HDAC6 regulates sensitivity to cell death in response to stress and post-stress recovery

Mutant p53 upregulates HDAC6 to resist ER stress and facilitates Ku70 deacetylation, which prevents its degradation and mitigates DNA damage in colon cancer cells

Cancer cells employ interconnected mechanisms to withstand intrinsic and extrinsic stress, with mutant p53 (mutp53) playing a key role in bolstering resistance to endoplasmic reticulum (ER) stress. In this study, we further investigated this phenomenon, focusing on the DNA damage triggered by ER stress. Our findings indicate that mutp53 mitigates ER stress-induced DNA damage by sustaining high levels of Ku70, a critical protein in DNA repair via the non-homologous end joining (NHEJ) pathway, which functions alongside Ku80. HDAC6 upregulation emerged as a crucial driver of this response. HDAC6 deacetylates Ku70, promoting its nuclear localization and protecting it from degradation. This mechanism ensures continuous activity of the NHEJ repair pathway, allowing mutp53-expressing cells to better manage DNA damage from ER stress, thus contributing to the genomic instability characteristic of cancer progression. Furthermore, HDAC6 maintains the activation of the ATF6 branch of the unfolded protein response (UPR), enhancing the ability of mutp53 cells to resist ER stress, as ATF6 supports cellular adaptation to misfolded proteins and stressful conditions. Since HDAC6 is central to this enhanced stress resistance and DNA repair, targeting it could disrupt these protective mechanisms, increasing the vulnerability of mutp53 cancer cells to ER stress and inhibiting cancer progression.

HDAC6 deficiency aggravates ductular reactions through aggresome-mediated hepatocyte apoptosis

Ductular reactions (DRs) contribute significantly to the occurrence and development of liver disease. While histone deacetylase 6 (HDAC6) is known to regulate injury repair in multiple tissues, its exact role in DRs remains unclear. This study examined the role and underlying mechanism of HDAC6 in DRs using an HDAC6 knockout (HDAC6-/y) male mouse model. Wild type and HDAC6-deficient male mice were administered 3,5 diethoxicarbonyl-1,4 dihydrocollidine (DDC) to induce DRs. The impact of HDAC6 inhibition on aggresome formation was assessed in vitro using AML-12 hepatocytes exposed to H2O2 and treated with tubastatin A (TSA), a selective HDAC6 inhibitor. Fluorescence immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) were employed to quantify protein and gene expression levels, respectively. Immunohistochemical and qRT-PCR analyses revealed that HDAC6 deficiency exacerbated DRs and fibrosis, accompanied by increased expression of transforming growth factor β (TGF-β) and activation of the Notch signaling pathway. Additionally, genetic knockout or pharmacological inhibition of HDAC6 promoted hepatocyte apoptosis in vivo and in vitro, as evidenced by elevated caspase3, caspase9, and p53 expression. Furthermore, TSA treatment induced the formation of aggresomes in H2O2-exposed AML-12 hepatocytes, which were encased by vimentin filaments. These findings demonstrate that HDAC6 deficiency promotes DRs and liver fibrosis through the formation of intracellular aggregates, ultimately leading to hepatocyte apoptosis.

Transcription factor ONECUT3 regulates HDAC6/HIF-1α activity to promote the Warburg effect and tumor growth in colorectal cancer

The Warburg effect, also known as aerobic glycolysis, plays a crucial role in the onset and progression of colorectal cancer (CRC), although its mechanism remains unclear. In this study, bioinformatics analysis of public databases combined with validation using clinical specimens identified the transcription factor ONECUT3 as a key regulator related to the Warburg effect in CRC. Functionally, silencing ONECUT3 reverses the Warburg effect and suppresses tumor growth. Importantly, ONECUT3 promotes tumor growth in a glycolysis-dependent manner through hypoxia-inducible factor 1α (HIF-1α). Mechanistically, ONECUT3 does not directly regulate the expression of HIF-1α but instead inhibits its acetylation via histone deacetylase 6 (HDAC6). This deacetylation enhances the transcriptional activity of HIF-1α, ultimately upregulating multiple glycolysis-related genes downstream of HIF-1α, thereby driving the Warburg effect and facilitating tumor growth in CRC. These findings reveal a novel mechanism by which ONECUT3 regulates the Warburg effect in CRC and suggest that targeting ONECUT3 may offer a promising therapeutic strategy for CRC.

