Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the world and the fourth principal cause of cancer deaths worldwide. Currently, there is a lack of low cost and noninvasive screening tests for CRC, becoming a serious health problem. In this context, a potential biomarker for the early detection of CRC has recently gained attention. Circular RNAs (circRNA), a re-discovered, abundant RNA specie, is a type of noncoding covalent closed RNAs formed from both exonic and intronic sequences. These circular molecules are widely expressed in cells, exceeding the abundance of the traditional linear mRNA transcript. They can regulate gene expression, acting as real sponges for miRNAs and also regulate alternative splicing or act as transcriptional factors and inclusive encoding for proteins. However, little is known about circRNA and its relationship with CRC. In this review, we focus on the biogenesis, function and role of these circRNAs in relation to CRC, including their potential as a new biomarker.

Background & aims: Gallbladder cancer (GBC) is a neglected disease with substantial geographical variability: Chile shows the highest incidence worldwide, while GBC is relatively rare in Europe. Here we investigate the causal effects of risk factors considered in current GBC prevention programmes as well as C-reactive protein (CRP) level as a marker of chronic inflammation. Approach & results: We applied two-sample Mendelian randomization (MR) using publicly available data and our own data from a retrospective Chilean and a prospective European study. Causality was assessed by inverse variance weighted (IVW), MR-Egger regression and weighted median estimates complemented with sensitivity analyses on potential heterogeneity and pleiotropy, two-step MR and mediation analysis. We found evidence for a causal effect of gallstone disease on GBC risk in Chileans (p = 9 × 10-5) and Europeans (p = 9 × 10-5). A genetically elevated body mass index (BMI) increased GBC risk in Chileans (p = 0.03), while higher CRP concentrations increased GBC risk in Europeans (p = 4.1 × 10-6). European results suggest causal effects of BMI on gallstone disease (p = 0.008); public Chilean data were not, however, available to enable assessment of the mediation effects among causal GBC risk factors. Conclusions: Two risk factors considered in the current Chilean programme for GBC prevention are causally linked to GBC risk: gallstones and BMI. For Europeans, BMI showed a causal effect on gallstone risk, which was itself causally linked to GBC risk.

RNA polymerase II (RNAPII) requires a set of general transcription factors ) TFIIA, TFIIB, TFIID, TFIIE, TFIIF and TFIIH ) to initiate transcription from a gene promoter in vitro. General transcription factors have been isolated from Saccharomyces cerevisiae, rat, human and Drosophila, and their corresponding cDNAs have been cloned. In this report, we describe a reconstituted in vitro transcription system that consists of the following preparations of factors from the yeast Schizosaccharomyces pombe: affinity-purified RNAPII, TFIIH, and recombinant TBP, TFIIB, TFIIE and TFIIF. We show that this system can support basal transcription from the adenovirus major late promoter when purified RNAPII is used and activated transcription when the RNAPII holoenzyme (RNAPII plus the Mediator proteins) is included in the reaction. In contrast, the TATA binding protein-associated factors had no effect on transcriptional activation in our Sc. pombe system. These results indicate that Sc. pombe uses the same set of general transcription factors as other eukaryotes and that the Mediator is involved in activated transcription.The ability to achieve basal levels of transcription from protein-encoding genes in eukaryotes requires RNA polymerase II (RNAPII) and a set of additional proteins called general transcription factors (GTFs). The GTFs have been purified to homogeneity from HeLa cells, rat liver, Drosophila and the yeast Saccharomyces cerevisiae, and have been named TFIIA, TFIID, TFIIE, TFIIF, TFIIB and TFIIH [1]. The cDNAs that encode these factors have been isolated, and their amino acid sequences show a high degree of evolutionary conservation. These findings indicate that the transcriptional machinery is highly conserved among eukaryotes.An in vitro transcription assay that consists of purified RNAPII and recombinant GTFs can carry out basal transcription but cannot respond to gene-specific transcriptional activators. Activated transcription requires additional multiprotein complexes named coactivators. The main coactivators required for activated transcription in in vitro systems are the TFIID complex and the Mediator [2]. Recent work suggests that the TFIID complex, which contains the TATA binding protein (TBP) and other TBPassociated factors (TAFs), plays an important role in facilitating activation by gene-specific transcription factors as wells as in recognition of the TATA box and other core promoter sequences (necessary for both basal and activated transcription) [3]. Mediator is a large multiprotein complex that is brought to promoters by DNA-bound, gene-specific transcriptional regulatory proteins and helps these proteins to communicate with factors bound to the core promoter. Mediator is required for transcription in vivo and for optimal levels of both basal and activated transcription in vitro in nuclear extracts from human cells [4,5]. Components of both the TFIID complex and Mediator are conserved from yeast to humans.The yeast Schizosaccharomyces pombe can be genetically manipulated and has served as an exce...

Gastric cancer (GC) is the one of the most prevalent cancers and one of the leading causes of cancer-induced deaths. Previously, we found that the expression of purinergic P2Y 2 receptor (P2Y 2 R) is increased in GC samples as compared to adjacent healthy mucosa taken from GC-diagnosed patients. In this work, we studied in detail purinergic signaling in the gastric adenocarcinoma-derived cell lines: AGS, MKN-45, and MKN-74, and compared them to a nontumoral epithelial cell line: GES-1. In GC-derived cells, we detected the expression of several purinergic receptors, and found important differences as compared to GES-1 cells. Functional studies revealed a strong contribution of P2Y 2 Rs in intracellular calcium increases, elicited by adenosine-triphosphate (ATP), uridine-triphosphate (UTP), and the P2Y 2 R agonist MRS2768. Responses were preserved in the absence of extracellular calcium and inhibited by P2Y 2 R antagonists. In GES-1 cells, ATP and UTP induced similar responses and the combination of P2X and P2Y receptor antagonists was able to block them. Proliferation studies showed that ATP regulates AGS and MKN-74 cells in a biphasic manner, increasing cell proliferation at 10–100 μM, but inhibiting at 300 μM ATP. On the other hand, 1–300 μM UTP, a P2Y 2 R agonist, increased concentration-dependent cell proliferation. The effects of UTP and ATP were prevented by both wide-range and specific purinergic antagonists. In contrast, in GES-1 cells ATP only decreased cell proliferation in a concentration-dependent manner, and UTP had no effect. Notably, the isolated application of purinergic antagonists was sufficient to change the basal proliferation of AGS cells, indicating that nucleotides released by the cells can act as paracrine/autocrine signals. Finally, in tumor-derived biopsies, we found an increase of P2Y 2 R and a decrease in P2X4R expression; however, we found high variability between seven different biopsies and their respective adjacent healthy gastric mucosa. Even so, we found a correlation between the expression levels of P2Y 2 R and P2X4R and survival rates of GC patients. Taken together, these results demonstrate the involvement of different purinergic receptors and signaling in GC, and the pattern of expression changes in tumoral cells, and this change likely directs ATP and nucleotide signaling from antiproliferative effects in healthy tissues to proliferative effects in cancer.

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