title: Mechanisms of kinetic stabilization by the drugs paclitaxel and vinblastine.
abstract: Microtubule-targeting agents (MTAs), widely used as biological probes and chemotherapeutic drugs, bind directly to tubulin subunits and "kinetically stabilize" microtubules, suppressing the characteristic self-assembly process of dynamic instability. However, the molecular-level mechanisms of kinetic stabilization are unclear, and the fundamental thermodynamic and kinetic requirements for dynamic instability and its elimination by MTAs have yet to be defined. Here we integrate a computational model for microtubule assembly with nanometer-scale fluorescence microscopy measurements to identify the kinetic and thermodynamic basis of kinetic stabilization by the MTAs paclitaxel, an assembly promoter, and vinblastine, a disassembly promoter. We identify two distinct modes of kinetic stabilization in live cells, one that truly suppresses on-off kinetics, characteristic of vinblastine, and the other a "pseudo" kinetic stabilization, characteristic of paclitaxel, that nearly eliminates the energy difference between the GTP- and GDP-tubulin thermodynamic states. By either mechanism, the main effect of both MTAs is to effectively stabilize the microtubule against disassembly in the absence of a robust GTP cap.
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Castle
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109.
authors.forename: Seth
authors.initials: S
authors.lastname: McCubbin
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Louis S
authors.initials: LS
authors.lastname: Prahl
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Jordan N
authors.initials: JN
authors.lastname: Bernens
authors.affiliation: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109.
authors.forename: David
authors.initials: D
authors.lastname: Sept
authors.affiliation: Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455 oddex002@umn.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Odde
mesh_terms: D000818:Animals; D003198:Computer Simulation; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D008856:Microscopy, Fluorescence / Q000379:methods; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism* / Q000502:physiology; D017239:Paclitaxel / Q000494:pharmacology*; D013552:Swine; D013816:Thermodynamics; D014404:Tubulin / Q000378:metabolism; D014747:Vinblastine / Q000494:pharmacology*
chemical_list: D008869:Microtubule-Associated Proteins; D014404:Tubulin; D014747:Vinblastine; D017239:Paclitaxel