1. Molecular Motors
The two largest families of DExD (DDX)- and DExH (DHX)-box RNA helicases belong to the helicase superfamily 2 and are named after their Asp-Glu-X-Asp/His motifs. DDX and DHX members play crucial roles in RNA metabolism across all eukaryotic cells. DDX and DHX proteins contain two recombinase A-like (RecA) domains, on which nucleoside triphosphate (NTP) binding/hydrolysis and nucleic acid binding sites lie. N-and C-terminal extensions promote specific interactions of each member
[1]. DDX3X is ubiquitously expressed in all
Eutheria and is implicated in IFN-α and IFN-β induction upon virus infection
[2], in Wnt/β-catenin signaling
[3], and in RNA interference (RNAi)
[4]. Unbalanced DDX3X expression occurs in many cancer types, and DDX3 usually, but not always, provides oncogenic effects, suggesting it as a target for inhibition with small molecules
[5][6].
The first known function of DDX60 was in the RIG-I-like receptor-mediated pathways that induce inflammatory cytokines after viral infection
[7]. DDX60 has not been studied in detail in cancer, although lower levels in breast cancer are associated with radiosensitivity
[8], and high a level of DDX60 is a proposed biomarker and prognostic factor for oral squamous cell carcinoma
[9], as well as an indicator of response to immune checkpoint inhibitors in glioma
[10].
DHX9 and DHX36 are G-quadruplex- (G4) and polysome-associated proteins
[11][12]. DHX9 maintains translation of α1 and α2 type I collagen, which is the most abundant protein in humans
[13]. Its association with translational control protein 80 (TCP80) following DNA damage and its co-overexpression leads to enhanced expression of
TP53 via regulation of its internal ribosome entry site
[14]. DHX36 plays a role in mediating antiviral innate immunity as a sensor for viral nucleic acids
[15], recognizes non-methylated DNA together with DHX9, and can activate antimicrobial responses
[16]. DHX36 is also associated with the translocation of miRNAs and interactions with Argonaute (AGO) proteins
[17] and may regulate TP53 pre-mRNA 3′-end processing after DNA damage
[18]. DHX9 and DHX36 are upregulated in advanced stage colorectal cancer (CRC)
[19]. DHX9 promotes migration of lung adenocarcinoma cells
[20], whereas
DHX36 knockdown increases migration and proliferation and reduces chemotherapeutic responses in non-small-cell lung carcinoma (NSCLC)
[21].
DHX36 is commonly overexpressed in head and neck cancers
[22].
Chromodomain Helicase DNA Binding Protein 3 (CHD3, also called Mi-2α) belongs to the family of ATP-dependent chromatin remodeling proteins and forms part of the nucleosome remodeling and histone deacetylase (NuRD/Mi-2) complex
[23]. The RNA binding properties of CHD3 were identified by ChIP-seq
[24]. Inherited missense mutations in the helicase domain of
CHD3 affect chromatin remodeling activity and are associated with neurodevelopmental disorders
[25]. Many CHD proteins act as context-dependent tumor suppressors and although not as common as other members, somatic mutations in
CHD3 are reported to be associated with prostate cancer, breast cancer, gastric cancer, and CRC
[26][27].
UPF1 (regulator of nonsense transcripts 1) is a highly processive helicase, using its two RecA-like domains for RNA and DNA unwinding in a 5′->3′ manner
[28][29]. UPF1 contains a cysteine-histidine-rich (CH) domain at its N-terminus that reduces its helicase activity, and this inhibitory effect is released by interaction with proteins such as UPF2/UPF3
[30]. UPF1 contains an SQ (rich in serine and glutamine) domain at the C-terminus that blocks its helicase activity independent of the CH domain or phosphorylation
[31]. Cancer-related mutations occur mainly in the CH domain and the ATP binding site
[32]. Apart from its crucial role in nonsense-mediated mRNA decay (NMD), UPF1 is involved in DNA repair and replication
[33][34]. Lower levels of UPF1 are seen in many cancer types, including pancreatic adenosquamous carcinoma
[35], ovarian cancer
[36], glioma
[37], and HCC
[38][39]. Lower UPF1 is associated with poor survival in lung adenocarcinoma
[40], but its potential as a biomarker or therapeutic target requires further investigation.
2. Transcription Modifiers
TP53 is the most frequently mutated gene in cancer, with over 50% of cancers carrying loss of function mutations
[41][42][43]. The p53 tumor suppressor protein plays a central role in cellular stress responses and promotes cell cycle arrest, apoptosis, or senescence
[41][42]. The N-terminal region contains two tandem transcription activation domains (TADs) required for target gene induction and tumor suppressor activities. The TADs are followed by a proline-rich domain that contributes to transcriptional activation and is essential for cell growth restriction
[44]. Following this is the DNA-binding domain, which has been crystallized in complex with DNA and is the hotspot for cancer-associated mutations
[45]. The oligomerization domain is essential for dimer/tetramer formation and together with the C-terminal domain facilitates, DNA binding
[46]. It was shown many years ago that p53 can bind to its own mRNA at the 5′-UTR to regulate its expression
[47]. p53 also binds the 5ʹ-UTR of
Mdmx mRNA and the coding sequence of
Hspa5 (Bip) mRNA to regulate their translation
[48][49]. The interaction of p53 with RNA may also regulate its oligomerization and DNA-binding activity
[50].
IFN-γ-inducible protein-16 (IFI16) is a member of the PYHIN-200 family composed of one PYRIN domain and two HIN domains. The PYRIN domain serves as the location for homotypic protein–protein interactions. HIN domains are 200 amino acid motifs mediating interactions with DNA
[51]. IFI16 acts as a DNA sensor involved in innate immune response to many viruses
[52][53][54][55] and activates inflammasome formation upon infection
[56]. IFI16 forms filamentous complexes on DNA and can recognize inverted repeats, DNA breaks, or G4 structures
[57][58][59]. IFI16 is also involved in the response to RNA viruses such as Influenza A
[60]. IFI16 may play a role in cancer by binding to p53, and thereby enhancing its transcriptional activity
[61], and is involved in DNA damage responses via BRCA-1 interaction
[62]. Higher levels of IFI16 are reported in renal cell carcinoma
[63][64] and cervical cancer
[65]. Its positive role was shown in HCC
[66], head and neck squamous cell carcinoma
[67], prostate cancer
[68], and breast cancer
[69]. As IFI16 is multifunctional, more studies will be needed to uncover its potential for diagnosis and treatment.
Topoisomerase II alpha (TOP2A) is an ATP-dependent enzyme that regulates the topological state of DNA during transcription. Binding to dsDNA is essential for stimulating its ATPase activity and the generation of dsDNA breaks. TOP2A is a key player in the decatenation checkpoint, and depletion leads to chromosomal mis-segregation. TOP2A is highly expressed in the G2 and M phases of the cell cycle
[70] and is negatively regulated by p53 at the transcriptional level and by BRCA1 at the post-translational level via ubiquitination
[70][71]. TOP2A was recently reported to associate with the transcription start site of numerous genes to regulate their transcription
[72]. TOP2A is regarded as a marker of cell proliferation, and several of its interacting partners are associated with oncogenesis. Amplification or deletion of
TOP2A and altered enzymatic activity occurs in numerous types of cancers
[70][73][74][75][76].
Sex determining region Y-box 2 (SOX2) is a transcription factor belonging to the SRY homolog box 2 family and plays roles in pluripotency, somatic cell reprogramming, and neurogenesis. SOX2 complexes with other transcription factors, such as octamer-binding transcription factor 3/4 (Oct3/4), and binds to DNA motifs located adjacent to promoter/enhancer regions of several genes involved in development
[77]. SOX2 can be post-translationally modified by methylation, acetylation, sumoylation, and phosphorylation, which control its function as a transcriptional regulator
[78]. SOX2 also interacts with long non-coding RNAs (lncRNAs) involved in embryonic development and neural differentiation
[79][80]. SOX2 can bind directly to ES2 lncRNA with high affinity through its DNA-binding HMG domain
[81]. Numerous studies have reported aberrant expression of SOX2 in cancer (see review
[82][83]), and
SOX2 is recognized as a powerful oncogene, where it regulates cancer stem cells
[78].
AGO proteins are core components of the RNA-induced silencing complex (RISC), which is part of RNA interference (RNAi) processing. They bind guide RNAs (siRNA, miRNA) and process them for subsequent site-specific cleavage for the silencing of target mRNAs involved in development, differentiation, and protection against viral infection
[84]. AGO2 consists of four domains: the N-terminal, PAZ, Mid, and PIWI domains. The PAZ domain binds single-stranded nucleic acids, the PIWI domain has an RNase-H-like fold denoting its endonuclease activity, and Mid shows similarity to the MC domain, which binds to the mRNA cap and is required for efficient translation
[85]. The functions of AGO2 in tumorigenesis are diverse and range from high levels associated with poor prognosis in HCC
[86], ovarian carcinoma
[87], and gastric cancer
[88], or mediating the elevation of oncogenic miR-378a-3p in Burkitt lymphoma
[89], to its low expression as an indicator of poor prognosis in CRC patients
[90]. AGO2 protein–protein interactions (e.g., KRAS and AGO2) are involved in the progression of pancreatic ductal adenocarcinoma
[91] and NSCLC
[92]. Studies of these multilevel effects are in progress and may offer patient specific targeted treatment, e.g., AGO2, as a delivery vehicle for inhibitory miRNAs
[93].
