Beta-Catenin stabilizes cyclooxygenase-2 mRNA by interacting with AU-rich elements of 3'-UTR

β-Catenin interacts with canonical RBPs including MSI2 to associate with a Wnt signalling mRNA network in myeloid leukaemia cells

Wnt/β-catenin signalling is important for normal hematopoietic stem/progenitor cell (HSPC) biology and heavily implicated in acute and chronic myeloid leukaemia (AML and CML). The central mediator β-catenin is an attractive therapeutic target in myeloid neoplasms however its targeting has been hampered by a poor characterisation of its molecular interactions in haematopoietic cells, which will differ from its network in solid tissues. Our previous β-catenin interactome study identified the significant enrichment of RNA-binding proteins (RBP) implying post-transcriptional roles for β-catenin in myeloid cells. To identify β-catenin interacting mRNAs we performed β-catenin RNA-immunoprecipitation coupled to RNA-sequencing (RIP-seq) and identified significantly enriched Wnt signalling pathway transcripts. Using β-catenin cross-linking immunoprecipitation (CLIP) we demonstrated a limited capacity for β-catenin to bind RNA directly, implying dependence on other RBPs. β-Catenin was found to interact with Musashi-2 (MSI2) in both myeloid cell lines and primary AML patient samples, where expression was significantly correlated. MSI2 knockdown reduced Wnt signalling output (TCF/LEF activity), through suppression of LEF-1 expression and nuclear localisation. Through both RIP and CLIP we demonstrate MSI2 binds LEF1 mRNA in a partly β-catenin dependent fashion, and may impact the post-transcriptional control of LEF-1 expression. Finally, we show that MSI2-mediated expansion of human HSPCs could be partly driven through LEF1 regulation. This is the first study to experimentally demonstrate functional crosstalk between MSI2 and Wnt signalling in human cells, and indicates potential novel post-transcriptional roles for β-catenin in a haematological context.

3'UTR Diversity: Expanding Repertoire of RNA Alterations in Human mRNAs

Genomic information stored in the DNA is transcribed to the mRNA and translated to proteins. The 3' untranslated regions (3'UTRs) of the mRNA serve pivotal roles in posttranscriptional gene expression, regulating mRNA stability, translation, and localization. Similar to DNA mutations producing aberrant proteins, RNA alterations expand the transcriptome landscape and change the cellular proteome. Recent global analyses reveal that many genes express various forms of altered RNAs, including 3'UTR length variants. Alternative polyadenylation and alternative splicing are involved in diversifying 3'UTRs, which could act as a hidden layer of eukaryotic gene expression control. In this review, we summarize the functions and regulations of 3'UTRs and elaborate on the generation and functional consequences of 3'UTR diversity. Given that dynamic 3'UTR length control contributes to phenotypic complexity, dysregulated 3'UTR diversity might be relevant to disease development, including cancers. Thus, 3'UTR diversity in cancer could open exciting new research areas and provide avenues for novel cancer theragnostics.

Wnt Signaling Pathway Collapse upon β-Catenin Destruction by a Novel Antimicrobial Peptide SKACP003: Unveiling the Molecular Mechanism and Genetic Activities Using Breast Cancer Cell Lines

Despite progress in breast cancer treatment, the survival rate for patients with metastatic breast cancer remains low due to chemotherapeutic agent resistance and the lack of specificity of the current generation of cancer drugs. Our previous findings indicated that the antimicrobial peptide SKACP003 exhibited anticancer properties, particularly against the MCF-7, MDA-MB-231, and MDA-MB-453 breast cancer cell lines. However, the mechanism of SKACP003-induced cancer cell death is unknown. Here, we investigated the molecular mechanism by which SKACP003 inhibits the cell cycle, cell proliferation, and angiogenesis in breast cancer cell lines. The results revealed that all the breast cancer cell lines treated at their IC₅₀ values significantly inhibited the replicative phase of the cell cycle. The SKACP003-induced growth inhibition induced apoptosis, as evidenced by a decrease in BCL-2 and an increase in BAX and caspase gene (Cas-3, Cas-8, and Cas-9) expression. Reduced expression of the β-Catenin signaling pathway was associated with the SKACP003-induced apoptosis. SKACP003-treated breast cancer cells showed decreased expression of Wnt/β-Catenin targeting genes such as C-Myc, P⁶⁸, and COX-2 and significant downregulation of CDK-4 and CDK-6 genes. Furthermore, cytoplasmic β-catenin protein levels in SKACP003-treated cell lines were significantly lower than in control cell lines. The results of the current study suggest that the newly identified antimicrobial peptide SKACP003 has great potential as a candidate for specifically targeting the β-catenin and thus significantly reducing the progression and prognosis of breast cancer cell lines.

Aspirin sensitivity of PIK3CA-mutated Colorectal Cancer: potential mechanisms revisited

PIK3CA mutations are amongst the most prevalent somatic mutations in cancer and are associated with resistance to first-line treatment along with low survival rates in a variety of malignancies. There is evidence that patients carrying PIK3CA mutations may benefit from treatment with acetylsalicylic acid, commonly known as aspirin, particularly in the setting of colorectal cancer. In this regard, it has been clarified that Class IA Phosphatidylinositol 3-kinases (PI3K), whose catalytic subunit p110α is encoded by the PIK3CA gene, are involved in signal transduction that regulates cell cycle, cell growth, and metabolism and, if disturbed, induces carcinogenic effects. Although PI3K is associated with pro-inflammatory cyclooxygenase-2 (COX-2) expression and signaling, and COX-2 is among the best-studied targets of aspirin, the mechanisms behind this clinically relevant phenomenon are still unclear. Indeed, there is further evidence that the protective, anti-carcinogenic effect of aspirin in this setting may be mediated in a COX-independent manner. However, until now the understanding of aspirin's prostaglandin-independent mode of action is poor. This review will provide an overview of the current literature on this topic and aims to analyze possible mechanisms and targets behind the aspirin sensitivity of PIK3CA-mutated cancers.

Roles of Embryonic Lethal Abnormal Vision-Like RNA Binding Proteins in Cancer and Beyond

Embryonic lethal abnormal vision-like (ELAVL) proteins are RNA binding proteins that were originally discovered as indispensable regulators of the development and functioning of the nervous system. Subsequent studies have shown that ELAVL proteins not only exist in the nervous system, but also have regulatory effects in other tissues. ELAVL proteins have attracted attention as potential therapeutic targets because they stabilize multiple mRNAs by binding within the 3′-untranslated region and thus promote the development of tumors, including hepatocellular carcinoma, pancreatic cancer, ovarian cancer, breast cancer, colorectal carcinoma and lung cancer. Previous studies have focused on these important relationships with downstream mRNAs, but emerging studies suggest that ELAVL proteins also interact with non-coding RNAs. In this review, we will summarize the relationship of the ELAVL protein family with mRNA and non-coding RNA and the roles of ELAVL protein family members in a variety of physiological and pathological processes.

Targeting β-catenin in acute myeloid leukaemia: past, present, and future perspectives

Acute myeloid leukaemia (AML) is an aggressive disease of the bone marrow with a poor prognosis. Evidence suggests long established chemotherapeutic regimens used to treat AML are reaching the limits of their efficacy, necessitating the urgent development of novel targeted therapies. Canonical Wnt signalling is an evolutionary conserved cascade heavily implicated in normal developmental and disease processes in humans. For over 15 years its been known that the central mediator of this pathway, β-catenin, is dysregulated in AML promoting the emergence, maintenance, and drug resistance of leukaemia stem cells. Yet, despite this knowledge, and subsequent studies demonstrating the therapeutic potential of targeting Wnt activity in haematological cancers, β-catenin inhibitors have not yet reached the clinic. The aim of this review is to summarise the current understanding regarding the role and mechanistic dysregulation of β-catenin in AML, and assess the therapeutic merit of pharmacologically targeting this molecule, drawing on lessons from other disease contexts.

