MiR-138 inhibits EZH2 methyltransferase expression and methylation of histone H3 at lysine 27, and affects thermotolerance acquisition

Thermotolerance acquisition involves neuronal network remodeling and, hence, alteration in the repertoire of expressed proteins. We have previously demonstrated the role of histone H3 methylation at lysine 27 (H3K27) by EZH2 methyltransferase in the regulation of gene expression during the critical period for the establishment of thermal control in chicks. Here we describe another level of biological regulation, demonstrating the inhibitory role of microRNAs (miRNAs) in the regulation of EZH2 expression in thermoregulatory system development and functioning. During heat conditioning in the critical period for the establishment of thermal control, a decrease in expression of the EZH2‐targeting miR‐138 occurred simultaneously with an increase in EZH2 levels in the preoptic anterior hypothalamus. Intracranial injection of miR‐138 during the critical period led to a transient reduction in EZH2 levels, which was accompanied by a decrease in H3K27 methylation. Injection of miR‐138 followed by heat conditioning also abolished EZH2 induction during heat conditioning. Moreover, this miR‐138‐induced inhibition of EZH2 during the critical period resulted in a long‐term effect on EZH2 expression. A week after the treatment, the EZH2 protein levels in conditioned and in nonconditioned chicks were different from those in their saline‐injected counterparts and the directions of change were opposite to each other. Finally, miR‐138 injection during the critical period disrupted the establishment of thermoregulation, manifested as a defective body temperature response to heat. These data demonstrate a role for miRNAs in regulating the expression of histone‐modifying enzymes, and thus emphasize the multilevel regulation mechanism which includes both epigenetic and miRNA regulatory mechanisms in neuronal network organization during the critical period of sensory development.     

Expression patterns and potential roles of SIRT1 in human medulloblastoma cells in vivo and in vitro

Medulloblastoma is a primitive neuroectodermal tumor, which originates in the cerebellum, presumably due to the alterations of some neurogenetic elements. Sirtuin 1 (SIRT1), a class III histone deacetylase (HDAC), regulates differentiation of neuronal stem cells but its status in medulloblastomas remains largely unknown. The current study aimed to address this issue by checking SIRT1 expression in noncancerous cerebellar tissues, medulloblastoma tissues and established cell lines. The roles of SIRT1 in proliferation and survival of UW228‐3 medulloblastoma cells were analyzed by SIRT1 small interfering RNA (siRNA) transfection and SIRT1 inhibitor nicotinamide treatment. The results revealed that the frequency of SIRT1 expression in medulloblastoma tissues was 64.17% (77/120), while only one out of seven tumor‐surrounding noncancerous cerebellar tissues showed restricted SIRT1 expression in the cells within the granule layer. Of the three morphological subtypes, the rates of SIRT1 detection in the large cell/anaplastic cell (79.07%; 34/43) and the classic medulloblastomas (60.29%; 41/68) are higher than that (22.22%; 2/9) in nodular/desmoplastic medulloblastomas (P < 0.01 and P < 0.05, respectively). Heterogeneous SIRT1 expression was commonly observed in classic medulloblastoma. Inhibition of SIRT1 expression by siRNA arrested 64.96% of UW228‐3 medulloblastoma cells in the gap 1 (G1) phase and induced 14.53% of cells to apoptosis at the 48‐h time point. Similarly, inhibition of SIRT1 enzymatic activity with nicotinamide brought about G1 arrest and apoptosis in a dose‐related fashion. Our data thus indicate: (i) that SIRT1 may act as a G1‐phase promoter and a survival factor in medulloblastoma cells; and (ii) that SIRT1 expression is correlated with the formation and prognosis of human medulloblastomas. In this context, SIRT1 would be a potential therapeutic target of medulloblastomas.     