Interleukin enhancer-binding factor 3 (ILF3) and ILF2 (also named NF45) were originally discovered as positive regulators of IL2 transcription as part of the NFAT-AP1-NF-kB enhanceosome in activated T-cells and have roles in cancer
[94][95][96], autoimmune and inflammatory conditions
[97][98], and psychiatric disorders
[99]. ILF3 and ILF2 are involved in almost all steps of RNA metabolism, including transcription, post transcription, translation, pri-miRNA, lncRNA, circular RNA processing, and RNA editing
[100][101]. ILF2 contains disordered N-terminal (amino acids 1–20) and C-terminal (amino acids 351–390) domains, and a central (amino acids 24–371) DZF (double strand RNA binding motif, dsRBM and zinc finger associated) domain. ILF2 forms heterodimers with ILF3, which itself contains two dsRBMs in the center and one tri-RG motif (three repeated RG sequences)
[102] that interacts with ssRNA and ssDNA. In addition, two glycine-rich motifs (GQSY) in the C-terminus of ILF2 provide protein–protein interactions and are implicated in RNA granule assembly by association with mRNA ribonucleoprotein complexes
[103]. ILF3/ILF2 dimers bind to chromatin and regulate expression of transcription factors that promote proliferation and suppress differentiation
[104][105]. ILF3/ILF2 acts as a trans-regulator of RNA editing by interacting with adenosine deaminase RNA specific proteins (DAR1 and ADAR2, providing a link to cancer and epithelial-to-mesenchymal transition
[106][107]). Further regulation of RNA metabolism involves stabilizing mRNAs by 3′UTR binding. ILF3 affects non-coding RNA activities and, for example, stabilizes miR-144 when bound to BUD13 or interacting with the lncRNA UBE2CP3/IGFBP7 duplex, which is linked to gastric cancers. ILF3 and ILF2 are overexpressed in several cancer types and contribute to tumorigenesis
[108][109][110].
In addition to roles that are in common with ILF3, ILF2 also shows specific functions in tumorigenesis: In 1q21 amplified multiple myeloma, 1q21-driven ILF2 binds to YB1, interacts with the splicing factor U2AF65, and influences transcription of DNA damage response factors
[111][112]. By interacting with E2F1, ILF2 promotes small cell lung cancer growth through maintaining mitochondrial quality
[113]. ILF2 can bind to the regulatory region of the phosphatase and tensin homolog gene (PTEN) to promote anchorage-independence of NSCLC
[114]. More recently, ILF2 was reported to bind the multiprotein transcription-export (TREX) complex component THOC4 and facilitate nuclear mRNA export via nicotine induced JAK2/STAT3 signaling in esophageal cancer
[110].
Cell division cycle 5-like protein (CDC5L) was first discovered as a DNA-binding protein
[115]. Its N-terminus contains a nuclear import site, DNA binding domains, and nuclear localization sites; the central region contains a hydrophilic proline-rich TAD, and the C-terminus preferentially associates with the spliceosome
[116][117]. CDC5L and PRP19 (pre-mRNA processing factor 19) form a 700–1000-kDa complex with RBMX (RNA-binding motif protein X-linked), which is bound by lncRNA NORAD (non-coding RNA activated by DNA damage), ALYREF (Aly/REF export factor), and TOP1 (topoisomerase I). This complex plays important roles in genomic stability
[118]. CDC5L is one of the core members of the pre-mRNA spliceosome
[119] and is essential for cell cycle progression in yeast, plants, and mammals and in G2/M
[120] and metaphase-to-anaphase transition in oocyte meiosis
[121]. Phosphorylation by cyclin-dependent kinases is required for CDC5L-mediated pre-mRNA splicing
[122].
