Search

To elucidate the mechanisms of malignant progression of lower-grade glioma, molecular profiling using methylation array, whole-exome sequencing, and RNA sequencing was performed for 122, 36 and 31 gliomas, respectively. This cohort included 24 matched pairs of initial lower-grade gliomas and recurrent tumors, most of which showed malignant progression. Nearly half of IDH-mutant glioblastomas that had progressed from lower-grade gliomas exhibited characteristic partial DNA demethylation in previously methylated genomic regions of their corresponding initial tumors, which had the glioma CpG island methylator phenotype (G-CIMP). In these glioblastomas, cell cycle-related genes, RB and PI3K-AKT pathway genes were frequently altered. Notably, late-replicating domain was significantly enriched in the demethylated regions that were mostly located in non-regulatory regions, suggesting that the loss of DNA methylation during malignant transformation may involve mainly passive demethylation due to a delay in maintenance of methylation during accelerated cell division. Nonetheless, a limited number of genes including IGF2BP3, which potentially drives cell proliferation, were presumed to be upregulated due to demethylation of their promoter. Our data indicated that demethylation of the G-CIMP profile found in a subset of recurrent gliomas reflects accelerated cell divisions accompanied by malignant transformation. Oncogenic genes activated by such epigenetic change represent potential therapeutic targets.

OBJECTIVEChordoma is a slow-growing but clinically malignant tumor, and the prognosis remains poor in many cases. There is a strong impetus to develop more effective targeted molecular therapies. On this basis, the authors investigated the potential of Brachyury, a transcription factor involved in notochord development, as a candidate molecular target for the treatment of chordoma.METHODSBrachyury gene copy number and expression levels were evaluated by quantitative polymerase chain reaction in 27 chordoma samples, and the transcriptomes of Brachyury high-expression tumors (n = 4) and Brachyury low-expression tumors (n = 4) were analyzed. A chordoma cell line (U-CH2) was used to investigate the signaling pathways that regulate Brachyury expression.RESULTSAll chordoma specimens expressed Brachyury, and expression levels varied widely. Patients with higher Brachyury expression had significantly shorter progression-free survival (5 months, n = 11) than those with lower expression (13 months, n = 16) (p = 0.03). Somatic copy number gain was confirmed in 12 of 27 (44%) cases, and copy number was positively correlated with Brachyury expression (R = 0.61, p < 0.001). Expression of PI3K/Akt pathway genes was upregulated in Brachyury high-expression tumors, and suppression of PI3K signaling led to reduced Brachyury expression and inhibition of cell growth in the U-CH2 chordoma cell line.CONCLUSIONSActivation of the PI3K/Akt pathway and Brachyury copy number gain are strongly associated with Brachyury overexpression, which appears to be a key event in chordoma growth regulation. These findings suggest that targeting Brachyury and PI3K/Akt signaling may be an effective new approach for treating chordoma.

Background Although inactivation of the von Hippel-Lindau gene (VHL), located on chromosome 3p25, is considered to be a major cause of hemangioblastomas (HBs), the incidence of biallelic inactivation of VHL is reportedly low. The aim of this study was to determine the prevalence of VHL alterations in HBs, as well as to identify additional molecular aberrations. Methods Genetic and epigenetic alterations were comprehensively and comparatively analyzed in 11 VHL-related and 21 sporadic HBs. Results VHL alterations detected by sequencing and multiplex ligation-dependent probe amplification (MLPA) analysis were more frequent in VHL-related HBs than in sporadic HBs (100% vs 62%; P = 0.029). VHL alterations were found only in 4 sporadic HBs by direct sequencing; however, targeted deep sequencing detected 9 additional alterations. Loss of heterozygosity (LOH) on chromosome 3 was found in 64% and 57% of VHL-related and sporadic HBs, respectively, by single nucleotide polymorphism (SNP) array analysis. Among 19 tumors with chromosome 3 LOH, 5 were classified as copy-neutral LOH. VHL promoter hypermethylation was detected only in sporadic HBs (33%), indicating that epigenetic suppression of VHL is a common mechanism in sporadic HBs. The rate of biallelic VHL inactivation among VHL-related and sporadic HBs was 64% and 52%, respectively. LOH on either chromosome 6 or 10 was detected only in sporadic HBs (43%). Conclusion Although biallelic inactivation of VHL is a dominant mechanistic cause of the pathogenesis of HB, other unknown mechanisms may also be involved, and such mechanisms may be different between VHL-related and sporadic HB.

