CD45-mediated apoptosis and IL2R downregulation by serine proteases from diarrheagenic bacteria

Abstract

Most enteropathogens secrete one or more members of the serine protease autotransporters of Enterobacteriaceae (SPATE). We previously demonstrated that SPATE cleaves various O-linked glycoproteins on leukocytes, including the tyrosine phosphatase CD45RO. SPATE impairs leukocyte functions and triggers apoptosis in activated T cells in vitro. Here, we show that SPATE produced by pathogenic E. coli, Shigella, and the mouse pathogen Citrobacter rodentium cleaves not only CD45RO but also CD45 isoforms containing exons A and B. We found that the cleavage of CD45 in primary T cells from both human and murine sources correlated with decreased IL2RA (CD25) surface expression in a concentration-dependent manner. SPATE did not cleave CD25 or affect T cell activation. However, SPATE requires CD45 expression for the depletion of CD25 in activated T cells, as SPATE did not significantly impact CD25 in the Jurkat J45.01 cell line, which lacks CD45. More importantly, we discovered that J45.01 cells resisted SPATE-mediated apoptosis, whereas apoptotic wild-type Jurkat cells exhibited decreased surface expression of CD25. Furthermore, we observed that mice infected with C. rodentium lacking SPATE displayed lower mortality, delayed intestinal colonization, reduced inflammatory cytokines, and decreased leukocyte infiltration in the lamina propria while having a higher number of CD25+ T cells compared to mice infected with wild-type CR or the CR SPATE mutant expressing Crc2 in trans. Our data suggest that SPATE-producing pathogens trigger T-cell apoptosis through CD45 via a mechanism akin to IL2 deprivation, demonstrating that SPATE can act as immunomodulators at various levels of the immune system. SIGNIFICANCEWe have demonstrated for the first time that serine proteases (C2S) from clinically relevant pathogens, such as E. coli pathotypes and Shigella, can cleave leukocyte glycoproteins, including the tyrosine phosphatase CD45, which play crucial roles in cellular and immune functions. In this study, we discovered that C2S induces apoptosis in activated T cells through a previously unknown mechanism resembling IL-2 deprivation, mediated by CD45. Furthermore, we found that C2S is essential for bacterial virulence in vivo. This suggests that pathogens producing C2S may possess previously undescribed immunoregulatory functions that enhance their survival in the host and contribute to the disease process by eliminating T cells through the targeting of CD45 and the IL-2 receptor.