Inhibition of H3K9 methyltransferase G9a induces autophagy and apoptosis in oral squamous cell carcinoma

EHMT2 Suppresses ARRB1 Transcription and Activates the Hedgehog Signaling to Promote Malignant Phenotype and Stem Cell Property in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) represents the primary subtype of head and neck squamous cell carcinoma (HNSCC), characterized by a high morbidity and mortality rate. Although previous studies have established specific correlations between euchromatic histone lysine methyltransferase 2 (EHMT2), a histone lysine methyltransferase, and the malignant phenotype of OSCC cells, its biological functions in OSCC remain largely unknown. This study, grounded in bioinformatics predictions, aims to clarify the influence of EHMT2 on the malignant behavior of OSCC cells and delve into the underlying mechanisms. EHMT2 exhibited high expression in OSCC tissues and demonstrated an association with poor patient outcomes. Artificial EHMT2 silencing in OSCC cells, achieved through lentiviral vector infection, significantly inhibited colony formation, migration, invasion, and cell survival. Regarding the mechanism, EHMT2 was found to bind the promoter of arrestin beta 1 (ARRB1), thereby suppressing its transcription through H3K9me2 modification. ARRB1, in turn, was identified as a negative regulator of the Hedgehog pathway, leading to a reduction in the proteins GLI1 and PTCH1. Cancer stem cells (CSCs) were enriched through repeated sphere formation assays in two OSCC cell lines. EHMT2 was found to activate the Hedgehog pathway, thus promoting sphere formation, migration and invasion, survival, and tumorigenic activity of the OSCC-CSCs. Notably, these effects were counteracted by the additional overexpression of ARRB1. In conclusion, this study provides novel evidence suggesting that EHMT2 plays specific roles in enhancing stem cell properties in OSCC by modulating the ARRB1-Hedgehog signaling cascade.

Inhibition of the Tumor Suppressor Gene SPINK5 via EHMT2 Induces the Oral Squamous Cell Carcinoma Development

Serine protease inhibitor Kazal-type 5 (SPINK5) has been revealed as a significant prognostic biomarker in oral squamous cell carcinoma (OSCC). However, there is little information regarding the detailed epigenetics mechanism underlying its dysregulation in OSCC. Using the Gene Expression Omnibus database, we identified SPINK5 as a significantly downregulated gene in OSCC tissues. Moreover, SPINK5 inhibited the malignant aggressiveness of HSC3 and squamous cell carcinomas (SCC)9 cells, whereas depletion of SPINK5 using shRNAs led to the opposite trend. The euchromatic histone lysine methyltransferase 2 (EHMT2) was found to bind to the SPINK5 promoter, and EHMT2 repressed the SPINK5 expression. SPINK5 reversed the stimulating effects of EHMT2 on the aggressiveness of HSC3 and SCC9 cells by impairing the Wnt/β-catenin pathway. Wnt/β-catenin inhibitor IWR-1 treatment reverted the malignant phenotype of OSCC cells in the presence of short hairpin RNA (sh)-SPINK5. Silencing of EHMT2 inhibited tumor growth and blocked the Wnt/β-catenin signaling in OSCC, which was reversed by SPINK5 knockdown. Our study shows that SPINK5, mediated by the loss of EHMT2, can inhibit the development of OSCC by inhibiting Wnt/β-catenin signaling and may serve as a treatment target for OSCC.

Discovery of SDS-347 as a specific peptide competitive inhibitor of G9a with promising anti-cancer potential

BACKGROUND

G9a is a histone H3K9 methyltransferase enzyme found highly upregulated in many cancers. H3 binds to the rigid I-SET domain and the cofactor, S-adenosyl methionine, binds to the flexible post-SET domain of G9a. Inhibition of G9a is known to inhibit the growth of cancer cell-lines.

METHODS

Recombinant G9a and H3 were used to develop radioisotope-based inhibitor screening assay. The identified inhibitor was evaluated for isoform selectivity. The mode of enzymatic inhibition was studied by enzymatic assays and bioinformatics. Anti-proliferative activity of the inhibitor was studied in cancer cell lines by utilizing MTT assay. The mechanism of cell death was studied by western blotting and microscopy.

RESULTS

We developed a robust G9a inhibitor screening assay that led to the discovery of SDS-347 as a potent G9a inhibitor with IC₅₀ of 3.06 μM. It was shown to reduce the levels of H3K9me2 in cell-based assay. The inhibitor was found to be peptide competitive and highly specific as it did not show any significant inhibition of other histone methyltransferases and DNA methyltransferase. Docking studies showed that SDS-347 could form direct bonding interaction with Asp1088 of the peptide-binding site. SDS-347 showed anti-proliferative effect against various cancer cell lines especially the K562 cells. Our data suggested that SDS-347 mediated antiproliferative action via ROS generation, induction of autophagy and apoptosis.

CONCLUSION

Overall, the findings of the current study include development of a new G9a inhibitor screening assay and identification of SDS-347, as a novel, peptide competitive and highly specific G9a inhibitor with promising anticancer potential.

Role and mechanism of FOXG1-related epigenetic modifications in cisplatin-induced hair cell damage

Cisplatin is widely used in clinical tumor chemotherapy but has severe ototoxic side effects, including tinnitus and hearing damage. This study aimed to determine the molecular mechanism underlying cisplatin-induced ototoxicity. In this study, we used CBA/CaJ mice to establish an ototoxicity model of cisplatin-induced hair cell loss, and our results showed that cisplatin treatment could reduce FOXG1 expression and autophagy levels. Additionally, H3K9me2 levels increased in cochlear hair cells after cisplatin administration. Reduced FOXG1 expression caused decreased microRNA (miRNA) expression and autophagy levels, leading to reactive oxygen species (ROS) accumulation and cochlear hair cell death. Inhibiting miRNA expression decreased the autophagy levels of OC-1 cells and significantly increased cellular ROS levels and the apoptosis ratio in vitro. In vitro, overexpression of FOXG1 and its target miRNAs could rescue the cisplatin-induced decrease in autophagy, thereby reducing apoptosis. BIX01294 is an inhibitor of G9a, the enzyme in charge of H3K9me2, and can reduce hair cell damage and rescue the hearing loss caused by cisplatin in vivo. This study demonstrates that FOXG1-related epigenetics plays a role in cisplatin-induced ototoxicity through the autophagy pathway, providing new ideas and intervention targets for treating ototoxicity.

Identification of an Epi-metabolic dependency on EHMT2/G9a in T-cell acute lymphoblastic leukemia

Genomic studies have identified recurrent somatic alterations in genes involved in DNA methylation and post-translational histone modifications in acute lymphoblastic leukemia (ALL), suggesting new opportunities for therapeutic interventions. In this study, we identified G9a/EHMT2 as a potential target in T-ALL through the intersection of epigenome-centered shRNA and chemical screens. We subsequently validated G9a with low-throughput CRISPR-Cas9-based studies targeting the catalytic G9a SET-domain and the testing of G9a chemical inhibitors in vitro, 3D, and in vivo T-ALL models. Mechanistically we determined that G9a repression promotes lysosomal biogenesis and autophagic degradation associated with the suppression of sestrin2 (SESN2) and inhibition of glycogen synthase kinase-3 (GSK-3), suggesting that in T-ALL glycolytic dependent pathways are at least in part under epigenetic control. Thus, targeting G9a represents a strategy to exhaust the metabolic requirement of T-ALL cells.

