Dynamic antagonism between RNA-binding protein CUGBP2 and cyclooxygenase-2-mediated prostaglandin E2 in radiation damage

The Role of VEGFA, COX2, HUR and CUGBP2 in Predicting the Response to Neoadjuvant Therapy in Rectal Cancer Patients

Background and objectives: The effectiveness of neoadjuvant therapy, which is commonly used for stage II-III rectal cancer (RC) treatment, is limited. Genes associated with the pathogenesis of RC could determine response to this treatment. Therefore, the aim of this study was to investigate the potential predictive value of VEGFA, COX2, HUR and CUGBP2 genes and the associations between post-treatment changes in gene expression and the efficacy of neoadjuvant therapy. Materials and Methods: Biopsies from RC and healthy rectal tissue of 28 RC patients were collected before neoadjuvant therapy and 6-8 weeks after neoadjuvant therapy. The expression levels of VEGFA, COX2, HUR, CUGBP2 genes were evaluated using a quantitative real-time polymerase chain reaction. Results: The results reveal a significantly higher expression of VEGFA, COX2 and HUR mRNA in RC tissue compared to healthy rectal tissue (p < 0.05), and elevated VEGFA gene expression in pre-treatment tissues was associated with a better response to neoadjuvant therapy based on T-stage downstaging (p < 0.05). The expression of VEGFA, HUR and CUGBP2 genes significantly decreased after neoadjuvant therapy (p < 0.05). Responders to treatment demonstrated a significantly stronger decrease of VEGFA and COX2 expression after neoadjuvant therapy than non-responders (p < 0.05). Conclusions: The findings of this study suggest that the pre-treatment VEGFA gene expression might have predictive value for the response to neoadjuvant therapy, while the post-treatment decrease in VEGFA and COX2 gene expression could indicate the effectiveness of neoadjuvant therapy in RC patients.

mRNA Metabolism in Cardiac Development and Disease: Life After Transcription

The central dogma of molecular biology illustrates the importance of mRNAs as critical mediators between genetic information encoded at the DNA level and proteomes/metabolomes that determine the diverse functional outcome at the cellular and organ levels. Although the total number of protein-producing (coding) genes in the mammalian genome is ~20,000, it is evident that the intricate processes of cardiac development and the highly regulated physiological regulation in the normal heart, as well as the complex manifestation of pathological remodeling in a diseased heart, would require a much higher degree of complexity at the transcriptome level and beyond. Indeed, in addition to an extensive regulatory scheme implemented at the level of transcription, the complexity of transcript processing following transcription is dramatically increased. RNA processing includes post-transcriptional modification, alternative splicing, editing and transportation, ribosomal loading, and degradation. While transcriptional control of cardiac genes has been a major focus of investigation in recent decades, a great deal of progress has recently been made in our understanding of how post-transcriptional regulation of mRNA contributes to transcriptome complexity. In this review, we highlight some of the key molecular processes and major players in RNA maturation and post-transcriptional regulation. In addition, we provide an update to the recent progress made in the discovery of RNA processing regulators implicated in cardiac development and disease. While post-transcriptional modulation is a complex and challenging problem to study, recent technological advancements are paving the way for a new era of exciting discoveries and potential clinical translation in the context of cardiac biology and heart disease.

miR-615-3p promotes proliferation and migration and inhibits apoptosis through its potential target CELF2 in gastric cancer

Gastric cancer incidence is relatively higher in China than that in developed countries; however, molecular mechanisms considering the initiation and progression of gastric cancer are still unclear. For decades, numerous microRNAs have been found to regulate a wide range of biological functions in gastric cancer. However, the oncogenic function of miR-615-3p in gastric cancer has not been reported to date. With the help of gene and microRNA chips in 10 patients, we were able to screen differential expressed genes and microRNAs compared with normal gastric tissues. After that, online bioinformatics analysis tools were used to predict microRNAs' potential targets. As a result, miR-615-3p and its potential target, CELF2, were selected for further experiments. QRT-PCR and western blot results indicated the aberrant high expression of miR-615-3p and low expression of CELF2 in gastric cancer both in vivo and in vitro. Moreover, miR-615-3p expression correlated to T and M stage. Up regulation of miR-615-3p inhibited the apoptosis, promoted proliferation and migration and led to the down-regulation of CELF2. Meanwhile, down-regulation of miR-615-3p resulted in anti-tumor effects. Immunochemistry staining of CELF2 showed its association with T, N and M stage. In addition, overexpression of CELF2 could reverse miR-615-3p's oncogenic functions stated before. These findings indicate that miR-615-3p promotes gastric cancer proliferation and migration by suppressing CELF2 expression for the first time, providing clues for future clinical practices.

