Long noncoding RNAs (lncRNA) have been implicated in human cancer but their mechanisms of action are mainly undocumented. In this study, we investigated lncRNA alterations that contribute to gastric cancer through an analysis of The Cancer Genome Atlas RNA sequencing data and other publicly available microarray data. Here we report the gastric cancer-associated lncRNA HOXA11-AS as a key regulator of gastric cancer development and progression. Patients with high HOXA11-AS expression had a shorter survival and poorer prognosis. In vitro and in vivo assays of HOXA11-AS alterations revealed a complex integrated phenotype affecting cell growth, migration, invasion, and apoptosis. Strikingly, high-throughput sequencing analysis after HOXA11-AS silencing highlighted alterations in cell proliferation and cell-cell adhesion pathways. Mechanistically, EZH2 along with the histone demethylase LSD1 or DNMT1 were recruited by HOXA11-AS, which functioned as a scaffold. HOXA11-AS also functioned as a molecular sponge for miR-1297, antagonizing its ability to repress EZH2 protein translation. In addition, we found that E2F1 was involved in HOXA11-AS activation in gastric cancer cells. Taken together, our findings support a model in which the EZH2/HOXA11-AS/LSD1 complex and HOXA11-AS/miR-1297/EZH2 cross-talk serve as critical effectors in gastric cancer tumorigenesis and progression, suggesting new therapeutic directions in gastric cancer. Cancer Res; 76(21); 6299-310. ©2016 AACR.

Long noncoding RNAs (lncRNAs) have emerged as important regulators in a variety of human diseases, including cancers. However, the biological function of these molecules and the mechanisms responsible for their alteration in gastric cancer (GC) are not fully understood. In this study, we found that lncRNA LINC00673 is significantly upregulated in gastric cancer. Knockdown of LINC00673 inhibited cell proliferation and invasion and induced cell apoptosis, whereas LINC00673 overexpression had the opposite effect. Online transcription factor binding site prediction analysis showed that there are SP1 binding sites in the LINC00673 promoter region. Next, luciferase reporter and chromatin immunoprecipitation (ChIP) assays provided evidence that SP1 could bind directly to the LINC00673 promoter region and activate its transcription. Moreover, mechanistic investigation showed that CADM4, KLF2, and LATS2 might be the underlying targets of LINC00673 in GC cells, and RNA immunoprecipitation, RNA pull-down, and ChIP assays showed that LINC00673 can interact with EZH2 and LSD1, thereby repressing KLF2 and LATS2 expression. Taken together, these findings show that SP1-activated LINC00673 exerts an oncogenic function that promotes GC development and progression, at least in part, by functioning as a scaffold for LSD1 and EZH2 and repressing KLF2 and LATS2 expression.

Translation is principally regulated at the initiation stage. The development of the translation initiation (TI) sequencing (TI-seq) technique has enabled the global mapping of TIs and revealed unanticipated complex translational landscapes in metazoans. Despite the wide adoption of TI-seq, there is no computational tool currently available for analyzing TI-seq data. To fill this gap, we develop a comprehensive toolkit named Ribo-TISH, which allows for detecting and quantitatively comparing TIs across conditions from TI-seq data. Ribo-TISH can also predict novel open reading frames (ORFs) from regular ribosome profiling (rRibo-seq) data and outperform several established methods in both computational efficiency and prediction accuracy. Applied to published TI-seq/rRibo-seq data sets, Ribo-TISH uncovers a novel signature of elevated mitochondrial translation during amino-acid deprivation and predicts novel ORFs in 5′UTRs, long noncoding RNAs, and introns. These successful applications demonstrate the power of Ribo-TISH in extracting biological insights from TI-seq/rRibo-seq data.

Complex diseases such as cancer are often associated with aberrant gene expression at both the transcriptional and post-transcriptional level. In the past several years, competing endogenous RNAs (ceRNAs) have emerged as an important class of post-transcriptional regulators that alter gene expression through a microRNA-mediated mechanism. Recent studies in both solid tumors and hematopoietic malignancies showed that ceRNAs play significant roles in cancer pathogenesis by altering the expression of key tumorigenic or tumor suppressive genes. Characterizing the identity, function and mechanism of the ceRNAs will not only further our fundamental understanding of RNA-mediated cancer pathogenesis, but also may shed light on developing new RNA-based therapeutic strategies for treating cancer.

Recently, the non-protein-coding functional elements in the human genome have been identified as key regulators in postgenomic biology, and a large number of pseudogenes as well as long non-coding RNAs (lncRNAs) have been found to be transcribed in multiple human cancers. However, only a small proportion of these pseudogenes has been functionally characterized. In this study, we screened for pseudogenes associated with human non-small-cell lung cancer (NSCLC) by comparative analysis of several independent datasets from the GEO. We identified a transcribed pseudogene named DUXAP8 that is upregulated in tumor tissues. Patients with higher DUXAP8 expression exhibited shorter survival, suggesting DUXAP8 as a new candidate prognostic marker for NSCLC patients. Knockdown of DUXAP8 impairs cell growth, migration, and invasion, and induces apoptosis both in vitro and in vivo. Mechanistically, DUXAP8 represses the tumor suppressors EGR1 and RHOB by recruiting histone demethylase LSD1 and histone methyltransferase EZH2, thereby promoting cell proliferation, migration, and invasion. These findings indicate that the pseudogene DUXAP8 may act as an oncogene in NSCLC by silencing EGR1 and RHOB transcription by binding with EZH2 and LSD1, which may offer a novel therapeutic target for this disease.