Tubulin Deacetylation Research Articles

A novel GRK2/HDAC6 interaction modulates cell spreading and motility

Cell motility and adhesion involves dynamic microtubule (MT) acetylation/deacetylation, a process regulated by enzymes as HDAC6, a major cytoplasmic α-tubulin deacetylase. We identify G protein-coupled receptor kinase 2 (GRK2) as a key novel stimulator of HDAC6. GRK2, which levels inversely correlate with the extent of α-tubulin acetylation in epithelial cells and fibroblasts, directly associates with and phosphorylates HDAC6 to stimulate α-tubulin deacetylase activity. Remarkably, phosphorylation of GRK2 itself at S670 specifically potentiates its ability to regulate HDAC6. GRK2 and HDAC6 colocalize in the lamellipodia of migrating cells, leading to local tubulin deacetylation and enhanced motility. Consistently, cells expressing GRK2-K220R or GRK2-S670A mutants, unable to phosphorylate HDAC6, exhibit highly acetylated cortical MTs and display impaired migration and protrusive activity. Finally, we find that a balanced, GRK2/HDAC6-mediated regulation of tubulin acetylation differentially modulates the early and late stages of cellular spreading. This novel GRK2/HDAC6 functional interaction may have important implications in pathological contexts.

BDNF‐deficiency upregulates SIRT2 expression but does not affect cellular metabolism in mouse retina

AbstractPurpose Brain derived neurotrophic factor (BDNF) is essential for cell development, function and survival. Mammalian sirtuins (SIRT) are deacetylase enzymes that are known to play an important role in longevity. In the present study we aimed to compare SIRT1 and SIRT2 expression in retinas of mice that lack brain derived neurotrophic factor (BDNF+/‐) and their wild type littermates (WT) at young age in relation to cellular metabolism.Methods Eyes from 2‐months old WT and BDNF+/‐ mice (The Jackson Laboratory, Bar Harbor, ME, USA) were used. SIRT1 and SIRT2 protein levels in retina were determined by Western blotting. Paraffin‐embedded retinal sections were immunostained for SIRT1 and SIRT2 to determine their localisation and abundance in various retinal layers. Metabolic state of mouse retinal cells was assessed by measuring NAD+, NADH and total NAD levels using resazurin‐based assay.Results Western blot analysis of the whole retina showed that SIRT1 expression is similar in WT and BDNF+/‐ mice. However, there was a significant upregulation of SIRT2 protein level in BDNF+/‐ mice compared to WT littermates. Assessment of NAD+, NADH and total NAD levels showed similar cellular metabolic state in retinas of WT and BDNF+/‐ mice.Conclusion Our results indicate increased tubulin deacetylation in retinas of BDNF+/‐ mice, which is independent from cellular energy metabolism.

Mitochondria: The Common Upstream Driver of Amyloid-β and Tau Pathology in Alzheimers Disease

Mitochondrial dysfunction has been widely implicated in the etiology of Alzheimer's disease (AD). Evidence shows a mitochondrial-mediated impairment of autophagy that potentiates amyloid-β (Aβ) deposition. Accordingly, recent data obtained from AD models, in which mitochondrial alterations are a prominent feature, demonstrated abnormalities in microtubule network, involving tubulin and tau post-translational modifications. In this review we will discuss mitochondrial-regulated processes where mitochondrial malfunction is likely to start a sequence of events leading to sirtuin-2 activation, microtubule network breakdown, and impairment of the autophagic pathway. Because sirtuin-2 activity depends on cellular NAD+ availability, mitochondrial regulation of NAD+ levels may contribute to an increase in sirtuin-mediated tubulin deacetylation. A vicious cycle become installed which potentiates tau hyperphosphorylation, together with Aβ overproduction and deposition. Overall, targeting microtubule network constitutes a promising strategy for pharmacological therapy in AD.

