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Mutations of the RAS oncogene are found in around 30% of all human cancers yet direct targeting of RAS is still considered clinically impractical except for the KRASG12C mutant. Here we report that RAS-ON (RASON), a novel protein encoded by the long intergenic non-protein coding RNA 00673 (LINC00673), is a positive regulator of oncogenic RAS signaling. RASON is aberrantly overexpressed in pancreatic ductal adenocarcinoma (PDAC) patients, and it promotes proliferation of human PDAC cell lines in vitro and tumor growth in vivo. CRISPR/Cas9-mediated knockout of Rason in mouse embryonic fibroblasts inhibits KRAS-mediated tumor transformation. Genetic deletion of Rason abolishes oncogenic KRAS-driven pancreatic and lung cancer tumorigenesis in LSL-KrasG12D; Trp53R172H/+ mice. Mechanistically, RASON directly binds to KRASG12D/V and inhibits both intrinsic and GTPase activating protein (GAP)-mediated GTP hydrolysis, thus sustaining KRASG12D/V in the GTP-bound hyperactive state. Therapeutically, deprivation of RASON sensitizes KRAS mutant pancreatic cancer cells and patient-derived organoids to EGFR inhibitors. Our findings identify RASON as a critical regulator of oncogenic KRAS signaling and a promising therapeutic target for KRAS mutant cancers.

Activated by its single ligand, hepatocyte growth factor (HGF), the receptor tyrosine kinase MET is pivotal in promoting glioblastoma stem cell (GSC) self-renewal, invasiveness and tumorigenicity. Nevertheless, HGF/MET-targeted therapy has shown limited clinical benefits in glioblastoma patients, suggesting hidden mechanisms of MET signalling in glioblastoma. Here, we show that circular MET RNA (circMET) encodes a 404 amino acid novel MET variant (MET404) facilitated by the N6-methyladenosine (m6A) reader YTHDF2. Genetic ablation of circMET inhibited MET404 expression in mice and attenuated MET signalling. Conversely, MET404 knock-in plus P53 knock-out in mouse astrocytes initiated glioblastoma tumorigenesis and shortened overall survival. MET404 directly interacts with the MET β subunit and forms a constitutively activated MET receptor whose activity does not require HGF stimulation. High MET404 expression predicts poor prognosis in glioblastoma patients, indicating its clinical relevance. Targeting MET404 through a neutralizing antibody or genetic ablation reduced glioblastoma tumorigenicity in vitro and in vivo, with combinatorial benefits when a traditional MET inhibitor was added. Overall, we identified a novel MET variant that promotes glioblastoma tumorigenicity, offering a potential new therapeutic strategy for glioblastoma.

Background Aberrant epidermal growth factor receptor (EGFR) activation is observed in over 50% of cases of adult glioblastoma (GBM). Nevertheless, EGFR antibodies are ineffective in clinical GBM treatment, suggesting the existence of redundant EGFR activation mechanisms. Whether circular RNA (circRNA) encodes a protein involved in EGFR-driven GBM remains unclear. We reported an unexpected mechanism in which circular EGFR RNA (circ-EGFR) encodes a novel EGFR variant to sustained EGFR activation. Method We used RNA-seq, Northern blot, and Sanger sequencing to confirm the existence of circ-EGFR. Antibodies and a liquid chromatograph tandem mass spectrometer were used to identify circ-EGFR protein products. Lentivirus-transfected stable cell lines were used to assess the biological functions of the novel protein in vitro and in vivo. Clinical implications of circ-EGFR were assessed using 97 pathologically diagnosed GBM patient samples. Results The infinite open reading frame (iORF) in circ-EGFR translated repeating amino acid sequences via rolling translation and programmed −1 ribosomal frameshifting (-1PRF) induced out-of-frame stop codon (OSC), forming a polymetric novel protein-complex, which we termed rolling-translated EGFR (rtEGFR). rtEGFR directly interacted with EGFR, maintained EGFR membrane localization and attenuated EGFR endocytosis and degradation. Importantly, circ-EGFR levels correlated with the EGFR signature and predicted the poor prognosis of GBM patients. Deprivation of rtEGFR in brain tumor-initiating cells (BTICs) attenuated tumorigenicity and enhanced the anti-GBM effect. Conclusion Our findings identified the endogenous rolling-translated protein and provided strong clinical evidence that targeting rtEGFR could improve the efficiency of EGFR-targeting therapies in GBM.