Upregulation of cugbp2 increases response of pancreatic cancer cells to chemotherapy

PURPOSE

Altered expression and/or function of ribosomal RNA (rRNA)-binding proteins CUGBP2/CELF2 might influence post-transcriptional regulation of the HO-1- and COX-2-mediated cytoprotective pathways and represents an important therapeutic target. The aim of this study was to assess the effects of CUGBP2-mediated post-transcriptional regulation of COX-2 and HO-1 in pancreatic cancer cells in regard of response to gemcitabine (GEM) treatment.

METHODS

Expression of CUGBP2, COX-2, and HO-1 was evaluated using qRT-PCR and Western blot methods. Cell viability after treatment with GEM and/or curcumin and siCUGBP2 was evaluated using MTT and crystal violet tests. RNA immunoprecipitation analysis was used to confirm COX-2 and HO-1 post-transcriptional regulation by CUGBP2 protein.

RESULTS

CUGBP2 expression at the messenger RNA (mRNA) level was 2.2-fold lower (p = 0.007), but HO-1 and COX-2 expression was increased 6.9- (p = 0.023) and 2.3- (p = 0.046) fold in pancreatic cancer tissues. The median survival of patients with low CUGBP2 expression from the lowest tercile was 13.8 months. The median survival of patients in terciles of middle and high CUGBP2 expression levels was 21.9 month (p = 0.123). Induction of CUGBP2 expression by curcumin resulted in the downregulation of HO-1 and COX-2 and strongly sensitized tumor cells to GEM treatment. However, CUGBP2 silencing upregulated HO-1 and COX-2 protein expression and had a high effect on cells viability.

CONCLUSION

Decreased activity of CUGBP2 could be associated with high chemoresistance and early dissemination of pancreatic cancer through the HO-1- and COX-2-mediated cytoprotective and carcinogenesis pathways. Curcumin significantly increased the effectiveness of GEM treatment in vitro via the CUGBP2-mediated post-transcriptional regulation pathway.

Role of cyclooxygenase-2 in Trypanosoma cruzi survival in the early stages of parasite host-cell interaction

Chagas disease, caused by the intracellular protozoan Trypanosoma cruzi, is a serious health problem in Latin America. During this parasitic infection, the heart is one of the major organs affected. The pathogenesis of tissue remodelling, particularly regarding cardiomyocyte behaviour after parasite infection and the molecular mechanisms that occur immediately following parasite entry into host cells are not yet completely understood. When cells are infected with T. cruzi, they develop an inflammatory response, in which cyclooxygenase-2 (COX-2) catalyses rate-limiting steps in the arachidonic acid pathway. However, how the parasite interaction modulates COX-2 activity is poorly understood. In this study, the H9c2 cell line was used as our model and we investigated cellular and biochemical aspects during the initial 48 h of parasitic infection. Oscillatory activity of COX-2 was observed, which correlated with the control of the pro-inflammatory environment in infected cells. Interestingly, subcellular trafficking was also verified, correlated with the control of Cox-2 mRNA or the activated COX-2 protein in cells, which is directly connected with the assemble of stress granules structures. Our collective findings suggest that in the very early stage of the T. cruzi-host cell interaction, the parasite is able to modulate the cellular metabolism in order to survives.

A novel function for CUGBP2 in controlling the pro-inflammatory stimulus in H9c2 cells: subcellular trafficking of messenger molecules

Accumulating evidence demonstrates that chronic inflammation plays an important role in heart hypertrophy and cardiac diseases. However, the fine-tuning of cellular and molecular mechanisms that connect inflammatory process and cardiac diseases is still under investigation. Many reports have demonstrated that the overexpression of the cyclooxygenase-2 (COX-2), a key enzyme in the conversion of arachidonic acid to prostaglandins and other prostanoids, is correlated with inflammatory processes. Increased level of prostaglandin E2 was also found in animal model of left ventricle of hypertrophy. Based on previous observations that demonstrated a regulatory loop between COX-2 and the RNA-binding protein CUGBP2, we studied cellular and molecular mechanisms of a pro-inflammatory stimulus in a cardiac cell to verify if the above two molecules could be correlated with the inflammatory process in the heart. A cellular model of investigation was established and H9c2 was used. We also demonstrated a regulatory connection between COX-2 and CUGBP2 in the cardiac cells. Based on a set of different assays including gene silencing and fluorescence microscopy, we describe a novel function for the RNA-binding protein CUGBP2 in controlling the pro-inflammatory stimulus: subcellular trafficking of messenger molecules to specific cytoplasmic stress granules to maintain homeostasis.

