Granzyme A released upon stimulation of cytotoxic T lymphocytes activates the thrombin receptor on neuronal cells and astrocytes.

Abstract

Granzymes are a family of serine proteases that are harbored in cytoplasmic granules of activated T lymphocytes and are released upon target cell interaction. Immediate and complete neurite retraction was induced in a mouse neuronal cell line when total extracts of granule proteins were added. This activity was isolated and identified as granzyme A. This protease not only induced neurite retraction at nanomolar concentrations but also reversed the stellation of astrocytes. Both effects were critically dependent on the esterolytic activity of granzyme A. As neurite retraction is known to be induced by thrombin, possible cleavage and activation of the thrombin receptor were investigated. A synthetic peptide spanning the N-terminal thrombin receptor activation sequence was cleaved by granzyme A at the authentic thrombin cleavage site Leu-Asp-Pro-Arg -Ser. Antibodies to the thrombin receptor inhibited both thrombin and granzyme A-mediated neurite retraction. Thus, T-cell-released granzyme A induces cellular responses by activation of the thrombin receptor. As braininfiltrating CD4+ lymphocytes are the effector cells in experimental allergic encephalomyelitis, granzyme A released in the brain may contribute to the etiology of autoimmune disorders in the nervous system.

Granzyme B is expressed in mouse mast cells in vivo and in vitro and causes delayed cell death independent of perforin

“…It is possible that the tryptase, mMCP-6, with similar substrate specificity to that of gzmA, but distinct from gzmB, 8,27 may substitute for gzmA in mast cell-induced biological processes. Thus, mMCP-6 and gzmB not only may execute differing nonredundant extracellular processes reminiscent of gzmA and gzmB from CTL/NK cells, [8][9][10] but may also act in concert with gzmB on the same substrates, such as fibronectin, although with distinct cleavage specificities. 8,10,28 Activated BMMC from B6 but not gzmB À/À mice caused cell death in adherent MEFs (Figure 7a), but not anchorageindependent EL4 cells (Figure 7b).…”

“…These processes are strictly dependent on perf. 5,7 However, evidence of extracellular function(s) of gzmA 8,9 and gzmB, 10,11 independent of perf exists. These extracellular activities of gzms are implicated in inflammation and processes of leukocyte extravasation.…”

Granzyme A and thrombin differentially promote the release of interleukin-8 from alveolar epithelial A549 cells

“…In other words, rGrA is not thought to activate PAR-1 expressed in this cell line. GrA was found previously to stimulate PAR-1 expressed in neuronal cells (Suidan et al 1994). One possible explanation for this discrepancy is that neuronal cells may express unknown PAR-1-associated molecules that assist in interaction of GrA with PAR-1, whereas A549 cells may not.…”

“…GrA has been considered as a low-affinity ligand of PAR-1 (Parry et al 1996;Steinhoff et al 2005;Suidan et al 1994). For instance, this protease induced neurite retraction, which was inhibited in the presence of an anti-PAR-1 antibody (Suidan et al 1994).…”

“…For instance, this protease induced neurite retraction, which was inhibited in the presence of an anti-PAR-1 antibody (Suidan et al 1994). This consideration lead us to assess whether GrA promotes IL-8 release via a mechanism involving activation of the G-protein-coupled receptor.…”