Target-directed microRNA degradation

Reviewing the ZSWIM8 ligase axis and its Argonaute substrates

AI Gene Review · projects/MIRNA_DEGRADATION · 2026

Bottom line

  • In TDMD, the ZSWIM8–CUL3 ligase recognizes AGO-miRNA complexes bound to a highly complementary trigger RNA and ubiquitylates AGO, which leads to loss of the miRNA.
  • We reviewed the 9 human proteins of that layer (ZSWIM8, CUL3, ARIH1, ELOB, ELOC, AGO1–4): 1,106 annotations.
  • ZSWIM8 now points at GO:0140958 target-directed miRNA degradation and a Cul3-RING complex; 83 of 90 removals are bare protein binding rows.

The mechanism

Scope: the dedicated protein layer only

  • In: ZSWIM8, CUL3, ARIH1, ELOB, ELOC (the ligase) and AGO1–4 (the substrate layer).
  • Context, not reviewed: trigger RNAs and trigger-bearing transcripts (CYRANO, NREP, SERPINE1, HSUR1, fly AGO1 mRNA).
  • Out: miRNA biogenesis (DROSHA, DICER1…), effector repression (TNRC6, CCR4-NOT), generic CRL/proteasome parts, and the TUT4/7–DIS3L2 tailing branch.
  • Aim: keep core TDMD function separate from generic silencing and ubiquitin biology.

What the reviews concluded

A TDMD-specific correction

ZSWIM8: the IBA Cul2-RING complex row is modified to Cul3-RING, because CUL3, not CUL2, was required in the TDMD screen follow-up (PMID:33184234).

Key changes

  • ZSWIM8: positive regulation of miRNA catabolic process (IDA ×2) → GO:0140958 target-directed miRNA degradation; core MF GO:1990756 ligase-substrate adaptor.
  • CUL3: ligase and transferase activity rows → GO:0160072 ubiquitin ligase complex scaffold activity; 78 rows over-annotated.
  • AGO4: IBA RNA endonuclease activity removed, not supported as a physiological activity.
  • ELOB / ELOC: 58 protein binding IPIs and a Pol II transcription-initiation row removed.

Status and next steps

  • ✅ 9/9 human reviews exist; 8 marked COMPLETE, CUL3 fully actioned but still INITIALIZED.
  • ⬜ Set CUL3 status; update the status checklist on the project page.
  • ⬜ Comparative fly / worm / mouse TDMD machinery.
  • ⬜ Deferred: TUT4/TUT7–DIS3L2 branch; viral trigger subproject.

Read more: projects/MIRNA_DEGRADATION.md · projects/MIRNA_DEGRADATION/sources.md · genes/human/ZSWIM8/