Background & Aims During tumorigenesis, loss of rapid messenger RNA (mRNA) decay allows for overexpression of cancer-associated genes. The RNA-binding proteins Hu antigen R (HuR) and tristetraprolin ...(TTP) bind AU-rich elements in the 3′ untranslated region of many cancer-associated mRNAs and target them for stabilization or rapid decay, respectively. We examined the functions of HuR and TTP during colon tumorigenesis and their ability to regulate cyclooxygenase (COX-2), a mediator of prostaglandin synthesis that increases in the colon tumor microenvironment. Methods We evaluated expression of HuR and TTP during colorectal tumorigenesis and in colon cancer cells and associated them with COX-2 expression. HuR and TTP-inducible cells were created to investigate HuR- and TTP-mediated regulation of COX-2. Results In normal colon tissues, low levels of nuclear HuR and higher levels of TTP were observed. By contrast, increased HuR expression and cytoplasmic localization were observed in 76% of adenomas and 94% of adenocarcinomas, and TTP expression was lost in >75% of adenomas and adenocarcinomas. Similar results were obtained for HuR and TTP mRNA levels in normal and staged tumor samples. In both adenomas and adenocarcinomas, COX-2 overexpression was associated with increased HuR and decreased TTP ( P < .0001); similar associations were observed in colon cancer cells. HuR overexpression in cells up-regulated COX-2 expression, whereas overexpression of TTP inhibited it; limited TTP expression antagonized HuR-mediated COX-2 overexpression. Conclusions Increased expression of the mRNA stability factor HuR and loss of the decay factor TTP occurs during early stages of colorectal tumorigenesis. These changes promote COX-2 overexpression and could contribute to colon tumorigenesis.
HuR, an RNA binding protein, binds to adenine- and uridine-rich elements (ARE) in the 3′-untranslated region (UTR) of target mRNAs, regulating their stability and translation. HuR is highly abundant ...in many types of cancer, and it promotes tumorigenesis by interacting with cancer-associated mRNAs, which encode proteins that are implicated in different tumor processes including cell proliferation, cell survival, angiogenesis, invasion, and metastasis. Drugs that disrupt the stabilizing effect of HuR upon mRNA targets could have dramatic effects on inhibiting cancer growth and persistence. In order to identify small molecules that directly disrupt the HuR–ARE interaction, we established a fluorescence polarization (FP) assay optimized for high throughput screening (HTS) using HuR protein and an ARE oligo from Musashi RNA-binding protein 1 (Msi1) mRNA, a HuR target. Following the performance of an HTS of ∼6000 compounds, we discovered a cluster of potential disruptors, which were then validated by AlphaLISA (Amplified Luminescent Proximity Homogeneous Assay), surface plasmon resonance (SPR), ribonucleoprotein immunoprecipitation (RNP IP) assay, and luciferase reporter functional studies. These compounds disrupted HuR–ARE interactions at the nanomolar level and blocked HuR function by competitive binding to HuR. These results support future studies toward chemical probes for a HuR function study and possibly a novel therapy for HuR-overexpressing cancers.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
Efforts to conserve bats in the western United States have long been impeded by a lack of information on their winter whereabouts, particularly bats in the genus Myotis. The recent arrival of ...white-nose syndrome in western North America has increased the urgency to characterize winter roost habitats in this region. We compiled 4,549 winter bat survey records from 2,888 unique structures across 11 western states. Myotis bats were reported from 18.5% of structures with 95% of aggregations composed of ≤10 individuals. Only 11 structures contained ≥100 Myotis individuals and 6 contained ≥500 individuals. Townsend's big-eared bat (Corynorhinus townsendii) were reported from 38% of structures, with 72% of aggregations composed of ≤10 individuals. Aggregations of ≥100 Townsend's big-eared bats were observed at 41 different caves or mines across 9 states. We used zero-inflated negative binomial regression to explore biogeographic patterns of winter roost counts. Myotis counts were greater in caves than mines, in more recent years, and in more easterly longitudes, northerly latitudes, higher elevations, and in areas with higher surface temperatures and lower precipitation. Townsend's big-eared bat counts were greater in caves, during more recent years, and in more westerly longitudes. Karst topography was associated with higher Townsend's big-eared bat counts but did not appear to influence Myotis counts. We found stable or slightly-increasing trends over time in counts for both Myotis and Townsend's big-eared bats from 82 hibernacula surveyed ≥5 winters since 1990. Highly-dispersed winter roosting of Myotis in the western USA complicates efforts to monitor population trends and impacts of disease. However, our results reveal opportunities to monitor winter population status of Townsend's big-eared bats across this region.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
