title: Tumor necrosis factor-alpha-stimulated cell proliferation is mediated through sphingosine kinase-dependent Akt activation and cyclin D expression.
abstract: Tumor necrosis factor-alpha (TNF-alpha) has been shown to activate sphingosine kinase (SphK) in a variety of cell types. The extent to which SphK signaling mediates the pleiotropic effects of TNF-alpha is not entirely clear. The current study examined the role of SphK activity in TNF-alpha-stimulated cell proliferation in 1321N1 glioblastoma cells. We first demonstrated that pharmacological inhibitors of SphK markedly decrease TNF-alpha-stimulated DNA synthesis. Signaling mechanisms through which SphK mediated the effect of TNF-alpha on DNA synthesis were then examined. Inhibition of Rho proteins with C3 exoenzyme or of Rho kinase with Y27632 attenuated TNF-alpha-stimulated DNA synthesis. However, RhoA activation by TNF-alpha was not blocked by SphK inhibition. ERK activation was also required for TNF-alpha-stimulated DNA synthesis but likewise TNF-alpha-induced ERK activation was not blocked by inhibition of SphK. Thus, neither RhoA nor ERK activation are the SphK-dependent transducers of TNF-alpha-induced proliferation. In contrast, TNF-alpha-stimulated Akt phosphorylation, which was also required for DNA synthesis, was attenuated by SphK inhibition or SphK1 knockdown by small interfering RNA. Furthermore, cyclin D expression was increased by TNF-alpha in a SphK- and Akt-dependent manner. Additional studies demonstrated that TNF-alpha effects on DNA synthesis, ERK, and Akt phosphorylation are not mediated through cell surface Gi -coupled S1P receptors, because none of these responses were inhibited by pertussis toxin. We conclude that SphK-dependent Akt activation plays a significant role in TNF-alpha-induced cyclin D expression and cell proliferation.
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Julie
authors.initials: J
authors.lastname: Radeff-Huang
authors.forename: Tammy M
authors.initials: TM
authors.lastname: Seasholtz
authors.forename: Jenny W
authors.initials: JW
authors.lastname: Chang
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Smith
authors.forename: Colin T
authors.initials: CT
authors.lastname: Walsh
authors.forename: Joan Heller
authors.initials: JH
authors.lastname: Brown
mesh_terms: D001932:Brain Neoplasms; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D056741:Cyclin D; D016213:Cyclins / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005909:Glioblastoma; D006801:Humans; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface / Q000378:metabolism; D049349:Receptors, Lysosphingolipid / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D000099157:Sphingosine Kinase
chemical_list: D056741:Cyclin D; D016213:Cyclins; D004247:DNA; D017853:Phosphotransferases (Alcohol Group Acceptor); D051057:Proto-Oncogene Proteins c-akt; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; D049349:Receptors, Lysosphingolipid; D014409:Tumor Necrosis Factor-alpha; D020741:rho GTP-Binding Proteins; D000099157:Sphingosine Kinase