DOK2

DOK2 is a broadly expressed adaptor protein that functions as a negative feedback regulator of Ras-ERK, PI3K-Akt, and NF-κB signaling downstream of diverse receptor and non-receptor tyrosine kinases in hematopoietic and epithelial cells. Upon tyrosine phosphorylation by upstream kinases such as Lyn, Tec, Bcr-Abl, and EGFR, DOK2 recruits RasGAP through its C-terminal phosphotyrosine motifs and assembles inhibitory complexes with SHIP-1 and Grb-2 at activated receptors including TCR/LAT, CD200R, TLR4, TLR2, and integrin αIIbβ3, thereby attenuating downstream MAPK activation, cytokine production, and cellular proliferation (PMID:15611294, PMID:15699069, PMID:17043143, PMID:19786546, PMID:24385425). PTB domain-mediated oligomerization (requiring Tyr139) and PH domain binding to phosphatidylinositol 5-phosphate are essential for DOK2 membrane recruitment and tyrosine phosphorylation in T cells (PMID:16177091, PMID:19299694). DOK2 acts as a tumor suppressor in lung adenocarcinoma, where it opposes EGFR-mutant-driven RAS activation, and its co-deletion with DUSP4 synergistically activates MAPK signaling to promote tumorigenesis (PMID:24255704, PMID:30475228).

1. 1998 High

   Identification of DOK2 as a multi-domain adaptor protein with RasGAP-binding capacity established that a second Dok-family member exists and is a substrate of Bcr-Abl, opening questions about its role in CML and Ras regulation.

   Evidence Protein purification, cDNA cloning, and co-immunoprecipitation in CML cells

   PMID:9478921

   Open questions at the time

   • No in vivo loss-of-function data
   • Physiological upstream activators beyond Bcr-Abl unknown
   • Functional consequence of RasGAP binding not tested
2. 2004 High

   Genetic ablation of Dok-1 and Dok-2 in mice demonstrated that these adaptors are non-redundant negative regulators of Ras-ERK signaling downstream of tyrosine kinases, with loss causing myeloproliferative disease—resolving whether RasGAP recruitment had physiological consequences.

   Evidence Dok-1/Dok-2 double knockout mice with myeloproliferative phenotype and elevated ERK/Akt activation, reproduced by two independent labs

   PMID:15611294 PMID:15611295

   Open questions at the time

   • Individual contributions of Dok-1 vs Dok-2 to the phenotype unresolved
   • Downstream effectors beyond ERK/Akt not mapped
   • No structural model of RasGAP recruitment
3. 2005 High

   Discovery that DOK2 is phosphorylated and inhibits ERK and TNF-α production downstream of TLR4, and that PTB-domain-mediated oligomerization is required for DOK2 function, revealed that DOK2 operates in innate immunity and that its self-assembly is mechanistically essential.

   Evidence Dok-2 KO macrophages with elevated TLR4 responses plus phosphorylation-dead mutant rescue; PTB domain mutagenesis in Jurkat T cells with ERK and NFAT readouts

   PMID:15699069 PMID:16177091

   Open questions at the time

   • Kinase responsible for DOK2 phosphorylation at TLR4 not identified
   • Oligomerization stoichiometry and structure undefined
   • Relative contribution of Dok-1 vs Dok-2 in macrophages unclear
4. 2006 High

   Identification of a DOK2–SHIP-1–Grb-2 complex at LAT after TCR stimulation, and DOK2's role in restraining ZAP-70 and Akt activation, established the adaptor as a core component of TCR negative signaling architecture.

   Evidence Co-immunoprecipitation and siRNA knockdown in primary T cells with Akt and ZAP-70 readouts; forced expression and KO mice confirming ZAP-70 regulation

   PMID:17043143 PMID:17329234

   Open questions at the time

   • How SHIP-1 promotes DOK2 recruitment to LAT mechanistically unresolved
   • C-terminal SH2-target motifs dispensable for ZAP-70 inhibition—alternative mechanism unknown
   • Whether DOK2 acts identically in CD4+ and CD8+ T cells untested
5. 2009 High

   Quantitative binding studies showed DOK2 is the preferred adaptor for CD200R's NPXY motif and is essential for CD200R-mediated myeloid inhibition via RasGAP recruitment, providing a receptor-specific non-redundant role distinct from Dok-1.

   Evidence Direct binding assay with Kd measurement, siRNA knockdown of Dok-2 vs Dok-1 in U937 cells with functional readouts

   PMID:19786546

   Open questions at the time

   • Whether DOK2 similarly dominates at other ITIM/NPXY-containing receptors unknown
   • No structural basis for the 10-fold affinity difference over Dok-1
6. 2009 Medium

   Demonstration that the PH domain binds PtdIns5P and that this lipid interaction regulates DOK2 tyrosine phosphorylation in T cells introduced a lipid-sensing step upstream of DOK2 activation.

   Evidence In vitro lipid binding assay and PH domain deletion with phosphorylation readouts in T cells

   PMID:19299694

   Open questions at the time

   • In vivo PtdIns5P–DOK2 interaction not confirmed by structural or live-cell methods
   • Whether PtdIns5P regulation applies in non-T cell contexts untested
   • Source kinase for PtdIns5P-dependent DOK2 phosphorylation not identified
7. 2013 High

   Identification of DOK2 as a negative feedback element opposing mutant EGFR in lung adenocarcinoma, where its loss accelerates EGFR-driven but not KRAS-driven tumorigenesis, positioned DOK2 as an EGFR-specific tumor suppressor.

   Evidence Genetically engineered mouse models with co-immunoprecipitation of DOK2–EGFR and RAS activation assays; epistasis with KRAS-mutant model

   PMID:24255704

   Open questions at the time

   • Whether DOK2 loss alone (without cooperating hits) suffices for tumorigenesis unknown
   • Mechanism of DOK2 silencing in human tumors (epigenetic vs genomic) not resolved
8. 2014 High

   Lyn was identified as the primary kinase phosphorylating DOK2 in platelets, and Dok-2 deficiency caused dysregulated integrin αIIbβ3-dependent calcium flux and enhanced thrombus formation, establishing DOK2 as a negative regulator of platelet activation and thrombosis.

   Evidence Dok-2 KO mice, Lyn inhibition/deficiency, calcium flux and PI(3,4)P2 measurement, in vivo thrombosis model

   PMID:24385425

   Open questions at the time

   • Direct substrates or downstream effectors of DOK2 in the integrin pathway not fully mapped
   • Whether Lyn→DOK2 axis operates in non-platelet hematopoietic cells not tested
9. 2018 High

   Compound haploinsufficiency of DOK2 and DUSP4—frequently co-deleted in human lung adenocarcinoma—synergistically activates MAPK signaling, demonstrating that DOK2's tumor-suppressive function is dosage-sensitive and cooperates with parallel phosphatase-mediated MAPK control.

   Evidence Compound heterozygous mouse models, DOK2 restoration in lung cancer cell lines, MAPK and proliferation assays

   PMID:30475228

   Open questions at the time

   • Whether restoration of DOK2 alone is sufficient for tumor regression in vivo unknown
   • Epigenetic regulation of DOK2 expression in human tumors not characterized

• Key unresolved questions include the structural basis for DOK2 oligomerization and receptor engagement, whether DOK2 has bona fide nuclear functions, and the full spectrum of cancers in which DOK2 loss is functionally consequential.
• No high-resolution structure of DOK2 or its complexes
• Nuclear localization and Klf1 ChIP finding from a single low-confidence study awaits independent replication
• Mechanism by which HSV-1 VP11/12 targets DOK2 for degradation and its immunological consequence remain unclear