A novel insight into neurological disorders through HDAC6 protein-protein interactions

Due to its involvement in physiological and pathological processes, histone deacetylase 6 (HDAC6) is considered a promising pharmaceutical target for several neurological manifestations. However, the exact regulatory role of HDAC6 in the central nervous system (CNS) is still not fully understood. Hence, using a semi-automated literature screening technique, we systematically collected HDAC6-protein interactions that are experimentally validated and reported in the CNS. The resulting HDAC6 network encompassed 115 HDAC6-protein interactions divided over five subnetworks: (de)acetylation, phosphorylation, protein complexes, regulatory, and aggresome-autophagy subnetworks. In addition, 132 indirect interactions identified through HDAC6 inhibition were collected and categorized. Finally, to display the application of our HDAC6 network, we mapped transcriptomics data of Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis on the network and highlighted that in the case of Alzheimer's disease, alterations predominantly affect the HDAC6 phosphorylation subnetwork, whereas differential expression within the deacetylation subnetwork is observed across all three neurological disorders. In conclusion, the HDAC6 network created in the present study is a novel and valuable resource for the understanding of the HDAC6 regulatory mechanisms, thereby providing a framework for the integration and interpretation of omics data from neurological disorders and pharmacodynamic assessments.

Synergistic therapeutics: Co-targeting histone deacetylases and ribonucleotide reductase for enhanced cancer treatment

The development of cancer is influenced by several variables, including altered protein expression, and signaling pathways. Cancers are inherently heterogeneous and exhibit genetic and epigenetic aberrations; therefore, developing therapies that act on numerous biological targets is encouraged. To achieve this, two approaches are employed: combination therapy and dual/multiple targeting chemotherapeutics. Two enzymes, histone deacetylases (HDACs) and ribonucleotide reductase (RR), are crucial for several biological functions, including replication and repair of DNA, division of cells, transcription of genes, etc. However, it has been noted that different cancers exhibit abnormal functions of these enzymes. Potent inhibitors for each of these proteins have been extensively researched. Many medications based on these inhibitors have been successfully food and drug administration (FDA) approved, and the majority are undergoing various stages of clinical testing. This review discusses various studies of HDAC and RR inhibitors in combination therapy and dual-targeting chemotherapeutics.

ACY-241, a histone deacetylase 6 inhibitor, suppresses the epithelial-mesenchymal transition in lung cancer cells by downregulating hypoxia-inducible factor-1 alpha

Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor activated under hypoxic conditions, and it plays a crucial role in cellular stress regulation. While HIF-1α activity is essential in normal tissues, its presence in the tumor microenvironment represents a significant risk factor as it can induce angiogenesis and confer resistance to anti-cancer drugs, thereby contributing to poor prognoses. Typically, HIF-1α undergoes rapid degradation in normoxic conditions via oxygen-dependent degradation mechanisms. However, certain cancer cells can express HIF-1α even under normoxia. In this study, we observed an inclination toward increased normoxic HIF-1α expression in cancer cell lines exhibiting increased HDAC6 expression, which prompted the hypothesis that HDAC6 may modulate HIF-1α stability in normoxic conditions. To prove this hypothesis, several cancer cells with relatively higher HIF-1α levels under normoxic conditions were treated with ACY-241, a selective HDAC6 inhibitor, and small interfering RNAs for HDAC6 knockdown. Our data revealed a significant reduction in HIF-1α expression upon HDAC6 inhibition. Moreover, the downregulation of HIF-1α under normoxic conditions decreased zinc finger E-box-binding homeobox 1 expression and increased E-cadherin levels in lung cancer H1975 cells, consequently suppressing cell invasion and migration. ACY-241 treatment also demonstrated an inhibitory effect on cell invasion and migration by reducing HIF-1α level. This study confirms that HDAC6 knockdown and ACY-241 treatment effectively decrease HIF-1α expression under normoxia, thereby suppressing the epithelial-mesenchymal transition. These findings highlight the potential of selective HDAC6 inhibition as an innovative therapeutic strategy for lung cancer.

Acetylation and Phosphorylation in the Regulation of Hypoxia-Inducible Factor Activities: Additional Options to Modulate Adaptations to Changes in Oxygen Levels

O2 is essential for the life of eukaryotic cells. The ability to sense oxygen availability and initiate a response to adapt the cell to changes in O2 levels is a fundamental achievement of evolution. The key switch for adaptation consists of the transcription factors HIF1A, HIF2A and HIF3A. Their levels are tightly controlled by O2 through the involvement of the oxygen-dependent prolyl hydroxylase domain-containing enzymes (PHDs/EGNLs), the von Hippel-Lindau tumour suppressor protein (pVHL) and the ubiquitin-proteasome system. Furthermore, HIF1A and HIF2A are also under the control of additional post-translational modifications (PTMs) that positively or negatively regulate the activities of these transcription factors. This review focuses mainly on two PTMs of HIF1A and HIF2A: phosphorylation and acetylation.