Selective histone methyltransferase G9a inhibition reduces metastatic development of Ewing sarcoma through the epigenetic regulation of NEU1

Ewing sarcoma (EWS) is an aggressive bone and soft tissue tumor with high susceptibility to metastasize. The underlying molecular mechanisms leading to EWS metastases remain poorly understood. Epigenetic changes have been implicated in EWS tumor growth and progression. Linking epigenetics and metastases may provide insight into novel molecular targets in EWS and improve its treatment. Here, we evaluated the effects of a selective G9a histone methyltransferase inhibitor (BIX01294) on EWS metastatic process. Our results showed that overexpression of G9a in tumors from EWS patients correlates with poor prognosis. Moreover, we observe a significantly higher expression of G9a in metastatic EWS tumor as compared to either primary or recurrent tumor. Using functional assays, we demonstrate that pharmacological G9a inhibition using BIX01294 disrupts several metastatic steps in vitro, such as migration, invasion, adhesion, colony formation and vasculogenic mimicry. Moreover, BIX01294 reduces tumor growth and metastases in two spontaneous metastases mouse models. We further identified the sialidase NEU1 as a direct target and effector of G9a in the metastatic process in EWS. NEU1 overexpression impairs migration, invasion and clonogenic capacity of EWS cell lines. Overall, G9a inhibition impairs metastases in vitro and in vivo through the overexpression of NEU1. G9a has strong potential as a prognostic marker and may be a promising therapeutic target for EWS patients.

Cinnamaldehyde induces autophagy-mediated cell death through ER stress and epigenetic modification in gastric cancer cells

Previous reports suggested that cinnamaldehyde (CA), the bioactive ingredient in Cinnamomum cassia, can suppress tumor growth, migratory, and invasive abilities. However, the role and molecular mechanisms of CA in GC are not completely understood. In the present study, we found that CA-induced ER stress and cell death via the PERK-CHOP axis and Ca²⁺ release in GC cells. Inhibition of ER stress using specific-siRNA blocked CA-induced cell death. Interestingly, CA treatment resulted in autophagic cell death by inducing Beclin-1, ATG5, and LC3B expression and by inhibiting p62 expression whereas autophagy inhibition suppressed CA-induced cell death. We showed that CA induces the inhibition of G9a and the activation of LC3B. Moreover, CA inhibited G9a binding on Beclin-1 and LC3B promoter. Overall, these results suggested that CA regulates the PERK-CHOP signaling, and G9a inhibition activates autophagic cell death via ER stress in GC cells.

Targeting Autophagy-Related Epigenetic Regulators for Cancer Drug Discovery

Existing evidence has demonstrated that epigenetic modifications (including DNA methylation, histone modifications, and microRNAs), which are associated with the occurrence and development of tumors, can directly or indirectly regulate autophagy. In particular, nuclear events induced by several epigenetic regulators can regulate the autophagic process and expression levels of tumor-associated genes, thereby promoting tumor progression. Tumor-associated microRNAs, including oncogenic and tumor-suppressive microRNAs, are of great significance to autophagy during tumor progression. Targeting autophagy with emerging epigenetic drugs is expected to be a promising therapeutic strategy for human tumors. From this perspective, we aim to summarize the role of epigenetic modification in the autophagic process and the underlying molecular mechanisms of tumorigenesis. Furthermore, the regulatory efficacy of epigenetic drugs on the autophagic process in tumors is also summarized. This perspective may provide a theoretical basis for the combined treatment of epigenetic drugs/autophagy mediators in tumors.

Cross-talk Between Histone and DNA Methylation Mediates Bone Loss in Hind Limb Unloading

Bone loss induced by mechanical unloading is a common skeletal disease, but the precise mechanism remains unclear. The current study investigated the role of histone methylation, a key epigenetic marker, and its cross-talk with DNA methylation in bone loss induced by mechanical unloading. The expression of G9a, ubiquitin-like with PHD and ring finger domains 1 (UHRF1), and DNA methylation transferase 1 (DNMT1) were increased in hind limb unloading (HLU) rats. This was accompanied by an increased level of histone H3 lysine 9 (H3K9) di-/tri-methylation at lncH19 promoter. Then, alteration of G9a, DNMT1, or UHRF1 expression significantly affected lncH19 level and osteogenic activity in UMR106 cells. Osteogenic gene expression and matrix mineralization were robustly promoted after simultaneous knockdown of G9a, DNMT1, and UHRF1. Furthermore, physical interactions of lncH19 promoter with G9a and DNMT1, as well as direct interactions among DNMT1, G9a, and UHRF1 were detected. Importantly, overexpression of DNMT1, G9a, or UHRF1, respectively, resulted in enrichment of H3K9me2/me3 and 5-methylcytosine at lncH19 promoter. Finally, in vivo rescue experiments indicated that knockdown of DNMT1, G9a, or UHRF1 significantly relieved bone loss in HLU rats. In conclusion, our research demonstrated the critical role of H3K9 methylation and its cross-talk with DNA methylation in regulating lncH19 expression and bone loss in HLU rats. Combined targeting of DNMT1, G9a, and UHRF1 could be a promising strategy for the treatment of bone loss induced by mechanical unloading. © 2021 American Society for Bone and Mineral Research (ASBMR).

Insight into the multi-faceted role of the SUV family of H3K9 methyltransferases in carcinogenesis and cancer progression

Growing evidence implicates histone H3 lysine 9 methylation in tumorigenesis. The SUV family of H3K9 methyltransferases, which include G9a, GLP, SETDB1, SETDB2, SUV39H1 and SUV39H2 deposit H3K9me1/2/3 marks at euchromatic and heterochromatic regions, catalyzed by their conserved SET domain. In cancer, this family of enzymes can be deregulated by genomic alterations and transcriptional mis-expression leading to alteration of transcriptional programs. In solid and hematological malignancies, studies have uncovered pro-oncogenic roles for several H3K9 methyltransferases and accordingly, small molecule inhibitors are being tested as potential therapies. However, emerging evidence demonstrate onco-suppressive roles for these enzymes in cancer development as well. Here, we review the role H3K9 methyltransferases play in tumorigenesis focusing on gene targets and biological pathways affected due to misregulation of these enzymes. We also discuss molecular mechanisms regulating H3K9 methyltransferases and their influence on cancer. Finally, we describe the impact of H3K9 methylation on therapy induced resistance in carcinoma. Converging evidence point to multi-faceted roles for H3K9 methyltransferases in development and cancer that encourages a deeper understanding of these enzymes to inform novel therapy.

