Mice Lacking Histone Deacetylase 6 Have Hyperacetylated Tubulin but Are Viable and Develop Normally

Abstract

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, ␣-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.Protein acetylation/deacetylation is involved in the regulation of protein structure and function, and therefore has potentially important roles in most cellular processes. In particular, the impact of histone N-terminal acetylation on chromatin organization and gene expression has been well documented (15). Acetylation and deacetylation of histone tails or of other proteins are catalyzed by histone acetyltransferases and histone deacetylases (HDACs), respectively. In mammals, there are 18 HDACs identified so far that can be grouped into three classes (reviewed in references 35, 36, and 39). In cells, most, if not all, class I and II HDACs are part of high-molecular-weight complexes that typically contain several HDAC polypeptides and are recruited to DNA via their interactions with sequence-specific or nonspecific DNA-binding proteins.HDAC 6 (HDAC6) was first identified through its homology to the Saccharomyces cerevisiae histone deacetylase HDA1 (9, 34). Like other class II HDACs, HDAC6 is mainly localized in the cytoplasm, but it can also shuttle between the nucleus and cytoplasm (33). This process is regulated by an N-terminally located nuclear export signal and possibly other uncharacterized mechanisms. HDAC6 has not been found in any class I or II HDAC-containing repressor complexes, which suggests it may have a unique regulation and possibly substrates different from those of other HDACs. However, it was shown biochemically and in genome-wide two-hybrid experiments to associate with the class III deacetylase SirT2 (22,26). Interestingly, HDAC6 contains two hdac catalyti...

CYLD mediates ciliogenesis in multiple organs by deubiquitinating Cep70 and inactivating HDAC6

“…Similarly, small-molecule inhibition of HDAC6 activity does not significantly affect the percentage of ciliated cells or ciliary length. These results are consistent with the findings that HDAC6 knockout mice are viable and fertile and develop normally, although they show hyperacetylated tubulin in many tissues [29,30]. It is possible that some redundancy exists in the regulation of ciliogenesis by tubulin deacetylases.…”

Microtubule-associated deacetylase HDAC6 promotes angiogenesis by regulating cell migration in an EB1-dependent manner

“…Alternatively, the HDAC6-EB1 complex may serve as a scaffold for the binding of additional proteins important for cell migration. Given our finding that HDAC6 is important for both embryonic and postnatal angiogenesis, it is surprising that HDAC6-deficient mice are viable and do not display obvious phenotype (Zhang et al, 2008). It is possible that HDAC10, another member of the HDAC family that is closely related to HDAC6 with functions less understood (Fischer et al, 2002;Guardiola and Yao, 2002), may complement the loss of HDAC6 in mice.…”

αTAT1 is the major α-tubulin acetyltransferase in mice

“…In addition to axons and cilia, microtubule acetylation is also present at lower levels in the cytoplasm of the majority of cells, including embryonic fibroblasts 30 . We therefore derived embryonic fibroblasts from E12.5 embryos and measured a-tubulin acetylation by immunostaining cells with the 6-11b-1 antibody.…”

“…Post-translational modifications of tubulin such as acetylation accumulate in stable microtubules 31 , however, it is unresolved as to whether acetylation actively stabilizes microtubules 30,[32][33][34][35][36] . As a measure of microtubule stability, we investigated their resistance to nocodazole, a microtubule depolymerizing drug.…”

“…This is in broad agreement with previous studies demonstrating that both Chlamydomonas and Tetrahymena have no observable phenotype upon genetic manipulation of native atubulin to a non-acetylable form in these organisms 39,40 . Moreover, disruption of the a-tubulin deacetylase HDAC6 in mouse results in hyperacetylation of a-tubulin, but does not affect ES cell proliferation or differentiation 41 , or produce substantial phenotypes in mice 30 . Collectively, our data indicate that cells and organisms are able to tolerate considerable shifts in the degree of tubulin acetylation.…”