Serpins prevent granzyme‐induced death in a species‐specific manner

Abstract

Summary Expression of serine protease inhibitors (serpins) is one of the mechanisms used by tumour cells to escape immune surveillance. Previously, we have shown that expression of serpins SPI-6 and SPI-CI, respectively, renders tumour cells resistant to granzyme B (GrB)-mediated death and granzyme M (GrM)-mediated death. To obtain better insight into the interaction between serpins and their target proteases, we investigated the roles of protease inhibitor (PI)-9 and SPI-6 in the resistance to GrB-mediated and CD95-mediated death in further detail. Neither human PI-9 nor its murine orthologue SPI-6 was capable of preventing CD95-induced apoptosis in murine or human cells, indicating that these serpins do not inhibit the activation of apical caspases in this pathway. High expression of PI-9 or SPI-6 did prevent apoptosis induced by human GrB. Strikingly, only SPI-6, and not PI-9, was capable of inhibiting murine GrB, suggesting that a difference in enzymatic specificity exists between the mouse and the human granzymes. In agreement with this suggestion, murine GrB was clearly less effective in inducing apoptosis in human cells. Similar species specificity was also observed for SPI-CI and GrM when either their capacity to associate or the effectiveness of GrM-induced cytotoxicity was analysed. Our findings therefore indicate a species diversity that has a clear effect on mixed in vitro effector target settings.

Granzyme M: behind enemy lines

“…92 SPI-CI has been initially identified in mouse cytotoxic T lymphocytes 93 and has later been found to inhibit purified rat GrM 38 and -to a lesser extent -hGrM. 94 SPI-CI forms the classical SDS-stable serpin-protease complex with rat GrM, and is expressed by purified murine CD8 þ T cells and even more by murine LAK cells. 38 Transfection of SPI-CI prevents both rat GrM and -with reduced efficiency -hGrMmediated cell death in tumor cells.…”

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

“…36 In mice, serine protease inhibitor 6 shares homology with human PI-9, in which it functions to regulate GrB activity. 37 Recently, Sipione et al 38 discovered an inhibitor of mouse and human GrB, serpina3n, expressed by mouse Sertoli cells. Serpina3n shares homology with the human a-1-antichymotrypsin, which interestingly does not appear to show any inhibitory effect on GrB in humans.…”

Analysis of Protein Processing by N-terminal Proteomics Reveals Novel Species-specific Substrate Determinants of Granzyme B Orthologs

“…Next to GrB, GrA was also reported to display altered substrate specificity and functionality fueled by structural differences between its orthologs (15, 18). Furthermore intracellular serine protease inhibitors (serpins) regulate granzymes in species-specific ways (15,19). …”