THEMIS2

THEMIS2 is an immune signaling scaffold protein that modulates signal amplitude downstream of multiple receptor systems in B cells, macrophages, and NK cells. In macrophages and B cells, THEMIS2 constitutively or inducibly assembles complexes containing GRB2, Lyn kinase, and PLCγ2, enhancing ERK/p38 MAPK activation and lowering activation thresholds for BCR and TLR4 signaling (PMID:20644716, PMID:27992403). In NK cells, THEMIS2 recruits SHP-1/SHP-2 phosphatases via GRB2 to attenuate ZAP70/Syk phosphorylation downstream of activating receptors, and translocates to the nucleus to promote Zfp740-mediated transcriptional repression that limits memory NK cell differentiation (PMID:37938555, PMID:38619282). In cancer contexts, THEMIS2 functions as a scaffold that displaces PTP1B from MET to enhance MET phosphorylation and recruits TBK1 to DOCK4 to activate Rap1 signaling, promoting stemness, EMT, and metastasis (PMID:34974522, PMID:40227532).

1. 2010 High

   Establishing THEMIS2 as a signaling scaffold in innate immunity resolved how it connects TLR4 engagement to selective MAPK activation: THEMIS2 assembles a Lyn–Vav–GRB2 complex upon LPS stimulation and selectively amplifies ERK/p38 but not JNK or NF-κB signaling.

   Evidence Co-immunoprecipitation, site-directed mutagenesis of Y660 and PPPRPPK motif, RNAi knockdown in primary human macrophages and RAW 264.7 cells

   PMID:20644716

   Open questions at the time

   • Whether Lyn kinase directly phosphorylates THEMIS2 Y660 was not shown
   • How THEMIS2 selectively channels signal to ERK/p38 while sparing JNK is unclear
   • No structural basis for the scaffold assembly
2. 2012 High

   Demonstrating that THEMIS2 can functionally rescue T cell development in Themis1-knockout mice established the two family members as interchangeable scaffolds within GRB2/LAT signaling complexes, revealing functional conservation despite divergent expression patterns.

   Evidence Transgenic rescue of Themis1−/− mice with Themis2, biochemical analysis of GRB2/LAT complex recruitment and tyrosine phosphorylation

   PMID:22732588

   Open questions at the time

   • Whether THEMIS2 naturally participates in TCR signaling in wild-type T cells is untested
   • The molecular determinants enabling cross-family rescue are uncharacterized
3. 2014 High

   A comprehensive Themis2-knockout mouse study found no defect in B cell development or antibody responses, raising questions about redundancy or context-dependent roles despite confirmed BCR-induced phosphorylation and GRB2/Vav1 interactions.

   Evidence Themis2-deficient mice, flow cytometry, BCR stimulation, in vivo immunization with model antigens and influenza

   PMID:24907343

   Open questions at the time

   • Whether compensatory mechanisms mask THEMIS2 function in this knockout was not addressed
   • Only high-avidity antigens were tested
4. 2016 High

   Resolving the apparent dispensability found in 2014, a subsequent study showed THEMIS2 constitutively binds GRB2–Lyn–PLCγ2 and is required to lower the activation threshold for low-avidity antigens, explaining its role in positive selection of B1 and germinal center B cells.

   Evidence Co-immunoprecipitation of constitutive complex, Themis2-deficient mouse B cell signaling (PLCγ2 phosphorylation, calcium flux), in vivo immunization with graded antigen avidity

   PMID:27992403

   Open questions at the time

   • How THEMIS2 lowers PLCγ2 activation threshold mechanistically (e.g., proximity vs. conformational change) is unknown
   • Whether THEMIS2 affects BCR microclustering or receptor organization is untested
5. 2022 Medium

   In cancer, THEMIS2 was shown to function as a scaffold that physically displaces PTP1B from MET, preventing dephosphorylation and sustaining MET activation to promote cancer stemness.

   Evidence Co-immunoprecipitation showing PTP1B–MET dissociation upon THEMIS2 overexpression, phospho-MET analysis, knockdown/overexpression in TNBC lines with sphere formation and in vivo tumorigenicity assays

   PMID:34974522

   Open questions at the time

   • Whether THEMIS2 directly binds MET or acts through an intermediary is not resolved
   • Single-lab finding in TNBC cell lines
   • Whether this mechanism operates in non-cancer cells is unknown
6. 2023 High

   THEMIS2 was revealed to have a dual inhibitory role in NK cells: it attenuates ZAP70/Syk signaling downstream of activating receptor Ly49H and translocates to the nucleus to promote Zfp740-mediated transcriptional repression, limiting memory NK cell differentiation and host defense against MCMV.

   Evidence Themis2-deficient mouse NK cell signaling assays, nuclear fractionation, genetic epistasis with Zfp740 knockout, in vivo MCMV infection model

   PMID:37938555

   Open questions at the time

   • The mechanism of nuclear translocation (signal, importin dependency) is uncharacterized
   • Whether Zfp740 recruitment is direct or mediated by additional factors is unclear
   • Target genes of the THEMIS2–Zfp740 repression program are not fully defined
7. 2024 High

   Extending NK cell findings to human cells, THEMIS2 was shown to recruit SHP-1/SHP-2 phosphatases via GRB2 proximal to DNAM-1 and NKG2D receptors, establishing a conserved inhibitory checkpoint across activating NK receptors.

   Evidence Co-immunoprecipitation with SHP-1/SHP-2/GRB2, siRNA knockdown in primary human NK cells, Themis2-deficient mouse metastasis model

   PMID:38619282

   Open questions at the time

   • Whether THEMIS2 directly interacts with the cytoplasmic tails of DNAM-1/NKG2D or signals through adaptor chains is unknown
   • Therapeutic potential of THEMIS2 inhibition for NK cell-based immunotherapy is untested
8. 2025 Medium

   THEMIS2 was identified as a scaffold recruiting TBK1 to DOCK4, enabling TBK1-mediated phosphorylation of DOCK4 at S1787 and downstream CRKII/Rap1 activation to promote EMT and metastasis in ovarian cancer.

   Evidence IP-mass spectrometry interactome, GST pull-down for Rap1-GTP, phospho-site mapping, knockdown/overexpression with in vivo metastasis models and Rap1 inhibitor rescue

   PMID:40227532

   Open questions at the time

   • Single-lab observation in ovarian cancer
   • Whether the THEMIS2–TBK1–DOCK4 axis operates in immune cells is unknown
   • Structural basis for TBK1 recruitment by THEMIS2 is lacking

• Key unresolved questions include the structural basis for THEMIS2's multi-partner scaffold function, how signal-dependent nuclear translocation is regulated, and whether THEMIS2's immune-inhibitory role in NK cells can be therapeutically targeted.
• No crystal or cryo-EM structure of THEMIS2 or its CABIT domains in complex with partners
• Mechanism of nuclear import/export not defined
• Relative contribution of cytoplasmic signaling vs. nuclear transcriptional roles in NK cells is unresolved