Histone Mark Profiling in Pediatric Astrocytomas Reveals Prognostic Significance of H3K9 Trimethylation and Histone Methyltransferase SUV39H1

Alterations in global histone methylation regulate gene expression and participate in cancer onset and progression. The profile of histone methylation marks in pediatric astrocytomas is currently understudied with limited data on their distribution among grades. The global expression patterns of repressive histone marks H3K9me3, H3K27me3, and H4K20me3 and active H3K4me3 and H3K36me3 along with their writers SUV39H1, SETDB1, EZH2, MLL2, and SETD2 were investigated in 46 pediatric astrocytomas and normal brain tissues. Associations between histone marks and modifying enzymes with clinicopathological characteristics and disease-specific survival were studied along with their functional impact in proliferation and migration of pediatric astrocytoma cell lines using selective inhibitors in vitro. Upregulation of histone methyltransferase gene expression and deregulation of histone code were detected in astrocytomas compared to normal brain tissues, with higher levels of SUV39H1, SETDB1, and SETD2 as well as H4K20me3 and H3K4me3 histone marks. Pilocytic astrocytomas exhibited lower MLL2 levels compared to diffusely infiltrating tumors indicating a differential pattern of epigenetic regulator expression between the two types of astrocytic neoplasms. Moreover, higher H3K9me3, H3K36me3, and SETDB1 expression was detected in grade IIΙ/IV compared to grade II astrocytomas. In univariate analysis, elevated H3K9me3 and MLL2 and diminished SUV39H1 expression adversely affected survival. Upon multivariate survival analysis, only SUV39H1 expression was revealed as an independent prognostic factor of adverse significance. Treatment of pediatric astrocytoma cell lines with SUV39H1 inhibitor reduced proliferation and cell migration. Our data implicate H3K9me3 and SUV39H1 in the pathobiology of pediatric astrocytomas, with SUV39H1 yielding prognostic information independent of other clinicopathologic variables.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13311-021-01090-x.     

EZH2 expression in gliomas: Correlation with CDKN2A gene deletion/ p16 loss and MIB‐1 proliferation index

Enhancer of zeste homolog 2 (EZH2) mediated down‐regulation of CDKN2A/p16 has been observed in cell lines as well as in a few carcinomas. However, there is no study correlating EZH2 expression with CDKN2A/p16 status in gliomas. Hence, the present study was conducted to evaluate EZH2 expression in astrocytic and oligodendroglial tumors and correlate with CDKN2A/p16 status as well as MIB‐1 labeling index (LI). Gliomas of all grades (n = 118) were studied using immunohistochemistry to assess EZH2, p16 and MIB‐1 LI and fluorescence in situ hybrization to evaluate CDKN2A gene status. EZH2 expression and CDKN2A homozygous deletion (HD) were both significantly more frequent in high‐grade gliomas (HGG). Further, strong EZH2 expression (LI ≥ 25%) was significantly more common in HGGs without CDKN2A HD (48.7%; 19/39) as compared to cases with deletion (15.8%; 3/19). Loss of p16 expression was noted in 100% and 51.3% of CDKN2A deleted and non‐deleted tumors, respectively. Notably, 80% (16/20) of the CDKN2A non‐deleted HGGs with p16 loss had strong EZH2 expression, in contrast to only 15.8% (3/19) in the deleted group. Loss of p16 expression significantly correlated with MIB‐1 LI, irrespective of EZH2 status. Thus, this study shows that EZH2 expression correlates with tumor grade in both astrocytic and oligodendroglial tumors and hence can be used as a diagnostic marker to differentiate between low and HGGs. Further, this is the first report demonstrating an inverse correlation of strong EZH2 expression with CDKN2A HD in HGGs. Loss of p16 protein expression is mostly attributable to CDKN2A HD and correlates significantly with MIB‐1 LI. Notably, our study for the first time suggests a possible epigenetic mechanism of p16 loss in CDKN2A non‐deleted HGGs mediated by strong EZH2 expression. A hypothetical model for control of proliferative activity in low versus HGGs is therefore proposed.     

