Oxaline, a fungal alkaloid, arrests the cell cycle in M phase by inhibition of tubulin polymerization

Oxaline and neoxaline, fungal alkaloids, were found to inhibit cell proliferation and to induce cell cycle arrest at the G 2 /M phase in Jurkat cells. CBP501 (a peptide corresponding to amino acids 211–221 of Cdc25C phosphatase), which inhibits the G 2 checkpoint, did not affect the G 2 /M arrest caused by oxaline, suggesting that oxaline causes M phase arrest but not G 2 phase arrest. The Cdc2 phosphorylation level of oxaline-treated cell lysate was lower than that of the control cells, indicating that oxaline arrests the M phase. Oxaline disrupted cytoplasmic microtubule assembly in 3T3 cells. Furthermore, oxaline inhibited polymerization of microtubule protein and purified tubulin dose-dependently in vitro. In a binding competition assay, oxaline inhibited the binding of [ 3 H]colchicine to tubulin, but not that of [ 3 H]vinblastine. These results indicate that oxaline inhibits tubulin polymerization, resulting in cell cycle arrest at the M phase.