Affinage

SAMSN1

SAM domain-containing protein SAMSN-1 · UniProt Q9NSI8

Length
373 aa
Mass
41.7 kDa
Annotated
2026-04-28
18 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

SAMSN1 is a multi-domain immunoinhibitory adaptor protein that negatively regulates lymphocyte and myeloid cell signaling through diverse protein–protein interactions. Its SH3 domain binds cortactin to control Rac1-dependent actin dynamics and cell spreading, engages the inhibitory receptor PirB/ITIM3 in competition with SHP2, and in macrophages stabilizes GAB1 to activate PKA/AMPKα2 signaling (PMID:21296879, PMID:33188360, PMID:35981417). Phosphorylation-dependent 14-3-3 binding retains SAMSN1 in the cytoplasm, whereas nuclear SAMSN1 associates with the SAP30/HDAC1 complex to regulate gene expression; in macrophages it also binds KEAP1 to liberate NRF2, driving transcription of coinhibitory molecules that suppress T-cell function (PMID:20478393, PMID:40293473). Genetic deletion in B cells augments BCR signaling and humoral responses, while NK cell–specific loss enhances granzyme B production and antitumor cytotoxicity, establishing SAMSN1 as a broad immune checkpoint (PMID:19923443, PMID:41565668).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2001 Medium

    Identification of SAMSN1 as an SH3- and SAM-domain adaptor with cell-type-dependent subcellular distribution established the basic architecture and raised the question of how localization is regulated.

    Evidence Immunostaining, cellular fractionation, and domain analysis in B-lineage and mast cells

    PMID:11536050 PMID:11594764

    Open questions at the time
    • No binding partners identified
    • Mechanism controlling nuclear vs. cytoplasmic localization unknown
    • Functional consequence of either localization uncharacterized
  2. 2004 High

    Demonstrating that SAMSN1 is induced by IL-4/STAT6 in B cells and binds the inhibitory receptor PirB placed it within an immunoinhibitory signaling axis downstream of cytokine and BCR stimulation.

    Evidence Immunoblot, signaling inhibitors, in vitro binding assay in primary B cells

    PMID:15381729

    Open questions at the time
    • In vivo relevance of PirB interaction not tested
    • Domain mediating PirB interaction not mapped
  3. 2009 High

    Genetic knockout revealed SAMSN1 as a bona fide negative regulator of BCR signaling, resolving whether it is stimulatory or inhibitory in B cells.

    Evidence Hacs1−/− mice with phosphotyrosine immunoblot, proliferation, and humoral response assays

    PMID:19923443

    Open questions at the time
    • Downstream phosphatase or kinase target not identified
    • Whether phenotype is cell-intrinsic not fully resolved
  4. 2010 High

    Discovery that phosphorylation creates a 14-3-3 binding site to retain SAMSN1 in the cytoplasm, while nuclear SAMSN1 engages SAP30/HDAC1, explained how its localization is regulated and linked it to chromatin-level gene control.

    Evidence Phosphorylation mapping, co-immunoprecipitation with 14-3-3 and SAP30/HDAC1, HDAC activity assay

    PMID:20478393

    Open questions at the time
    • Kinase responsible for the regulatory phosphorylation not identified
    • Target genes controlled via HDAC1 not defined
  5. 2011 High

    Mapping the SH3 domain–cortactin interaction and its requirement for Rac1-dependent membrane ruffling established a cytoskeletal effector mechanism and explained the B-cell spreading defect in SAMSN1 transgenic mice.

    Evidence Reciprocal co-IP, domain mutagenesis, Rac1 inhibition, transgenic B-cell spreading assays

    PMID:21296879

    Open questions at the time
    • How cortactin engagement activates Rac1 not delineated
    • Relevance of actin remodeling to immune inhibition unclear
  6. 2020 High

    NMR structural mapping of the SAMSN1 SH3–PirB ITIM3 interface at atomic resolution, with affinity comparable to SHP2, explained how SAMSN1 could compete with SHP2 for inhibitory receptor engagement.

    Evidence NMR chemical shift perturbation, SPR affinity measurement, molecular modeling

    PMID:33188360

    Open questions at the time
    • Competition with SHP2 not validated in living cells
    • Functional consequence of displacing SHP2 from PirB not shown
  7. 2022 High

    In macrophages, SAMSN1 was shown to stabilize GAB1 and activate PKA/AMPKα2 in a SHP2-dependent manner, extending its function beyond lymphocytes to myeloid anti-inflammatory signaling.

    Evidence Macrophage-specific KO and transgenic mice, Co-IP, LPS-induced acute lung injury model

    PMID:35981417

    Open questions at the time
    • Mechanism by which SAMSN1 prevents GAB1 degradation not defined
    • Whether GAB1 axis operates in lymphocytes unknown
  8. 2023 Medium

    Identification of Brn4 as a direct transcriptional activator of Samsn1 that mediates neural stem cell differentiation expanded SAMSN1 function beyond the immune system.