A novel histone deacetylase inhibitor, CG200745, potentiates anticancer effect of docetaxel in prostate cancer via decreasing Mcl-1 and Bcl-XL

We synthesized a novel hydroxamate-based pan-histone deacetylase inhibitor (HDACI), CG200745 {(E)-2-(Naphthalen-1-yloxymethyl)-oct-2-enedioic acid 1-[(3-dimethylamino-propyl)-amide] 8-hydroxyamide]}. Like other inhibitors, for example vorinostat and belinostat, CG200745 has the hydroxamic acid moiety to bind zinc at the bottom of catalytic pocket. Firstly, we analyzed its inhibitory activity against histone deacetylase (HDAC) in hormone-dependent LNCaP cells and hormone-independent DU145 and PC3 cells. CG200745 inhibited deacetylation of histone H3 and tubulin as much as vorinostat and belinostat did. CG200745 also inhibited growth of prostate cancer cells, increased sub-G1 population, and activated caspase-9, -3 and -8 in LNCaP, DU145 and PC3 cells. These results indicate that CG200745 induces apoptosis. Next, we examined the effect of CG200745 on cell death induced by docetaxel in DU145 cells in vitro and in vivo. Compared to mono-treatment with each drug, pre-treatment of DU145 cells with docetaxel followed by CG200745 showed synergistic cytotoxicity, and increased the apoptotic sub-G1 population, caspase activation, and tubulin acetylation. Moreover, the combination treatment decreased Mcl-1 and Bcl-(XL). Docetaxel and CG200745 combination reduced tumor size in the DU145 xenograft model. These preclinical results show that combination treatment with docetaxel and new HDACI, CG200745, potentiated anti-tumor effect in hormone-refractory prostate cancer (HRPC) cells via activation of apoptosis.

Angiotensin II induces microtubule reorganization mediated by a deacetylase SIRT2 in endothelial cells

Angiotensin II has been implicated in vascular remodeling. Microtubule composed of tubulins regulates cell shape, migration and survival. Tubulin acetylation has an important role in the control of microtubule structure and microtubule-based cellular functions. In this study, angiotensin II induced disassembly and deacetylation of α-tubulin, which were blocked by pretreatment with an angiotensin II type 1 receptor blocker losartan and a sirtuin class deacetylase inhibitor sirtinol, and by depletion of a deacetylase SIRT2 using RNA interference. We investigated the involvement of SIRT2 in angiotensin II-induced endothelial cell migration using the Boyden chamber method. Angiotensin II caused a significant increase in cell migration, which was blocked by pretreatment with sirtinol and SIRT2 depletion. It has been reported that angiotensin II is involved in cytoskeletal reorganization stimulated by mechanical stretch in endothelial cells. We also demonstrated that endothelial cells subjected to a 10% uniaxial stretch showed vertical alignment to the direction of tension and tubulin deacetylation in the peripheral side of cells, in comparison with control static cells. The mechanical stretch-induced changes of microtubules were blocked by pretreatment with sirtinol and SIRT2 depletion. Immunofluorescence microscopy showed that acetylated tubulin was decreased in platelet-endothelial cell adhesion molecule-1-positive cells in the intima of the aortic walls in mice loaded with angiotensin II, in comparison with mice loaded with control vehicle. These data show that angiotensin II and mechanical stretch stimulate microtubule redistribution and deacetylation via SIRT2 in endothelial cells, suggesting the emerging role of SIRT2 in hypertension-induced vascular remodeling.

Abstract 179: Histone deacetylase inhibitor; CG005, is a novel anticancer drug; as a combination drug with docetaxel in prostate cancer

