Affinage

RIOK2

Serine/threonine-protein kinase RIO2 · UniProt Q9BVS4

Length
552 aa
Mass
63.3 kDa
Annotated
2026-06-10
18 papers in source corpus 14 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

RIOK2 is an atypical ATPase/kinase that serves as a cytoplasmic assembly factor for the pre-40S ribosomal subunit, where its ATPase activity is required for late maturation and particle release, coupling the Ras/MAPK pathway to ribosome biogenesis: RSK phosphorylates RIOK2 to drive its release from pre-40S particles and nuclear re-import, supporting optimal protein synthesis and proliferation (PMID:34125833). Its ATPase function is selectively essential for leukemic cell survival, and pharmacological inhibition collapses protein synthesis, destabilizes ribosomes, and triggers apoptosis in AML cells in vivo while sparing fibroblasts (PMID:34359076, PMID:35584513). Crystal structures of inhibitor-bound RIOK2 define an ATP-binding pocket whose active-site residue conservation underlies selectivity over RIOK1 and RIOK3 (PMID:30991936, PMID:35584513). Beyond ribosome assembly, RIOK2 acts as a transcription factor through a winged helix-turn-helix DNA-binding domain and two transactivation domains, regulating hematopoietic transcription factors (GATA1, GATA2, SPI1, RUNX3, KLF1) to promote erythroid differentiation and suppress megakaryo- and myelopoiesis (PMID:34937919), and maintaining mRNA expression of TRiC chaperonin and dyskerin complex subunits to sustain telomerase activity and prevent telomere shortening (PMID:39164231). RIOK2 also functions in innate immunity, interacting with FADD and using its ATPase/kinase activity to drive myosin II-dependent lysosome-to-ER translocation of the FADD-RIPK1-caspase-8 complex and to directly cleave caspase-8 and gasdermin D, triggering pyroptosis during Yersinia infection (PMID:41249793). RIOK2 protein levels are controlled post-translationally, as it can be targeted for RNF126-mediated proteasomal degradation by molecular-glue degraders (PMID:39721086).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2019 High

    Structural definition of the RIOK2 ATP-binding site established the molecular basis for selective small-molecule targeting, distinguishing it from related RIO kinases.

    Evidence X-ray crystallography of human RIOK2 bound to a selective inhibitor with active-site residue analysis

    PMID:30991936

    Open questions at the time
    • Does not establish the catalytic cycle or physiological substrate
    • Selectivity over RIOK1/RIOK3 inferred from residue conservation, not measured for all paralogs in cells
  2. 2021 High

    Identifying RSK as the kinase that phosphorylates RIOK2 connected the Ras/MAPK pathway to a defined post-transcriptional step of ribosome biogenesis, namely pre-40S release and RIOK2 nuclear re-import.

    Evidence In vitro kinase assay, mass spectrometry, phosphomutant rescue, and nuclear re-import/proliferation assays in human cells

    PMID:34125833

    Open questions at the time
    • Phosphosite-to-conformational-change mechanism for particle release not resolved
    • Does not address how this couples to the transcription-factor roles
  3. 2021 High

    Mapping a functional wHTH DNA-binding domain and two transactivation domains established RIOK2 as a bona fide transcription factor controlling hematopoietic lineage commitment, a role independent of its ribosomal function.

    Evidence Domain mutagenesis, transcriptomic profiling, and loss-of-function in primary human HSPCs with reporter assays

    PMID:34937919

    Open questions at the time
    • Direct genomic binding sites/ChIP-seq targets not defined
    • Relationship between ribosomal-assembly and transcription-factor pools of RIOK2 unclear
  4. 2022 High

    A domain-focused CRISPR screen plus pharmacological and structural validation established the RIOK2 ATPase function as a selective dependency in AML, providing a therapeutic rationale.

    Evidence CRISPR-Cas9 kinome screen, siRNA, ATPase inhibitor (CQ211, Kd 6.1 nM), protein synthesis assays, and leukemia xenografts

    PMID:34359076 PMID:35584513

    Open questions at the time
    • Basis of leukemia-versus-fibroblast selectivity at the molecular level not defined
    • Whether transcription-factor functions contribute to AML dependency untested
  5. 2024 High

    Linking RIOK2 transcriptional activity to TRiC and dyskerin subunit expression explained how it sustains telomerase and prevents telomere shortening, extending its transcription-factor role to genome maintenance.