As a newly discovered type of RNA, circular RNAs (circRNAs) are widespread throughout the eukaryotic genome. The expression of circRNAs is regulated by both cis-elements and trans-factors, and the expression pattern of circRNAs is cell type- and disease-specific. Similar to other types of non-coding RNAs, functions of circRNAs are also versatile. CircRNAs have been reported previously to function as microRNA (miRNA) sponges, protein sponges, coding RNAs or scaffolds for protein complexes. Recently, several circRNAs have been reported to play important roles in human malignancies, including glioma. Here, we reviewed several reports related to circRNAs and glioma, as well as the potential diagnostic and therapeutic applications of circRNAs in brain cancer. In general, some circRNAs, such as circSMARCA5 and circCFH, are found to be expressed in a glioma-specific pattern, these circRNAs may be used as tumor biomarkers. In addition, some circRNAs have been found to play oncogenic roles in glioma (e.g., circNFIX and circNT5E), whereas others have been reported to function as tumor suppressors (e.g., circFBXW7 and circSHPRH). Furthermore, circRNA is a good tool for protein expression because of its higher stability compared to linear RNAs. Thus, circRNAs may also be an ideal choice for gene/protein delivery in future brain cancer therapies. There are some challenges in circRNA research in glioma and other diseases. Research related to circRNAs in glioma is comparatively new and many mysteries remain to be solved.

Ubiquitin-conjugating enzyme E2C (UBE2C) is characterized as a crucial molecule in cancer cell growth that plays an essential role in the development of gliomas, but the detailed mechanisms have not been fully elucidated. In this study, we found that Forkhead box transcription factor M1 (FoxM1) overexpression increased UBE2C expression, whereas FoxM1 suppression inhibited UBE2C expression in glioma cells. In addition, high FoxM1/UBE2C expression was significantly correlated with poor prognosis in glioma. We subsequently demonstrated that UBE2C was a direct transcriptional target of FoxM1, and site-directed mutations markedly down-regulated UBE2C promoter activity. Moreover, UBE2C siRNA (si-UBE2C) significantly induced glioma cell autophagy and increased both mCherry-LC3 punctate fluorescence and LC3B-II/LC3-I expression. Notably, the si-UBE2C-induced decrease in cell viability was markedly inhibited by the autophagy inhibitor bafilomycin A1. The silencing of UBE2C resulted in a distinct inhibition of the PI3K-Akt-mTOR pathway, which functions in the negative modulation of autophagy. Collectively, our findings provide clinical and molecular evidence that FoxM1 promotes glioma progression by enhancing UBE2C transcription and that the inhibition of UBE2C partially induces autophagic glioma cell death. Thus, targeting the FoxM1-UBE2C axis has therapeutic potential in the treatment of gliomas.

Background Circular RNAs (circRNAs) are RNA transcripts that are widespread in the eukaryotic genome. Recent evidence indicates that circRNAs play important roles in tissue development, gene regulation, and carcinogenesis. However, whether circRNAs encode functional proteins remains elusive, although translation of several circRNAs was recently reported.

Background The RTK/PI3K/AKT pathway plays key roles in the development and progression of many cancers, including GBM. As a regulatory molecule and a potential drug target, the oncogenic role of AKT has been substantially studied. Three isoforms of AKT have been identified, including AKT1, AKT2 and AKT3, but their individual functions in GBM remain controversial. Moreover, it is not known if there are more AKT alternative splicing variants. Methods High-throughput RNA sequencing and quantitative reverse transcription-PCR were used to identify the differentially expressed circRNAs in GBM samples and in paired normal tissues. High throughput RNA sequencing was used to identify circ-AKT3 regulated signaling pathways. Mass spectrometry, western blotting and immunofluorescence staining analyses were used to validate AKT3-174aa expression. The tumor suppressive role of AKT3-174aa was validated in vitro and in vivo. The competing interaction between AKT3-174aa and p-PDK1 was investigated by mass spectrometry and immunoprecipitation analyses. Results Circ-AKT3 is a previously uncharacterized AKT transcript variant. Circ-AKT3 is expressed at low levels in GBM tissues compared with the expression in paired adjacent normal brain tissues. Circ-AKT3 encodes a 174 amino acid (aa) novel protein, which we named AKT3-174aa, by utilizing overlapping start-stop codons. AKT3-174aa overexpression decreased the cell proliferation, radiation resistance and in vivo tumorigenicity of GBM cells, while the knockdown of circ-AKT3 enhanced the malignant phenotypes of astrocytoma cells. AKT3-174aa competitively interacts with phosphorylated PDK1, reduces AKT-thr308 phosphorylation, and plays a negative regulatory role in modulating the PI3K/AKT signal intensity. Conclusions Our data indicate that the impaired circRNA expression of the AKT3 gene contributes to GBM tumorigenesis, and our data corroborate the hypothesis that restoring AKT3-174aa while inhibiting activated AKT may provide more benefits for certain GBM patients.

Hypoxia is a general event in solid tumor growth. Therefore, induced cellular responses by hypoxia are important for tumorigenesis and tumor growth. MicroRNAs (miRNAs) have recently emerged as important regulators of hypoxia induced cellular responses. Here we report that miR-147a is a novel and crucial hypoxia induced miRNA. HIF-1α up-regulates the expression of miR-147a, and miR-147a in turn stabilizes and accumulates HIF-1α protein via directly targeting HIF-3α, a dominant negative regulator of HIF-1α. Subsequent studies in xenograft mouse model reveal that miR-147a is capable of inhibiting tumor growth. Collectively, these data demonstrate a positive feedback loop between HIF-1α, miR-147a and HIF-3α, which provide a new insight into the mechanism of miR-147a induced cell proliferation arrest under hypoxia.

The metabolic role of micropeptides generated from untranslated regions remains unclear. Here we describe MP31, a micropeptide encoded by the upstream open reading frame (uORF) of phosphatase and tensin homolog (PTEN) acting as a "circuit breaker" that limits lactate-pyruvate conversion in mitochondria by competing with mitochondrial lactate dehydrogenase (mLDH) for nicotinamide adenine dinucleotide (NAD+). Knocking out the MP31 homolog in mice enhanced global lactate metabolism, manifesting as accelerated oxidative phosphorylation (OXPHOS) and increased lactate consumption and production. Conditional knockout (cKO) of MP31 homolog in mouse astrocytes initiated gliomagenesis and shortened the overall survival of the animals, establishing a tumor-suppressing role for MP31. Recombinant MP31 administered intraperitoneally penetrated the blood-brain barrier and inhibited mice GBM xenografts without neurological toxicity, suggesting the clinical implication and application of this micropeptide. Our findings reveal a novel mode of MP31-orchestrated lactate metabolism reprogramming in glioblastoma.

It has been reported that persistent or excessive autophagy promotes cancer cell death during chemotherapy, either by enhancing the induction of apoptosis or mediating autophagic cell death. Here, we show that miR-15a and miR-16 are potent inducers of autophagy. Rictor, a component of mTORC2 complex, is directly targeted by miR-15a/16. Overexpression of miR-15a/16 or depletion of endogenous Rictor attenuates the phosphorylation of mTORC1 and p70S6K, inhibits cell proliferation and G1/S cell cycle transition in human cervical carcinoma HeLa cells. Moreover, miR-15a/16 dramatically enhances anticancer drug camptothecin (CPT)-induced autophagy and apoptotic cell death in HeLa cells. Collectively, these data demonstrate that miR-15a/16 induced autophagy contribute partly to their inhibition of cell proliferation and enhanced chemotherapeutic efficacy of CPT.

Circular RNAs (circRNAs) are recognized as functional non-coding transcripts in eukaryotic cells. Recent evidence has indicated that even though circRNAs are generally expressed at low levels, they may be involved in many physiological or pathological processes, such as gene regulation, tissue development and carcinogenesis. Although the ‘microRNA sponge’ function is well characterized, most circRNAs do not contain perfect trapping sites for microRNAs, which suggests the possibility that circRNAs have functions that have not yet been defined. In this study, we show that a circRNA containing an open reading frame (ORF) driven by the internal ribosome entry site (IRES) can translate a functional protein. The circular form of the SNF2 histone linker PHD RING helicase (SHPRH) gene encodes a novel protein that we termed SHPRH-146aa. Circular SHPRH (circ-SHPRH) uses overlapping genetic codes to generate a ‘UGA’ stop codon, which results in the translation of the 17 kDa SHPRH-146aa. Both circ-SHPRH and SHPRH-146aa are abundantly expressed in normal human brains and are down-regulated in glioblastoma. The overexpression of SHPRH-146aa in U251 and U373 glioblastoma cells reduces their malignant behavior and tumorigenicity in vitro and in vivo. Mechanistically, SHPRH-146aa protects full-length SHPRH from degradation by the ubiquitin proteasome. Stabilized SHPRH sequentially ubiquitinates proliferating cell nuclear antigen (PCNA) as an E3 ligase, leading to inhibited cell proliferation and tumorigenicity. Our findings provide a novel perspective regarding circRNA function in physiological and pathological processes. Specifically, SHPRH-146aa generated from overlapping genetic codes of circ-SHPRH is a tumor suppressor in human glioblastoma.

As a newly discovered type of RNA, circular RNAs (circRNAs) are widespread throughout the eukaryotic genome. The expression of circRNAs is regulated by both cis-elements and trans-factors, and the expression pattern of circRNAs is cell type- and disease-specific. Similar to other types of non-coding RNAs, functions of circRNAs are also versatile. CircRNAs have been reported previously to function as microRNA (miRNA) sponges, protein sponges, coding RNAs or scaffolds for protein complexes. Recently, several circRNAs have been reported to play important roles in human malignancies, including glioma. Here, we reviewed several reports related to circRNAs and glioma, as well as the potential diagnostic and therapeutic applications of circRNAs in brain cancer. In general, some circRNAs, such as circSMARCA5 and circCFH, are found to be expressed in a glioma-specific pattern, these circRNAs may be used as tumor biomarkers. In addition, some circRNAs have been found to play oncogenic roles in glioma (e.g., circNFIX and circNT5E), whereas others have been reported to function as tumor suppressors (e.g., circFBXW7 and circSHPRH). Furthermore, circRNA is a good tool for protein expression because of its higher stability compared to linear RNAs. Thus, circRNAs may also be an ideal choice for gene/protein delivery in future brain cancer therapies. There are some challenges in circRNA research in glioma and other diseases. Research related to circRNAs in glioma is comparatively new and many mysteries remain to be solved.

Previous studies showed that miR-378a plays important roles in adipogenesis and obesity; however, the precise mechanisms of action remain unknown. Here, we found that miR-378a-3p expression is up-regulated in adipose tissues of high fat diet-induced obese mice, as well as during the differentiation of 3T3-L1 preadipocytes. Mir-378a-3p induced adipogenesis by targeting mitogen-activated protein kinase 1 (MAPK1). Overexpression of miR-378a-3p or silencing MAPK1 reduced MAPK1 expression and enhanced adipogenesis, whereas blockage of endogenous miR-378a-3p had the opposite effect, suggesting that miR-378a-3p promotes the adipogenesis of 3T3-L1 cells by targeting MAPK1.

