title: The Syk tyrosine kinase localizes to the centrosomes and negatively affects mitotic progression.
abstract: We showed previously that the spleen tyrosine kinase Syk is expressed by mammary epithelial cells and that it suppresses malignant growth of breast cancer cells. The exact molecular mechanism of its tumor-suppressive activity remains, however, to be identified. Here, we show that Syk colocalizes and copurifies with the centrosomal component gamma-tubulin and exhibits a catalytic activity within the centrosomes. Moreover, its centrosomal localization depends on its intact kinase activity. Centrosomal Syk expression is persistent in interphase but promptly drops during mitosis, obviously resulting from its ubiquitinylation and proteasomal degradation. Conversely, unrestrained exogenous expression of a fluorescently tagged Discosoma sp. red fluorescent protein (DsRed)-Syk chimera engenders abnormal cell division and cell death. Transient DsRed-Syk overexpression triggers an abrupt cell death lacking hallmarks of classic apoptosis but reminiscent of mitotic catastrophe. Surviving stable DsRed-Syk-transfected cells exhibit multipolar mitotic spindles and contain multiple abnormally sized nuclei and supernumerary centrosomes, revealing anomalous cell division. Taken together, these results show that Syk is a novel centrosomal kinase that negatively affects cell division. Its expression is strictly controlled in a spatiotemporal manner, and centrosomal Syk levels need to decline to allow customary progression of mitosis.
authors.affiliation: Centre National de la Recherche Scientifique UMR5539, Université Montpellier II, Montpellier, France.
authors.forename: Déborah
authors.initials: D
authors.lastname: Zyss
authors.forename: Philippe
authors.initials: P
authors.lastname: Montcourrier
authors.forename: Benjamin
authors.initials: B
authors.lastname: Vidal
authors.forename: Christelle
authors.initials: C
authors.lastname: Anguille
authors.forename: Fabrice
authors.initials: F
authors.lastname: Mérezègue
authors.forename: Alain
authors.initials: A
authors.lastname: Sahuquet
authors.forename: Paul H
authors.initials: PH
authors.lastname: Mangeat
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Coopman
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology*; D019556:COS Cells; D002384:Catalysis; D045744:Cell Line, Tumor; D018385:Centrosome / Q000201:enzymology*; D002522:Chlorocebus aethiops; D006801:Humans; D019169:Jurkat Cells; D008938:Mitosis / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D014162:Transfection; D014404:Tubulin / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D014404:Tubulin; D025801:Ubiquitin; D051746:ZAP-70 Protein-Tyrosine Kinase; D046988:Proteasome Endopeptidase Complex