Histone demethylase JARID1B promotes cell proliferation but is downregulated by N-Myc oncoprotein

Neuroblastoma and the epigenome

Neuroblastoma (NB) is a pediatric cancer of the sympathetic nervous system and one of the most common solid tumors in infancy. Amplification of MYCN, copy number alterations, numerical and segmental chromosomal aberrations, mutations, and rearrangements on a handful of genes, such as ALK, ATRX, TP53, RAS/MAPK pathway genes, and TERT, are attributed as underlying causes that give rise to NB. However, the heterogeneous nature of the disease-along with the relative paucity of recurrent somatic mutations-reinforces the need to understand the interplay of genetic factors and epigenetic alterations in the context of NB. Epigenetic mechanisms tightly control gene expression, embryogenesis, imprinting, chromosomal stability, and tumorigenesis, thereby playing a pivotal role in physio- and pathological settings. The main epigenetic alterations include aberrant DNA methylation, disrupted patterns of posttranslational histone modifications, alterations in chromatin composition and/or architecture, and aberrant expression of non-coding RNAs. DNA methylation and demethylation are mediated by DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) proteins, respectively, while histone modifications are coordinated by histone acetyltransferases and deacetylases (HATs, HDACs), and histone methyltransferases and demethylases (HMTs, HDMs). This article focuses predominately on the crosstalk between the epigenome and NB, and the implications it has on disease diagnosis and treatment.

Myc-mediated SDHA acetylation triggers epigenetic regulation of gene expression and tumorigenesis

The transcriptional role of cMyc (or Myc) in tumorigenesis is well appreciated; however, it remains to be fully established how extensively Myc is involved in the epigenetic regulation of gene expression. Here, we show that by deactivating succinate dehydrogenase complex subunit A (SDHA) via acetylation, Myc triggers a regulatory cascade in cancer cells that leads to H3K4me3 activation and gene expression. We find that Myc facilitates the acetylation-dependent deactivation of SDHA by activating the SKP2-mediated degradation of SIRT3 deacetylase. We further demonstrate that Myc inhibition of SDH-complex activity leads to cellular succinate accumulation, which triggers H3K4me3 activation and tumour-specific gene expression. We demonstrate that acetylated SDHA at Lys 335 contributes to tumour growth in vitro and in vivo, and we confirm increased tumorigenesis in clinical samples. This study illustrates a link between acetylation-dependent SDHA deactivation and Myc-driven epigenetic regulation of gene expression, which is critical for cancer progression.

JARID1B Expression Plays a Critical Role in Chemoresistance and Stem Cell-Like Phenotype of Neuroblastoma Cells

Neuroblastoma (NB) is a common neural crest-derived extracranial solid cancer in children. Among all childhood cancers, NB causes devastating loss of young lives as it accounts for 15% of childhood cancer mortality. Neuroblastoma, especially high-risk stage 4 NB with MYCN amplification has limited treatment options and associated with poor prognosis. This necessitates the need for novel effective therapeutic strategy. JARID1B, also known as KDM5B, is a histone lysine demethylase, identified as an oncogene in many cancer types. Clinical data obtained from freely-accessible databases show a negative correlation between JARID1B expression and survival rates. Here, we demonstrated for the first time the role of JARID1B in the enhancement of stem cell-like activities and drug resistance in NB cells. We showed that JARID1B may be overexpressed in either MYCN amplification (SK-N-BE(2)) or MYCN-non-amplified (SK-N-SH and SK-N-FI) cell lines. JARID1B expression was found enriched in tumor spheres of SK-N-BE(2) and SK-N-DZ. Moreover, SK-N-BE(2) spheroids were more resistant to chemotherapeutics as compared to parental cells. In addition, we demonstrated that JARID1B-silenced cells acquired a decreased propensity for tumor invasion and tumorsphere formation, but increased sensitivity to cisplatin treatment. Mechanistically, reduced JARID1B expression led to the downregulation of Notch/Jagged signaling. Collectively, we provided evidence that JARID1B via modulation of stemness-related signaling is a putative novel therapeutic target for treating malignant NB.

Overexpression of JARID1B is associated with poor prognosis and chemotherapy resistance in epithelial ovarian cancer

JARID1B, a histone demethylase, has been reported to be highly expressed in various human cancers. In the present study, we investigated the association of JARID1B level with epithelial ovarian cancer (EOC) and prognosis of patients with EOC. We analyzed JARID1B expression in 20 normal ovaries, 20 benign ovarian tumor (BOT) samples, and 45 epithelial ovarian carcinoma specimens by quantitative PCR (qRT-PCR) and western blotting analyses. JARID1B was further examined in 120 EOC specimens from patients with different histological stages via immunohistochemistry. Possible correlations between JARID1B levels and prognosis as well as chemotherapy resistance of EOC patients were determined by univariate and multivariate analyses. JARID1B level was significantly increased in EOC, as compared to normal ovaries and BOT. Among 120 EOC cases examined, the 5-year progression-free survival (PFS) rates were 17 and 85 % in patients with high and low JARID1B expression, respectively (hazard ratio = 17.85, 95 % confidence interval (CI) 6.31–50.51, P < 0.001). Similarly, the 5-year overall survival (OS) rates for patients with high and low JARID1B expression were 28 and 92 % respectively (hazard ratio = 21.8, 95 % CI 5.92–71.81, P < 0.001). Positive correlation between JARID1B level and chemotherapy resistance was observed in patients with EOC (odds ratio (OR) 36.81, 95 % CI 4.84–280.11, P < 0.001). JARID1B could serve as an important biomarker for prognosis and chemotherapy resistance of EOC patients.