Biomedical subjects
Michael Bots
Publications and source records attributed to Michael Bots.
Does the serpin PI-9 protect tumor cells?
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Serpins prevent granzyme-induced death in a species-specific manner.
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.
SPI-CI and SPI-6 cooperate in the protection from effector cell-mediated cytotoxicity.
Tumors have several mechanisms to escape from the immune system. One of these involves expression of intracellular anticytotoxic proteins that modulate the execution of cell death. Previously, we have shown that the serine protease inhibitor (serpin) SPI-6, which inactivates the cytotoxic protease granzyme B (GrB), is capable of preventing cytotoxic T lymphocyte (CTL)-mediated apoptosis. Despite its potent antiapoptotic activity, SPI-6 does not prevent membranolysis induced by cytotoxic lymphocytes. We now provide evidence that several colon carcinoma cell lines do resist membranolysis and that this protection is dependent on SPI-6 but also requires expression of a closely related serpin called SPI-CI (serine protease inhibitor involved in cytotoxicity inhibition). Expression of SPI-CI is absent from normal colon but observed in placenta, testis, early during embryogenesis, and in cytotoxic lymphocytes. SPI-CI encodes a chymotrypsin-specific inhibitor and irreversibly interacts with purified granzyme M. Moreover, SPI-CI can protect cells from purified perforin/GrM-induced lysis. Our data therefore indicate that SPI-CI is a novel immune escape molecule that acts in concert with SPI-6 to prevent cytotoxic lymphocyte-mediated killing of tumor cells.