Adenylate‐ and uridylate‐rich element (ARE) motifs are cis‐acting elements present in the 3′ untranslated region of mRNA transcripts that encode many inflammation‐ and cancer‐associated genes. The ...TIS11 family of RNA‐binding proteins, composed of tristetraprolin (TTP) and butyrate response factors 1 and 2 (BRF‐1 and ‐2), plays a critical role in regulating the expression of ARE‐containing mRNAs. Through their ability to bind and target ARE‐containing mRNAs for rapid degradation, this class of RNA‐binding proteins serves a fundamental role in limiting the expression of a number of critical genes, thereby exerting anti‐inflammatory and anti‐cancer effects. Regulation of TIS11 family members occurs on a number of levels through cellular signaling events to control their transcription, mRNA turnover, phosphorylation status, cellular localization, association with other proteins, and proteosomal degradation, all of which impact TIS11 members' ability to promote ARE‐mediated mRNA decay along with decay‐independent functions. This review summarizes our current understanding of posttranscriptional regulation of ARE‐containing gene expression by TIS11 family members and discusses their role in maintaining normal physiological processes and the pathological consequences in their absence. WIREs RNA 2011 2 42–57 DOI: 10.1002/wrna.28
This article is categorized under:
RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms
RNA Turnover and Surveillance > Regulation of RNA Stability
RNA in Disease and Development > RNA in Disease
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Messenger RNA decay is a critical mechanism to control the expression of many inflammation- and cancer-associated genes. These transcripts are targeted for rapid degradation through AU-rich element ...(ARE) motifs present in the mRNA 3' untranslated region (3'UTR). Tristetraprolin (TTP) is an RNA-binding protein that plays a significant role in regulating the expression of ARE-containing mRNAs. Through its ability to bind AREs and target the bound mRNA for rapid degradation, TTP can limit the expression of a number of critical genes frequently overexpressed in inflammation and cancer. Regulation of TTP occurs on multiple levels through cellular signaling events to control transcription, mRNA turnover, phosphorylation status, cellular localization, association with other proteins, and proteosomal degradation, all of which impact TTP's ability to promote ARE-mediated mRNA decay along with decay-independent functions of TTP. This review summarizes the current understanding of post-transcriptional regulation of ARE-containing gene expression by TTP and discusses its role in maintaining homeostasis and the pathological consequences of losing TTP expression.
The Human antigen R protein (HuR) is an RNA-binding protein that recognizes U/AU-rich elements in diverse RNAs through two RNA-recognition motifs, RRM1 and RRM2, and post-transcriptionally regulates ...the fate of target RNAs. The natural product dihydrotanshinone-I (DHTS) prevents the association of HuR and target RNAs in vitro and in cultured cells by interfering with the binding of HuR to RNA. Here, we report the structural determinants of the interaction between DHTS and HuR and the impact of DHTS on HuR binding to target mRNAs transcriptome-wide. NMR titration and Molecular Dynamics simulation identified the residues within RRM1 and RRM2 responsible for the interaction between DHTS and HuR. RNA Electromobility Shifts and Alpha Screen Assays showed that DHTS interacts with HuR through the same binding regions as target RNAs, stabilizing HuR in a locked conformation that hampers RNA binding competitively. HuR ribonucleoprotein immunoprecipitation followed by microarray (RIP-chip) analysis showed that DHTS treatment of HeLa cells paradoxically enriched HuR binding to mRNAs with longer 3'UTR and with higher density of U/AU-rich elements, suggesting that DHTS inhibits the association of HuR to weaker target mRNAs. In vivo, DHTS potently inhibited xenograft tumor growth in a HuR-dependent model without systemic toxicity.
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