Signaling coupled epigenomic regulation of gene expression

Nuclear functions regulated by the VRK1 kinase

In the nucleus, the VRK1 Ser-Thr kinase is distributed in nucleoplasm and chromatin, where it has different roles. VRK1 expression increases in response to mitogenic signals. VRK1 regulates cyclin D1 expression at G0 exit and facilitates chromosome condensation at the end of G2 and G2/M progression to mitosis. These effects are mediated by the phosphorylation of histone H3 at Thr3 by VRK1, and later in mitosis by haspin. VRK1 regulates the apigenetic patterns of histones in processes requiring chromating remodeling, such as transcription, replication and DNA repair. VRK1 is overexpressed in tumors, facilitating tumor progression and resistance to genotoxic treatments. VRK1 also regulates the organization of Cajal bodies assembled on coilin, which are necessary for the assembly of different types of RNP complexes. VRK1 pathogenic variants cuase defects in Cajal bodies, functionally altering neurons with long axons and leading to neurological diseases, such as amyotrophic laterla sclerosis, spinal muscular atrophy, distal hereditay motor neuropathies and Charcot-Marie-Tooth.

The Revelation of Continuously Organized, Co-Overexpressed Protein-Coding Genes with Roles in Cellular Communications in Breast Cancer

Many human cancers, including breast cancer, are polygenic and involve the co-dysregulation of multiple regulatory molecules and pathways. Though the overexpression of genes and amplified chromosomal regions have been closely linked in breast cancer, the notion of the co-upregulation of genes at a single locus remains poorly described. Here, we describe the co-overexpression of 34 continuously organized protein-coding genes with diverse functions at 8q.24.3(143437655-144326919) in breast and other cancer types, the CanCord34 genes. In total, 10 out of 34 genes have not been reported to be overexpressed in breast cancer. Interestingly, the overexpression of CanCord34 genes is not necessarily associated with genomic amplification and is independent of hormonal or HER2 status in breast cancer. CanCord34 genes exhibit diverse known and predicted functions, including enzymatic activities, cell viability, multipotency, cancer stem cells, and secretory activities, including extracellular vesicles. The co-overexpression of 33 of the CanCord34 genes in a multivariant analysis was correlated with poor survival among patients with breast cancer. The analysis of the genome-wide RNAi functional screening, cell dependency fitness, and breast cancer stem cell databases indicated that three diverse overexpressed CanCord34 genes, including a component of spliceosome PUF60, a component of exosome complex EXOSC4, and a ribosomal biogenesis factor BOP1, shared roles in cell viability, cell fitness, and stem cell phenotypes. In addition, 17 of the CanCord34 genes were found in the microvesicles (MVs) secreted from the mesenchymal stem cells that were primed with MDA-MB-231 breast cancer cells. Since these MVs were important in the chemoresistance and dedifferentiation of breast cancer cells into cancer stem cells, these findings highlight the significance of the CanCord34 genes in cellular communications. In brief, the persistent co-overexpression of CanCord34 genes with diverse functions can lead to the dysregulation of complementary functions in breast cancer. In brief, the present study provides new insights into the polygenic nature of breast cancer and opens new research avenues for basic, preclinical, and therapeutic studies in human cancer.

Epicardial HDAC3 Promotes Myocardial Growth Through a Novel MicroRNA Pathway

BACKGROUND

Establishment of the myocardial wall requires proper growth cues from nonmyocardial tissues. During heart development, the epicardium and epicardium-derived cells instruct myocardial growth by secreting essential factors including FGF (fibroblast growth factor) 9 and IGF (insulin-like growth factor) 2. However, it is poorly understood how the epicardial secreted factors are regulated, in particular by chromatin modifications for myocardial formation. The current study is to investigate whether and how HDAC (histone deacetylase) 3 in the developing epicardium regulates myocardial growth.

METHODS

Various cellular and mouse models in conjunction with biochemical and molecular tools were employed to study the role of HDAC3 in the developing epicardium.

