Fig. 3. Vincristine depolymerizes microtubules in both asynchronous and G1-phase ALL cells.

Asynchronous (A) or G1-phase (B) ALL-5 cells were treated with 0.1 % DMSO (Ctrl) or 100 nM vincristine (VCR) for 1 h and harvested. Cells were also treated with 100 nM Taxol (TAX) for 1 h or 2mM CaCl₂ for 5 min to serve as polymerization and depolymerization controls, respectively. Soluble tubulin (S) and polymerized tubulin (P) were separated as described in Materials and Methods and subjected to immunoblotting for α-tubulin. Total tubulin, present in cell homogenates prior to centrifugation, was used as a loading control. The relative proportions of α-tubulin present in soluble and pellet fractions, determined as described in Materials and Methods and given as %S/%P, is as follows. Panel A: Cont., 42/58; TAX, 21/79; CaCl₂, 50/50; VCR, 56/44. Panel B: Cont., 60/40; TAX, 51/49; CaCl₂, 75/25; VCR, 76/24.