HDAC6: A unique HDAC family member as a cancer target

BACKGROUND

HDAC6, a structurally and functionally distinct member of the HDAC family, is an integral part of multiple cellular functions such as cell proliferation, apoptosis, senescence, DNA damage and genomic stability, all of which when deregulated contribute to carcinogenesis. Among several HDAC family members known so far, HDAC6 holds a unique position. It differs from the other HDAC family members not only in terms of its subcellular localization, but also in terms of its substrate repertoire and hence cellular functions. Recent findings have considerably expanded the research related to the substrate pool, biological functions and regulation of HDAC6. Studies in HDAC6 knockout mice highlighted the importance of HDAC6 as a cell survival player in stressful situations, making it an important anticancer target. There is ample evidence stressing the importance of HDAC6 as an anti-cancer synergistic partner of many chemotherapeutic drugs. HDAC6 inhibitors have been found to enhance the effectiveness of conventional chemotherapeutic drugs such as DNA damaging agents, proteasome inhibitors and microtubule inhibitors, thereby highlighting the importance of combination therapies involving HDAC6 inhibitors and other anti-cancer agents.

CONCLUSIONS

Here, we present a review on HDAC6 with emphasis on its role as a critical regulator of specific physiological cellular pathways which when deregulated contribute to tumorigenesis, thereby highlighting the importance of HDAC6 inhibitors as important anticancer agents alone and in combination with other chemotherapeutic drugs. We also discuss the synergistic anticancer effect of combination therapies of HDAC6 inhibitors with conventional chemotherapeutic drugs.

Gene regulation by histone-modifying enzymes under hypoxic conditions: a focus on histone methylation and acetylation

Oxygen, which is necessary for sustaining energy metabolism, is consumed in many biochemical reactions in eukaryotes. When the oxygen supply is insufficient for maintaining multiple homeostatic states at the cellular level, cells are subjected to hypoxic stress. Hypoxia induces adaptive cellular responses mainly through hypoxia-inducible factors (HIFs), which are stabilized and modulate the transcription of various hypoxia-related genes. In addition, many epigenetic regulators, such as DNA methylation, histone modification, histone variants, and adenosine triphosphate-dependent chromatin remodeling factors, play key roles in gene expression. In particular, hypoxic stress influences the activity and gene expression of histone-modifying enzymes, which controls the posttranslational modification of HIFs and histones. This review covers how histone methylation and histone acetylation enzymes modify histone and nonhistone proteins under hypoxic conditions and surveys the impact of epigenetic modifications on gene expression. In addition, future directions in this area are discussed.

New sequencing technologies are revealing how cells respond to hypoxia, insufficient oxygen, by managing gene activation. In multicellular organisms, gene activation is managed by how tightly a section of DNA is wound around proteins called histones; genes in tightly packed regions are inaccessible and inactive, whereas those in looser regions can be activated. Kyunghwan Kim, Sun-Ju Yi, and co-workers at Chungbuk National University in South Korea have reviewed recent data on how cells regulate gene activity under hypoxic conditions. Advances in sequencing technology have allowed genome-wide studies of how hypoxia affects DNA structure and gene activation, revealing that gene-specific modifications may be more important than genome-wide modifications. Hypoxia is implicated in several diseases, such as cancer and chronic metabolic diseases, and a better understanding of how it affects gene activation may help identify new treatments for hypoxia-related diseases.

Inhibition of Histone Deacetylase 6 (HDAC6) as a therapeutic strategy for Alzheimer's disease: A review (2010-2020)

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders, which is characterized by the primary risk factor, age. Several attempts have been made to treat AD, while most of them end in failure. However, with the deepening study of pathogenesis of AD, the expression of HDAC6 in the hippocampus, which plays a major role of the memory formation, is becoming worth of notice. Neurofibrillary tangles (NFTs), a remarkable lesion in AD, has been characterized in association with the abnormal accumulation of hyperphosphorylated Tau, which is mainly caused by the high expression of HDAC6. On the other hand, the hypoacetylated tubulin induced by HDAC6 is also fatal for the neuronal transport, which is the key impact of the formation of axons and dendrites. Overall, the significantly increased expression of HDAC6 in brain regions is deleterious to neuron survival in AD patients. Based on the above research, the inhibition of HDAC6 seems to be a potential therapeutic method for the treatment of AD. Up to now, various types of HDAC6 inhibitors have been discovered. This review mainly analyzes the HDAC6 inhibitors reported amid 2010-2020 in terms of their structure, selectivity and pharmacological impact towards AD. And we aim at facilitating the design and development of better HDAC6 inhibitors in the future.

