Myocyte enhancer factor 2D promotes colorectal cancer angiogenesis downstream of hypoxia-inducible factor 1α

MEF2D facilitates liver metastasis of gastric cancer cells through directly inducing H1X under IL-13 stimulation

Liver metastasis is the most common metastatic occurrence in gastric cancer patients, although the precise mechanism behind it remains unclear. Through a combination of proteomics and quantitative RT-PCR, our study has revealed a significant correlation between the upregulation of myocyte enhancer factor-2D (MEF2D) and both distant metastasis and poor prognosis in gastric cancer patients. In mouse models, we observed that overexpressing or knocking down MEF2D in gastric cancer cells respectively promoted or inhibited liver metastasis. Furthermore, our research has demonstrated that MEF2D regulates the transcriptional activation of H1X by binding to the H1X promoter. This regulation leads to the upregulation of H1X, which, in turn, promotes the in vivo metastasis of gastric cancer cells along with the upregulation of the downstream gene β-CATENIN. Additionally, we found that the expression of MEF2D and H1X at both mRNA and protein levels can be induced by the inflammatory factor IL-13, and this induction exhibits a time gradient dependence. In human gastric cancer tissues, the expression of IL13RA1, the receptor for IL-13, positively correlates with the expression of MEF2D and H1X. IL13RA1 has been identified as an intermediate receptor through which IL-13 regulates MEF2D. In conclusion, our findings suggest that MEF2D plays a crucial role in promoting liver metastasis of gastric cancer by upregulating H1X and downstream target β-CATENIN in response to IL-13 stimulation. Targeting MEF2D could therefore be a promising therapeutic strategy for the clinical management of gastric cancer. STATEMENT OF SIGNIFICANCE: MEF2D promotes its transcriptional activation in gastric cancer cells by binding to the H1X promoter and is upregulated by IL-13-IL13RA1, thereby promoting distant metastasis of gastric cancer.

Brusatol enhances MEF2A expression to inhibit RCC progression through the Wnt signalling pathway in renal cell carcinoma

Renal cell carcinoma (RCC) is the most aggressive subtype of kidney tumour with a poor prognosis and an increasing incidence rate worldwide. Brusatol, an essential active ingredient derived from Brucea javanica, exhibits potent antitumour properties. Our study aims to explore a novel treatment strategy for RCC patients. We predicted 37 molecular targets of brusatol based on the structure of brusatol, and MEF2A (Myocyte Enhancer Factor 2A) was selected as our object through bioinformatic analyses. We employed various experimental techniques, including RT-PCR, western blot, CCK8, colony formation, immunofluorescence, wound healing, flow cytometry, Transwell assays and xenograft mouse models, to investigate the impact of MEF2A on RCC. MEF2A expression was found to be reduced in patients with RCC, indicating a close correlation with MEF2A deubiquitylation. Additionally, the protective effects of brusatol on MEF2A were observed. The overexpression of MEF2A inhibits RCC cell proliferation, invasion and migration. In xenograft mice, MEF2A overexpression in RCC cells led to reduced tumour size compared to the control group. The underlying mechanism involves the inhibition of RCC cell proliferation, invasion, migration and epithelial-mesenchymal transition (EMT) through the modulation of Wnt/β-catenin signalling. Altogether, we found that MEF2A overexpression inhibits RCC progression by Wnt/β-catenin signalling, providing novel insight into diagnosis, treatment and prognosis for RCC patients.

A Ubiquitin-Dependent Switch on MEF2D Senses Pro-Metastatic Niche Signals to Facilitate Intrahepatic Metastasis of Liver Cancer

