DDX3X

DDX3X
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 2I4I, 2JGN, 3JRV, 4O2C, 4O2E, 4O2F, 4PX9, 4PXA, 5E7J, 5E7M, 5E7I
Identifiers
Aliases	DDX3X, DBX, DDX14, DDX3, HLP2, CAP-Rf, MRX102, DEAD-box helicase 3, X-linked, DEAD-box helicase 3 X-linked, MRXSSB
External IDs	OMIM: 300160; MGI: 103064; HomoloGene: 3425; GeneCards: DDX3X; OMA:DDX3X - orthologs
Gene location (Human) Chr. X chromosome (human)[1] Band Xp11.4 Start 41,333,348 bp[1] End 41,364,472 bp[1]
Gene location (Mouse) Chr. X chromosome (mouse)[2] Band X A1.1|X 8.17 cM Start 13,147,209 bp[2] End 13,160,291 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in oocyte sperm secondary oocyte palpebral conjunctiva lactiferous duct tibia amniotic fluid parotid gland mucosa of urinary bladder bone marrow cells Top expressed in maxillary prominence cumulus cell primitive streak lacrimal gland epithelium of stomach ureter parotid gland seminal vesicula hair follicle dermis More reference expression data BioGPS More reference expression data
Gene ontology Molecular function DNA binding nucleotide binding nucleoside-triphosphatase activity CTPase activity helicase activity poly(A) binding ribosomal small subunit binding RNA stem-loop binding DNA helicase activity transcription factor binding ATPase activity protein binding GTPase activity eukaryotic initiation factor 4E binding RNA binding nucleic acid binding mRNA 5'-UTR binding translation initiation factor binding hydrolase activity ATP binding RNA strand annealing activity cadherin binding protein serine/threonine kinase activator activity Cellular component cytoplasm eukaryotic translation initiation factor 3 complex nuclear speck membrane mitochondrial outer membrane cytosolic small ribosomal subunit mitochondrion cytoplasmic stress granule extracellular exosome nucleus extracellular region cytosol secretory granule lumen ficolin-1-rich granule lumen nucleolus Biological process stress granule assembly apoptotic process negative regulation of translation negative regulation of cysteine-type endopeptidase activity involved in apoptotic process intracellular signal transduction regulation of transcription, DNA-templated ribosome biogenesis negative regulation of intrinsic apoptotic signaling pathway immune system process chromosome segregation negative regulation of protein-containing complex assembly response to virus negative regulation of apoptotic process Wnt signaling pathway positive regulation of translation protein localization to cytoplasmic stress granule transcription, DNA-templated cellular response to osmotic stress positive regulation of G1/S transition of mitotic cell cycle intrinsic apoptotic signaling pathway positive regulation of cysteine-type endopeptidase activity involved in apoptotic process positive regulation of cell growth positive regulation of gene expression mature ribosome assembly cellular response to arsenic-containing substance negative regulation of cell growth positive regulation of chemokine (C-C motif) ligand 5 production RNA secondary structure unwinding positive regulation of apoptotic process positive regulation of viral genome replication viral process innate immune response positive regulation of translational initiation regulation of translation extrinsic apoptotic signaling pathway via death domain receptors positive regulation of transcription by RNA polymerase II positive regulation of interferon-beta production DNA duplex unwinding neutrophil degranulation positive regulation of protein serine/threonine kinase activity positive regulation of canonical Wnt signaling pathway translational initiation Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 1654 13205 Ensembl ENSG00000215301 ENSMUSG00000000787 UniProt O00571 Q62167 RefSeq (mRNA) NM_001193416 NM_001193417 NM_001356 NM_024005 NM_001363819 NM_010028 NM_008015 RefSeq (protein) NP_001180345 NP_001180346 NP_001347 NP_001350748 NP_034158 Location (UCSC) Chr X: 41.33 – 41.36 Mb Chr X: 13.15 – 13.16 Mb PubMed search [3] [4]
Wikidata
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ATP-dependent RNA helicase DDX3X is an enzyme that in humans is encoded by the DDX3X gene.^[5][6][7]

