Histone deacetylase 6-mediated downregulation of TMEM100 expedites the development and progression of non-small cell lung cancer.

The significance of epigenetic modulation, involving acetylation, methylation, as well as ubiquitination has been indicated in the regulation of gene expression and tumor progression. Here, we elucidated the role of histone deacetylase 6 (HDAC6) in regulating epithelial-mesenchymal transition (EMT)-mediated metastasis via mRNA in non-small cell lung cancer (NSCLC). Three microarrays associated with lung cancer metastasis or recurrence, GSE23361, GSE7880 and GSE162102, were downloaded from the GEO database. Transmembrane protein 100 (TMEM100) was revealed to be the only one mRNA that was significantly downregulated in three microarrays. TMEM100, poorly expressed in lung cancer tissues, was associated with poor prognosis of lung cancer patients. Moreover, TMEM100 transcription was regulated by HDAC6 which repressed TMEM100 expression by deacetylation modification on the TMEM100 promoter. Knockdown of HDAC6 or overexpression of TMEM100 in NSCLC cells significantly inhibited TGF-ß1-induced EMT and metastasis and suppressed the activation of Wnt/ß-catenin signaling pathway. Altogether, our study highlights HDAC6 as a lung cancer metastasis supporter through the suppression of TMEM100 and the induction of Wnt/ß-catenin signaling pathway.

HDAC6 inhibitors sensitize non-mesenchymal triple-negative breast cancer cells to cysteine deprivation.

Triple-negative breast cancer (TNBC) is a highly malignant type of breast cancer and lacks effective therapy. Targeting cysteine-dependence is an emerging strategy to treat the mesenchymal TNBC. However, many TNBC cells are non-mesenchymal and unresponsive to cysteine deprivation. To overcome such resistance, three selective HDAC6 inhibitors (Tubacin, CAY10603, and Tubastatin A), identified by epigenetic compound library screening, can synergize with cysteine deprivation to induce cell death in the non-mesenchymal TNBC. Despite the efficacy of HDAC6 inhibitor, knockout of HDAC6 did not mimic the synthetic lethality induced by its inhibitors, indicating that HDAC6 is not the actual target of HDAC6 inhibitor in this context. Instead, transcriptomic profiling showed that tubacin triggers an extensive gene transcriptional program in combination with erastin, a cysteine transport blocker. Notably, the zinc-related gene response along with an increase of labile zinc was induced in cells by the combination treatment. The disturbance of zinc homeostasis was driven by PKCγ activation, which revealed that the PKCγ signaling pathway is required for HDAC6 inhibitor-mediated synthetic lethality. Overall, our study identifies a novel function of HDAC6 inhibitors that function as potent sensitizers of cysteine deprivation and are capable of abolishing cysteine-independence in non-mesenchymal TNBC.

Up-regulation of HDAC6 Results in Poor Prognosis and Chemoresistance in Patients With Advanced Ovarian High-grade Serous Carcinoma.

BACKGROUND: Ovarian high-grade serous carcinoma (HGSC) gradually acquires chemoresistance after recurrence. Our previous study on ovarian clear-cell carcinoma found histone deacetylase 6 (HDAC6) overexpression led to chemoresistance. This study aimed to evaluate HDAC6 as a predictor of chemoresistance and a therapeutic target for ovarian HGSC. PATIENTS AND METHODS: The clinical significance of HDAC6 as a predictor of prognosis and chemoresistance in HGSC was immunohistochemically evaluated. In addition, expression of programmed cell death ligand-1 (PD-L1), and hypoxia-inducible factor-1α (HIF1α) were analyzed using clinical samples from 88 patients with ovarian HGSC, and their clinicopathological characteristics were reviewed. RESULTS: Twenty-three patients had high HDAC6 expression, 10 positive PD-L1 expression, and 33 high HIF-1α expression. HDAC6 up-regulation was correlated with not undergoing interval debulking surgery (p<0.001), incomplete surgical resection (p=0.002), and frequent occurrence of stable disease/progressive disease according to the Response Evaluation Criteria in Solid Tumors (p=0.005) criteria. On Kaplan-Meier analysis, high HDAC6 expression was significantly associated with reduced progression-free (p=0.001) and overall (p=0.008) survival. On multivariate analysis, high HDAC6 expression (hazard ratio=1.65, 95% confidence interval 1.03-2.66; p=0.039) and surgery status were independent prognostic factors of progression-free survival. PD-L1 and HIF1α expression positively correlated with that of HDAC6. CONCLUSION: HDAC6 may become a potential therapeutic target in patients with ovarian HGSC since its up-regulation is considered to be associated with a poor prognosis in patients with this cancer.