Apobec-1 increases cyclooxygenase-2 and aggravates injury in oxygen-deprived neurogenic cells and middle cerebral artery occlusion rats

Given that cyclooxygenase-2 (COX-2) plays a crucial role during cerebral ischemia and Apobec-1 is a critical regulator of COX-2 mRNA stabilization in gastrointestinal settings, the correlation of COX-2 and Apobec-1 was investigated in neurogenic cells and rat model of cerebral ischemia. After neurogenic SH-SY5Y, NG108-15 and PC12 cells were exposed to oxygen-glucose deprivation, cell viability, LDH leakage and Apobec-1 expression were determined. The effect of Apobec-1 overexpression on injury severity of oxygen-glucose deprivation, COX-2 expression, C-to-U editing of COX-2 mRNA were measured in vitro. Then the correlation of Apobec-1 level and injury severity was analyzed in cells with oxygen-glucose deprivation and in rats with middle cerebral artery occlusion. Apobec-1 expression was elevated along with upregulation of COX-2 and injury severity of oxygen-glucose deprivation in the three cell lines. Apobec-1 overexpression aggravated injury of oxygen-glucose deprivation in vitro and could be correlated to injury severity in vivo. Meanwhile, Apobec-1 increased COX-2 expression and COX-2 mRNA stabilization in neurogenic cells, and failed to catalyze C-to-U editing of COX-2 mRNA. Apobec-1 could upregulate COX-2 expression in neurogenic cells by stabilizing COX-2 mRNA, and might aggravate injury of oxygen-glucose deprivation in neurogenic cells as well as in rats with cerebral ischemia.

CELFish ways to modulate mRNA decay

The CELF family of RNA-binding proteins regulates many steps of mRNA metabolism. Although their best characterized function is in pre-mRNA splice site choice, CELF family members are also powerful modulators of mRNA decay. In this review we focus on the different modes of regulation that CELF proteins employ to mediate mRNA decay by binding to GU-rich elements. After starting with an overview of the importance of CELF proteins during development and disease pathogenesis, we then review the mRNA networks and cellular pathways these proteins regulate and the mechanisms by which they influence mRNA decay. Finally, we discuss how CELF protein activity is modulated during development and in response to cellular signals. We conclude by highlighting the priorities for new experiments in this field. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Mechanistic aspects of COX-2 expression in colorectal neoplasia

The cyclooxygenase-2 (COX-2) enzyme catalyzes the rate-limiting step of prostaglandin formation in pathogenic states and a large amount of evidence has demonstrated constitutive COX-2 expression to be a contributing factor promoting colorectal cancer (CRC). Various genetic, epigenetic, and inflammatory pathways have been identified to be involved in the etiology and development of CRC. Alteration in these pathways can influence COX-2 expression at multiple stages of colon carcinogenesis allowing for elevated prostanoid biosynthesis to occur in the tumor microenvironment. In normal cells, COX-2 expression levels are potently regulated at the post-transcriptional level through various RNA sequence elements present within the mRNA 3' untranslated region (3'UTR). A conserved AU-rich element (ARE) functions to target COX-2 mRNA for rapid decay and translational inhibition through association with various RNA-binding proteins to influence the fate of COX-2 mRNA. Specific microRNAs (miRNAs) bind regions within the COX-2 3'UTR and control COX-2 expression. In this chapter, we discuss novel insights in the mechanisms of altered post-transcriptional regulation of COX-2 in CRC and how this knowledge may be used to develop novel strategies for cancer prevention and treatment.

MicroRNA and AU-rich element regulation of prostaglandin synthesis

Many lines of evidence demonstrate that prostaglandins play an important role in cancer, and enhanced synthesis of prostaglandin E(2) (PGE(2)) is often observed in various human malignancies often associated with poor prognosis. PGE(2) synthesis is initiated with the release of arachidonic acid by phospholipase enzymes, where it is then converted into the intermediate prostaglandin prostaglandin H(2) (PGH(2)) by members of the cyclooxygenase family. The synthesis of PGE(2) from PGH(2) is facilitated by three different PGE synthases, and functional PGE(2) can promote tumor growth by binding to four EP receptors to activate signaling pathways that control cell proliferation, migration, apoptosis, and angiogenesis. An integral method of controlling gene expression is by posttranscriptional mechanisms that regulate mRNA stability and protein translation. Messenger RNA regulatory elements typically reside within the 3' untranslated region (3'UTR) of the transcript and play a critical role in targeting specific mRNAs for posttranscriptional regulation through microRNA (miRNA) binding and adenylate- and uridylate-rich element RNA-binding proteins. In this review, we highlight the current advances in our understanding of the impact these RNA sequence elements have upon regulating PGE(2) levels. We also identify various RNA sequence elements consistently observed within the 3'UTRs of the genes involved in the PGE(2) pathway, indicating these binding sites for miRNAs and RNA-binding proteins to be central regulators of PGE(2) synthesis and function. These findings may provide a rationale for the development of new therapeutic approaches to control tumor growth and metastasis promoted by elevated PGE(2) levels.

