{"gene":"MAP4K1","run_date":"2026-06-10T02:59:50","timeline":{"discoveries":[{"year":1996,"finding":"HPK1 (MAP4K1) is a Ste20-related serine/threonine kinase that directly binds and phosphorylates MEKK1, and activates JNK1 specifically; JNK1 activation by HPK1 is inhibited by dominant-negative MEKK1 or MKK4/SEK1 mutants, placing HPK1 upstream of MEKK1→MKK4→JNK1 in the JNK/SAPK pathway. Unlike PAK65, HPK1 does not bind Rac1 or Cdc42, indicating Rac1/Cdc42-independent activation.","method":"Transient transfection assays with dominant-negative mutants, direct in vitro binding and phosphorylation assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro phosphorylation assay plus dominant-negative epistasis, replicated across two independent labs (PMID:8824585 and PMID:9003777)","pmids":["8824585","9003777"],"is_preprint":false},{"year":1996,"finding":"HPK1 specifically activates the SAPK/JNK pathway but not p38/RK or ERK; activation requires a functional HPK1 kinase domain and proceeds via the mixed lineage kinase MLK-3 and the SAPK activator SEK1.","method":"Transfection in COS1 cells with kinase-inactive mutants and dominant-negative pathway components","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple dominant-negative epistasis experiments, replicated with complementary data from PMID:8824585","pmids":["9003777"],"is_preprint":false},{"year":1997,"finding":"TAK1 acts downstream of HPK1 and upstream of MKK4/SEK1 in a HPK1→TAK1→MKK4/SEK1→JNK kinase cascade; a kinase-defective TAK1 mutant suppressed HPK1-induced JNK activity, while dominant-negative MEKK1 and MLK3 did not inhibit TAK1-induced JNK, indicating TAK1 is an alternative HPK1 downstream effector independent of MEKK1/MLK3.","method":"Transient transfection assays with dominant-negative and constitutively active mutants of TAK1, MEKK1, MLK3, and MKK4/SEK1","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal dominant-negative and constitutively active mutant epistasis experiments in a single study","pmids":["9278437"],"is_preprint":false},{"year":1997,"finding":"The SH3 domains of Grb2 bind to specific proline-rich motifs in the HPK1 C-terminal tail, forming a stable Grb2·HPK1 complex in transfected cells. EGF stimulation recruits the Grb2·HPK1 complex to the autophosphorylated EGF receptor and to Shc. Multiple activated receptor and cytoplasmic tyrosine kinases (including EGFR) stimulate tyrosine phosphorylation of HPK1, demonstrating SH2/SH3 adaptor-mediated cross-talk between tyrosine kinase and HPK1 pathways.","method":"In vitro SH3-domain binding assay, co-immunoprecipitation in transfected COS1 cells, EGF stimulation experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus in vitro binding assay with multiple tyrosine kinases, single lab","pmids":["9346925"],"is_preprint":false},{"year":1998,"finding":"HPK1 binds selectively to the first SH3 domains of c-Crk and CRKL via proline-rich motifs in its C-terminal non-catalytic portion; in vitro and in vivo Crk/CRKL–HPK1 complexes were detected by co-immunoprecipitation. HPK1 phosphorylates c-Crk II and CRKL in vitro, suggesting HPK1 can regulate adaptor protein function downstream.","method":"In vitro SH3-domain binding assays with >25 SH3 domains, co-immunoprecipitation of endogenous proteins, in vitro kinase assay","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus co-IP with endogenous proteins, single lab but multiple orthogonal methods","pmids":["9788432"],"is_preprint":false},{"year":1999,"finding":"HPK1 is cleaved by caspase-3 during apoptosis at the conserved DDVD site (Asp385), separating the N-terminal kinase domain from the C-terminal regulatory domain. Caspase-3 cleavage enhances HPK1 kinase activity. The N-terminal cleavage product fails to bind adaptors Grb2 and Crk, while the C-terminal fragment binds them less efficiently than full-length HPK1.","method":"In vitro caspase-3 cleavage assay, site-directed mutagenesis of Asp385, in vivo/in vitro cleavage assays, co-immunoprecipitation","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with recombinant caspase-3, mutagenesis identifying exact cleavage site, and functional co-IP studies","pmids":["10602493"],"is_preprint":false},{"year":1999,"finding":"HPK1 activates both IKK-alpha and IKK-beta, which phosphorylate IκB constitutively (IKK-beta) or upon stimulation (IKK-alpha), placing HPK1 upstream of the IκB/NF-κB pathway via a HPK1–MEKK1 stress response signaling pathway.","method":"Transient transfection with HPK1 and MEKK1 constructs, IKK kinase activity assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — overexpression kinase assay in single lab without mutagenesis confirmation of direct interaction","pmids":["10523828"],"is_preprint":false},{"year":2000,"finding":"TCR or BCR engagement induces HPK1 catalytic activity; Src and Syk/ZAP-70 tyrosine kinases and adaptor proteins LAT, SLP-76, BLNK, Grb2, and Grap are required for HPK1 activation. Overexpression of HPK1 inhibits TCR-induced AP-1 and ERK2 activation, while kinase-inactive HPK1 potentiates these responses, establishing HPK1 as a negative regulator of the TCR-induced AP-1 pathway.","method":"Antigen receptor stimulation assays, overexpression and kinase-inactive mutant transfections in T and B cells","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal gain/loss-of-function with kinase-dead mutant and multiple adaptor knockouts, replicated in both TCR and BCR settings","pmids":["10795738"],"is_preprint":false},{"year":2001,"finding":"Caspase-mediated cleavage of HPK1 converts it from an activator to an inhibitor of NF-κB. Full-length, kinase-active HPK1 activates NF-κB via IKKβ (independently of SAPK/JNK); the isolated kinase domain activates SAPK/JNK but not NF-κB. The C-terminal cleavage fragment (HPK1-C) inhibits NF-κB by dominant-negative mechanism, blocking NIK- and TNFα-mediated NF-κB activation, suggesting impairment of the IKK complex.","method":"Dominant-negative IKKβ cotransfection, overexpression of HPK1 truncation fragments, NF-κB reporter assays in myeloid progenitor cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple truncation constructs, dominant-negative epistasis, and reporter assays in a single rigorous study","pmids":["11278403"],"is_preprint":false},{"year":2001,"finding":"Grap2 (GADS) interacts with HPK1 via its C-terminal SH3 domain binding to the second proline-rich motif of HPK1 in vitro and in Jurkat T cells. Coexpression of Grap2 with HPK1 increases HPK1 kinase activity and has an additive effect on JNK activation, and promotes IL-2 gene transcription.","method":"In vitro binding assay, co-immunoprecipitation in Jurkat T cells, kinase activity assay, IL-2 reporter assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with endogenous and overexpressed proteins plus kinase activity assay, single lab","pmids":["11313918"],"is_preprint":false},{"year":2001,"finding":"Clnk (a SLP-76 family adaptor) physically and functionally interacts with HPK1 in hematopoietic cells; their interaction is augmented by immunoreceptor stimulation. Clnk and HPK1 cooperate to increase IL-2 promoter activity, and kinase-defective HPK1 blocks Clnk-mediated IL-2 induction, demonstrating functional dependence on HPK1 kinase activity.","method":"Yeast two-hybrid screen, cotransfection in COS-1 cells, IL-2 reporter assay in Jurkat T cells, kinase-dead HPK1 epistasis","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast 2-hybrid plus co-IP plus functional reporter assay, single lab","pmids":["11509653"],"is_preprint":false},{"year":2003,"finding":"PGE2 activates HPK1 catalytic activity in hematopoietic cells, and ectopic HPK1 expression negatively regulates PGE2-induced fos gene transcription, establishing HPK1 as a negative regulator downstream of PGE2/GPCR signaling.","method":"PGE2 stimulation assays, HPK1 kinase activity measurements, ectopic expression studies with Fos reporter assays","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — kinase activity measurement plus reporter assay, single lab, single study","pmids":["12522005"],"is_preprint":false},{"year":2004,"finding":"The Mona/Gads C-terminal SH3 domain binds HPK1 via an atypical combined RXXK + PXXP motif; crystal structure of the complex at molecular resolution shows that an RXXK charge interaction is essential and a PXXP motif strongly complements binding, defining an unusual SH3-binding mode distinct from Mona/Gads·SLP-76 interaction.","method":"Isothermal titration calorimetry, X-ray crystallography of the HPK1-peptide/Mona-Gads SH3C complex","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with ITC validation, rigorous biophysical characterization of the interaction","pmids":["15100220"],"is_preprint":false},{"year":2005,"finding":"HPK1 is a functional component of the endogenous IKK complex and is required for TCR-mediated NF-κB activation; full-length HPK1 enhances IKKβ phosphorylation. siRNA knockdown of HPK1 blunts TCR-mediated NF-κB activation and increases T-cell death. HPK1-C (caspase cleavage product) sequesters the inactive IKK complex and suppresses NF-κB by binding IKKα and IKKβ, sensitizing T cells to activation-induced cell death (AICD). HPK1-C transgenic mice show enhanced TCR-mediated AICD.","method":"siRNA knockdown, co-immunoprecipitation with endogenous IKK complex, NF-κB reporter assays, transgenic mouse model, IKKβ phosphorylation assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous co-IP, siRNA, transgenic mouse model, and functional reporter assays; replicated findings from Arnold 2001","pmids":["16341093"],"is_preprint":false},{"year":2006,"finding":"During monocytic differentiation, HPK1 is proteolytically processed by sub-apoptotic caspase-3 to generate a constitutively active N-terminal kinase fragment (HPK1-N) that drives sustained JNK activation, Bad phosphorylation, IL-3-independent progenitor cell survival, and monocytic lineage commitment. Blocking caspase activity reduces HPK1-N