Microtubules are cylindrical cytoskeletal structures found in almost all eukaryotic cell types which are involved in a great variety of cellular processes. Reversible acetylation on the ϵ‐amino group of α‐tubulin Lys40 marks stabilized microtubule structures and may contribute to regulating microtubule dynamics. Yet, the enzymes catalysing this acetylation/deacetylation have remained unidentified until recently. Here we report that β‐tubulin interacts with histone deacetylase‐6 (HDAC‐6) in a yeast two‐hybrid assay and in vitro. We find that HDAC‐6 is a micro tubule‐associated protein capable of deacetylating α‐tubulin in vivo and in vitro. HDAC‐69s microtubule binding and deacetylation functions both depend on the hdac domains. Overexpression of HDAC‐6 in mammalian cells leads to tubulin hypoacetylation. In contrast, inhibition of HDAC‐6 function by two independent mechanisms—pharmacological (HDAC inhibitors) or genetic (targeted inactivation of HDAC‐6 in embryonic stem cells)—leads to hyperacetylation of tubulin and microtubules. Taken together, our data provide evidence that HDAC‐6 might act as a dual deacetylase for tubulin and histones, and suggest the possibility that acetylated non‐histone proteins might represent novel targets for pharmacological therapy by HDAC inhibitors.

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, α‐tubulin was identified as an HDAC6 substrate. HDAC6 deacetylated α‐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.

Large-scale detection of ectopic gene activations reveals a source of potential cancer biomarkers and correlates with aggressive metastasis-prone lung tumors.

Posttranslational modifications play important roles in regulating protein structure and function. Histone deacetylase 6 (HDAC6) is a mostly cytoplasmic class II HDAC, which has a unique structure with two catalytic domains and a domain binding ubiquitin with high affinity. This enzyme was recently identified as a multisubstrate protein deacetylase that can act on acetylated histone tails, α-tubulin and Hsp90. To investigate the in vivo functions of HDAC6 and the relevance of tubulin acetylation/deacetylation, we targeted the HDAC6 gene by homologous recombination in embryonic stem cells and generated knockout mice. HDAC6-deficient mice are viable and fertile and show hyperacetylated tubulin in most tissues. The highest level of expression of HDAC6 is seen in the testis, yet development and function of this organ are normal in the absence of HDAC6. Likewise, lymphoid development is normal, but the immune response is moderately affected. Furthermore, the lack of HDAC6 results in a small increase in cancellous bone mineral density, indicating that this deacetylase plays a minor role in bone biology. HDAC6-deficient mouse embryonic fibroblasts show apparently normal microtubule organization and stability and also show increased Hsp90 acetylation correlating with impaired Hsp90 function. Collectively, these data demonstrate that mice survive well without HDAC6 and that tubulin hyperacetylation is not detrimental to normal mammalian development.