Abstract We synthesized a novel hydroxamate-based HDACi, CG0005 {(E)-2-(Naphthalen-1-yloxymethyl)-oct-2-enedioic acid 1-[(3-dimethylamino-propyl)-amide] 8-hydroxyamide]}. Like other inhibitors, for example SAHA and PXD 101, CG0005 has the hydroxamic acid moiety to bind zinc at the bottom of catalytic pocket. The aliphatic chain of CG0005, which is presumed to be positioned at the narrow channel of pocket, is less flexible than that of SAHA and less rigid than that of PXD101. Of the other moieties, the tertiary amine was adopted to improve water solubility. Firstly, we analyzed its activity in hormone-dependent LNCaP cells and hormone-refractory DU145 and PC3 cells. CG0005 inhibited deacetylation of histone3 and tubulin as much as vorinostat and belinostat. CG0005 also inhibited growth of prostate cancer cells and increased sub-G1 population and activated caspase-9, -3 and -8. These results indicated that CG0005 induced apoptosis in prostate cancer cell lines. Next, we examined the effect of CG0005 on cell death induced by docetaxel in DU145 cells in vitro and in vivo. Pre-treatment of DU145 cells with docetaxel followed by CG0005 showed synergistic cytotoxicity, and increased the apoptotic sub-G1 population, caspase activation, and tubulin acetylation, compared with docetaxel alone. Moreover, the combination treatment decreased Mcl-1, Bcl-xl and cyclin D1. Docetaxel and CG0005 combination reduced tumor size in the DU145 xenograft model. These preclinical results show that post-treatment with CG0005 potentiated anti-tumor effect of docetaxel in hormone-refractory prostate cancer (HRPC) cells via intrinsic and extrinsic apoptotic pathway in vitro and in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 179. doi:10.1158/1538-7445.AM2011-179

Clostridium difficile Toxin A Decreases Acetylation of Tubulin, Leading to Microtubule Depolymerization through Activation of Histone Deacetylase 6, and This Mediates Acute Inflammation

Clostridium difficile toxin A is known to cause actin disaggregation through the enzymatic inactivation of intracellular Rho proteins. Based on the rapid and severe cell rounding of toxin A-exposed cells, we speculated that toxin A may be involved in post-translational modification of tubulin, leading to microtubule instability. In the current study, we observed that toxin A strongly reduced α-tubulin acetylation in human colonocytes and mouse intestine. Fractionation analysis demonstrated that toxin A-induced α-tubulin deacetylation yielded monomeric tubulin, indicating the presence of microtubule depolymerization. Inhibition of the glucosyltransferase activity against Rho proteins of toxin A by UDP-2',3'-dialdehyde significantly abrogated toxin A-induced α-tubulin deacetylation. In colonocytes treated with trichostatin A (TSA), an inhibitor of the HDAC6 tubulin deacetylase, toxin A-induced α-tubulin deacetylation and loss of tight junction were completely blocked. Administration of TSA also attenuated proinflammatory cytokine production, mucosal damage, and epithelial cell apoptosis in mouse intestine exposed to toxin A. These results suggest that toxin A causes microtubule depolymerization by activation of HDAC6-mediated tubulin deacetylation. Indeed, blockage of HDAC6 by TSA markedly attenuates α-tubulin deacetylation, proinflammatory cytokine production, and mucosal damage in a toxin A-induced mouse enteritis model. Tubulin deacetylation is an important component of the intestinal inflammatory cascade following toxin A-mediated Rho inactivation in vitro and in vivo.

TPPP/p25 Promotes Tubulin Acetylation by Inhibiting Histone Deacetylase 6

TPPP/p25 (tubulin polymerization-promoting protein/p25) is an unstructured protein that induces microtubule polymerization in vitro and is aligned along the microtubule network in transfected mammalian cells. In normal human brain, TPPP/p25 is expressed predominantly in oligodendrocytes, where its expression is proved to be crucial for their differentiation process. Here we demonstrated that the expression of TPPP/p25 in HeLa cells, in doxycycline-inducible CHO10 cells, and in the oligodendrocyte CG-4 cells promoted the acetylation of alpha-tubulin at residue Lys-40, whereas its down-regulation by specific small interfering RNA in CG-4 cells or by the withdrawal of doxycycline from CHO10 cells decreased the acetylation level of alpha-tubulin. Our results indicate that TPPP/p25 binds to HDAC6 (histone deacetylase 6), an enzyme responsible for tubulin deacetylation. Moreover, we demonstrated that the direct interaction of these two proteins resulted in the inhibition of the deacetylase activity of HDAC6. The measurement of HDAC6 activity showed that TPPP/p25 is able to induce almost complete (90%) inhibition at 3 microM concentration. In addition, treatment of the cells with nocodazole, vinblastine, or cold exposure revealed that microtubule acetylation induced by trichostatin A, a well known HDAC6 inhibitor, does not cause microtubule stabilization. In contrast, the microtubule bundling activity of TPPP/p25 was able to protect the microtubules from depolymerization. Finally, we demonstrated that, similarly to other HDAC6 inhibitors, TPPP/p25 influences the microtubule dynamics by decreasing the growth velocity of the microtubule plus ends and also affects cell motility as demonstrated by time lapse video experiments. Thus, we suggest that TPPP/p25 is a multiple effector of the microtubule organization.

