CYLD interacts with microtubule outer surface and promotes noscapine binding to microtubules. (A) Purified GST, GST-CYLD, or GST-CYLD-ΔCG1 was incubated with subtilisin-treated or control untreated microtubules. Microtubules were pelleted by centrifugation and proteins present in the pellet (P) and supernatant (S) fractions were detected by immunoblotting with anti-GST antibody. (B) Paclitaxel was incubated with microtubules in the presence of GST or GST-CYLD. The dissociation constant (Kd) between paclitaxel and microtubules was then determined by fluorescence titration assays. (C) Vinblastine was incubated with microtubules in the presence of GST or GST-CYLD. The dissociation constant between vinblastine and microtubules was then determined by fluorescence titration assays. (D) Noscapine was incubated with microtubules in the presence of GST, GST-CYLD, or GST-CYLD-ΔCG1. The dissociation constant between noscapine and microtubules was then determined by fluorescence titration assays. (E) A model illustrating the role of CYLD in promoting noscapine activity in leukemia cells. When CYLD expression in leukemia cells is low, noscapine interacts weakly with microtubules, arrests only a small subset of cells at mitosis (round cells with mitotic spindles and chromosomes), and then induce these mitotically arrested cells to undergo apoptosis (cells with blebs and apoptotic bodies). When CYLD expression is high, noscapine interacts strongly with microtubules, arrests a large subset of cells at mitosis, and then triggers these cells to undergo apoptosis.