title: Hypoxia enhances sphingosine kinase 2 activity and provokes sphingosine-1-phosphate-mediated chemoresistance in A549 lung cancer cells.
abstract: Hypoxia and signaling via hypoxia-inducible factor-1 (HIF-1) is a key feature of solid tumors and is related to tumor progression as well as treatment failure. Although it is generally accepted that HIF-1 provokes tumor cell survival and induces chemoresistance under hypoxia, HIF-1-independent mechanisms operate as well. We present evidence that conditioned medium obtained from A549 cells, incubated for 24 h under hypoxia, protected naive A549 cells from etoposide-induced cell death. Lipid extracts generated from hypoxia-conditioned medium still rescued cells from apoptosis induced by etoposide. Specifically, the bioactive lipid sphingosine-1-phosphate (S1P) not only was essential for cell viability of A549 cells but also protected cells from apoptosis. We noticed an increase in sphingosine kinase 2 (SphK2) protein level and enzymatic activity under hypoxia, which correlated with the release of S1P into the medium. Knockdown of SphK2 using specific small interfering RNA relieved chemoresistance of A549 cells under hypoxia and conditioned medium obtained from SphK2 knockdown cells was only partially protective. Coincubations of conditioned medium with VPC23019, a S1P(1)/S1P(3) antagonist, reduced protection of conditioned medium, with the further notion that p42/44 mitogen-activated protein kinase transmits autocrine or paracrine survival signaling downstream of S1P(1)/S1P(3) receptors. Our data suggest that hypoxia activates SphK2 to promote the synthesis and release of S1P, which in turn binds to S1P(1)/S1P(3) receptors, thus activating p42/44 mitogen-activated protein kinase to convey autocrine or paracrine protection of A549 cells.
authors.affiliation: Faculty of Medicine, Institute of Biochemistry I/ZAFES, Goethe-University, Frankfurt am Main, Germany.
authors.forename: Steffen E
authors.initials: SE
authors.lastname: Schnitzer
authors.forename: Andreas
authors.initials: A
authors.lastname: Weigert
authors.forename: Jie
authors.initials: J
authors.lastname: Zhou
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brüne
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D015687:Cell Hypoxia / Q000502:physiology; D045744:Cell Line, Tumor; D003470:Culture Media; D019008:Drug Resistance, Neoplasm; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D008246:Lysophospholipids / Q000096:biosynthesis / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D049349:Receptors, Lysosphingolipid / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000378:metabolism; D014162:Transfection; D000099157:Sphingosine Kinase
chemical_list: D003470:Culture Media; D005047:Etoposide; D008246:Lysophospholipids; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D017853:Phosphotransferases (Alcohol Group Acceptor); D034741:RNA, Small Interfering; D049349:Receptors, Lysosphingolipid; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate