Circular RNA (circRNA) is a class of non-coding RNA whose functions remain mostly unknown. Recent studies indicate circRNA may be involved in disease pathogenesis, but direct evidence is scarce. Here we characterize the functional role of a novel circRNA, circCCDC66, in colorectal cancer (CRC). RNA-Seq data from matched normal and tumor colon tissue samples identified numerous circRNAs specifically elevated in cancer cells, several of which were verified by quantitative RT-PCR. CircCCDC66 expression was elevated in polyps and colon cancer and was associated with poor prognosis. Gain-of-function and loss-of-function studies in CRC cell-lines demonstrated that circCCDC66 controlled multiple pathological processes, including cell proliferation, migration, invasion, and anchorage-independent growth. In-depth characterization revealed that circCCDC66 exerts its function via regulation of a subset of oncogenes, and knockdown of circCCDC66 inhibited tumor growth and cancer invasion in xenograft and orthotopic mouse models, respectively. Taken together, these findings highlight a novel oncogenic function of circRNA in cancer progression and metastasis.

Direct-current electrical fields (EFs) promote nerve growth and axon regeneration. We report here that at physiological strengths, EFs guide the migration of neuronal stem/progenitor cells (NSPCs) toward the cathode. EF-directed NSPC migration requires activation of Nmethyl-D-aspartate receptors (NMDARs), which leads to an increased physical association of Rho GTPase Rac1-associated signals to the membrane NMDARs and the intracellular actin cytoskeleton. Thus, this study identifies the EF as a directional guidance cue in controlling NSPC migration and reveals a role of the NMDAR/Rac1/ actin signal transduction pathway in mediating EF-induced NSPC migration. These results suggest that as a safe physical approach in clinical application, EFs may be developed as a practical therapeutic strategy for brain repair by directing NSPC migration to the injured brain regions to replace cell loss.

Despite the prominent pro-apoptotic role of p53, this protein has also been shown to promote cell survival in response to metabolic stress. However, the specific mechanism by which p53 protects cells from metabolic stress-induced death is unknown. Earlier we reported that carnitine palmitoyltransferase 1C (CPT1C), a brain-specific member of a family of mitochondria-associated enzymes that have a central role in fatty acid metabolism promotes cell survival and tumor growth. Unlike other members of the CPT family, the subcellular localization of CPT1C and its cellular function remains elusive. Here, we report that CPT1C is a novel p53-target gene with a bona fide p53-responsive element within the first intron. CPT1C is upregulated in vitro and in vivo in a p53-dependent manner. Interestingly, expression of CPT1C is induced by metabolic stress factors such as hypoxia and glucose deprivation in a p53 and AMP activated kinase-dependent manner. Furthermore, in a murine tumor model, depletion of Cpt1c leads to delayed tumor development and a striking increase in survival. Taken together, our results indicate that p53 protects cells from metabolic stress via induction of CPT1C and that CPT1C may have a crucial role in carcinogenesis. CPT1C may therefore represent an exciting new therapeutic target for the treatment of hypoxic and otherwise treatment-resistant tumors. Hypoxia is an important chronic stress on tumor cell growth and has been shown to correlate with poor disease-free and reduced overall survival in a variety of carcinomas and sarcomas. 1 To enhance survival in an altered environment such as hypoxia cancer cells undergo a so-called metabolic transformation. [2][3][4] The best-known aspect of metabolic transformation is the Warburg effect, whereby cancer cells upregulate glycolysis to limit their energy consumption. However, there is increasing evidence that not only glucose metabolism, but also fatty acid oxidation (FAO) is involved in metabolic transformation. Although glucose seems to be the major energy source for tumor growth and survival, there is increasing evidence that alternative energy sources such as fatty acid metabolism are altered in cancer cells, even under hypoxic conditions. Indeed, fatty acid synthase has been found to be upregulated in many human cancers, 5 and inhibitors of the fatty acid synthase show antitumor activity. 6 As recently published, we identified carnitine palmitoyltransferase (CPT) 1C (CPT1C) as a potential novel p53-target gene. 7 By their restriction of fatty acid import into mitochondria, 4 the CPT 1 (CPT1) family of enzymes represent key regulatory factors of FAO. There are three tissue-specific isoforms of CPT1: CPT1A that is found in liver, CPT1B in muscle and CPT1C in brain and testes. Loss-of-function of CPT1C was generated in mouse embryonic stem cells (Cpt1c gt/gt ES cells). Importantly, Cpt1c gt/gt ES cells readily succumbed to cell death under hypoxic conditions, whereas control cells were resistant. ES cells deficient for CPT1C showed a spontaneous induction in...

Background and Purpose-Downregulation of the tumor suppressor, phosphatase and tensin homolog deleted on chromosome 10 (PTEN), is thought to be a novel neuroprotective strategy in ischemic stroke, but the underlying mechanisms remain unclear. In this study, we aimed to validate the use of PTEN regulation of ␥-aminobutyric acid subtype A receptors (GABA A Rs) as a molecular target for the treatment of ischemic stroke. Because suppression of GABA A Rs contributes to ischemic neuron death, describing the intracellular signaling that interacts with GABA A Rs in ischemic neurons would provide a molecular basis for novel stroke therapies. Methods-We measured surface GABA A R expression by immunocytochemical labeling and surface protein biotinylation assay. Knockdown and overexpression approaches were used to test the effects of PTEN on the expression and function of GABA A Rs. Neuronal death was detected in both in vitro and in vivo stroke models. Results-The knockdown and overexpression approaches provided the first evidence that PTEN negatively regulated membrane expression and function of GABA A Rs in rat hippocampal neurons. Importantly, we demonstrated that a PTEN inhibitor prevented the reduction of surface GABA A Rs in injured hippocampal neurons subjected to oxygen-glucose deprivation, an in vitro insult that mimics ischemic injury, whereas a GABA A R antagonist significantly reduced this PTEN inhibitor-induced neuroprotection in both the in vitro and in vivo ischemic stroke models. Conclusions-Our study provides direct evidence that downregulation of PTEN protects against ischemic neuron death by preserving GABA A R function. Targeting this pathway may be an effective strategy for development of selective, potent stroke treatments.