Cell-cycle gene expression in lovastatin-induced medulloblastoma apoptosis

BACKGROUND: 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a key rate-limiting enzyme in the mevalonate pathway, which generates precursors both for cholesterol biosynthesis and for the production of nonsteroidal mevalonate derivatives that are involved in a number of growth-regulatory processes. We have reported that lovastatin, a competitive inhibitor of HMG-CoA reductase, not only inhibits medulloblastoma proliferation in vitro, but also induces near-complete cell death via apoptosis. The mechanism of this phenomenon is unclear. Possible involvement of changes in expression of certain cell-cycle related genes led us to study some of them in more detail. METHODS: Medulloblastoma cell lines were exposed in vitro to lovastatin, and the effects of gene expression changes were studied using RT-PCR, antisense oligonucleotide, DNA electrophoresis and Western blotting analysis. RESULTS: 1) Levels of total Ras gene mRNA and individual Ras gene mRNA are stable in lovastatin treatment in all examined medulloblastoma cell lines. 2) Blocking c-myc gene over-expression does not enhance medulloblastoma cell sensitivity to lovastatin. 3) Following lovastatin treatment, p16 expression exhibits no change, but pronounced increases of p27KIP1 protein are observed in all examined cell lines. Lovastatin induces pronounced increases of p21WAF1 protein only in Daoy and UW228, but not in D283 Med and D341 Med. 4) Following lovastatin treatment, increased p53 protein is detected only in D341 Med, and bax protein is unchanged in all cell lines. CONCLUSIONS: Lovastatin-induced growth inhibition and apoptosis in medulloblastoma are not dependent on the regulation of Ras and c-myc gene expression, but may be mediated by p27KIP1 gene expression. Lovastatin-induced apoptosis in medulloblastoma is probably p53 independent, but p53 and p21WAF1 gene expression may also mediate anti-proliferative effects of lovastatin on specific medulloblastoma cell lines.     

APO2L/TRAIL expression in human brain tumors

APO2 ligand (APO2L)/TRAIL is a novel member of the tumor necrosis factor cytokine family and a potent inducer of apoptosis in tumor cell lines. We recently reported that APO2L is consistently expressed in low-grade astrocytomas, anaplastic astrocytomas, glioblastomas, and cell lines derived thereof, and that malignant glioma cell lines are susceptible to APO2L-induced apoptosis. In this study, we investigated whether APO2L is expressed in medulloblastoma or neuroblastoma cell lines and whether these cells are sensitive to APO2L-induced apoptosis. Immunoblot analyses revealed full-length APO2L protein expression in one (DAOY) of three medulloblastoma cell lines but not in two neuroblastoma cell lines (SKN-BE and SKN-LE). Viability assay performed after exposure to soluble APO2L for 16 h showed that DAOY medulloblastoma cells were the most sensitive and that apoptosis induced by APO2L was greatly enhanced when protein synthesis was inhibited by cycloheximide. Neuroblastoma cell lines were almost completely resistant to APO2L-induced apoptosis. We also carried out APO2L immunohistochemistry in a total of 115 tumors of the nervous system with different histogenesis and biological behavior. In all 9 pilocytic astrocytomas, the areas of dense fibrillary network showed diffuse and strong APO2L expression. In oligodendrogliomas, APO2L expression was observed in areas with a significant admixture of astrocytic cells, but was absent in neoplastic oligodendrocytes. In 13 of 14 ependymomas, APO2L was expressed in perivascular pseudorosettes. In all 12 medulloblastomas, strong APO2L expression was observed in intra-tumoral-reactive astrocytes, but neoplastic cells did not show APO2L immunoreactivity. Thus, the pattern of APO2L expression was largely similar to that of glial fibrillary acidic protein (GFAP), except for choroid plexus tumors and 3 of 8 anaplastic meningiomas, in which APO2L was focally expressed without concomitant GFAP expression. APO2L expression was absent in meningiomas, neurocytomas, and schwannomas. Thus, there is considerable heterogeneity of APO2L expression and susceptibility to APO2L-induced apoptosis among human brain tumors. Received: 18 August 1999 / Revised, accepted: 29 September 1999     