The importance of CELF control: molecular and biological roles of the CUG-BP, Elav-like family of RNA-binding proteins

RNA processing is important for generating protein diversity and modulating levels of protein expression. The CUG-BP, Elav-like family (CELF) of RNA-binding proteins regulate several steps of RNA processing in the nucleus and cytoplasm, including pre-mRNA alternative splicing, C to U RNA editing, deadenylation, mRNA decay, and translation. In vivo, CELF proteins have been shown to play roles in gametogenesis and early embryonic development, heart and skeletal muscle function, and neurosynaptic transmission. Dysregulation of CELF-mediated programs has been implicated in the pathogenesis of human diseases affecting the heart, skeletal muscles, and nervous system.

Mesenchymal stem cells engraftment in the injured intestine of mice

AIM: To investigate the engraftment of murine bone marrow mesenchymal stem cells (MSCs) in the irradiated intestine of mice to provide some clues about the mechanism of intestine epithelium healing and lay an experimental foundation for treatment of intestine diseases by intravenous transplantation of MSCs.

METHODS: MSCs from male mice were isolated, expanded, identified, suspended in sterile normal saline (1 × 10⁶ cells/mL), and slowly infused into irradiated female mice via the tail vein. Meanwhile, a group of irradiated female mice receiving an equal volume of sterile normal saline were used as controls. For tracing male MSC residence in the intestine after intravenous transplantation, in situ hybridization (ISH) was used to detect the Sry gene on the Y chromosome.

RESULTS: In the transplantation group, ISH analysis revealed the presence of male donor MSCs in the submucosa of the intestine of female mice, but not in the mucosal epithelium. At week 1 after cell transplantation, Sry-positive cells were scattered around the crypt, with a percentage of 19.48% ± 5.01%. At week 2, this percentage rose to 30.86% ± 12.14%, significantly higher than that at week 1 (P < 0.05). However, there was no significant difference in the percentage of Sry-positive cells between at week 2 and week 4 (week 4: 35.95% ± 11.98%, P > 0.05). In the control group, no Sry-positive cells were found.

CONCLUSION: After MSCs were transplanted into mice, they were attracted to and retained in the irradiated intestine and colonized in the intestinal submucosa.

Role of RNA-Binding Proteins in Colorectal Carcinogenesis

RNA-binding proteins (RBPs) play key roles in the posttranscriptional regulation of gene expression. RBPs control various posttranscriptional events, including splicing, polyadenylation, mRNA stability, transport, and translation. It is becoming apparent that RBPs play a significant role in pathophysiologic conditions such as inflammation and cancer. More importantly, we and others have begun dissecting the role of mRNA stability and translation in regulating gene expression, dysregulation of which has serious consequences for the fate of the cell. In this article, we discuss this emerging area of posttranscriptional gene regulation and the role of RBPs in the aberrant expression of proteins in tumorigenesis.

Posttranscriptional Regulation of Cyclooxygenase 2 Expression in Colorectal Cancer

Cyclooxygenase (COX)-2 enzyme catalyzes the rate-limiting step of prostaglandin formation in pathogenic states, and overexpression of COX-2 occurs at multiple stages of colon carcinogenesis, allowing elevated prostaglandin synthesis to occur in the tumor microenvironment. In normal cells, COX-2 expression levels are potently regulated at the posttranscriptional level through various RNA sequence elements present within the mRNA 3' untranslated region (3'UTR). A conserved AU-rich element functions to target COX-2 mRNA for rapid decay and translational inhibition through association with various RNA-binding proteins to influence the fate of COX-2 mRNA. The 3'UTR contains alternative polyadenylation signals that result in a shortened 3'UTR and loss of regulatory elements. Specific microRNAs have been identified to bind regions within the COX-2 3'UTR and control COX-2 expression. Recent evidence demonstrates the functional significance of the COX-2 3'UTR and how improper recognition of the 3'UTR can contribute to COX-2 overexpression in colorectal cancer.