Effective treatment for metastasis, a leading cause of cancer-associated death, is still lacking. To seed on a distal organ, disseminated cancer cells (DCCs) must adapt to the local tissue microenvironment. However, it remains elusive how DCCs respond the pro-metastatic niche signals. Here, systemic motif-enrichment identified myocyte enhancer factor 2D (MEF2D) as a critical sensor of niche signals to regulate DCCs adhesion and colonization, leading to intrahepatic metastasis and recurrence of liver cancer. In this context, MEF2D transactivates Itgb1 (coding β1-integrin) and Itgb4 (coding β4-integrin) to execute temporally unique functions, where ITGB1 recognizes extracellular matrix for early seeding, and ITGB4 acts as a novel sensor of neutrophil extracellular traps-DNA (NETs-DNA) for subsequent chemotaxis and colonization. In turn, an integrin-FAK circuit promotes a phosphorylation-dependent USP14-orchastrated deubiquitination switch to stabilize MEF2D via circumventing degradation by the E3-ubiquitin-ligase MDM2. Clinically, the USP14(pS432)-MEF2D-ITGB1/4 feedback loop is often hyper-active and indicative of inferior outcomes in human malignancies, while its blockade abrogated intrahepatic metastasis of DCCs. Together, DCCs exploit a deubiquitination-dependent switch on MEF2D to integrate niche signals in the liver mesenchyme, thereby amplifying the pro-metastatic integrin-FAK signaling. Disruption of this feedback loop is clinically applicable with fast-track potential to block microenvironmental cues driving metastasis.

Prediction of immunotherapy efficacy and immunomodulatory role of hypoxia in colorectal cancer

Immunotherapy has been used in the clinical treatment of colorectal cancer (CRC); however, most patients fail to achieve satisfactory survival benefits. Biomarkers with high specificity and sensitivity are being increasingly developed to predict the efficacy of CRC immunotherapy. In addition to DNA alteration markers, such as microsatellite instability/mismatch repair and tumor mutational burden, immune cell infiltration and immune checkpoints (ICs), epigenetic changes and no-coding RNA, and gut microbiomes all show potential predictive ability. Recently, the hypoxic tumor microenvironment (TME) has been identified as a key factor mediating CRC immune evasion and resistance to treatment. Hypoxia-inducible factor-1α is the central transcription factor in the hypoxia response that drives the expression of a vast number of survival genes by binding to the hypoxia response element in cancer and immune cells in the TME. Hypoxia regulates angiogenesis, immune cell infiltration and activation, expression of ICs, and secretion of various immune molecules in the TME and is closely associated with the immunotherapeutic efficacy of CRC. Currently, various agents targeting hypoxia have been found to improve the TME and enhance the efficacy of immunotherapy. We reviewed current markers commonly used in CRC to predict therapeutic efficacy and the mechanisms underlying hypoxia-induced angiogenesis and tumor immune evasion. Exploring the mechanisms by which hypoxia affects the TME will assist the discovery of new immunotherapeutic predictive biomarkers and development of more effective combinations of agents targeting hypoxia and immunotherapy.

Apigenin suppresses tumor angiogenesis and growth via inhibiting HIF-1α expression in non-small cell lung carcinoma

Tumor angiogenesis inhibitors such as Bevacizumab, Ramucirumab and Endostar have been applied to the therapy of non-small cell lung carcinoma (NSCLC) patients, especially for lung adenocarcinoma (LUAD). However, several safe concerns such as neutropenia, febrile neutropenia and hypertension pulmonary hemorrhage limit their further development. And they often showed poor efficacy and serious side effect for lung squamous cell carcinoma (LUSC) patient. Thus, identification of effective and safe tumor angiogenesis inhibitor for NSCLC therapy is warranted. Apigenin is a bioflavonoid with potential anti-tumor effect and perfect safety, but its effect on tumor angiogenesis and underlying mechanism are still unclear. Herein, we found that apigenin not merely suppressed endothelial cells related motilities but also reduced pericyte coverage. Further research showed that apigenin had strong suppressive activity against HIF-1α expression and its downstream VEGF-A/VEGFR2 and PDGF-BB/PDGFβR signaling pathway. Apigenin also reduced microvessel density and pericyte coverage on the xengraft model of NCI-H1299 cells, leading to suppression of tumor growth. Moreover, apigenein showed perfect anti-angiogenic effect in xengraft model of LUSC cell NCI-H1703 cells, indicating it may be developed into a potential angiogenesis inhibitor for LUSC patient. Collectively, our study provides new insights into the anti-tumor mechanism of apigenin and suggests that apigenin is a safe and effective angiogenesis inhibitor for NSCLC therapy.

