Immunocytochemistry and confocal microscopy of parental CCRF-CEM and 2ME2-resistant leukemia cells demonstrating differences in their microtubule networks. Parental CCRF-CEM (A) and CEM/2ME2-28.8R (B) cells were cytospun onto glass slides and double-immunofluorescent detection performed for α-tubulin (green, panel ii) and acetylated α-tubulin (red, panel iii). Channels for α-tubulin and acetylated α-tubulin were overlayed and demonstrate that 2ME2-resistant cells (B, panel iii) have a denser microtubule network compared to parental cells (A, panel iii). Scale bar, represents 10 μm (B, panel iv). Location of four β-tubulin mutated residues, Asn25, Asn197, Thr248, and Asn350 in the αβ-tubulin heterodimer relative to the known colchicine-binding site identified in 2ME2-resistant leukemia cells. The locations of the mutated residues are shown in green. Blue and orange ribbons represent β-
and α-tubulin, respectively. Thr248 and Asn350 mutations are situated in close proximity to the colchicine-binding site whereas Asn197 and Asn25 mutations are distinctly remote from the colchicine-binding site. For details, see Liaw et al., in this issue.