Posttranscriptional and posttranslational determinants of cyclooxygenase expression

Cyclooxygenases (COX-1 and COX-2) are ER-resident proteins that catalyze the committed step in prostanoid synthesis. COX-1 is constitutively expressed in many mammalian cells, whereas COX-2 is usually expressed inducibly and transiently. Abnormal expression of COX-2 has been implicated in the pathogenesis of chronic inflammation and various cancers; therefore, it is subject to tight and complex regulation. Differences in regulation of the COX enzymes at the posttranscriptional and posttranslational levels also contribute significantly to their distinct patterns of expression. Rapid degradation of COX-2 mRNA has been attributed to AU-rich elements (AREs) at its 3' UTR. Recently, microRNAs that can selectively repress COX-2 protein synthesis have been identified. The mature forms of these COX proteins are very similar in structure except that COX-2 has a unique 19-amino acid (19-aa) segment located near the C-terminus. This C-terminal 19-aa cassette plays an important role in mediation of the entry of COX-2 into the ER-associated degradation (ERAD) system, which transports ER proteins to the cytoplasm for degradation by the 26S proteasome. A second pathway for COX-2 protein degradation is initiated after the enzyme undergoes suicide inactivation following cyclooxygenase catalysis. Here, we discuss these molecular determinants of COX-2 expression in detail. [BMB reports 2009; 42(9): 552-560].

Transcriptional induction and translational inhibition of Arc and Cugbp2 in mice hippocampus after transient global ischemia under normothermic condition

Mild hypothermia protects against neuronal damage after transient global ischemia in experimental animals. The exact mechanism of this protective effect remains to be elucidated. The purpose of the present study was to investigate the molecular mechanisms relevant to different neurologic responses to hypothermia and normothermia. Transient global ischemia was induced in C57BL/6 mice by bilateral common carotid artery occlusion for 10 min. Hypothermia provided robust neuroprotection in the hippocampus region and dramatically reduced the mortality rate. Using adaptor-tagged competitive polymerase chain reaction, we obtained the relative transcription levels of 1210 genes in the hippocampal region and compared the expression patterns of these genes. Two genes, Activity-regulated cytoskeleton-associated protein (Arc) and CUG-binding protein-2 (Cugbp2), showed remarkable and persistent increases in their expression levels in normothermic mice, compared with in both sham and hypothermic mice. Despite the increased transcription of Arc and Cugbp2, an immunohistochemistry analysis did not show comparable increases in the translations of both genes. Only a transient increase in Arc protein was observed in the granule cells of the dentate gyrus at 6 h after reperfusion. A remarkable decrease in Cugbp2 protein was observed in the pyramidal cells of the hippocampal CA1-CA3, in accordance with the progress of neuronal degeneration. A decrease in Cugbp2 protein was not observed in hypothermic mice. These results suggest that transient global ischemia induces the translational inhibition of genes with increased expression not in hypothermic, but in normothermic mice. Thus, translational inhibition might play an important role in the progress of neuronal injury after transient global ischemia.

The aryl hydrocarbon receptor attenuates tobacco smoke-induced cyclooxygenase-2 and prostaglandin production in lung fibroblasts through regulation of the NF-kappaB family member RelB

Diseases such as chronic obstructive pulmonary disease and lung cancer caused by cigarette smoke affect millions of people worldwide. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that influences responses to certain environmental pollutants such as tobacco smoke. However, the physiological function(s) of the AhR is unknown. Herein we propose that the physiologic role of the AhR is to limit inflammation. We show that lung fibroblasts from AhR(-/-) mice produce a heightened inflammatory response to cigarette smoke, typified by increased levels of cyclooxygenase-2 (COX-2) and prostaglandins (PGs), when compared with wild type (AhR(+/+)) fibroblasts. This response was dependent on AhR expression as transient transfection of an AhR expression plasmid into AhR(-/-) fibroblasts significantly attenuated the smoke-induced COX-2 and PG production, confirming the anti-inflammatory role of the AhR. The AhR can interact with NF-kappaB. However, the heightened inflammatory response observed in AhR(-/-) fibroblasts was not the result of NF-kappaB (p50/p65) activation. Instead it was coupled with a loss of the NF-kappaB family member RelB in AhR(-/-) fibroblasts. Taken together, these studies provide compelling evidence that AhR expression limits proinflammatory COX-2 and PG production by maintaining RelB expression. The association between RelB and AhR may represent a new therapeutic and more selective target with which to combat inflammation-associated diseases.