β-Catenin safeguards the ground state of mousepluripotency by strengthening the robustness of the transcriptional apparatus

Mouse embryonic stem cells cultured with MEK (mitogen-activated protein kinase kinase) and GSK3 (glycogen synthase kinase 3) inhibitors (2i) more closely resemble the inner cell mass of preimplantation blastocysts than those cultured with SL [serum/leukemia inhibitory factor (LIF)]. The transcriptional mechanisms governing this pluripotent ground state are unresolved. Release of promoter-proximal paused RNA polymerase II (Pol2) is a multistep process necessary for pluripotency and cell cycle gene transcription in SL. We show that β-catenin, stabilized by GSK3 inhibition in medium with 2i, supplies transcriptional coregulators at pluripotency loci. This selectively strengthens pluripotency loci and renders them addicted to transcription initiation for productive gene body elongation in detriment to Pol2 pause release. By contrast, cell cycle genes are not bound by β-catenin, and proliferation/self-renewal remains tightly controlled by Pol2 pause release under 2i conditions. Our findings explain how pluripotency is reinforced in the ground state and also provide a general model for transcriptional resilience/adaptation upon network perturbation in other contexts.

Limited Proteolysis of Cyclooxygenase-2 Enhances Cell Proliferation

Accumulating evidence suggests that the cyclooxygenase-2 (COX-2) enzyme has additional catalytic-independent functions. Here we show that COX-2 appears to be cleaved in mouse and human tumors, which led us to hypothesize that COX-2 proteolysis may play a role in cell proliferation. The data presented herein show that a K598R point mutation at the carboxyl-terminus of COX-2 causes the appearance of several COX-2 immunoreactive fragments in nuclear compartments, and significantly enhances cell proliferation. In contrast, insertion of additional mutations at the border of the membrane-binding and catalytic domains of K598R COX-2 blocks fragment formation and prevents the increase in proliferation. Transcriptomic analyses show that K598R COX-2 significantly affects the expression of genes involved in RNA metabolism, and subsequent proteomics suggest that it is associated with proteins that regulate mRNA processing. We observe a similar increase in proliferation by expressing just that catalytic domain of COX-2 (ΔNT- COX-2), which is completely devoid of catalytic activity in the absence of its other domains. Moreover, we show that the ΔNT- COX-2 protein also interacts in the nucleus with β-catenin, a central regulator of gene transcription. Together these data suggest that the cleavage products of COX-2 can affect cell proliferation by mechanisms that are independent of prostaglandin synthesis.

Human antigen R: A potential therapeutic target for liver diseases

Human antigen R (HuR), also known as HuA and embryonic lethal abnormal vision-like 1 (ELAVL1), is a ubiquitously expressed RNA binding protein and functions as an RNA regulator and mediates the expression of various proteins by diverse post-transcriptional mechanisms. HuR has been well characterized in the inflammatory responses and in the development of various cancers. The importance of HuR-mediated roles in cell signaling, inflammation, fibrogenesis and cancer development in the liver has attracted a great deal of attention. However, there is still a substantial gap between the current understanding of the potential roles of HuR in the progression of liver disease and whether HuR can be targeted for the treatment of liver diseases. In this review, we introduce the function and mechanistic characterization of HuR, and then focus on the physiopathological roles of HuR in the development of different liver diseases, including hepatic inflammation, alcoholic liver diseases, non-alcoholic fatty liver diseases, viral hepatitis, liver fibrosis and liver cancers. We also summarize existing approaches targeting HuR function. In conclusion, although characterizing the liver-specific HuR function and demonstrating the multi-level regulative networks of HuR in the liver are still required, emerging evidence supports the notion that HuR represents a potential therapeutic target for the treatment of chronic liver diseases.

Tumor suppressor role of cytoplasmic polyadenylation element binding protein 2 (CPEB2) in human mammary epithelial cells

Background

Over-expression of cyclooxygenase (COX)-2 promotes breast cancer progression by multiple mechanisms, including induction of stem-like cells (SLC). Combined gene expression and microRNA microarray analyses of empty vector vs COX-2- transfected COX-2 low MCF7 breast cancer cell line identified two COX-2-upregulated microRNAs, miR-526b and miR-655, both found to be oncogenic and SLC-promoting. Cytoplasmic Polyadenylation Element-Binding Protein 2 (CPEB2) was the single common target of both microRNAs, the functions of which remain controversial. CPEB2 has multiple isoforms (A-F), and paradoxically, a high B/A ratio was reported to impart anoikis-resistance and metastatic phenotype in triple- negative breast cancer cells. We tested whether CPEB2 is a tumor suppressor in mammary epithelial cells.

Methods

We knocked-out CPEB2 in the non-tumorigenic mammary epithelial cell line MCF10A by CRISPR/Cas9-double nickase approach, and knocked-down CPEB2 with siRNAs in the poorly malignant MCF7 cell line, both lines being high CPEB2-expressing. The resultant phenotypes for oncogenity were tested in vitro for both lines and in vivo for CPEB2KO cells. Finally, CPEB2 expression was compared between human breast cancer and non-tumor breast tissues.

Results

CPEB2 (isoform A) expression was inversely correlated with COX-2 or the above microRNAs in COX-2-divergent breast cancer cell lines. CPEB2KO MCF10A cells exhibited oncogenic properties including increased proliferation, migration, invasion, EMT (decreased E-Cadherin, increased Vimentin, N-Cadherin, SNAI1, and ZEB1) and SLC phenotype (increased tumorsphere formation and SLC marker-expression). Tumor-suppressor p53 protein was shown to be a novel translationally-regulated target of CPEB2, validated with polysome profiling. CPEB2KO, but not wild-type cells produced lung colonies upon intravenous injection and subcutaneous tumors and spontaneous lung metastases upon implantation at mammary sites in NOD/SCID/IL2Rϒ-null mice, identified with HLA immunostaining. Similarly, siRNA-mediated CPEB2 knockdown in MCF7 cells promoted oncogenic properties in vitro. Human breast cancer tissues (n = 105) revealed a lower mRNA expression for CPEB2 isoform A and also a lower A/B isoform ratio than in non-tumour breast tissues (n = 20), suggesting that CPEB2A accounts for the tumor-suppressor functions of CPEB2.

Conclusions

CPEB2, presumably the isoform A, plays a key role in suppressing tumorigenesis in mammary epithelial cells by repressing EMT, migration, invasion, proliferation and SLC phenotype, via multiple targets, including a newly-identified translational target p53.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5771-5) contains supplementary material, which is available to authorized users.

Mutation Hotspots in the β-Catenin Gene: Lessons from the Human Cancer Genome Databases

Mutations in the β-catenin gene (CTNNB1) have been implicated in the pathogenesis of some cancers. The recent development of cancer genome databases has facilitated comprehensive and focused analyses on the mutation status of cancer-related genes. We have used these databases to analyze the CTNNB1 mutations assembled from different tumor types. High incidences of CTNNB1 mutations were detected in endometrial, liver, and colorectal cancers. This finding agrees with the oncogenic role of aberrantly activated β-catenin in epithelial cells. Elevated frequencies of missense mutations were found in the exon 3 of CTNNB1, which is responsible for encoding the regulatory amino acids at the N-terminal region of the protein. In the case of metastatic colorectal cancers, inframe deletions were revealed in the region spanning exon 3. Thus, exon 3 of CTNNB1 can be considered to be a mutation hotspot in these cancers. Since the N-terminal region of the β-catenin protein forms a flexible structure, many questions arise regarding the structural and functional impacts of hotspot mutations. Clinical identification of hotspot mutations could provide the mechanistic basis for an oncogenic role of mutant β-catenin proteins in cancer cells. Furthermore, a systematic understanding of tumor-driving hotspot mutations could open new avenues for precision oncology.

