title: Non-phosphorylated FTY720 induces apoptosis of human microglia by activating SREBP2.
abstract: A synthetic analog of sphingosine named FTY720 (Fingolimod), phosphorylated by sphingosine kinase-2, interacts with sphingosine-1-phosphate (S1P) receptors expressed on various cells. FTY720 suppresses the disease activity of multiple sclerosis (MS) chiefly by inhibiting S1P-dependent egress of autoreactive T lymphocytes from secondary lymphoid organs, and possibly by exerting anti-inflammatory and neuroprotective effects directly on brain cells. However, at present, biological effects of FTY720 on human microglia are largely unknown. We studied FTY720-mediated apoptosis of a human microglia cell line HMO6. The exposure of HMO6 cells to non-phosphorylated FTY720 (FTY720-non-P) induced apoptosis in a dose-dependent manner with IC50 of 10.6 ± 2.0 μM, accompanied by the cleavage of caspase-7 and caspase-3 but not of caspase-9. The apoptosis was inhibited by Z-DQMD-FMK, a caspase-3 inhibitor, but not by Pertussis toxin, a Gi protein inhibitor, suramin, a S1P3/S1P5 inhibitor, or W123, a S1P1 competitive antagonist, although HMO6 expressed S1P1, S1P2, and S1P3. Furthermore, both phosphorylated FTY720 (FTY720-P) and SEW2871, S1P1 selective agonists, did not induce apoptosis of HMO6. Genome-wide gene expression profiling and molecular network analysis indicated activation of transcriptional regulation by sterol regulatory element-binding protein (SREBP) in FTY720-non-P-treated HMO6 cells. Western blot verified activation of SREBP2 in these cells, and apoptosis was enhanced by pretreatment with simvastatin, an activator of SREBP2, and by overexpression of the N-terminal fragment of SREBP2. These observations suggest that FTY720-non-P-induced apoptosis of HMO6 human microglia is independent of S1P receptor binding, and positively regulated by the SREBP2-dependent proapoptotic signaling pathway.
authors.affiliation: Department of Bioinformatics and Molecular Neuropathology, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshino
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tabunoki
authors.forename: Shigeo
authors.initials: S
authors.lastname: Sugiyama
authors.forename: Keitaro
authors.initials: K
authors.lastname: Ishii
authors.forename: Seung U
authors.initials: SU
authors.lastname: Kim
authors.forename: Jun-Ichi
authors.initials: J
authors.lastname: Satoh
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D061945:Caspase Inhibitors; D002460:Cell Line; D000068876:Fingolimod Hydrochloride; D020869:Gene Expression Profiling; D053263:Gene Regulatory Networks; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology* / Q000627:therapeutic use; D046228:Microarray Analysis; D017628:Microglia / Q000166:cytology / Q000187:drug effects* / Q000473:pathology* / Q000502:physiology*; D009103:Multiple Sclerosis / Q000188:drug therapy / Q000276:immunology / Q000473:pathology; D037342:Pertussis Toxin / Q000494:pharmacology; D010766:Phosphorylation; D011409:Propylene Glycols / Q000494:pharmacology* / Q000627:therapeutic use; D049349:Receptors, Lysosphingolipid / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D051782:Sterol Regulatory Element Binding Protein 2 / Q000235:genetics / Q000378:metabolism*
chemical_list: D061945:Caspase Inhibitors; D007166:Immunosuppressive Agents; D011409:Propylene Glycols; D049349:Receptors, Lysosphingolipid; C497390:SREBF2 protein, human; D051782:Sterol Regulatory Element Binding Protein 2; D037342:Pertussis Toxin; D053148:Caspase 3; D053179:Caspase 7; D000068876:Fingolimod Hydrochloride; D013110:Sphingosine