3. Nuclear Organizers
CHTOP (chromatin target of protein arginine methyltransferase 1, PRMT1, also called small protein rich in arginine and glycine, SRAG, or Friend of Prmt1—Fop) was identified by two research groups as a nuclear/nucleolar protein
[123][124]. The N-terminal region regulates localization within the nucleolus
[123], and the arginine and glycine rich domain binds to PRMT1
[124]. CHTOP binds RNA and associates with facultative heterochromatin that affects estrogen responsive genes
[123][124]. In addition, CHTOP is a component of the TREX complex and regulates alternative polyadenylation of target genes
[125][126]. CHTOP is controlled through an autoregulatory negative feedback loop by an intron retention mechanism
[127]. The characteristic chromatin binding of CHTOP hints at a role in epigenetic regulation of gene expression. In glioblastoma cells, the CHTOP-associated-methylosome complex binds to 5-hydroxymethylcytosine and methylates arginine 3 of Histone H4 (H4R3) to unwrap chromatin and transactivate cancer-related genes
[128]. CHTOP is associated with apoptosis, stemness, and metastasis in chemoresistant epithelial ovarian cancer cells and may be a target to overcome chemoresistance
[129][130].
HNRNPU is involved in many levels of gene regulation, including the maintenance of the chromosomal 3D structure
[131][132], transcription, RNA splicing, and DNA repair. The N-terminal region (amino acids 1–160) is Asp/Glu rich and is the DNA binding site. HNRNPU also contains a nuclear localization site (NLS), a GX2GXGKT consensus sequence (amino acids 485–492) for putative NTP binding, an RNA polymerase II binding domain (amino acids 269–536), an actin binding site, and the RGG (Arg-Gly-Gly) region in the C-terminal region (amino acids 683–806) that binds to RNA
[133]. These structural characteristics give rise to its diverse functions: the N-terminal acidic domain binds to matrix-associated region (MAR) DNA elements involved in chromosome organization
[134]. By associating with different co-factors, it is involved in many regulation processes: HNRNPU can stabilize E3RS (an F-box protein, a receptor subunit of beta-TrCP ubiquitin E3 ligase) through the acidic N-terminal domain
[135]. By cooperating with p300, HNRNPU binds to the scaffold/matrix-associated region (S/MAR) in the transiently silent topoisomerase I gene, where local acetylation of nucleosomes facilitates transcription
[136].
The middle region of HNRNPU is bound by RNA polymerase II
[137], colocalizes with Wilms’ tumor (WT1), and modulates WT1 transcription
[138]. A short actin binding site close to the C-terminus of HNRNPU then further associates with the phosphorylated C-terminal domain of Pol II, thus carrying out actin’s regulatory role during the initial phases of transcription activation
[137]. The RGG box is important in gene silencing, RNA splicing processing, and mRNA stabilization. HNRNPU co-localizes with the inactive X chromosome, which is RGG box-dependent
[139][140]. As a nuclear organizer, it is not surprising that HNRNPU binds to almost all classes of regulatory noncoding RNAs, including all snRNAs required for splicing both major and minor classes of introns
[141]. HNRNPU also plays important roles in DNA damage responses, in which DNA-PK phosphorylates HNRNPU at S59 to modulate protein–protein–RNA interactions that favor DNA repair enzymes
[142]. One recent report showed that HNRNPU binds to telomeric G4 structures, thus regulating accessibility
[143].
HNRNPU is involved in several cancers. In HCC, HNRNPU mediates the alternative splicing of Ras-related C3 botulinum toxin substrate 1 (Rac-1), yielding the variant Rac1b that stimulates tumorigenesis
[144]. In CRC, hnRNPU and hnRNPA1 bind to the second exon of transformer 2-beta (TRA2β4) and upregulate the transformer 2 beta homolog (TRA2B)
[145]. In neuroblastoma, HNRNPU activates the CCCTC-binding factor (CTCF) by binding to hepatocyte nuclear factor 4 alpha (HNF4A)-derived long noncoding RNA (HNF4A-AS1)
[146]. The lncRNA, called HNRNPU processed transcript (also termed ncRNA00201), is up-regulated and provides oncogenic properties in pancreatic carcinoma
[147].
