Molecular genetic and epigenetic analysis of NCX2/SLC8A2 at 19q13.3 in human gliomas

NCX2 Regulates Intracellular Calcium Homeostasis and Translocation of HIF-1α into the Nucleus to Inhibit Glioma Invasion

Glioma is the most common tumor of the central nervous system, and its poor prognosis can be linked to hypoxia and gene inactivation. Na+/Ca2+ exchanger 2 (NCX2) is expressed only in the normal brain and not in other tissues or glioma. We constructed a hypoxic microenvironment to more accurately understand the effect of NCX2 in glioma. Our previous experiments confirmed that NCX2 inhibited the growth of U87 cells in nude mice, indicating that NCX2 is a potential tumor suppressor gene. Malignant tumor cells are often exposed to an anoxic environment. To more accurately understand the effect of NCX2 in glioma, we constructed a hypoxic microenvironment. To detect the localization of NCX2 in transfected U87 cells, immunofluorescence was used. We tested the function of NCX2 in glioma, i.e., how it contributes to the cytosolic Ca2+ homeostasis by X-Rhod-1. We tested the cell proliferation of NCX2 in glioma in hypoxic using Cell counting kit-8 (CCK8). Cell migration and invasion were evaluated in 24-well transwell matrigel-coated or non-matrigel-coated in hypoxia. NCX2 promoted the proliferation of U87 cells in the hypoxic microenvironment. It inhibited the invasion and migration abilities of U87 cells. We demonstrated that NCX2 was located on the cell membrane and that it reduced intracellular Ca2+ levels and reactivated P53 and PTEN. We further demonstrated that NCX2 impaired cell invasion through the HIF-1α pathway in glioma. The results indicated that NCX2 plays a key role in glioma formation and tumor invasion functionality.

The miR-193a-5p/NCX2/AKT axis promotes invasion and metastasis of osteosarcoma

MiR-193a-5p has been observed to have oncogenic or tumor suppressive functions in different kinds of cancers, but its role and molecular mechanism in osteosarcoma are elusive. Na⁺/Ca²⁺ exchangers (NCX1, NCX2 and NCX3) normally extrude Ca²⁺ from the cell, and deregulation of the intracellular Ca²⁺ homeostasis is related to several kinds of diseases, including cancer. The present study demonstrated that miR-193a-5p was upregulated in osteosarcoma tissues compared with the corresponding adjacent noncancerous tissues, and promoted colony formation, migration, invasion and epithelial-mesenchymal transition (EMT) in osteosarcoma cells (SaOS-2 and U-2OS), as well as metastasis in a murine xenograft model. Tandem mass tag-based quantitative proteomics analysis identified NCX2 as a potential target of miR-193a-5p. Luciferase activity assays and Western blotting further confirmed that miR-193a-5p recognized the 3′-untranslated region of NCX2 mRNA, and negatively regulated NCX2 expression. NCX2 was downregulated in osteosarcoma tissues, and its expression was negatively correlated with miR-193a-5p levels. Ectopic expression of NCX2 in osteosarcoma cells could reverse the oncogenicity of miR-193a-5p, indicating that miR-193a-5p exerted its effects by targeting NCX2. Further study demonstrated that NCX2 suppresses Ca²⁺-dependent Akt phosphorylation by decreasing intracellular Ca²⁺ concentration, and then inhibited EMT process. Treatment with the antagomir against miR-193a-5p sensitized osteosarcoma to the Akt inhibitor afuresertib in a murine xenograft model. In conclusion, a miR-193a-5p/NCX2/AKT signaling axis contributes to the progression of osteosarcoma, which may provide a new therapeutic target for osteosarcoma treatment.

