DOK5

DOK5 is a membrane-targeted docking/adapter protein that couples activated receptor tyrosine kinases to MAPK signaling in neuronal and developmental contexts (PMID:11470823, PMID:16647839). Its PH domain drives constitutive targeting to the plasma membrane and partitioning into membrane microdomains, while its PTB domain engages the NPQY/Y1062 motifs of c-Ret, TrkB, and TrkC in a kinase-activity-dependent manner, positioning DOK5 as a direct substrate of these receptors (PMID:11470823, PMID:16647839, PMID:18455289). Receptor engagement leads to DOK5 tyrosine phosphorylation and enhanced MAPK pathway activation; at the TrkB/C site DOK5 competes with N-Shc for binding, and a c-Ret/DOK5 fusion is sufficient to drive ligand-dependent axonal outgrowth in PC12 cells (PMID:11470823, PMID:16647839). DOK5 is also a substrate of the insulin and IGF-1 receptors but, unlike the related DOK4, does not associate with the canonical SH2-domain effectors RasGAP, Crk, Grb2, SHP-2, Nck, PI3K p85, or PLCγ (PMID:12730241). Functionally, DOK5 supports NT-3/TrkC survival signaling in dorsal root ganglia neurons (PMID:23954828) and is required for cardiomyocyte differentiation, where its transcription is repressed by FOXO3a acting downstream of PI3K/PKB signaling (PMID:19800350). DOK5 additionally acts downstream of IGFBP-5 to promote a pro-fibrotic, dermal-thickening program in fibroblasts (PMID:24551065).

1. 2001 High

   Established DOK5 as a c-Ret docking protein that positively couples receptor activation to MAPK signaling and neurite outgrowth, distinguishing it from the inhibitory DOK1/DOK2 adapters.

   Evidence Co-immunoprecipitation, direct binding assays, c-Ret/DOK5 fusion constructs, and PC12 neurite outgrowth and MAPK activation assays

   PMID:11470823

   Open questions at the time

   • Did not resolve which downstream effectors transmit the MAPK signal, since DOK5 lacks canonical SH2 effector binding
   • Structural basis of the Y1062 interaction not defined
2. 2002 Low

   Crystallization of the DOK5 PTB domain provided the structural reagent needed to understand receptor-motif recognition.

   Evidence Recombinant expression, vapor diffusion crystallization, and X-ray diffraction to 2.3 Å from a selenomethionine derivative

   PMID:12454490

   Open questions at the time

   • Preliminary diffraction report only; no functional or complex structure described
   • No co-crystal with a receptor phosphopeptide
3. 2003 Medium

   Identified DOK5 as a substrate of the insulin and IGF-1 receptors and defined its negative interaction profile, showing it does not engage the SH2 effectors used by other DOK family members.

   Evidence Transfection, tyrosine phosphorylation assays, SH2-domain binding panels, and MAPK activation assays

   PMID:12730241

   Open questions at the time

   • Effectors that DOK5 does recruit remain unidentified
   • Physiological relevance in insulin/IGF-1 signaling not tested beyond transfected cells
4. 2006 High

   Extended DOK5's receptor repertoire to neurotrophin receptors, showing PTB-domain binding to the TrkB/TrkC NPQY motif in a kinase-dependent manner and competition with N-Shc.

   Evidence Yeast two-hybrid, GST pulldown, Co-IP, mutagenesis, competition assays, and MAPK activation in differentiated PC12 cells

   PMID:16647839

   Open questions at the time

   • Selectivity against TrkA explained only descriptively
   • Quantitative balance between DOK5 and N-Shc occupancy in cells not determined
5. 2008 Medium

   Defined the membrane-targeting logic of DOK5, showing the PH domain is necessary for constitutive plasma membrane localization and microdomain partitioning.

   Evidence Single-molecule fluorescence microscopy of eYFP-tagged DOK5 and PH-domain variants in live CHO cells

   PMID:18455289

   Open questions at the time

   • Lipid ligand of the PH domain not identified
   • Single method and cell type
6. 2009 Medium

   Placed DOK5 transcription under negative control by FOXO3a downstream of PI3K/PKB and showed DOK5 is required for cardiomyocyte differentiation.

   Evidence Promoter truncation/mutation, EMSA, ChIP, FOXO3a overexpression, and siRNA knockdown with cardiomyocyte differentiation readout in P19CL6 cells

   PMID:19800350

   Open questions at the time

   • Receptor input driving DOK5's role in differentiation not identified
   • Mechanism linking DOK5 to the differentiation program not defined
7. 2013 Medium

   Demonstrated a survival function for DOK5 in NT-3/TrkC signaling in primary neurons, linking its receptor docking role to anti-apoptotic output.

   Evidence Co-IP, immunofluorescence colocalization, siRNA knockdown, and caspase-3 activity assays in DRG neurons and HEK293T apoptosis assays

   PMID:23954828

   Open questions at the time

   • Knockdown only partially abrogated protection, leaving parallel pathways unaccounted
   • Direct anti-apoptotic effectors downstream of DOK5 not identified
8. 2014 Medium

   Identified a pro-fibrotic role for DOK5 downstream of IGFBP-5, including transcriptional upregulation, nuclear translocation, and increased dermal thickness.

   Evidence Expression profiling, Western blot, siRNA/overexpression, nuclear translocation assay, human skin organ culture ex vivo, and in vivo mouse model

   PMID:24551065

   Open questions at the time

   • Function of nuclear DOK5 not mechanistically explained
   • Direct fibrotic targets downstream of DOK5 unidentified
9. 2022 Low

   Proposed DOK5 as a positive regulator of osteoblast proliferation and differentiation acting upstream of canonical Wnt/β-catenin signaling.

   Evidence Lentiviral knockdown, overexpression, CCK-8 proliferation, ALP/AR-S staining, Western blot, and RT-PCR

   PMID:35234166

   Open questions at the time

   • No direct binding or epistasis data confirming Wnt pathway placement
   • Single lab, no in vivo validation

• The downstream effectors that DOK5 recruits to transmit receptor signals to MAPK remain unidentified, given its lack of canonical SH2-effector binding.
• No DOK5-binding effector defined
• Phospho-tyrosine sites on DOK5 and their readers not mapped
• Function of nuclear-translocated DOK5 unknown