Posttranslational modification and beyond: interplay between histone deacetylase 6 and heat-shock protein 90

Posttranslational modification (PTM) and regulation of protein stability are crucial to various biological processes. Histone deacetylase 6 (HDAC6), a unique histone deacetylase with two functional catalytic domains (DD1 and DD2) and a ZnF-UBP domain (ubiquitin binding domain, BUZ), regulates a number of biological processes, including gene expression, cell motility, immune response, and the degradation of misfolded proteins. In addition to the deacetylation of histones, other nonhistone proteins have been identified as substrates for HDAC6. Hsp90, a molecular chaperone that is a critical modulator of cell signaling, is one of the lysine deacetylase substrates of HDAC6. Intriguingly, as one of the best-characterized regulators of Hsp90 acetylation, HDAC6 is the client protein of Hsp90. In addition to regulating Hsp90 at the post-translational modification level, HDAC6 also regulates Hsp90 at the gene transcription level. HDAC6 mainly regulates the Hsp90-HSF1 complex through the ZnF-UBP domain, thereby promoting the HSF1 entry into the nucleus and activating gene transcription. The mutual interaction between HDAC6 and Hsp90 plays an important role in the regulation of protein stability, cell migration, apoptosis and other functions. Plenty of of studies have indicated that blocking HDAC6/Hsp90 has a vital regulatory role in multifarious diseases, mainly in cancers. Therefore, developing inhibitors or drugs against HDAC6/Hsp90 becomes a promising development direction. Herein, we review the current knowledge on molecular regulatory mechanisms based on the interaction of HDAC6 and Hsp90 and inhibition of HDAC6 and/or Hsp90 in oncogenesis and progression, antiviral and immune-related diseases and other vital biological processes.

HDAC6-Selective Inhibitor Overcomes Bortezomib Resistance in Multiple Myeloma

Although multiple myeloma (MM) patients benefit from standard bortezomib (BTZ) chemotherapy, they develop drug resistance, resulting in relapse. We investigated whether histone deacetylase 6 (HDAC6) inhibitor A452 overcomes bortezomib resistance in MM. We show that HDAC6-selective inhibitor A452 significantly decreases the activation of BTZ-resistant markers, such as extracellular signal-regulated kinases (ERK) and nuclear factor kappa B (NF-κB), in acquired BTZ-resistant MM cells. Combination treatment of A452 and BTZ or carfilzomib (CFZ) synergistically reduces BTZ-resistant markers. Additionally, A452 synergizes with BTZ or CFZ to inhibit the activation of NF-κB and signal transducer and activator of transcription 3 (STAT3), resulting in decreased expressions of low-molecular-mass polypeptide 2 (LMP2) and LMP7. Furthermore, combining A452 with BTZ or CFZ leads to synergistic cancer cell growth inhibition, viability decreases, and apoptosis induction in the BTZ-resistant MM cells. Overall, the synergistic effect of A452 with CFZ is more potent than that of A452 with BTZ in BTZ-resistant U266 cells. Thus, our findings reveal the HDAC6-selective inhibitor as a promising therapy for BTZ-chemoresistant MM.

Selective Histone Deacetylase 6 Inhibitors Restore Cone Photoreceptor Vision or Outer Segment Morphology in Zebrafish and Mouse Models of Retinal Blindness