Genome-Wide Analysis of DNA Methylation and Antituberculosis Drug-Induced Liver Injury in the Han Chinese Population

Tuberculosis (TB) is one of the most prevalent infections. However, anti-TB drugs induce adverse liver injury in up to 40% of patients. Studies on candidate genes have suggested that single-nucleotide polymorphisms account for only a small contribution to the occurrence of anti-TB drug-induced liver injury (ATLI). In this study, whole-genome DNA methylation analysis was performed to systematically screen the ATLI-associated factors in a 49 vs. 51 case-control population. Next, 34 identified candidate probes were validated using MassARRAY in 296 cases and 288 controls. Our results indicated that 12 CpG sites on seven probes were positively associated with ATLI risk. Furthermore, we applied a CRISPR/Cas9-mediated methylation modifiable cell model and demonstrated that four CpGs in or near the gene region of AK2, SLC8A2, and PSTPIP2 affected the cellular response to rifampicin treatment. This study provides new biomarkers associated with ATLI occurrence.

The Candidate Tumor Suppressor Gene SLC8A2 Inhibits Invasion, Angiogenesis and Growth of Glioblastoma

Glioblastoma is the most frequent and most aggressive brain tumor in adults. Solute carrier family 8 member 2 (SLC8A2) is only expressed in normal brain, but not present in other human normal tissues or in gliomas. Therefore, we hypothesized that SLC8A2 might be a glioma tumor suppressor gene and detected the role of SLC8A2 in glioblastoma and explored the underlying molecular mechanism. The glioblastoma U87MG cells stably transfected with the lentivirus plasmid containg SLC8A2 (U87MG-SLC8A2) and negative control (U87MG-NC) were constructed. In the present study, we found that the tumorigenicity of U87MG in nude mice was totally inhibited by SLC8A2. Overexpression of SLC8A2 had no effect on cell proliferation or cell cycle, but impaired the invasion and migration of U87MG cells, most likely through inactivating the extracellular signal-related kinases (ERK)1/2 signaling pathway, inhibiting the nuclear translocation and DNA binding activity of nuclear factor kappa B (NF-κB), reducing the level of matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA)-its receptor (uPAR) system (ERK1/2-NF-κB-MMPs/uPA-uPAR), and altering the protein levels of epithelial to mesenchymal transitions (EMT)-associated proteins E-cardherin, vimentin and Snail. In addition, SLC8A2 inhibited the angiogenesis of U87MG cells, probably through combined inhibition of endothelium-dependent and endothelium-nondependent angiogenesis (vascular mimicry pattern). Totally, SLC8A2 serves as a tumor suppressor gene and inhibits invasion, angiogenesis and growth of glioblastoma.

Global analysis of H3K4me3 and H3K27me3 profiles in glioblastoma stem cells and identification of SLC17A7 as a bivalent tumor suppressor gene

Epigenetic changes, including H3K4me3 and H3K27me3 histone modification, play an important role in carcinogenesis. However, no genome-wide histone modification map has been generated for gliomas. Here, we report a genome-wide map of H3K4me3 and H3K27me3 histone modifications for 8 glioma stem cell (GSC) lines, together with the associated gene activation or repression patterns. In addition, we compared the genome-wide histone modification maps of GSC lines to those of astrocytes to identify unique gene activation or repression profiles in GSCs and astrocytes. We also identified a set of bivalent genes, which are genes that are associated with both H3K4me3 and H3K27me3 marks and are poised for action in embryonic stem cells. These bivalent genes are potential targets for inducing differentiation in glioblastoma (GBM) as a therapeutic approach. Finally, we identified SLC17A7 as a bivalent tumor suppressor gene in GBM, as it is down-regulated at both the protein and RNA levels in GBM tissues compared with normal brain tissues, and it inhibits GBM cell proliferation, migration and invasion.

Clinical Significance of SASH1 Expression in Glioma

OBJECTIVE

SAM and SH3 domain containing 1 (SASH1) is a recently discovered tumor suppressor gene. The role of SASH1 in glioma has not yet been described. We investigated SASH1 expression in glioma cases to determine its clinical significance on glioma pathogenesis and prognosis.

