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DEAD-box RNA helicase Belle posttranscriptionally promotes gene expression in an ATPase activity-dependent manner.

ABSTRACT: Drosophila Belle (human ortholog DDX3) is a conserved DEAD-box RNA helicase implicated in regulating gene expression. However, the molecular mechanisms by which Belle/DDX3 regulates gene expression are poorly understood. Here we performed systematic mutational analysis to determine the contributions of conserved motifs within Belle to its in vivo function. We found that Belle RNA-binding and RNA-unwinding activities and intrinsically disordered regions (IDRs) are required for Belle in vivo function. Expression of Belle ATPase mutants that cannot bind, hydrolyze, or release ATP resulted in dominant toxic phenotypes. Mechanistically, we discovered that Belle up-regulates reporter protein level when tethered to reporter mRNA, without corresponding changes at the mRNA level, indicating that Belle promotes translation of mRNA that it binds. Belle ATPase activity and amino-terminal IDR were required for this translational promotion activity. We also found that ectopic ovary expression of dominant Belle ATPase mutants decreases levels of cyclin proteins, including Cyclin B, without corresponding changes in their mRNA levels. Finally, we found that Belle binds endogenous cyclin B mRNA. We propose that Belle promotes translation of specific target mRNAs, including cyclin B mRNA, in an ATPase activity-dependent manner.

SUBMITTER: Liao SE

PROVIDER: S-EPMC6573787 | biostudies-literature |

REPOSITORIES: biostudies-literature

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DEAD-box RNA helicase Belle/DDX3 and the RNA interference pathway promote mitotic chromosome segregation.

Project description:During mitosis, faithful inheritance of genetic material is achieved by chromosome segregation, as mediated by the condensin I and II complexes. Failed chromosome segregation can result in neoplasm formation, infertility, and birth defects. Recently, the germ-line-specific DEAD-box RNA helicase Vasa was demonstrated to promote mitotic chromosome segregation in Drosophila by facilitating robust chromosomal localization of Barren (Barr), a condensin I component. This mitotic function of Vasa is mediated by Aubergine and Spindle-E, which are two germ-line components of the Piwi-interacting RNA pathway. Faithful segregation of chromosomes should be executed both in germ-line and somatic cells. However, whether a similar mechanism also functions in promoting chromosome segregation in somatic cells has not been elucidated. Here, we present evidence that belle (vasa paralog) and the RNA interference pathway regulate chromosome segregation in Drosophila somatic cells. During mitosis, belle promotes robust Barr chromosomal localization and chromosome segregation. Belle's localization to condensing chromosomes depends on dicer-2 and argonaute2. Coimmunoprecipitation experiments indicated that Belle interacts with Barr and Argonaute2 and is enriched at endogenous siRNA (endo-siRNA)-generating loci. Our results suggest that Belle functions in promoting chromosome segregation in Drosophila somatic cells via the endo-siRNA pathway. DDX3 (human homolog of belle) and DICER function in promoting chromosome segregation and hCAP-H (human homolog of Barr) localization in HeLa cells, indicating a conserved function for those proteins in human cells. Our results suggest that the RNA helicase Belle/DDX3 and the RNA interference pathway perform a common role in regulating chromosome segregation in Drosophila and human somatic cells.

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Translational control by the DEAD Box RNA helicase belle regulates ecdysone-triggered transcriptional cascades.

Project description:Steroid hormones act, through their respective nuclear receptors, to regulate target gene expression. Despite their critical role in development, physiology, and disease, however, it is still unclear how these systemic cues are refined into tissue-specific responses. We identified a mutation in the evolutionarily conserved DEAD box RNA helicase belle/DDX3 that disrupts a subset of responses to the steroid hormone ecdysone during Drosophila melanogaster metamorphosis. We demonstrate that belle directly regulates translation of E74A, an ets transcription factor and critical component of the ecdysone-induced transcriptional cascade. Although E74A mRNA accumulates to abnormally high levels in belle mutant tissues, no E74A protein is detectable, resulting in misregulation of E74A-dependent ecdysone response genes. The accumulation of E74A mRNA in belle mutant salivary glands is a result of auto-regulation, fulfilling a prediction made by Ashburner nearly 40 years ago. In this model, Ashburner postulates that, in addition to regulating secondary response genes, protein products of primary response genes like E74A also inhibit their own ecdysone-induced transcription. Moreover, although ecdysone-triggered transcription of E74A appears to be ubiquitous during metamorphosis, belle-dependent translation of E74A mRNA is spatially restricted. These results demonstrate that translational control plays a critical, and previously unknown, role in refining transcriptional responses to the steroid hormone ecdysone.

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The ATPase cycle mechanism of the DEAD-box rRNA helicase, DbpA.

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DEAD-box RNA Helicase 39 Promotes Invasiveness and Chemoresistance of ER-positive Breast Cancer.