LncRNA CASC15 regulates breast cancer cell stemness via the miR-654-5p/MEF2D axis

Emerging evidence has demonstrated the prognostic and diagnostic potential of long noncoding RNA (lncRNA) cancer susceptibility candidate 15 (lncRNA CASC15) for the progression and tumorigenesis of human cancer. However, how CASC15 modulates the stemness of breast cancer stem cells (BCSCs) is not well understood. In this study, high expression of CASC15 in MCF-7 CSCs was reported, relative to MCF-7 cells, and this phenomenon was associated with metastatic lymph nodes, higher TNM stage, and shorter breast cancer survival rates. Further experiments revealed that CASC15 promoted the acquisition of stemness properties of breast cancer cells (BSCCs) by competing with endogenous RNA for miR-654-5p, resulting in overexpression of MEF2D in BCSCs. Overall, breast cancer stemness and tumor development are regulated via the CASC15/miR-654-5p/MEF2D axis. Accordingly, this pathway can be explored for breast cancer therapy.

ERK5 signalling pathway is a novel target of sorafenib: Implication in EGF biology

Sorafenib is a multikinase inhibitor widely used in cancer therapy with an antitumour effect related to biological processes as proliferation, migration or invasion, among others. Initially designed as a Raf inhibitor, Sorafenib was later shown to also block key molecules in tumour progression such as VEGFR and PDGFR. In addition, sorafenib has been connected with key signalling pathways in cancer such as EGFR/EGF. However, no definitive clue about the molecular mechanism linking sorafenib and EGF signalling pathway has been established so far. Our data in HeLa, U2OS, A549 and HEK293T cells, based on in silico, chemical and genetic approaches demonstrate that the MEK5/ERK5 signalling pathway is a novel target of sorafenib. In addition, our data show how sorafenib is able to block MEK5-dependent phosphorylation of ERK5 in the Ser218/Tyr220, affecting the transcriptional activation associated with ERK5. Moreover, we demonstrate that some of the effects of this kinase inhibitor onto EGF biological responses, such as progression through cell cycle or migration, are mediated through the effect exerted onto ERK5 signalling pathway. Therefore, our observations describe a novel target of sorafenib, the ERK5 signalling pathway, and establish new mechanistic insights for the antitumour effect of this multikinase inhibitor.

DYRK1A phosphorylates MEF2D and decreases its transcriptional activity

Myocyte enhancer factor 2D (MEF2D) is predominantly expressed in the nucleus and associated with cell growth, differentiation, survival and apoptosis. Previous studies verified that phosphorylation at different amino acids determined MEF2's transcriptional activity which was essential in regulating downstream target genes expression. What regulates phosphorylation of MEF2D and affects its function has not been fully elucidated. Here, we uncovered that dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A), a kinase critical in Down's syndrome pathogenesis, directly bound to and phosphorylated MEF2D at Ser251 in vitro. Phosphorylation of MEF2D by DYRK1A significantly increased MEF2D protein level but attenuated its transcriptional activity, which resulted in decreased transcriptions of MEF2D target genes. Phosphorylation mutated Ser251A MEF2D exhibited enhanced transcriptional activity compared with wild type MEF2D. MEF2D and DYRK1A were observed co-localized in HEK293 and U87MG cells. Moreover, DYRK1A-mediated MEF2D phosphorylation in vitro might influence its nuclear export upon subcellular fractionation, which partially explained the reduction of MEF2D transcriptional activity by DYRK1A. Our results indicated that DYRK1A might be a regulator of MEF2D transcriptional activity and indirectly get involved in regulation of MEF2D target genes.