Histone deacetylase-mediated regulation of chondroitin 4-O-sulfotransferase-1 (Chst11) gene expression by Wnt/β-catenin signaling

Chondroitin sulfate (CS) proteoglycans are abundant extracellular and cell surface molecules that consist of a protein core to which highly sulfated CS chains are covalently attached. The CS backbone is composed of repeating disaccharide units [-GlcA-GalNAc-]_n, and during synthesis the CS chains acquire structural variability due to the action of sulfotransferases. Specific sulfation patterns are recognized by a large variety of proteins, including growth factors, morphogens, and extracellular matrix proteins, and these interactions regulate key events in development and normal physiology. Therefore, it is important to understand how gene expression of CS sulfotransferases is regulated. We previously found that Wnt signaling regulates the sulfation patterns of cell-associated CS chains by suppressing expression of chondroitin 4-O-sulfotaransferase-1 (C4ST-1), a CS biosynthetic enzyme. Here we investigated the mechanism underlying the regulation of C4ST-1 gene expression by Wnt/β-catenin signaling. Although C4ST-1 mRNA of 3'-UTR contains three binding sites for microRNAs (miRNA), these miRNAs played little role in controlling C4ST-1 gene expression. In contrast, the suppression of C4ST-1 gene expression by Wnt/β-catenin signaling can be recovered by treatment with trichostatin A, but not with 5'-aza-2'-deoxycytidine. These results suggest that the Wnt/β-catenin signal pathway controls C4ST-1 gene expression mainly through histone deacetylase.

Microarray gene expression analysis in ovine ductus arteriosus during fetal development and birth transition

BACKGROUND

Patent ductus arteriosus (PDA) in the newborn is the most common congenital heart anomaly and is significantly more common in preterm infants. Contemporary pharmacological treatment is effective in only 70-80% of the cases. Moreover, indomethacin or ibuprofen, which are used to close a PDA may be accompanied by serious side effects in premature infants. To explore the novel molecular pathways, which may be involved in the maturation and closure of the ductus arteriosus (DA), we used fetal and neonatal sheep to test the hypothesis that maturational development of DA is associated with significant alterations in specific mRNA expression.

METHODS

We conducted oligonucleotide microarray experiments on the isolated mRNA from DA and ascending aorta from three study groups (premature fetus-97 ± 0 d, near-term fetus-136 ± 0.8 d, and newborn lamb-12 ± 0 h). We compared the alterations in mRNA expression in DA and aorta to identify genes specifically involved in DA maturation.

RESULTS

Results demonstrate significant changes in wingless-integrin1, thrombospondin 1, receptor activator of nuclear factor-kappa B, nitric oxide synthase, and retinoic acid receptor activation signaling pathways.

CONCLUSION

We conclude that these pathways may play an important role during both development and postnatal DA closure and warrant further investigation.

Taurocholic acid metabolism by gut microbes and colon cancer

Colorectal cancer (CRC) is one of the most frequent causes of cancer death worldwide and is associated with adoption of a diet high in animal protein and saturated fat. Saturated fat induces increased bile secretion into the intestine. Increased bile secretion selects for populations of gut microbes capable of altering the bile acid pool, generating tumor-promoting secondary bile acids such as deoxycholic acid and lithocholic acid. Epidemiological evidence suggests CRC is associated with increased levels of DCA in serum, bile, and stool. Mechanisms by which secondary bile acids promote CRC are explored. Furthermore, in humans bile acid conjugation can vary by diet. Vegetarian diets favor glycine conjugation while diets high in animal protein favor taurine conjugation. Metabolism of taurine conjugated bile acids by gut microbes generates hydrogen sulfide, a genotoxic compound. Thus, taurocholic acid has the potential to stimulate intestinal bacteria capable of converting taurine and cholic acid to hydrogen sulfide and deoxycholic acid, a genotoxin and tumor-promoter, respectively.

High-mobility group box 1 enhances the inflammatory process in diabetic lung

Diabetes mellitus generates metabolic changes associated with inflammatory events that may eventually affect all body tissues. Both high-mobility group box 1 (HMGB1) and β-catenin are active players in inflammation. The study aimed to determine whether HMGB1 modulates the β-catenin activity in supporting inflammation, using an experimental type 1 diabetes mouse model. The protein and gene expression of HMGB1 were significantly increased (2-fold) in the diabetic lung compared to control and were positively correlated with the HMGB1 levels detected in serum. Co-immunoprecipitation of HMGB1 with RAGE co-exists with activation of PI3K/AKT1 and NF-kB signaling pathways. At the same time β-catenin was increased in nuclear fraction (3.5 fold) while it was down-regulated in diabetic plasma membrane (2-fold). There was no difference of β-catenin gene expression between the control and diabetic mice. β-Catenin phosphorylation at Ser552 was higher in diabetic nuclear fraction, suggesting that AKT1 activation promotes β-catenin nuclear translocation. In addition, c-Jun directly binds β-catenin indicating the transcriptional activity of β-catenin in diabetes, sustained by significantly COX2 increase by 6-fold in the cytosolic extract of diabetic lung compared to control. Taken together, the data support the new concept that HMGB1 maintains the inflammation through RAGE/AKT1/β-catenin pathway in the diabetic lung.

The human gut sterolbiome: bile acid-microbiome endocrine aspects and therapeutics

The human body is now viewed as a complex ecosystem that on a cellular and gene level is mainly prokaryotic. The mammalian liver synthesizes and secretes hydrophilic primary bile acids, some of which enter the colon during the enterohepatic circulation, and are converted into numerous hydrophobic metabolites which are capable of entering the portal circulation, returned to the liver, and in humans, accumulating in the biliary pool. Bile acids are hormones that regulate their own synthesis, transport, in addition to glucose and lipid homeostasis, and energy balance. The gut microbial community through their capacity to produce bile acid metabolites distinct from the liver can be thought of as an “endocrine organ” with potential to alter host physiology, perhaps to their own favor. We propose the term “sterolbiome” to describe the genetic potential of the gut microbiome to produce endocrine molecules from endogenous and exogenous steroids in the mammalian gut. The affinity of secondary bile acid metabolites to host nuclear receptors is described, the potential of secondary bile acids to promote tumors, and the potential of bile acids to serve as therapeutic agents are discussed.

HuR represses Wnt/β-catenin-mediated transcriptional activity by promoting cytoplasmic localization of β-catenin

β-Catenin is the key transcriptional activator of canonical Wnt signaling in the nucleus; thus, nuclear accumulation of β-catenin is a critical step for expressing target genes. β-Catenin accumulates in the nucleus of cancer cells where it activates oncogenic target genes. Hu antigen R (HuR) is a RNA binding protein that regulates multiple post-transcriptional processes including RNA stability. Thus, cytoplasmic HuR protein may be involved in tumorigenesis by stabilizing oncogenic transcripts, but the molecular mechanism remains unclear. Here, we observed that Wnt/β-catenin signaling induced export of the HuR protein, whereas HuR overexpression promoted accumulation of the β-catenin protein in the cytoplasm. Thus, Wnt/β-catenin-mediated transcriptional activity in the nucleus was reduced by overexpressing HuR. These results suggest novel and uncharacterized cytoplasmic β-catenin functions related to HuR-mediated RNA metabolism in cancer cells.