levels, suppresses JNK, and attenuates monocytic differentiation.","method":"Caspase inhibitor treatment of primary mouse progenitor cells, HPK1-N overexpression, JNK and Bad phosphorylation assays, cell survival and differentiation analysis","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 2 / Moderate — loss-of-function with caspase inhibitors plus gain-of-function with HPK1-N overexpression, primary cell system","pmids":["17024227"],"is_preprint":false},{"year":2007,"finding":"HPK1-C (caspase cleavage product) generated by sub-apoptotic caspase-3 activity in IL-2-expanded T cells selectively blocks NF-κB-dependent anti-apoptotic Bcl-2 family members but not pro-apoptotic Bim, inducing CD95L-independent AICD involving caspase-9. This pathway complements CD95L-dependent AICD in primary T and B lymphocytes.","method":"HPK1-C transgenic mice, siRNA knockdown of HPK1/Bim, primary T and B cell apoptosis assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — transgenic mouse model plus siRNA loss-of-function, primary cells, mechanistic pathway dissection","pmids":["17712048"],"is_preprint":false},{"year":2007,"finding":"PGE2 activates HPK1 kinase via a PKA-dependent pathway: changing Ser171 (an optimal PKA phosphorylation site in the activation loop) to Ala completely prevents HPK1 from responding to PGE2. HPK1 activation by PGE2 does not require phosphotyrosine-based signaling molecules (Lck, ZAP-70, SLP-76, Lat) or proline-rich/SH3-domain interactions required for TCR-induced HPK1 activation. PKA-deficient S49 cells fail to activate HPK1 in response to PGE2.","method":"Site-directed mutagenesis (S171A), PKA-deficient S49 cell line, HPK1 kinase activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — site-directed mutagenesis of specific phosphorylation site plus PKA-deficient cell line validation, single lab with two orthogonal approaches","pmids":["17895239"],"is_preprint":false},{"year":2009,"finding":"HPK1 phosphorylates the linker region of CARMA1 at residues S549, S551, and S552 (different from PKC consensus sites) in a TCR stimulation-dependent interaction. Mutations S551A or S549A/S551A abrogated CARMA1 phosphorylation by HPK1 in vitro and failed to restore HPK1-mediated and TCR-mediated NF-κB activation and IL-2 expression in CARMA1-deficient T cells.","method":"In vitro kinase assay with HPK1 and CARMA1-linker construct, site-directed mutagenesis of CARMA1, co-immunoprecipitation, NF-κB reporter assay and IL-2 expression in CARMA1-deficient T cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assay plus mutagenesis plus functional reconstitution in CARMA1-deficient cells, multiple orthogonal methods","pmids":["19706536"],"is_preprint":false},{"year":2010,"finding":"HPK1 competes with ADAP for SLP-76 binding upon TCR stimulation. HPK1 dampens Rap1 activation, resulting in decreased LFA-1 integrin activity. HPK1-deficient T cells show increased ADAP recruitment to SLP-76, elevated Rap1 activation, and increased adhesion to ICAM-1 and cell spreading.","method":"Co-immunoprecipitation, HPK1-deficient mouse T cells, Rap1 activation assay, ICAM-1 adhesion assay","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — HPK1 knockout T cells plus co-IP plus functional adhesion assays, single lab","pmids":["20957749"],"is_preprint":false},{"year":2010,"finding":"HPK1 associates with SKAP-HOM in B cells; HPK1 loss leads to increased Rap1 activation, LFA-1-dependent homotypic aggregation, and increased ICAM-1 adhesion. This is downstream of Src, independent of PI3K and PLC, involving HPK1, SKAP-HOM, and RIAM, and alters actin dynamics with constitutive FAK phosphorylation.","method":"shRNA knockdown in WEHI231 cells, HPK1(-/-) mouse B cells, Rap1 activation assay, adhesion assay, FAK phosphorylation assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two loss-of-function models (shRNA and KO mice) with mechanistic pathway dissection, single lab","pmids":["20824186"],"is_preprint":false},{"year":2012,"finding":"HPK1 phosphorylates BLNK at threonine 152 upon BCR activation, inducing BLNK/14-3-3 binding. Thr152-phosphorylated BLNK is ubiquitinated at lysines 37, 38, and 42, leading to BLNK degradation and attenuation of MAPK (ERK, p38, JNK) and IKK activation in B cells. HPK1-deficient B cells display hyper-proliferation and hyper-activation of IκB kinase and MAPKs.","method":"HPK1-deficient B cells, in vitro kinase/phosphorylation assay, co-immunoprecipitation, site-directed mutagenesis of BLNK (T152), ubiquitination assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro kinase assay with mutagenesis plus HPK1 knockout cells plus ubiquitination assay, multiple orthogonal methods","pmids":["22334673"],"is_preprint":false},{"year":2013,"finding":"HPK1 is required for CXCL1-induced LFA-1-mediated neutrophil adhesion to ICAM-1 under flow conditions, and for LFA-1 high-affinity conformation induction. HPK1 co-localizes with mAbp1 and actin at the lamellipodium of polarized neutrophil-like cells. HPK1-deficient mice show severely compromised neutrophil adhesion and extravasation upon TNFα treatment in vivo.","method":"Co-immunoprecipitation in HL-60 cells, confocal microscopy (HPK1 localization), HPK1-deficient mouse PMN adhesion assays under flow, intravital microscopy","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — HPK1 knockout mice, co-IP, live imaging/microscopy, and intravital microscopy in vivo, multiple orthogonal methods","pmids":["23460610"],"is_preprint":false},{"year":2019,"finding":"Crystal structures of the HPK1 kinase domain in non-phosphorylated and doubly phosphorylated states (complexed with sunitinib) at 2.17–3.00 Å resolution reveal: (1) the non-phosphorylated kinase forms an inactive dimer in which the activation loop of each monomer partially occupies the ATP- and substrate-binding sites of the partner; (2) the doubly phosphorylated activation loop adopts an active kinase conformation with reduced dimer interface; (3) a phosphomimetic double mutant (T165E, S171E) exhibits an alternative domain-swapped configuration. HPK1 undergoes trans-regulation via dimer formation and activation-loop remodeling.","method":"X-ray crystallography (multiple structures), phosphorylation-state mutant constructs","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple high-resolution crystal structures of distinct phosphorylation states with functional interpretation, rigorous structural study","pmids":["31018963"],"is_preprint":false},{"year":2019,"finding":"PDIA6 interacts with MAP4K1 (HPK1) by co-immunoprecipitation and inhibits HPK1 phosphorylation, leading to reduced JNK/c-Jun signaling and decreased cisplatin-induced apoptosis in NSCLC cells.","method":"Co-immunoprecipitation, human phospho-kinase array, gain- and loss-of-function overexpression/knockdown experiments","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP plus phospho-kinase array plus gain/loss-of-function, single lab","pmids":["30922965"],"is_preprint":false},{"year":2020,"finding":"HPK1 mediates T cell dysfunction via an HPK1–NF-κB–Blimp1 axis. MAP4K1 knockout mice show slower tumor growth with less exhausted, more active, and more proliferative tumor-infiltrating T cells. Pharmacological inhibition or PROTAC-mediated degradation of HPK1 improves CAR-T cell efficacy in preclinical tumor models.","method":"MAP4K1 knockout mice, CAR-T adoptive transfer tumor models, pharmacological inhibition, PROTAC degradation","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple loss-of-function strategies (KO mice, pharmacological inhibition, PROTAC) in multiple preclinical tumor models","pmids":["32860752"],"is_preprint":false},{"year":2021,"finding":"MAP4K1 acts as a negative regulator in the RLR (RIG-I-like receptor) innate immune signaling pathway by promoting K48-linked ubiquitination and proteasomal degradation of TBK1 and IKKε via the ubiquitin ligase DTX4. MAP4K1 was identified as an interacting partner of TBK1 by yeast two-hybrid; overexpression inhibits RNA-virus-triggered IFN-β and pro-inflammatory cytokine production; knockdown/knockout has opposite effects; DTX4 knockdown abrogates TBK1/IKKε ubiquitination and degradation.","method":"Yeast two-hybrid screen, co-immunoprecipitation, overexpression and knockdown/knockout assays, K48-linked ubiquitination assay, IFN-β reporter assay","journal":"Microbiology spectrum","confidence":"High","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus co-IP plus ubiquitination assay plus KO confirmation, single lab with multiple orthogonal methods","pmids":["34908452"],"is_preprint":false},{"year":2022,"finding":"An allosteric, inactive-conformation-selective HPK1 inhibitor (triazolopyrimidinone compound 1) binds unphosphorylated HPK1 >24-fold more potently than active HPK1, is not competitive with ATP, requires domains outside the isolated kinase domain for binding, and attenuates HPK1 autophosphorylation. This demonstrates that HPK1 has a druggable allosteric pocket outside the kinase domain.","method":"Cascade kinase assay, ATP competition assay, binding assays with isolated KD vs. full-length protein, selectivity profiling","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — novel biochemical assay system, single lab, single study; allosteric mechanism proposed but binding site not structurally characterized","pmids":["34608799"],"is_preprint":false},{"year":2024,"finding":"The citron homology domain (CHD) of HPK1 adopts a seven-bladed β-propellor fold and directly binds the HPK1 kinase domain (KD). Mutagenesis studies show a direct correlation between CHD–KD interaction and negative regulation of kinase activity. The CHD also contributes to docking of the substrate SLP76 and provides stability to HPK1 protein in cells.","method":"X-ray crystallography (CHD structure), hydrogen-deuterium exchange mass spectrometry, CHD–KD binding mutagenesis, functional kinase activity assays, co-immunoprecipitation, cellular stability assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus HDX-MS plus mutagenesis with functional validation, multiple orthogonal methods in a single rigorous study","pmids":["38697971"],"is_preprint":false},{"year":2024,"finding":"HPK1 aberrantly overexpressed in NK cells restrains NK cell cytotoxicity and expansion via activating receptors; conditional HPK1 overexpression in NK cells exacerbates melanoma lung metastasis while MAP4K1-deficient mice are resistant to metastasis. HPK1 limits human NK cell activation and is associated with melanoma NK cell dysfunction coupled to TGF-β1.","method":"Conditional HPK1 overexpression in NK cells (in vivo mouse model), MAP4K1-deficient mice, NK cell cytotoxicity assays, in vitro activation assays","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional overexpression and KO mouse models with defined NK cell functional phenotype, single lab","pmids":["38828677"],"is_preprint":false},{"year":2025,"finding":"HPK1 promotes neutrophil mobilization, LPS-induced neutrophil activation, NF-κB/STAT3/p38-MAPK pathway activation, and gasdermin D cleavage. Following acute ischemic stroke, HPK1 promotes CXCR2high bone marrow neutrophil mobilization. HPK1 loss inhibits peripheral neutrophil hyperactivation, neutrophil extracellular trap aggregation, and alleviates post-stroke pulmonary and neurological injuries.","method":"HPK1 loss-of-function mouse model, pharmacological HPK1 inhibition, neutrophil activation assays, stroke model (MCAO), pathway analysis (NF-κB/STAT3/p38)","journal":"EMBO molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mice plus pharmacological inhibition in in vivo stroke model, single lab, defined cellular phenotype","pmids":["40169896"],"is_preprint":false},{"year":2008,"finding":"In rat hippocampus after cerebral ischemia/reperfusion, activated Src tyrosine-phosphorylates HPK1, which then activates the downstream MLK3–MKK7–JNK3 pathway, promoting ischemic neuron death. PP2 (Src inhibitor) and MK801 (NMDA receptor antagonist) reduce activation of Src, HPK1, MLK3, JNK3, and c-Jun and protect against neuron death.","method":"Co-immunoprecipitation and immunoblot in rat hippocampal CA1, pharmacological inhibition (PP2, MK801), histology and TUNEL staining","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — co-IP plus pharmacological epistasis in vivo, single lab, correlative but consistent with pathway model","pmids":["18498770"],"is_preprint":false},{"year":2022,"finding":"In neutrophil-like HL-60 cells, HPK1 exists in a pre-assembled signaling cluster with DAP12, Syk, and Rac1; activation by β2 integrin-mediated adhesion changes the composition of the HPK1-interacting proteome (identified 115 interacting proteins by co-IP/MS, with 58 unique to non-activated and 39 unique to Mn2+-activated conditions).","method":"Co-immunoprecipitation followed by mass spectrometry (proteomics), two adhesion states (non-activated vs Mn2+-activated HL-60 cells)","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — co-IP/MS interactome in a single lab; large-scale interaction data for specific proteins (DAP12, Syk, Rac1) validated in this context","pmids":["35099066"],"is_preprint":false}],"current_model":"MAP4K1/HPK1 is a hematopoietic-restricted Ste20-related serine/threonine kinase that functions as a central negative regulator of adaptive and innate immune signaling: it activates the JNK/SAPK pathway (via MEKK1, TAK1, MLK3→MKK4/SEK1) and NF-κB (via IKKβ and CARMA1 phosphorylation) downstream of TCR/BCR engagement—mediated by adaptor proteins Grb2, Gads, SLP-76, Crk/CrkL, and Clnk—while PGE2 activates it through a distinct PKA-dependent phosphorylation of Ser171 in the activation loop; caspase-3 cleavage at Asp385 generates an N-terminal kinase fragment (HPK1-N) with enhanced, constitutive activity driving JNK-dependent survival/differentiation, and a C-terminal fragment (HPK1-C) that sequesters the IKK complex to suppress NF-κB and sensitize lymphocytes to activation-induced cell death; structurally, the kinase domain undergoes trans-regulation through phosphorylation-state-dependent dimer remodeling, while its citron homology domain (CHD) adopts a β-propellor fold that directly binds the kinase domain to negatively regulate activity and contribute to substrate (SLP76) docking; HPK1 also phosphorylates BLNK (Thr152) to trigger its ubiquitination and degradation, dampening BCR signaling, competes with ADAP for SLP-76 to suppress Rap1/LFA-1 adhesion in T and B cells, and in innate immunity promotes TBK1/IKKε proteasomal degradation via K48-ubiquitination through DTX4 to limit antiviral interferon responses."},"narrative":{"mechanistic_narrative":"MAP4K1/HPK1 is a hematopoietic Ste20-related serine/threonine kinase that operates as a signal-integrating hub linking immunoreceptor and stress inputs to the JNK/SAPK and NF-κB pathways, predominantly functioning as a negative regulator of lymphocyte and innate immune activation [PMID:8824585, PMID:9003777, PMID:10795738]. It directly binds and phosphorylates MEKK1 and triggers JNK1 activation through parallel MEKK1→MKK4/SEK1 and TAK1→MKK4 and MLK3 routes, independently of Rac1/Cdc42 [PMID:8824585, PMID:9003777, PMID:9278437], and acts upstream of the IKK/NF-κB axis, in part by phosphorylating the CARMA1 linker at S549/S551/S552 to enable TCR-induced NF-κB activation [PMID:10523828, PMID:16341093, PMID:19706536]. HPK1 is recruited into antigen-receptor signaling through proline-rich-motif interactions with the SH3 domains of Grb2, Gads/Grap2, Crk/CrkL, and the SLP-76-family adaptors SLP-76 and Clnk, and its catalytic activation upon TCR/BCR engagement depends on Src- and Syk/ZAP-70-family kinases and the LAT/SLP-76/BLNK adaptor network [PMID:9346925, PMID:9788432, PMID:10795738, PMID:11313918, PMID:11509653, PMID:15100220]. Despite enabling NF-κB, HPK1 restrains the broader response: it suppresses TCR-induced AP-1/ERK signaling, phosphorylates BLNK at Thr152 to drive its 14-3-3 binding, ubiquitination, and degradation in B cells, and competes with ADAP for SLP-76 to dampen Rap1/LFA-1-mediated adhesion in T and B cells [PMID:10795738, PMID:20957749, PMID:22334673]. A distinct PGE2/GPCR input activates HPK1 via PKA-dependent phosphorylation of activation-loop Ser171, bypassing the phosphotyrosine adaptor machinery [PMID:12522005, PMID:17895239]. Caspase-3 cleavage at Asp385 splits HPK1 into a constitutively active N-terminal kinase fragment that drives JNK-dependent survival and monocytic differentiation, and a C-terminal fragment that sequesters the IKK complex to suppress NF-κB and sensitize lymphocytes to activation-induced cell death [PMID:10602493, PMID:11278403, PMID:16341093, PMID:17024227, PMID:17712048]. Structurally, the kinase domain is trans-regulated through phosphorylation-state-dependent dimer remodeling, and the citron homology domain folds into a seven-bladed β-propellor that binds the kinase domain to inhibit activity, dock SLP-76, and stabilize the protein [PMID:31018963, PMID:38697971]. In innate immunity HPK1 promotes DTX4-dependent K48-ubiquitination and proteasomal degradation of TBK1/IKKε to limit antiviral interferon responses, and loss or pharmacologic/PROTAC-mediated inhibition of HPK1 relieves T-cell and NK-cell dysfunction and enhances antitumor immunity [PMID:32860752, PMID:34908452, PMID:38828677].","teleology":[{"year":1996,"claim":"Established HPK1 as a kinase that selectively channels signals into the JNK/SAPK pathway, defining its core catalytic output.","evidence":"Transfection epistasis with dominant-negative MEKK1/MKK4 and in vitro binding/phosphorylation in two independent studies","pmids":["8824585","9003777"],"confidence":"High","gaps":["Did not identify physiological upstream activators","Selectivity for JNK over p38/ERK explained mechanistically only at pathway level"]},{"year":1997,"claim":"Mapped redundant MAP3K effectors (MLK3, TAK1) downstream of HPK1, showing the kinase feeds multiple parallel routes to JNK.","evidence":"Dominant-negative and constitutively active mutant epistasis in transfected cells","pmids":["9003777","9278437"],"confidence":"High","gaps":["Direct phosphorylation of TAK1/MLK3 by HPK1 not demonstrated","Context determining which effector is used unknown"]},{"year":1997,"claim":"Identified adaptor-mediated recruitment of HPK1, explaining how it couples to tyrosine-kinase receptor signaling via Grb2 and to Crk/CrkL.","evidence":"In vitro SH3-domain binding, co-IP, and EGF stimulation assays","pmids":["9346925","9788432"],"confidence":"High","gaps":["Functional consequence of Crk/CrkL phosphorylation not established","In vivo relevance of EGFR coupling unclear"]},{"year":1999,"claim":"Discovered caspase-3 cleavage at Asp385 as a switch that splits HPK1 into functionally distinct fragments, reframing it as an apoptosis-regulated kinase.","evidence":"In vitro caspase-3 cleavage, Asp385 mutagenesis, and adaptor co-IP","pmids":["10602493"],"confidence":"High","gaps":["Physiological trigger of cleavage not defined at this stage","Fate of fragments in vivo unknown"]},{"year":1999,"claim":"Placed HPK1 upstream of the IKK/NF-κB pathway, extending its reach beyond JNK.","evidence":"Overexpression IKK kinase activity assays","pmids":["10523828"],"confidence":"Medium","gaps":["No mutagenesis confirming direct IKK interaction","Whether activation is direct or via MEKK1 unresolved"]},{"year":2000,"claim":"Defined HPK1 as a TCR/BCR-activated negative regulator of the AP-1 pathway, establishing its central immunoregulatory role.","evidence":"Antigen-receptor stimulation with reciprocal gain/kinase-dead loss-of-function and adaptor requirements in T and B cells","pmids":["10795738"],"confidence":"High","gaps":["Substrates mediating AP-1 suppression not yet identified","Distinction between positive NF-κB and negative AP-1 outputs unexplained"]},{"year":2001,"claim":"Resolved the activator-to-inhibitor switch: full-length kinase-active HPK1 