RESULTS

We deleted Hdac3 in the developing murine epicardium, and mutant hearts showed ventricular myocardial wall hypoplasia with reduction of epicardium-derived cells. The cultured embryonic cardiomyocytes with supernatants from Hdac3 knockout (KO) mouse epicardial cells also showed decreased proliferation. Genome-wide transcriptomic analysis revealed that Fgf9 and Igf2 were significantly downregulated in Hdac3 KO mouse epicardial cells. We further found that Fgf9 and Igf2 expression is dependent on HDAC3 deacetylase activity. The supplementation of FGF9 or IGF2 can rescue the myocardial proliferation defects treated by Hdac3 KO supernatant. Mechanistically, we identified that microRNA (miR)-322 and miR-503 were upregulated in Hdac3 KO mouse epicardial cells and Hdac3 epicardial KO hearts. Overexpression of miR-322 or miR-503 repressed FGF9 and IGF2 expression, while knockdown of miR-322 or miR-503 restored FGF9 and IGF2 expression in Hdac3 KO mouse epicardial cells.

CONCLUSIONS

Our findings reveal a critical signaling pathway in which epicardial HDAC3 promotes compact myocardial growth by stimulating FGF9 and IGF2 through repressing miR-322 or miR-503, providing novel insights in elucidating the etiology of congenital heart defects and conceptual strategies to promote myocardial regeneration.

Connections between metabolism and epigenetic modifications in cancer

How cells sense and respond to environmental changes is still a key question. It has been identified that cellular metabolism is an important modifier of various epigenetic modifications, such as DNA methylation, histone methylation and acetylation and RNA N6-methyladenosine (m6A) methylation. This closely links the environmental nutrient availability to the maintenance of chromatin structure and gene expression, and is crucial to regulate cellular homeostasis, cell growth and differentiation. Cancer metabolic reprogramming and epigenetic alterations are widely observed, and facilitate cancer development and progression. In cancer cells, oncogenic signaling-driven metabolic reprogramming modifies the epigenetic landscape via changes in the key metabolite levels. In this review, we briefly summarized the current evidence that the abundance of key metabolites, such as S-adenosyl methionine (SAM), acetyl-CoA, α-ketoglutarate (α-KG), 2-hydroxyglutarate (2-HG), uridine diphospho-N-acetylglucosamine (UDP-GlcNAc) and lactate, affected by metabolic reprogramming plays an important role in dynamically regulating epigenetic modifications in cancer. An improved understanding of the roles of metabolic reprogramming in epigenetic regulation can contribute to uncover the underlying mechanisms of metabolic reprogramming in cancer development and identify the potential targets for cancer therapies.

Prognostic Significance of Dysregulated Epigenomic and Chromatin Modifiers in Cervical Cancer

To broaden the understanding of the epigenomic and chromatin regulation of cervical cancer, we examined the status and significance of a set of epigenomic and chromatin modifiers in cervical cancer using computational biology. We observed that 61 of 917 epigenomic and/or chromatin regulators are differentially upregulated in human cancer, including 25 upregulated in invasive squamous cell carcinomas and 29 in cervical intraepithelial neoplasia 3 (CIN3), of which 14 are upregulated in cervical intraepithelial neoplasia 2 (CIN2). Interestingly, 57 of such regulators are uniquely upregulated in cervical cancer, but not ovarian and endometrial cancers. The observed overexpression of 57 regulators was found to have a prognostic significance in cervical cancer. The collective overexpression of these regulators, as well as its subsets belonging to specific histone modifications and corresponding top ten positively co-overexpressed genes, correlated with reduced survival of patients with high expressions of the tested overexpressed regulators compared to cases with low expressions. Using cell-dependency datasets from human cervical cancer cells, we found that 20 out of 57 epigenomic and chromatin regulators studied here appeared to be essential genes, as the depletion of these genes was accompanied by the loss in cellular viability. In brief, the results presented here provide further insights into the role of epigenomic and chromatin regulators in the oncobiology of cervical cancer and broaden the list of new potential molecules of therapeutic importance.

