Figure 6.

Cells with monoastral spindles cleave without mitotic exit after loss of Cdk1 activity in the presence of proteasome inhibitor. (A and B) HeLa cells collected in mitosis by 16-h exposure to STLC followed by mitotic shake-off were maintained in STLC and treated with roscovitine in the presence or absence of MG132 for 2 h. Cells were then fixed and stained for microscopy with antibodies to tubulin (A) or to the cleavage furrow–associated proteins survivin, Aurora B, TD60, PRC1, or anillin (B). Exposure of STLC-treated cells to roscovitine induced a furrowing event, characteristically with formation of a bud devoid of chromatin. The passenger proteins survivin, Aurora B, and TD60 associated with the furrow, as did PRC1 and anillin. (C) The percentage of cells with a bud was quantitated after 1 or 2 h of exposure to drugs. The data represent the mean of three counts of >60 cells per count. White bars, cells treated with roscovitine; black bars, cells treated with both roscovitine and MG132. All cells were in the continuous presence of STLC. Error bars represent SD. Bar, 16.5 μm.