Blindness arising from retinal or macular degeneration results in significant social, health and economic burden. While approved treatments exist for neovascular (‘wet’) age-related macular degeneration, new therapeutic targets/interventions are needed for the more prevalent atrophic (‘dry’) form of age-related macular degeneration. Similarly, in inherited retinal diseases, most patients have no access to an effective treatment. Although macular and retinal degenerations are genetically and clinically distinct, common pathological hallmarks can include photoreceptor degeneration, retinal pigment epithelium atrophy, oxidative stress, hypoxia and defective autophagy. Here, we evaluated the potential of selective histone deacetylase 6 inhibitors to preserve retinal morphology or restore vision in zebrafish atp6v0e1^–/– and mouse rd10 models. Histone deacetylase 6 inhibitor, tubastatin A-treated atp6v0e1^–/– zebrafish show marked improvement in photoreceptor outer segment area (44.7%, p = 0.027) and significant improvement in vision (8-fold, p ≤ 0.0001). Tubastatin A-treated rd10/rd10 retinal explants show a significantly (p = 0.016) increased number of outer-segment labeled cone photoreceptors. In vitro, ATP6V0E1 regulated HIF-1α activity, but significant regulation of HIF-1α by histone deacetylase 6 inhibition in the retina was not detected. Proteomic profiling identified ubiquitin-proteasome, phototransduction, metabolism and phagosome as pathways, whose altered expression correlated with histone deacetylase 6 inhibitor mediated restoration of vision.

Hypoxia-induced NAD+ interventions promote tumor survival and metastasis by regulating mitochondrial dynamics

Hypoxia, an important feature of the tumor microenvironment, is responsible for the chemo-resistance and metastasis of malignant solid tumors. Recent studies indicated that mitochondria undergo morphological transitions as an adaptive response to maintain self-stability and connectivity under hypoxic conditions. NAD⁺ may not only provide reducing equivalents for biosynthetic reactions and in determining energy production, but also functions as a signaling molecule in mitochondrial dynamics regulation. In this review, we describe the upregulated KDAC deacetylase expression in the mitochondria and cytoplasm of tumor cells that results from sensing the changes in NAD⁺ to control mitochondrial dynamics and distribution, which is responsible for survival and metastasis in hypoxia.

Pseudophosphatase MK-STYX: the atypical member of the MAP kinase phosphatases

The regulation of the phosphorylation of mitogen-activated protein kinases (MAPKs) is essential for cellular processes such as proliferation, differentiation, survival, and death. Mutations within the MAPK signaling cascades are implicated in diseases such as cancer, neurodegenerative disorders, arthritis, obesity, and diabetes. MAPK phosphorylation is controlled by an intricate balance between MAPK kinases (enzymes that add phosphate groups) and MAPK phosphatases (MKPs) (enzymes that remove phosphate groups). MKPs are complex negative regulators of the MAPK pathway that control the amplitude and spatiotemporal regulation of MAPKs. MK-STYX (MAPK phosphoserine/threonine/tyrosine-binding protein) is a member of the MKP subfamily, which lacks the critical histidine and nucleophilic cysteine residues in the active site required for catalysis. MK-STYX does not influence the phosphorylation status of MAPK, but even so it adds to the complexity of signal transduction cascades as a signaling regulator. This review highlights the function of MK-STYX, providing insight into MK-STYX as a signal regulating molecule in the stress response, HDAC 6 dynamics, apoptosis, and neurite differentiation.

HDAC6-specific inhibitor suppresses Th17 cell function via the HIF-1α pathway in acute lung allograft rejection in mice

Background: Previous animal experiments and clinical studies indicated the critical role of Th17 cells in lung transplant rejection. Therefore, the downregulation of Th17 cell function in lung transplant recipients is of great interest. Methods: We established an orthotopic mouse lung transplantation model to investigate the role of histone deacetylase 6-specific inhibitor (HDAC6i), Tubastatin A, in the suppression of Th17 cells and attenuation of pathologic lesions in lung allografts. Moreover, mechanism studies were conducted in vitro. Results: Tubastatin A downregulated Th17 cell function in acute lung allograft rejection, prolonged the survival of lung allografts, and attenuated acute rejection by suppressing Th17 cell accumulation. Consistently, exogenous IL-17A supplementation eliminated the protective effect of Tubastatin A. Also, hypoxia-inducible factor-1α (HIF-1α) was overexpressed in a lung transplantation mouse model. HIF-1α deficiency suppressed Th17 cell function and attenuated lung allograft rejection by downregulating retinoic acid-related orphan receptor γt (ROR γt) expression. We showed that HDAC6i downregulated HIF-1α transcriptional activity under Th17-skewing conditions in vitro and promoted HIF-1α protein degradation in lung allografts. HDAC6i did not affect the suppression of HIF-1α^-/- naïve CD4⁺ T cell differentiation into Th17 cell and attenuation of acute lung allograft rejection in HIF-1α-deficient recipient mice. Conclusion: These findings suggest that Tubastatin A downregulates Th17 cell function and suppresses acute lung allograft rejection, at least partially, via the HIF-1α/ RORγt pathway.