T‐cadherin modulates endothelial barrier function

T-cadherin is an atypical member of the cadherin family, which lacks the transmembrane and intracellular domains and is attached to the plasma membrane via a glycosylphosphatidylinositol anchor. Unlike canonical cadherins, it is believed to function primarily as a signaling molecule. T-cadherin is highly expressed in endothelium. Using transendothelial electrical resistance measurements and siRNA-mediated depletion of T-cadherin in human umbilical vein endothelial cells, we examined its involvement in regulation of endothelial barrier. We found that in resting confluent monolayers adjusted either to 1% or 10% serum, T-cadherin depletion modestly, but consistently reduced transendothelial resistance. This was accompanied by increased phosphorylation of Akt and LIM kinase, reduced phosphorylation of p38 MAP kinase, but no difference in tubulin acetylation and in phosphorylation of an actin filament severing protein cofilin and myosin light chain kinase. Serum stimulation elicited a biphasic increase in resistance with peaks at 0.5 and 4-5 h, which was suppressed by a PI3 kinase/Akt inhibitor wortmannin and a p38 inhibitor SB 239063. T-cadherin depletion increased transendothelial resistance between the two peaks and reduced the amplitude of the second peak. T-cadherin depletion abrogated serum-induced Akt phosphorylation at Thr308 and reduced phosphorylation at Ser473, reduced phosphorylation of cofilin, and accelerated tubulin deacetylation. Adiponectin slightly improved transendothelial resistance irrespectively of T-cadherin depletion. T-cadherin depletion also resulted in a reduced sensitivity and delayed responses to thrombin. These data implicate T-cadherin in regulation of endothelial barrier function, and suggest a complex signaling network that links T-cadherin and regulation of barrier function.

Abstract 4848: Angintensin II Stimulates Microtubule Reorganization Mediated by SIRT2 in Endothelial Cells

Angiotensin II has been implicated in the pathophysiology of vascular remodeling. Microtubule composed of tubulins regulates cell shape, migration and survival. Tubulin acetylation plays an important role in the control of microtubule structure and microtubule-based cellular functions. We studied angiotensin II-induced changes in microtubules in endothelial cells. Immunofluorescence microscopy showed that acetylated tubulin was decreased in PECAM-1-positive cells in the intima of the aortic walls in mice loaded with angiotensin II, compared to mice loaded with control vehicle. In cultured human endothelial cells in quiescence, α -tubulin-positive microtubules were acetylated and showed radial layout from microtubule-organizing center to peripheral edge of cells. Angiotensin II induced disassembly and deacetylation of α -tubulin, which were blocked by pretreatment with losartan that is an angiotensin II type 1 receptor blocker, sirtinol that is an inhibitor for sirtuin class deacetylases, and depletion of a deacetylase SIRT2 by RNA interference. We investigated the involvement of SIRT2 in angiotensin II-induced endothelial cell migration using Boyden chamber method. Angiotensin II caused a significant increase in cell migration, which was blocked by pretreatment with sirtinol and SIRT2 depletion. It has been reported that angiotensin II is involeved in cytoskeletal reorganization stimulated by mechanical stretch in endothelial cells. To investigate the effects of mechanical stretch on microtubule reorganization, cultured endothelial cells were subjected to 10% uniaxial stretch and examnied by immunofluorescence. Mechanically stretched cells showed vertical alignment to tension direction and tubulin deacetylation in peripheral side of cells, compared to control static cells. Mechanical stretch-induced changes of microtubules were blocked by pretreatment with sirtinol and SIRT2 depletion. These data suggest that angiotensin II and mechanical stretch stimulate microtubule redistribution and deacetylation via SIRT2 in endothelial cells. Further studies are necessary to elucidate the roles of SIRT2-mediated microtubule reorganization in vascular remodeling.