Hypoxia activates autophagy, an evolutionarily conserved cellular catabolic process. Dysfunction in the autophagy pathway has been implicated in an increasing number of human diseases, including cancer. Hypoxia induces upregulation of a specific set of microRNAs (miRNAs) in a variety of cell types. Here, we describe hypoxia-induced MIR155 as a potent inducer of autophagy. Enforced expression of MIR155 increases autophagic activity in human nasopharyngeal cancer and cervical cancer cells. Knocking down endogenous MIR155 inhibits hypoxia-induced autophagy. We demonstrated that MIR155 targets multiple players in MTOR signaling, including RHEB, RICTOR, and RPS6KB2. MIR155 suppresses target-gene expression by directly interacting with their 3' untranslated regions (UTRs), mutations of the binding sites abolish their MIR155 responsiveness. Furthermore, by downregulating MTOR signaling, MIR155 also attenuates cell proliferation and induces G 1/S cell cycle arrest. Collectively, these data present a new role for MIR155 as a key regulator of autophagy via dysregulation of MTOR pathway.

miR-181a has been presumed to target the 3′-untranslated regions (3′-UTR) of IL1a based on software predictions. miR-181a and IL1a have opposite expression levels in monocytes and macrophages in the inflammatory state. This led us to suspect that mir-181a has an important function in regulating inflammatory response by targeting IL1a. Fluorescence reporter assays showed that miR-181a effectively binds to the 3′-UTR of IL1a. The anti-inflammatory functions of miR-181a were investigated in lipopolysaccharides (LPS)-induced Raw264.7 and phorbol 12-myristate 13-acetate (PMA)/LPS-induced THP-1 cells. We found that miR-181a mimics significantly lowered IL1a expression levels in these cells and, interestingly, miR-181a inhibitors reversed this decrease. In addition, miR-181a mimics significantly inhibited increase in the levels of inflammatory factors (IL1b, IL6, and TNFa) in these cells. Furthermore, miR-181a mimics and inhibitors decreased and increased, respectively, production of reactive oxygen species in PMA/LPS-induced THP-1 cells. These results indicate that miR-181a regulates inflammatory responses by directly targeting the 3′-UTR of IL1a and down-regulating IL1a levels. Interestingly, we found that miR-181a inhibited production of inflammatory factors even in IL1a-induced THP-1 cells, suggesting that the anti-inflammatory effects of miR-181a possibly involves other targets in addition to IL1a. Thus, we provide the first evidence for anti-inflammatory effects of miR-181a mediated at least in part by down-regulating IL1a.

Background Accelerated cell cycle progression is the common feature of most cancers. MiRNAs can act as oncogenes or tumor suppressors by directly modulating cell cycle machinery. It has been shown that miR-188 is upregulated in UVB-irradiated mouse skin and human nasopharyngeal carcinoma CNE cells under hypoxic stress. However, little is known about the function of miR-188 in cell proliferation and growth control. Results Overexpression of miR-188 inhibits cell proliferation, tumor colony formation and G1/S cell cycle transition in human nasopharyngeal carcinoma CNE cells. Using bioinformatics approach, we identify a series of genes regulating G1/S transition as putative miR-188 targets. MiR-188 inhibits both mRNA and protein expression of CCND1, CCND3, CCNE1, CCNA2, CDK4 and CDK2, suppresses Rb phosphorylation and downregulates E2F transcriptional activity. The expression level of miR-188 also inversely correlates with the expression of miR-188 targets in human nasopharyngeal carcinoma (NPC) tissues. Moreover, studies in xenograft mouse model reveal that miR-188 is capable of inhibiting tumor initiation and progression by suppressing target genes expression and Rb phosphorylation. Conclusions This study demonstrates that miR-188 exerts anticancer effects, via downregulation of multiple G1/S related cyclin/CDKs and Rb/E2F signaling pathway. Electronic supplementary material The online version of this article (doi:10.1186/s12964-014-0066-6) contains supplementary material, which is available to authorized users.