Beta-catenin/HuR post-transcriptional machinery governs cancer stem cell features in response to hypoxia

Hypoxia has been long-time acknowledged as major cancer-promoting microenvironment. In such an energy-restrictive condition, post-transcriptional mechanisms gain importance over the energy-expensive gene transcription machinery. Here we show that the onset of hypoxia-induced cancer stem cell features requires the beta-catenin-dependent post-transcriptional up-regulation of CA9 and SNAI2 gene expression. In response to hypoxia, beta-catenin moves from the plasma membrane to the cytoplasm where it binds and stabilizes SNAI2 and CA9 mRNAs, in cooperation with the mRNA stabilizing protein HuR. We also provide evidence that the post-transcriptional activity of cytoplasmic beta-catenin operates under normoxia in basal-like/triple-negative breast cancer cells, where the beta-catenin knockdown suppresses the stem cell phenotype in vitro and tumor growth in vivo. In such cells, we unravel the generalized involvement of the beta-catenin-driven machinery in the stabilization of EGF-induced mRNAs, including the cancer stem cell regulator IL6. Our study highlights the crucial role of post-transcriptional mechanisms in the maintenance/acquisition of cancer stem cell features and suggests that the hindrance of cytoplasmic beta-catenin function may represent an unprecedented strategy for targeting breast cancer stem/basal-like cells.

A subpopulation of smooth muscle cells, derived from melanocyte-competent precursors, prevents patent ductus arteriosus

BACKGROUND

Patent ductus arteriosus is a life-threatening condition frequent in premature newborns but also present in some term infants. Current mouse models of this malformation generally lead to perinatal death, not reproducing the full phenotypic spectrum in humans, in whom genetic inheritance appears complex. The ductus arteriosus (DA), a temporary fetal vessel that bypasses the lungs by shunting the aortic arch to the pulmonary artery, is constituted by smooth muscle cells of distinct origins (SMC1 and SMC2) and many fewer melanocytes. To understand novel mechanisms preventing DA closure at birth, we evaluated the importance of cell fate specification in SMC that form the DA during embryonic development. Upon specific Tyr::Cre-driven activation of Wnt/β-catenin signaling at the time of cell fate specification, melanocytes replaced the SMC2 population of the DA, suggesting that SMC2 and melanocytes have a common precursor. The number of SMC1 in the DA remained similar to that in controls, but insufficient to allow full DA closure at birth. Thus, there was no cellular compensation by SMC1 for the loss of SMC2. Mice in which only melanocytes were genetically ablated after specification from their potential common precursor with SMC2, demonstrated that differentiated melanocytes themselves do not affect DA closure. Loss of the SMC2 population, independent of the presence of melanocytes, is therefore a cause of patent ductus arteriosus and premature death in the first months of life. Our results indicate that patent ductus arteriosus can result from the insufficient differentiation, proliferation, or contractility of a specific smooth muscle subpopulation that shares a common neural crest precursor with cardiovascular melanocytes.

Crosstalk between Wnt Signaling and RNA Processing in Colorectal Cancer

RNA processing involves a variety of processes affecting gene expression, including the removal of introns through RNA splicing, as well as 3' end processing (cleavage and polyadenylation). Alternative RNA processing is fundamentally important for gene regulation, and aberrant processing is associated with the initiation and progression of cancer. Deregulated Wnt signaling, which is the initiating event in the development of most cases of human colorectal cancer (CRC), has been linked to modified RNA processing, which may contribute to Wnt-mediated colonic carcinogenesis. Crosstalk between Wnt signaling and alternative RNA splicing with relevance to CRC includes effects on the expression of Rac1b, an alternatively spliced gene associated with tumorigenesis, which exhibits alternative RNA splicing that is influenced by Wnt activity. In addition, Tcf4, a crucial component of Wnt signaling, also exhibits alternative splicing, which is likely involved in colonic tumorigenesis. Modulation of 3' end formation, including of the Wnt target gene COX-2, also can influence the neoplastic process, with implications for CRC. While many human genes are dependent on introns and splicing for normal levels of gene expression, naturally intronless genes exist with a unique metabolism that allows for intron-independent gene expression. Effects of Wnt activity on the RNA metabolism of the intronless Wnt-target gene c-jun is a likely contributor to cancer development. Further, butyrate, a breakdown product of dietary fiber and a histone deacetylase inhibitor, upregulates Wnt activity in CRC cells, and also modulates RNA processing; therefore, the interplay between Wnt activity, the modulation of this activity by butyrate, and differential RNA metabolism in colonic cells can significantly influence tumorigenesis. Determining the role played by altered RNA processing in Wnt-mediated neoplasia may lead to novel interventions aimed at restoring normal RNA metabolism for therapeutic benefit. Therefore, this minireview presents a brief overview of several aspects of RNA processing of relevance to cancer, which potentially influence, or are influenced by, Wnt signaling activity.

Wnt signaling in the pathogenesis of multiple sclerosis-associated chronic pain

Many multiple sclerosis (MS) patients develop chronic pain, but the underlying pathological mechanism is unknown. Mice with experimental autoimmune encephalomyelitis (EAE) have been widely used to model MS-related neurological complications, including CNS demyelination, neuroinflammation and motor impairments. Similar to MS patients, EAE mice also develop chronic pain. We are interested in elucidating the potential involvement of Wnt signaling in the pathogenesis of chronic pain in EAE mice. In this study, we characterized the expression of Wnt signaling proteins in the spinal cord dorsal horn (SCDH) of EAE mice, by immunoblotting and immunostaining. The EAE model was created by immunization of adult mice (C57BL/6, 10 weeks) with myelin oligodendrocyte glycoprotein (MOG) 35-55. Robust mechanical hyperalgesia and allodynia were developed in both fore- and hindpaws of the EAE mice. Wnt3a, a prototypical Wnt ligand for the canonical pathway, was significantly increased in the SCDH of the EAE mice. Another key protein in the canonical pathway, ß-catenin, was also significantly up-regulated. In addition, Wnt5a, a prototypic Wnt ligand for the non-canonical pathway, and its receptor (co-receptor) Ror2 were also up-regulated in the SCDH of the EAE mice. We further found that Wnt5a antagonist Box5 and β-catenin inhibitor indomethacin attenuated mechanical allodynia in the EAE mice. Our data collectively suggest that Wnt signaling pathways are up-regulated in the SCDH of the EAE mice and that aberrant activation of Wnt signaling contributes to the development of EAE-related chronic pain.

