Affinage

DLK2

Protein delta homolog 2 · UniProt Q6UY11

Length
383 aa
Mass
40.5 kDa
Annotated
2026-04-28
15 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

DLK2 is a transmembrane EGF-like repeat protein that functions as a non-canonical inhibitory ligand of Notch signaling and a regulator of mesenchymal and myeloid cell differentiation. DLK2 directly binds the extracellular EGF-like repeat region of NOTCH1 and homodimerizes or heterodimerizes with DLK1, with DLK1 and DLK2 mutually antagonizing each other's Notch-inhibitory activity to fine-tune signaling output; this mechanism controls adipogenic and osteogenic differentiation of mesenchymal precursors and modulates melanoma cell proliferation (PMID:21419176, PMID:17320102, PMID:25093684, PMID:39473022). In osteoclasts, DLK2 interacts with Syap1 to activate Akt (Ser473), ERK1/2, and p38 MAPK signaling, and its deletion inhibits osteoclastogenesis in vitro and produces a high-bone-mass phenotype in vivo (PMID:37669921). Basal transcription of Dlk2 is driven by Sp1 through a TATA-less, GC-box-containing promoter, and is further upregulated by KLF4 during early adipogenesis (PMID:22185379, PMID:22306741).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2006 Medium

    The identification of DLK2 as a DLK1 paralog that modulates adipogenesis in an opposing manner established a new player in mesenchymal differentiation and revealed that DLK1 and DLK2 expression levels are coordinately regulated.

    Evidence Overexpression and knockdown in 3T3-L1 and C3H10T1/2 preadipocyte lines with adipogenesis assays

    PMID:17320102

    Open questions at the time
    • Mechanism by which DLK2 opposes DLK1 in adipogenesis was not resolved
    • Whether DLK2 acts through Notch or another pathway was unknown
    • In vivo relevance of the adipogenesis phenotype not tested
  2. 2011 High

    Demonstrating that DLK2 directly binds NOTCH1 EGF-like repeats, homodimerizes, and heterodimerizes with DLK1 provided the molecular basis for its Notch-inhibitory function and explained how DLK1 and DLK2 mutually modulate each other's signaling output.

    Evidence Reciprocal co-immunoprecipitation, NOTCH reporter assays, TACE-cleavage-resistant DLK1 mutant, multiple cell lines

    PMID:21419176

    Open questions at the time
    • Structural details of DLK2–NOTCH1 interaction not resolved
    • Stoichiometry and dynamics of DLK1/DLK2 heterodimers unknown
    • Whether DLK2 also interacts with NOTCH2/3/4 was not addressed
  3. 2011 Medium

    Mapping the Dlk2 promoter and identifying Sp1 as a direct transcriptional activator defined the basal transcriptional control of the gene and its TATA-less, CpG-island architecture.

    Evidence 5′ RACE, ChIP for Sp1, promoter deletion and luciferase reporter assays, Sp1 overexpression/knockdown

    PMID:22185379

    Open questions at the time
    • Whether DNA methylation of the CpG island regulates DLK2 expression was not tested
    • Tissue-specific transcription factors beyond Sp1 were not examined
  4. 2012 Medium

    Showing that KLF4 directly activates the Dlk2 promoter during IBMX-induced early adipogenesis connected DLK2 transcription to external differentiation cues and placed it downstream of a key adipogenic transcription factor.

    Evidence ChIP for KLF4, luciferase reporter assay, KLF4 knockdown during C3H10T1/2 adipogenesis

    PMID:22306741

    Open questions at the time
    • Whether KLF4 regulation of DLK2 is sufficient to explain IBMX-driven Notch modulation is unclear
    • Upstream signaling from IBMX to KLF4 to DLK2 not fully dissected
  5. 2014 Medium

    Establishing that DLK2-mediated Notch inhibition controls melanoma cell proliferation in vitro and in vivo extended DLK2's functional relevance beyond normal differentiation to cancer biology and showed additive effects with γ-secretase inhibition.

    Evidence Overexpression/knockdown in SK-MEL-2 cells, NOTCH reporter assays, proliferation assays, xenograft model, DAPT treatment

    PMID:25093684

    Open questions at the time
    • Generalizability across melanoma subtypes or other tumor types not tested
    • Mechanism linking graded Notch inhibition to proliferative outcome not defined at the transcriptional target level
  6. 2017 Medium

    Dlk2 knockout mice revealed an unexpected in vivo role in anxiety- and depression-related behaviors, with altered Notch target and stress-axis gene expression in the brain, expanding DLK2 function to the central nervous system.

