain/cysteine and cathepsin proteases had no effect. A screen for proteins labeled by a fluorescent TPCK derivative in necroptotic cells identified HtrA2/Omi (a serine protease previously implicated in PCD) as a promising candidate. Demonstrating its functional impact, pharmacological inhibition or genetic deletion of HtrA2/Omi protected from TNF-induced necroptosis. Unlike in apoptosis, HtrA2/Omi did not cleave another protease, ubiquitin C-terminal hydrolase (UCH-L1) during TNF-induced necroptosis, but rather induced monoubiquitination indicative for UCH-L1 activation. Correspondingly, pharmacologic or RNA interference-mediated inhibition of UCH-L1 protected from TNF-induced necroptosis. We found that UCH-L1 is a mediator of caspase-independent, non-apoptotic cell death also in diseased kidney podocytes by measuring cleavage of the protein PARP-1, caspase activity, cell death and cell morphology. Indicating a role of TNF in this process, podocytes with stably downregulated UCH-L1 proved resistant to TNF-induced necroptosis.

Conclusions

The proteases HtrA2/Omi and UCH-L1 represent two key components of TNF-induced necroptosis, validating the relevance of proteolysis not only for apoptosis, but also for caspase-independent PCD. Since UCH-L1 clearly contributes to the non-apoptotic death of podocytes, interference with the necroptotic properties of HtrA2/Omi and UCH-L1 may prove beneficial for the treatment of patients, e.g. in kidney failure.

Keywords:
Tumor necrosis factor; Necroptosis; Programmed necrosis; Apoptosis; Proteases; HtrA2/Omi; UCH-L1; Kidney failure