FAM53C

FAM53C is a cytoplasmic regulator of the DYRK1A kinase that couples kinase sequestration to control of the G1/S cell cycle transition (PMID:37802655, PMID:42059432, PMID:39713326). It binds directly to the catalytic domain of DYRK1A—at a site distinct from that used by DCAF7/WDR68, which engages the kinase's N-terminal domain—forming a tri-protein FAM53C–DYRK1A–DCAF7/WDR68 complex (PMID:37802655, PMID:42059432), and inhibits DYRK1A autophosphorylation and its phosphorylation of the substrate Tau/MAPT (PMID:37802655). Functionally, FAM53C anchors DYRK1A in the cytoplasm, redistributing the kinase away from the nucleus and concomitantly suppressing DYRK1A-dependent nuclear accumulation of DCAF7/WDR68 (PMID:37802655). FAM53C is required for the G1/S transition, acting upstream of the CyclinD–CDK4/6–RB axis and p53; its loss causes G1 arrest that is rescued by pharmacological DYRK1A inhibition, placing FAM53C functionally upstream of DYRK1A in cell cycle control (PMID:39713326, PMID:42059432), with knockout human cortical organoids showing increased cell cycle arrest and growth defects (PMID:39713326, PMID:42059432). Although first described as a nuclear protein with a bipartite NLS (PMID:11087669), its characterized mechanism centers on cytoplasmic DYRK1A regulation; it also binds the related kinase DYRK1B (PMID:37802655).

1. 2000 Medium

   Established the basic molecular identity of the gene, defining the protein it encodes and its predicted features before any functional role was known.

   Evidence cDNA cloning, genomic structure and sequence analysis of C5ORF6/FAM53C

   PMID:11087669

   Open questions at the time

   • No molecular function assigned
   • Predicted nuclear localization not functionally tested
   • No interacting partners identified
2. 2023 High

   Identified DYRK1A as a direct binding partner and mapped the interaction to the kinase catalytic domain, revealing a tripartite assembly with DCAF7/WDR68 and assigning FAM53C its first molecular role.

   Evidence Co-immunoprecipitation, pulldown, and domain-mapping assays

   PMID:37802655 PMID:42059432

   Open questions at the time

   • Structural basis of catalytic-domain binding not resolved
   • Stoichiometry of the tri-protein complex not defined
3. 2023 High

   Demonstrated that FAM53C binding is functionally inhibitory toward DYRK1A, showing it blocks both autophosphorylation and substrate (Tau) phosphorylation.

   Evidence In vitro kinase assay with purified proteins

   PMID:37802655

   Open questions at the time

   • Whether inhibition occurs at physiological stoichiometry in cells not established
   • Other DYRK1A substrates not tested
4. 2023 High

   Showed FAM53C acts as a cytoplasmic anchor, redistributing DYRK1A out of the nucleus and suppressing DYRK1A-driven nuclear accumulation of DCAF7/WDR68, linking complex formation to spatial control of the kinase.

   Evidence Fluorescence imaging of co-expressed proteins and subcellular fractionation

   PMID:37802655

   Open questions at the time

   • Reliance on overexpression for localization readouts
   • Mechanism of cytoplasmic retention unknown
5. 2023 Medium

   Extended FAM53C binding to the related kinase DYRK1B, indicating the interaction is not restricted to DYRK1A.

   Evidence Co-immunoprecipitation

   PMID:37802655

   Open questions at the time

   • Single Co-IP without functional follow-up
   • Effect on DYRK1B activity or localization untested
6. 2024 High

   Placed FAM53C in cell cycle control, demonstrating it is required for the G1/S transition upstream of the CyclinD-CDK4/6-RB axis and p53, with DYRK1A inhibition rescuing FAM53C-loss arrest to establish the epistatic relationship.

   Evidence Dependency Map analysis, siRNA knockdown, cell cycle FACS, pharmacological DYRK1A inhibition, and epistasis; organoid CRISPR knockout

   PMID:39713326 PMID:42059432

   Open questions at the time

   • Direct biochemical link between DYRK1A inhibition and CyclinD/p53 regulation not delineated
   • Whether cytoplasmic anchoring or kinase inhibition drives the cell cycle effect not separated

• How FAM53C-mediated DYRK1A sequestration mechanistically connects to the CyclinD-CDK4/6-RB and p53 nodes, and whether its originally predicted nuclear role is physiologically relevant, remain unresolved.
• No structural model of the FAM53C-DYRK1A interface
• Effectors bridging DYRK1A to CyclinD/p53 not identified
• Reconciliation of cytoplasmic function with predicted NLS-driven nuclear localization absent