    Evidence Dlk2 knockout mice, behavioral assays, gene expression profiling in brain regions

    PMID:28863347

    Open questions at the time
    • Cell-type-specific role of DLK2 in the brain not determined
    • Whether behavioral phenotypes are Notch-dependent or Notch-independent is unknown
    • Mechanism linking DLK2 loss to GABAergic receptor subunit changes not established
  7. 2023 High

    Identifying Syap1 as a direct DLK2 interaction partner that mediates Akt/ERK/p38 activation during osteoclastogenesis revealed a Notch-independent signaling axis for DLK2 and explained the high-bone-mass phenotype in Dlk2 knockout mice.

    Evidence Co-immunoprecipitation of DLK2–Syap1, osteoclast-specific Dlk2 knockout, in vitro differentiation assays, in vivo bone phenotyping including ovariectomy model, phosphorylation western blots

    PMID:37669921

    Open questions at the time
    • How DLK2–Syap1 interaction activates Akt phosphorylation at Ser473 is mechanistically undefined
    • Whether DLK2–Syap1 interaction is relevant outside osteoclasts is untested
    • Relative contributions of Notch-dependent vs. Syap1-dependent DLK2 signaling in bone homeostasis not dissected
  8. 2024 Medium

    Demonstrating that DLK2 promotes osteogenic differentiation (opposing DLK1) with concomitant ERK1/2 MAPK activation unified the adipogenic and osteogenic phenotypes under a model where DLK2 steers mesenchymal lineage fate through coordinated Notch and MAPK modulation.

    Evidence DLK1/DLK2 overexpression and knockdown in C3H10T1/2 cells, osteogenic differentiation assays, DAPT treatment, western blots for ERK1/2 and p38 phosphorylation

    PMID:39473022

    Open questions at the time
    • Whether ERK activation during osteogenesis requires Syap1 or another adaptor is unknown
    • In vivo osteoblast-specific DLK2 function not confirmed by conditional knockout

Open questions

Synthesis pass · forward-looking unresolved questions
  • The mechanism by which DLK2 integrates its Notch-inhibitory and Syap1/MAPK-activating functions to control lineage-specific differentiation outcomes, and whether these pathways operate independently or converge, remains unresolved.
  • No structural model of DLK2–NOTCH1 or DLK2–Syap1 complexes exists
  • Relative contribution of Notch-dependent vs. MAPK-dependent DLK2 signaling in each cell type is undefined
  • Conditional tissue-specific knockout studies for osteoblasts and neural lineages are lacking

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0098772 molecular function regulator activity 3 GO:0048018 receptor ligand activity 1
Localization
GO:0005886 plasma membrane 2
Pathway
R-HSA-162582 Signal Transduction 4 R-HSA-1266738 Developmental Biology 3
Partners
DLK1KLF4NOTCH1SP1SYAP1