BIX-01294-enhanced chemosensitivity in nasopharyngeal carcinoma depends on autophagy-induced pyroptosis

Nasopharyngeal carcinoma (NPC) is a common cancer in southern China and Southeast Asia. Nowadays, radiotherapy is the therapy of choice for NPC patients, and chemotherapy has been found as an alternative treatment for advanced NPC patients. However, finding novel drugs and pharmacologically therapeutic targets for NPC patients is still urgent and beneficial. Our study showed that BIX-01294 (BIX) can induce autophagic vacuoles formation and conversion of LC3B-I to LC3B-II in NPC cells in both dose- and time-dependent manners. Notably, the combination of BIX and chemotherapeutic drugs significantly decreased the cell viability and increased the lactate dehydrogenase release. Meanwhile, BIX plus cis-platinum (Cis) treatment induced pyroptosis in NPC cells as featured by cell swelling and bubble blowing from the plasma membrane, the increased frequency of annexin V and propidium iodide (PI) double-positive cells, as well as the cleavage of gasdermin E (GSDME) and caspase-3. Moreover, the deficiency of GSDME completely shifted pyroptosis to apoptosis. Furthermore, the inhibition of autophagy by chloroquine and the knockout of ATG5 gene significantly blocked the BIX-induced autophagy as well as pyroptosis in both in vitro and in vivo studies. Our data demonstrated that BIX-combined chemotherapeutic drugs could induce the Bax/caspase-3/GSDME-mediated pyroptosis through the activation of autophagy to enhance the chemosensitivity in NPC.

SH003 activates autophagic cell death by activating ATF4 and inhibiting G9a under hypoxia in gastric cancer cells

In gastric cancer (GC), hypoxia is one of the greatest obstacles to cancer therapy. In this present study, we report that SH003, an herbal formulation, induces ER stress via PERK-ATF4-CHOP signaling in GC. SH003-mediated ER stress inhibits G9a, a histone methyltransferase, by reducing STAT3 phosphorylation and activates autophagy, indicating to the dissociation of Beclin-1 and autophagy initiation from Bcl-2/Beclin-1 complex. However, the inhibition of PERK and CHOP inhibited SH003-induced cell death and autophagy activation. Moreover, targeting autophagy using specific siRNAs of LC3B or p62 or the autophagy inhibitor 3-MA also inhibited SH003-induced cell death in GC. Interestingly, SH003 induces BNIP3-mediated autophagic cell death under hypoxia than normoxia in GC. These findings reveal that SH003-induced ER stress regulates BNIP3-induced autophagic cell death via inhibition of STAT3-G9a axis under hypoxia in GC. Therefore, SH003 may an important tumor therapeutic strategy under hypoxia-mediated chemo-resistance.

The role of epigenetics and non-coding RNAs in autophagy: A new perspective for thorough understanding

Autophagy is a major self-degradative intracellular process required for the maintenance of homeostasis and promotion of survival in response to starvation. It plays critical roles in a large variety of physiological and pathological processes. On the other hand, aberrant regulation of autophagy can lead to various cancers and neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Crohn's disease. Emerging evidence strongly supports that epigenetic signatures, related non-coding RNA profiles, and their cross-talking are significantly associated with the control of autophagic responses. Therefore, it may be helpful and promising to manage autophagic processes by finding valuable markers and therapeutic approaches. Although there is a great deal of information on the components of autophagy in the cytoplasm, the molecular basis of the epigenetic regulation of autophagy has not been completely elucidated. In this review, we highlight recent research on epigenetic changes through the expression of autophagy-related genes (ATGs), which regulate autophagy, DNA methylation, histone modifications as well as non-coding RNAs, including long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and their relationship with human diseases, that play key roles in causing autophagy-related diseases.

The Promise for Histone Methyltransferase Inhibitors for Epigenetic Therapy in Clinical Oncology: A Narrative Review

Epigenetic processes are essential for normal development and the maintenance of tissue-specific gene expression in mammals. Changes in gene expression and malignant cellular transformation can result from disruption of epigenetic mechanisms, and global disruption in the epigenetic landscape is a key feature of cancer. The study of epigenetics in cancer has revealed that human cancer cells harbor both genetic alterations and epigenetic abnormalities that interplay at all stages of cancer development. Unlike genetic mutations, epigenetic aberrations are potentially reversible through epigenetic therapy, providing a therapeutically relevant treatment option. Histone methyltransferase inhibitors are emerging as an epigenetic therapy approach with great promise in the field of clinical oncology. The recent accelerated approval of the enhancer of zeste homolog 2 (EZH2; also known as histone-lysine N-methyltransferase EZH2) inhibitor tazemetostat for metastatic or locally advanced epithelioid sarcoma marks the first approval of such a compound for the treatment of cancer. Many other histone methyltransferase inhibitors are currently in development, some of which are being tested in clinical studies. This review focuses on histone methyltransferase inhibitors, highlighting their potential in the treatment of cancer. We also discuss the role for such epigenetic drugs in overcoming epigenetically driven drug resistance mechanisms, and their value in combination with other therapeutic approaches such as immunotherapy.

JMJD2B-induced amino acid alterations enhance the survival of colorectal cancer cells under glucose-deprivation via autophagy

Rationale: Post-translational modifications have emerged as vital players in alterations to tumor metabolism, including amino acid metabolic reprogramming. Jumonji domain-containing protein 2B (JMJD2B) enhances colorectal cancer (CRC) cell survival upon glucose deficiency. In the present study, we hypothesized that JMJD2B affects tumor cell amino acid metabolism in CRC and consequently promotes survival of CRC cells upon glucose deprivation. Methods: Non-target metabolic profiling was used to evaluate the roles of JMJD2B in CRC cell metabolism under glucose starvation. The roles of amino acid alterations induced by JMJD2B on CRC cell survival were determined by cell viability, immunoblotting, and clonogenic assays, and flow cytometry. The underlying mechanisms by which JMJD2B affected CRC cell metabolism were assessed using immunofluorescence staining, chromatin immunoprecipitation assays, electron microscopy in CRC cell lines, and using xenograft models. The correlation between JMJD2B and LC3B expression in human CRC specimens was assessed using immunohistochemistry. Results: Profound metabolic reprogramming was detected in JMJD2B knockdown CRC cells under glucose deficiency, especially those involving amino acid metabolites. Silencing of JMJD2B reduced the levels of certain amino acids that were induced by glucose deficiency. Among these amino acids, asparagine (Asn), phenylalanine (Phe), and histidine (His) promoted CRC cell survival under glucose starvation when JMJD2B was knocked down. Mechanistically, downregulation of JMJD2B inhibited autophagy in CRC cells through epigenetic regulation of microtubule associated protein 1 light chain 3 beta (LC3B), and subsequently decreased intracellular amino acid (Asn, Phe, His) levels under glucose deprivation, thus suppressing the survival of CRC cells. Using a nude mouse xenograft model, we verified that inhibiting JMJD2B could decrease the levels of amino acids (Asn, Phe, His). In addition, the inhibitory effects of JMJD2B-knockdown on tumor growth and amino acids level were rescued by overexpression of LC3B. Furthermore, we observed that the high expression of LC3B was more likely detected in tissuses with high expression of JMJD2B (P < 0.001) in 60 human CRC tissues. Conclusion: These results indicated that JMJD2B sustained the intracellular amino acids derived from autophagy in CRC cells upon glucose deficiency, partly through epigenetic regulation of LC3B, thus driving the malignancy of CRC.

