CDK1 and PKC kinase activities drive mitotic lamin B1 disassembly. (A) HeLa cells stably expressing H2B-mCherry were transiently transfected with mutated GFP–lamin B1 reporters (see also Fig. 1), and mean mitotic lamin B1 disassembly was quantified as described in Fig. 2. (B) Mean mitotic durations of cells quantified in A. Mitotic progression in the transfected H2B-mCherry cells took longer than in the stable GFP–lamin B1– and H2B-mCherry–coexpressing cells in D. (C) HeLa cells stably coexpressing H2B-mCherry and GFP–lamin B1 were synchronized by double thymidine arrest. Approximately 30–60 min before mitotic entry, cells were treated with DMSO (mock), 2 µM Gö6976 (PKC inhibition), 50 µM roscovitine (CDK1 inhibition), or a combination of 2 µM Gö6976 and 50 µM roscovitine, and mean lamin B1 disassembly was determined as in A. (D) Mean mitosis durations of cells quantified in C. The data represent the mitotic events from at least three replicate experiments. n > 100 for each condition with *, P < 0.05 and ***, P < 0.0001 compared with control (U test; Table S1 and Table S2). Dotted lines indicate mean control timing. Error bars indicate 95% confidence intervals.