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2006 DLK2 (EGFL9) protein, highly homologous to DLK1 in structural features, modulates adipogenesis of 3T3-L1 preadipocytes and mesenchymal C3H10T1/2 cells in an opposite manner to DLK1; enforced changes in expression of one gene affect expression levels of the other, indicating coordinated regulation. Overexpression and knockdown in 3T3-L1 and C3H10T1/2 cell lines, adipogenesis assays Journal of molecular biology Medium 17320102
2011 DLK2 interacts with itself (homodimerizes), with DLK1, and with the same extracellular EGF-like repeat region of NOTCH1 receptor as DLK1; this interaction inhibits basal NOTCH signaling in preadipocytes and mouse embryo fibroblasts. Overexpression of DLK1 reverses NOTCH inhibition induced by DLK2, and vice versa, demonstrating mutual modulation. Co-immunoprecipitation, overexpression in cell lines, NOTCH reporter assays, use of TACE-cleavage-resistant DLK1 variant Biochimica et biophysica acta High 21419176
2011 Sp1 transcription factor directly binds to the Dlk2 promoter and activates its transcription; the Dlk2 gene has a TATA-less promoter with GC-boxes and a CpG island; transcription start site was mapped by 5' RACE. 5' RACE, promoter deletion analysis, ChIP, Sp1 overexpression/knockdown, luciferase reporter assay BMC molecular biology Medium 22185379
2012 KLF4 transcription factor directly binds to the Dlk2 promoter and increases Dlk2 expression in response to IBMX during early adipogenesis of 3T3-L1 cells; KLF4 knockdown downregulates Dlk2 promoter transcriptional activity and is required for adipogenic differentiation of C3H10T1/2 cells. ChIP, KLF4 overexpression and knockdown, luciferase reporter assay, adipogenesis assays Journal of molecular biology Medium 22306741
2014 DLK2 inhibits NOTCH1 signaling in SK-MEL-2 metastatic melanoma cells, and the level of NOTCH inhibition by DLK proteins determines proliferation rate: high NOTCH inhibition decreases, while lower inhibition increases, melanoma cell proliferation both in vitro and in vivo. DLK proteins and the γ-secretase inhibitor DAPT show additive effects on cell proliferation. Overexpression and knockdown in SK-MEL-2 cells, NOTCH reporter assays, proliferation assays in vitro and xenograft in vivo Biochimica et biophysica acta Medium 25093684
2017 Dlk2 deletion in mice increases vulnerability to anxiety-like and depressive-like behaviors, alters expression of NOTCH pathway targets (Hes1, Hes5, Hey1), stress axis genes (Crh, Nr3c1, Fkbp5), and GABAergic receptor subunits (Gabra2, Gabrg2), and abolishes the anxiolytic effect of alprazolam. Dlk2 knockout mice, behavioral assays (anxiety, depression), gene expression analysis in specific brain regions Psychoneuroendocrinology Medium 28863347
2023 DLK2 interacts with synapse-associated protein 1 (Syap1), and this interaction is required for Syap1-mediated phosphorylation of Akt at Ser473 and activation of ERK1/2 and p38 signaling cascades during osteoclast formation; Dlk2 deletion inhibits osteoclast formation in vitro and produces a high-bone-mass phenotype in vivo, including in ovariectomized mice. Co-immunoprecipitation (Dlk2–Syap1 interaction), Dlk2 knockout in osteoclast-specific context, in vitro osteoclast differentiation assays, in vivo bone phenotype analysis, phosphorylation western blots Cell death & disease High 37669921
2024 DLK2 promotes osteogenic differentiation of mesenchymal C3H10T1/2 cells (in contrast to DLK1 which inhibits it), coinciding with increased ERK1/2 MAPK phosphorylation; DLK2 overexpression modulates NOTCH signaling and MAPK pathway phosphorylation during osteoblast differentiation. Overexpression and knockdown of DLK1/DLK2 in C3H10T1/2 cells, osteogenic differentiation assays, DAPT treatment, western blots for ERK1/2 and p38 MAPK phosphorylation Biological research Medium 39473022

Source papers

Stage 0 corpus · 15 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2011 The EGF-like proteins DLK1 and DLK2 function as inhibitory non-canonical ligands of NOTCH1 receptor that modulate each other's activities. Biochimica et biophysica acta 86 21419176
2006 The novel gene EGFL9/Dlk2, highly homologous to Dlk1, functions as a modulator of adipogenesis. Journal of molecular biology 48 17320102
2019 EGFL9 promotes breast cancer metastasis by inducing cMET activation and metabolic reprogramming. Nature communications 40 31695034
2017 Comprehensive Analysis of DWARF14-LIKE2 (DLK2) Reveals Its Functional Divergence from Strigolactone-Related Paralogs. Frontiers in plant science 38 28970845
2014 The proteins DLK1 and DLK2 modulate NOTCH1-dependent proliferation and oncogenic potential of human SK-MEL-2 melanoma cells. Biochimica et biophysica acta 34 25093684
2020 DLK2 regulates arbuscule hyphal branching during arbuscular mycorrhizal symbiosis. The New phytologist 24 32966595
2017 Therapeutic efficacy of combined vaccination against tumor pericyte-associated antigens DLK1 and DLK2 in mice. Oncoimmunology 22 28405524
2012 DLK2 is a transcriptional target of KLF4 in the early stages of adipogenesis. Journal of molecular biology 20 22306741
2017 Deletion of Dlk2 increases the vulnerability to anxiety-like behaviors and impairs the anxiolytic action of alprazolam. Psychoneuroendocrinology 11 28863347
2019 Similarities and differences in tissue distribution of DLK1 and DLK2 during E16.5 mouse embryogenesis. Histochemistry and cell biology 10 30888503
2023 Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation. Cell death & disease 7 37669921
2011 Characterization of a proximal Sp1 response element in the mouse Dlk2 gene promoter. BMC molecular biology 7 22185379
2024 DLK1 and DLK2, two non-canonical ligands of NOTCH receptors, differentially modulate the osteogenic differentiation of mesenchymal C3H10T1/2 cells. Biological research 4 39473022
2022 Crystal structure of Arabidopsis DWARF14-LIKE2 (DLK2) reveals a distinct substrate binding pocket architecture. Plant direct 4 36172078
2025 EGFL9 regulates the growth and metastasis of hepatocellular carcinoma through EGFR/PI3K/AKT signaling pathway and amino acid modulation. Discover oncology 0 41003932