PERK/NRF2 and autophagy form a resistance mechanism against G9a inhibition in leukemia stem cells

BACKGROUND

The histone methyltransferase G9a has recently been identified as a potential target for epigenetic therapy of acute myeloid leukemia (AML). However, the effect of G9a inhibition on leukemia stem cells (LSCs), which are responsible for AML drug resistance and recurrence, is unclear. In this study, we investigated the underlying mechanisms of the LSC resistance to G9a inhibition.

METHODS

We evaluated the effects of G9a inhibition on the unfolded protein response and autophagy in AML and LSC-like cell lines and in primary CD34+CD38- leukemic blasts from patients with AML and investigated the underlying mechanisms. The effects of treatment on cells were evaluated by flow cytometry, western blotting, confocal microscopy, reactive oxygen species (ROS) production assay.

RESULTS

The G9a inhibitor BIX-01294 effectively induced apoptosis in AML cell lines; however, the effect was limited in KG1 LSC-like cells. BIX-01294 treatment or siRNA-mediated G9a knockdown led to the activation of the PERK/NRF2 pathway and HO-1 upregulation in KG1 cells. Phosphorylation of p38 and intracellular generation of reactive oxygen species (ROS) were suppressed. Pharmacological or siRNA-mediated inhibition of the PERK/NRF2 pathway synergistically enhanced BIX-01294-induced apoptosis, with suppressed HO-1 expression, increased p38 phosphorylation, and elevated ROS generation, indicating that activated PERK/NRF2 signaling suppressed ROS-induced apoptosis in KG1 cells. By contrast, cotreatment of normal hematopoietic stem cells with BIX-01294 and a PERK inhibitor had no significant proapoptotic effect. Additionally, G9a inhibition induced autophagy flux in KG1 cells, while autophagy inhibitors significantly increased the BIX-01294-induced apoptosis. This prosurvival autophagy was not abrogated by PERK/NRF2 inhibition.

CONCLUSIONS

PERK/NRF2 signaling plays a key role in protecting LSCs against ROS-induced apoptosis, thus conferring resistance to G9a inhibitors. Treatment with PERK/NRF2 or autophagy inhibitors could overcome resistance to G9a inhibition and eliminate LSCs, suggesting the potential clinical utility of these unique targeted therapies against AML.

EHMT2/G9a Inhibits Aortic Smooth Muscle Cell Death by Suppressing Autophagy Activation

Although EHMT2 (also known as G9a) plays a critical role in several kinds of cancers and cardiac remodeling, its function in vascular smooth muscle cells (VSMCs) remains unknown. In the present study, we revealed a novel function of EHMT2 in regulating autophagic cell death (ACD) of VSMC. Inhibition of EHMT2 by BIX01294 or knockdown of EHMT2 resulted in reduced VSMC numbers which were independent of proliferation and apoptosis. Interestingly, EHMT2 protein levels were significantly decreased in VSMCs treated with autophagic inducers. Moreover, more autophagic vacuoles and accumulated LC3II were detected in VSMCs treated with BIX01294 or lenti-shEHMT2 than their counterparts. Furthermore, we found that EHMT2 inhibited the ACD of VSMCs by suppressing autophagosome formation. Mechanistically, the pro-autophagic effect elicited by EHMT2 inhibition was associated with SQSTM1 and BECN1 overexpression. Moreover, these detrimental effects were largely nullified by SQSTM1 or BECN1 knockdown. More importantly, similar results were observed in primary human aortic VSMCs. Overall, these findings suggest that EHMT2 functions as a crucial negative regulator of ACD via decreasing SQSTM1 or BECN1 expression and that EHMT2 could be a potent therapeutic target for cardiovascular diseases (e.g., aortic dissection).

Epigenetic Control of Autophagy in Cancer Cells: A Key Process for Cancer-Related Phenotypes

Although autophagy is a well-known and extensively described cell pathway, numerous studies have been recently interested in studying the importance of its regulation at different molecular levels, including the translational and post-translational levels. Therefore, this review focuses on the links between autophagy and epigenetics in cancer and summarizes the. following: (i) how ATG genes are regulated by epigenetics, including DNA methylation and post-translational histone modifications; (ii) how epidrugs are able to modulate autophagy in cancer and to alter cancer-related phenotypes (proliferation, migration, invasion, tumorigenesis, etc.) and; (iii) how epigenetic enzymes can also regulate autophagy at the protein level. One noteable observation was that researchers most often reported conclusions about the regulation of the autophagy flux, following the use of epidrugs, based only on the analysis of LC3B-II form in treated cells. However, it is now widely accepted that an increase in LC3B-II form could be the consequence of an induction of the autophagy flux, as well as a block in the autophagosome-lysosome fusion. Therefore, in our review, all the published results describing a link between epidrugs and autophagy were systematically reanalyzed to determine whether autophagy flux was indeed increased, or inhibited, following the use of these potentially new interesting treatments targeting the autophagy process. Altogether, these recent data strongly support the idea that the determination of autophagy status could be crucial for future anticancer therapies. Indeed, the use of a combination of epidrugs and autophagy inhibitors could be beneficial for some cancer patients, whereas, in other cases, an increase of autophagy, which is frequently observed following the use of epidrugs, could lead to increased autophagy cell death.

Upregulated expression of G9a is correlated with poor prognosis of gastric cancer patients

As one of the most serious cancers, gastric cancer (GC) represents the third leading cause of malignancy-related deaths. G9a is a histone lysine methyltransferase and has been reported to be involved in the progression of some human cancers. In the present study, we aimed to explore the expression patterns and clinical value of G9a in GC patients.The expression of G9a in 142 paired GC tissues and adjacent non-cancerous tissues (no less than 5 cm from tumor edge) was examined with quantitative real-time polymerase chain reaction (qRT-PCR). To estimate the association of G9a expression with clinical characteristics of GC patients, Chi-square test and t test were conducted. Kaplan-Meier survival and multivariate Cox regression analyses were performed to explore the prognostic value of G9a in GC.Upregulated expression of G9a was found in GC tissues compared with noncancerous tissues (P < .001). Elevated G9a expression was significantly correlated with patients' lymph node metastasis (P = .007) and TNM stage (P < .001). Kaplan-Meier survival curves demonstrated that patients with high G9a expression had shorter survival time than those with low expression (log-rank test, P < .05), reaching a median OS of 24 months. According to the results of Cox regression, G9a could be considered as an independent prognostic biomarker in patients with GC (HR = 3.912, 95% CI = 2.213-6.915, P < .001). Additionally, the diagnosis cut-off value of G9a in GC patients was 1.515.Taken together, G9a expression was upregulated in GC tissues and could be an effective prognostic biomarker for GC.

