ANKRD54

ANKRD54 (Liar) is an ankyrin repeat-containing nucleocytoplasmic shuttling protein that functions as a specificity adaptor controlling the subcellular distribution of SH3-domain-bearing tyrosine kinases (PMID:19064729, PMID:22527282). Its three ankyrin repeats constitute a non-canonical SH3-binding module, and unbiased phage-display screening of the entire human SH3 repertoire establishes the BTK SH3 domain as its prime interactor (PMID:28369144). Through this interaction ANKRD54 drives CRM1-dependent nuclear export of the Tec-family kinases BTK and Txk/Rlk, binding preferentially to non-phosphorylated kinase and discriminating against an activation-state-mimicking SH3 mutant, conferring selectivity over other nuclear proteins (PMID:22527282). ANKRD54 was originally isolated as a Lyn-interacting protein forming a complex with Lyn and HS1 in erythroid cells, where its ectopic expression perturbs erythropoietin-activated signaling (Erk2, STAT5, Akt, Lyn) and inhibits erythroid differentiation (PMID:19064729). Its own nuclear export and cytoplasmic accumulation are regulated by PKCδ-mediated phosphorylation at Ser18 within an N-terminal serine cluster, which also enhances its cytoplasmic association with Lyn (PMID:28924458).

1. 2008 Medium

   Establishing that ANKRD54/Liar physically links a Src-family kinase to a nucleocytoplasmic shuttling machinery answered whether ankyrin repeats could serve as a kinase-binding and trafficking module relevant to erythroid signaling.

   Evidence Yeast two-hybrid screen, reciprocal co-IP, nuclear export/fractionation assays, and ectopic overexpression with erythroid differentiation and Epo-signaling readouts

   PMID:19064729

   Open questions at the time

   • Did not define which kinase SH3 domain is the preferred ANKRD54 ligand
   • Mechanistic basis for differentiation inhibition versus shuttling not separated
   • Direct nuclear export carrier not identified
2. 2012 High

   Identifying BTK and Txk/Rlk as CRM1-dependent export cargoes and mapping the interaction to the kinase SH3 domain converted ANKRD54 from a binding partner into a defined export adaptor with activation-state selectivity.

   Evidence AP-MS of Flag-BTK, reciprocal co-IP, SH3 domain mutagenesis, synthetic peptide pulldown, and leptomycin B CRM1-inhibition assays

   PMID:22527282

   Open questions at the time

   • Physiological consequence of BTK/Txk nuclear export not established
   • Structure of the ankyrin-repeat:SH3 interface not solved
   • Whether export is constitutive or signal-regulated in B cells unclear
3. 2017 Medium

   Screening all 296 human SH3 domains answered whether BTK-SH3 selectivity was genuine or one of many partners, confirming BTK-SH3 as the prime interactor across the human SH3 repertoire.

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

   PMID:28369144

   Open questions at the time

   • In vitro selection may not reflect cellular partner availability
   • Affinity ranking of secondary SH3 partners not quantified
   • Functional outcome of preferential BTK binding not addressed
4. 2017 Medium

   Mapping PKCδ phosphorylation at Ser18 answered how ANKRD54's own localization is controlled, linking a signaling kinase to its cytoplasmic redistribution and enhanced Lyn association.

   Evidence MRM phosphopeptide proteomics, Phos-tag gels, alanine mutagenesis, PMA stimulation, fractionation/immunofluorescence, and co-IP in HEK293T cells

   PMID:28924458

   Open questions at the time

   • Whether PKCδ phosphorylation directly regulates kinase-cargo export not tested
   • Done in HEK293T rather than physiological lymphoid/erythroid context
   • Kinase responsible in vivo not confirmed beyond co-expression

• The physiological and disease relevance of ANKRD54-mediated kinase export in B-cell or erythroid biology remains undefined.
• No loss-of-function/knockout phenotype reported
• No structural model of the ankyrin:SH3 interaction
• Consequence of sequestering non-phosphorylated BTK in the nucleus versus cytoplasm unresolved