METHODS

We produced tissue microarrays using 121 patient-derived glioma samples and 30 patient-derived nontumor cerebral samples. Immunohistochemistry and Western blotting were used to evaluate SASH1 expression. We used Fisher's exact tests to determine relationships between SASH1 expression and clinicopathological characteristics; Cox regression analysis to evaluate the independency of different SASH1 expression; Kaplan-Meier analysis to determine any correlation of SASH1 expression with survival rate.

RESULTS

SASH1 expression was closely correlated with the WHO glioma grade. Of the 121 cases, 66.9% with low SASH1 expression were mostly grade III-IV cases, whereas 33.1% with high SASH1 expression were mostly grades I-II. Kaplan-Meier analysis revealed a significant positive correlation between SASH1 expression and postoperative survival.

CONCLUSIONS

SASH1 was widely expressed in normal and low-grade glioma tissues. SASH1 expression strongly correlated with glioma grades, showing higher expression at a lower grade, which decreased significantly as grade increased. Furthermore, SASH1 expression was positively correlated with better postoperative survival in patients with glioma.

Beyond the island: epigenetic biomarkers of colorectal and prostate cancer

Epigenetic dysregulation is a common feature across all cancer types. Epigenetic mechanisms, from DNA methylation to histone modifications, allow for a vast number of cellular phenotypes to be created from the same genetic material. Just as certain genetic changes play a key role in tumor initiation and progression, epigenetic changes may also set the course of tumor development and be required for malignant transformation. The most frequently studied epigenetic changes investigated thus far are global genomic DNA hypomethylation along with specific hypermethylation, predominantly at promoter CpG islands of tumor suppressor genes. In addition to DNA methylation changes at CpG islands, there is an abundance of other epigenetic alterations occurring within cancer cells including DNA methylation alterations outside of CpG islands, non-CpG methylation, changes in cytosine oxidative species (hydroxymethylcytosine, formylcytosine, carboxylcytosine) levels, and histone modifications. This chapter examines epigenetic alterations beyond the island, and summarizes recent findings in DNA-based epigenetic regulation of the two most commonly diagnosed cancers in the Western world: colorectal cancer and prostate cancer.

LOH 19q indicates shorter disease progression-free interval in low-grade oligodendrogliomas with EMP3 methylation

We previously described a cohort of grade II oligodendroglioma (OII) patients, in whom the loss of heterozygosity (LOH) 19q was present in the subgroup at a higher risk of relapse. In this study, we evaluated the CpG methylation of the putative tumor suppressor epithelial membrane protein 3 (EMP3, 19q13.3) gene promoter in the same OII cohort, to investigate whether a correlation could be found between EMP3 cytogenetic and epigenetic loss and higher risk of relapse. Twenty-three tumor samples from OII patients were collected over a period of 10 years. Seventeen glioblastoma (GBM) samples (2 of which were relapses) were collected from 15 patients. The EMP3, O6-methylguanine methyltransferase (MGMT) and cyclooxygenase 2 (COX2) promoter methylation, evaluated by methylation-specific PCR, and the isocitrate dehydrogenase 1 (IDH1) mutation, identified by sequencing, were compared between the OII and GBM histotypes. The EMP3 promoter methylation was correlated with the analysis of LOH 19q, performed by microsatellite amplification, in OII patients. Disease progression-free interval was evaluated in the OII patients with the EMP3 methylation with either LOH 19q or conserved chromosome 19 arms. The EMP3 and MGMT promoter methylation was more frequent in OII than in GBM patients, and the IDH1 mutation was absent in GBM. The COX2 promoter was unmethylated in both histotypes. Both LOH+/- 19q OII patients showed EMP3 hypermethylation. Concomitant LOH 19q and EMP3 gene promoter methylation was observed in the OII patients at a higher risk of relapse. Our results suggest that a total (cytogenetic and epigenetic) functional loss of both EMP3 alleles accounts for the reduced disease progression-free interval in OII patients. Although the small sample size limits the strength of this study, our results support testing this hypothesis in larger cohorts of patients, considering the methylation of the EMP3 gene promoter together with LOH 19q as an indication for treatment with adjuvant therapy ab initio in order to improve the overall survival of OII patients.