KDM1A Promotes Immunosuppression in Hepatocellular Carcinoma by Regulating PD-L1 through Demethylating MEF2D

Background

Immune checkpoint inhibitor therapy targeting antiprogrammed cell death-1 (anti-PD-1) or its ligand (anti-PD-L1) is effective in the treatment of some hepatocellular carcinomas (HCC). Hence, further identification of biological targets related to PD-L1 regulation in HCC is beneficial to improve the clinical efficacy of immunotherapy. Some HCC cells express lysine-specific demethylase 1A (KDM1A), which is implicated in the reduced survival time of patients. Here, we studied whether the level of PD-L1 and the immunosuppression are regulated by KDM1A and its miRNA in HCC cells.

Methods

In the present study, we studied clinical data from The Cancer Genome Atlas (TCGA) database. We performed qPCR and western blotting assays to measure the expression level of genes of interest. PD-L1 expression was also analyzed by FACS. Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 was used to generate gene knockout cells to investigate the relationships of genes of interest. We also developed a reporter gene assay (RGA) to explore the changes in T cell-induced antitumor immunity relative to PD-L1 expression in HCC cells. The binding between proteins and promoters or miRNAs and their target genes was explored by luciferase reporter assays.

Results

The results showed that PD-L1 and KDM1A were increased in HCC patients and cells, and KDM1A promoted the expression of PD-L1 in HCC cells. Our findings showed that the enhancement of PD-L1 expression was not attributed to mitochondrial dysfunction caused by increases in KDM1A in HCC cells. Furthermore, we observed a lower level of MEF2D methylation in HCC cells than in normal human liver cells. Demethylated MEF2D could bind to the promoter of PD-L1 and activate its expression, while KDM1A interacted with MEF2D and acted as a demethylase to reduce its methylation. Moreover, a new miRNA, miR-329-3p, targeting KDM1A was found to regulate the PD-L1 expression profile in HCC cells. In the xenograft model, the tumors treated with miR-329-3p showed growth inhibition.

Conclusions

Mechanistically, miR-329-3p inhibits tumor cellular immunosuppression and reinforces the response of tumor cells to T cell-induced cytotoxic effect by targeting KDM1A mRNA and downregulating its expression, which contributed to MEF2D demethylation and activation of PD-L1 expression.

MEF2A transcriptionally upregulates the expression of ZEB2 and CTNNB1 in colorectal cancer to promote tumor progression

Colorectal cancer (CRC) is one of the leading cancers worldwide, accounting for high morbidity and mortality. The mechanisms governing tumor growth and metastasis in CRC require detailed investigation. The results of the present study indicated that the transcription factor (TF) myocyte enhancer factor 2A (MEF2A) plays a dual role in promoting proliferation and metastasis of CRC by inducing the epithelial-mesenchymal transition (EMT) and activation of WNT/β-catenin signaling. Aberrant expression of MEF2A in CRC clinical specimens was significantly associated with poor prognosis and metastasis. Functionally, MEF2A directly binds to the promoter region to initiate the transcription of ZEB2 and CTNNB1. Simultaneous activation of the expression of EMT-related TFs and Wnt/β-catenin signaling by MEF2A overexpression induced the EMT and increased the frequency of tumor formation and metastasis. The present study identified a new critical oncogene involved in the growth and metastasis of CRC, providing a potential novel therapeutic target for CRC intervention.

Silencing of MEF2D by siRNA Loaded Selenium Nanoparticles for Ovarian Cancer Therapy

BACKGROUND

Delivery of therapeutic small interfering RNA (siRNA) via functionalized nanoparticles holds great promise for cancer therapy. However, developing a safe and efficient delivery carrier of siRNA is a challenging issue.

METHODS

RGDfC peptide was used to modify the surface of selenium nanoparticles (SeNPs) to synthesize a biocompatible siRNA delivery vehicle (R-SeNPs), and MEF2D-siRNA was loaded onto R-SeNPs to prepare a functionalized selenium nanoparticle R-Se@MEF2D-siRNA. The chemical properties of R-SeNPs were characterized, and the anticancer efficacy as well as related mechanisms of R-Se@MEF2D-siRNA were further explored.

