title: Phosphatidylinositol 3-kinase translocation to the nucleus is an early event in the interleukin-1 signalling mechanism in human osteosarcoma Saos-2 cells.
abstract: Interleukin 1 (IL-1) is a proinflammatory cytokine which can elicit proliferative, differentiative, or metabolic responses. The molecular mechanisms by which IL-1 signals are transduced from the plasma membrane to the nucleus, although extensively studied, have not been completely elucidated. We previously demonstrated that human osteosarcoma Saos-2 cells incubated with IL-1 presented a rapid and transient increase of phospholipase C activity exclusively at the nuclear level. Moreover, we presented evidence that not only the canonical inositol lipid signalling pathway was involved, but also the D3-phosphorylated lipids generated by phosphatidylinositol 3-kinase (PI 3-kinase) were affected. The results of this study indicate that in Saos-2 cells PI 3-kinase is recruited and activated by IL-1 receptor I (IL-1RI) through binding of the SH2 domains to the consensus sequence on the C-terminal tail of the receptor, and that Tyr-479 is essential for PI 3-kinase activation. Moreover, IL-1 treatment triggers PI 3-kinase translocation to the nucleus; this event is rapid and transient in cells expressing high levels of IL-1RI (Saos-2/IL-1R) as well as in untransfected cells, although to a lesser extent. The data, based on immunochemical and immunocytochemical quantitative methods, indicate that PI 3-kinase translocation to the nucleus depends on PI 3-kinase activation. In fact, inactivation by two independent mechanisms, addition of specific PI 3-kinase inhibitors, or overexpression of a mutant form of IL-1RI, resulted in a substantial inhibition of PI 3-kinase translocation to the nucleus. These data suggest that PI 3-kinase recruitment by the activated receptor is a limiting step in PI 3-kinase activation and nuclear translocation. This early event in the IL-1 signalling mechanisms confirms that D3 inositides, as well as canonical inositides produced by nuclear phospholipase C isoforms, are involved in this pathway of activation of transcription factors.
authors.affiliation: Institute of Cytomorphology, C.N.R., Chieti, Italy.
authors.forename: N M
authors.initials: NM
authors.lastname: Maraldi
authors.forename: S
authors.initials: S
authors.lastname: Marmiroli
authors.forename: R
authors.initials: R
authors.lastname: Rizzoli
authors.forename: G
authors.initials: G
authors.lastname: Mazzotti
authors.forename: F A
authors.initials: FA
authors.lastname: Manzoli
mesh_terms: D001693:Biological Transport, Active; D002467:Cell Nucleus / Q000201:enzymology; D003593:Cytoplasm / Q000201:enzymology; D004789:Enzyme Activation; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism* / Q000494:pharmacology; D009154:Mutation; D012516:Osteosarcoma / Q000201:enzymology / Q000276:immunology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017472:Receptors, Interleukin-1 / Q000235:genetics / Q000378:metabolism; D053573:Receptors, Interleukin-1 Type I; D015398:Signal Transduction; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D007375:Interleukin-1; D017472:Receptors, Interleukin-1; D053573:Receptors, Interleukin-1 Type I; D019869:Phosphatidylinositol 3-Kinases