Roles of lncRNA MAGI2-AS3 in human cancers

Long noncoding RNAs (lncRNAs) are noncoding RNAs more than 200 nucleotides in length. A growing number of reports indicate that lncRNAs play a key role in multiple cancers by serving as oncogenes or tumor suppressor genes. MAGI2 antisense RNA 3 (MAGI2-AS3) is ubiquitously expressed in human cancers, and the level of MAGI2-AS3 expression is associated with the progression and prognosis of cancers. Moreover, dysregulation of MAGI2-AS3 has been found to regulate cancer cell proliferation, cell death, invasion and metastasis and treatment resistance by serving as a competing endogenous RNA (ceRNA), epigenomic regulator, and transcriptional regulator. Moreover, increasing evidence shows that MAGI2-AS3 may be a potential biomarker for cancer prognosis and a potential target for cancer therapy. In this review, we summarize current research on the functions, mechanisms and clinical significance of the lncRNA MAGI2-AS3 in cancer development.

The influence of sensory experience on the glutamatergic synapse

The ability of glutamatergic synaptic strength to change in response to prevailing neuronal activity is believed to underlie the capacity of animals, including humans, to learn from experience. This learning better equips animals to safely navigate challenging and potentially harmful environments, while reinforcing behaviours that are conducive to survival. Early descriptions of the influence of experience on behaviour were provided by Donald Hebb who showed that an enriched environment improved performance of rats in a variety of behavioural tasks, challenging the widely-held view at the time that psychological development and intelligence were largely predetermined through genetic inheritance. Subsequent studies in a variety of species provided detailed cellular and molecular insights into the neurobiological adaptations associated with enrichment and its counterparts, isolation and deprivation. Here we review those experience-dependent changes that occur at the glutamatergic synapse, and which likely underlie the enhanced cognition associated with enrichment. We focus on the importance of signalling initiated by the release of BDNF and a prime downstream effector, MSK1, in orchestrating the many structural and functional neuronal adaptations associated with enrichment. In particular we discuss the MSK1-dependent expansion of the dynamic range of the glutamatergic synapse, which may allow enhanced information storage or processing, and the establishment of a genomic homeostasis that may both stabilise the enriched brain, and may make it better able to respond to novel experiences.

Apoptotic mechanisms of gastric cancer cells induced by isolated erinacine S through epigenetic histone H3 methylation of FasL and TRAIL

Erinacine S, the new bioactive diterpenoid compound isolated from the ethanol extract of the mycelia of Hericium erinaceus, displays great health-promoting properties. However, the effects of erinacine S on inductive apoptosis in cancer cells such as gastric cancer and its molecular mechanisms remain unclear. Our results demonstrated that erinacine S treatment significantly induces cell apoptosis with increased ROS production in gastric cancer cells, but not in normal cells. Significantly, erinacine S also showed its inhibitory effects on tumor growth in an in vivo xenograft mouse model. Furthermore, immunohistochemical analyses revealed that erinacine S treatment significantly increases the FasL and TRAIL protein, whereas it decreases the levels of PCNA and cyclin D1 in the gastric cancer xenograft mice. Consistently, in AGS cells, erinacine S treatment not only triggers the activation of extrinsic apoptosis pathways (TRAIL, Fas-L and caspase-8, -9, -3), but it also suppresses the expression of the anti-apoptotic molecules Bcl-2 and Bcl-XL in a time-dependent manner. In addition, erinacine S also causes cell cycle G1 arrest by the inactivation of CDKs/cyclins. Moreover, our data revealed that activation of the ROS-derived and AKT/FAK/PAK1 pathways is involved in the erinacine S-mediated transcriptional activation of Fas-L and TRAIL through H3K4 trimethylation on their promoters. Together, this study sheds light on the anticancer effects of erinacine S on gastric cancer and its molecular mechanism in vitro and in vivo.