G9a promotes cell proliferation and suppresses autophagy in gastric cancer by directly activating mTOR

As an important methyltransferase, G9a has been reported to be abnormally expressed in various human cancers and plays essential roles in tumorigenesis. However, the biologic functions and molecular mechanisms of G9a in gastric cancer (GC) remain unclear. GC is the fifth most frequent cancer around the world and seriously threatens human health, especially in developing countries. Here, our results showed that high expression of G9a was intensively correlated with poor prognosis and more advanced stages of GCs. Knockdown of G9a or treatment with its inhibitor, BIX01294, significantly reduced cell growth by cell cycle arrest and autophagy. In addition, the mechanistic target of rapamycin (mTOR) was evidently decreased after G9a silencing or inhibition, and mTOR activation partially rescued the effects of cell proliferation inhibition and autophagy induced by G9a knockdown or inhibition. Down-regulation of G9a effectively inhibited mTOR expression and tumor growth in the xenograft tumor model of GC cells. We also showed that G9a regulates mTOR and cell proliferation and autophagy depending on its histone methylase activity. Using chromatin immunoprecipitation analysis, we found that mTOR expression was associated with promoter methylation and an enrichment for mono- and dimethylated histone 3 lys 9 (H3K9). G9a knockdown revealed an apparent decrease in H3K9 monomethylation levels, but no apparent change in H3K9 dimethylation levels at the mTOR promoter. These results indicate that G9a is a novel and promising therapeutic target for GC treatment.-Yin, C., Ke, X., Zhang, R., Hou, J., Dong, Z., Wang, F., Zhang, K., Zhong, X., Yang, L., Cui, H. G9a promotes cell proliferation and suppresses autophagy in gastric cancer by directly activating mTOR.

Protein methylation functions as the posttranslational modification switch to regulate autophagy

Studies over the past decades have elucidated the critical role of autophagy in human health and diseases. Although the processes of autophagy in the cytoplasm have been well studied, the posttranscriptional and epigenetic regulation mechanisms of autophagy are still poorly understood. Protein methylation, including histone methylation and non-histone protein methylation, is the most important type of posttranscriptional and epigenetic modification. Recent studies have shown that protein methylation is associated with effects on autophagosome formation, autophagy-related protein expression, and signaling pathway activation, but the details are still unclear. Thus, it is important to summarize the current status and discuss the future directions of research on protein methylation in the context of autophagy.

Inhibition of Euchromatic Histone Lysine Methyltransferase 2 (EHMT2) Suppresses the Proliferation and Invasion of Cervical Cancer Cells

EHMT2 (euchromatic histone lysine methyltransferase 2), a histone methyltransferase, has been shown to be involved in multiple human cancers. In this study, we determined mRNA and protein expression of EHMT2 in cervical cancer cells and normal cervical epithelial cells. EHMT2 was inhibited with short hairpin RNA (shEHMT2) in cervical cancer cells. Cell viability, colony proliferation, apoptosis, adhesion, and invasion assays and Western blot were performed to assess the function of EHMT2. As a result, EHMT2 was upregulated in human cervical cancer cells compared to normal cervical epithelial cells. Suppression of EHMT2 expression impairs cell proliferation and induces apoptosis. Furthermore, EHMT2 silencing inhibited cell adhesion and invasion. Finally, knockdown of EHMT2 resulted in a reduction of the expression of the tumorigenic proteins Bcl-2, Mcl-1, and Survivin and in an increase in the expression of the anti-malignant protein E-cadherin. In conclusion, our data suggest that EHMT2 plays a key role in cell proliferation and metastatic capacity in cervical cancer cells and could serve as a potential therapeutic target.

Insights for the design of protein lysine methyltransferase G9a inhibitors

The epigenetic control of gene expression could be affected by addition and/or removal of post-translational modifications such as phosphorylation, acetylation and methylation of histone proteins, as well as methylation of DNA (5-methylation on cytosines). Misregulation of these modifications is associated with altered gene expression, resulting in various disease conditions. G9a belongs to the protein lysine methyltransferases that specifically methylates the K9 residue of histone H3, leading to suppression of several tumor suppressor genes. In this review, G9a functions, role in various diseases, structural biology aspects for inhibitor design, structure-activity relationship among the reported inhibitors are discussed which could aid in the design and development of potent G9a inhibitors for cancer treatment in the future.

Regulation Is in the Air: The Relationship between Hypoxia and Epigenetics in Cancer

Hypoxia is an inherent condition of tumors and contributes to cancer development and progression. Hypoxia-inducible factors (HIFs) are the major transcription factors involved in response to low O₂ levels, orchestrating the expression of hundreds of genes involved in cancer hallmarks’ acquisition and modulation of epigenetic mechanisms. Epigenetics refers to inheritable mechanisms responsible for regulating gene expression, including genes involved in the hypoxia response, without altering the sequence of DNA bases. The main epigenetic mechanisms are DNA methylation, non-coding RNAs, and histone modifications. These mechanisms are highly influenced by cell microenvironment, such as O₂ levels. The balance and interaction between these pathways is essential for homeostasis and is directly linked to cellular metabolism. Some of the major players in the regulation of HIFs, such as prolyl hydroxylases, DNA methylation regulators, and histone modifiers require oxygen as a substrate, or have metabolic intermediates as cofactors, whose levels are altered during hypoxia. Furthermore, during pathological hypoxia, HIFs’ targets as well as alterations in epigenetic patterns impact several pathways linked to tumorigenesis, such as proliferation and apoptosis, among other hallmarks. Therefore, this review aims to elucidate the intricate relationship between hypoxia and epigenetic mechanisms, and its crucial impact on the acquisition of cancer hallmarks.

PHF8 upregulation contributes to autophagic degradation of E-cadherin, epithelial-mesenchymal transition and metastasis in hepatocellular carcinoma

Background

Plant homeodomain finger protein 8 (PHF8) serves an activator of epithelial-mesenchymal transition (EMT) and is implicated in various tumors. However, little is known about PHF8 roles in hepatocellular carcinoma (HCC) and regulating E-cadherin expression.

Methods

PHF8 expression pattern was investigated by informatic analysis and verified by RT-qPCR and immunochemistry in HCC tissues and cell lines. CCK8, xenograft tumor model, transwell assay, and tandem mCherry-GFP-LC3 fusion protein assay were utilized to assess the effects of PHF8 on proliferation, metastasis and autophagy of HCC cells in vitro and in vivo. ChIP, immunoblot analysis, rescue experiments and inhibitor treatment were used to clarify the mechanism by which PHF8 facilitated EMT, metastasis and autophagy.

