TARBP2

TARBP2 (TRBP) is a multifunctional double-stranded RNA-binding protein that operates in both miRNA biogenesis and direct sequence-specific control of mRNA stability across cancer, cell cycle, and innate immune contexts (PMID:19219043, PMID:25043050). As a DICER1 cofactor, TARBP2 stabilizes DICER1 protein and is required for accurate Dicer cleavage-site selection on a subset of pre-miRNAs; loss-of-function frameshift mutations in microsatellite-instable carcinomas diminish TRBP, destabilize DICER1, and impair miRNA processing, while genetic knockout shifts Dicer processing sites without abolishing global miRNA abundance or Argonaute loading, an activity not shared with its paralog PACT (PMID:19219043, PMID:25437560). SUMOylation at K52 stabilizes TARBP2 by repressing K48-linked ubiquitination and recruits Ago2 to assemble the RISC-loading complex, thereby enhancing small-RNA silencing efficiency (PMID:26582366). Independent of miRNAs, cytoplasmic TARBP2 binds GC-rich structural elements (TBSEs) in the 3'UTRs of metastasis-suppressor (APP, ZNF395) and antiangiogenic (THBS1/2, TIMP1, SERPINF1) transcripts via its dsRNA-binding domains to destabilize them, promoting invasion, metastasis, and tumor angiogenesis (PMID:25043050, PMID:33484209). In the nucleus, TARBP2 binds pre-mRNAs, recruits the m6A methylation machinery to drive intron retention, and engages the nucleoprotein TPR to target the modified transcripts for nuclear exosome degradation (PMID:31300274). During M phase TARBP2 is hyperphosphorylated by JNK, potentiating its inhibition of PKR to permit the M-G1 transition (PMID:25437560), and it negatively regulates antiviral signaling by disrupting MAVS-RIG-I/TRAF3 complexes and impairing TRAF6-mediated K63-ubiquitination of IRF7 (PMID:30390472, PMID:30927622). TARBP2 protein levels are themselves tightly controlled by proteasomal and autophagic-lysosomal turnover, with the interactor Merlin promoting its degradation (PMID:30657254, PMID:30759864).

1. 2001 Medium

   Established the genomic architecture of the TARBP2 locus, showing two adjacent promoters generate TRBP1/TRBP2 isoforms with cell-type-specific promoter regulation.

   Evidence Gene isolation, promoter deletion/reporter assays and 5' RACE across HeLa and astrocytic cells

   PMID:11641396

   Open questions at the time

   • Functional consequences of isoform choice not defined
   • Mechanism of astrocyte-specific repression unknown
2. 2009 High

   Linked TARBP2 to tumor suppression by showing its frameshift mutation impairs DICER1 stability and miRNA processing, addressing how miRNA biogenesis fails in microsatellite-instable cancers.

   Evidence Mutational analysis, western blot, miRNA processing and rescue assays in cancer cell lines

   PMID:19219043

   Open questions at the time

   • Did not resolve which specific miRNAs drive the tumor phenotype
   • Mechanism of DICER1 stabilization by TRBP not detailed
3. 2014 High

   Refined the DICER1 cofactor role by demonstrating TARBP2 governs Dicer processing-site accuracy rather than Dicer stability or global miRNA output, and is non-redundant with PACT.

   Evidence CRISPR/Cas9 single and double knockout, small RNA sequencing, western blot in human cells

   PMID:25437560

   Open questions at the time

   • Apparent discrepancy with 2009 DICER1 stability finding not reconciled
   • Determinants of which miRNAs require TRBP for accuracy unknown
4. 2014 High

   Defined a cell-cycle role: JNK hyperphosphorylates TARBP2 in M phase to potentiate PKR inhibition, answering how PKR is restrained during M-G1 transition.

   Evidence Knockout cells, JNK inhibitor, phosphorylation and PKR activity assays across cell cycle

   PMID:25437560

   Open questions at the time

   • Phosphosites mediating PKR inhibition not mapped
   • Identity of the M-phase dsRNAs activating PKR unclear
5. 2014 High

   Revealed a miRNA-independent function in which TARBP2 directly binds structural 3'UTR elements to destabilize metastasis-suppressor mRNAs, explaining a pro-metastatic role.