25-Hydroxycholesterol 3-sulfate is an endogenous ligand of DNA methyltransferases in hepatocytes

The oxysterol sulfate, 25-hydroxycholesterol 3-sulfate (25HC3S), has been shown to play an important role in lipid metabolism, inflammatory response, and cell survival. However, the mechanism(s) of its function in global regulation is unknown. The current study investigates the molecular mechanism by which 25HC3S functions as an endogenous epigenetic regulator. To study the effects of oxysterols/sterol sulfates on epigenetic modulators, 12 recombinant epigenetic enzymes were used to determine whether 25HC3S acts as their endogenous ligand. The enzyme kinetic study demonstrated that 25HC3S specifically inhibited DNA methyltransferases (DNMTs), DNMT1, DNMT3a, and DNMT3b with IC₅₀ of 4.04, 3.03, and 9.05 × 10^-6 M, respectively. In human hepatocytes, high glucose induces lipid accumulation by increasing promoter CpG methylation of key genes involved in development of nonalcoholic fatty liver diseases. Using this model, whole genome bisulfate sequencing analysis demonstrated that 25HC3S converts the ^5mCpG to CpG in the promoter regions of 1,074 genes. In addition, we observed increased expression of the demethylated genes, which are involved in the master signaling pathways, including MAPK-ERK, calcium-AMP-activated protein kinase, and type II diabetes mellitus pathways. mRNA array analysis showed that the upregulated genes encoded for key elements of cell survival; conversely, downregulated genes encoded for key enzymes that decrease lipid biosynthesis. Taken together, our results indicate that the expression of these key elements and enzymes are regulated by the demethylated signaling pathways. We summarized that 25HC3S DNA demethylation of ^5mCpG in promoter regions is a potent regulatory mechanism.

Epigenetics in hepatocellular carcinoma development and therapy: The tip of the iceberg

Hepatocellular carcinoma (HCC) is a deadly tumour whose causative agents are generally well known, but whose pathogenesis remains poorly understood. Nevertheless, key genetic alterations are emerging from a heterogeneous molecular landscape, providing information on the tumorigenic process from initiation to progression. Among these molecular alterations, those that affect epigenetic processes are increasingly recognised as contributing to carcinogenesis from preneoplastic stages. The epigenetic machinery regulates gene expression through intertwined and partially characterised circuits involving chromatin remodelers, covalent DNA and histone modifications, and dedicated proteins reading these modifications. In this review, we summarise recent findings on HCC epigenetics, focusing mainly on changes in DNA and histone modifications and their carcinogenic implications. We also discuss the potential drugs that target epigenetic mechanisms for HCC treatment, either alone or in combination with current therapies, including immunotherapies.

SARS-CoV-2 multifaceted interaction with the human host. Part II: Innate immunity response, immunopathology, and epigenetics

The SARS-CoV-2 makes its way into the cell via the ACE2 receptor and the proteolytic action of TMPRSS2. In response to the SARS-CoV-2 infection, the innate immune response is the first line of defense, triggering multiple signaling pathways to produce interferons, pro-inflammatory cytokines and chemokines, and initiating the adaptive immune response against the virus. Unsurprisingly, the virus has developed strategies to evade detection, which can result in delayed, excessive activation of the innate immune system. The response elicited by the host depends on multiple factors, including health status, age, and sex. An overactive innate immune response can lead to a cytokine storm, inflammation, and vascular disruption, leading to the vast array of symptoms exhibited by COVID-19 patients. What is known about the expression and epigenetic regulation of the ACE2 gene and the various players in the host response are explored in this review.

