The post-translational modification of tubulin appears to be a highly controlled 
mechanism that regulates microtubule functioning. Acetylation of the ε-amino 
group of Lys-40 of α-tubulin marks stable microtubules, although the causal 
relationship between tubulin acetylation and microtubule stability has remained 
poorly understood. HDAC6, the tubulin deacetylase, plays a key role in 
maintaining typical distribution of acetylated microtubules in cells. Here, by 
using tubastatin A, an HDAC6-specific inhibitor, and siRNA-mediated depletion of 
HDAC6, we have explored whether tubulin acetylation has a role in regulating 
microtubule stability. We found that whereas both pharmacological inhibition of 
HDAC6 as well as its depletion enhance microtubule acetylation, only 
pharmacological inhibition of HDAC6 activity leads to an increase in microtubule 
stability against cold and nocodazole-induced depolymerizing conditions. 
Tubastatin A treatment suppressed the dynamics of individual microtubules in 
MCF-7 cells and delayed the reassembly of depolymerized microtubules. 
Interestingly, both the localization of HDAC6 on microtubules and the amount of 
HDAC6 associated with polymeric fraction of tubulin were found to increase in 
the tubastatin A-treated cells compared with the control cells, suggesting that 
the pharmacological inhibition of HDAC6 enhances the binding of HDAC6 to 
microtubules. The evidence presented in this study indicated that the increased 
binding of HDAC6, rather than the acetylation per se, causes microtubule 
stability. The results are in support of a hypothesis that in addition to its 
deacetylase function, HDAC6 might function as a MAP that regulates microtubule 
dynamics under certain conditions.