Human parathyroid hormone-related protein and human parathyroid hormone receptor type 1 are expressed in human medulloblastomas and regulate cell proliferation and apoptosis in medulloblastoma-derived cell lines

Human parathyroid hormone-related protein (hPTHrP), identified in patients with paraneoplastic hypercalcemia and expressed by different cell types during development and adult life, plays important roles in many human neoplasms. Immunohistochemical and RT-PCR analyses of hPTHrP and human parathyroid hormone receptor type 1 (PTHR-1) in primary medulloblastoma confirmed their expression in both classic and desmoplastic variants at RNA and protein levels. To evaluate the functional role of hPTHrP, DAOY and D283 medulloblastoma and U87MG glioma cells, expressing high levels of hPTHrP and PTHR-1, were treated with anti-sense oligonucleotides for hPTHrP. Anti-sense treatment produced in all cell lines a decrease of cell proliferation and clonogenic activity and an increase of apoptosis, while addition of exogenous hPTHrP (1-37) prevented these effects. Anti-sense induced the increase of Caspase-3, Fas (CD95) mRNAs and Bax/Bcl-2 mRNA ratio after 12 h of cell treatment. Exogenous hPTHrP (1-37) increased intracellular Ca(2+) concentration in DAOY cells as revealed by FURA. Anti-sense treated cells showed a significant decrease of steady-state levels of intracellular Ca(2+), which was reverted by addition of exogenous hPTHrP (1-37). This study indicates that hPTHrP and PTHR-1 are expressed in medulloblastoma and could promote tumor growth, protecting cells from apoptosis.     

Enhancer of Zeste 2 (EZH2) is up-regulated in malignant gliomas and in glioma stem-like cells

F. Orzan, S. Pellegatta, P. L. Poliani, F. Pisati, V. Caldera, F. Menghi, D. Kapetis, C. Marras, D. Schiffer and G. Finocchiaro (2011) Neuropathology and Applied Neurobiology 37, 381–394
Enhancer of Zeste 2 (EZH2) is up‐regulated in malignant gliomas and in glioma stem‐like cells Aims: Proteins of the Polycomb repressive complex 2 (PRC2) are epigenetic gene silencers and are involved in tumour development. Their oncogenic function might be associated with their role in stem cell maintenance. The histone methyltransferase Enhancer of Zeste 2 (EZH2) is a key member of PRC2 function: we have investigated its expression and function in gliomas. Methods: EZH2 expression was studied in grade II–IV gliomas and in glioma stem‐like cells (GSC) by quantitative PCR and immunohistochemistry. Effects of EZH2 down‐regulation were analysed by treating GSC with the histone deacetylase (HDAC) inhibitor suberoylanide hydroxamic acid (SAHA) and by shRNA. Results: DNA microarray analysis showed that EZH2 is highly expressed in murine and human GSC. Real‐time PCR on gliomas of different grade (n = 66) indicated that EZH2 is more expressed in glioblastoma multiforme (GBM) than in low‐grade gliomas (P = 0.0013). This was confirmed by immunohistochemistry on an independent set of 106 gliomas. Treatment with SAHA caused significant up‐regulation of PRC2 predicted target genes, GSC disruption and decreased expression of EZH2 and of the stem cell marker CD133. Inhibition of EZH2 expression by shRNA was associated with a significant decrease of glioma proliferation. Conclusion: The data suggest that EZH2 plays a role in glioma progression and encourage the therapeutic targeting of these malignancies by HDAC inhibitors.     