SARS-CoV-2 multifaceted interaction with human host. Part I: What we have learnt and done so far, and the still unknown realities

SARS-CoV-2, the causing agent of the ongoing COVID-19 pandemic, is a beta-coronavirus which has 80% genetic homology with SARS-CoV, but displays increased virulence and transmissibility. Initially, SARS-CoV-2 was considered a respiratory virus generally causing a mild disease, only severe and fatal in the elderly and individuals with underlying conditions. Severe illnesses and fatalities were attributed to a cytokine storm, an excessive response from the host immune system. However, with the number of infections over 10 millions and still soaring, the insidious and stealthy nature of the virus has emerged, as it causes a vast array of diverse unexpected symptoms among infected individuals, including the young and healthy. It has become evident that besides infecting the respiratory tract, SARS-CoV-2 can affect many organs, possibly through the infection of the endothelium. This review presents an overview of our learning curve with the novel virus emergence, transmission, pathology, biological properties and host-interactions. It also briefly describes remedial measures taken until an effective vaccine is available, that is non-pharmaceutical interventions to reduce the viral spread and the repurposing of existing drugs, approved or in development for other conditions to eliminate the virus or mitigate the cytokine storm.

Coordinated dysregulation of cancer progression by the HER family and p21-activated kinases

Most epithelial cancer types are polygenic in nature and are driven by coordinated dysregulation of multiple regulatory pathways, genes, and protein modifications. The process of coordinated regulation of cancer promoting pathways in response to extrinsic and intrinsic signals facilitates the dysregulation of several pathways with complementary functions, contributing to the hallmarks of cancer. Dysregulation and hyperactivation of cell surface human epidermal growth factor receptors (HERs) and cytoskeleton remodeling by p21-activated kinases (PAKs) are two prominent interconnected aspects of oncogenesis. We briefly discuss the discoveries and significant advances in the area of coordinated regulation of HERs and PAKs in the development and progression of breast and other epithelial cancers. We also discuss how initial studies involving heregulin signaling via HER3-HER2 axis and HER2-overexpressing breast cancer cells not only discovered a mechanistic role of PAK1 in breast cancer pathobiology but also acted as a bridge in generating a broader cancer research interest in other PAK family members and cancer types and catalyzed establishing the role of PAKs in human cancer, at-large. In addition, growth factor stimulation of the PAK pathway also helped to recognize new facets of PAKs, connecting the PAK pathway to oncogenesis, nuclear signaling, gene expression, mitotic progression, DNA damage response, among other phenotypic responses, and shaped the field of PAK cancer research. Finally, we recount some of the current limitations of HER- and PAK-directed therapeutics in counteracting acquired therapeutic resistance and discuss how cancer's as a polygenic disease may be best targeted with a polygenic approach.

Epigenetic Dysregulation at the Crossroad of Women's Cancer

An increasingly number of women of all age groups are affected by cancer, despite substantial progress in our understanding of cancer pathobiology, the underlying genomic alterations and signaling cascades, and cellular-environmental interactions. Though our understanding of women’s cancer is far more complete than ever before, there is no comprehensive model to explain the reasons behind the increased incidents of certain reproductive cancer among older as well as younger women. It is generally suspected that environmental and life-style factors affecting hormonal and growth control pathways might help account for the rise of women’s cancers in younger age, as well, via epigenetic mechanisms. Epigenetic regulators play an important role in orchestrating an orderly coordination of cellular signals in gene activity in response to upstream signaling and/or epigenetic modifiers present in a dynamic extracellular milieu. Here we will discuss the broad principles of epigenetic regulation of DNA methylation and demethylation, histone acetylation and deacetylation, and RNA methylation in women’s cancers in the context of gene expression, hormonal action, and the EGFR family of cell surface receptor tyrosine kinases. We anticipate that a better understanding of the epigenetics of women’s cancers may provide new regulatory leads and further fuel the development of new epigenetic biomarkers and therapeutic approaches.

