Extracellular Cystatin F Is Internalised by Cytotoxic T Lymphocytes and Decreases Their Cytotoxicity

Abstract

Cystatin F is a protein inhibitor of cysteine cathepsins, peptidases involved in the activation of the effector molecules of the perforin/granzyme pathway. Cystatin F was previously shown to regulate natural killer cell cytotoxicity. Here, we show that extracellular cystatin F has a role in regulating the killing efficiency of cytotoxic T lymphocytes (CTLs). Extracellular cystatin F was internalised into TALL-104 cells, a cytotoxic T cell line, and decreased their cathepsin C and H activity. Correspondingly, granzyme A and B activity was also decreased and, most importantly, the killing efficiency of TALL-104 cells as well as primary human CTLs was reduced. The N-terminally truncated form of cystatin F, which can directly inhibit cathepsin C (unlike the full-length form), was more effective than the full-length inhibitor. Furthermore, cystatin F decreased cathepsin L activity, which, however, did not affect perforin processing. Cystatin F derived from K-562 target cells could also decrease the cytotoxicity of TALL-104 cells. These results clearly show that, by inhibiting cysteine cathepsin proteolytic activity, extracellular cystatin F can decrease the cytotoxicity of CTLs and thus compromise their function.

The Role of Cysteine Peptidases in Hematopoietic Stem Cell Differentiation and Modulation of Immune System Function

“…Cystatin F is only partially targeted to endo-lysosomes upon its synthesis, and can also be secreted and taken up by surrounding cells (188). The uptake of exogenous cystatin F was also shown to reduce the cytotoxicity of NK cells and T cells (188,216). Furthermore, proinflammatory cytokines, such as IFN-g and TNF-a, increase cathepsin S and B activities in DCs (217,218), whereas IL-10, which induces tolerogenic DCs and consequently T lymphocyte anergy (219), prevents the upregulation of cathepsin S and B activities in DCs (220).…”

“…Silencing of naturally occurring cathepsin inhibitors, such as cystatins and serpins, which attenuate the cytosolic activity of cathepsins and hence LMP-driven apoptosis, may induce apoptosis and consequently be therapeutically useful in autoimmune lymphocyte populations, pathogen-infected cells, and tumor cells. In addition, recent findings (188,216) suggest that decreasing the intracellular uptake or activation of cystatin F could increase the efficacy of target cell killing by cytotoxic cells (NK cells and CD8+ T cells), thus improving the antitumor immune response.…”

Lysosomes and lysosome‐related organelles in immune responses

“…This raises the possibility that CF‐producing cells can regulate the endo‐lysosomal cysteine protease activities of non‐producing neighbours. Indeed uptake of CF into human CTL resulted in the suppression of multiple cathepsin activities, reduced granzyme activity and reduced killing ability [ 136 ]. Since some tumour cells express cystatin F [ 137 ], this might have been adopted as a strategy to evade a CTL response.…”

Lysosomal peptidases—intriguing roles in cancer progression and neurodegeneration

“…Finally, CysF was found to be expressed in patient‐derived glioblastoma stem‐like cells [ 211 ]. Recently, it was shown that extracellular CysF attenuates granzyme‐mediated cytotoxicity in CTLs [ 213 ] and decreases the susceptibility of a glioblastoma cell line to NK cytotoxicity [ 211 ]. Apart from the effects on properforin and granzyme activation, increased extracellular CysF levels can affect the activity of immune cells through several additional mechanisms.…”