Abstract 5613: Class IIa HDAC6 Contributes to Angiogenesis and Endothelial Cell Function

Acetylation of histone proteins contributes to the regulation of gene expression by alteration of chromatin structure. Histone deacetylases (HDACs) act as modulators of gene expression by deacetylation of histone proteins as well as non-histone proteins. Previous studies identified the class IIa histone deacetylases HDAC5 and HDAC7 as regulators of angiogenesis. The class IIb HDAC6 is the only HDAC that possesses two functional deacetylase domains and is known to be involved in lymphocyte chemotaxis and in cancer development. However, the function of HDAC6 in endothelial cells is unknown. Therefore, we analyzed the effect of HDAC6 for endothelial cell functions during angiogenesis. HDAC6 is mainly localized in the cytoplasm of human umbilical vein endothelial cells. Knockdown of HDAC6 with siRNA oligonucleotides significantly decreased endothelial cell sprouting from spheroids (42%±7, p<0.05, N=5), tube formation in matrigel assay (81%±2, p<0.05, N=3) and endothelial cell migration in a scratched wound assay (65%±5, p<0.05, N=3) without affecting cell viability. These results were confirmed using a second unrelated oligonucleotide. Consistently, overexpression of HDAC6 wild-type increased endothelial cell sprouting (122%±8, N=4), indicating that HDAC6 is a positive regulator of angiogenesis. The catalytic activity of the second HDAC-domain seems to be necessary for the pro-angiogenic effect of HDAC6, because overexpression of a deletion mutant, which lacks the second deacetylase domain, did not affect sprouting (95%±10, N=4). Because the second HDAC-domain is known to be responsible for α -tubulin deacetylation and acetylation of α -tubulin might play a role in cell migration, we assessed the effect of the HDAC6 specific tubulin deacetylation inhibitor tubacin on endothelial sprout formation. Application of tubacin did not affect sprouting, indicating that the mechanism is independent of α -tubulin deacetylation. In summary, we found that the cytoplasmic HDAC6 is necessary for in vitro angiogenesis as assessed by endothelial sprouting, tube formation and migration. Mechanistically, the pro-angiogenic effect of HDAC6 in endothelial cells requires the second deacetylase domain, but is independent of α -tubulin deacetylation.

Association of Estrogen Receptor α and Histone Deacetylase 6 Causes Rapid Deacetylation of Tubulin in Breast Cancer Cells

Estrogen receptor alpha (ERalpha) is a nuclear receptor that functions as a ligand-activated transcription factor. Besides its genomic action in nuclei, ERalpha could exert nongenomic actions at the plasma membrane. To investigate the mechanism underlying the nongenomic action of ERalpha in breast cancer cells, we generated a construct of membrane-targeted ERalpha (memER), an expression vector of ERalpha without the nuclear localizing signal and including instead the membrane-targeting sequence of Src kinase. MemER was stably expressed in human breast cancer MCF-7 cells. Cell migration test and tumorigenic assay in nude mice revealed that the in vitro motility and the in vivo proliferation activity of MCF-7 cells expressing memER were significantly enhanced compared with those of vector-transfected cells. Interestingly, the acetylation level of tubulin in memER-overexpressing cells was lower than that in control cells. We found that histone deacetylase (HDAC) 6 translocated to the plasma membrane shortly after estrogen stimulation, and rapid tubulin deacetylation subsequently occurred. We also showed that memER associated with HDAC6 in a ligand-dependent manner. Although tamoxifen is known for its antagonistic role in the ERalpha genomic action in MCF-7 cells, the agent showed an agonistic function in the memER-HDAC6 association and tubulin deacetylation. These findings suggest that ERalpha ligand dependently forms a complex with HDAC6 and tubulin at the plasma membrane. Estrogen-dependent tubulin deacetylation could provide new evidence for the nongenomic action of estrogen, which potentially contributes to the aggressiveness of ERalpha-positive breast cancer cells.