    Evidence ChIP, luciferase reporter, siRNA knockdown, EdU incorporation in hippocampal neural stem cells

    PMID:37091532

    Open questions at the time
    • Downstream effector pathway in neural stem cells not mapped
    • Single-lab finding in one cell model
    • Whether immune-relevant SAMSN1 partners operate in neural cells unknown
  9. 2025 Medium

    SAMSN1 was found to bind KEAP1, releasing NRF2 to drive transcription of coinhibitory molecules (CD48/CD86/CEACAM1) in macrophages, providing a direct mechanism for SAMSN1-mediated T-cell exhaustion.

    Evidence CRISPR KO in RAW264.7, KO mice, Co-IP of SAMSN1–KEAP1, T-cell co-culture

    PMID:40293473

    Open questions at the time
    • Single-lab finding not yet independently replicated
    • Structural basis of SAMSN1–KEAP1 interaction not characterized
    • Whether this axis operates in other antigen-presenting cells unknown
  10. 2026 High

    NK cell–specific conditional deletion established SAMSN1 as an NK cell immune checkpoint that suppresses granzyme B and antitumor cytotoxicity, broadening its role from adaptive to innate lymphocyte regulation.

    Evidence Samsn1f/f-Ncr1Cre+ conditional KO, orthotopic HCC model, scRNA-seq, flow cytometry

    PMID:41565668

    Open questions at the time
    • Direct molecular target suppressing granzyme B transcription/translation not identified
    • Whether therapeutic anti-SAMSN1 strategies are feasible in human NK cells unknown

Open questions

Synthesis pass · forward-looking unresolved questions
  • The kinase(s) controlling SAMSN1 phosphorylation and 14-3-3 retention, the target genes regulated via SAP30/HDAC1, and whether the KEAP1–NRF2 and GAB1 axes converge in the same cell types remain unresolved.
  • No kinase identified for the regulatory phosphorylation site
  • HDAC1-dependent target genes not defined
  • Integration of KEAP1/NRF2 and GAB1/PKA pathways not tested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 5
Localization
GO:0005634 nucleus 2 GO:0005829 cytosol 2
Pathway
R-HSA-168256 Immune System 6 R-HSA-162582 Signal Transduction 3
Partners
CORTGAB1HDAC1KEAP1PIRBSAP30YWHAB
Complex memberships
SAP30/HDAC1 complex

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 HACS1 (SAMSN1) encodes a 441 amino acid adaptor protein containing an SH3 domain (most similar to Crk) and a SAM domain, and is localized predominantly to the cytoplasm as determined by immunostaining and cellular fractionation. Immunostaining and cellular fractionation; domain analysis Oncogene Medium 11536050
2001 Nash1 (SAMSN1), which contains a nuclear localization signal (NLS), SAM, and SH3 domain, localizes to the nucleus in mast cells, consistent with its NLS. Subcellular localization by immunostaining/reporter assay Biochemical and biophysical research communications Medium 11594764
2004 HACS1 (SAMSN1) is up-regulated by IL-4 in B cells through a STAT6-dependent mechanism that can also be impaired by inhibitors of PI3K, PKC, and NF-κB; HACS1 associates with tyrosine-phosphorylated proteins after B cell activation and binds in vitro to the inhibitory receptor paired Ig-like receptor B (PirB). Immunoblot, signaling inhibitor experiments, in vitro binding assay, siRNA knockdown, overexpression The Journal of experimental medicine High 15381729
2009 Hacs1 (SAMSN1) functions as an immunoinhibitory adaptor in B cells; Hacs1-/- mice (with SH3 and SAM domains deleted) show increased global tyrosine phosphorylation including Lyn and Akt kinases, increased BCR-stimulated proliferation, and enhanced humoral responses, placing HACS1 as a negative regulator of BCR signaling. Genetic knockout mouse model, phosphotyrosine immunoblot, flow cytometry, immunization assays FASEB journal High 19923443
2010 SLy2 (SAMSN1) is phosphorylated and directly interacts with 14-3-3 proteins via a phosphorylation site, which retains phosphorylated SLy2 in the cytoplasm to control nucleo-cytoplasmic shuttling. In the nucleus, SLy2 interacts with the SAP30/HDAC1 complex and regulates HDAC1 activity. Immunoprecipitation, phosphorylation mapping, subcellular fractionation, HDAC activity assay The international journal of biochemistry & cell biology High 20478393
2011 SLy2 (SAMSN1) induces Rac1-dependent membrane ruffle formation and regulates cell spreading and polarization; the SH3 domain is essential for these effects and directly interacts with the actin nucleation-promoting factor cortactin; SLy2-transgenic B cells are severely defective in cell spreading. Transgenic mouse overexpression, immunoprecipitation, confocal microscopy, Rac1 inhibition, domain mutagenesis The Journal of biological chemistry High 21296879
2014 SLy2 (SAMSN1) overexpression attenuates IL-5 receptor α chain expression on B-1 cells, resulting in decreased B-1 cell numbers and decreased differentiation into antibody-secreting cells. Transgenic mouse model, flow cytometry, ELISA European journal of immunology Medium 25330943
2020 The HACS1 (SAMSN1) SH3 domain binds a sequence near the third ITIM (ITIM3) of paired immunoglobulin receptor B (PIRB) with micromolar affinity comparable to SHP2 N-SH2, using an atypical binding mode mapped by NMR chemical shift perturbation; molecular modeling suggests HACS1 SH3 and SHP2 SH2 cannot simultaneously bind PIRB ITIM3. Surface plasmon resonance, NMR structure determination, chemical shift mapping, molecular modeling Communications biology High 33188360
2022 Macrophage SAMSN1 directly binds to GAB1 to prevent its protein degradation, subsequently enhancing PKA/AMPKα2 activation in a SHP2-dependent manner; this pathway mediates protection against LPS-induced inflammation and acute lung injury. Macrophage-specific KO and transgenic mice, co-immunoprecipitation, bone marrow transplantation, adoptive transfer, in vitro BMDM assays Redox biology High 35981417
2023 Brn4 transcription factor binds to the Samsn1 promoter and upregulates its expression; Samsn1 mediates Brn4-induced inhibition of hippocampal neural stem cell proliferation and promotion of neuronal differentiation. ChIP, dual luciferase reporter assay, RNA-seq, siRNA knockdown, EdU incorporation, immunofluorescence Stem cells international Medium 37091532
2025 In macrophages, SAMSN1 binds to KEAP1, causing NRF2 to dissociate from the KEAP1-NRF2 complex and translocate into the nucleus, promoting transcription of coinhibitory molecules CD48/CD86/CEACAM1 that bind receptors 2B4/CD152/TIM3 on T cells and induce T-cell exhaustion. CRISPR/Cas9 KO in RAW264.7, KO mice, flow cytometry, co-immunoprecipitation, primary cell co-culture Chinese medical journal Medium 40293473
2026 SAMSN1 functions as an NK cell checkpoint in hepatocellular carcinoma; NK cell-specific deletion of Samsn1 reduces tumor burden and enhances granzyme B production, demonstrating SAMSN1 suppresses NK cell activation, proliferation, and granzyme B production in the tumor microenvironment. NK cell-specific conditional KO mice (Samsn1f/f-Ncr1Cre+), orthotopic tumor model, scRNA-seq, flow cytometry Nature communications High 41565668

