Regulation of split anergy in natural killer cells by inhibition of cathepsins C and H and cystatin F

// Špela Magister 1 , Han-Ching Tseng 2 , Vickie T. Bui 2 , Janko Kos 1, 3 , Anahid Jewett 2, 4 1 Jožef Stefan Institute, Department of Biotechnology, 1000 Ljubljana, Slovenia 2 The Jane and Jerry Weintraub Center for Reconstructive Biotechnology, Division of Oral Biology and Medicine, UCLA School of Dentistry, University of California-Los Angeles, Los Angeles, CA, USA 3 University of Ljubljana, Faculty of Pharmacy, 1000 Ljubljana, Slovenia 4 The Jonsson Comprehensive Cancer Center, UCLA School of Dentistry and Medicine, University of California-Los Angeles, Los Angeles, CA, USA Correspondence to: Anahid Jewett, e-mail: ajewett@ucla.edu Keywords: NK cells, anergy, cathepsins C, cathepsin H, cystatin F Received: April 15, 2015      Accepted: June 01, 2015      Published: June 13, 2015 ABSTRACT Freshly isolated human primary NK cells induce preferential lysis of Oral Squamous Carcinoma Stem Cells (OSCSCs) when compared to differentiated Oral Squamous Carcinoma Cells (OSCCs), while anti-CD16 antibody and monocytes induce functional split anergy in primary NK cells by decreasing the cytotoxic function of NK cells and increasing the release of IFN-γ. Since NK92 cells have relatively lower levels of cytotoxicity when compared to primary NK cells, and have the ability to increase secretion of regulatory cytokines IL-10 and IL-6, we used these cells as a model of NK cell anergy to identify and to study the upstream regulators of anergy. We demonstrate in this paper that the levels of truncated monomeric cystatin F, which is known to inhibit the functions of cathepsins C and H, is significantly elevated in NK92 cells and in anergized primary NK cells. Furthermore, cystatin F co-localizes with cathepsins C and H in the lysosomal/endosomal vesicles of NK cells. Accordingly, the mature forms of aminopeptidases cathepsins C and H, which regulate the activation of effector granzymes in NK cells, are significantly decreased, whereas the levels of pro-cathepsin C enzyme is increased in anergized NK cells after triggering of the CD16 receptor. In addition, the levels of granzyme B is significantly decreased in anti-CD16mAb and target cell anergized primary NK cells and NK92 cells. Our study provides the cellular and molecular mechanisms by which target cells may utilize to inhibit the cytotoxic function of NK cells.