The Protein Farnesyltransferase Regulates HDAC6 Activity in a Microtubule-dependent Manner

The cytoplasmic deacetylase HDAC6 is an important regulator of cellular pathways that include response to stress, protein folding, microtubule stability, and cell migration, thus representing an attractive target for cancer chemotherapy. However, little is known about its upstream regulation. Our previous work has implicated HDAC6 as a new protein target for the farnesyltransferase inhibitors (FTIs), although HDAC6 lacks a farnesylation motif. Here we show that the protein farnesyltransferase (FTase) and HDAC6 are present in a protein complex together with microtubules in vivo and in vitro. FTase binds microtubules directly via its alpha subunit, and this association requires the C terminus of tubulin. Treatment with an FTI removed FTase, but not HDAC6, from the protein complex, suggesting that the active form of FTase is bound to microtubules. Importantly, the removal of FTase from microtubules abrogated HDAC6 activity, as did a stable knockdown of the alpha subunit of FTase (FTalphaKD). Interestingly, the FTalphaKD cells showed increased sensitivity to the antiproliferative effects of Taxol and the FTI lonafarnib when used either as single agents or in combination as compared with parental cells. Altogether, these data suggest that FTase, via its tubulin-association, is a critical upstream regulator of HDAC6 activity and that FTase expression could help stratify cancer patients that would most benefit from this treatment.

Acetylation of histone deacetylase 6 by p300 attenuates its deacetylase activity

Protein acetyltransferases and deacetylases affect the activities of each other. This is well documented by the acetylation and inhibition of HDAC1 by p300, a transcriptional co-activator with protein acetyltransferase activity. However, the relationship between HDAC6 and p300 is poorly understood. HDAC6 is a class II histone deacetylase and differs from other members of HDAC family in that it contains two HDAC domains and an ubiquitin-binding motif. HDAC6 is a microtubule-associated deacetylase. It predominantly deacetylates non-histone proteins, including α-tubulin, and regulates cell motility. Here, we report that p300 interacts with and acetylates HDAC6 resulting down-regulation of HDAC6 deacetylase activity. Furthermore, we provide evidences that acetylation of HDAC6 by p300 inhibits tubulin deacetylation and suppression of Sp1 transcriptional activity by HDAC6. Our results demonstrate that p300 can inactivate HDAC6 by acetylation, and that p300 may regulate the activity of Sp1 indirectly through HDAC6 in addition to its direct modification of Sp1.

Histone deacetylase inhibitors that target tubulin

Epigenetics is defined as heritable changes in gene expression that occur without changes in DNA sequence. Major mechanisms of epigenetics are post-translational histone modifications such as reversible acetylation. Histone deacetylases (HDACs) maintain the acetylation level of histones but also act on non-histone substrates that are involved in signal transduction or cellular transport processes. One important non-histone substrate is tubulin. The isotypes responsible for tubulin deacetylation are HDAC6 and the NAD +-dependent histone deacetylase (sirtuin) Sirt2. Here we review the action of those enzymes on tubulin and present an overview over existing inhibitors with a focus on their structural interaction with the targets.

Direct Binding with Histone Deacetylase 6 Mediates the Reversible Recruitment of Parkin to the Centrosome

Histone deacetylase 6 (HDAC6), a microtubule-associated tubulin deacetylase, plays a significant role in the formation of protein aggregates in many neurodegenerative disorders. Parkin, a protein-ubiquitin E3 ligase linked to Parkinson's disease, accumulates at the centrosome in a microtubule-dependent manner in response to proteasome inhibition. Here, we show that the centrosome recruitment of parkin was mediated by its direct binding to HDAC6 through multiple interaction domains. The tubulin deacetylase activity of HDAC6 was required for the accumulation of parkin as well as its dispersion upon the reversal of proteasome inhibition. The bidirectional movements of parkin required intact microtubule network and were dependent on dynein and kinesin 1, respectively. Tubulin deacetylation increases microtubule dynamicity and may thus facilitate microtubule-based trafficking of the parkin-HDAC6 complex. The results suggest that HDAC6 acts as a sensor of proteasome inhibition and directs the trafficking of parkin by using different motor proteins.