Nrf2 knockout enhances intestinal tumorigenesis in Apc(min/+) mice due to attenuation of anti-oxidative stress pathway while potentiates inflammation

Mutations in adenomatous polyposis coli (APC) gene are found in more than 80% of colorectal cancer (CRC) patients. The nuclear transcription factor Nrf2 plays a central role in the regulation of oxidative stress and inflammation. Previously, we have shown that chronic inflammation in Nrf2(-/-) (Nrf2 knockout; KO) mice resulted in higher expression of inflammatory markers and cytokines, coupled with higher inflammatory damage to the colonic crypt cells, as compared to the Nrf2(+/+) (wild type; WT) mice. Induction of mutation in the colon by administration of carcinogen, AOM prior to DSS-induced inflammation resulted in higher tumor incidence and numbers in Nrf2KO mice. These results indicate that Nrf2-dependent inhibition of inflammation appears to be critical in inhibiting mutation-initiated colorectal carcinogenesis. In this study, we aim to investigate if loss of Nrf2 would dose-dependently promote intestinal tumorigenesis in Apc(min/+) mice. To demonstrate the in vivo mechanisms, we constructed both Apc mutated and Nrf2 deficient strain Apc(min/+) mice with C57BL/6 Nrf2KO mice to obtain F1, Apc(min/+) ;Nrf2(+/-) and F2, Apc(min/+) ;Nrf2(-/-) mice. Nrf2KO decreased the protein expression of antioxidant enzyme NQO1 in Apc(min/+) . In contrast, Nrf2KO enhanced the expression of inflammatory markers such as COX-2, cPLA, LTB4 in Apc(min/+) . Finally, Nrf2KO resulted in higher level of PCNA and c-Myc expression in intestinal tissue, indicating the deficiency of Nrf2 promotes proliferation of intestinal crypt cells in Apc(min/+) . Taken together, our results suggest that Nrf2KO attenuates anti-oxidative stress pathway, induces inflammation, and increases proliferative potential in the intestinal crypts leading to enhanced intestinal carcinogenesis and adenomas in Apc(min/+) .

Knockdown of hMex-3A by small RNA interference suppresses cell proliferation and migration in human gastric cancer cells

RNA-binding proteins (RBPs) play essential roles in RNA metabolism, regulating RNA splicing, transport, surveillance, decay and translation. The aberrant expression of RBPs leads to gene expression alteration and frequently causes various diseases, such as cancer. In this study, we are the first to provide evidence that hMex-3A, a RBP that belongs to the human Mex-3 family with two K-homology RNA-binding domains, is involved in the regulation of tumorigenesis. We show that the silencing of hMex-3A by small interference RNA effectively inhibits cell proliferation in SNU-16 and AGS gastric cancer cells. Flow cytometry analysis confirmed this effect on SNU-16 cell growth and indicated that hMex-3A may function in the G1/M phase. Notably, hMex-3A knockdown also reduced the colony formation ability of SNU-16 and AGS cells in soft agar, implying that hMex-3A is required for cell transformation. Furthermore, the hMex-3A knockdown markedly affected the migratory ability of BCG-823 cells by transwell chamber and wound healing assays. Clinical relevance analysis using 22 paired gastric cancer specimens by quantitative real-time PCR showed that hMex-3A was significantly upregulated (63.6%) in cancer tissues compared with matched adjacent non-cancerous tissues. Taken together, these results suggest that hMex-3A functions as an oncogene candidate in the development and metastasis of gastric cancer; thus it may serve as a potential target for the therapy of tumors.

β-Catenin recognizes a specific RNA motif in the cyclooxygenase-2 mRNA 3'-UTR and interacts with HuR in colon cancer cells

RNA-binding proteins regulate multiple steps of RNA metabolism through both dynamic and combined binding. In addition to its crucial roles in cell adhesion and Wnt-activated transcription in cancer cells, β-catenin regulates RNA alternative splicing and stability possibly by binding to target RNA in cells. An RNA aptamer was selected for specific binding to β-catenin to address RNA recognition by β-catenin more specifically. Here, we characterized the structural properties of the RNA aptamer as a model and identified a β-catenin RNA motif. Similar RNA motif was found in cellular RNA, Cyclooxygenase-2 (COX-2) mRNA 3'-untranslated region (3'-UTR). More significantly, the C-terminal domain of β-catenin interacted with HuR and the Armadillo repeat domain associated with RNA to form the RNA-β-catenin-HuR complex in vitro and in cells. Furthermore, the tertiary RNA-protein complex was predominantly found in the cytoplasm of colon cancer cells; thus, it might be related to COX-2 protein level and cancer progression. Taken together, the β-catenin RNA aptamer was valuable for deducing the cellular RNA aptamer and identifying novel and oncogenic RNA-protein networks in colon cancer cells.

Annexin A2 binds RNA and reduces the frameshifting efficiency of infectious bronchitis virus

Annexin A2 (ANXA2) is a protein implicated in diverse cellular functions, including exocytosis, DNA synthesis and cell proliferation. It was recently proposed to be involved in RNA metabolism because it was shown to associate with some cellular mRNA. Here, we identified ANXA2 as a RNA binding protein (RBP) that binds IBV (Infectious Bronchitis Virus) pseudoknot RNA. We first confirmed the binding of ANXA2 to IBV pseudoknot RNA by ultraviolet crosslinking and showed its binding to RNA pseudoknot with ANXA2 protein in vitro and in the cells. Since the RNA pseudoknot located in the frameshifting region of IBV was used as bait for cellular RBPs, we tested whether ANXA2 could regulate the frameshfting of IBV pseudoknot RNA by dual luciferase assay. Overexpression of ANXA2 significantly reduced the frameshifting efficiency from IBV pseudoknot RNA and knockdown of the protein strikingly increased the frameshifting efficiency. The results suggest that ANXA2 is a cellular RBP that can modulate the frameshifting efficiency of viral RNA, enabling it to act as an anti-viral cellular protein, and hinting at roles in RNA metabolism for other cellular mRNAs.

Sulindac sulfide reverses aberrant self-renewal of progenitor cells induced by the AML-associated fusion proteins PML/RARα and PLZF/RARα

Chromosomal translocations can lead to the formation of chimeric genes encoding fusion proteins such as PML/RARα, PLZF/RARα, and AML-1/ETO, which are able to induce and maintain acute myeloid leukemia (AML). One key mechanism in leukemogenesis is increased self renewal of leukemic stem cells via aberrant activation of the Wnt signaling pathway. Either X-RAR, PML/RARα and PLZF/RARα or AML-1/ETO activate Wnt signaling by upregulating γ-catenin and β-catenin. In a prospective study, a lower risk of leukemia was observed with aspirin use, which is consistent with numerous studies reporting an inverse association of aspirin with other cancers. Furthermore, a reduction in leukemia risk was associated with use of non-steroidal anti-inflammatory drug (NSAID), where the effects on AML risk was FAB subtype-specific. To better investigate whether NSAID treatment is effective, we used Sulindac Sulfide in X-RARα-positive progenitor cell models. Sulindac Sulfide (SSi) is a derivative of Sulindac, a NSAID known to inactivate Wnt signaling. We found that SSi downregulated both β-catenin and γ-catenin in X-RARα-expressing cells and reversed the leukemic phenotype by reducing stem cell capacity and increasing differentiation potential in X-RARα-positive HSCs. The data presented herein show that SSi inhibits the leukemic cell growth as well as hematopoietic progenitors cells (HPCs) expressing PML/RARα, and it indicates that Sulindac is a valid molecular therapeutic approach that should be further validated using in vivo leukemia models and in clinical settings.

Associations between variants in the cyclooxygenase 2 enzyme gene (PTGS2) and development of benign prostate enlargement

OBJECTIVE

To determine if polymorphisms in the cyclooxygenase 2 (COX-2) enzyme gene (prostaglandin synthase 2; PTGS2) were associated with development of benign prostate enlargement (BPE), and whether associations were modified by use of nonsteroidal anti-inflammatory drugs (NSAIDs).

MATERIALS AND METHODS

Participants were men residing in Olmsted County, MN, who were between 40 and 79 years of age in 1990 (N= 356). Prostate volume was measured by transrectal ultrasound and men reported all the medications that they were taking at the time of the examination. Men were followed biennially for 16 years. Ten tagging single nucleotide polymorphisms (SNPs) in the PTGS2 gene were typed using the Illumina GoldenGate(TM) Assay. Associations between SNPs and development of BPE (volume >30 mL) were assessed by Cox proportional hazards models. Models were also stratified by NSAID use.