CUGBP2 downregulation by prostaglandin E2 protects colon cancer cells from radiation-induced mitotic catastrophe

Prostaglandin E(2) (PGE(2)) is a potent inhibitor of ionizing radiation (IR)-induced cell death. Exposure of colon cancer cells to IR leads to increased CUGBP2 expression. Therefore, we tested the hypothesis that PGE(2) radioprotects colon cancer cells by inhibiting CUGBP2 expression. Exposure of HCT-116 cells to gamma-IR (0-12 Gy) resulted in a dose-dependent reduction in cell growth and an increase in the G(2)-M phase of the cell cycle. Western blot analyses demonstrated increased levels of activated caspase 9 and caspase 3. In addition, whereas Bax expression is increased, that of Bcl-2 and Bcl-x(L) was reduced. Further analyses demonstrated increased activation of Chk1 and Chk2 kinases, coupled with higher levels of nuclear cyclin B1 and Cdc2. Pretreatment with PGE(2) suppressed the activation of caspase 3 and caspase 7 and inhibited Bax expression. In addition, PGE(2) treatment restored growth and colony formation to control levels. IR significantly upregulated the expression of CUGBP2 in the cells, which was suppressed when cells were pretreated with PGE(2). Ectopic overexpression of CUGBP2 also induced apoptosis. Furthermore, it reversed the PGE(2)-mediated protection from IR-induced mitotic catastrophe. Furthermore, there was an increase in nuclear localization of cyclin B1 and Cdc2 coupled with increased phosphorylation of p53, Chk1, Chk2, and Cdc25c proteins. Cell cycle analysis also demonstrated increased G(2)-M transition. In contrast, siRNA-mediated suppression of CUGBP2 expression restored normal cell cycle progression and decreased IR-induced apoptosis. Taken together, these data demonstrate that PGE(2) protects colon cancer cells from IR-induced mitotic catastrophe in part through suppression of CUGBP2 expression.

Novel intestinal splice variants of RNA-binding protein CUGBP2: isoform-specific effects on mitotic catastrophe

CUG triplet repeat-binding protein 2 (CUGBP2) is a RNA-binding protein that regulates mRNA translation and modulates apoptosis. Here, we report the identification of two splice variants (termed variants 2 and 3) in cultured human intestinal epithelial cells and in mouse gastrointestinal tract. The variants are generated from alternative upstream promoters resulting in the inclusion of additional NH(2)-terminal residues. Although variant 2 is the predominant isoform in normal intestine, its expression is reduced, whereas variant 1 is overexpressed following gamma-irradiation. All three variants bind cyclooxygenase-2 (COX-2) mRNA. However, only variant 1 inhibits the translation of the endogenous COX-2 mRNA and a chimeric luciferase mRNA containing the COX-2 3'untranslated region. Furthermore, whereas variant 1 is predominantly nuclear, variants 2 and 3 are predominantly cytoplasmic. These data imply that the additional amino acids affect CUGBP2 function. Previous studies have demonstrated that variant 1 induces intestinal epithelial cells to undergo apoptosis. However, in contrast to variant 1, the two novel variants do not affect proliferation or apoptosis of HCT116 cells. In addition, only variant 1 induced G(2)/M cell cycle arrest, which was overcome by prostaglandin E(2). Moreover, variant 1 increased cellular levels of phosphorylated p53 and Bax and decreased Bcl2. Caspase-3 and -9 were also activated, suggesting the initiation of the intrinsic apoptotic pathway. Furthermore, increased phosphorylation of checkpoint kinase (Chk)1 and Chk2 kinases and increased nuclear localization of Cdc2 and cyclin B1 suggested that cells were in mitotic transition. Taken together, these data demonstrate that cells expressing CUGBP2 variant 1 undergo apoptosis during mitosis, suggesting mitotic catastrophe.

Translation inhibition during cell cycle arrest and apoptosis: Mcl-1 is a novel target for RNA binding protein CUGBP2

CUGBP2, a translation inhibitor, induces colon cancer cells to undergo apoptosis. Mcl-1, an antiapoptotic Bcl-2 family protein, interferes with mitochondrial activation to inhibit apoptosis. Here, we have determined the effect of CUGBP2 on Mcl-1 expression. We developed a HCUG2 cell line by stably expressing CUGBP2 in the HCT-116 colon cancer cells. HCUG2 cells demonstrate decreased levels of proliferation and increased apoptosis, compared with HCT-116 cells. Flow cytometry analysis demonstrated higher levels of cells in the G(2)-M phase. Western blot analyses demonstrated that there was decreased Bcl-2 and Mcl-1 protein but increased expression of Bax, cyclin B1, and Cdc2. Immunocytochemistry also demonstrated increased levels of cyclin B1 and Cdc2 in the nucleus of HCUG2 cells. However, there was colocalization of phosphorylated histone H3 with transferase-mediated dUTP nick-end labeling (TUNEL). Furthermore, immunostaining for alpha-tubulin demonstrated that there was disorganization of microtubules. These data suggest that CUGBP2 expression in HCUG2 cells induces the cells to undergo apoptosis during the G(2)-M phase of the cell cycle. We next determined the mechanism of CUGBP2-mediated reduction in Mcl-1 expression. Mcl-1 protein, but not Mcl-1 mRNA, was lower in HCUG2 cells, suggesting translation inhibition. CUGBP2 binds to Mcl-1 3'-untranslated region (3'-UTR) both in vitro and in HCUG2 cells. Furthermore, CUGBP2 increased the stability of both endogenous Mcl-1 and luciferase mRNA containing the Mcl-1 3'-UTR. However, luciferase protein expression from the luciferase-Mcl-1 3'-UTR mRNA was suppressed. Taken together, these data demonstrate that CUGBP2 inhibits Mcl-1 expression by inhibiting Mcl-1 mRNA translation, resulting in driving the cells to apoptosis during the G(2) phase of the cell cycle.