    Evidence siRNA with DNA-binding-domain mutants, RT-qPCR, telomere/telomerase assays, and ectopic rescue in IPF patient-derived fibroblasts

    PMID:39164231

    Open questions at the time
    • Direct promoter occupancy at TRiC/dyskerin genes not shown
    • Disease relevance to IPF beyond rescue of telomere length not established
  6. 2025 High

    Discovery that RIOK2 interacts with FADD and drives organelle relocalization and direct caspase-8/GSDMD cleavage placed RIOK2 in a pyroptotic innate-immune pathway, a role distinct from its biogenesis and transcription functions.

    Evidence Co-IP, ATPase-dead mutants, in vitro cleavage assays, lysosome-to-ER transport imaging, myosin II activation assays, and Yersinia infection models

    PMID:41249793

    Open questions at the time
    • Mechanism by which an ATPase directly cleaves caspase-8/GSDMD not biochemically reconciled with protease activity
    • How RIOK2 is recruited to the FADD complex at the molecular level unresolved
  7. 2025 Medium

    Identifying RIOK2 as the kinase that rephosphorylates CLK1-Ser341 during thermal stress recovery defined a role in dynamic splicing control via nuclear stress body localization.

    Evidence Phosphosite identification and kinase assay for CLK1-Ser341, with nSB localization assays during stress/recovery (preprint)

    PMID:bio_10.1101_2025.10.21.683800

    Open questions at the time
    • Single preprint, not independently confirmed
    • Physiological scope of affected transcripts and link to other RIOK2 functions unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the distinct activities of RIOK2 — ribosomal ATPase assembly factor, sequence-specific transcription factor, splicing-regulatory kinase, and pyroptotic effector — are partitioned within a single protein and regulated across cellular compartments remains unresolved.
  • No unifying model reconciling enzymatic and transcription-factor roles
  • Compartment-specific pools and their interconversion not defined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140657 ATP-dependent activity 4 GO:0140096 catalytic activity, acting on a protein 2 GO:0140110 transcription regulator activity 2 GO:0003677 DNA binding 1
Localization
GO:0005634 nucleus 2 GO:0005829 cytosol 2 GO:0005783 endoplasmic reticulum 1
Pathway
R-HSA-8953854 Metabolism of RNA 3 R-HSA-74160 Gene expression (Transcription) 2 R-HSA-168256 Immune System 1 R-HSA-5357801 Programmed Cell Death 1
Partners
CASP8CLK1FADDRIPK1RNF126
Complex memberships
pre-40S ribosomal subunit