RESULTS

We observed significant associations between four polymorphisms in the PTGS2 gene and development of BPE (all P < 0.05). These associations were not observed among men who used NSAIDs.

CONCLUSION

Variants in the PTGS2 gene may increase the risk of prostate enlargement, but the increased risk may be minimized by use of NSAIDs.

Cyclooxygenase-2 in oncogenesis

Compelling experimental and clinical evidence supports the notion that cyclooxygenase-2, the inducible isoform of cyclooxygenase, plays a crucial role in oncogenesis. Clinical and epidemiological data indicate that aberrant regulation of cyclooxygenase-2 in certain solid tumors and hematological malignancies is associated with adverse clinical outcome. Moreover, findings extrapolated from experimental studies in cultured tumor cells and animal tumor models indicate that cyclooxygenase-2 critically influences all stages of tumor development from tumor initiation to tumor progression. Cyclooxygenase-2 elicits cell-autonomous effects on tumor cells resulting in stimulation of growth, increased cell survival, enhanced tumor cell invasiveness, stimulation of neovascularization, and tumor evasion from the host immune system. Additionally, the oncogenic effects of cyclooxygenase-2 stem from its unique ability to impact tumor cell surroundings and create a proinflammatory environment conducive for tumor development, growth and progression. The initial enthusiasm generated by the availability of cyclooxygenase-2 selective inhibitors for cancer prevention and therapy has been lessened by the severe cardiovascular adverse side effects associated with their long-term use, as well as by the mixed results of recent clinical trials evaluating the efficacy of cyclooxygenase-2 inhibitors in adjuvant chemotherapy. Therefore, our ability to efficiently target the oncogenic effects of cyclooxygenase-2 for therapeutic and preventive purposes strictly depends on a better understanding of the spatial and temporal aspects of its activation in tumor cells along with a clearer elucidation of the signaling networks whereby cyclooxygenase-2 affects tumor cells and their interactions with the tumor microenvironment. This knowledge has the potential of leading to the identification of novel cyclooxygenase-2-dependent molecular and signaling networks that can be exploited to improve cancer prevention and therapy.

Leptin receptor JAK2/STAT3 signaling modulates expression of Frizzled receptors in articular chondrocytes

OBJECTIVE

Differentiated articular chondrocytes express a functional bisoform of the leptin receptor (LRb); however, leptin-LRb signaling in these cells is poorly understood. We hypothesized that leptin-LRb signaling in articular chondrocytes functions to modulate canonical Wnt signaling events by altering the expression of Frizzled (FZD) receptors.

METHODS

Human chondrocyte cell lines and primary articular chondrocytes were grown in serum containing growth media for 24h, followed by a media change to Dulbecco's modified Eagle's medium (DMEM) containing 1% Nutridoma-SP to obtain a serum-deficient environment for 24h before treatment. Treatments included recombinant human leptin (10-100nM), recombinant human IL-6 (0.3-3nM), or recombinant human erythropoietin (Epo) (10mU/ml). Cells were harvested 30min-48h after treatment and whole cell lysates were analyzed using immunoblots or luciferase assays.

RESULTS

Treatment of cells with leptin resulted in activation of Janus kinase 2 (JAK2) and subsequent phosphorylation of specific tyrosine residues on LRb, followed by dose- and time-dependent increases in the expression of Frizzled-1 (FZD1) and Frizzled-7 (FZD7). Leptin-mediated increases in the expression of FZD1 were blocked by pre-treatment with the protein synthesis inhibitor cycloheximide or the JAK2 inhibitor AG490. Experiments using a series of hybrid Epo extracellular domain-leptin intracellular domain receptors (ELR) harboring mutations of specific tyrosine residues in the cytoplasmic tail showed that increases in the expression of FZD1 were dependent on LRb-mediated phosphorylation of STAT3, but not ERK1/2 or STAT5. Leptin pre-treatment of chondrocytes prior to Wnt3a stimulation resulted in an increased magnitude of canonical Wnt signaling.

CONCLUSION

These experiments show that leptin-LRb signaling in articular chondrocytes modulates expression of canonical Wnt signaling receptors and suggests that direct cross-talk between these pathways is important in determining chondrocyte homeostasis.

Redox control in mammalian embryo development

The development of an embryo constitutes a complex choreography of regulatory events that underlies precise temporal and spatial control. Throughout this process the embryo encounters ever changing environments, which challenge its metabolism. Oxygen is required for embryogenesis but it also poses a potential hazard via formation of reactive oxygen and reactive nitrogen species (ROS/RNS). These metabolites are capable of modifying macromolecules (lipids, proteins, nucleic acids) and altering their biological functions. On one hand, such modifications may have deleterious consequences and must be counteracted by antioxidant defense systems. On the other hand, ROS/RNS function as essential signal transducers regulating the cellular phenotype. In this context the combined maternal/embryonic redox homeostasis is of major importance and dysregulations in the equilibrium of pro- and antioxidative processes retard embryo development, leading to organ malformation and embryo lethality. Silencing the in vivo expression of pro- and antioxidative enzymes provided deeper insights into the role of the embryonic redox equilibrium. Moreover, novel mechanisms linking the cellular redox homeostasis to gene expression regulation have recently been discovered (oxygen sensing DNA demethylases and protein phosphatases, redox-sensitive microRNAs and transcription factors, moonlighting enzymes of the cellular redox homeostasis) and their contribution to embryo development is critically reviewed.

Post-transcriptional control during chronic inflammation and cancer: a focus on AU-rich elements

A considerable number of genes that code for AU-rich mRNAs including cytokines, growth factors, transcriptional factors, and certain receptors are involved in both chronic inflammation and cancer. Overexpression of these genes is affected by aberrations or by prolonged activation of several signaling pathways. AU-rich elements (ARE) are important cis-acting short sequences in the 3'UTR that mediate recognition of an array of RNA-binding proteins and affect mRNA stability and translation. This review addresses the cellular and molecular mechanisms that are common between inflammation and cancer and that also govern ARE-mediated post-transcriptional control. The first part examines the role of the ARE-genes in inflammation and cancer and sequence characteristics of AU-rich elements. The second part addresses the common signaling pathways in inflammation and cancer that regulate the ARE-mediated pathways and how their deregulations affect ARE-gene regulation and disease outcome.

Persistent cyclooxygenase-2 inhibition downregulates NF-{kappa}B, resulting in chronic intestinal inflammation in the min/+ mouse model of colon tumorigenesis

Cyclooxygenase-2 (COX-2) inhibition prevents adenoma formation in humans and mouse models of colon cancer. The selective COX-2 inhibitor celecoxib reduces COX-2 and prostaglandin E(2) (PGE(2)) expression and adenomas in the intestine of Min/+ mice after treatment for several weeks, but prolonged treatment increases PGE(2) production, resulting in drug-resistant tumor formation and transforming growth factor beta (TGFbeta)-dependent intestinal fibrosis. In this study, we examined pathways that regulate COX-2 expression and suppress chronic intestinal inflammation. We show that NF-kappaB signaling was inhibited in the ileum of Min/+ mice receiving long-term treatment with celecoxib. This effect was associated with inhibition of TGFbeta-associated kinase-1 and IkappaB kinase alpha/beta activities and reduced expression of the Toll-like receptor (TLR) 2 and TLR4 that enhance colonic barrier function. Additionally, we observed reduced activities of protein kinases c-Jun NH(2)-terminal kinase 1 and protein kinase A and transcription factor cyclic AMP-responsive element binding protein, regulators of COX-2 expression, which cross-talk with NF-kappaB. In ileum subjected to long-term celecoxib treatment, we noted relatively higher expression of COX-2, vascular endothelial growth factor, and interleukin-1beta in Paneth cells, whereas NF-kappaB and COX-2 were more strongly expressed by an expanded population of stromal myofibroblasts. Our findings argue that celecoxib resistance is an acquired adaptation to changes in the crypt microenvironment that is associated with chronic intestinal inflammation and impaired acute wound-healing responsiveness.