Overexpression of SASH1 related to the decreased invasion ability of human glioma U251 cells

The purpose of this study was to investigate the impact of SAM- and SH3-domain containing 1 (SASH1) on the biological behavior of glioma cells, including its effects on cellular growth, proliferation, apoptosis, invasion, and metastasis, and thereby to provide an experimental basis for future therapeutic treatments. A pcDNA3.1-SASH1 eukaryotic expression vector was constructed and transfected into the U251 human glioma cell line. Using the tetrazolium-based colorimetric (MTT) assay, flow cytometry analyses, transwell invasion chamber experiments, and other methods, we examined the impact of SASH1 on the biological behaviors of U251 cells, including effects on viability, cell cycle, apoptosis, and invasion. Furthermore, the effect of SASH1 on the expression of cyclin D1, caspase-3, matrix metalloproteinase (MMP)-2, MMP-9, and other proteins was observed. Compared to the empty vector and blank control groups, the pcDNA3.1-SASH1 group of U251 cells exhibited significantly reduced cell viability, proliferation, and invasion (p < 0.05), although there was no difference between the empty vector and blank control groups. The pcDNA3.1-SASH1 group demonstrated a significantly higher apoptotic index than did the empty vector and blank control groups (p < 0.05), and the percentage of apoptotic cells was similar between the empty vector and blank control groups. In addition, the pcDNA3.1-SASH1 group expressed significantly lower protein levels of cyclin D1 and MMP-2/9 compared to the control and empty vector groups (p < 0.05) and significantly higher protein levels of caspase-3 than the other two groups (p < 0.05). Cyclin D1, caspase-3, and MMP-2/9 expression was unchanged between the empty vector and blank control groups. SASH1 gene expression might be related to the inhibition of the growth, proliferation, and invasion of U251 cells and the promotion of U251 cells apoptosis.

Suppression of breast tumor growth and metastasis by an engineered transcription factor

Maspin is a tumor and metastasis suppressor playing an essential role as gatekeeper of tumor progression. It is highly expressed in epithelial cells but is silenced in the onset of metastatic disease by epigenetic mechanisms. Reprogramming of Maspin epigenetic silencing offers a therapeutic potential to lock metastatic progression. Herein we have investigated the ability of the Artificial Transcription Factor 126 (ATF-126) designed to upregulate the Maspin promoter to inhibit tumor progression in pre-established breast tumors in immunodeficient mice. ATF-126 was transduced in the aggressive, mesenchymal-like and triple negative breast cancer line, MDA-MB-231. Induction of ATF expression in vivo by Doxycycline resulted in 50% reduction in tumor growth and totally abolished tumor cell colonization. Genome-wide transcriptional profiles of ATF-induced cells revealed a gene signature that was found over-represented in estrogen receptor positive (ER+) "Normal-like" intrinsic subtype of breast cancer and in poorly aggressive, ER+ luminal A breast cancer cell lines. The comparison transcriptional profiles of ATF-126 and Maspin cDNA defined an overlapping 19-gene signature, comprising novel targets downstream the Maspin signaling cascade. Our data suggest that Maspin up-regulates downstream tumor and metastasis suppressor genes that are silenced in breast cancers, and are normally expressed in the neural system, including CARNS1, SLC8A2 and DACT3. In addition, ATF-126 and Maspin cDNA induction led to the re-activation of tumor suppressive miRNAs also expressed in neural cells, such as miR-1 and miR-34, and to the down-regulation of potential oncogenic miRNAs, such as miR-10b, miR-124, and miR-363. As expected from its over-representation in ER+ tumors, the ATF-126-gene signature predicted favorable prognosis for breast cancer patients. Our results describe for the first time an ATF able to reduce tumor growth and metastatic colonization by epigenetic reactivation of a dormant, normal-like, and more differentiated gene program.