Effect of auristatin PHE on microtubule integrity and nuclear localization in Cryptococcus neoformans

The mechanism of action of the fungicidal peptide auristatin PHE was investigated in Cryptococcus neoformans. Since auristatin PHE causes budding arrest in C. neoformans (T. Woyke, G. R. Pettit, G. Winkelmann, and R. K. Pettit, Antimicrob. Agents Chemother. 45:3580-3584, 2001), microtubule integrity and nuclear localization in auristatin PHE-treated cells were examined. Iterative deconvolution in conjunction with an optimized C. neoformans microtubule immunolabeling procedure enabled detailed visualization of the microtubule cytoskeleton in auristatin PHE-treated C. neoformans. The effect of auristatin PHE on C. neoformans microtubule organization was compared with that of the tubulin-binding agent nocodazole. Both drugs produced complete disruption first of cytoplasmic and then of spindle microtubules in a time- and concentration-dependent manner. Sub-MICs of auristatin PHE caused complete microtubule disruption within 4.5 h, while 1.5 times the nocodazole MIC was required for the same effect. For both drugs, disruption of microtubules was accompanied by blockage of nuclear migration and of nuclear and cellular division, resulting in cells arrested in a uninucleate, large-budded stage. Nocodazole and the linear peptide auristatin PHE are remarkably different in structure and spectrum of activity, yet on the cellular level, they have similar effects.