Histone deacetylase 6 interacts with the microtubule‐associated protein tau

Histone deacetylase 6 (HDAC6), a unique cytoplasmic deacetylase, likely plays a role in neurodegeneration by coordinating cell responses to abnormal protein aggregation. Here, we provide in vitro and in vivo evidence that HDAC6 interacts with tau, a microtubule-associated protein that forms neurofibrillary tangles in Alzheimer's disease. This interaction is mediated by the microtubule-binding domain on tau and the Ser/Glu tetradecapeptide domain on HDAC6. Treatment with tubacin, a selective inhibitor of tubulin deacetylation activity of HDAC6, did not disrupt HDAC6-tau interaction. Nonetheless tubacin treatment attenuated site-specific tau phosphorylation, as did shRNA-mediated knockdown of HDAC6. Proteasome inhibition potentiated HDAC6-tau interactions and facilitated the concentration and co-localization of HDAC6 and tau in a perinuclear aggresome-like compartment, independent of HDAC6 tubulin deacetylase activity. Furthermore, we observed that in Alzheimer's disease brains the protein level of HDAC6 was significantly increased. These findings establish HDAC6 as a tau-interacting protein and as a potential modulator of tau phosphorylation and accumulation.

Paths of Convergence: Sirtuins in Aging and Neurodegeneration

Members of the sirtuin family of protein deacetylases support and promote longevity in diverse organisms and can extend life span when upregulated. Sirtuin pathways also modulate fundamental mechanisms in aging-related neurodegenerative diseases, including protein aggregation, stress responses, mitochondrial homeostasis, and inflammatory processes. In this minireview, we will discuss how progress in understanding the neurobiology of sirtuins is shedding light on the pathogenesis of these devastating conditions. We will also examine the potential and challenges of targeting sirtuin pathways therapeutically.

SIRT2, tubulin deacetylation, and oligodendroglia differentiation

The mammalian silent information regulator 2 (SIRT2) is an NAD-dependent histone deacetylase with known roles in the regulation of the cell cycle. SIRT2 is also a tubulin deacetylase functioning as an early mitotic checkpoint, but its roles in regulating cytoplasmic microtubule dynamics were unknown. Novel findings now indicate that SIRT2 is specifically enriched in brain oligodendroglia, where it functions specifically in modulating the oligodendrocyte cytoskeleton during its differentiation and maturation.

Mammalian Sir2-related protein (SIRT) 2–mediated modulation of resistance to axonal degeneration in slow Wallerian degeneration mice: A crucial role of tubulin deacetylation

It has been shown that Wallerian degeneration, an anterograde degeneration of transected axons, is markedly delayed in a mutant mouse called slow Wallerian degeneration ( Wld S ). These mice also show resistance to axonal degeneration caused by microtubule depolymerizing drugs, suggesting that axonal microtubules are stabilized. Here, we have focused on tubulin acetylation, a post-translational modification associated with microtubule stability. We found that the basal level of microtubule acetylation was increased in cultured cerebellar granule cells from Wld S mice. Nicotinamide but not 3-aminobenzamide, an inhibitor for poly(ADP)ribose polymerase, enhanced tubulin acetylation and resistance to axonal degeneration in cultured cerebellar granule cells from wild-type (WT) mice, suggesting that mammalian Sir2-related protein (SIRT) 2, a nicotinamide adenine dinucleotide (NAD)–dependent tubulin deacetylase, could modulate resistance to axonal degeneration. Indeed, the levels of NAD and SIRT2 were decreased in the cytoplasm from Wld S granule cells. Moreover, SIRT2 overexpression abrogated microtubule hyperacetylation and resistance to axonal degeneration in these cells. Conversely, SIRT2 knockdown by using a lentiviral vector expressing small interfering RNA, enhanced microtubule acetylation and resistance to axonal degeneration in WT granule cells. Taken together, these results suggest that SIRT2-mediated tubulin deacetylation is involved in both microtubule hyperacetylation and resistance to axonal degeneration in Wld S granule cells.