Project description:Purpose: DDX39 is a DEAD-box RNA helicase that unwinds double-stranded RNA in an ATP-dependent manner. This study evaluated the prognostic and predictive significance of DDX39 in breast cancer (BC). Methods: The cellular proliferation, invasion, and drug cytotoxicity by DDX39 siRNA were evaluated in MCF7 (ER-positive) and MDA-MB-231 (ER-negative) cell lines. A total of 27 datasets (total 8110 accessible cases) with following-up information were collected from Asia, Europe, and North America to explore associations between DDX39 gene expression and clinical parameters of BC patients. Results: Down-regulation of DDX39 by siRNA significantly reduce the cell growth and invasion ability in MCF7 cells, but only slightly in MDA-MB-231 cells. The DDX39 mRNA level was elevated in breast adenocarcinoma compared with normal breast tissue (p<0.01). Higher DDX39 level was significantly correlated with larger tumor size (p<0.01) and poorer tumor differentiation (p<0.01). The prognostic significance of DDX39 for BC was assessed by pooled-analysis and meta-analysis. Kaplan-Meier analysis demonstrated that increased DDX39 mRNA expression was associated with poor outcomes significantly in a dose-dependent manner in ER-positive BC. The prognostic performance of DDX39 mRNA was comparable to 21-gene, 70-gene, and wound-response gene signatures, and it was superior to the TNM stage. Lower DDX39 expression was associated with reduced relative risk death on ER-positive BC with chemotherapy or radiotherapy. Inhibition of DDX39 by siRNA could significantly enhance the sensitivity of MCF-7 to doxorubicin. Conclusion: DDX39 may be a potential novel prognostic and predictive biomarker for BC patients with ER-positive status.

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Project description:RNA helicases represent a large family of proteins implicated in many biological processes including ribosome biogenesis, splicing, translation and mRNA degradation. However, these proteins have little substrate specificity, making inhibition of selected helicases a challenging problem. The prototypical DEAD box RNA helicase, eIF4A, works in conjunction with other translation factors to prepare mRNA templates for ribosome recruitment during translation initiation. Herein, we provide insight into the selectivity of a small molecule inhibitor of eIF4A, hippuristanol. This coral-derived natural product binds to amino acids adjacent to, and overlapping with, two conserved motifs present in the carboxy-terminal domain of eIF4A. Mutagenesis of amino acids within this region allowed us to alter the hippuristanol-sensitivity of eIF4A and undertake structure/function studies. Our results provide an understanding into how selective targeting of RNA helicases for pharmacological intervention can be achieved.

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| S-EPMC10236181 | biostudies-literature

The DEAD-Box RNA Helicase DDX3 Interacts with m6A RNA Demethylase ALKBH5.

Project description:DDX3 is a member of the family of DEAD-box RNA helicases. DDX3 is a multifaceted helicase and plays essential roles in key biological processes such as cell cycle, stress response, apoptosis, and RNA metabolism. In this study, we found that DDX3 interacted with ALKBH5, an m6A RNA demethylase. The ATP domain of DDX3 and DSBH domain of ALKBH5 were indispensable to their interaction with each other. Furthermore, DDX3 could modulate the demethylation of mRNAs. We also showed that DDX3 regulated the methylation status of microRNAs and there was an interaction between DDX3 and AGO2. The dynamics of m6A RNA modification is still a field demanding further investigation, and here, we add a link by showing that RNA demethylation can be regulated by proteins such as DDX3.

| S-EPMC5733242 | biostudies-literature

DEAD-box Helicase 27 Promotes Hepatocellular Carcinoma Progression Through ERK Signaling.

Project description:Introduction: DEAD-box helicase 27 (DDX27) belongs to DEAD-Box nucleic acid helicase family. The function of DDX27 in hepatocellular carcinoma (HCC) remain enigmatic. In light of this, we tried to investigate the regulatory role and underlying mechanism of DDX27 in HCC. Materials and methods: DDX27 expression levels were detected by qRT-PCR, Western blot and immunohistochemistry assays in HCC tissues and cells. Colony formation, CCK-8, growth curve, wound healing and transwell assays were conducted to investigate the effect of DDX27 on the proliferation and metastasis of HCC cells. RNA-sequencing was performed to detect the effect of DDX27 on downstream signaling pathway. The effect of DDX27 on HCC progression was evaluated using in vivo murine xenograft model. Results: we found an increased expression of DDX27 in HCC tissues with comparison to its para-tumor tissues. The high expression levels of DDX27 were associated with poor prognosis in HCC patients. DDX27 upregulation promoted cell metastasis. Mechanistic studies suggested that DDX27 overexpression induces the major vault protein (MVP) expression and enhances the phosphorylation levels of ERK1/2. Inhibition of ERK pathway impaired the cellular metastastic abilities induced by DDX27. The induction of DDX27 in HCC progression was further confirmed from tumors in mouse model. Conclusion: our results disclose a novel mechanism by which DDX27 enhances ERK signaling during HCC progression. DDX27 might be used in targeted therapy for HCC patients.

| S-EPMC8649435 | biostudies-literature

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