CNOT8

CNOT8 (hCAF1/hPOP2) is a DEDD-family deadenylase subunit of the CCR4-NOT complex that shortens mRNA poly(A) tails to drive transcript decay and post-transcriptional gene regulation (PMID:19605561, PMID:35390160). Its catalytic domain most closely resembles yeast Pop2 and human PARN, and it associates with the conserved CCR4-NOT machinery through binding to the human CCR4 ortholog via its LRR domain (PMID:11747467, PMID:19276069). CNOT8 occupies the complex in competition with its paralog CNOT7, which binds the scaffold subunit CNOT1 with higher affinity and can displace CNOT8; incorporation into CCR4-NOT stabilizes the otherwise intrinsically labile CNOT8 protein (PMID:35248544). CNOT8 is recruited to specific transcripts by the antiproliferative BTG/TOB proteins, which engage hCaf1 through their Box A and Box B motifs; this physical interaction—rather than deadenylase activity per se—is required for BTG/TOB-mediated growth inhibition, mRNA destabilization, and translational repression (PMID:19276069, PMID:23236473). Through its deadenylase function CNOT8 controls developmental gene expression programs: its loss elongates poly(A) tails and stabilizes target mRNAs, blocking the naïve-to-formative pluripotency transition (dependent on CCR4-NOT integration and binding to Tob1 and Pabpc1) and distorting mesoderm specification and axial patterning during gastrulation [PMID:35390160, PMID:bio_10.1101_2025.07.22.666114]. CNOT8 additionally interacts with PRMT1 in nuclear speckles to modulate its substrate-specific arginine methylation activity and is implicated in the ionizing-radiation DNA damage response (PMID:17264152, PMID:33178865).

1. 2001 Medium

   Established that human CNOT8 is a bona fide CCR4-NOT component, defining the LRR domain as the determinant of its association with human CCR4 and demonstrating conservation of the complex from yeast to human.

   Evidence two-hybrid and far-Western assays mapping the hCCR4-binding LRR domain

   PMID:11747467

   Open questions at the time

   • Did not test deadenylase activity or assembly with other CCR4-NOT subunits
   • No structural or affinity quantification of the interaction
2. 2007 Medium

   Linked CNOT8 to protein arginine methylation by showing it binds and modulates PRMT1 activity, broadening its role beyond mRNA decay.

   Evidence reciprocal Co-IP, nuclear speckle co-localization, in vitro methylation assay, and siRNA knockdown

   PMID:17264152

   Open questions at the time

   • Mechanism by which CNOT8 alters PRMT1 substrate selectivity is undefined
   • Connection between methylation regulation and deadenylase function not established
3. 2009 High

   Defined the structural basis for CNOT8 recruitment by antiproliferative TOB and showed that complex formation, not catalysis, drives growth inhibition.

   Evidence crystal structure of Tob N-terminus bound to hCaf1 plus cell growth assays with catalytic and interface mutants

   PMID:19276069

   Open questions at the time

   • Full Tob-hCaf1 complex with substrate not captured
   • How TOB binding alters target selection on mRNA unresolved
4. 2009 Medium

   Demonstrated CNOT8 is a catalytically active deadenylase with partial redundancy with CNOT7, and that it represses antiproliferative target genes.

   Evidence siRNA single and double knockdown, proliferation assays, and expression profiling identifying MSMB and PMP22 de-repression

   PMID:19605561

   Open questions at the time

   • Direct deadenylation of named targets not biochemically reconstituted
   • Extent of CNOT7/CNOT8 redundancy not quantified at transcript level
5. 2012 High

   Placed CNOT8 downstream of BTG/TOB as the obligatory effector of their antiproliferative and mRNA-regulatory activity, independent of other CCR4-NOT subunits.

   Evidence interface mutagenesis, Co-IP, proliferation, mRNA abundance and translation assays across multiple BTG/TOB members

   PMID:23236473

   Open questions at the time

   • Specific mRNA targets of the BTG/TOB-CNOT8 module not enumerated
   • Whether deadenylase activity is dispensable in this context not fully separated from CNOT7 contribution
6. 2020 Low

   Implicated CNOT8 in the DNA damage response by showing its depletion alters damage-marker foci after ionizing radiation.

   Evidence siRNA knockdown, foci immunofluorescence (γH2AX, RPA, 53BP1, RAD51), phospho-DDR western blotting

   PMID:33178865

   Open questions at the time

   • Descriptive foci assay without rescue or pathway placement
   • No mRNA target linking deadenylation to DDR identified
7. 2022 Medium

   Revealed that paralog competition governs CNOT8 abundance in the complex—CNOT7 outcompetes CNOT8 for CNOT1, and incorporation stabilizes the intrinsically labile CNOT8 protein.

   Evidence reciprocal Co-IP, knockdown, protein and mRNA stability assays, polysome profiling

   PMID:35248544

   Open questions at the time

   • Structural basis of the CNOT1 affinity difference not solved
   • Functional consequences of paralog swapping on specific transcripts unclear
8. 2022 High

   Established CNOT8 deadenylase activity as essential for the naïve-to-formative pluripotency transition, requiring CCR4-NOT integration and binding to Tob1 and Pabpc1.

   Evidence CRISPR knockout in mouse ESCs, poly(A) tail and mRNA half-life measurements, Co-IP, target-gene knockdown rescue

   PMID:35390160

   Open questions at the time

   • Which transcripts are direct versus indirect targets not fully resolved
   • Relative contribution of CNOT7 redundancy in vivo not addressed
9. 2024 Low

   Identified MSI2 as a paralog-specific CNOT8 partner connecting it to post-transcriptional control of Prdx4 in pancreatic β cells.

   Evidence Co-IP (CNOT8-MSI2), RNA-IP (MSI2-Prdx4 mRNA), western blotting (preprint)

   PMID:bio_10.1101_2024.06.26.599433

   Open questions at the time

   • Single Co-IP without reciprocal validation; functional consequence of the CNOT8-MSI2 interaction not directly tested for CNOT8
   • Preprint, not peer-reviewed
10. 2025 Medium

    Extended CNOT8 deadenylase function to mammalian body plan formation, showing its loss elongates poly(A) tails and redirects mesoderm toward ectopic notochord fate.

    Evidence CRISPR screen, single-cell transcriptomics, poly(A) tail profiling in gastruloids (preprint)

    PMID:bio_10.1101_2025.07.22.666114

    Open questions at the time

    • Direct target transcripts driving the fate shift not pinpointed
    • Preprint, not peer-reviewed

• How CNOT8 versus CNOT7 substrate selectivity is encoded, and how its diverse partners (TOB/BTG, PRMT1, MSI2) direct it to distinct transcript pools across cell types, remains unresolved.
• No transcriptome-wide map distinguishing CNOT8- from CNOT7-specific targets
• No structure of CNOT8 engaging a poly(A) substrate within CCR4-NOT
• Mechanistic link between deadenylation and the DDR phenotype undefined