activates NF-κB via IKKβ, while the C-terminal cleavage fragment is a dominant-negative NF-κB inhibitor.","evidence":"Truncation constructs, dominant-negative IKKβ, and NF-κB reporter assays in myeloid cells","pmids":["11278403"],"confidence":"High","gaps":["Mechanism of IKK impairment by HPK1-C not yet structural","Endogenous IKK association not yet shown"]},{"year":2001,"claim":"Extended the adaptor map to Gads/Grap2 and Clnk, showing these SH3 partners enhance HPK1 activity and IL-2 transcription.","evidence":"In vitro binding, co-IP in Jurkat/COS cells, kinase and IL-2 reporter assays with kinase-dead epistasis","pmids":["11313918","11509653"],"confidence":"Medium","gaps":["Single-lab functional assays","Apparent positive effect on IL-2 contrasts with negative regulatory role"]},{"year":2003,"claim":"Identified PGE2/GPCR signaling as a non-immunoreceptor input activating HPK1 to suppress fos transcription.","evidence":"PGE2 stimulation, kinase activity, and Fos reporter assays","pmids":["12522005"],"confidence":"Medium","gaps":["Molecular mechanism of PGE2-induced activation not defined here","Single study"]},{"year":2004,"claim":"Provided structural definition of an atypical Gads SH3-binding mode on HPK1, explaining adaptor selectivity.","evidence":"ITC and X-ray crystallography of the HPK1 peptide·Mona/Gads SH3C complex","pmids":["15100220"],"confidence":"High","gaps":["Structure of full-length adaptor·HPK1 complex not solved","Functional impact in cells not addressed"]},{"year":2005,"claim":"Demonstrated HPK1 is a bona fide component of the endogenous IKK complex required for TCR-driven NF-κB and that HPK1-C sequesters IKK to drive activation-induced cell death.","evidence":"siRNA knockdown, endogenous IKK co-IP, NF-κB reporters, and HPK1-C transgenic mice","pmids":["16341093"],"confidence":"High","gaps":["Stoichiometry within IKK complex unresolved","Trigger generating HPK1-C physiologically not defined"]},{"year":2006,"claim":"Showed sub-apoptotic caspase-3 generates active HPK1-N to drive JNK-dependent progenitor survival and monocytic differentiation, giving cleavage a developmental role.","evidence":"Caspase inhibition and HPK1-N overexpression in primary mouse progenitors with JNK/Bad phosphorylation readouts","pmids":["17024227"],"confidence":"High","gaps":["How sub-apoptotic caspase activity is restrained from killing the cell unclear","Direct HPK1-N substrates beyond JNK pathway not mapped"]},{"year":2007,"claim":"Defined two complementary roles for cleavage fragments in lymphocyte death and revealed PKA-dependent Ser171 phosphorylation as the mechanism of PGE2 activation.","evidence":"HPK1-C transgenic mice and siRNA for AICD; S171A mutagenesis and PKA-deficient S49 cells for PGE2 pathway","pmids":["17712048","17895239"],"confidence":"High","gaps":["Connection between the PKA-Ser171 input and physiological outputs incompletely mapped","Selectivity of HPK1-C for anti-apoptotic Bcl-2 members mechanistically open"]},{"year":2008,"claim":"Implicated HPK1 in a Src→HPK1→MLK3→JNK3 cascade promoting ischemic neuronal death, extending its kinase circuitry beyond immune cells.","evidence":"Co-IP, pharmacological inhibition (PP2, MK801), and histology in rat hippocampus","pmids":["18498770"],"confidence":"Medium","gaps":["Correlative in vivo epistasis without genetic loss-of-function","HPK1 expression/role in neurons not independently confirmed"]},{"year":2009,"claim":"Identified CARMA1 as a direct HPK1 substrate, providing the molecular link by which HPK1 promotes TCR-induced NF-κB and IL-2.","evidence":"In vitro kinase assay, CARMA1 site mutagenesis, and reconstitution in CARMA1-deficient T cells","pmids":["19706536"],"confidence":"High","gaps":["How positive CARMA1 phosphorylation reconciles with overall negative regulation unresolved","Kinetics versus other HPK1 substrates not compared"]},{"year":2010,"claim":"Established HPK1 as a brake on integrin-mediated adhesion by competing with ADAP for SLP-76 and associating with SKAP-HOM to limit Rap1/LFA-1 activity in T and B cells.","evidence":"HPK1-deficient T and B cells, co-IP, Rap1 activation, and ICAM-1 adhesion assays","pmids":["20957749","20824186"],"confidence":"High","gaps":["Whether kinase activity or scaffolding drives SLP-76 competition unclear","Direct phosphorylation targets in the adhesion module not all identified"]},{"year":2012,"claim":"Defined a degradative mechanism by which HPK1 dampens BCR signaling: BLNK Thr152 phosphorylation triggers 14-3-3 binding, ubiquitination, and degradation.","evidence":"HPK1-deficient B cells, in vitro kinase assay, BLNK mutagenesis, and ubiquitination assays","pmids":["22334673"],"confidence":"High","gaps":["Ubiquitin ligase mediating BLNK degradation not identified","Generality to T-cell SLP-76 not tested"]},{"year":2013,"claim":"Showed HPK1 is required for chemokine-induced LFA-1 high-affinity adhesion and neutrophil extravasation in vivo, revealing a positive adhesion role in innate cells.","evidence":"HPK1-deficient mice, co-IP, confocal imaging, flow adhesion, and intravital microscopy","pmids":["23460610"],"confidence":"High","gaps":["Opposite adhesion roles in lymphocytes versus neutrophils mechanistically unreconciled","Direct neutrophil substrates not defined"]},{"year":2019,"claim":"Provided the structural basis for HPK1 trans-regulation through phosphorylation-state-dependent dimer remodeling of the kinase domain.","evidence":"Multiple crystal structures of non-phosphorylated, doubly phosphorylated, and phosphomimetic kinase domains","pmids":["31018963"],"confidence":"High","gaps":["In-cell relevance of the dimer interface not validated","Trigger of activation-loop autophosphorylation not structurally captured"]},{"year":2019,"claim":"Identified PDIA6 as an inhibitor of HPK1 phosphorylation that dampens JNK/c-Jun signaling and apoptosis in non-hematopoietic NSCLC cells.","evidence":"Co-IP, phospho-kinase array, and gain/loss-of-function in NSCLC cells","pmids":["30922965"],"confidence":"Medium","gaps":["Direct versus indirect inhibition not distinguished","Single-lab non-hematopoietic context"]},{"year":2020,"claim":"Established HPK1 as a therapeutic target for antitumor immunity via an HPK1–NF-κB–Blimp1 axis driving T-cell dysfunction.","evidence":"MAP4K1 knockout mice, CAR-T tumor models, pharmacological inhibition, and PROTAC degradation","pmids":["32860752"],"confidence":"High","gaps":["Direct HPK1 substrate in the Blimp1 axis not pinpointed","Catalytic versus scaffolding contribution to T-cell dysfunction unresolved"]},{"year":2021,"claim":"Revealed an innate-immune negative-regulatory function: HPK1 promotes DTX4-dependent K48-ubiquitination and degradation of TBK1/IKKε to limit interferon responses.","evidence":"Yeast two-hybrid, co-IP, ubiquitination assays, knockdown/knockout, and IFN-β reporters","pmids":["34908452"],"confidence":"High","gaps":["Whether HPK1 kinase activity is required for DTX4 recruitment unclear","Single-lab characterization"]},{"year":2022,"claim":"Characterized a druggable allosteric pocket outside the kinase domain and an integrin-induced HPK1 signaling cluster, refining inhibitor strategy and interactome.","evidence":"ATP-noncompetitive allosteric inhibitor binding assays; co-IP/MS interactome of HL-60 cells with DAP12/Syk/Rac1","pmids":["34608799","35099066"],"confidence":"Medium","gaps":["Allosteric binding site not structurally resolved","Functional validation of most interactome members lacking"]},{"year":2024,"claim":"Defined the citron homology domain structure and its autoinhibitory, substrate-docking, and stabilizing functions, completing the intramolecular regulatory picture.","evidence":"CHD crystal structure, HDX-MS, CHD–KD mutagenesis, kinase assays, co-IP, and stability assays","pmids":["38697971"],"confidence":"High","gaps":["How adaptor binding relieves CHD autoinhibition not shown","Conformational coupling between CHD and dimer remodeling unexplored"]},{"year":2024,"claim":"Extended HPK1's immunosuppressive role to NK cells, where aberrant overexpression restrains cytotoxicity and promotes metastasis.","evidence":"Conditional NK overexpression and MAP4K1-deficient mice with cytotoxicity and metastasis assays","pmids":["38828677"],"confidence":"Medium","gaps":["NK-specific substrates not identified","TGF-β1 linkage mechanistically incomplete"]},{"year":2025,"claim":"Identified HPK1 as a driver of pathological neutrophil hyperactivation and mobilization after ischemic stroke.","evidence":"HPK1 loss-of-function mice, pharmacological inhibition, and MCAO stroke model with NF-κB/STAT3/p38 and gasdermin D readouts","pmids":["40169896"],"confidence":"Medium","gaps":["Direct HPK1 substrates in neutrophil pyroptosis/NET pathway not defined","Single-lab study"]},{"year":null,"claim":"How HPK1 reconciles opposing roles (NF-κB/CARMA1 activation versus AP-1/adhesion suppression; lymphocyte versus neutrophil adhesion) and how adaptor engagement relieves CHD/dimer autoinhibition to direct catalysis toward specific substrates remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unified model linking conformational state to substrate choice","Catalytic versus scaffolding contributions across contexts not systematically dissected"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,17,20]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,4,16,17,20]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[22,26]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[7,11]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[3,13]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[21]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[7,13,24,25]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,2,6,17]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[5,13,14,15]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[20,25]}],"complexes":["IKK