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.