Loss of 15-hydroxyprostaglandin dehydrogenase increases prostaglandin E2 in pancreatic tumors

OBJECTIVES

Prostaglandin E2 (PGE2) is a product of cyclooxygenase (COX) and PGE synthase (PGES) and deactivated by 15-hydroxyprostaglandin dehydrogenase (PGDH). Down-regulation of PGDH contributes to PGE2 accumulation in lung and colon cancers but has not been identified in pancreatic cancer.

METHODS

Normal human pancreatic and tumor-matched tissues, as well as MiaPaCa-2 and BxPC-3 cell lines, were assessed for COX-2, microsomal PGES-1, PGDH, and snail homolog 1 (SNAI1) and SNAI2 expressions by real-time polymerase chain reaction and Western blotting and PGE2 by enzyme-linked immunosorbent assay.

RESULTS

Normal tissues exhibited low COX-2 messenger RNA (mRNA) and protein expressions and high PGDH mRNA and protein expressions and PGE2 levels at 13 pg/mg of protein. In contrast, tumor tissues exhibited high COX-2 mRNA and protein expressions and low PGDH mRNA and protein expressions and PGE2 levels at 32 pg/mg of protein. Tumor tissues exhibited significantly elevated expressions of SNAI2 mRNA and protein but not SNAI1 because SNAI1 and SNAI2 reportedly down-regulate PGDH expression. The COX-2-positive BxPC-3 but not the COX-2-negative MiaPaCa-2 treated with 100-nmol/L PGE2 induced phosphorylated extracellular signal-related kinase that was blocked by the mitogen-activated protein kinase kinase inhibitor U0126, demonstrating the ability of PGE2 to activate ERK.

CONCLUSIONS

These results suggest that enhanced PGE2 production proceeds through the expressions of COX-2 and microsomal PGES-1 and down-regulation of PGDH by SNAI2 in pancreatic tumors.

Germinated brown rice (GBR) reduces the incidence of aberrant crypt foci with the involvement of beta-catenin and COX-2 in azoxymethane-induced colon cancer in rats

Chemoprevention has become an important area in cancer research due to the failure of current therapeutic modalities. Epidemiological and preclinical studies have demonstrated that nutrition plays a vital role in the etiology of cancer. This study was conducted to determine the chemopreventive effects of germinated brown rice (GBR) in rats induced with colon cancer. GBR is brown rice that has been claimed to be richer in nutrients compared to the common white rice. The male Sprague Dawley rats (6 weeks of age) were randomly divided into 5 groups: (G1) positive control (with colon cancer, unfed with GBR), (G2) fed with 2.5 g/kg of GBR (GBR (g)/weight of rat (kg)), (G3) fed with 5 g/kg of GBR, (G4) fed with 10 g/kg of GBR and (G5) negative control (without colon cancer, unfed with GBR). GBR was administered orally once daily via gavage after injection of 15 mg/kg of body weight of azoxymethane (AOM) once a week for two weeks, intraperitonially. After 8 weeks of treatment, animals were sacrificed and colons were removed. Colonic aberrant crypt foci (ACF) were evaluated histopathologically. Total number of ACF and AC, and multicrypt of ACF, and the expression of beta-catenin and COX-2 reduced significantly (p < 0.05) in all the groups treated with GBR (G2, G3 and G4) compared to the control group (G1). Spearman rank correlation test showed significant positive linear relationship between total beta-catenin and COX-2 score (Spearman's rho = 0.616, p = 0.0001). It is demonstrated that GBR inhibits the development of total number of ACF and AC, and multicrypt of ACF, reduces the expression of beta-catenin and COX-2, and thus can be a promising dietary supplement in prevention of colon cancer.

Therapeutic RNA manipulation in liver disease

Posttranscriptional regulation of gene expression is increasingly recognized as a model for inherited and acquired disease. Recent work has expanded understanding of the range of mechanisms that regulate several of these distinct steps, including messenger RNA (mRNA) splicing, trafficking, and/or stability. Each of these pathways is implicated in disease pathogenesis, and each represents important avenues for therapeutic intervention. This review summarizes important mechanisms controlling mRNA processing and the regulation of mRNA degradation, including the role of microRNAs and RNA binding proteins. These pathways provide important opportunities for therapeutic targeting directed at splicing and degradation in order to attenuate genetic defects in RNA metabolism. We will highlight developments in vector development and validation for therapeutic manipulation of mRNA expression with a focus on potential applications in metabolic and immunomediated liver disease.

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.

A model system of development regulated by the long-distance transport of mRNA

BEL1-like transcription factors are ubiquitous in plants and interact with KNOTTED1-types to regulate numerous developmental processes. In potato, the RNA of several BEL1-like transcription factors has been identified in phloem cells. One of these, StBEL5, and its Knox protein partner regulate tuber formation by targeting genes that control growth. RNA detection methods and grafting experiments demonstrated that StBEL5 transcripts move across a graft union to localize in stolon tips, the site of tuber induction. This movement of RNA originates in source leaf veins and petioles and is induced by a short-day photoperiod, regulated by the untranslated regions, and correlated with enhanced tuber production. Addition of the StBEL5 untranslated regions to another BEL1-like mRNA resulted in its preferential transport to stolon tips leading to increased tuber production. Upon fusion of the untranslated regions of StBEL5 to a beta-glucuronidase marker, translation in tobacco protoplasts was repressed by those constructs containing the 3' untranslated sequence. The untranslated regions of the StBEL5 mRNA are involved in mediating its long-distance transport and in controlling translation. The 3' untranslated sequence contains an abundance of conserved motifs that may serve as binding motifs for RNA-binding proteins. Because of their presence in the phloem sieve tube system, their unique untranslated region sequences and their diverse RNA accumulation patterns, the family of BEL1-like RNAs from potato represents a valuable model for studying the long-distance transport of full-length mRNAs and their role in development.

Untranslated regions of a mobile transcript mediate RNA metabolism

BEL1-like transcription factors are ubiquitous in plants and interact with KNOTTED1 types to regulate numerous developmental processes. In potato (Solanum tuberosum subsp. andigena), the BEL1-like transcription factor StBEL5 and its Knox protein partner regulate tuber formation by targeting genes that control growth. RNA detection methods and heterografting experiments demonstrated that StBEL5 transcripts are present in phloem cells and move across a graft union to localize in stolon tips, the site of tuber induction. This movement of RNA originates in leaf veins and petioles and is induced by a short-day photoperiod, regulated by the untranslated regions, and correlated with enhanced tuber production. Assays for RNA mobility suggest that both 5' and 3' untranslated regions contribute to the preferential accumulation of the StBEL5 RNA but that the 3' untranslated region may contribute more to transport from the leaf to the stem and into the stolons. Addition of the StBEL5 untranslated regions to another BEL1-like mRNA resulted in its preferential transport to stolon tips and enhanced tuber production. Transcript stability assays showed that the untranslated regions and a long-day photoperiod enhanced StBEL5 RNA stability in shoot tips. Upon fusion of the untranslated regions of StBEL5 to a beta-glucuronidase marker, translation in tobacco (Nicotiana tabacum) protoplasts was repressed by those constructs containing the 3' untranslated sequence. These results demonstrate that the untranslated regions of the mRNA of StBEL5 are involved in mediating its long-distance transport, in maintaining transcript stability, and in controlling translation.