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 HACS1 encodes a novel SH3-SAM adaptor protein differentially expressed in normal and malignant hematopoietic cells. Oncogene 57 11536050
2004 The SH3-SAM adaptor HACS1 is up-regulated in B cell activation signaling cascades. The Journal of experimental medicine 51 15381729
2014 SAMSN1 is a tumor suppressor gene in multiple myeloma. Neoplasia (New York, N.Y.) 43 25117979
2022 Macrophage SAMSN1 protects against sepsis-induced acute lung injury in mice. Redox biology 29 35981417
2011 Immunoinhibitory adapter protein Src homology domain 3 lymphocyte protein 2 (SLy2) regulates actin dynamics and B cell spreading. The Journal of biological chemistry 26 21296879
2009 Enhanced adaptive immunity in mice lacking the immunoinhibitory adaptor Hacs1. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 24 19923443
2015 Suppression of SAMSN1 Expression is Associated with the Malignant Phenotype of Hepatocellular Carcinoma. Annals of surgical oncology 18 25805236
2001 Identification of Nash1, a novel protein containing a nuclear localization signal, a sterile alpha motif, and an SH3 domain preferentially expressed in mast cells. Biochemical and biophysical research communications 18 11594764
2010 SLy2 targets the nuclear SAP30/HDAC1 complex. The international journal of biochemistry & cell biology 15 20478393
2020 Characterization of the role of Samsn1 loss in multiple myeloma development. FASEB bioAdvances 8 32923989
2014 SLy2 controls the antibody response to pneumococcal vaccine through an IL-5Rα-dependent mechanism in B-1 cells. European journal of immunology 7 25330943
2020 SLy2-deficiency promotes B-1 cell immunity and triggers enhanced production of IgM and IgG2 antibodies against pneumococcal vaccine. Immunity, inflammation and disease 5 33098380
2020 HACS1 signaling adaptor protein recognizes a motif in the paired immunoglobulin receptor B cytoplasmic domain. Communications biology 5 33188360
2025 SAMSN1 causes sepsis immunosuppression by inducing macrophages to express coinhibitory molecules that cause T-cell exhaustion via KEAP1-NRF2 signaling. Chinese medical journal 4 40293473
2023 Lama2 And Samsn1 Mediate the Effects of Brn4 on Hippocampal Neural Stem Cell Proliferation and Differentiation. Stem cells international 3 37091532
2022 Suppression of SAMSN1 contributes to neuroprotection in neonatal rats suffering from hypoxic-ischemic encephalopathy injury. Ibrain 3 37786523
2021 SLy2-overexpression impairs B-cell development in the bone marrow and the IgG response towards pneumococcal conjugate-vaccine. Immunity, inflammation and disease 3 33592135
2026 SAMSN1 restrains NK cell mediated anti-tumor immunity in hepatocellular carcinoma. Nature communications 0 41565668