Function

DEAD box proteins, characterized by the conserved motif Asp-Glu-Ala-Asp (DEAD), are putative RNA helicases. They are implicated in a number of cellular processes involving alteration of RNA secondary structure such as translation initiation, nuclear and mitochondrial splicing, and ribosome and spliceosome assembly. Based on their distribution patterns, some members of this family are believed to be involved in embryogenesis, spermatogenesis, and cellular growth and division. This gene encodes a DEAD box protein, which interacts specifically with hepatitis C virus core protein resulting a change in intracellular location. This gene has a homolog located in the nonrecombining region of the Y chromosome. The protein sequence is 91% identical between this gene and the Y-linked homolog.^[7]

Sub-cellular trafficking

DDX3X performs its functions in the cell nucleus and cytoplasm, exiting the nucleus via the exportin-1/CRM1 nuclear export pathway. It was initially reported that the DDX3X helicase domain was necessary for this interaction, while the canonical features of the trafficking pathway, namely the presence of a nuclear export signal (NES) on DDX3X and Ran-GTP binding to exportin-1, were dispensable.^[8] DDX3X binding to, and trafficking by, exportin-1 has since been shown not to require the DDX3X helicase domain and be explicitly NES- and Ran-GTP-dependent.^[9]

Role in cancer

DDX3X is involved in many different types of cancer. For example, it is abnormally expressed in breast epithelial cancer cells in which its expression is activated by HIF1A during hypoxia.^[10] Increased expression of DDX3X by HIF1A in hypoxia is initiated by the direct binding of HIF1A to the HIF1A response element,^[10] as verified with chromatin immunoprecipitation and luciferase reporter assay. Since the expression of DDX3X is affected by the activity of HIF1A, the co-localization of these proteins has also been demonstrated in MDA-MB-231 xenograft tumor samples.^[10]

In HeLa cells DDX3X is reported to control cell cycle progression through Cyclin E1.^[11] More specifically, DDX3X was shown to directly bind to the 5´ UTR of Cyclin E1 and thereby facilitating the translation of the protein. Increased protein levels of Cyclin E1 was demonstrated to mediate the transition of S phase entry.^[11]

Melanoma survival, migration and proliferation is affected by DDX3X activity.^[12] Melanoma cells with low DDX3X expression exhibit a high migratory capacity, low proliferation rate and reduced vemurafenib sensitivity. While high DDX3X expressing cells are drug sensitive, more proliferative and less migratory. These phenotypes can be explained by the translational effects on the melanoma transcription factor MITF.^[12] The 5' UTR of the MITF mRNA contains a complex RNA regulon (IRES) that is bound and activated by DDX3X. Activation of the IRES leads to translation of the MITF mRNA. Mice injected with melanoma cells with a deleted IRES display more aggressive tumor progression including increased lung metastasis.^[12] Interestingly, the DDX3X in melanoma is affected by vemurafenib via an undiscovered mechanism. It is unknown how DDX3X is downregulated by the presence of vemurafenib. However, reduced levels of DDX3X during drug treatment explains the development of drug resistant cells frequently detected with low MITF expression.^[12][13][14]

Clinical significance

Mutations of the DDX3X gene are associated with medulloblastoma.^[15][16][17] In melanoma the low expression of the gene is linked to a poor distant metastasis free survival.^[12] In addition, the mRNA level of DDX3X is lower in matched post-relapse melanoma biopsies for patients receiving vemurafenib and in progressing tumors.

Mutations of the DDX3X gene also cause DDX3X syndrome, which affects predominantly females and presents with developmental delay or disability, autism, ADHD, and low muscle tone.

See also

• Eukaryotic translation
• DExD/H box proteins
• DHX29

References

Further reading