Fluid secretion caused by aerolysin-like hemolysin of Aeromonas sobria in the intestines is due to stimulation of production of prostaglandin E2 via cyclooxygenase 2 by intestinal cells

To clarify the mechanisms of diarrheal disease induced by Aeromonas sobria, we examined whether prostaglandin E2 (PGE2) was involved in the intestinal secretory action of A. sobria hemolysin by use of a mouse intestinal loop model. The amount of PGE2 in jejunal fluid and the fluid accumulation ratio were directly related to the dose of hemolysin. The increase over time in the level of PGE2 was similar to that of the accumulated fluid. In addition, hemolysin-induced fluid secretion and PGE2 synthesis were inhibited by the selective cyclooxygenase 2 (COX-2) inhibitor NS-398 but not the COX-1 inhibitor SC-560. Western blot analysis revealed that hemolysin increased the COX-2 protein levels but reduced the COX-1 protein levels in mouse intestinal mucosa in vivo. These results suggest that PGE2 functions as an important mediator of diarrhea caused by hemolysin and that PGE2 is produced primarily through a COX-2-dependent mechanism. Subsequently, we examined the relationship between PGE2, cyclic AMP (cAMP), and cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in mouse intestinal mucosa exposed to hemolysin. Hemolysin increased the levels of cAMP in the intestinal mucosa. NS-398 inhibited the increase in cAMP production, but SC-560 did not. In addition, H-89, a cAMP-dependent protein kinase A (PKA) inhibitor, and glibenclamide, a CFTR inhibitor, inhibited fluid accumulation. Taken together, these results indicate that hemolysin activates PGE2 production via COX-2 and that PGE2 stimulates cAMP production. cAMP then activates PKA, which in turn stimulates CFTR Cl- channels and finally leads to fluid accumulation in the intestines.

COX-2 and the vasculature: angel or evil?

Cyclooxygenase-2 (COX-2) may modulate atherosclerotic plaque stability or instability according to the prostaglandin synthase coupled with it. Whereas upregulation of COX-2 and prostaglandin (PG) E synthase is associated with plaque instability, overexpression of COX-2 and lipocalin-type PGD synthase leads to plaque stability. Thus, the role of COX-2 in atherothrombosis appears to be quite complex. In this article we summarize our recent papers investigating mechanisms regulating the expression and pharmacologic modulation of COX-2 in atherosclerotic plaques.

Functional antagonism between RNA binding proteins HuR and CUGBP2 determines the fate of COX-2 mRNA translation

BACKGROUND AND AIMS

Cyclooxygenase-2 (COX-2) expression is regulated at the levels of messenger RNA (mRNA) stability and translation by AU-rich elements (ARE) located in its 3' untranslated region (3'UTR). Although structurally homologous RNA binding proteins HuR and CUGBP2 stabilize COX-2 mRNA, HuR induces whereas CUGBP2 inhibits COX-2 mRNA translation. This study aimed to determine the antagonism between these proteins on COX-2 expression.

METHODS

COX-2 ARE binding activity was determined by nitrocellulose filter binding and UV cross-linking assays using recombinant glutathione S-transferase (GST)/HuR and GST/CUGBP2. Protein:protein interactions were determined by GST pull-down, yeast 2-hybrid, and immunocytochemistry assays. Nucleocytoplasmic shutting was determined by heterokaryon analyses. The effect of CUGBP2 and HuR on COX-2 ARE-dependent translation was shown by a chimeric luciferase mRNA containing COX-2 3'UTR. HT-29 cells were subjected to 12 Gy gamma-irradiation in a cesium irradiator.