complex"],"partners":["GRB2","GADS/GRAP2","SLP-76","CRKL","CARMA1","BLNK","TBK1","MEKK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q92918","full_name":"Mitogen-activated protein kinase kinase kinase kinase 1","aliases":["Hematopoietic progenitor kinase","MAPK/ERK kinase kinase kinase 1","MEK kinase kinase 1","MEKKK 1"],"length_aa":833,"mass_kda":91.3,"function":"Serine/threonine-protein kinase, which plays a role in the response to environmental stress (PubMed:24362026). Appears to act upstream of the JUN N-terminal pathway (PubMed:8824585). Activator of the Hippo signaling pathway which plays a pivotal role in organ size control and tumor suppression by restricting proliferation and promoting apoptosis. MAP4Ks act in parallel to and are partially redundant with STK3/MST2 and STK4/MST2 in the phosphorylation and activation of LATS1/2, and establish MAP4Ks as components of the expanded Hippo pathway (PubMed:26437443). May play a role in hematopoietic lineage decisions and growth regulation (PubMed:24362026, PubMed:8824585). Together with CLNK, it enhances CD3-triggered activation of T-cells and subsequent IL2 production (By similarity)","subcellular_location":"","url":"https://www.uniprot.org/uniprotkb/Q92918/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MAP4K1","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/MAP4K1","total_profiled":1310},"omim":[{"mim_id":"610106","title":"DREBRIN-LIKE; DBNL","url":"https://www.omim.org/entry/610106"},{"mim_id":"601983","title":"MITOGEN-ACTIVATED PROTEIN KINASE KINASE KINASE KINASE 1; MAP4K1","url":"https://www.omim.org/entry/601983"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"intestine","ntpm":28.3},{"tissue":"lymphoid tissue","ntpm":55.1}],"url":"https://www.proteinatlas.org/search/MAP4K1"},"hgnc":{"alias_symbol":["HPK1"],"prev_symbol":[]},"alphafold":{"accession":"Q92918","domains":[{"cath_id":"3.30.200.20","chopping":"2-94","consensus_level":"medium","plddt":80.1065,"start":2,"end":94},{"cath_id":"1.10.510.10","chopping":"98-295","consensus_level":"medium","plddt":82.943,"start":98,"end":295}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92918","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92918-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92918-F1-predicted_aligned_error_v6.png","plddt_mean":68.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MAP4K1","jax_strain_url":"https://www.jax.org/strain/search?query=MAP4K1"},"sequence":{"accession":"Q92918","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92918.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92918/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92918"}},"corpus_meta":[{"pmid":"8824585","id":"PMC_8824585","title":"Human 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Unlike PAK65, HPK1 does not bind Rac1 or Cdc42, indicating Rac1/Cdc42-independent activation.\",\n      \"method\": \"Transient transfection assays with dominant-negative mutants, direct in vitro binding and phosphorylation assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro phosphorylation assay plus dominant-negative epistasis, replicated across two independent labs (PMID:8824585 and PMID:9003777)\",\n      \"pmids\": [\"8824585\", \"9003777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"HPK1 specifically activates the SAPK/JNK pathway but not p38/RK or ERK; activation requires a functional HPK1 kinase domain and proceeds via the mixed lineage kinase MLK-3 and the SAPK activator SEK1.\",\n      \"method\": \"Transfection in COS1 cells with kinase-inactive mutants and dominant-negative pathway components\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple dominant-negative epistasis experiments, replicated with complementary data from PMID:8824585\",\n      \"pmids\": [\"9003777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"TAK1 acts downstream of HPK1 and upstream of MKK4/SEK1 in a HPK1→TAK1→MKK4/SEK1→JNK kinase cascade; a kinase-defective TAK1 mutant suppressed HPK1-induced JNK activity, while dominant-negative MEKK1 and MLK3 did not inhibit TAK1-induced JNK, indicating TAK1 is an alternative HPK1 downstream effector independent of MEKK1/MLK3.\",\n      \"method\": \"Transient transfection assays with dominant-negative and constitutively active mutants of TAK1, MEKK1, MLK3, and MKK4/SEK1\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal dominant-negative and constitutively active mutant epistasis experiments in a single study\",\n      \"pmids\": [\"9278437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The SH3 domains of Grb2 bind to specific proline-rich motifs in the HPK1 C-terminal tail, forming a stable Grb2·HPK1 complex in transfected cells. EGF stimulation recruits the Grb2·HPK1 complex to the autophosphorylated EGF receptor and to Shc. Multiple activated receptor and cytoplasmic tyrosine kinases (including EGFR) stimulate tyrosine phosphorylation of HPK1, demonstrating SH2/SH3 adaptor-mediated cross-talk between tyrosine kinase and HPK1 pathways.\",\n      \"method\": \"In vitro SH3-domain binding assay, co-immunoprecipitation in transfected COS1 cells, EGF stimulation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus in vitro binding assay with multiple tyrosine kinases, single lab\",\n      \"pmids\": [\"9346925\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"HPK1 binds selectively to the first SH3 domains of c-Crk and CRKL via proline-rich motifs in its C-terminal non-catalytic portion; in vitro and in vivo Crk/CRKL–HPK1 complexes were detected by co-immunoprecipitation. HPK1 phosphorylates c-Crk II and CRKL in vitro, suggesting HPK1 can regulate adaptor protein function downstream.\",\n      \"method\": \"In vitro SH3-domain binding assays with >25 SH3 domains, co-immunoprecipitation of endogenous proteins, in vitro kinase assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus co-IP with endogenous proteins, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"9788432\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"HPK1 is cleaved by caspase-3 during apoptosis at the conserved DDVD site (Asp385), separating the N-terminal kinase domain from the C-terminal regulatory domain. Caspase-3 cleavage enhances HPK1 kinase activity. The N-terminal cleavage product fails to bind adaptors Grb2 and Crk, while the C-terminal fragment binds them less efficiently than full-length HPK1.\",\n      \"method\": \"In vitro caspase-3 cleavage assay, site-directed mutagenesis of Asp385, in vivo/in vitro cleavage assays, co-immunoprecipitation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with recombinant caspase-3, mutagenesis identifying exact cleavage site, and functional co-IP studies\",\n      \"pmids\": [\"10602493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"HPK1 activates both IKK-alpha and IKK-beta, which phosphorylate IκB constitutively (IKK-beta) or upon stimulation (IKK-alpha), placing HPK1 upstream of the IκB/NF-κB pathway via a HPK1–MEKK1 stress response signaling pathway.\",\n      \"method\": \"Transient transfection with HPK1 and MEKK1 constructs, IKK kinase activity assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — overexpression kinase assay in single lab without mutagenesis confirmation of direct interaction\",\n      \"pmids\": [\"10523828\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"TCR or BCR engagement induces HPK1 catalytic activity; Src and Syk/ZAP-70 tyrosine kinases and adaptor proteins LAT, SLP-76, BLNK, Grb2, and Grap are required for HPK1 activation. Overexpression of HPK1 inhibits TCR-induced AP-1 and ERK2 activation, while kinase-inactive HPK1 potentiates these responses, establishing HPK1 as a negative regulator of the TCR-induced AP-1 pathway.\",\n      \"method\": \"Antigen receptor stimulation assays, overexpression and kinase-inactive mutant transfections in T and B cells\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal gain/loss-of-function with kinase-dead mutant and multiple adaptor knockouts, replicated in both TCR and BCR settings\",\n      \"pmids\": [\"10795738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Caspase-mediated cleavage of HPK1 converts it from an activator to an inhibitor of NF-κB. Full-length, kinase-active HPK1 activates NF-κB via IKKβ (independently of SAPK/JNK); the isolated kinase domain activates SAPK/JNK but not NF-κB. The C-terminal cleavage fragment (HPK1-C) inhibits NF-κB by dominant-negative mechanism, blocking NIK- and TNFα-mediated NF-κB activation, suggesting impairment of the IKK complex.\",\n      \"method\": \"Dominant-negative IKKβ cotransfection, overexpression of HPK1 truncation fragments, NF-κB reporter assays in myeloid progenitor cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple truncation constructs, dominant-negative epistasis, and reporter assays in a single rigorous study\",\n      \"pmids\": [\"11278403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Grap2 (GADS) interacts with HPK1 via its C-terminal SH3 domain binding to the second proline-rich motif of HPK1 in vitro and in Jurkat T cells. Coexpression of Grap2 with HPK1 increases HPK1 kinase activity and has an additive effect on JNK activation, and promotes IL-2 gene transcription.\",\n      \"method\": \"In vitro binding assay, co-immunoprecipitation in Jurkat T cells, kinase activity assay, IL-2 reporter assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with endogenous and overexpressed proteins plus kinase activity assay, single lab\",\n      \"pmids\": [\"11313918\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Clnk (a SLP-76 family adaptor) physically and functionally interacts with HPK1 in hematopoietic cells; their interaction is augmented by immunoreceptor stimulation. Clnk and HPK1 cooperate to increase IL-2 promoter activity, and kinase-defective HPK1 blocks Clnk-mediated IL-2 induction, demonstrating functional dependence on HPK1 kinase activity.