Results

PHF8 upregulation was quite prevalent in HCC tissues and closely correlated with worse overall survival and disease-relapse free survival. Furthermore, PHF8-knockdown dramatically suppressed cell growth, migration, invasion and autophagy, and the expression of SNAI1, VIM, N-cadherin and FIP200, and increased E-cadherin level, while PHF8-overexpression led to the opposite results. Additionally, FIP200 augmentation reversed the inhibited effects of PHF8-siliencing on tumor migration, invasion and autophagy. Mechanistically, PHF8 was involved in transcriptionally regulating the expression of SNAI1, VIM and FIP200, rather than N-cadherin and E-cadherin. Noticeably, E-cadherin degradation could be accelerated by PHF8-mediated FIP200-dependent autophagy, a crucial pathway complementary to transcriptional repression of E-cadherin by SNAI1 activation.

Conclusion

These findings suggested that PHF8 played an oncogenic role in facilitating FIP200-dependent autophagic degradation of E-cadherin, EMT and metastasis in HCC. PHF8 might be a promising target for prevention, treatment and prognostic prediction of HCC.

Electronic supplementary material

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Kaempferol induces autophagic cell death via IRE1-JNK-CHOP pathway and inhibition of G9a in gastric cancer cells

Kaempferol, a flavonoid, found in traditional medicine, fruits, and vegetables, and an HDAC inhibitor, is a powerful anti-cancer reagent against various cancer cell lines. However, detailed mechanisms involved in the treatment of gastric cancer (GC) using kaempferol are not fully understood. In our study, we investigated the biological activity and molecular mechanism involved in kaempferol-mediated treatment of GC. Kaempferol promoted autophagy and cell death, and increased LC3-I to LC3-II conversion and the downregulation of p62 in GC. Furthermore, our results showed that kaempferol induces autophagic cell death via the activation of the IRE1-JNK-CHOP signaling, indicating ER stress response. Indeed, the inhibition of ER stress suppressed kaempferol-induced autophagy and conferred prolonged cell survival, indicating autophagic cell death. We further showed that kaempferol mediates epigenetic change via the inhibition of G9a (HDAC/G9a axis) and also activates autophagic cell death. Taken together, our findings indicate that kaempferol activates the IRE1-JNK-CHOP signaling from cytosol to nucleus, and G9a inhibition activates autophagic cell death in GC cells.

Lung Cancer Therapy Targeting Histone Methylation: Opportunities and Challenges

Lung cancer is one of the most common malignancies. In spite of the progress made in past decades, further studies to improve current therapy for lung cancer are required. Dynamically controlled by methyltransferases and demethylases, methylation of lysine and arginine residues on histone proteins regulates chromatin organization and thereby gene transcription. Aberrant alterations of histone methylation have been demonstrated to be associated with the progress of multiple cancers including lung cancer. Inhibitors of methyltransferases and demethylases have exhibited anti-tumor activities in lung cancer, and multiple lead candidates are under clinical trials. Here, we summarize how histone methylation functions in lung cancer, highlighting most recent progresses in small molecular inhibitors for lung cancer treatment.

GLP overexpression is associated with poor prognosis in Chronic Lymphocytic Leukemia and its inhibition induces leukemic cell death

Background Heterodimeric methyltransferases GLP (EHMT1/KMT1D) and G9a (EHMT2/KMT1C) are two closely related enzymes that promote the monomethylation and dimethylation of histone H3 lysine 9. Dysregulation of their activity has been implicated in several types of human cancer. Patients and methods Here, in order to investigate whether GLP/G9a exerts any impact on Chronic Lymphocytic Leukemia (CLL), GLP/G9a expression levels were assessed in a cohort of 50 patients and the effects of their inhibition were verified for the viability of CLL cells. Also, qRT-PCR was used to investigate the transcriptional levels of GLP/G9a in CLL patients. In addition, patient samples were classified according to ZAP-70 protein expression by flow cytometry and according to karyotype integrity by cytogenetics analysis. Finally, a selective small molecule inhibitor for GLP/G9a was used to ascertain whether these methyltransferases influenced the viability of MEC-1 CLL cell lineage. Results mRNA analysis revealed that CLL samples had higher levels of GLP, but not G9a, when compared to non-leukemic controls. Interestingly, patients with unfavorable cytogenetics showed higher expression levels of GLP compared to patients with favorable karyotypes. More importantly, GLP/G9a inhibition markedly induced cell death in CLL cells. Conclusion Taken together, these results indicate that GLP is associated with a worse prognosis in CLL, and that the inhibition of GLP/G9a influences CLL cell viability. Altogether, the present data demonstrate that these methyltransferases can be potential markers for disease progression, as well as a promising epigenetic target for CLL treatment and the prevention of disease evolution.

The role of protein methyltransferases as potential novel therapeutic targets in squamous cell carcinoma of the head and neck

Squamous cell carcinoma of the head and neck is a lethal disease with suboptimal survival outcomes and standard therapies with significant comorbidities. Whole exome sequencing data recently revealed an abundance of genetic and expression alterations in a family of enzymes known as protein methyltransferases in a variety of cancer types, including squamous cell carcinoma of the head and neck. These enzymes are mostly known for their chromatin-modifying functions through methylation of various histone substrates, though evidence supports their function also through methylation of non-histone substrates. This review summarizes the current knowledge on the function of protein methyltransferases in squamous cell carcinoma of the head and neck and highlights their promising potential as the next generation of therapeutic targets in this disease.

Autophagy and Hallmarks of Cancer

Autophagy is a catabolic program that is responsible for the degradation of dysfunctional or unnecessary proteins and organelles to maintain cellular homeostasis. Mechanistically, it involves the formation of double-membrane autophagosomes that sequester cytoplasmic material and deliver it to lysosomes for degradation. Eventually, the material is recycled back to the cytoplasm. Abnormalities of autophagy often lead to human diseases, such as neurodegeneration and cancer. In the case of cancer, increasing evidence has revealed the paradoxical roles of autophagy in both tumor inhibition and tumor promotion. Here, we summarize the context-dependent role of autophagy and its complicated molecular mechanisms in the hallmarks of cancer. Moreover, we discuss how therapeutics targeting autophagy can counter malignant transformation and tumor progression. Overall, the findings of studies discussed here shed new light on exploiting the complicated mechanisms of the autophagic machinery and relevant small-molecule modulators as potential antitumor agents to improve therapeutic outcomes.

Histone methyltransferase G9a promotes liver cancer development by epigenetic silencing of tumor suppressor gene RARRES3

BACKGROUND & AIMS

Hepatocellular carcinoma (HCC) is a major leading cause of cancer mortality worldwide. Epigenetic deregulation is a common trait of human HCC. G9s is an important epigenetics regulator however, its role in liver carcinogenesis remains to be investigated.

METHODS

Gene expressions were determined by RNA-Seq and qRT-PCR. G9a knockdown and knockout cell lines were established by lentiviral-based shRNA and CRISPR/Cas9 gene editing system. Tumor-promoting functions of G9a was studied in both HCC cell lines and nude mice model. The downstream targets of G9a were identified by RNA-Seq and confirmed by ChIP assay. The therapeutic value of G9a inhibitors was evaluated both in vitro and in vivo.