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2021 RIOK2 phosphorylation by the MAPK-activated kinase RSK stimulates cytoplasmic maturation of late pre-40S particles. Phosphorylation of RIOK2 by RSK facilitates its release from pre-40S particles and its nuclear re-import, prior to completion of small ribosomal subunits, thereby coupling the Ras/MAPK pathway to post-transcriptional stages of human ribosome synthesis and optimal protein synthesis and cell proliferation. In vitro kinase assay, mass spectrometry, phosphomutant analysis, nuclear re-import assays, cell proliferation assays PLoS genetics High 34125833
2019 Crystal structure of human RIOK2 bound to a specific inhibitor was solved, revealing the inhibitor binds in the ATP-binding site and forms extensive hydrophobic interactions with residues at the entrance to the ATP-binding site. Active site residue conservation explains selectivity of the inhibitor for RIOK2 over RIOK1 and RIOK3. X-ray crystallography Open biology High 30991936
2022 Crystal structure of RIOK2 bound to inhibitor CQ211 (Kd = 6.1 nM) was determined, revealing the molecular mechanism of inhibition. Pharmacological inhibition of RIOK2 ATPase activity led to loss of protein synthesis and apoptosis in leukemic cells in vivo. X-ray crystallography, enzymatic inhibition assays, cell viability assays, mouse xenograft model Journal of medicinal chemistry High 35584513
2022 Loss of RIOK2 or inhibition of its ATPase function in AML cells leads to decreased protein synthesis, ribosomal instability, and apoptosis. The ATPase function of RIOK2 is necessary for cell survival in leukemic but not fibroblast cells. A domain-focused CRISPR-Cas9 screen identified RIOK2 as required for AML cell viability. CRISPR-Cas9 domain-focused kinome screen, siRNA knockdown, small-molecule ATPase inhibitor, protein synthesis assays, in vivo leukemia xenograft model Blood High 34359076
2021 RIOK2 contains a winged helix-turn-helix (wHTH) DNA-binding domain and two transactivation domains. These domains are critical for RIOK2 to function as a transcription factor driving erythroid differentiation and suppressing megakaryopoiesis and myelopoiesis, by regulating key hematopoietic transcription factors GATA1, GATA2, SPI1, RUNX3, and KLF1 in primary human stem and progenitor cells. Domain mutagenesis, transcriptomic profiling, loss-of-function in primary human hematopoietic stem/progenitor cells, reporter assays Nature immunology High 34937919
2024 RIOK2 acts as a transcription factor whose DNA-binding and transactivation properties are required to maintain mRNA expression of TRiC chaperonin complex and dyskerin complex subunits. Loss of these activities impairs telomerase activity, causing telomere shortening. Ectopic RIOK2 expression alleviates telomere shortening in IPF patient-derived primary lung fibroblasts. siRNA knockdown with DNA-binding domain mutations, RT-qPCR, telomere length assays, telomerase activity assays, ectopic expression rescue experiments in primary fibroblasts Nature communications High 39164231
2025 RIOK2 interacts with FADD (Fas-associated protein with death domain) and its kinase activity drives transport of lysosomes to the ER by activating myosin II, thereby translocating the FADD-RIPK1-caspase-8 complex from lysosome to ER. RIOK2's ATPase activity enhances binding to this complex and directly triggers caspase-8 and gasdermin D (GSDMD) cleavage both at the ER and in vitro, driving pyroptosis and host defense against Yersinia infection. Co-immunoprecipitation, in vitro cleavage assay, ATPase-dead mutant analysis, lysosome-to-ER transport imaging, myosin II activation assays, infection models Nature communications High 41249793
2025 RIOK2 rephosphorylates CLK1 at Ser341 during thermal stress recovery, enabling CLK1 localization to nuclear stress bodies (nSBs) specifically during recovery and thereby promoting intron detention in specific transcripts. PP1 dephosphorylates CLK1-Ser341 during stress, and RIOK2 reverses this modification during recovery. Phosphosite identification, kinase assay showing RIOK2 as writer for CLK1-Ser341, nSB localization assays during thermal stress/recovery bioRxivpreprint Medium bio_10.1101_2025.10.21.683800
2020 RIOK2 knockdown in glioma cells inhibits migration and invasion and downregulates MMP2, MMP9, and mesenchymal markers (N-cadherin, β-catenin, Twist1, fibronectin, ZEB-1), while overexpression promotes these effects. miR-4744 directly binds the 3'-UTR of RIOK2 and negatively regulates its expression, thereby suppressing EMT. siRNA knockdown, overexpression, wound healing assay, Transwell invasion assay, dual luciferase reporter assay for miR-4744 binding to RIOK2 3'-UTR, Western blot for EMT markers Journal of cellular and molecular medicine Medium 32125767
2022 RIOK2 knockdown in oral squamous cell carcinoma cells decreased cell growth and reduced S6 ribosomal protein expression and protein synthesis, consistent with its role in pre-40S ribosomal subunit maturation. siRNA knockdown, cell proliferation assay, protein synthesis assay, S6 ribosomal protein Western blot Current oncology Medium 36661680
2022 In porcine intestinal epithelial cells, RIOK2 knockdown promoted activation of the MAPK signaling pathway by increasing phosphorylation of ERK and JNK. Additionally, the transcription factor Sp1 binds to the RIOK2 promoter region to regulate RIOK2 expression, as demonstrated by dual-luciferase reporter and ChIP assays. siRNA knockdown, Western blot for pERK/pJNK, dual-luciferase reporter assay, ChIP assay for Sp1 binding to RIOK2 promoter International journal of molecular sciences Medium 36361502
2020 In the parasitic nematode Strongyloides stercoralis, Ss-RIOK-2 encodes a catalytically active kinase located primarily in the cytoplasm of intestinal and hypodermal cells. Expression of a dominant-negative ATP-binding site mutant (K123A) abrogated egg hatching, which was rescued by wild-type Ss-RIOK-2 but not by the Ss-RIOK-1 ortholog, demonstrating a specific and essential catalytic role for RIOK-2 in larval development. Transgenic nematode overexpression, catalytic mutant (D228A, K123A), rescue experiment with wild-type vs. RIOK-1, localization by transgenic reporter International journal for parasitology Medium 32592810
2018 miR-145 directly targets the 3'-UTR of both RIOK2 and NOB1 mRNAs as validated by dual luciferase reporter assay. Overexpression of miR-145 inhibited RIOK2 and NOB1 protein expression and suppressed NSCLC cell viability, migration, and invasion. Dual luciferase reporter assay, miR-145 overexpression, Western blot, cell viability and invasion assays International journal of oncology Low 29749434
2015 RIOK2 molecular glue degrader CQ627 induces degradation of RIOK2 (DC50 = 410 nM in MOLT4 cells) via the ubiquitin-proteasome system by recruiting E3 ubiquitin ligase RNF126, establishing RNF126 as an E3 ligase capable of mediating RIOK2 degradation. Degrader compound treatment, UPS inhibitor rescue, E3 ligase identification by pulldown/MS, DC50 measurement in leukemia cell line European journal of medicinal chemistry Medium 39721086

