ANKRD54

ANKRD54 (Liar) is a nucleocytoplasmic shuttling protein that functions as a selective SH3-domain-binding adaptor mediating Crm1-dependent nuclear export of specific signaling kinases. Its ankyrin repeat domain defines a novel SH3-binding interface that preferentially engages the SH3 domains of Btk and Lyn—with Btk SH3 selectivity confirmed across all 296 human SH3 domains—and it facilitates nuclear export of Btk and Txk/Rlk but not other nuclear proteins such as Abl, ERβ, or T-bet (PMID:22527282, PMID:28369144). PKCδ-mediated phosphorylation at Ser18 and neighboring N-terminal residues drives ANKRD54 cytoplasmic accumulation and enhances its co-localization and interaction with Lyn, linking kinase signaling to ANKRD54 subcellular distribution (PMID:28924458). In erythroid cells, ANKRD54 forms a complex with Lyn and HS1, and its ectopic expression inhibits erythroid differentiation while modulating Epo-activated signaling through Erk2, STAT5, Akt, and Lyn (PMID:19064729).

1. 2008 High

   The discovery that ANKRD54 is a Lyn-binding nucleocytoplasmic shuttling protein with functional NLS/NES established it as a novel adaptor linking SH3-mediated kinase interactions to nuclear-cytoplasmic trafficking and erythroid differentiation signaling.

   Evidence Yeast two-hybrid screen, co-immunoprecipitation, live-cell shuttling imaging, and ectopic expression in erythroid differentiation assays

   PMID:19064729

   Open questions at the time

   • Mechanism by which ANKRD54 inhibits erythroid differentiation not resolved at molecular level
   • Whether ANKRD54 shuttling is functionally required for its effects on Epo signaling not tested
   • Identity of kinase(s) regulating ANKRD54 localization unknown at this point
2. 2012 High

   Demonstrating that ANKRD54 directly exports Btk and Txk/Rlk from the nucleus via a Crm1-dependent mechanism—while selectively binding non-phosphorylated Btk SH3—resolved ANKRD54's role as a cargo-specific nuclear export adaptor for Tec-family kinases.

   Evidence Flag-Btk affinity purification with tandem MS, domain mapping with synthetic peptides, phosphomimetic SH3 mutagenesis, and Crm1 inhibition assays

   PMID:22527282

   Open questions at the time

   • Physiological consequence of Btk/Txk nuclear export by ANKRD54 on downstream signaling not established
   • Whether ANKRD54 acts catalytically (shuttling multiple Btk molecules) or stoichiometrically not determined
   • Structural basis of the ankyrin-repeat–SH3 interaction unresolved
3. 2017 High

   Comprehensive screening of all 296 human SH3 domains confirmed that ANKRD54 is a uniquely selective Btk SH3 binder, establishing the exceptional specificity of this adaptor interaction within the SH3 interactome.

   Evidence Phage-display screening of complete human SH3 domain library with quantitative western blot validation

   PMID:28369144

   Open questions at the time

   • Affinity constants for the ANKRD54–Btk SH3 interaction not quantified
   • Whether the selectivity extends to all Tec-family SH3 domains not fully tested
4. 2017 High

   Identification of PKCδ as the kinase that phosphorylates ANKRD54 at Ser18 to drive its cytoplasmic retention and enhanced Lyn interaction resolved the upstream signal controlling ANKRD54 subcellular distribution.

   Evidence Phos-tag gel retardation, MRM phosphoproteomics, site-directed alanine mutagenesis, immunofluorescence, and co-immunoprecipitation with active PKCδ overexpression

   PMID:28924458

   Open questions at the time

   • Whether PKCδ-mediated phosphorylation also affects ANKRD54–Btk interaction or Btk nuclear export not tested
   • Phosphatase responsible for ANKRD54 dephosphorylation not identified
   • In vivo relevance of PKCδ-ANKRD54 axis in hematopoietic cells not demonstrated

• The physiological requirement for ANKRD54 in vivo—including its role in immune cell signaling, erythropoiesis, and potential disease relevance—remains uncharacterized, as does the structural basis of its ankyrin-repeat–SH3 interaction.
• No knockout or knockdown studies in animal models reported
• No structural model (crystal or cryo-EM) of the ankyrin-repeat–SH3 complex
• Functional interplay between PKCδ phosphorylation and Btk export activity not addressed