Reas CTLs kill differentiated tumor cells, NK cells also IL-6 Inducer Source possess the ability to kill stem-like tumor cells [192,193]. Each CTLs and NK cells deploy precisely the same killing mechanisms, through either the death receptor pathway or cytotoxic granule release [194]. Cytotoxic granules contain proforms of perforin and many peptidases, including granzymes (granzymes A, B, H, M,FEBS Open Bio 12 (2022) 70838 2022 The Authors. FEBS Open Bio published by John Wiley Sons Ltd on behalf of Federation of European Biochemical SocietiesJ. Kos et al.Peptidases in cancer and neurodegenerationand K in humans) [195]. Perforin can be a calciumdependent pore-forming protein that requires proteolytic removal of 20 amino acids at its C terminus for liberation of its C2 domain and activation. Perforin release and binding towards the cell membrane is expected for granzyme entry and apoptosis induction in target cells [196]. CatL has been implicated within the C-terminal processing and activation of perforin, because the selective inhibition of CatL reduced perforin activation and the killing capacity of human NK cell lines and major mouse CTLs. However, in vivo, CatL deficiency decreased the amount of active perforin but did not have an effect on the general cytotoxicity of NK cells in mice [197]. Granzymes are serine peptidases which might be stored in cytotoxic granules as inactive precursors that require the removal from the DP Agonist Formulation N-terminal dipeptide for their activation [198]. Although CatC has an crucial function in the in vivo activation of granzymes A and B, residual granzyme B activity is enough to combat viral infection in CatCmice [199]. In addition, CatH has been identified as an further progranzyme convertase [200]. The endogenous inhibitor cystatin F (CysF), a member from the kind II cystatin loved ones, predominantly acts on peptidases positioned inside the endo/lysosomal method, including cytotoxic granules. The molecular form of CysF governs its inhibitory profile. After synthesis, CysF forms disulfide-linked dimers that usually do not inhibit the C1 family of cysteine peptidases but strongly inhibit legumain through a distant, second binding internet site [201]. N-terminal cleavage after CysF translocation to endo/lysosomes [202] produces active monomeric CysF that is a powerful inhibitor of cathepsins C, H, and L [203,204]. In addition, secreted CysF may be internalized, transported to endo/lysosomes, and, as such, can regulate cysteine peptidase activity in trans [49,205]. In NK cells, CysF was shown to reduce granulemediated cytotoxicity by regulating the activity on the main granzyme convertases, cathepsins C and H [49]. In addition, improved CysF levels and decreased CatC and CatH levels are related with targetinduced inactivation of NK cytotoxicity, referred to as `split anergy’ [206]. Split anergy of NK cells could be triggered via interaction with tumor cells and monocytes and is characterized by high cytokine secretion and decreased efficacy in killing target cells [206]. Improved CysF levels were also detected in anergic CTLs [207]. Recently, CysF was also found in CD4+ T cells that acquired cytotoxic functions during longterm cultivation [208]. In contrast to most other sort II cystatins, that are frequently downregulated in tumors [62], CysF was discovered to become markedly upregulated in numerous sorts of cancer. In colorectal tumors,high CysF mRNA levels had been shown to correlate with an elevated risk of liver metastasis and poor survival [209,210]. Furthermore, CysF gene expression was shown to be hig.