Heterogeneous nuclear ribonucleoprotein L (HNRNPL) has a distinctive structure compared to other hnRNPs: The N-terminus is rich in glycine and contains two RNA-recognition motifs (RRM), RRM1 and RRM2; the central region contains a proline-rich linker, and the C-terminus contains RRM3 and RRM4. RRM1 has weak RNA binding. RRM3 and RRM4 are indispensable and are sufficient to bind to two appropriately separate binding sites within the same RNA by inducing RNA looping. RRM2 provides moderate RNA-binding affinity
[148][149]. HNRNPL functions in DNA repair, RNA splicing, transcription, and translation, and is involved in several tumor types
[150]. HNRNPL was found to directly regulate the alternative splicing of a set of prostate cancer-specific RNAs
[151]. In lymph node-positive bladder cancer, HNRPL is recruited to the chemokine (C-C motif) ligand 2 (
CCL2) promoter by lymph node metastasis associated transcript 1 (LNMAT1) and enhances transcription
[152]. Similarly, lncRNA cancer susceptibility 9 (CASC9) forms a complex with HNRNPL that affects AKT signaling and DNA damage sensing in HCC
[153]. LncRNA retinoblastoma associated transcript-1 (RBAT1) recruits HNPNPL to the promoter of the transcription factor E2F3 gene to upregulate its expression
[154]. Most recently, HNRNPL was reported to facilitate the formation of circular Rho GTPase activating protein 35 (ARHGAP35) to promote cancer progression by interacting with the transcription factor TFII-I
[155].
4. Signal Transmitters
PRKDC encodes the DNA-dependent protein kinase catalytic subunit, also called DNA-PKcs, which forms the catalytic sub-unit of the serine/threonine-protein kinase DNA-dependent protein kinase (DNA-PK). DNA-PK acts as a sensor of DNA damage, contributing to non-homologous end joining (NHEJ) and homologous recombination (HR) DNA repair pathways
[156]. DNA-PKcs contains a large N-terminal helical domain, followed by the Circular Cradle that contains multiple HEAT (Huntingtin, Elongation Factor 3, PP2A, and TOR1) repeats, well-conserved phosphorylation clusters, and a C-terminal domain containing the highly conserved catalytic kinase domain
[157]. DNA-PK was originally discovered as part of a transcription complex, but has been more extensively studied in DNA damage responses
[156][158]. Aberrant expression and deregulated activity of DNA-PK is associated with numerous cancers and is correlated with poor prognosis
[156][157].
UPF1, SMG1 (SMG1 nonsense-mediated mRNA decay associated PI3K related kinase) and SMG5 (SMG5 nonsense-mediated mRNA decay factor) are important parts of nonsense-mediated mRNA decay (NMD), a surveillance mechanism ensuring degradation of mRNA containing premature stop codons and regulating the stability of many wild type transcripts. In brief, NMD starts when there is an exon junction complex downstream of a stop codon. Eukaryotic peptide chain release factors 1 and 3, UPF1, and SMG1 are recruited to the stop codon site and form the SURF complex. Interaction of SURF with the exon junction complex leads to phosphorylation of UPF1 by SMG1 to activate its endonucleolytic activity or enable recruitment of SMG5 and SMG7 to mediate mRNA degradation
[159][160]. NMD may have tumor suppressive or oncogenic activities
[161]. Targeting NMD and thus enabling the translation of mRNAs with premature termination codons can lead to tumor suppression, as evidenced for CRC characterized by widespread instability in microsatellite sequences
[162].
SMG1 is a member of the phosphoinositide 3-kinase related kinase (PIKK) family involved in NMD
[163], DNA damage response
[164][165], and telomere integrity maintenance
[166]. Similar to its family member ataxia-telangiectasia mutated (ATM), it phosphorylates p53 on Ser15 upon DNA damage
[164] and binds p53 mRNA under normal conditions, but dissociates upon ionizing radiation, leading to alternative splicing
[165]. SMG1 is indispensable for alternative splicing of many mRNAs important during embryogenesis
[167], and SMG1 haploinsufficiency plays roles in cancer development
[168]. SMG1 can also be inactivated via promotor hypermethylation
[169] or various miRNAs
[170][171][172][173]. Low level SMG1 is associated with poor survival in HCC
[174].
5. Telomere Organizers
TERT and telomerase RNA are the core components of telomerase, a reverse transcriptase serving to elongate chromosome ends. TERT is composed of TEN (telomerase essential N-terminal domain), TRBD (telomerase RNA-binding domain), RT (reverse transcriptase), and CTE (C-terminal extension domain)
[175]. TERT activity is minimal in somatic cells, whereas ~90% of human tumors are characterized by telomerase activation
[176] to provide cell immortality. Higher expression is caused mainly by
TERT promoter mutations or focal amplification/rearrangements
[177] and is associated with poor survival in many cancer types
[178][179][180][181]. Therapeutic silencing of TERT activity is under evaluation, and several molecules have entered clinical trials
[182].
