BackgroundExosomes play a major role in cell-to-cell communication, targeting cells to transfer exosomal molecules including proteins, mRNAs, and microRNAs (miRNAs) by an endocytosis-like pathway. miRNAs are small noncoding RNA molecules on average 22 nucleotides in length that regulate numerous biological processes including cancer pathogenesis and mediate gene down-regulation by targeting mRNAs to induce RNA degradation and/or interfering with translation. Recent reports imply that miRNAs can be stably detected in circulating plasma and serum since miRNAs are packaged by exosomes to be protected from RNA degradation. Thus, profiling exosomal miRNAs are in need to clarify intercellular signaling and discover a novel disease marker as well.Methodology/Principal FindingsExosomes were isolated from cultured cancer cell lines and their quality was validated by analyses of transmission electron microscopy and western blotting. One of the cell lines tested, a metastatic gastric cancer cell line, AZ-P7a, showed the highest RNA yield in the released exosomes and distinctive shape in morphology. In addition, RNAs were isolated from cells and culture media, and profiles of these three miRNA fractions were obtained using microarray analysis. By comparing signal intensities of microarray data and the following validation using RT-PCR analysis, we found that let-7 miRNA family was abundant in both the intracellular and extracellular fractions from AZ-P7a cells, while low metastatic AZ-521, the parental cell line of AZ-P7a, as well as other cancer cell lines showed no such propensity.Conclusions/SignificanceThe enrichment of let-7 miRNA family in the extracellular fractions, particularly, in the exosomes from AZ-P7a cells may reflect their oncogenic characteristics including tumorigenesis and metastasis. Since let-7 miRNAs generally play a tumor-suppressive role as targeting oncogenes such as RAS and HMGA2, our results suggest that AZ-P7a cells release let-7 miRNAs via exosomes into the extracellular environment to maintain their oncogenesis.

Apelin is a recently discovered peptide that is the endogenous ligand for the APJ receptor. The aim of this study was to characterize apelin expression (mRNA levels) in the rat gastrointestinal tract and pancreas, to localize distribution of apelin peptide-containing cells in the stomach by immunohistochemistry, and to characterize the ontogeny of gastric apelin expression and peptide and the influence of apelin on gastric cell proliferation in vitro. Additionally, the effect of apelin on cholecystokinin (CCK) secretion and the involvement of MAPK, protein kinase C, and changes in intracellular Ca(2+) in apelin-induced CCK secretion in vitro were examined. Northern analysis showed a maximal apelin expression in the stomach with a lower expression level in the intestine. Apelin expression was not detected in the pancreas. Immunohistochemistry revealed abundant apelin-positive cells in the glandular epithelium of the stomach. The ontogeny study showed a higher apelin expression in the fetal and postnatal rat stomachs when compared with the adult stomach. In contrast to apelin expression, apelin peptide was not detected in the rat stomach until 20 d of age and then increased progressively with age. Apelin was shown to stimulate gastric cell proliferation in vitro. Apelin also stimulated CCK secretion from a murine enteroendocrine cell line (STC-1); apelin-stimulated CCK secretion is mediated through MAPK but not by intracellular Ca(2+) signaling. Together, these data indicate that apelin is an important new stomach peptide with a potential physiological role in the gastrointestinal tract.

Identification of driver genes contributes to the understanding of cancer etiology and is imperative for the development of individualized therapies. Gene amplification is a major event in oncogenesis. Driver genes with tumor-specific amplification-dependent overexpression can be therapeutic targets. In this study, we aimed to identify amplification-dependent driver genes in 1,454 solid tumors, across more than 15 cancer types, by integrative analysis of gene expression and copy number. Amplification-dependent overexpression of 64 known driver oncogenes were found in 587 tumors (40%); genes frequently observed were MYC (25%) and MET (18%) in colorectal cancer; SKP2 (21%) in lung squamous cell carcinoma; HIST1H3B (19%) and MYCN (13%) in liver cancer; KIT (57%) in gastrointestinal stromal tumors; and FOXL2 (12%) in squamous cell carcinoma across tissues. Genomic aberrations in 138 known cancer driver genes and 491 established fusion genes were found in 1,127 tumors (78%). Further analyses of 820 cancer-related genes revealed 16 as potential driver genes, with amplification-dependent overexpression restricted to the remaining 22% of samples (327 tumors) initially undetermined genetic drivers. Among them, AXL, which encodes a receptor tyrosine kinase, was recurrently overexpressed and amplified in sarcomas. Our studies of amplification-dependent overexpression identified potential drug targets in individual tumors.

This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

No abstract