In vivo destabilization of dynamic microtubules by HDAC6-mediated deacetylation

Deactylase inhibitors disrupt cellular complexes containing protein phosphatases and deacetylases

Affinity isolation of protein serine/threonine phosphatases on the immobilized phosphatase inhibitor microcystin-LR identified histone deacetylase 1(HDAC1), HDAC6, and HDAC10 as novel components of cellular phosphatase complexes. Other HDACs, specifically HDAC2, -3, -4, and -5, were excluded from such complexes. In vitro biochemical studies showed that recombinant HDAC6, but not HDAC4, bound directly to the protein phosphatase (PP)1 catalytic subunit. No association was observed between HDAC6 and PP2A, another major protein phosphatase. PP1 binding was mapped to the second catalytic domain and adjacent C-terminal sequences in HDAC6, and treatment of cells with trichostatin A (TSA) disrupted endogenous HDAC6.PP1 complexes. Consistent with the inhibition of tubulin deactylase activity of HDAC6, TSA enhanced cellular tubulin acetylation, and acetylated tubulin was present in the PP1 complexes from TSA-treated cells. Trapoxin B, a weak HDAC6 inhibitor, and calyculin A, a cell-permeable phosphatase inhibitor, had no effect on the stability of the HDAC6.PP1 complexes or on tubulin acetylation. Mutations that inactivated HDAC6 prevented its incorporation into cellular PP1 complexes and suggested that when bound together both enzymes were active. Interestingly, TSA disrupted all the cellular HDAC.phosphatase complexes analyzed. This study provided new insight into the mechanism by which HDAC inhibitors elicited coordinate changes in cellular protein phosphorylation and acetylation and suggested that changes in these protein modifications at multiple subcellular sites may contribute to the known ability of HDAC inhibitors to suppress cell growth and transformation.

Class II histone deacetylases: versatile regulators

Histone acetylation and deacetylation play essential roles in modifying chromatin structure and regulating gene expression in eukaryotes. Histone deacetylases (HDACs) catalyze the deacetylation of lysine residues in the histone N-terminal tails and are found in large multiprotein complexes with transcriptional co-repressors. Human HDACs are grouped into three classes based on their similarity to known yeast factors: class I HDACs are similar to the yeast transcriptional repressor yRPD3, class II HDACs to yHDA1 and class III HDACs to ySIR2. In this review, we focus on the biology of class II HDACs. These newly discovered enzymes have been implicated as global regulators of gene expression during cell differentiation and development. We discuss their emerging biological functions and the molecular mechanisms by which they are regulated.

Domain-selective small-molecule inhibitor of histone deacetylase 6 (HDAC6)-mediated tubulin deacetylation

Protein acetylation, especially histone acetylation, is the subject of both research and clinical investigation. At least four small-molecule histone deacetylase inhibitors are currently in clinical trials for the treatment of cancer. These and other inhibitors also affect microtubule acetylation. A multidimensional, chemical genetic screen of 7,392 small molecules was used to discover "tubacin," which inhibits alpha-tubulin deacetylation in mammalian cells. Tubacin does not affect the level of histone acetylation, gene-expression patterns, or cell-cycle progression. We provide evidence that class II histone deacetylase 6 (HDAC6) is the intracellular target of tubacin. Only one of the two catalytic domains of HDAC6 possesses tubulin deacetylase activity, and only this domain is bound by tubacin. Tubacin treatment did not affect the stability of microtubules but did decrease cell motility. HDAC6 overexpression disrupted the localization of p58, a protein that mediates binding of Golgi elements to microtubules. Our results highlight the role of alpha-tubulin acetylation in mediating the localization of microtubule-associated proteins. They also suggest that small molecules that selectively inhibit HDAC6-mediated alpha-tubulin deacetylation, a first example of which is tubacin, might have therapeutic applications as antimetastatic and antiangiogenic agents.

Collaborative spirit of histone deacetylases in regulating chromatin structure and gene expression

The flexible N-terminal tails of core histones are subject to dynamic, reversible lysine acetylation. At least 10 histone deacetylases have been identified in Saccharomyces cerevisiae and 19 in humans. Emerging themes regarding the function and regulation of these enzymes include the following: targeted and non-targeted chromatin deacetylation; their collaboration with each other and with other chromatin regulators to promote transcriptional repression and silencing; deacetylation of transcription factors and other non-histone proteins; and regulation by subcellular compartmentalization and subunit association. Histone deacetylases are important targets for drugs with potential therapeutic value in the treatment of cancer, neurodegenerative disorders, cardiac hypertrophy and other human diseases.

Four different clones of mouse anti-acetyllysine monoclonal antibodies having different recognition properties share a common immunoglobulin framework structure

By employing two different immunogens and two different antibody-screening strategies, we established four mouse hybridoma clones producing monoclonal antibodies against N epsilon -acetyllysine. Three different protocols were used in this study; i.e., mice were (1) immunized with an N epsilon -acetyllysine-containing peptide, Gly-Lys(Ac)- epsilon -aminocaproic acid (Aca)-Cys, conjugated to KLH, and the hybridoma clones were screened for their reactivity to a histone H3 peptide containing five acetyllysines; (2) immunized as in "1" and screened with chemically acetylated bovine serum albumin (BSA); (3) immunized with chemically acetylated keyhole limpet hemocyanin (KLH) and screened with chemically acetylated BSA. Antibodies produced by the four different hybridomas established here all reacted with acetyllysine residues, but their reactivity was not the same when evaluated with enzyme-linked immunosorbent assay (ELISA), Western blotting, and resonant mirror sensor analyses. Among the three protocols examined, protocol "3" was especially useful to obtain hybridomas producing anti-N epsilon -acetyllysine antibodies that could detect not only the acetylated histones but also other acetylated proteins. By cloning and sequencing the cDNAs encoding the variable regions of the antibodies, we found that their framework sequences were almost the same, which suggests that some framework amino acids in addition to their complementarity determining regions (CDRs) directly contribute to their recognition function.