Mechanical loading regulates NFATc1 and beta-catenin signaling through a GSK3beta control node

Mechanical stimulation can prevent adipogenic and improve osteogenic lineage allocation of mesenchymal stem cells (MSC), an effect associated with the preservation of beta-catenin levels. We asked whether mechanical up-regulation of beta-catenin was critical to reduction in adipogenesis as well as other mechanical events inducing alternate MSC lineage selection. In MSC cultured under strong adipogenic conditions, mechanical load (3600 cycles/day, 2% strain) inactivated GSK3beta in a Wnt-independent fashion. Small interfering RNA targeting GSK3beta prevented both strain-induced induction of beta-catenin and an increase in COX2, a factor associated with increased osteoprogenitor phenotype. Small interfering RNA knockdown of beta-catenin blocked mechanical reduction of peroxisome proliferator-activated receptor gamma and adiponectin, implicating beta-catenin in strain inhibition of adipogenesis. In contrast, the effect of both mechanical and pharmacologic inhibition of GSK3beta on the putative beta-catenin target, COX2, was unaffected by beta-catenin knockdown. GSK3beta inhibition caused accumulation of nuclear NFATc1; mechanical strain increased nuclear NFATc1, independent of beta-catenin. NFATc1 knockdown prevented mechanical stimulation of COX2, implicating NFATc1 signaling. Finally, inhibition of GSK3beta caused association of RNA polymerase II with the COX2 gene, suggesting transcription initiation. These results demonstrate that mechanical inhibition of GSK3beta induces activation of both beta-catenin and NFATc1 signaling, limiting adipogenesis via the former and promoting osteoblastic differentiation via NFATc1/COX2. Our novel findings suggest that mechanical loading regulates mesenchymal stem cell differentiation through inhibition of GSK3beta, which in turn regulates multiple downstream effectors.

Use of RNA aptamers for the modulation of cancer cell signaling

Aptamers are in vitro evolved molecules that bind to target proteins with high affinity and specificity by adapting three-dimensional structures upon binding. Because cancer cells exhibit the activation of signaling pathways that are not usually activated in normal cells, RNA aptamers against such a cancer cell-specific signal can be useful lead molecules for cancer gene therapy. The Wnt/beta-catenin signaling pathway plays important roles in a critical initiating event in the formation of various human cancers. Because mutations in beta-catenin have been found to be responsible for human tumorigenesis, beta-catenin is the molecular target for effective anticancer therapies. Here, we describe the selection of RNA aptamers against beta-catenin/T-Cell Factor (TCF) proteins and their intracellular expression as intramers. The RNA aptamers acted as central inhibitory players for multiple oncogenic functions of beta-catenin in colon cancer cells. These data provide the proof-of-principle for the use of RNA aptamers for an effective anticancer gene therapy.

Emerging roles of RNA and RNA-binding protein network in cancer cells

Recent advances in RNA biology reveal unexpected diversity and complexity of cellular RNA metabolism. RNA-binding proteins (RBPs) are essential players in RNA metabolism, regulating RNA splicing, transport, surveillance, decay and translation. Aberrant expression of RBPs affects many steps of RNA metabolism, significantly altering expression of RNA. Thus, altered expression and dysfuncting of RBPs are implicated in the development of various diseases including cancer. In this minireview, we briefly describe emerging roles of RBPs as a global coordinator of post-transcriptional steps and altered RBP as a global generator of cancer related RNA alternative splicing. Identification and characterization of the RNA-RBP network would expand the scope of cellular RNA metabolism and provide novel anti-cancer therapeutic targets based on cancer specific RNA-RBP interaction.

Post-transcriptional regulation of cadherin-11 expression by GSK-3 and beta-catenin in prostate and breast cancer cells

Background

The cell-cell adhesion molecule cadherin-11 is important in embryogenesis and bone morphogenesis, invasion of cancer cells, lymphangiogenesis, homing of cancer cells to bone, and rheumatoid arthritis. However, very little is known about the regulation of cadherin-11 expression.

Methodology/Principal Findings

Here we show that cell density and GSK-3β regulate cadherin-11 levels in cancer cells. Inactivation of GSK3β with lithium chloride or the GSK3 inhibitor BIO and GSK3β knockdown with siRNA repressed cadherin-11 mRNA and protein levels. RNA Polymerase II chromatin immunoprecipitation experiments showed that inhibition of GSK3 does not affect cadherin-11 gene transcription. Although the cadherin-11 3′UTR contains putative microRNA target sites and is regulated by Dicer, its stability is not regulated by GSK3 inhibition or density. Our data show that GSK3β regulates cadherin-11 expression in two ways: first a β-catenin-independent regulation of cadherin-11 steady state mRNA levels, and second a β-catenin-dependent effect on cadherin-11 3′UTR stability and protein translation.

Conclusions

Cadherin-11 mRNA and protein levels are regulated by the activity of GSK3β and a significant degree of this regulation is exerted by the GSK3 target, β-catenin, at the level of the cadherin-11 3′UTR

RNA localization and polarity: from A(PC) to Z(BP)

Cell polarization relies on the asymmetric organization of cellular structures and activities, and is fundamentally important both during development and for the proper function of most somatic cells. Asymmetries in the distribution and activity of proteins can be achieved through localization of RNA molecules that usually give rise to proteins at specific subcellular sites. It is increasingly appreciated that this is a widely used mechanism affecting protein function at multiple levels. The description of a new RNA localization pathway involving the tumor-suppressor protein APC raises questions regarding coordination between distinct localization pathways and their effects on protein function and cell polarity.

Enhancement of p53 expression in keratinocytes by the bioflavonoid apigenin is associated with RNA-binding protein HuR

We have reported previously that apigenin, a naturally occurring nonmutagenic flavonoid, increased wild-type p53 protein expression in the mouse keratinocyte 308 cell line by a mechanism involving p53 protein stabilization. Here we further demonstrated that the increase in p53 protein level induced by apigenin treatment of 308 keratinoyctes was not the result of enhanced transcription, mRNA stabilization or cytoplasmic export of p53 mRNA. Instead, biosynthetic labeling showed that apigenin increased nascent p53 protein synthesis by enhancing p53 translation. The AU-rich element (ARE) within the 3'-untranslated region (UTR) of p53 mRNA was found to be responsible for apigenin's ability to increase p53 translation, as demonstrated in studies wherein the 3'-UTR of p53 mRNA containing the ARE was fused downstream of a luciferase reporter gene. Furthermore, apigenin treatment increased the level of association of the RNA binding protein HuR with endogenous p53 mRNA. Apigenin treatment also augmented HuR translocation into the cytoplasm. Overexpression of HuR enhanced apigenin-induced p53 protein expression in 308 keratinocytes, whereas siRNA-mediated HuR reduction suppressed apigenin-induced p53 protein expression and de novo translation of p53. Moreover, apigenin treatment of cells induced p16 protein expression, which in turn was correlated with cytoplasmic localization of HuR induced by apigenin. Overall, these findings indicate that, in addition to modulating p53 protein stability, one of the mechanisms by which apigenin induces p53 protein expression is enhancement of translation through the RNA binding protein HuR.