title: Coordinated involvement of cathepsins S, D and cystatin C in the commitment of hematopoietic stem cells to dendritic cells.
abstract: The identity of biochemical players which underpin the commitment of CD34(+) hematopoietic stem cells to immunogenic or tolerogenic dendritic cells is largely unknown. To explore this issue, we employed a previously established cell-based system amenable to shift dendritic cell differentiation from the immunogenic into the tolerogenic pathway upon supplementation with a conventional cytokine cocktail containing thrombopoietin (TPO) and IL-16. We show that stringent regulation of cathepsins S and D, two proteases involved in antigen presentation, is crucial to engage cell commitment to either route. In response to TPO+IL-16-dependent signaling, both cathepsins undergo earlier maturation and down-regulation. Additionally, cystatin C orchestrates cathepsin S expression through a tight but reversible interaction that, based on a screen of adult stem cells from disparate origins, CD14(+) cells, primary fibroblasts and the MCF7 cell line, appears unique to CD34(+) stem cells from peripheral and cord blood. As shown by CD4(+) T cell proliferation in mixed-lymphocyte reactions, cell commitment to either pathway is disrupted upon cathepsin knockdown by RNAi. Surprisingly, similar effects were also observed upon gene overexpression, which prompts atypically accelerated maturation of cathepsins S and D in cells of the immunogenic pathway, similar to the tolerogenic route. Furthermore, RNAi studies revealed that cystatin C is a proteolytic target of cathepsin D and has a direct, causal impact on cell differentiation. Together, these findings uncover a novel biochemical cluster that is subject to time-controlled and rigorously balanced expression to mediate specific stem cell commitment at the crossroads towards tolerance or immunity.
authors.affiliation: Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Italy. martinos@unipg.it
authors.forename: Sabata
authors.initials: S
authors.lastname: Martino
authors.forename: Roberto
authors.initials: R
authors.lastname: Tiribuzi
authors.forename: Elisa
authors.initials: E
authors.lastname: Ciraci
authors.forename: Georgia
authors.initials: G
authors.lastname: Makrypidi
authors.forename: Francesco
authors.initials: F
authors.lastname: D'Angelo
authors.forename: Ilaria
authors.initials: I
authors.lastname: di Girolamo
authors.forename: Angela
authors.initials: A
authors.lastname: Gritti
authors.forename: Gabriella M Cusella
authors.initials: GM
authors.lastname: de Angelis
authors.forename: Gianpaolo
authors.initials: G
authors.lastname: Papaccio
authors.forename: Maurilio
authors.initials: M
authors.lastname: Sampaolesi
authors.forename: Anna Concetta
authors.initials: AC
authors.lastname: Berardi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Datti
authors.forename: Aldo
authors.initials: A
authors.lastname: Orlacchio
mesh_terms: D000328:Adult; D053687:Adult Stem Cells / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D018952:Antigens, CD34 / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism*; D002403:Cathepsins / Q000378:metabolism*; D002454:Cell Differentiation; D055316:Cystatin C / Q000378:metabolism*; D003713:Dendritic Cells / Q000166:cytology*; D004792:Enzyme Precursors / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology; D013997:Time Factors
chemical_list: D018952:Antigens, CD34; D055316:Cystatin C; D004792:Enzyme Precursors; D002403:Cathepsins; C028217:cathepsin S; D002402:Cathepsin D