RESULTS

R-Se@MEF2D-siRNA was significantly taken up by SKOV3 cells and could enter SKOV3 cells mainly in the clathrin-associated endocytosis way. The result of in vitro siRNA release demonstrated that R-Se@MEF2D-siRNA could release MEF2D-siRNA quicker in a microenvironment simulating a lysosomal environment in tumor cells compared to a normal physiological environment. The results of qRT-PCR assay proved that R-Se@MEF2D-siRNA could effectively silence the expression of the MEF2D gene in SKOV3 cells. R-Se@MEF2D-siRNA remarkably suppressed the proliferation of SKOV3 cells and further triggered its apoptosis. In addition, R-Se@MEF2D-siRNA had the capability to disrupt mitochondrial membrane potential (MMP) in SKOV3 cells and resulted in the overproduction of reactive oxygen species (ROS), indicating that mitochondrial dysfunction and ROS generation played an important role in the apoptosis of SKOV3 cells induced by R-Se@MEF2D-siRNA. In vivo, R-Se@MEF2D-siRNA also exhibited excellent antitumor activity mainly through decreasing tumor cells proliferation and triggering their apoptosis in tumor-bearing nude mice.

CONCLUSION

R-Se@MEF2D-siRNA provides an alternative strategy for ovarian cancer treatment in the clinic.

Purification, crystallization, and X-ray diffraction analysis of myocyte enhancer factor 2D and DNA complex

MEF2D-fusions have recently been identified as one of the major oncogenic drivers in precursor B-cell acute lymphoblastic leukemia (B-ALL). More importantly, they are often associated with patients with poor prognosis in B-ALL. To have a better understanding of the pathogenic mechanism underpinning MEF2D-fusions-driven leukemogenesis, it's essential to uncover the related structure information. In this study, we expressed and purified the MEF2D N-terminal DNA binding domain. The recombinant protein was engineered by cloning the encoding gene into the expression vector pET-32 m. A series of chromatographic steps involving affinity, ion-exchange and gel-filtration chromatography were used to achieve a final purity of >95%. For the crystallization of the MEF2D-DNA complex, a double-stranded DNA encoding 5'-AACTATTTATAAGA-3' and 5'-TTCTTATAAATAGT-3' was used (Wu et al., 2010) [1]. The MEF2D-DNA crystal with the size of about 20 μm × 20 μm × 20 μm was obtained at a final concentration of 12 mg/ml at the reservoir condition containing 30% PEG1500. The X-ray examination showed that the MEF2D-DNA crystal diffracted to 4.5 Å resolution, and belonged to space group P1, with unit-cell parameters of a = 77.2 Å, b = 77.2 Å, c = 231.4 Å.

The Role of Oxidative Stress and Its Counteractive Utility in Colorectal Cancer (CRC)

An altered redox status accompanied by an elevated generation of reactive oxygen/nitrogen species (ROS/RNS) has been implicated in a number of diseases including colorectal cancer (CRC). CRC, being one of the most common cancers worldwide, has been reported to be associated with multiple environmental and lifestyle factors (e.g., dietary habits, obesity, and physical inactivity) and harboring heightened oxidative stress that results in genomic instability. Although under normal condition ROS regulate many signal transduction pathways including cell proliferation and survival, overwhelming of the antioxidant capacity due to metabolic abnormalities and oncogenic signaling leads to a redox adaptation response that imparts drug resistance. Nevertheless, excessive reliance on elevated production of ROS makes the tumor cells increasingly vulnerable to further ROS insults, and the abolition of such drug resistance through redox perturbation could be instrumental to preferentially eliminate them. The goal of this review is to demonstrate the evidence that links redox stress to the development of CRC and assimilate the most up-to-date information that would facilitate future investigation on CRC-associated redox biology. Concomitantly, we argue that the exploitation of this distinct biochemical property of CRC cells might offer a fresh avenue to effectively eradicate these cells.