RESULTS

We identified G9a as a frequently upregulated histone methyltransferase in human HCCs. Upregulation of G9a was significantly associated with HCC progression and aggressive clinicopathological features. Functionally, we demonstrated that inactivation of G9a by RNAi knockdown, CRISPR/Cas9 knockout, and pharmacological inhibition remarkably abolished H3K9 di-methylation and suppressed HCC cell proliferation and metastasis in both in vitro and in vivo models. Mechanistically, we showed that the frequent upregulation of G9a in human HCCs was attributed to gene copy number gain at chromosome 6p21. In addition, we identified miR-1 as a negative regulator of G9a. Loss of miR-1 relieved the post-transcriptional repression on G9a and contributed to its upregulation in human HCC. Utilizing RNA sequencing, we identified the tumor suppressor RARRES3 as a critical target of G9a. Epigenetic silencing of RARRES3 contributed to the tumor-promoting function of G9a.

CONCLUSION

This study shows a frequent deregulation of miR-1/G9a/RARRES3 axis in liver carcinogenesis, highlighting the pathological significance of G9a and its therapeutic potential in HCC treatment. Lay summary: In this study, we identified G9a histone methyltransferase was frequently upregulated in human HCC and contributes to epigenetic silencing of tumor suppressor gene RARRES3 in liver cancer. Targeting G9a may be a novel approach for HCC treatment.

Epigenetic regulation of starvation-induced autophagy in Drosophila by histone methyltransferase G9a

Epigenetics is now emerging as a key regulation in response to various stresses. We herein identified the Drosophila histone methyltransferase G9a (dG9a) as a key factor to acquire tolerance to starvation stress. The depletion of dG9a led to high sensitivity to starvation stress in adult flies, while its overexpression induced starvation stress resistance. The catalytic domain of dG9a was not required for starvation stress resistance. dG9a plays no apparent role in tolerance to other stresses including heat and oxidative stresses. Metabolomic approaches were applied to investigate global changes in the metabolome due to the loss of dG9a during starvation stress. The results obtained indicated that dG9a plays an important role in maintaining energy reservoirs including amino acid, trehalose, glycogen, and triacylglycerol levels during starvation. Further investigations on the underlying mechanisms showed that the depletion of dG9a repressed starvation-induced autophagy by controlling the expression level of Atg8a, a critical gene for the progression of autophagy, in a different manner to that in cancer cells. These results indicate a positive role for dG9a in starvation-induced autophagy.

Methyltransferase G9a promotes cervical cancer angiogenesis and decreases patient survival

Research suggests that the epigenetic regulator G9a, a H3K9 histone methyltransferase, is involved in cancer invasion and metastasis. Here we show that G9a is linked to cancer angiogenesis and poor patient survival. Invasive cervical cancer has a higher G9a expression than cancer precursors or normal epithelium. Pharmacological inhibition and genetic silencing of G9a suppresses H3K9 methylation, cancer cell proliferation, angiogenesis, and cancer cell invasion/migration, but not apoptosis. Microarray and quantitative reverse transcription polymerase chain reaction analyses reveal that G9a induces a cohort of angiogenic factors that include angiogenin, interleukin-8, and C-X-C motif chemokine ligand 16. Depressing G9a by either pharmacological inhibitor or gene knock down significantly reduces angiogenic factor expression. Moreover, promoting G9a gene expression augments transcription and angiogenic function. A luciferase reporter assay suggests that knockdown of G9a inhibits transcriptional activation of interleukin-8. G9a depletion suppresses xenograft tumor growth in mouse model, which is linked to a decrease in microvessel density and proliferating cell nuclear antigen expression. Clinically, higher G9a expression correlates with poorer survival for cancer patients. For patients’ primary tumors a positive correlation between G9a expression and microvessel density also exists. In addition to increasing tumor cell proliferation, G9a promotes tumor angiogenesis and reduces the patient survival rate. G9a may possess great value for targeted therapies.

Histone Methyltransferase G9a Drives Chemotherapy Resistance by Regulating the Glutamate-Cysteine Ligase Catalytic Subunit in Head and Neck Squamous Cell Carcinoma

Transient chemotherapeutic response is a major obstacle to treating head and neck squamous cell carcinomas (HNSCC). Histone methyltransferase G9a has recently been shown to be abundantly expressed in HNSCC, and is required to maintain the malignant phenotype. In this study, we found that high G9a expression is significantly associated with poor chemotherapeutic response and disease-free survival in HNSCC patients. Similarly, G9a expression and enzymatic activity were elevated in cisplatin-resistant HNSCC cells. Genetic or pharmacologic inhibition of G9a sensitized the resistant cells to cisplatin, increasing cellular apoptosis. Mechanistic investigations indicated that G9a contributes to transcriptional activation of the glutamate-cysteine ligase catalytic subunit (GCLC), which results in upregulation of cellular glutathione (GSH) and drug resistance. In addition, we observed a significant positive correlation between G9a and GCLC expression in tumors of HNSCC patients. Taken together, our findings provide evidence that G9a protects HNSCC cells against chemotherapy by increasing the synthesis of GSH, and imply G9a as a promising target for overcoming cisplatin resistance in HNSCC. Mol Cancer Ther; 16(7); 1421-34. ©2017 AACR.

Involvement of histone methylation in macrophage apoptosis and unstable plaque formation in methionine-induced hyperhomocysteinemic ApoE-/- mice

AIMS

Hyperhomocysteinemia (Hhcy) is an independent risk factor of atherosclerosis and promotes unstable plaque formation. Epigenetic mechanisms play an important role in the pathogenesis of atherosclerosis induced by Hhcy. However, the exact mechanism is still undefined. Lesional apoptotic cells and necrotic core formation contribute greatly to the progression of plaque. The present study sought to determine whether modification of histone methylation is involved in macrophage apoptosis and unstable plaque formation in the condition of Hhcy.

MATERIALS AND METHODS

The unstable plaque formation, lesional apoptotic cells and status of histone methylation were monitored in the aortas of Hhcy ApoE^-/- mice induced by a high-methionine (HM) diet for 20weeks. Involvement of histone methylation in macrophage apoptosis and foam cell formation were assessed in macrophage Raw 264.7 cells after being challenged with homocysteine alone or in combination with the histone methylation inhibitor BIX 01294.

KEY FINDINGS

The unstable plaque formation and lesion apoptotic cells are increased in ApoE^-/- mice supplemented with high-methionine (HM), accompanied with a decreased expression of histone H3 lysine 9 dimethylation. Hhcy increases the apoptosis of macrophages and inhibits the histone H3 lysine 9 dimethylation, as well as the expression of histone methyltransferase G9a in vitro. Inhibition of histone methylation by BIX01294 enhances macrophage apoptosis and foam cell formation in vitro.

SIGNIFICANCE

Our data suggest that Hhcy promotes the progression of atherosclerosis via macrophage apoptosis. Histone methylation might be involved in macrophage apoptosis and unstable plaque formation in methionine induced hyperhomocysteinemic ApoE^-/- mice.

