Circular RNA (circRNA) is a class of noncoding 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. 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 colorectal cancer 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. Cancer Res; 77(9); 2339–50. ©2017 AACR.

A growing body of evidence indicates that circular RNAs are not simply a side product of splicing but a new class of noncoding RNAs in higher eukaryotes. The progression for the studies of circular RNAs is accelerated by combination of several advanced technologies such as next generation sequencing, gene silencing (small interfering RNAs) and editing (CRISPR/Cas9). More and more studies showed that dysregulated expression of circular RNAs plays critical roles during the development of several human diseases. Herein, we review the current advance of circular RNAs for their biosynthesis, molecular functions, and implications in human diseases. Impact statement: The accumulating evidence indicate that circular RNA (circRNA) is a novel class of noncoding RNA with diverse molecular functions. Our review summarizes the current hypotheses for the models of circRNA biosynthesis including the direct interaction between upstream and downstream introns and lariat-driven circularization. In addition, molecular functions such as a decoy of microRNA (miRNA) termed miRNA sponge, transcriptional regulator, and protein-like modulator are also discussed. Finally, we reviewed the potential roles of circRNAs in neural system, cardiovascular system as well as cancers. These should provide insightful information for studying the regulation and functions of circRNA in other model of human diseases.

53BP1 and other DNA damage response (DDR) proteins form foci at double-strand breaks (DSBs) which promote their repair by nonhomologous end joining (NHEJ). Focal accumulation of 53BP1 depends on the specific interaction of its tandem Tudor domain with dimethylated lysine 20 in histone H4 (H4K20me2). How 53BP1 foci dynamics are regulated is unclear since H4K20me2 is highly abundant, established largely in the absence of DNA damage, and uncertainty exists about the roles of candidate H4K20 methyltransferases in 53BP1 foci formation. Here, we show that 53BP1 foci assemble primarily on H4K20me2 established prior to DNA damage by the SETD8 and SUV420 methyltransferases rather than de novo H4K20 methylation mediated by MMSET/WHSC1. Moreover, we define a novel role for H4K16 acetylation in regulating 53BP1 foci dynamics. Concurrent acetylation at H4K16 antagonizes 53BP1 binding to extant H4K20me2 until DSBs elicit transient, localized H4 deacetylation that facilitates 53BP1 foci formation and NHEJ, and is associated with global repression of gene transcription. Our findings demonstrate that rapid induction of H4 deacetylation by DSBs affects multiple aspects of the DDR, and also suggest that antagonism of 53BP1 binding to H4K20me2 by H4K16 hyperacetylation may contribute to the efficacy of histone deacetylase inhibitors for cancer therapy.

Significance: Endometriosis is a highly prevalent proinflammatory disease without reliable diagnostic biomarkers and cannot be cured by nowadays’ medical treatments. Herein, we identified that extracellular vesicle (EV)-associated VEGF-C, secreted by proinflammatory cytokine-stimulated endometriotic stromal cells, is a critical modulator for endometriosis progression by promoting lymphangiogenesis. Invaded lymphatic vessels may serve as a canal for the infiltration of immune cells, which further enhances the inflammatory status in the endometriotic microenvironment and produces more EV-VEGF-C. The elevated circulating EV-VEGF-C is a sensitive and reliable biomarker for detecting endometriosis. These data advance our understanding of the pathophysiology of endometriosis and suggest VEGF-C can be a noninvasive diagnostic biomarker and a potential therapeutic target for endometriosis.

Prostaglandin (PG) E₂ has been shown to stimulate steroidogenesis in ectopic endometriotic stromal cells and may be involved in the development of endometriosis since this disorder is highly estrogen dependent. The biosynthesis of PGE₂ is controlled by the rate-limiting enzyme termed cyclooxygenase (COX). The objective of the current study was to investigate the expression of COX in peritoneal macrophages isolated from women with and without endometriosis, and to explore the effects of pro-inflammatory agents on COX expression in peritoneal macrophages. Using quantitative RT–PCR and Western blot analyses, we found that expression of COX-2 was markedly increased (P < 0.05) in peritoneal macrophages isolated from women with early or severe endometriosis, whereas expression of COX-1 was elevated only in the severe stage (P < 0.05). On the contrary, monocytes/macrophages purified from peripheral blood of patients with endometriosis had minimal or undetectable levels of COX-2, and this was not different from disease-free women. Treatment with interleukin-1β, tumour necrosis factor-α or PGE₂ caused a significant increase in COX-2 (P < 0.05) but not COX-1 expression in peritoneal macrophages isolated from disease-free women. In contrast, these agents had no substantial effect on COX-1 and COX-2 expression in peritoneal macrophages from women with endometriosis. In summary, expression of COX in peritoneal macrophages was associated with the severity of endometriosis. Elevated expression of both COX-1 and COX-2 in peritoneal macrophages may contribute to the increased peritoneal fluid PGE₂ concentrations and may thus play an important role in the development of endometriosis.

Steroidogenic acute regulatory protein (StAR) regulates the first committed step in the biosynthesis of steroids, and thus aberrant expression of StAR in endometriotic implants plays a critical role in the etiology of endometriosis. However, the mechanism responsible for abnormal expression of StAR in ectopic endometriotic tissues remains unknown. In the present study, we demonstrate that prostaglandin (PG) E₂ stimulates StAR protein expression at the cellular and molecular levels. PGE₂ caused a rapid increase in StAR expression that involves activation of the EP2 receptor-coupled protein kinase A pathway. Activation of EP2 receptor-induced phosphorylation of ERK and cAMP response element binding protein (CREB). However, activation of ERK did not involve in CREB phosphorylation or concomitantly StAR expression. Phosphorylation of CREB induced by PGE₂ increased the recruitment of CREB binding protein and thus histone H3 acetylation. Chromatin immunoprecipitation experiments showed that acetylated histone H3 bound to the proximal region of the StAR promoter was increased after 30 min treatment with PGE₂, and this was mirrored by an increase in nascent StAR RNA transcription. Treatment with the histone deacetylase inhibitor, tricostatin A, enhanced PGE₂-induced nascent StAR RNA transcription. We conclude that increased histone H3 acetylation involving the EP2 receptor, protein kinase A, CREB, and CREB binding protein is responsible for PGE₂-induced StAR gene activation in endometriotic stromal cells. Our current report may provide new insights in understanding mechanism of abnormally local production of estrogen and the etiology of endometriosis.