Amygdalar expression of the microRNA miR‐101a and its target Ezh2 contribute to rodent anxiety‐like behaviour

A greater understanding of neural mechanisms contributing to anxiety is needed in order to develop better therapeutic interventions. This study interrogates a novel molecular mechanism that shapes anxiety‐like behaviour, demonstrating that the microRNA miR‐101a‐3p and its target, enhancer of zeste homolog 2 (Ezh2) in the amygdala, contribute to rodent anxiety‐like behaviour. We utilized rats that were selectively bred for differences in emotionality and stress reactivity, showing that high‐novelty‐responding (HR) rats, which display low trait anxiety, have lower miR‐101a‐3p levels in the amygdala compared to low‐novelty‐responding (LR) rats that characteristically display high trait anxiety. To determine whether there is a causal relationship between amygdalar miR‐101a‐3p and anxiety behaviour, we used a viral approach to overexpress miR‐101a‐3p in the amygdala of HR rats and test whether it would increase their typically low levels of anxiety‐like behaviour. We found that increasing miR‐101a‐3p in the amygdala increased HRs' anxiety‐like behaviour in the open‐field test and elevated plus maze. Viral‐mediated miR‐101a‐3p overexpression also reduced expression of the histone methyltransferase Ezh2, which mediates gene silencing via trimethylation of histone 3 at lysine 27 (H3K27me3). Knockdown of Ezh2 with short‐interfering RNA (siRNA) also increased HRs' anxiety‐like behaviour, but to a lesser degree than miR‐101a‐3p overexpression. Overall, our data demonstrate that increasing miR‐101a‐3p expression in the amygdala increases anxiety‐like behaviour and that this effect is at least partially mediated via repression of Ezh2. This work adds to the growing body of evidence implicating miRNAs and epigenetic regulation as molecular mediators of anxiety behaviour.     

脑胶质瘤EZH2基因的表达分析

目的探讨脑胶质瘤果蝇zeste基因增强子同源物2（EZH2）蛋白的表达变化。方法选取2010年5月至2011年12月手术切除的胶质瘤组织标本83例,其中2008年WHO分级Ⅰ级15例,Ⅱ级20,Ⅲ级26例,Ⅳ级22例;术前均未接受放疗或化疗。另外,收集30例颅脑损伤内减压手术切除的无肿瘤脑组织作为对照。采用实时荧光定量PCR法检测EZH2 m RNA表达。根据EZH2 m RNA表达水平分为高表达组（EZH2 m RNA≥0.3,48例）和低表达组（EZH2 m RNA〈0.3,35例）,分析两组术后生存期。结果胶质瘤组织EZH2 m RNA表达水平明显高于对照组（P〈0.01）,高级别胶质瘤（WHOⅢ、Ⅳ级）组织EZH2 m RNA表达水平明显高于低级别胶质瘤（WHOⅠ、Ⅱ级）组织（P〈0.01）。低表达组患者术后生存期较高表达组显著延长（P〈0.01）。结论脑胶质瘤组织EZH2 m RNA呈高表达,且其表达水平与病理分级具有相关性。     

Epigenetic‐Imprinting Changes Caused by Neonatal Fasting Stress Protect From Future Fasting Stress

Unfavourable nutritional conditions during the neonatal critical period can cause both acute metabolic disorders and severe metabolic syndromes in later life. These phenomena have been tightly related to the epigenetic modification controlling the balance between satiety and hunger in the hypothalamus. In the present study, we investigated epigenetic modification associated with both the fasting stress effects and the short‐term resilience to fasting stress in the hypothalamic paraventricular nucleus (PVN) of chicks. Fasting for 24 h at 3 days of age (D) (i.e. D3) significantly increased global methylation at lysine 27 of histone 3 (H3K27) and its specific histone methyltransferase (HMT) expression level in the PVN. Because global methylation could not fully reveal the changes at specific genes, the regulation of the gene for brain‐derived neurotrophic factor (Bdnf), which was recently also found to have an anorexigenic effect, was evaluated as a potential target. Chromatin immunoprecipitation assay analysis revealed that tri‐ (me3) and di‐methylated (me2) H3K27 exhibited an instant (on D4 only) and latent increase (on both D11 and D41), respectively, at the putative promoter of Bdnf after 24 h of fasting on D3. This indicated that fasting could regulate energy‐expenditure‐related genes via modifying methylation at H3K27, which we suspected might be a protective mechanism for keeping the inner environment homeostatic. To test this hypothesis, a short‐term repetitive fasting stress was applied to chickens, which were fasted for 24 h either on D10 only or on both D3 and D10. It was found that pre‐existing fasting on D3 could induce a short‐term fasting resilience, which rescued the reduction of Bdnf expression from future fasting on D10. We call this phenomenon the ‘molecular memory’, which was mainly conducted by HMTs and H3K27me2/me3 in the PVN. In conclusion, chicks respond to fasting with dynamic methylation at H3K27 in the PVN during the neonatal critical period. This allows the PVN to form a ‘molecular memory’, which keeps the individual inner environment homeostatic and resilient to future fasting over the short term.     

