Dipeptidylpeptidase IV (CD26) is a multifunctional ectoenzyme involved in T cell activation that has been implicated in autoimmune pathophysiology. Because IL-17–producing CD4+ T cells (Th17 cells) are important mediators of autoimmune disease, we analyzed the expression of CD26 and its enzymatic function on human Th17 cells. Analysis of CD26 expression on different CD4+ T helper subsets showed that CD26 expression is highest on CD4+ T cells producing type 17 cytokines (e.g., IL-22, IL-17, GM-CSF, or TNF) compared with Th1, Th2, and regulatory T cells. Phenotypic analysis revealed that CD26++CD4+ T cells express the type 17 differentiation molecules CD161, CCR6, lL-23R, and retinoic acid-related orphan receptor-γt. Furthermore, sorted CD26++CD4+ T cells contain >90–98% of Th17 cells, indicating that CD26++ T cells harbor the Th17 lineage. A comparison with CD161 and CCR6 indicated that analysis of CD26 coexpression may improve the phenotypic characterization of Th17 cells. Of note, CD26++ Th17 cells are enriched in the inflamed tissue of patients with hepatitis and inflammatory bowel disease. Functional analysis in migration assays revealed that CD26 expressed on Th17 cells is enzymatically active. Indeed, CD26 negatively regulates the chemotactic CD4+ T cell response to the inflammatory chemokines CXCL9–12 that can be restored by pharmacological blockade of the enzymatic center of CD26. In summary, these results strongly suggest that CD26 may contribute to the orchestration of the immune response by Th17 cells in human inflammatory diseases. They also suggest that the phenotypic analysis of Th17 cells may be facilitated by determination of CD26 expression.

Cell-autonomous induction of type I interferon must be stringently regulated. Rapid induction is key to control virus infection, whereas proper limitation of signaling is essential to prevent immunopathology and autoimmune disease. Using unbiased kinome-wide RNAi screening followed by thorough validation, we identified 22 factors that regulate RIG-I/IRF3 signaling activity. We describe a negative-feedback mechanism targeting RIG-I activity, which is mediated by death associated protein kinase 1 (DAPK1). RIG-I signaling triggers DAPK1 kinase activation, and active DAPK1 potently inhibits RIG-I stimulated IRF3 activity and interferon-beta production. DAPK1 phosphorylates RIG-I in vitro at previously reported as well as other sites that limit 5'ppp-dsRNA sensing and virtually abrogate RIG-I activation.

Background: Translational regulation might underlie the high expression levels of the protease cathepsin L (CTSL) associated with poor breast cancer prognosis. Results: Translation of CTSL mRNA is highly stress-resistant and promotes metastasis of murine breast cancer. Conclusion: CTSL mRNA circumvents translational shutdown in cancer-associated stress conditions. Significance: High expression of a metastasis promoting protease is maintained by translational regulation.

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