Trichostatin A (TSA) inhibits all histone deacetylases (HDACs) of both class I and II, whereas trapoxin (TPX) cannot inhibit HDAC6, a cytoplasmic member of class II HDACs. We took advantage of this differential sensitivity of HDAC6 to TSA and TPX to identify its substrates. Using this approach, a-tubulin was identi®ed as an HDAC6 substrate. HDAC6 deacetylated a-tubulin both in vivo and in vitro. Our investigations suggest that HDAC6 controls the stability of a dynamic pool of microtubules. Indeed, we found that highly acetylated microtubules observed after TSA treatment exhibited delayed drug-induced depolymerization and that HDAC6 overexpression prompted their induced depolymerization. Depolymerized tubulin was rapidly deacetylated in vivo, whereas tubulin acetylation occurred only after polymerization. We therefore suggest that acetylation and deacetylation are coupled to the microtubule turnover and that HDAC6 plays a key regulatory role in the stability of the dynamic microtubules.

New inhibitors of histone deacetylase (HDAC) containing a sulfhydryl group were designed on the basis of the corresponding hydroxamic acid (CHAP31) and FK228. Their disulfide dimers and hybrids exhibited potent HDAC inhibitory activity in vivo with potential as anticancer prodrugs. [structure: see text]

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