Complex epigenetic regulation of Engrailed-2 (EN-2) homeobox gene in the autism cerebellum

The elucidation of epigenetic alterations in the autism brain has potential to provide new insights into the molecular mechanisms underlying abnormal gene expression in this disorder. Given strong evidence that engrailed-2 (EN-2) is a developmentally expressed gene relevant to cerebellar abnormalities and autism, the epigenetic evaluation of this candidate gene was undertaken in 26 case and control post-mortem cerebellar samples. Assessments included global DNA methylation, EN-2 promoter methylation, EN-2 gene expression and EN-2 protein levels. Chromatin immunoprecipitation was used to evaluate trimethylation status of histone H3 lysine 27 (H3K27) associated with gene downregulation and histone H3 lysine 4 (H3K4) associated with gene activation. The results revealed an unusual pattern of global and EN-2 promoter region DNA hypermethylation accompanied by significant increases in EN-2 gene expression and protein levels. Consistent with EN-2 overexpression, histone H3K27 trimethylation mark in the EN-2 promoter was significantly decreased in the autism samples relative to matched controls. Supporting a link between reduced histone H3K27 trimethylation and increased EN-2 gene expression, the mean level of histone H3K4 trimethylation was elevated in the autism cerebellar samples. Together, these results suggest that the normal EN-2 downregulation that signals Purkinje cell maturation during late prenatal and early-postnatal development may not have occurred in some individuals with autism and that the postnatal persistence of EN-2 overexpression may contribute to autism cerebellar abnormalities.     

Histopathological and molecular prognostic markers in medulloblastoma: c-myc, N-myc, TrkC, and anaplasia

Several molecular and histopathological prognostic markers have been proposed for the therapeutic stratification of medulloblastoma patients. Amplification of the c-myc oncogene, elevated levels of c-myc mRNA, or tumor anaplasia have been associated with worse clinical outcomes. In contrast, high TrkC mRNA expression generally presages longer survival. The goal of this study was to evaluate the prognostic value of c-myc, N-myc and TrkC expression in medulloblastomas and compare them to histopathological classification. We used in situ hybridization to measure expression of these molecular markers. c-myc mRNA was detected in 18 of 59 (31%) cases, and was significantly associated with shorter patient survival times on both univariate and multivariate analyses (p = 0.04). The presence of c-myc mRNA was also significantly associated with tumor anaplasia. While survival rates were higher for patients with low N-myc or high TrkC expression, these differences were not statistically significant. The group of patients with either moderate or severely anaplastic tumors showed only a trend towards shorter survival (p = 0.11). However, severe anaplasia alone was significantly prognostic (p = 0.002). Given the prognostic import of c-myc, we investigated 2 potential mechanisms by which its expression might be regulated: Wnt signaling and Mxi-1 mutation. Nuclear translocation of beta-catenin, a marker of Wnt pathway activation, was more common in medulloblastomas with high c-myc than in tumors overall, but the difference was not statistically significant. No Mxi-1 mutations were detected in the 22 cases examined. The association we describe between c-myc expression, tumor anaplasia, and worse clinical outcomes provides further evidence for the importance of this oncogene in medulloblastoma pathobiology.