title: Spleen tyrosine kinase functions as a tumor suppressor in melanoma cells by inducing senescence-like growth arrest.
abstract: Loss of tumor-suppressive pathways that control cellular senescence is a crucial step in malignant transformation. Spleen tyrosine kinase (Syk) is a cytoplasmic tyrosine kinase that has been recently implicated in tumor suppression of melanoma, a deadly skin cancer derived from pigment-producing melanocytes. However, the mechanism by which Syk suppresses melanoma growth remains unclear. Here, we report that reexpression of Syk in melanoma cells induces a p53-dependent expression of the cyclin-dependent kinase (cdk) inhibitor p21 and a senescence program. We first observed that Syk expression is lost in a subset of melanoma cell lines, primarily by DNA methylation-mediated gene silencing and restored after treatment with the demethylating agent 5-aza-2-deoxycytidine. We analyzed the significance of epigenetic inactivation of Syk and found that reintroduction of Syk in melanoma cells dramatically reduces clonogenic survival and three-dimensional tumor spheroid growth and invasion. Remarkably, melanoma cells reexpressing Syk display hallmarks of senescent cells, including reduction of proliferative activity and DNA synthesis, large and flattened morphology, senescence-associated beta-galactosidase activity, and heterochromatic foci. This phenotype is accompanied by hypophosphorylated retinoblastoma protein (Rb) and accumulation of p21, which depends on functional p53. Our results highlight a new role for Syk tyrosine kinase in regulating cellular senescence and identify Syk-mediated senescence as a novel tumor suppressor pathway the inactivation of which may contribute to melanoma tumorigenicity.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U895, Team 1, Biology and Pathologies of Melanocytes, Nice, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Bailet
authors.forename: Nina
authors.initials: N
authors.lastname: Fenouille
authors.forename: Patricia
authors.initials: P
authors.lastname: Abbe
authors.forename: Guillaume
authors.initials: G
authors.lastname: Robert
authors.forename: Stéphane
authors.initials: S
authors.lastname: Rocchi
authors.forename: Nadège
authors.initials: N
authors.lastname: Gonthier
authors.forename: Christophe
authors.initials: C
authors.lastname: Denoyelle
authors.forename: Michel
authors.initials: M
authors.lastname: Ticchioni
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Ortonne
authors.forename: Robert
authors.initials: R
authors.lastname: Ballotti
authors.forename: Marcel
authors.initials: M
authors.lastname: Deckert
authors.forename: Sophie
authors.initials: S
authors.lastname: Tartare-Deckert
mesh_terms: D048708:Cell Growth Processes / Q000502:physiology; D016922:Cellular Senescence / Q000502:physiology; D002633:Chemotaxis; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000235:genetics; D019175:DNA Methylation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008545:Melanoma / Q000201:enzymology* / Q000235:genetics / Q000473:pathology*; D014411:Neoplastic Stem Cells / Q000473:pathology; D011401:Promoter Regions, Genetic; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction; D018874:Spheroids, Cellular; D000072377:Syk Kinase; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation; D018909:src Homology Domains
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase