title: Sphingosine mediates TNFα-induced lysosomal membrane permeabilization and ensuing programmed cell death in hepatoma cells.
abstract: Normally, cell proliferation and death are carefully balanced in higher eukaryotes, but one of the most important regulatory mechanisms, apoptosis, is upset in many malignancies, including hepatocellular-derived ones. Therefore, reinforcing cell death often is mandatory in anticancer therapy. We previously reported that a combination of tumor necrosis factor-α (TNF) and cycloheximide (CHX) efficiently kill HTC cells, a rat hepatoma line, in an apoptosis-like mode. Death is actively mediated by the lysosomal compartment, although lysosomal ceramide was previously shown not to be directly implicated in this process. In the present study, we show that TNF/CHX increase lysosomal ceramide that is subsequently converted into sphingosine. Although ceramide accumulation does not significantly alter the acidic compartment, the sphingosine therein generated causes lysosomal membrane permeabilization (LMP) followed by relocation of lysosomal cathepsins to the cytoplasm. TNF/CHX-induced LMP is effectively abrogated by siRNAs targeting acid sphingomyelinase or acid ceramidase, which prevent both LMP and death induced by TNF/CHX. Taken together, our results demonstrate that lysosomal accumulation of ceramide is not detrimental per se, whereas its degradation product sphingosine, which has the capacity to induce LMP, appears responsible for the observed apoptotic-like death.
authors.affiliation: Department of Experimental Medicine and Oncology, University of Turin, Turin, Italy.
authors.forename: Chiara
authors.initials: C
authors.lastname: Ullio
authors.forename: Josefina
authors.initials: J
authors.lastname: Casas
authors.forename: Ulf T
authors.initials: UT
authors.lastname: Brunk
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Sala
authors.forename: Gemma
authors.initials: G
authors.lastname: Fabriàs
authors.forename: Riccardo
authors.initials: R
authors.lastname: Ghidoni
authors.forename: Gabriella
authors.initials: G
authors.lastname: Bonelli
authors.forename: Francesco M
authors.initials: FM
authors.lastname: Baccino
authors.forename: Riccardo
authors.initials: R
authors.lastname: Autelli
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000473:pathology*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D055572:Ceramidases / Q000172:deficiency / Q000235:genetics; D002518:Ceramides / Q000096:biosynthesis / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D020868:Gene Silencing; D007425:Intracellular Membranes / Q000187:drug effects* / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D010539:Permeability / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D018124:Receptors, Tumor Necrosis Factor / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000172:deficiency / Q000235:genetics; D013110:Sphingosine / Q000096:biosynthesis / Q000378:metabolism / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D002518:Ceramides; D034741:RNA, Small Interfering; D018124:Receptors, Tumor Necrosis Factor; D014409:Tumor Necrosis Factor-alpha; D003513:Cycloheximide; D013108:Sphingomyelin Phosphodiesterase; D055572:Ceramidases; D013110:Sphingosine