Multiple distinct pathways lead to hyperubiquitylated insoluble TDP-43 protein independent of its translocation into stress granules

Insoluble, hyperubiquitylated TAR DNA-binding protein of 43 kDa (TDP-43) in the central nervous system characterizes frontotemporal dementia and ALS in many individuals with these neurodegenerative diseases. The causes for neuropathological TDP-43 aggregation are unknown, but it has been suggested that stress granule (SG) formation is important in this process. Indeed, in human embryonic kidney HEK293E cells, various SG-forming conditions induced very strong TDP-43 ubiquitylation, insolubility, and reduced splicing activity. Osmotic stress-induced SG formation and TDP-43 ubiquitylation occurred rapidly and coincided with colocalization of TDP-43 and SG markers. Washout experiments confirmed the rapid dissolution of SGs, accompanied by normalization of TDP-43 ubiquitylation and solubility. Surprisingly, interference with the SG process using a protein kinase R-like endoplasmic reticulum kinase inhibitor (GSK2606414) or the translation blocker emetine did not prevent TDP-43 ubiquitylation and insolubility. Thus, parallel pathways may lead to pathological TDP-43 modifications independent of SG formation. Using a panel of kinase inhibitors targeting signaling pathways of the osmotic shock inducer sorbitol, we could largely rule out the stress-activated and extracellular signal-regulated protein kinase modules and glycogen synthase kinase 3β. For arsenite, but not for sorbitol, quenching oxidative stress with N-acetylcysteine did suppress both SG formation and TDP-43 ubiquitylation and insolubility. Thus, sodium arsenite appears to promote SG formation and TDP-43 modifications via oxidative stress, but sorbitol stimulates TDP-43 ubiquitylation and insolubility via a novel pathway(s) independent of SG formation. In conclusion, pathological TDP-43 modifications can be mediated via multiple distinct pathways for which SGs are not essential.

Pseudophosphatase MK-STYX Alters Histone Deacetylase 6 Cytoplasmic Localization, Decreases Its Phosphorylation, and Increases Detyrosination of Tubulin

The catalytically inactive mitogen-activated protein (MAP) kinase phosphatase, MK-STYX (MAPK (mitogen-activated protein kinase) phosphoserine/threonine/tyrosine-binding protein) interacts with the stress granule nucleator G3BP-1 (Ras-GAP (GTPase-activating protein) SH3 (Src homology 3) domain-binding protein-1), and decreases stress granule (stalled mRNA) formation. Histone deacetylase isoform 6 (HDAC6) also binds G3BP-1 and serves as a major component of stress granules. The discovery that MK-STYX and HDAC6 both interact with G3BP-1 led us to investigate the effects of MK-STYX on HDAC6 dynamics. In control HEK/293 cells, HDAC6 was cytosolic, as expected, and formed aggregates under conditions of stress. In contrast, in cells overexpressing MK-STYX, HDAC6 was both nuclear and cytosolic and the number of stress-induced aggregates significantly decreased. Immunoblots showed that MK-STYX decreases HDAC6 serine phosphorylation, protein tyrosine phosphorylation, and lysine acetylation. HDAC6 is known to regulate microtubule dynamics to form aggregates. MK-STYX did not affect the organization of microtubules, but did affect their post-translational modification. Tubulin acetylation was increased in the presence of MK-STYX. In addition, the detyrosination of tubulin was significantly increased in the presence of MK-STYX. These findings show that MK-STYX decreases the number of HDAC6-containing aggregates and alters their localization, sustains microtubule acetylation, and increases detyrosination of microtubules, implicating MK-STYX as a signaling molecule in HDAC6 activity.

Anti-cancer effects of naturally derived compounds targeting histone deacetylase 6-related pathways

Alterations of the epigenetic machinery, affecting multiple biological functions, represent a major hallmark enabling the development of tumors. Among epigenetic regulatory proteins, histone deacetylase (HDAC)6 has emerged as an interesting potential therapeutic target towards a variety of diseases including cancer. Accordingly, this isoenzyme regulates many vital cellular regulatory processes and pathways essential to physiological homeostasis, as well as tumor multistep transformation involving initiation, promotion, progression and metastasis. In this review, we will consequently discuss the critical implications of HDAC6 in distinct mechanisms relevant to physiological and cancerous conditions, as well as the anticancer properties of synthetic, natural and natural-derived compounds through the modulation of HDAC6-related pathways.