BIX01294, an inhibitor of histone methyltransferase, induces autophagy-dependent differentiation of glioma stem-like cells

Glioblastoma (GBM) contains rare glioma stem-like cells (GSCs) with capacities of self-renewal, multi-lineage differentiation, and resistance to conventional therapy. Drug-induced differentiation of GSCs is recognized as a promising approach of anti-glioma therapy. Accumulating evidence suggests that unique properties of stem cells depend on autophagy. Here we demonstrate that BIX01294, an inhibitor of a G9a histone methyltransferase (introducing H3K9me2 and H3K27me3 repressive marks) triggers autophagy in human glioma cells. Pharmacological or genetic inhibition of autophagy decreased LC3-II accumulation and GFP-LC3 punctation in BIX01294-treated cells. GSCs-enriched spheres originating from glioma cells and GBM patient-derived cultures express lower levels of autophagy related (ATG) genes than the parental glioma cell cultures. Typical differentiation inducers that upregulate neuronal and astrocytic markers in sphere cultures, increase the level of ATG mRNAs. G9a binds to the promoters of autophagy (LC3B, WIPI1) and differentiation-related (GFAP, TUBB3) genes in GSCs. Higher H3K4me3 (an activation mark) and lower H3K9me2 (the repressive mark) levels at the promoters of studied genes were detected in serum-differentiated cells than in sphere cultures. BIX01294 treatment upregulates the expression of autophagy and differentiation-related genes in GSCs. Pharmacological inhibition of autophagy decreases GFAP and TUBB3 expression in BIX01294-treated GSCs suggesting that BIX01294-induced differentiation of GSCs is autophagy-dependent.

Pharmacological inhibition of arginine and lysine methyltransferases induces nuclear abnormalities and suppresses angiogenesis in human endothelial cells

Posttranslational modifications of histone tails can alter chromatin structure and regulate gene transcription. While recent studies implicate the lysine/arginine protein methyltransferases in the regulation of genes for endothelial metabolism, the role of AMI-1 and AMI-5 compounds in angiogenesis remains unknown. Here, we show that global inhibition of arginine and lysine histone methyltransferases (HMTs) by AMI-5 induced an angiostatic profile in human microvascular endothelial cells and human umbilical vein endothelial cells. Based on FACS analysis, we found that inhibition of HMTs significantly affects proliferation of endothelial cells, by suppressing cell cycle progression in the G₀/G₁ phase. Immunofluorescent studies of the endothelial cells replication pattern by 5-ethynyl-2'-deoxyuridine incorporation disclosed that AMI-5, and the arginine methyltransferase inhibitor AMI-1, induced heterochromatin formation and a number of nuclear abnormalities, such as formation of micronuclei (MNs) and nucleoplasmic bridges (NPBs), which are markers of chromosomal instability. In addition to the modification of the cell cycle machinery in response to AMIs treatment, also endothelial cells migration and capillary-like tube formation processes were significantly inhibited, implicating a stimulatory role of HMTs in angiogenesis.

Hyperthermia induced HIF-1a expression of lung cancer through AKT and ERK signaling pathways

Background

Hyperthermia is a promising treatment for human lung cancer, but recurrence of the primary lesion is common, as the residual tumor becomes adapted to heat treatment and growth is induced by hypoxia-triggered HIF-1a expression. Here, we explored the effects of hyperthermia on HIF-1a expression, proliferation, and lung cancer angiogenesis.

Methods

Human NSCLC NCI-H1650 and SCLC NCI-H446 cell lines were used to examine cell viability, apoptosis, and HIF-1a expression level under a gradient of thermal conditions (37, 42 and 47 °C for 40 min). The 47 °C heat-adapted NCI-H1650 and NCI-H446 sublines (also called NCI-H1650-b and NCI-H446-b cells) had enhanced viability and HIF-1a expression levels compared to the parental and 42 °C heat-adapted cells and were thus used for subsequent research. Concentration gradients of wortmannin and PD98095 were used to inhibit AKT and ERK expression, respectively in the NSCLC NCI-H1650-b and SCLC NCI-H446-b cell lines, and cell growth curves were drawn. Western blots were used to detect the expression of HIF-1a, extracellular signal-regulated kinase (ERK), protein kinase B (AKT), phospho-ERK, and phospho-AKT. We established a subcutaneous transplantation tumor model with wortmannin and PD98095 intervention. Immunohistochemistry was used to detect the expression of HIF-1a and the vascular specific marker CD34, and tumor growth curves were drawn.

Results

Following hyperthermia treatment, HIF-1a expression in 47 °C heat-adapted NSCLC and SCLC cell lines was regulated by the AKT pathway. However, HIF-1a expression was also regulated by the ERK pathway in NSCLCs, while SCLCs did not exhibit changes in ERK. These biological behaviors are governed by signaling pathway protein phosphorylation. Furthermore, inhibiting the AKT pathway can suppress the proliferation and angiogenesis potential of both 47 °C heat-adapted NSCLCs and SCLCs, but inhibiting the ERK pathway only affects SCLCs.

Conclusion

Our study suggests that following hyperthermia, the proliferation and angiogenesis potential of residual NSCLCs and SCLCs is induced by HIF-1a. However, HIF-1a expression in NSCLCs is regulated by both the AKT and ERK signaling pathway, but HIF-1a expression in SCLCs is regulated only by the AKT signaling pathway. This study sheds light on the molecular regulatory mechanisms of lung cancer recurrence following hyperthermia treatment.

G9a Inhibition Induces Autophagic Cell Death via AMPK/mTOR Pathway in Bladder Transitional Cell Carcinoma

G9a has been reported to highly express in bladder transitional cell carcinoma (TCC) and G9a inhibition significantly attenuates cell proliferation, but the underlying mechanism is not fully understood. The present study aimed at examining the potential role of autophagy in the anti-proliferation effect of G9a inhibition on TCC T24 and UMUC-3 cell lines in vitro. We found that both pharmaceutical and genetical G9a inhibition significantly attenuated cell proliferation by MTT assay, Brdu incorporation assay and colony formation assay. G9a inhibition induced autophagy like morphology as determined by transmission electron microscope and LC-3 fluorescence assay. In addition, autophagy flux was induced by G9a inhibition in TCC cells, as determined by p62 turnover assay and LC-3 turnover assay. The autophagy induced positively contributed to the inhibition of cell proliferation because the growth attenuation capacity of G9a inhibition was reversed by autophagy inhibitors 3-MA. Mechanically, AMPK/mTOR pathway was identified to be involved in the regulation of G9a inhibition induced autophagy. Intensively activating mTOR by Rheb overexpression attenuated autophagy and autophagic cell death induced by G9a inhibition. In addition, pre-inhibiting AMPK by Compound C attenuated autophagy together with the anti-proliferation effect induced by G9a inhibition while pre-activating AMPK by AICAR enhanced them. In conclusion, our results indicate that G9a inhibition induces autophagy through activating AMPK/mTOR pathway and the autophagy induced positively contributes to the inhibition of cell proliferation in TCC cells. These findings shed some light on the functional role of G9a in cell metabolism and suggest that G9a might be a therapeutic target in bladder TCC in the future.