\",\n      \"method\": \"Yeast two-hybrid screen, cotransfection in COS-1 cells, IL-2 reporter assay in Jurkat T cells, kinase-dead HPK1 epistasis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast 2-hybrid plus co-IP plus functional reporter assay, single lab\",\n      \"pmids\": [\"11509653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PGE2 activates HPK1 catalytic activity in hematopoietic cells, and ectopic HPK1 expression negatively regulates PGE2-induced fos gene transcription, establishing HPK1 as a negative regulator downstream of PGE2/GPCR signaling.\",\n      \"method\": \"PGE2 stimulation assays, HPK1 kinase activity measurements, ectopic expression studies with Fos reporter assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — kinase activity measurement plus reporter assay, single lab, single study\",\n      \"pmids\": [\"12522005\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The Mona/Gads C-terminal SH3 domain binds HPK1 via an atypical combined RXXK + PXXP motif; crystal structure of the complex at molecular resolution shows that an RXXK charge interaction is essential and a PXXP motif strongly complements binding, defining an unusual SH3-binding mode distinct from Mona/Gads·SLP-76 interaction.\",\n      \"method\": \"Isothermal titration calorimetry, X-ray crystallography of the HPK1-peptide/Mona-Gads SH3C complex\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with ITC validation, rigorous biophysical characterization of the interaction\",\n      \"pmids\": [\"15100220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"HPK1 is a functional component of the endogenous IKK complex and is required for TCR-mediated NF-κB activation; full-length HPK1 enhances IKKβ phosphorylation. siRNA knockdown of HPK1 blunts TCR-mediated NF-κB activation and increases T-cell death. HPK1-C (caspase cleavage product) sequesters the inactive IKK complex and suppresses NF-κB by binding IKKα and IKKβ, sensitizing T cells to activation-induced cell death (AICD). HPK1-C transgenic mice show enhanced TCR-mediated AICD.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation with endogenous IKK complex, NF-κB reporter assays, transgenic mouse model, IKKβ phosphorylation assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous co-IP, siRNA, transgenic mouse model, and functional reporter assays; replicated findings from Arnold 2001\",\n      \"pmids\": [\"16341093\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"During monocytic differentiation, HPK1 is proteolytically processed by sub-apoptotic caspase-3 to generate a constitutively active N-terminal kinase fragment (HPK1-N) that drives sustained JNK activation, Bad phosphorylation, IL-3-independent progenitor cell survival, and monocytic lineage commitment. Blocking caspase activity reduces HPK1-N levels, suppresses JNK, and attenuates monocytic differentiation.\",\n      \"method\": \"Caspase inhibitor treatment of primary mouse progenitor cells, HPK1-N overexpression, JNK and Bad phosphorylation assays, cell survival and differentiation analysis\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with caspase inhibitors plus gain-of-function with HPK1-N overexpression, primary cell system\",\n      \"pmids\": [\"17024227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"HPK1-C (caspase cleavage product) generated by sub-apoptotic caspase-3 activity in IL-2-expanded T cells selectively blocks NF-κB-dependent anti-apoptotic Bcl-2 family members but not pro-apoptotic Bim, inducing CD95L-independent AICD involving caspase-9. This pathway complements CD95L-dependent AICD in primary T and B lymphocytes.\",\n      \"method\": \"HPK1-C transgenic mice, siRNA knockdown of HPK1/Bim, primary T and B cell apoptosis assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — transgenic mouse model plus siRNA loss-of-function, primary cells, mechanistic pathway dissection\",\n      \"pmids\": [\"17712048\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"PGE2 activates HPK1 kinase via a PKA-dependent pathway: changing Ser171 (an optimal PKA phosphorylation site in the activation loop) to Ala completely prevents HPK1 from responding to PGE2. HPK1 activation by PGE2 does not require phosphotyrosine-based signaling molecules (Lck, ZAP-70, SLP-76, Lat) or proline-rich/SH3-domain interactions required for TCR-induced HPK1 activation. PKA-deficient S49 cells fail to activate HPK1 in response to PGE2.\",\n      \"method\": \"Site-directed mutagenesis (S171A), PKA-deficient S49 cell line, HPK1 kinase activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — site-directed mutagenesis of specific phosphorylation site plus PKA-deficient cell line validation, single lab with two orthogonal approaches\",\n      \"pmids\": [\"17895239\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"HPK1 phosphorylates the linker region of CARMA1 at residues S549, S551, and S552 (different from PKC consensus sites) in a TCR stimulation-dependent interaction. Mutations S551A or S549A/S551A abrogated CARMA1 phosphorylation by HPK1 in vitro and failed to restore HPK1-mediated and TCR-mediated NF-κB activation and IL-2 expression in CARMA1-deficient T cells.\",\n      \"method\": \"In vitro kinase assay with HPK1 and CARMA1-linker construct, site-directed mutagenesis of CARMA1, co-immunoprecipitation, NF-κB reporter assay and IL-2 expression in CARMA1-deficient T cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assay plus mutagenesis plus functional reconstitution in CARMA1-deficient cells, multiple orthogonal methods\",\n      \"pmids\": [\"19706536\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HPK1 competes with ADAP for SLP-76 binding upon TCR stimulation. HPK1 dampens Rap1 activation, resulting in decreased LFA-1 integrin activity. HPK1-deficient T cells show increased ADAP recruitment to SLP-76, elevated Rap1 activation, and increased adhesion to ICAM-1 and cell spreading.\",\n      \"method\": \"Co-immunoprecipitation, HPK1-deficient mouse T cells, Rap1 activation assay, ICAM-1 adhesion assay\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — HPK1 knockout T cells plus co-IP plus functional adhesion assays, single lab\",\n      \"pmids\": [\"20957749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HPK1 associates with SKAP-HOM in B cells; HPK1 loss leads to increased Rap1 activation, LFA-1-dependent homotypic aggregation, and increased ICAM-1 adhesion. This is downstream of Src, independent of PI3K and PLC, involving HPK1, SKAP-HOM, and RIAM, and alters actin dynamics with constitutive FAK phosphorylation.\",\n      \"method\": \"shRNA knockdown in WEHI231 cells, HPK1(-/-) mouse B cells, Rap1 activation assay, adhesion assay, FAK phosphorylation assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two loss-of-function models (shRNA and KO mice) with mechanistic pathway dissection, single lab\",\n      \"pmids\": [\"20824186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HPK1 phosphorylates BLNK at threonine 152 upon BCR activation, inducing BLNK/14-3-3 binding. Thr152-phosphorylated BLNK is ubiquitinated at lysines 37, 38, and 42, leading to BLNK degradation and attenuation of MAPK (ERK, p38, JNK) and IKK activation in B cells. HPK1-deficient B cells display hyper-proliferation and hyper-activation of IκB kinase and MAPKs.\",\n      \"method\": \"HPK1-deficient B cells, in vitro kinase/phosphorylation assay, co-immunoprecipitation, site-directed mutagenesis of BLNK (T152), ubiquitination assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro kinase assay with mutagenesis plus HPK1 knockout cells plus ubiquitination assay, multiple orthogonal methods\",\n      \"pmids\": [\"22334673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"HPK1 is required for CXCL1-induced LFA-1-mediated neutrophil adhesion to ICAM-1 under flow conditions, and for LFA-1 high-affinity conformation induction. HPK1 co-localizes with mAbp1 and actin at the lamellipodium of polarized neutrophil-like cells. HPK1-deficient mice show severely compromised neutrophil adhesion and extravasation upon TNFα treatment in vivo.\",\n      \"method\": \"Co-immunoprecipitation in HL-60 cells, confocal microscopy (HPK1 localization), HPK1-deficient mouse PMN adhesion assays under flow, intravital microscopy\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — HPK1 knockout mice, co-IP, live imaging/microscopy, and intravital microscopy in vivo, multiple orthogonal methods\",\n      \"pmids\": [\"23460610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structures of the HPK1 kinase domain in non-phosphorylated and doubly phosphorylated states (complexed with sunitinib) at 2.17–3.00 Å resolution reveal: (1) the non-phosphorylated kinase forms an inactive dimer in which the activation loop of each monomer partially occupies the ATP- and substrate-binding sites of the partner; (2) the doubly phosphorylated activation loop adopts an active kinase conformation with reduced dimer interface; (3) a phosphomimetic double mutant (T165E, S171E) exhibits an alternative domain-swapped configuration. HPK1 undergoes trans-regulation via dimer formation and activation-loop remodeling.\",\n      \"method\": \"X-ray crystallography (multiple structures), phosphorylation-state mutant constructs\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple high-resolution crystal structures of distinct phosphorylation states with functional interpretation, rigorous structural study\",\n      \"pmids\": [\"31018963\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PDIA6 interacts with MAP4K1 (HPK1) by co-immunoprecipitation and inhibits HPK1 phosphorylation, leading to reduced JNK/c-Jun signaling and decreased cisplatin-induced apoptosis in NSCLC cells.