Nc886 is epigenetically repressed in prostate cancer and acts as a tumor suppressor through the inhibition of cell growth

Abstract

BackgroundNc886 is a 102 bp non-coding RNA transcript initially classified as a microRNA precursor (Pre-miR-886), later as a divergent homologue of the vault RNAs (vtRNA 2–1) and more recently as a novel type of RNA (nc886). Although nc886/vtRNA2–1/Pre-miR-886 identity is still controversial, it was shown to be epigenetically controlled, presenting both tumor suppressor and oncogenic function in different cancers. Here, we study for the first time the role of nc886 in prostate cancer.MethodsNc886 promoter methylation status and its correlation with patient clinical parameters or DNMTs levels were evaluated in TCGA and specific GEO prostate tissue datasets. Nc886 level was measured by RT-qPCR to compare normal/neoplastic prostate cells from radical prostatectomies and cell lines, and to assess nc886 response to demethylating agents. The effect of nc886 recovery in cell proliferation (in vitro and in vivo) and invasion (in vitro) was evaluated using lentiviral transduced DU145 and LNCaP cell lines. The association between the expression of nc886 and selected genes was analyzed in the TCGA-PRAD cohort.ResultsNc886 promoter methylation increases in tumor vs. normal prostate tissue, as well as in metastatic vs. normal prostate tissue. Additionally, nc886 promoter methylation correlates with prostate cancer clinical staging, including biochemical recurrence, Clinical T-value and Gleason score. Nc886 transcript is downregulated in tumor vs. normal tissue -in agreement with its promoter methylation status- and increases upon demethylating treatment. In functional studies, the overexpression of nc886 in the LNCaP and DU145 cell line leads to a decreased in vitro cell proliferation and invasion, as well as a reduced in vivo cell growth in NUDE-mice tumor xenografts. Finally, nc886 expression associates with the prostate cancer cell cycle progression gene signature in TCGA-PRAD.ConclusionsOur data suggest a tumor suppressor role for nc886 in the prostate, whose expression is epigenetically silenced in cancer leading to an increase in cell proliferation and invasion. Nc886 might hold clinical value in prostate cancer due to its association with clinical parameters and with a clinically validated gene signature.Electronic supplementary materialThe online version of this article (10.1186/s12885-018-4049-7) contains supplementary material, which is available to authorized users.

Protein kinase R and its cellular regulators in cancer: An active player or a surveillant?

“…nc886 was initially thought to be a tumor suppressor, because epigenetic silencing in cancer is a hallmark of tumor suppressor genes. To support this notion, ectopic expression of nc886 was shown to inhibit cell proliferation (Fort et al, ; Lee, Park, et al, ). However, we do not think that this can be attributed to PKR suppression, because PKR mostly stays inactive in normal tissues.…”

“…nc886 has a strong CpG island at the promoter region and its expression is silenced in a subset of malignant cells by DNA hypermethylation at the CpG island (Park et al, ). nc886 silencing occurs frequently in a number of malignancies (Ahn et al, ; Cao et al, ; Fort et al, ; Lee, Lee, et al, ; Lee, Park, et al, ; Park et al, ; Treppendahl et al, ), presumably because nc886 is an imprinted gene (Carpenter et al, ; Paliwal et al, ; Romanelli et al, ). Unlike typical imprinted genes which show monoallelic methylation in 100% of individuals, nc886 is estimated to be methylated in the maternal allele in approximately 75% of individuals (Treppendahl et al, ).…”

“…For all those reasons, we surmise that nc886 is vastly superior to other PKR repressors. nc886 silencing has been observed in diverse cancers including AML (Treppendahl et al, ), small cell lung cancer (Cao et al, ), gastric cancer (Lee, Park, et al, ), esophageal cell squamous carcinoma (Lee, Lee, et al, ), breast cancer (Park et al, ), and prostate cancer (Fort et al, ). Except nc886, there is one report about P58 whose expression was shown to be lower in more malignant breast cancer cells as compared to nontransformed breast cells (Kim et al, ).…”

“…Thus, the cellular outcome upon nc886 up‐regulation should be distinguished from nc886 silencing that activates PKR to trigger tumor surveillance role. In fact, ectopic expression of nc886 leads to delayed cell cycle progression, which seems to be independent of PKR (Fort et al, ). By contrast, PKR activation is a key event when nc886 knockdown causes apoptosis (Kunkeaw et al, ; Lee, Lee, et al, ).…”

Uncovering Tumour Heterogeneity through PKR and nc886 Analysis in Metastatic Colon Cancer Patients Treated with 5-FU-Based Chemotherapy

“…We have previously identified PKR as a molecular target of 5-FU in several colon and breast cancer cells lines, playing an important role in the cytotoxic effect of 5-FU at least, in part, through the induction of cell death by apoptosis [14]. Because PKR has also been implicated in the anti-tumour activity of chemotherapeutic drugs such as doxorubicin (DOX) and etoposide [15,16], and nc886 has been identified as an interesting tumour suppressor [17][18][19], we consider the analysis of PKR and the nc886 in patients as potential predictive biomarkers to be of clinical importance. For this reason, the aim of this work was to carry out an ambispective study in 197 metastatic colon cancer patients to evaluate the expression levels of PKR and its pre-microRNA-nc886 by qPCR in colon tumour samples and their respective healthy tissues and plasma, analysing its relation with the patient's clinical evolution.…”