SLAC2B-dependent microtubule acetylation regulates extracellular matrix-mediated intracellular TM4SF5 traffic to the plasma membranes.

Transmembrane 4 L six family member 5 (TM4SF5) translocates intracellularly and promotes cell migration, but how subcellular TM4SF5 traffic is regulated to guide cellular migration is unknown. We investigated the influences of the extracellular environment and intracellular signaling on the TM4SF5 traffic with regard to migration directionality. Cell adhesion to fibronectin (FN) but not poly-l-lysine enhanced the traffic velocity and straightness of the TM4SF5WT (but not palmitoylation-deficient mutant TM4SF5Pal- ) toward the leading edges, depending on tubulin acetylation. Acetylated-microtubules in SLAC2B-positive cells reached mostly the juxtanuclear regions, but reached-out toward the leading edges upon SLAC2B suppression. TM4SF5 expression caused SLAC2B not to be localized at the leading edges. TM4SF5 colocalization with HDAC6 depended on paxillin expression. The trimeric complex consisting of TM4SF5, HDAC6, and SLAC2B might, thus, be enriched at the perinuclear cytosols toward the leading edges. More TM4SF5WT translocation to the leading edges was possible when acetylated-microtubules reached the frontal edges following HDAC6 inhibition by paxillin presumably at new cell-FN adhesions, leading to persistent cell migration. Collectively, this study revealed that cell-FN adhesion and microtubule acetylation could control intracellular traffic of TM4SF5 vesicles to the leading edges via coordinated actions of paxillin, SLAC2B, and HDAC6, leading to TM4SF5-dependent cell migration.

Alleviation of depression-like behavior in a cystic fibrosis mouse model by Hdac6 depletion.

Cystic fibrosis (CF) patients experience heightened levels of anxiety and depression. Stress from dealing with chronic disease and rigorous treatment regimens certainly are primary contributors to these outcomes. We previously have demonstrated that microtubule alterations in CF are linked to a number of CF phenotypes including growth regulation and inflammatory responses to airway bacterial challenge. Deletion of histone deactelyase 6 (HDAC6), a cytosolic deacetylase that regulates tubulin acetylation, in CF mice restores growth and inflammatory phenotypes to wild type (WT) profiles. In this study, the hypothesis that Hdac6 depletion in CF mice would impact behaviors since Hda6 inhibition has been previously reported to have anti-depressive properties. Data demonstrate that CF mice exhibit reduced activity and reduced open arm time in an elevated plus maze test which can be consistent with anxiety-like behavior. CF mice also exhibit depression-like behaviors compared to WT mice in an age dependent manner. By eight weeks of age, CF mice exhibit significantly more immobile time in the tail-suspension test, however, Hdac6 depletion reverses the depressive phenotype. These data demonstrate that loss of CFTR function may predispose patients to experience depression and that this behavior is Hdac6 dependent.

Honokiol ameliorates angiotensin II-induced hypertension and endothelial dysfunction by inhibiting HDAC6-mediated cystathionine γ-lyase degradation.

Hypertension and endothelial dysfunction are associated with various cardiovascular diseases. Hydrogen sulphide (H2 S) produced by cystathionine γ-lyase (CSE) promotes vascular relaxation and lowers hypertension. Honokiol (HNK), a natural compound in the Magnolia plant, has been shown to retain multifunctional properties such as anti-oxidative and anti-inflammatory activities. However, a potential role of HNK in regulating CSE and hypertension remains largely unknown. Here, we aimed to demonstrate that HNK co-treatment attenuated the vasoconstriction, hypertension and H2 S reduction caused by angiotensin II (AngII), a well-established inducer of hypertension. We previously found that histone deacetylase 6 (HDAC6) mediates AngII-induced deacetylation of CSE, which facilitates its ubiquitination and proteasomal degradation. Our current results indicated that HNK increased endothelial CSE protein levels by enhancing its stability in a sirtuin-3-independent manner. Notably, HNK could increase CSE acetylation levels by inhibiting HDAC6 catalytic activity, thereby blocking the AngII-induced degradative ubiquitination of CSE. CSE acetylation and ubiquitination occurred mainly on the lysine 73 (K73) residue. Conversely, its mutant (K73R) was resistant to both acetylation and ubiquitination, exhibiting higher protein stability than that of wild-type CSE. Collectively, our findings suggested that HNK treatment protects CSE against HDAC6-mediated degradation and may constitute an alternative for preventing endothelial dysfunction and hypertensive disorders.

Novel Selective Histone Deacetylase 6 (HDAC6) Inhibitors: A Patent Review (2016-2019).

