DCAF4

DCAF4 (WDR21A) is a substrate receptor subunit of the CRL4 Cullin-RING E3 ubiquitin ligase, assembling with CUL4A/4B and DDB1 to target specific proteins for ubiquitination and degradation (PMID:30945288). In colitis-associated and colorectal cancer cells, CRL4DCAF4 ubiquitinates the tumor suppressor ST7 and directs it to proteasomal degradation, thereby promoting tumor cell growth; this activity requires intact CUL4-DDB1 scaffolding, since disrupting that interaction abolishes ST7 turnover and inhibits tumor growth (PMID:30945288, PMID:32140073). The complex's output is set transcriptionally upstream: inflammation-driven loss of miR-34b-5p elevates c-MYC, which activates CUL4A/4B transcription and downstream CRL4DCAF4 activity toward ST7 (PMID:31972160). Beyond this oncogenic axis, DCAF4 also mediates ubiquitination of the autophagy receptor optineurin (OPTN), promoting autophagic clearance of misfolded SOD1 and linking the ligase to proteostasis relevant to ALS (PMID:32014991).

1. 2012 Low

   An initial structural hypothesis asked what fold DCAF4/WDR21A adopts and what it might bind, establishing it as a WD-repeat protein potentially engaging the glucocorticoid receptor.

   Evidence Template-based structure prediction and computational docking (Zdock), no experimental binding validation

   PMID:22366774

   Open questions at the time

   • Purely computational prediction with no experimental confirmation of the GR interaction
   • Does not establish any enzymatic or ligase function
   • WD-repeat fold inferred, not solved
2. 2019 High

   Defined DCAF4's biochemical identity by showing it serves as a substrate receptor within a CRL4 complex that ubiquitinates and degrades the tumor suppressor ST7, establishing its oncogenic role in colitis-associated cancer.

   Evidence Reciprocal Co-IP, in vitro and in vivo ubiquitination assays, and knockdown with colony formation and tumor growth readouts across multiple cell lines and models

   PMID:30945288

   Open questions at the time

   • Substrate range beyond ST7 not mapped
   • Structural basis of ST7 recognition by the WD-repeat domain not resolved
   • Whether ST7 is a direct or indirect substrate of the receptor not fully dissected
3. 2020 Medium

   Extended DCAF4 function beyond cancer by showing it ubiquitinates the autophagy receptor OPTN to drive autophagic clearance of misfolded SOD1, linking the ligase to proteostasis and ALS.

   Evidence Genome-wide siRNA screen, time-resolved FRET for SOD1 conformation, ubiquitination assays, and autophagy flux experiments in a single lab

   PMID:32014991

   Open questions at the time

   • Two orthogonal methods but not independently replicated
   • Whether OPTN ubiquitination uses the same CUL4-DDB1 scaffold not directly tested
   • Type/topology of ubiquitin chains on OPTN unspecified
4. 2020 Medium

   Validated the scaffolding requirement for DCAF4 ligase activity by showing small-molecule disruption of CUL4A-DDB1 blocks complex assembly, ST7 degradation, and tumor growth.

   Evidence AlphaScreen protein-protein interaction assay, biochemical assembly assays, proliferation/colony formation, and in vivo xenograft growth

   PMID:32140073

   Open questions at the time

   • Single lab with one inhibitor compound
   • Selectivity of NSC1892 for this complex not exhaustively established
   • Does not address DCAF4-specific (versus general CRL4) dependence
5. 2020 Medium

   Placed CRL4DCAF4 in a regulatory hierarchy by showing that inflammation-driven loss of miR-34b-5p de-represses c-MYC, which transcriptionally activates CUL4A/4B to elevate ligase activity against ST7.

   Evidence miRNA-target luciferase assays, oncogenic phenotype assays, in vivo tumor formation, and c-MYC rescue experiments

   PMID:31972160

   Open questions at the time

   • Single lab; mechanism inferred from rescue rather than endogenous chromatin occupancy data
   • Whether DCAF4 itself is transcriptionally regulated by this axis not shown
   • Generalizability beyond colitis-associated cancer not tested

• The full substrate repertoire of CRL4DCAF4 and the structural basis by which its WD-repeat domain selects ST7 versus OPTN remain unresolved.
• No structure of DCAF4 bound to a substrate
• Determinants of substrate choice across cancer versus autophagy contexts unknown
• Unbiased substrate identification (e.g. degradomics) not reported