Hypoxia-Inducible Lysine Methyltransferases: G9a and GLP Hypoxic Regulation, Non-histone Substrate Modification, and Pathological Relevance

Oxygen sensing is inherent among most animal lifeforms and is critical for organism survival. Oxygen sensing mechanisms collectively trigger cellular and physiological responses that enable adaption to a reduction in ideal oxygen levels. The major mechanism by which oxygen-responsive changes in the transcriptome occur are mediated through the hypoxia-inducible factor (HIF) pathway. Upon reduced oxygen conditions, HIF activates hypoxia-responsive gene expression programs. However, under normal oxygen conditions, the activity of HIF is regularly suppressed by cellular oxygen sensors; prolyl-4 and asparaginyl hydroxylases. Recently, these oxygen sensors have also been found to suppress the function of two lysine methyltransferases, G9a and G9a-like protein (GLP). In this manner, the methyltransferase activity of G9a and GLP are hypoxia-inducible and thus present a new avenue of low-oxygen signaling. Furthermore, G9a and GLP elicit lysine methylation on a wide variety of non-histone proteins, many of which are known to be regulated by hypoxia. In this article we aim to review the effects of oxygen on G9a and GLP function, non-histone methylation events inflicted by these methyltransferases, and the clinical relevance of these enzymes in cancer.

Cordycepin Inhibits Cancer Cell Proliferation and Angiogenesis through a DEK Interaction via ERK Signaling in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is a malignant tumor that arises from the epithelial cells of the bile duct and is notorious for its poor prognosis. The clinical outcome remains disappointing, and thus more effective therapeutic options are urgently required. Cordycepin, a traditional Chinese medicine, provides multiple pharmacological strategies in antitumors, but its mechanisms have not been fully elucidated. In this study, we reported that cordycepin inhibited the viability and proliferation capacity of CCA cells in a time- and dose-dependent manner determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and colony formation assay. Flow cytometry and Hoechst dye showed that cordycepin induced cancer cell apoptosis via extracellular signal-regulated kinase (ERK) 1/2 deactivation. Moreover, cordycepin significantly reduced the angiogenetic capabilities of CCA in vitro as examined by tube formation assay. We also discovered that cordycepin inhibited DEK expression by using Western blot assay. DEK serves as an oncogenic protein that is overexpressed in various gastrointestinal tumors. DEK silencing inhibited CCA cell viability and angiogenesis but not apoptosis induction determined by Western blot and flow cytometry. Furthermore, cordycepin significantly inhibited tumor growth and angiogenic capacities in a xenograft model by downregulating the expression of DEK, phosphorylated ERK1/2 CD31 and von Willebrand factor (vWF). Taken together, we demonstrated that cordycepin inhibited CCA cell proliferation and angiogenesis with a DEK interaction via downregulation in ERK signaling. These data indicate that cordycepin may serve as a novel agent for CCA clinical treatment and prognosis improvement. SIGNIFICANCE STATEMENT: Cordycepin provides multiple strategies in antitumors, but its mechanisms are not fully elucidated, especially on cholangiocarcinoma (CCA). We reported that cordycepin inhibited the viability of CCA cells, induced apoptosis via extracellular signal-regulated kinase 1/2 deactivation and DEK inhibition, and reduced the angiogenetic capabilities of CCA both in vivo and in vitro.

Disruption of SIRT7 Increases the Efficacy of Checkpoint Inhibitor via MEF2D Regulation of Programmed Cell Death 1 Ligand 1 in Hepatocellular Carcinoma Cells

BACKGROUND & AIMS

Immune checkpoint inhibitors have some efficacy in the treatment of hepatocellular carcinoma (HCC). Programmed cell death 1 ligand 1 (PD-L1), expressed on some cancer cells, binds to the receptor programmed cell death 1 (PDCD1, also called PD1) on T cells to prevent their proliferation and reduce the antigen-tumor immune response. Immune cells that infiltrate some types of HCCs secrete interferon gamma (IFNG). Some HCC cells express myocyte enhancer factor 2D (MEF2D), which has been associated with shorter survival times of patients. We studied whether HCC cell expression of MEF2D regulates expression of PD-L1 in response to IFNG.

