The RNA helicase DDX3 is a component of neuronal granules, and its gene mutations are linked to intellectual disability (ID). Here we demonstrate that DDX3 depletion in neurons impairs neurite development by downregulating Rac1 level and activation. Moreover, DDX3 activates the translation of functionally coherent mRNAs involved in Rac1 activation including Rac1. Among the DDX3 regulon, Prkaca encodes the catalytic subunit of PKA, a potential activator of Rac1 in neurons. DDX3-modulated PKAc␣ and Rac1 expression tunes the strength of PKA-Rac1 signaling and thereby contributes to neurite outgrowth and dendritic spine formation. Inhibition of DDX3 activity or expression in neonatal mice impaired dendritic outgrowth and spine formation of hippocampal neurons, echoing neuronal deficits underling DDX3 mutation-associated ID. Finally, we provide evidence that DDX3 activates local protein synthesis through a 5Ј UTR-dependent mechanism in neurons. The novel DDX3 regulon may conduct a spatial and temporal control of Rac1 signaling to regulate neurite development.
RBM4 modulates alternative exon selection of Numb and up-regulates proneural Mash1 gene expression, possibly via specific Numb isoforms. RBM4 overexpression promotes neuronal cell differentiation. Moreover, RBM4 is essential for neurite outgrowth in primary cortical neurons by modulating specific Numb isoform expression.
Using antibody arrays, we found that the RNA helicase DDX3 modulates the expression of secreted signaling factors in oral squamous cell carcinoma (OSCC) cells. Ribo-seq analysis confirmed amphiregulin (AREG) as a translational target of DDX3. AREG exerts important biological functions in cancer, including promoting cell migration and paracrine effects of OSCC cells and reprogramming the tumor microenvironment (TME) of OSCC in mice. DDX3-mediated translational control of AREG involves its 3 0 -untranslated region. Proteomics identified the signal recognition particle (SRP) as an unprecedented interacting partner of DDX3. DDX3 and SRP54 were located near the endoplasmic reticulum, regulated the expression of a common set of secreted factors, and were essential for targeting AREG mRNA to membrane-bound polyribosomes. Finally, OSCC-associated mutant DDX3 increased the expression of AREG, emphasizing the role of DDX3 in tumor progression via SRP-dependent, endoplasmic reticulum-associated translation. Therefore, pharmacological targeting of DDX3 may inhibit the tumor-promoting functions of the TME.
<div>Abstract<p>Mutated or dysregulated <i>DDX3</i> participates in the progression and metastasis of cancer via its multiple roles in regulating gene expression and cellular signaling. Here, we show that the high expression levels of DDX3 in head and neck squamous cell carcinoma (HNSCC) correlate with lymph node metastasis and poor prognosis and demonstrate that DDX3 is essential for the proliferation, invasion, and metastasis of oral squamous cell carcinoma (OSCC) cells. Microarray analyses revealed that DDX3 is required for the expression of a set of pro-metastatic genes, including ATF4-modulated genes in an aggressive OSCC cell line. DDX3 activated translation of <i>ATF4</i> and a set of its downstream targets, all of which contain upstream open reading frames (uORF). DDX3 promoted translation of these targets, likely by skipping the inhibitory uORF. DDX3 specifically enhanced the association of the cap-binding complex (CBC) with uORF-containing mRNAs and facilitated recruitment of the eukaryotic initiation factor 3 (eIF3). CBC and certain eIF3 subunits contributed to the expression of metastatic-related gene expression. Taken together, our results indicate a role for the novel DDX3–CBC–eIF3 translational complex in promoting metastasis.</p><p><b>Significance:</b> The discovery of DDX3-mediated expression of oncogenic uORF-containing genes expands knowledge on translational control mechanisms and provides potential targets for cancer therapy.</p><p><b>Graphical Abstract:</b> <a href="http://cancerres.aacrjournals.org/content/canres/78/16/4512/F1.large.jpg" target="_blank">http://cancerres.aacrjournals.org/content/canres/78/16/4512/F1.large.jpg</a> <i>Cancer Res; 78(16); 4512–23. ©2018 AACR</i>.</p></div>
<p>Figure S1. DDX3 expression is correlated with cell invasive activity and ATF4 expression. Figure S2. Microarray-identified genes are enriched for pro-metastatic genes and ATF4 targets, and DDX3 is required for migration and ATF4 expression in all of the HNSCC cell lines examined. Figure S3. DDX3 and ATF4 are required for EMT gene expression. Figure S4. DDX3 does not regulate ATF4 protein stability. Figure S5. DDX3 regulate ATF4 translation independent of ER Stress. Figure S6. The DDX3/CBC/eIF3 complex directly activates the translation of uORF-containing mRNAs in vitro and in vivo. Figure S7. RT-qPCR analysis of luciferase mRNAs in the in vivo translation assay. Figure S8. The CBC and eIF3 complexes are involved in the translation of uORF-containing mRNAs. Table S1. List of sense shRNA or siRNA sequences Table S2. Univariate and multivariate cox regression analyses in HNSCC patient samples. Table S3. List of genes that showed more than two-fold changes upon DDX3 knockdown. Table S4. GO terms enriched in DDX3 knockdown-upregulated or -downregulated genes analyzed by DAVID software. Table S5. List of upstream transcription factors potentially involved in DDX3-regulated genes predicted by IPA software. Table S6. Percentages of siDDX3-downregulated, DDX3-upregulated or non-target genes overlapping with uTIS or non-uTIS genes from TIS-db or with uORF-containing genes from uORFdb. Table S7. Percentages of CBP20 CLIPs or eIF3 CLIPs overlapping with DDX3 CLIPs or eIF4A3 CLIPs. Table S8. Percentages of DDX3 CLIPs, CBP20 CLIPs, eIF3 CLIPs or eIF4A3 CLIPs overlapping with uTIS or non-uTIS genes from TIS-db.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.