\",\n      \"method\": \"Co-immunoprecipitation, human phospho-kinase array, gain- and loss-of-function overexpression/knockdown experiments\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP plus phospho-kinase array plus gain/loss-of-function, single lab\",\n      \"pmids\": [\"30922965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HPK1 mediates T cell dysfunction via an HPK1–NF-κB–Blimp1 axis. MAP4K1 knockout mice show slower tumor growth with less exhausted, more active, and more proliferative tumor-infiltrating T cells. Pharmacological inhibition or PROTAC-mediated degradation of HPK1 improves CAR-T cell efficacy in preclinical tumor models.\",\n      \"method\": \"MAP4K1 knockout mice, CAR-T adoptive transfer tumor models, pharmacological inhibition, PROTAC degradation\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple loss-of-function strategies (KO mice, pharmacological inhibition, PROTAC) in multiple preclinical tumor models\",\n      \"pmids\": [\"32860752\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"MAP4K1 acts as a negative regulator in the RLR (RIG-I-like receptor) innate immune signaling pathway by promoting K48-linked ubiquitination and proteasomal degradation of TBK1 and IKKε via the ubiquitin ligase DTX4. MAP4K1 was identified as an interacting partner of TBK1 by yeast two-hybrid; overexpression inhibits RNA-virus-triggered IFN-β and pro-inflammatory cytokine production; knockdown/knockout has opposite effects; DTX4 knockdown abrogates TBK1/IKKε ubiquitination and degradation.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, overexpression and knockdown/knockout assays, K48-linked ubiquitination assay, IFN-β reporter assay\",\n      \"journal\": \"Microbiology spectrum\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus co-IP plus ubiquitination assay plus KO confirmation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"34908452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"An allosteric, inactive-conformation-selective HPK1 inhibitor (triazolopyrimidinone compound 1) binds unphosphorylated HPK1 >24-fold more potently than active HPK1, is not competitive with ATP, requires domains outside the isolated kinase domain for binding, and attenuates HPK1 autophosphorylation. This demonstrates that HPK1 has a druggable allosteric pocket outside the kinase domain.\",\n      \"method\": \"Cascade kinase assay, ATP competition assay, binding assays with isolated KD vs. full-length protein, selectivity profiling\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — novel biochemical assay system, single lab, single study; allosteric mechanism proposed but binding site not structurally characterized\",\n      \"pmids\": [\"34608799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The citron homology domain (CHD) of HPK1 adopts a seven-bladed β-propellor fold and directly binds the HPK1 kinase domain (KD). Mutagenesis studies show a direct correlation between CHD–KD interaction and negative regulation of kinase activity. The CHD also contributes to docking of the substrate SLP76 and provides stability to HPK1 protein in cells.\",\n      \"method\": \"X-ray crystallography (CHD structure), hydrogen-deuterium exchange mass spectrometry, CHD–KD binding mutagenesis, functional kinase activity assays, co-immunoprecipitation, cellular stability assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus HDX-MS plus mutagenesis with functional validation, multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"38697971\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HPK1 aberrantly overexpressed in NK cells restrains NK cell cytotoxicity and expansion via activating receptors; conditional HPK1 overexpression in NK cells exacerbates melanoma lung metastasis while MAP4K1-deficient mice are resistant to metastasis. HPK1 limits human NK cell activation and is associated with melanoma NK cell dysfunction coupled to TGF-β1.\",\n      \"method\": \"Conditional HPK1 overexpression in NK cells (in vivo mouse model), MAP4K1-deficient mice, NK cell cytotoxicity assays, in vitro activation assays\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional overexpression and KO mouse models with defined NK cell functional phenotype, single lab\",\n      \"pmids\": [\"38828677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HPK1 promotes neutrophil mobilization, LPS-induced neutrophil activation, NF-κB/STAT3/p38-MAPK pathway activation, and gasdermin D cleavage. Following acute ischemic stroke, HPK1 promotes CXCR2high bone marrow neutrophil mobilization. HPK1 loss inhibits peripheral neutrophil hyperactivation, neutrophil extracellular trap aggregation, and alleviates post-stroke pulmonary and neurological injuries.\",\n      \"method\": \"HPK1 loss-of-function mouse model, pharmacological HPK1 inhibition, neutrophil activation assays, stroke model (MCAO), pathway analysis (NF-κB/STAT3/p38)\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mice plus pharmacological inhibition in in vivo stroke model, single lab, defined cellular phenotype\",\n      \"pmids\": [\"40169896\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In rat hippocampus after cerebral ischemia/reperfusion, activated Src tyrosine-phosphorylates HPK1, which then activates the downstream MLK3–MKK7–JNK3 pathway, promoting ischemic neuron death. PP2 (Src inhibitor) and MK801 (NMDA receptor antagonist) reduce activation of Src, HPK1, MLK3, JNK3, and c-Jun and protect against neuron death.\",\n      \"method\": \"Co-immunoprecipitation and immunoblot in rat hippocampal CA1, pharmacological inhibition (PP2, MK801), histology and TUNEL staining\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — co-IP plus pharmacological epistasis in vivo, single lab, correlative but consistent with pathway model\",\n      \"pmids\": [\"18498770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In neutrophil-like HL-60 cells, HPK1 exists in a pre-assembled signaling cluster with DAP12, Syk, and Rac1; activation by β2 integrin-mediated adhesion changes the composition of the HPK1-interacting proteome (identified 115 interacting proteins by co-IP/MS, with 58 unique to non-activated and 39 unique to Mn2+-activated conditions).\",\n      \"method\": \"Co-immunoprecipitation followed by mass spectrometry (proteomics), two adhesion states (non-activated vs Mn2+-activated HL-60 cells)\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — co-IP/MS interactome in a single lab; large-scale interaction data for specific proteins (DAP12, Syk, Rac1) validated in this context\",\n      \"pmids\": [\"35099066\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MAP4K1/HPK1 is a hematopoietic-restricted Ste20-related serine/threonine kinase that functions as a central negative regulator of adaptive and innate immune signaling: it activates the JNK/SAPK pathway (via MEKK1, TAK1, MLK3→MKK4/SEK1) and NF-κB (via IKKβ and CARMA1 phosphorylation) downstream of TCR/BCR engagement—mediated by adaptor proteins Grb2, Gads, SLP-76, Crk/CrkL, and Clnk—while PGE2 activates it through a distinct PKA-dependent phosphorylation of Ser171 in the activation loop; caspase-3 cleavage at Asp385 generates an N-terminal kinase fragment (HPK1-N) with enhanced, constitutive activity driving JNK-dependent survival/differentiation, and a C-terminal fragment (HPK1-C) that sequesters the IKK complex to suppress NF-κB and sensitize lymphocytes to activation-induced cell death; structurally, the kinase domain undergoes trans-regulation through phosphorylation-state-dependent dimer remodeling, while its citron homology domain (CHD) adopts a β-propellor fold that directly binds the kinase domain to negatively regulate activity and contribute to substrate (SLP76) docking; HPK1 also phosphorylates BLNK (Thr152) to trigger its ubiquitination and degradation, dampening BCR signaling, competes with ADAP for SLP-76 to suppress Rap1/LFA-1 adhesion in T and B cells, and in innate immunity promotes TBK1/IKKε proteasomal degradation via K48-ubiquitination through DTX4 to limit antiviral interferon responses.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"MAP4K1/HPK1 is a hematopoietic Ste20-related serine/threonine kinase that operates as a signal-integrating hub linking immunoreceptor and stress inputs to the JNK/SAPK and NF-\\u03baB pathways, predominantly functioning as a negative regulator of lymphocyte and innate immune activation [#0, #7]. It directly binds and phosphorylates MEKK1 and triggers JNK1 activation through parallel MEKK1\\u2192MKK4/SEK1 and TAK1\\u2192MKK4 and MLK3 routes, independently of Rac1/Cdc42 [#0, #1, #2], and acts upstream of the IKK/NF-\\u03baB axis, in part by phosphorylating the CARMA1 linker at S549/S551/S552 to enable TCR-induced NF-\\u03baB activation [#6, #13, #17]. HPK1 is recruited into antigen-receptor signaling through proline-rich-motif interactions with the SH3 domains of Grb2, Gads/Grap2, Crk/CrkL, and the SLP-76-family adaptors SLP-76 and Clnk, and its catalytic activation upon TCR/BCR engagement depends on Src- and Syk/ZAP-70-family kinases and the LAT/SLP-76/BLNK adaptor network [#3, #4, #7, #9, #10, #12]. Despite enabling NF-\\u03baB, HPK1 restrains the broader response: it suppresses TCR-induced AP-1/ERK signaling, phosphorylates BLNK at Thr152 to drive its 14-3-3 binding, ubiquitination, and degradation in B cells, and competes with ADAP for SLP-76 to dampen Rap1/LFA-1-mediated adhesion in T and B cells [#7, #18, #20]. A distinct PGE2/GPCR input activates HPK1 via PKA-dependent phosphorylation of activation-loop Ser171, bypassing the phosphotyrosine adaptor machinery [#11, #16]. Caspase-3 cleavage at Asp385 splits HPK1 into a constitutively active N-terminal kinase fragment that drives JNK-dependent survival and monocytic differentiation, and a C-terminal fragment that sequesters the IKK complex to suppress NF-\\u03baB and sensitize lymphocytes to activation-induced cell death [#5, #8, #13, #14, #15]. Structurally, the kinase domain is trans-regulated through phosphorylation-state-dependent dimer remodeling, and the citron homology domain folds into a seven-bladed \\u03b2-propellor that binds the kinase domain to inhibit activity, dock SLP-76, and stabilize the protein [#22, #27]. In innate immunity HPK1 promotes DTX4-dependent K48-ubiquitination and proteasomal degradation of TBK1/IKK\\u03b5 to limit antiviral interferon responses, and loss or pharmacologic/PROTAC-mediated inhibition of HPK1 relieves T-cell and NK-cell dysfunction and enhances antitumor immunity [#24, #25, #28].