   Evidence Transcript stability profiling, RNA binding assays, structure prediction, in vivo colonization assays in breast cancer cells

   PMID:25043050

   Open questions at the time

   • Decay machinery recruited by cytoplasmic TARBP2 not identified
   • Full target repertoire beyond APP/ZNF395 incomplete
6. 2015 High

   Identified SUMOylation at K52 as a regulatory switch that stabilizes TARBP2 and recruits Ago2 for RISC-loading complex assembly, connecting post-translational modification to silencing efficiency.

   Evidence K52R mutagenesis, in vivo SUMOylation, Co-IP, ubiquitination and RNAi reporter assays

   PMID:26582366

   Open questions at the time

   • SUMO ligase responsible not identified
   • Quantitative contribution of SUMOylation to physiological silencing unclear
7. 2018 Medium

   Extended TARBP2 to innate immunity by showing it disrupts MAVS-RIG-I/TRAF3 complexes to dampen IFN-β production.

   Evidence Co-IP, overexpression/knockdown in 293T, IFN-β reporter and viral infection assays

   PMID:30390472

   Open questions at the time

   • Single overexpression system without endogenous validation
   • Direct binding interface with MAVS not mapped
8. 2019 High

   Defined a nuclear pathway in which TARBP2 recruits m6A machinery and TPR to drive intron retention and exosome-mediated decay of pre-mRNAs, establishing a chromatin-proximal mode of gene control.

   Evidence RNA-protein binding, m6A assays, Co-IP with TPR, intron-retention RNA-seq, xenograft models

   PMID:31300274

   Open questions at the time

   • Which m6A writer subunit TARBP2 contacts not specified
   • Signals partitioning TARBP2 between nucleus and cytoplasm unknown
9. 2019 Medium

   Showed TARBP2 inhibits IRF7-driven IFN-β by impairing TRAF6-mediated K63-ubiquitination of IRF7 and destabilizing TRAF6, broadening its antiviral suppressor role.

   Evidence Co-IP, ubiquitination and phosphorylation assays, Sendai virus infection in 293T

   PMID:30927622

   Open questions at the time

   • Endogenous physiological context limited to overexpression system
   • Relationship to the MAVS-disruption mechanism not integrated
10. 2019 Medium

    Demonstrated TARBP2 protein abundance is set by competing turnover routes (autophagic-lysosomal and Merlin-promoted proteasomal degradation), with miRNA-independent downstream effects on Nanog and SOX2 in drug resistance.

    Evidence Lysosomal/proteasomal inhibitors, Co-IP for Merlin, protein stability assays in HCC and breast cancer lines

    PMID:30657254 PMID:30759864

    Open questions at the time

    • Mechanism by which TARBP2 stabilizes Nanog/SOX2 not defined
    • In vivo relevance of these turnover routes not established
11. 2021 Medium

    Expanded the cytoplasmic mRNA-destabilization role to antiangiogenic transcripts and miR-145 processing, and revealed TARBP2 control of HIF-1α stability via E3 ligase downregulation.

    Evidence RIP, 3'UTR reporter and stability assays, domain deletion, miR-145 rescue, ubiquitination assays in cancer cells and xenografts

    PMID:33484209 PMID:34249676 PMID:35008634

    Open questions at the time

    • Whether HIF-1α and angiogenesis effects are direct or transcript-mediated unresolved
    • Cross-talk between TARBP2's miRNA and direct-binding functions unquantified
12. 2022 Low

    Reported TARBP2 acting as a general lncRNA-binding partner (SNHG7, LINC01526) to alter transcript fate in BBB permeability and gastric cancer.

    Evidence RIP, RNA pull-down, half-life and luciferase assays, xenograft models

    PMID:35562351 PMID:36230863

    Open questions at the time

    • Binding domains/structural determinants not mapped
    • Single-lab observations without reciprocal validation
    • Generality of lncRNA recognition unclear

• How TARBP2 is partitioned among its DICER1-cofactor, direct mRNA-destabilizing, nuclear m6A/exosome, cell-cycle, and antiviral functions, and what governs target selection in each compartment, remains unresolved.
• No unified model of subcellular trafficking
• Determinants distinguishing miRNA-dependent vs -independent targets unknown