A Tribute to John Mendelsohn: A Pioneer in Targeted Cancer Therapy

Cancer scientists and clinicians are mourning the death of one of the most accomplished members of their community: Dr. John Mendelsohn. He was a pioneer in targeted cancer therapy and was instrumental for the discovery and deployment of the first antagonist epidermal growth factor receptor (EGFR) therapeutic antibodies, broadening the concept of targeted EGFR therapy to encompass other receptor tyrosine kinases, such as HER2, and developing blocking antibody-combination therapy with chemotherapies or radiotherapy. Dr. Mendelsohn, who died on January 7, 2019, always led by the strength of his accomplishments and the humility of his character. Above all, he was a well-revered mentor and clinician, who extended compassion and the gift of his time to patients, colleagues, and mentees alike. In tribute to Dr. Mendelsohn, Cancer Research has invited his former mentees and colleagues who were associated with Dr. Mendelsohn for over three decades to reflect on the broad impact of his work. Here, we discuss Dr. Mendelsohn's illustrious career at three elite academic cancer institutions and hospitals in the United States, his acumen to build, grow, and uplift institutions, and train a generation of medical oncologists, physician scientists, and cancer biologists. His profound legacy on targeted therapy and cancer research and treatment continue to prolong and save the lives of cancer patients globally.

Cancer Chemoprevention: Classic and Epigenetic Mechanisms Inhibiting Tumorigenesis. What Have We Learned So Far?

Cancers derive from step by step processes which are differentiated by the progressively accumulated mutations. For some tumors there is a clear progressive advancement from benign lesions to malignancy and for these, preventive screening programs exist. In such cases having those benign lesions are a clear indicator of predisposition while for some other cases, familial patterns of cancer incidence and the identification of mutations are the main indicators of higher risk for having the disease. For patients identified as having predisposition, chemoprevention is a goal and in some cases a possibility. Chemoprevention is the use of any compound, either natural or synthetic that abrogates carcinogenesis or tumor progression, through different mechanisms, some of which have already been described. For example, the classic mechanisms may involve activation of free radical scavenging enzymes, control of chronic inflammation, and downregulation of specific signaling pathways. More recently, epigenetics allowed further understanding of the chemopreventive potential of several agents, such as sulforaphane, green tea derived compounds, resveratrol, isoflavones, and others which we exploit in this review article. Throughout the text we discuss the properties compounds should have in order to be classified as chemopreventive ones and the challenges in translational research in this area, as lots of the success achieved in vitro cannot be translated into the clinical settings, due to several different drawbacks, which include toxicity, cost, dose definition, patient adherence, and regimen of use.

Selective Sensing of Phosphorylated Peptides and Monitoring Kinase and Phosphatase Activity with a Supramolecular Tandem Assay

Simple tuning of a host:guest pair allows selective sensing of different peptide modifications, exploiting orthogonal recognition mechanisms. Excellent selectivity for either lysine trimethylations or alcohol phosphorylations is possible by simply varying the fluorophore guest. The phosphorylation sensor can be modulated by the presence of small (μM) concentrations of metal ions, allowing array-based sensing. Phosphorylation at serine, threonine, and tyrosine can be selectively sensed via discriminant analysis. The phosphopeptide sensing is effective in the presence of small-molecule phosphates such as ATP, which in turn enables the sensor to be employed in continuous optical assays of both serine kinase and tyrosine phosphatase activity. The activity of multiple different kinases can be monitored, and the sensor is capable of detecting the phosphorylation of peptides containing multiple different modifications, including lysine methylations and acetylation. A single deep cavitand can be used as a "one size fits all" sensor that can selectively detect multiple different modifications to oligopeptides, as well as monitoring the function of their post-translational modification writer and eraser enzymes in complex systems.