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2016 High Expression of RIOK2 and NOB1 Predict Human Non-small Cell Lung Cancer Outcomes. Scientific reports 31 27346559
2022 Targeting RIOK2 ATPase activity leads to decreased protein synthesis and cell death in acute myeloid leukemia. Blood 29 34359076
2018 miR‑145 inhibits human non‑small-cell lung cancer growth by dual-targeting RIOK2 and NOB1. International journal of oncology 23 29749434
2021 Identification of RIOK2 as a master regulator of human blood cell development. Nature immunology 21 34937919
2020 RIOK2 is negatively regulated by miR-4744 and promotes glioma cell migration/invasion through epithelial-mesenchymal transition. Journal of cellular and molecular medicine 21 32125767
2021 RIOK2 phosphorylation by RSK promotes synthesis of the human small ribosomal subunit. PLoS genetics 15 34125833
2019 Crystal structure of human RIOK2 bound to a specific inhibitor. Open biology 15 30991936
2022 Discovery of 8-(6-Methoxypyridin-3-yl)-1-(4-(piperazin-1-yl)-3-(trifluoromethyl)phenyl)-1,5-dihydro-4H-[1,2,3]triazolo[4,5-c]quinolin-4-one (CQ211) as a Highly Potent and Selective RIOK2 Inhibitor. Journal of medicinal chemistry 11 35584513
2021 RIOK2 Inhibitor NSC139021 Exerts Anti-Tumor Effects on Glioblastoma via Inducing Skp2-Mediated Cell Cycle Arrest and Apoptosis. Biomedicines 8 34572430
2024 RIOK2 transcriptionally regulates TRiC and dyskerin complexes to prevent telomere shortening. Nature communications 6 39164231
2022 Analysis of RIOK2 Functions in Mediating the Toxic Effects of Deoxynivalenol in Porcine Intestinal Epithelial Cells. International journal of molecular sciences 6 36361502
2022 RIOK2 Contributes to Cell Growth and Protein Synthesis in Human Oral Squamous Cell Carcinoma. Current oncology (Toronto, Ont.) 6 36661680
2020 RIOK-2 protein is essential for egg hatching in a common parasitic nematode. International journal for parasitology 5 32592810
2024 Discovery of the first examples of right open reading frame kinase 2 (RIOK2) molecular glue degraders. European journal of medicinal chemistry 4 39721086
2020 Towards a RIOK2 chemical probe: cellular potency improvement of a selective 2-(acylamino)pyridine series. RSC medicinal chemistry 4 34046605
2023 Exploration of tricyclic heterocycles as core structures for RIOK2 inhibitors. RSC medicinal chemistry 3 37859717
2025 RIOK2 kinase regulates the translocation of the FADD-RIPK1-Caspase-8 complex to the ER and the cleavage of Gasdermin D to drive pyroptosis. Nature communications 1 41249793
2025 Design, Synthesis and Evaluation of 4-Methoxy-1H-[1,2,3]triazolo[4,5-c]quinolines as Highly Potent and Oral Available RIOK2 Inhibitors. Journal of medicinal chemistry 0 40811658

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