Submitted October 11, 2006
Accepted April 3, 2007
Natural killer cell-derived human granzyme H induces an alternative, caspase-independent cell death program
Edward Fellows, Shirley Gil-Parrado, Dieter E Jenne, and Florian C Kurschus*
Department of Neuroimmunology, Max-Planck-Institute of Neurobiology, D-82152, Planegg-Martinsried, Germany
Abteilung fur Klinische Chemie und Klinische Biochemie, Chirurgische Klinik Innenstadt, Klinikum der LMU Munchen, D-80336 Munchen, Germany
* Corresponding author; email: kurschus{at}neuro.mpg.de.
Granzyme H (GzmH) belongs to a family of five human serine proteases that are expressed by cytotoxic immune effector cells. Although GzmH is most closely related to the caspase activating granzyme B (GzmB), neither a natural substrate nor a role in immune defense reactions has been demonstrated for this orphan granzyme. In rodents, multiple related genes exist, but none of these can be regarded as functional homologs. Here we show that host cells are efficiently killed by GzmH after perforin and streptolysin O-mediated delivery into the cytosol. Dying cells show typical hallmarks of programmed cell death, such as mitochondrial depolarization, reactive oxygen species (ROS) generation, DNA degradation and chromatin condensation. Contrary to GzmB, cell death by GzmH does not involve the activation of executioner caspases, the cleavage of Bid or ICAD, or the release of cytochrome c. The high expression levels of GzmH in naive NK cells and its potent killing ability strongly support the role of the protease in triggering an alternative cell death pathway in innate immunity.
