title: Extracellular sphingosine-1-phosphate: a novel actor in human glioblastoma stem cell survival.
abstract: Glioblastomas are the most frequent and aggressive intracranial neoplasms in humans, and despite advances and the introduction of the alkylating agent temozolomide in therapy have improved patient survival, resistance mechanisms limit benefits. Recent studies support that glioblastoma stem-like cells (GSCs), a cell subpopulation within the tumour, are involved in the aberrant expansion and therapy resistance properties of glioblastomas, through still unclear mechanisms. Emerging evidence suggests that sphingosine-1-phosphate (S1P) a potent onco-promoter able to act as extracellular signal, favours malignant and chemoresistance properties in GSCs. Notwithstanding, the origin of S1P in the GSC environment remains unknown. We investigated S1P metabolism, release, and role in cell survival properties of GSCs isolated from either U87-MG cell line or a primary culture of human glioblastoma. We show that both GSC models, grown as neurospheres and expressing GSC markers, are resistant to temozolomide, despite not expressing the DNA repair protein MGMT, a major contributor to temozolomide-resistance. Pulse experiments with labelled sphingosine revealed that both GSC types are able to rapidly phosphorylate the long-chain base, and that the newly produced S1P is efficiently degraded. Of relevance, we found that S1P was present in GSC extracellular medium, its level being significantly higher than in U87-MG cells, and that the extracellular/intracellular ratio of S1P was about ten-fold higher in GSCs. The activity of sphingosine kinases was undetectable in GSC media, suggesting that mechanisms of S1P transport to the extracellular environment are constitutive in GSCs. In addition we found that an inhibitor of S1P biosynthesis made GSCs sensitive to temozolomide (TMZ), and that exogenous S1P reverted this effect, thus involving extracellular S1P as a GSC survival signal in TMZ resistance. Altogether our data implicate for the first time GSCs as a pivotal source of extracellular S1P, which might act as an autocrine/paracrine signal contributing to their malignant properties.
authors.affiliation: Department of Medical Biotechnology and Translational Medicine, University of Milan, LITA-Segrate, Milan, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Riccitelli
authors.forename: Paola
authors.initials: P
authors.lastname: Giussani
authors.forename: Clara
authors.initials: C
authors.lastname: Di Vito
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Condomitti
authors.forename: Cristina
authors.initials: C
authors.lastname: Tringali
authors.forename: Manuela
authors.initials: M
authors.lastname: Caroli
authors.forename: Rossella
authors.initials: R
authors.lastname: Galli
authors.forename: Paola
authors.initials: P
authors.lastname: Viani
authors.forename: Laura
authors.initials: L
authors.lastname: Riboni
mesh_terms: D001932:Brain Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D002469:Cell Separation; D002470:Cell Survival / Q000187:drug effects; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005909:Glioblastoma / Q000201:enzymology / Q000473:pathology*; D006801:Humans; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008246:Lysophospholipids / Q000096:biosynthesis / Q000494:pharmacology*; D008954:Models, Biological; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000201:enzymology / Q000473:pathology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000494:pharmacology; D000077204:Temozolomide; D000099157:Sphingosine Kinase
chemical_list: D003606:Dacarbazine; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D013110:Sphingosine; D000077204:Temozolomide; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate