DDA1

DDA1 is a small, evolutionarily conserved chromatin-associated protein that functions as a core regulatory subunit of CRL4 (Cul4-DDB1) E3 ubiquitin ligase complexes, where it supports genome stability through control of substrate ubiquitination (PMID:19295130). Depletion of DDA1 phenocopies loss of other CRL4 components by causing spontaneous accumulation of double-stranded DNA breaks, establishing it as a physical and functional partner of these ligases (PMID:19295130). Its incorporation into CRL4 is governed by c-Abl-mediated phosphorylation of DDB1 at Tyr-316, which recruits DDA1 and drives ubiquitination of CRL4 substrates such as IKZF1 and IKZF3 (PMID:28087699). Within the CRL4CSA complex (DDB1, CUL4A/B, RBX1, and CSA), DDA1 is an integral structural component resolved by cryo-EM that coordinates ubiquitination dynamics during transcription-coupled nucleotide excision repair, being required for efficient turnover and progression of TC-NER at DNA damage-stalled RNA polymerase II (PMID:39075067). Independent of its ligase role, DDA1 acts as a positive regulator of proliferation and cell-cycle progression in cancer cells, where its overexpression upregulates cyclins and engages NFkB/CSN2/GSK-3beta signaling and where it is transcriptionally controlled by STAT3 (PMID:26942699, PMID:28211159, PMID:36891981).

1. 2009 High

   Established DDA1 as a bona fide CRL4-associated subunit by linking its physical interaction to a shared loss-of-function genome-stability phenotype, defining its role rather than merely cataloguing an interaction.

   Evidence Mass spectrometric CSN interactome plus RNAi depletion with gammaH2AX/DSB readout in mammalian cells

   PMID:19295130

   Open questions at the time

   • Did not define which CRL4 substrates or repair pathway DDA1 acts upon
   • Structural basis of DDA1 incorporation into CRL4 unresolved
   • Mechanism connecting DDA1 loss to DSB accumulation not delineated
2. 2017 High

   Resolved how DDA1 is recruited to CRL4, showing that c-Abl phosphorylation of DDB1 at Tyr-316 is the regulatory switch controlling DDA1 incorporation and downstream substrate ubiquitination.

   Evidence Site-directed mutagenesis of DDB1 Tyr-316, Co-IP, IKZF1/IKZF3 ubiquitination assays, and Abl pharmacological/genetic ablation in multiple myeloma cells

   PMID:28087699

   Open questions at the time

   • Whether the same recruitment mechanism operates in DNA-repair CRL4 complexes not tested
   • Structural consequence of DDB1 phosphorylation on DDA1 binding not visualized
   • Generality across other CRL4 substrate receptors unknown
3. 2023 Medium

   Identified DDA1 as a CSA-interacting integral component of CRL4CSA and implicated it in TC-NER dynamics, extending its function to a specific repair complex (preprint).

   Evidence Single-step protein-complex isolation with mass spectrometry, cryo-EM, and functional TC-NER depletion assays (Research Square preprint)

   PMID:37886519

   Open questions at the time

   • Preprint not yet peer-reviewed at time of posting
   • Quantitative kinetics of TC-NER turnover not fully defined
4. 2024 High

   Established the structural and functional basis of DDA1 within CRL4CSA, showing it is required for efficient ubiquitination turnover and TC-NER progression at stalled RNA Pol II.

   Evidence Cryo-EM structure of CRL4CSA, complex isolation with mass spectrometry, and functional depletion assays measuring TC-NER dynamics

   PMID:39075067

   Open questions at the time

   • Precise enzymatic step DDA1 modulates within the ubiquitination cycle not fully isolated
   • In vivo physiological consequences of DDA1-specific TC-NER defects not characterized
5. 2017 Medium

   Characterized a proliferative, oncogenic dimension of DDA1 distinct from its ligase role, linking its overexpression to cyclin-driven S-phase entry and tumor growth.

   Evidence Gain- and loss-of-function in colon and lung cancer lines, cyclin western blots, flow cytometry, NFkB/CSN2/GSK-3beta pathway assays, and xenografts

   PMID:26942699 PMID:28211159

   Open questions at the time

   • Whether proliferative effects require CRL4 ligase activity not resolved
   • Direct molecular targets connecting DDA1 to cyclin upregulation undefined
6. 2023 Medium

   Placed DDA1 downstream of STAT3 transcriptional control and within a drug-resistance circuit, linking its expression to chemoresistance.

   Evidence Dual-luciferase reporter for STAT3-DDA1, STAT3 and DDA1 knockdown, cell-cycle/apoptosis flow cytometry, and p-STAT3/cyclin western blots in cisplatin-resistant breast cancer cells

   PMID:36891981

   Open questions at the time

   • Direct STAT3 binding to the DDA1 promoter not confirmed by ChIP
   • Mechanistic link between DDA1 and cisplatin resistance not established
7. 2007 Low

   Earliest attempt to define DDA1/PCIA1 binding partners, nominating ACTN4, PSAP, and EIF3S10 as candidate interactors.

   Evidence Bacterial two-hybrid (BacterioMatch) screening of a fetal kidney cDNA library with sequencing validation

   PMID:17557237

   Open questions at the time

   • Bacterial two-hybrid only, no reciprocal validation or co-IP confirmation
   • Functional significance of these interactions never established
   • Not integrated with later CRL4-centric understanding of DDA1

• Whether DDA1's proliferative/oncogenic activities depend on its CRL4 ligase function, and how its repair and growth-regulatory roles are mechanistically connected, remains unresolved.
• No experiment links the CRL4-subunit role to the cyclin/NFkB proliferative phenotype
• Substrate spectrum of DDA1-containing CRL4 complexes incompletely defined
• Physiological and disease consequences of DDA1 loss in vivo uncharacterized