BACKGROUND: Many human diseases are associated with dysregulation of HDACs. HDAC6 exhibits deacetylase activity not only to histone protein but also to non-histone proteins such as α- tubulin, HSP90, cortactin, and peroxiredoxin. These unique functions of HDAC6 have gained significant attention in the medicinal chemistry community in recent years. Thus a great deal of effort has devoted to developing selective HDAC6 inhibitors for therapy with the hope to minimize the side effects caused by pan-HDAC inhibition. OBJECTIVE: The review intends to analyze the structural feature of the scaffolds, to provide useful information for those who are interested in this field, as well as to spark the future design of the new inhibitors. METHODS: The primary tool used for patent searching is SciFinder. All patents are retrieved from the following websites: the World Intellectual Property Organization (WIPO®), the United States Patent Trademark Office (USPTO®), Espacenet®, and Google Patents. The years of patents covered in this review are between 2016 and 2019. RESULTS: Thirty-six patents from seventeen companies/academic institutes were classified into three categories based on the structure of ZBG: hydroxamic acid, 1,3,4-oxadiazole, and 1,2,4-oxadiazole. ZBG connects to the cap group through a linker. The cap group can tolerate different functional groups, including amide, urea, sulfonamide, sulfamide, etc. The cap group appears to modulate the selectivity of HDAC6 over other HDAC subtypes. CONCLUSION: Selectively targeting HDAC6 over other subtypes represents two fold advantages: it maximizes the pharmacological effects and minimizes the side effects seen in pan-HDAC inhibitors. Many small molecule selective HDAC6 inhibitors have advanced to clinical studies in recent years. We anticipate the approval of selective HDAC6 inhibitors as therapeutic agents in the near future.

HDAC6 regulates dental mesenchymal stem cells and osteoclast differentiation.

BACKGROUND: Dental and periodontal tissue development is a complicated process involving a finely regulated network of communication among various cell types. Understanding the mechanisms involved in regulating dental mesenchymal stem cells (MSCs) and osteoclast cell differentiation is critical. However, it is still unclear whether histone deacetylase HDAC6 is involved in dental MSCs fate determination and osteoclast differentiation. METHODS: We used shRNA and siRNA knockdown to explore the role of HDAC6 in dental MSCs odontogenic differentiation and osteoclasts maturation. RESULTS: Based on HDAC6 knockdown dental MSCs, our data suggest that HDAC6 knockdown significantly increases alkaline phosphate activity and mineralized nodules formation. Additionally, mRNA expression of odontogenic marker genes (OSX, OCN, and OPN) was induced by HDAC6 knockdown. By using HDAC6 siRNA, we knocked down HDAC6 in osteoclast precursor RAW 264.7 cells. Our data suggests that HDAC6 knockdown significantly inhibited osteoclasts differentiation. Additionally, mRNA expression of osteoclast marker genes Trap, Mmp9, and Ctsk was decreased by HDAC6 knockdown. CONCLUSIONS: Our study demonstrated that HDAC6 plays an important role in regulating dental MSCs and osteoclasts differentiation.

Requirement of HDAC6 for activation of Notch1 by TGF-ß1.

TGF-ß1 is enriched in the tumor microenvironment and acts as a key inducer of epithelial to mesenchymal transition (EMT) in lung cancer. The NOTCH signaling pathway is conserved across species and is an essential pathway for development, cell differentiation, and cancer biology. Dysregulation of Notch signaling is a common feature of non-small cell lung cancer (NSCLC) and is correlated with poor prognosis. Crosstalk exists between the NOTCH and TGF-ß signaling pathways in EMT. Herein we report that histone deacetylase 6 (HDAC6) modulates TGF-ß1-mediated activation of the Notch pathway. HDAC6, a primarily cytoplasmic deacetylase, mediates TGF-ß1-induced EMT in human lung cancer cells. Inhibition of HDAC6 with a small molecule inhibitor, namely tubacin or with siRNA attenuated TGF-ß1-induced Notch-1 signaling. We show that TGFß-1-induced EMT is accompanied by rapid HDAC6-dependent deacetylation of heat shock protein 90 (HSP90). Consistently, inhibition of HSP90 with its small molecule inhibitor 17AAG attenuated expression of TGF-ß1-induced Notch-1 target genes, HEY-1 and HES-1. These findings reveal a novel function of HDAC6 in EMT via mediating the TGF-ß-Notch signaling cascade, and support HDAC6 as a key regulator of TGFß-induced EMT in NSCLC. This work suggests that HDAC6 may be an attractive therapeutic target against tumor progression and metastasis.