Among diffuse gliomas, oligodendrogliomas show relatively better prognosis, respond well to radiotherapy and chemotherapy, and seldom progress to very aggressive tumors. To elucidate the genetic and epigenetic background for such behavior and tumor evolution during tumor relapse, we comparatively analyzed 12 pairs of primary and recurrent oligodendrogliomas with 1p/19q-codeletion. Initial treatment for these patients was mostly chemotherapy alone. Temozolomide was used for 3, and procarbazine, nimustine and vincristine (PAV chemotherapy) were used for 7 patients. World Health Organization histological grade at recurrence was mostly stable; it was increased in 2, the same in 9, and decreased in 1 cases. Whole-exome sequencing demonstrated that the rate of shared mutation between the primary and recurrent tumors was relatively low, ranging from 3.2-57.9% (average, 33.3%), indicating a branched evolutionary pattern. The trunk alterations that existed throughout the course were restricted to IDH1 mutation, 1p/19q-codeletion, and TERT promoter mutation, and mutation of the known candidate tumor suppressor genes CIC and FUBP1 were not consistently observed between primary and recurrent tumors. Multiple sampling from different regions within a tumor showed marked intratumoral heterogeneity. Notably, in general, the number of mutations was not significantly different after recurrence, remaining under 100, and no hypermutator phenotype was observed. FUBP1 mutation, loss of chr. 9p21, and TCF12 mutation were among a few recurrent de novo alterations that were found at recurrence, indicating that these events were clonally selected at recurrence but were not enough to enhance malignancy. Genome-wide methylation status, measured by Illumina 450 K arrays, was stable between recurrence and the primary tumor. In summary, although oligodendroglioma displays marked mutational heterogeneity, histological malignant transformation accompanying events such as considerable increase in mutation number and epigenetic profile change were not observed at recurrence, indicating that noticeable temporal and spatial genetic heterogeneity in oligodendrogliomas does not result in rapid tumor progression. Electronic supplementary material The online version of this article (doi:10.1186/s40478-017-0422-z) contains supplementary material, which is available to authorized users.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Low-grade gliomas often undergo malignant progression, and these transformations are a leading cause of death in patients with low-grade gliomas. However, the molecular mechanisms underlying malignant tumor progression are still not well understood. Recent evidence indicates that epigenetic deregulation is an important cause of gliomagenesis; therefore, we examined the impact of epigenetic changes during malignant progression of low-grade gliomas. Specifically, we used the Illumina Infinium Human Methylation 450K BeadChip to perform genome-wide DNA methylation analysis of 120 gliomas and four normal brains. This study sample included 25 matched-pairs of initial low-grade gliomas and recurrent tumors (temporal heterogeneity) and 20 of the 25 recurring tumors recurred as malignant progressions, and one matched-pair of newly emerging malignant lesions and pre-existing lesions (spatial heterogeneity). Analyses of methylation profiles demonstrated that most low-grade gliomas in our sample (43/51; 84%) had a CpG island methylator phenotype (G-CIMP). Remarkably, approximately 50% of secondary glioblastomas that had progressed from low-grade tumors with the G-CIMP status exhibited a characteristic partial demethylation of genomic DNA during malignant progression, but other recurrent gliomas showed no apparent change in DNA methylation pattern. Interestingly, we found that most loci that were demethylated during malignant progression were located outside of CpG islands. The information of histone modifications patterns in normal human astrocytes and embryonal stem cells also showed that the ratio of active marks at the site corresponding to DNA demethylated loci in G-CIMP-demethylated tumors was significantly lower; this finding indicated that most demethylated loci in G-CIMP-demethylated tumors were likely transcriptionally inactive. A small number of the genes that were upregulated and had demethylated CpG islands were associated with cell cycle-related pathway. In summary, we demonstrated that characteristic DNA demethylation occurred during malignant progression of a subset of low-grade gliomas. The mechanisms underlying and consequences of such DNA demethylation should be studied further.

Low-grade glioma, especially astrocytomas often undergo malignant progression, and these transformations are a leading cause of death in patients with low-grade gliomas. However, the mechanisms underlying malignant tumor transformation are still not well understood. Recent evidence indicates that epigenetic deregulation is an important cause of gliomagenesis; therefore, we examined the epigenetic changes during malignant progression of gliomas. We used the Illumina Infinium Human Methylation 450K BeadChip to perform genome-wide DNA methylation analysis of 124 gliomas and four normal brains. These tumors comprised 37 grade IV gliomas, 32 grade III gliomas, and 55 grade II gliomas. This study sample included 26 matched-pairs of initial lower grade gliomas and recurrent tumors and 21 of the 26 recurring tumors recurred as malignant progressions. Analyses of methylation profiles demonstrated that most low-grade gliomas in our sample (84%) had a CpG island methylator phenotype (G-CIMP). Remarkably, approximately 25% of recurrent malignant gliomas that had progressed from low-grade tumors with the G-CIMP status exhibited a characteristic partial demethylation of genomic DNA during malignant progression, but other recurrent gliomas showed no apparent change in DNA methylation pattern. Interestingly, we found that most loci that were demethylated during malignant progression were located outside of CpG islands. The information of histone modifications patterns in normal human astrocytes and embryonal stem cells also showed that the ratio of active marks at the site corresponding to DNA demethylated loci in G-CIMP-demethylated tumors was significantly lower; this finding indicated that most demethylated loci in G-CIMP-demethylated tumors were likely transcriptionally inactive. A small number of the genes that were upregulated and had demethylated CpG islands were associated with cell cycle-related pathway. Here, we demonstrated that partial DNA demethylation occurred during malignant transfomrmation of a subset of lower grade gliomas. Citation Format: Mukasa Akitake, Kuniaki Saito, Koki Aihara, Genta Nagae, Mayu Omata, Ryohei Otani, Shunsaku Takayangi, Shota Tanaka, Yoshitaka Narita, Keisuke Ueki, Ryo Nishikawa, Motoo Nagane, Hiroyuki Aburatani, Nobuhito Saito. DNA methylation profile analysis of gliomas revealed a change in methylation status during malignant progression. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1072. doi:10.1158/1538-7445.AM2015-1072