title: Analysis of mammalian septin expression in human malignant brain tumors.
abstract: Septins are a highly conserved subfamily of GTPases that play an important role in the process of cytokinesis. To increase our understanding of the expression and localization of the different mammalian septins in human brain tumors, we used antibodies against septins 2, 3, 4, 5, 6, 7, 9, and 11 in immunofluorescence and Western blot analyses of astrocytomas and medulloblastomas. We then characterized the expression and subcellular distribution of the SEPT2 protein in aphidicolin-synchronized U373 MG astrocytoma cells by immunofluorescence and fluorescence-activated cell sorter analysis. To determine the role of SEPT2 in astrocytoma cytokinesis, we inducibly expressed a dominant-negative (DN) SEPT2 mutant in U373 MG astrocytoma cells. We show variable levels and expression patterns of the different septins in brain tissue, brain tumor specimens, and human brain tumor cell lines. SEPT2 was abundantly expressed in all brain tumor samples and cell lines studied. SEPT3 was expressed in medulloblastoma specimens and cell lines, but not in astrocytoma specimens or cell lines. SEPT2 expression was cell cycle-related, with maximal levels in G2-M. Immunocytochemical analysis showed endogenous levels of the different septins within the perinuclear and peripheral cytoplasmic regions. In mitosis, SEPT2 was concentrated at the cleavage furrow. By immunocytochemistry and flow cytometry, we show that a DN SEPT2 mutant inhibits the completion of cell division and results in the accumulation of multinucleated cells. These results suggest that septins are variably expressed in human brain tumors. Stable expression of the DN SEPT2 mutant leads to a G2-M cell cycle block in astrocytoma cells.
authors.affiliation: The Arthur and Sonia Labatt Brain Tumor Research Centre and Division of Neurosurgery, The Hospital for Sick Children, The University of Toronto, Toronto, Ontario, Canada.
authors.forename: Dong-Seok
authors.initials: DS
authors.lastname: Kim
authors.forename: Sherri-Lynn
authors.initials: SL
authors.lastname: Hubbard
authors.forename: Aurelia
authors.initials: A
authors.lastname: Peraud
authors.forename: Bodour
authors.initials: B
authors.lastname: Salhia
authors.forename: Keiichi
authors.initials: K
authors.lastname: Sakai
authors.forename: James T
authors.initials: JT
authors.lastname: Rutka
mesh_terms: D001254:Astrocytoma / Q000201:enzymology* / Q000473:pathology; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000201:enzymology* / Q000473:pathology; D005455:Fluorescent Antibody Technique; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D006801:Humans; D008527:Medulloblastoma / Q000201:enzymology* / Q000473:pathology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D009419:Nerve Tissue Proteins; D020558:GTP Phosphohydrolases