SMG5 consists of an N-terminal 14-3-3-like domain important for heterodimerization with SMG7
[183], an α-helical domain, and a C-terminal PIN (PilT N-terminus) domain that is present in proteins with ribonuclease activity, but is inactive in SMG5
[184]. In addition to its role in NMD
[185], as discussed above, SMG5 participates in telomere maintenance
[166], is often upregulated in HCC, and is associated with poor prognosis
[186].
Abbreviations
| AGO |
argonaute |
| ARHGAP35 |
Rho GTPase activating protein 35 |
| ATM |
ataxia-telangiectasia mutated |
| ATR |
ataxia-telangiectasia and Rad3-related protein |
| CASC9 |
cancer susceptibility 9 |
| CCL2 |
chemokine (C-C motif) ligand 2 |
| CDC5L |
cell division cycle 5-like protein |
| CH |
cysteine-histidine-rich domain |
| CHD3 |
chromodomain helicase DNA binding protein 3 |
| CHTOP |
chromatin target of protein arginine methyltransferase 1 |
| CRC |
colorectal cancer |
| CSPs |
cold shock domain proteins |
| CTCF |
CCCTC-binding factor |
| DDX |
Asp-Glu-X-Asp-box RNA helicase |
| DHX |
Asp-Glu-X-His-box RNA helicase |
| DNA-PK |
DNA-dependent protein kinase |
| DRBPs |
DNA and RNA binding proteins |
| dsRNA |
double-stranded |
| E3RS |
a receptor subunit of beta-TrCP ubiquitin E3 ligase |
| ENPD |
Eukaryotic Nucleic Acid Binding Protein Database |
| FAH |
fumarylacetoacetate hydrolase |
| G4 |
G-quadruplex |
| GO |
Gene Ontology |
| GQSY |
glycine-rich motifs |
| HCC |
hepatocellular carcinoma |
| HMG |
high mobility group |
| HNF4A |
hepatocyte nuclear factor 4 alpha |
| HNRNPL |
heterogeneous nuclear ribonucleoprotein L |
| HNRNPU |
heterogeneous nuclear ribonucleoprotein U |
| HOX |
homeodomain complexes |
| HTH |
helix-turn-helix |
| IFI16 |
IFN-γ-inducible protein-16 |
| ILF2 |
interleukin enhancer-binding factor 2 |
| ILF3 |
interleukin enhancer-binding factor 3 |
| lncRNAs |
long non-coding RNAs |
| LNMAT1 |
by lymph node metastasis associated transcript 1 |
| MAR |
matrix-associated region |
| NLS |
nuclear localization site |
| NMD |
nonsense-mediated mRNA decay |
| NMD |
nonsense-mediated mRNA decay |
| NORAD |
non-coding RNA activated by DNA damage |
| NSCLC |
non-small-cell lung carcinoma |
| NuRD |
nucleosome remodeling and histone deacetylase |
| PIN |
PilT N-terminus domain |
| PRKDC |
DNA-dependent protein kinase catalytic subunit |
| PTEN |
phosphatase and tensin homolog gene |
| RBAT1 |
retinoblastoma associated transcript-1 |
| RBMX |
RNA-binding motif protein X-linked |
| RBPDB |
RNA-Binding Protein Database |
| RecA |
recombinase A-like |
| RGG |
Arg-Gly-Gly region |
| RISC |
RNA-induced silencing complex |
| RNAi |
RNA interference |
| RNP |
ribonucleoprotein |
| RRMs |
RNA-recognition motifs |
| RT |
reverse transcriptase |
| SMG1 |
serin/threonin-protein kinase 1 |
| SMG5 |
serin/threonin-protein kinase 5 |
| SOX2 |
sex determining region Y-box 2 |
| SQ |
rich in serine and glutamine |
| ssRNA |
single-stranded |
| TADs |
transcription activation domains |
| TCP80 |
translational control protein 80 |
| TEN |
telomerase essential N-terminal domain |
| TFIIIA |
transcription factor |
| TFs |
transcription factors |
| TOP1 |
topoisomerase I |
| TOP2A |
topoisomerase II alpha |
| TRA2B |
transformer 2 beta homolog |
| TRA2β4 |
transformer 2-beta |
| TRBD |
telomerase RNA-binding domain |
| TREX |
multiprotein transcription-export complex |
| UPF1 |
regulator of nonsense transcripts 1 |
| WT1 |
Wilms’ tumor |