METHODS

We analyzed immune cells from 20 fresh HCC tissues by flow cytometry. We analyzed 225 fixed HCC tissues (from 2 cohorts) from patients in China by immunohistochemistry and obtained survival data. We created mice with liver-specific knockout of MEF2D (MEF2D^LPC-KO mice). We knocked out or knocked down MEF2D, E1A binding protein p300 (p300), or sirtuin 7 (SIRT7) in SMMC-7721, Huh7, H22, and Hepa1-6 HCC cell lines, some incubated with IFNG. We analyzed liver tissues from mice and cell lines by RNA sequencing, immunoblot, dual luciferase reporter, and chromatin precipitation assays. MEF2D protein acetylation and proteins that interact with MEF2D were identified by coimmunoprecipitation and pull-down assays. H22 cells, with MEF2D knockout or without (controls), were transplanted into BALB/c mice, and some mice were given antibodies to deplete T cells. Mice bearing orthotopic tumors grown from HCC cells, with or without knockout of SIRT7, were given injections of an antibody against PD1. Growth of tumors was measured, and tumors were analyzed by immunohistochemistry and flow cytometry.

RESULTS

In human HCC specimens, we found an inverse correlation between level of MEF2D and numbers of CD4⁺ and CD8⁺ T cells; level of MEF2D correlated with percentages of PD1-positive or TIM3-positive CD8⁺ T cells. Knockout of MEF2D from H22 cells reduced their growth as allograft tumors in immune-competent mice but not in immune-deficient mice or mice with depletion of CD8⁺ T cells. When MEF2D-knockout cells were injected into immune-competent mice, they formed smaller tumors that had increased infiltration and activation of T cells compared with control HCC cells. In human and mouse HCC cells, MEF2D knockdown or knockout reduced expression of PD-L1. MEF2D bound the promoter region of the CD274 gene (encodes PD-L1) and activated its transcription. Overexpression of p300 in HCC cells, or knockout of SIRT7, promoted acetylation of MEF2D and increased its binding, along with acetylated histones, to the promoter region of CD274. Exposure of HCC cells to IFNG induced expression of p300 and its binding MEF2D, which reduced the interaction between MEF2D and SIRT7. MEF2D-induced expression of PD-L1 upon IFNG exposure was independent of interferon-regulatory factors 1 or 9. In HCC cells not exposed to IFNG, SIRT7 formed a complex with MEF2D that attenuated expression of PD-L1. Knockout of SIRT7 reduced proliferation of HCC cells and growth of tumors in immune-deficient mice. Compared with allograft tumors grown from control HCC cells, in immune-competent mice, tumors grown from SIRT7-knockout HCC cells expressed higher levels of PD-L1 and had reduced infiltration and activation of T cells. In immune-competent mice given antibodies to PD1, allograft tumors grew more slowly from SIRT7-knockout HCC cells than from control HCC cells.

CONCLUSIONS

Expression of MEF2D by HCC cells increases their expression of PD-L1, which prevents CD8⁺ T-cell-mediated antitumor immunity. When HCC cells are exposed to IFNG, p300 acetylates MEF2D, causing it to bind the CD274 gene promoter and up-regulate PD-L1 expression. In addition to promoting HCC cell proliferation, SIRT7 reduced acetylation of MEF2D and expression of PD-L1 in HCC cells not exposed to IFNG. Strategies to manipulate this pathway might increase the efficacy of immune therapies for HCC.

Exploiting Current Understanding of Hypoxia Mediated Tumour Progression for Nanotherapeutic Development

Hypoxia is one of the most common phenotypes of malignant tumours. Hypoxia leads to the increased activity of hypoxia-inducible factors (HIFs), which regulate the expression of genes controlling a raft of pro-tumour phenotypes. These include maintenance of the cancer stem cell compartment, epithelial-mesenchymal transition (EMT), angiogenesis, immunosuppression, and metabolic reprogramming. Hypoxia can also contribute to the tumour progression in a HIF-independent manner via the activation of a complex signalling network pathway, including JAK-STAT, RhoA/ROCK, NF-κB and PI3/AKT. Recent studies suggest that nanotherapeutics offer a unique opportunity to target the hypoxic microenvironment, enhancing the therapeutic window of conventional therapeutics. In this review, we summarise recent advances in understanding the impact of hypoxia on tumour progression, while outlining possible nanotherapeutic approaches for overcoming hypoxia-mediated resistance.