RESULTS

CUGBP2 and HuR bind with similar affinities to COX-2 ARE, but CUGBP2 competes with HuR for binding. In vitro, HuR and CUGBP2 heterodimerize. Furthermore, FLAG-tagged HuR and myc-tagged CUGBP2 colocalize in the nucleus of HCT-116 cells. Moreover, both proteins shuttled between the nucleus and cytoplasm. In vitro, HuR enhanced whereas CUGBP2 inhibited translation of the chimeric luciferase COX-2 3'UTR mRNA. Furthermore, CUGBP2 competitively inhibited HuR-mediated translation of the transcript. In HT-29 cells transfected with HuR and CUGBP2, a switch in COX-2 mRNA binding from predominantly HuR to CUGBP2 occurred after radiation treatment, which was coupled with increased silencing of the COX-2 mRNA.

CONCLUSIONS

CUGBP2 overrides HuR and suppresses COX-2 mRNA translation.

Molecular biology of the small intestine

PURPOSE OF REVIEW

A concise report of published research is presented here that has provided new insights into the molecular and cell biology of the small intestine.

RECENT FINDINGS

The precise control of cell renewal lineage commitment, differentiation and apoptosis along the crypt-villus axis are regulated by paracrine and autocrine signaling pathways that include Wnt, Hedgehog and Notch ligands. The downstream signaling pathways and transcriptional control of gene expression are being elucidated. Conditional loss of functional c-myc in the intestinal mucosa may have no effect on the normal homeostasis of this tissue. Manipulation of CUGBP2 expression may modulate the response of normal intestine to radiation therapy.

SUMMARY

The cellular interactions at various levels in the small intestine are being understood and would provide a framework for interventional translational research in coming years.

Radiation-Induced Changes in Gene Expression Involve Recruitment of Existing Messenger RNAs to and away from Polysomes

Although ionizing radiation has been shown to influence gene transcription, little is known about the effects of radiation on gene translational efficiency. To obtain a genome-wide perspective of the effects of radiation on gene translation, microarray analysis was done on polysome-bound RNA isolated from irradiated human brain tumor cells; to allow for a comparison with the effects of radiation on transcription, microarray analysis was also done using total RNA. The number of genes whose translational activity was modified by radiation was approximately 10-fold greater than those whose transcription was affected. The radiation-induced change in a gene's translational activity was shown to involve the recruitment of existing mRNAs to and away from polysomes. Moreover, the change in a gene's translational activity after irradiation correlated with changes in the level of its corresponding protein. These data suggest that radiation modifies gene expression primarily at the level of translation. In contrast to transcriptional changes, there was considerable overlap in the genes affected at the translational level among brain tumor cell lines and normal astrocytes. Thus, the radiation-induced translational control of a subset of mRNAs seems to be a fundamental component of cellular radioresponse.

Emerging roles for cyclooxygenase-2 in gastrointestinal mucosal defense

The development of selective inhibitors of cyclooxygenase-2 (COX-2) was based on the concept that this enzyme played little, if any, role in modulating the ability of the gastrointestinal (GI) tract to resist and respond to injury. There is now overwhelming evidence that this is far from true. Indeed, COX-2 mediates several of the most important components of 'mucosal defense', contributes significantly to the resolution of GI inflammation and plays a crucial role in regulating ulcer healing. COX-2 also contributes to long-term changes in GI function after bouts of inflammation.

Novel determinants of plaque instability

Arachidonic acid metabolism plays an important role in acute ischemic syndromes affecting the coronary or cerebrovascular territory, as reflected by biochemical measurements of eicosanoid biosynthesis and the results of inhibitor trials in these settings. Two cyclooxygenase (COX)-isozymes have been characterized, COX-1 and COX-2, that differ in terms of regulatory mechanisms of expression, tissue distribution, substrate specificity, preferential coupling to upstream and downstream enzymes and susceptibility to inhibition by the extremely heterogeneous class of COX-inhibitors. While the role of platelet COX-1 in acute coronary syndromes and ischemic stroke is firmly established through approximately 20 years of thromboxane metabolite measurements and aspirin trials, the role of COX-2 expression and inhibition in atherothrombosis is substantially uncertain, because the enzyme was first characterized in 1991 and selective COX-2 inhibitors became commercially available only in 1998. In this review, we discuss the pattern of expression of COX-2 in the cellular players of atherothrombosis, its role as a determinant of plaque 'vulnerability,' and the clinical consequences of COX-2 inhibition. Recent studies from our group suggest that variable expression of upstream and downstream enzymes in the prostanoid biosynthetic cascade may represent important determinants of the functional consequences of COX-2 expression and inhibition in different clinical settings.