Sublethal β-lactam antibiotics induce PhpP phosphatase expression and StkP kinase phosphorylation in PBP-independent β-lactam antibiotic resistance of Streptococcus pneumoniae

StkP and PhpP of Streptococcus pneumoniae have been confirmed to compose a signaling couple, in which the former is a serine/threonine (Ser/Thr) kinase while the latter was annotated as a phosphotase. StkP has been reported to be involved in penicillin-binding protein (PBP)-independent penicillin resistance of S. pneumoniae. However, the enzymatic characterization of PhpP and the role of PhpP in StkP-PhpP couple remain poorly understood. Here we showed that 1/4 minimal inhibitory concentration (MIC) of penicillin (PCN) or cefotaxime (CTX), the representatives of β-lactam antibiotics, could induce the expression of stkP and phpP genes and phosphorylation of StkP in PCN/CTX-sensitive strain ATCC6306 and three isolates of S. pneumoniae (MICs: 0.02-0.5 μg/ml). The product of phpP gene hydrolyzed PP2C type Ser/Thr phosphotase-specific RRA (pT)VA phosphopeptide substrate with the Km and Kcat values of 277.35 μmoL/L and 0.71 S^-1, and the hydrolytic activity was blocked by sodium fluoride, a PP2C type Ser/Thr phosphatase inhibitor. The phosphorylation levels of StkP in the four phpP gene-knockout (ΔphpP) mutants were significantly higher than that in the wild-type strains. In particular, the MICs of PCN and CTX against the ΔphpP mutants were significantly elevated as 4-16 μg/ml. Therefore, our findings confirmed that sublethal PCN and CTX act as environmental inducers to cause the increase of phpP and stkP gene expression and StkP phosphorylation. PhpP is a PP2C type Ser/Thr protein phosphatase responsible for dephosphorylation of StkP. Knockout of the phpP gene results in a high level of StkP phosphorylation and PBP-independent PCN/CTX resistance of S. pneumoniae.

GR-regulating Serine/Threonine Kinases: New Physiologic and Pathologic Implications

Glucocorticoid hormones, end products of the hypothalamic-pituitary-adrenal axis, virtually influence all human functions both in a basal homeostatic condition and under stress. The glucocorticoid receptor (GR), a nuclear hormone receptor superfamily protein, mediates these actions of glucocorticoids by acting as a ligand-dependent transcription factor. Because glucocorticoid actions are diverse and strong, many biological pathways adjust them in local tissues by targeting the GR signaling pathway as part of the regulatory loop coordinating complex human functions. Phosphorylation of GR protein by serine/threonine kinases is one of the major regulatory mechanisms for this communication. In this review, recent progress in research investigating GR phosphorylation by these kinases is discussed, along with the possible physiologic and pathophysiologic implications.

HDAC6 inhibition induces glioma stem cells differentiation and enhances cellular radiation sensitivity through the SHH/Gli1 signaling pathway

The existence of small numbers of stem-like cells, called glioma stem cells (GSCs), in human glioblastoma multiforme (GBM) is responsible for recurrence due to resistance to radiotherapy and chemotherapy. Inhibition of histone deacetylase 6 (HDAC6) enhanced radiosensitivity of cancer cells. However, the effect of inhibiting HDAC6 on stemness and radioresistance of GSCs and its molecular mechanism are largely unknown. In the present study, we found that HDAC6 was upregulated in GSCs comparing to non-stem tumor cells. Inhibiting HDAC6 downregulated glioma-associated oncogene homolog 1 (Gli1), Patched (Ptch1 and Ptch2) receptors, components of SHH signal, expression and activity in GSCs. Restraining HDAC6 decreased cell proliferation, induces differentiation and increased apoptosis of GSCs via inactivation of SHH/Gli1 signaling pathway. Moreover, HDAC6 inhibition decreased DNA damage repair capacity of GSCs through degradation of checkpoint kinase (CHK) 1 caused by X-linked inhibitor of apoptosis (XIAP) downregulation, leading to elevated radiosensitivity. Taken together, these findings indicate that HDAC6 inhibition decreased stemness of GSCs and enhanced GSCs radiosensitivity through inactivating SHH/Gli1 pathway. This provides a promising novel drug target to overcome GSCs stemness and radioresistance.