title: Ceramide activates lysosomal cathepsin B and cathepsin D to attenuate autophagy and induces ER stress to suppress myeloid-derived suppressor cells.
abstract: Myeloid-derived suppressor cells (MDSCs) are immune suppressive cells that are hallmarks of human cancer. MDSCs inhibit cytotoxic T lymphocytes (CTLs) and NK cell functions to promote tumor immune escape and progression, and therefore are considered key targets in cancer immunotherapy. Recent studies determined a key role of the apoptosis pathways in tumor-induced MDSC homeostasis and it is known that ceramide plays a key role in regulation of mammalian cell apoptosis. In this study, we aimed to determine the efficacy and underlying molecular mechanism of ceramide in suppression of MDSCs. Treatment of tumor-bearing mice with LCL521, a lysosomotropic inhibitor of acid ceramidase, significantly decreased MDSC accumulation in vivo. Using a MDSC-like myeloid cell model, we determined that LCL521 targets lysosomes and increases total cellular C16 ceramide level. Although MDSC-like cells have functional apoptosis pathways, LCL521-induced MDSC death occurs in an apoptosis- and necroptosis-independent mechanism. LCL521 treatment resulted in an increase in the number of autophagic vesicles, heterolysosomes and swollen ERs. Finally, concomitant inhibition of cathepsin B and cathepsin D was required to significantly decrease LCL521-induced cell death. Our observations indicate that LCL521 targets lysosomes to activate cathepsin B and cathepsin D, resulting in interrupted autophagy and ER stress that culminates in MDSC death. Therefore, a ceramidase inhibitor is potentially an effective adjunct therapeutic agent for suppression of MDSCs to enhance the efficacy of CTL-based cancer immunotherapy.
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Feiyan
authors.initials: F
authors.lastname: Liu
authors.affiliation: College of Life Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA, USA.|Charlie Norwood VA Medical Center, Augusta, GA, USA.
authors.forename: Chunwan
authors.initials: C
authors.lastname: Lu
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Aiping
authors.initials: A
authors.lastname: Bai
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Jacek
authors.initials: J
authors.lastname: Bielawski
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: Alicja
authors.initials: A
authors.lastname: Bielawska
authors.affiliation: Department of Cell Biology and Anatomy, Medical College of Georgia, Augusta, GA, USA.
authors.forename: Brendan
authors.initials: B
authors.lastname: Marshall
authors.affiliation: Department of Cell Biology and Anatomy, Medical College of Georgia, Augusta, GA, USA.
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Schoenlein
authors.affiliation: Department of Chemistry and Physics, Augusta University, Augusta, GA, USA.
authors.forename: Iryna O
authors.initials: IO
authors.lastname: Lebedyeva
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, GA, USA.|Charlie Norwood VA Medical Center, Augusta, GA, USA.|Georgia Cancer Center, Augusta University, Augusta, GA, USA.
authors.forename: Kebin
authors.initials: K
authors.lastname: Liu
mesh_terms: D055573:Acid Ceramidase / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D002401:Cathepsin B / Q000378:metabolism*; D002402:Cathepsin D / Q000378:metabolism*; D045744:Cell Line, Tumor; D002518:Ceramides / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008247:Lysosomes / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D008807:Mice, Inbred BALB C; D000072737:Myeloid-Derived Suppressor Cells / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D012509:Sarcoma / Q000188:drug therapy* / Q000201:enzymology / Q000276:immunology / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D002518:Ceramides; D004791:Enzyme Inhibitors; C097760:N-palmitoylsphingosine; D002401:Cathepsin B; C533915:Ctsb protein, mouse; D002402:Cathepsin D; C533923:Ctsd protein, mouse; D055573:Acid Ceramidase; C526734:Asah1 protein, mouse
keywords: Immune response; Immunity; Immunology and Microbiology Section; Lysosomal cell death; MDSCs; autophagy flux; cathepsin; ceramide