Negative regulation of angiogenesis by novel micro RNAs

Angiopoietin-1 (Ang-1) is a ligand of Tie-2 receptors that promotes survival, migration, and differentiation of endothelial cells (ECs). Recent studies have identified several microRNA (miRNA) families that either promote or inhibit angiogenesis. To date, the nature and functional importance of miRNAs in Ang-1-induced angiogenesis are unknown. Microarray screening of known miRNAs in human umbilical vein endothelial cells (HUVECs) revealed that the expressions of miR-103b, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p significantly decrease following exposure to Ang-1 for 24 h. Exposure to the angiogenesis factors angiopoietin-2 (Ang-2), vascular endothelial growth factor, fibroblast growth factor 2, and transforming growth factor β also inhibits miR-103b expression, but exerts varying effects on the other miRNAs. By overexpressing miR-103b, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p with selective mimics, we demonstrated that the pro-survival effects of Ang-1 are eliminated, Caspase-3 activity increases, and cell migration, proliferation, and capillary-like tube formation decreases. Conversely, transfection with selective miRNA inhibitors increases cell survival, inhibits Caspase-3 activity, and stimulates migration, proliferation and tube formation. miRNet miRNA-target gene network analyses revealed that miR-103, miR-330-5p, miR-557, miR-575, miR-1287-5p, and miR-1468-5p directly interact with 47, 95, 165, 108, 49, and 16 gene targets, respectively. Since many of these genes are positive regulators of angiogenic processes, we conclude that these miRNAs function as anti-angiogenic miRNAs and that their downregulation may be essential for Ang-1-induced angiogenesis to occur.

MEF2 and the tumorigenic process, hic sunt leones

While MEF2 transcription factors are well known to cooperate in orchestrating cell fate and adaptive responses during development and adult life, additional studies over the last decade have identified a wide spectrum of genetic alterations of MEF2 in different cancers. The consequences of these alterations, including triggering and maintaining the tumorigenic process, are not entirely clear. A deeper knowledge of the molecular pathways that regulate MEF2 expression and function, as well as the nature and consequences of MEF2 mutations are necessary to fully understand the many roles of MEF2 in malignant cells. This review discusses the current knowledge of MEF2 transcription factors in cancer.

MEF2 transcription factors in human placenta and involvement in cytotrophoblast invasion and differentiation

Development of the human placenta and its trophoblast cell types is critical for a successful pregnancy. Defects in trophoblast invasion and differentiation are associated with adverse pregnancy outcomes, including preeclampsia. The members of myocyte enhancer factor-2 (MEF2) family of transcription factors are key regulators of cellular proliferation, differentiation, and invasion in various cell types and tissues and might play a similarly important role in regulating trophoblast proliferation, invasion, and differentiation during human placental development. In the present study, using human cytotrophoblast cell lines (HTR8/SVneo and BeWo) and primary human cytotrophoblasts (CTBs), we show that members of the MEF2 family are differentially expressed in human placental CTBs, with MEF2B and MEF2D being highly expressed in first trimester extravillous CTBs. Overexpression of MEF2D results in cytotrophoblast proliferation and enhances the invasion and migration of extravillous-like HTR8/SVneo cells. This invasive property is blocked by overexpression of a dominant negative MEF2 (dnMEF2). In contrast, MEF2A is the principal MEF2 isoform expressed in term CTBs, MEF2C and MEF2D being expressed more weakly, and MEF2B expression being undetected. Overexpression of MEF2A induces cytotrophoblast differentiation and syncytium formation in BeWo cells. During in vitro differentiation of primary CTBs, MEF2A expression is associated with CTB differentiation into syncytiotrophoblast. Additionally, the course of p38 MAPK and ERK5 activities parallels the increase in MEF2A expression. These findings suggest individual members of MEF2 family distinctively regulate cytotrophoblast proliferation, invasion, and differentiation. Dysregulation of expression of MEF2 family or of their upstream signaling pathways may be associated with placenta-related pregnancy disorders.