\",\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established HPK1 as a kinase that selectively channels signals into the JNK/SAPK pathway, defining its core catalytic output.\",\n      \"evidence\": \"Transfection epistasis with dominant-negative MEKK1/MKK4 and in vitro binding/phosphorylation in two independent studies\",\n      \"pmids\": [\"8824585\", \"9003777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify physiological upstream activators\", \"Selectivity for JNK over p38/ERK explained mechanistically only at pathway level\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Mapped redundant MAP3K effectors (MLK3, TAK1) downstream of HPK1, showing the kinase feeds multiple parallel routes to JNK.\",\n      \"evidence\": \"Dominant-negative and constitutively active mutant epistasis in transfected cells\",\n      \"pmids\": [\"9003777\", \"9278437\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct phosphorylation of TAK1/MLK3 by HPK1 not demonstrated\", \"Context determining which effector is used unknown\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Identified adaptor-mediated recruitment of HPK1, explaining how it couples to tyrosine-kinase receptor signaling via Grb2 and to Crk/CrkL.\",\n      \"evidence\": \"In vitro SH3-domain binding, co-IP, and EGF stimulation assays\",\n      \"pmids\": [\"9346925\", \"9788432\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of Crk/CrkL phosphorylation not established\", \"In vivo relevance of EGFR coupling unclear\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Discovered caspase-3 cleavage at Asp385 as a switch that splits HPK1 into functionally distinct fragments, reframing it as an apoptosis-regulated kinase.\",\n      \"evidence\": \"In vitro caspase-3 cleavage, Asp385 mutagenesis, and adaptor co-IP\",\n      \"pmids\": [\"10602493\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological trigger of cleavage not defined at this stage\", \"Fate of fragments in vivo unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Placed HPK1 upstream of the IKK/NF-\\u03baB pathway, extending its reach beyond JNK.\",\n      \"evidence\": \"Overexpression IKK kinase activity assays\",\n      \"pmids\": [\"10523828\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis confirming direct IKK interaction\", \"Whether activation is direct or via MEKK1 unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined HPK1 as a TCR/BCR-activated negative regulator of the AP-1 pathway, establishing its central immunoregulatory role.\",\n      \"evidence\": \"Antigen-receptor stimulation with reciprocal gain/kinase-dead loss-of-function and adaptor requirements in T and B cells\",\n      \"pmids\": [\"10795738\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrates mediating AP-1 suppression not yet identified\", \"Distinction between positive NF-\\u03baB and negative AP-1 outputs unexplained\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved the activator-to-inhibitor switch: full-length kinase-active HPK1 activates NF-\\u03baB via IKK\\u03b2, while the C-terminal cleavage fragment is a dominant-negative NF-\\u03baB inhibitor.\",\n      \"evidence\": \"Truncation constructs, dominant-negative IKK\\u03b2, and NF-\\u03baB reporter assays in myeloid cells\",\n      \"pmids\": [\"11278403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of IKK impairment by HPK1-C not yet structural\", \"Endogenous IKK association not yet shown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Extended the adaptor map to Gads/Grap2 and Clnk, showing these SH3 partners enhance HPK1 activity and IL-2 transcription.\",\n      \"evidence\": \"In vitro binding, co-IP in Jurkat/COS cells, kinase and IL-2 reporter assays with kinase-dead epistasis\",\n      \"pmids\": [\"11313918\", \"11509653\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab functional assays\", \"Apparent positive effect on IL-2 contrasts with negative regulatory role\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Identified PGE2/GPCR signaling as a non-immunoreceptor input activating HPK1 to suppress fos transcription.\",\n      \"evidence\": \"PGE2 stimulation, kinase activity, and Fos reporter assays\",\n      \"pmids\": [\"12522005\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular mechanism of PGE2-induced activation not defined here\", \"Single study\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Provided structural definition of an atypical Gads SH3-binding mode on HPK1, explaining adaptor selectivity.\",\n      \"evidence\": \"ITC and X-ray crystallography of the HPK1 peptide\\u00b7Mona/Gads SH3C complex\",\n      \"pmids\": [\"15100220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of full-length adaptor\\u00b7HPK1 complex not solved\", \"Functional impact in cells not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated HPK1 is a bona fide component of the endogenous IKK complex required for TCR-driven NF-\\u03baB and that HPK1-C sequesters IKK to drive activation-induced cell death.\",\n      \"evidence\": \"siRNA knockdown, endogenous IKK co-IP, NF-\\u03baB reporters, and HPK1-C transgenic mice\",\n      \"pmids\": [\"16341093\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry within IKK complex unresolved\", \"Trigger generating HPK1-C physiologically not defined\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed sub-apoptotic caspase-3 generates active HPK1-N to drive JNK-dependent progenitor survival and monocytic differentiation, giving cleavage a developmental role.\",\n      \"evidence\": \"Caspase inhibition and HPK1-N overexpression in primary mouse progenitors with JNK/Bad phosphorylation readouts\",\n      \"pmids\": [\"17024227\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How sub-apoptotic caspase activity is restrained from killing the cell unclear\", \"Direct HPK1-N substrates beyond JNK pathway not mapped\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Defined two complementary roles for cleavage fragments in lymphocyte death and revealed PKA-dependent Ser171 phosphorylation as the mechanism of PGE2 activation.\",\n      \"evidence\": \"HPK1-C transgenic mice and siRNA for AICD; S171A mutagenesis and PKA-deficient S49 cells for PGE2 pathway\",\n      \"pmids\": [\"17712048\", \"17895239\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Connection between the PKA-Ser171 input and physiological outputs incompletely mapped\", \"Selectivity of HPK1-C for anti-apoptotic Bcl-2 members mechanistically open\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Implicated HPK1 in a Src\\u2192HPK1\\u2192MLK3\\u2192JNK3 cascade promoting ischemic neuronal death, extending its kinase circuitry beyond immune cells.\",\n      \"evidence\": \"Co-IP, pharmacological inhibition (PP2, MK801), and histology in rat hippocampus\",\n      \"pmids\": [\"18498770\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Correlative in vivo epistasis without genetic loss-of-function\", \"HPK1 expression/role in neurons not independently confirmed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Identified CARMA1 as a direct HPK1 substrate, providing the molecular link by which HPK1 promotes TCR-induced NF-\\u03baB and IL-2.\",\n      \"evidence\": \"In vitro kinase assay, CARMA1 site mutagenesis, and reconstitution in CARMA1-deficient T cells\",\n      \"pmids\": [\"19706536\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How positive CARMA1 phosphorylation reconciles with overall negative regulation unresolved\", \"Kinetics versus other HPK1 substrates not compared\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Established HPK1 as a brake on integrin-mediated adhesion by competing with ADAP for SLP-76 and associating with SKAP-HOM to limit Rap1/LFA-1 activity in T and B cells.\",\n      \"evidence\": \"HPK1-deficient T and B cells, co-IP, Rap1 activation, and ICAM-1 adhesion assays\",\n      \"pmids\": [\"20957749\", \"20824186\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether kinase activity or scaffolding drives SLP-76 competition unclear\", \"Direct phosphorylation targets in the adhesion module not all identified\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined a degradative mechanism by which HPK1 dampens BCR signaling: BLNK Thr152 phosphorylation triggers 14-3-3 binding, ubiquitination, and degradation.\",\n      \"evidence\": \"HPK1-deficient B cells, in vitro kinase assay, BLNK mutagenesis, and ubiquitination assays\",\n      \"pmids\": [\"22334673\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Ubiquitin ligase mediating BLNK degradation not identified\", \"Generality to T-cell SLP-76 not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed HPK1 is required for chemokine-induced LFA-1 high-affinity adhesion and neutrophil extravasation in vivo, revealing a positive adhesion role in innate cells.\",\n      \"evidence\": \"HPK1-deficient mice, co-IP, confocal imaging, flow adhesion, and intravital microscopy\",\n      \"pmids\": [\"23460610\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Opposite adhesion roles in lymphocytes versus neutrophils mechanistically unreconciled\", \"Direct neutrophil substrates not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the structural basis for HPK1 trans-regulation through phosphorylation-state-dependent dimer remodeling of the kinase domain.\",\n      \"evidence\": \"Multiple crystal structures of non-phosphorylated, doubly phosphorylated, and phosphomimetic kinase domains\",\n      \"pmids\": [\"31018963\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In-cell relevance of the dimer interface not validated\", \"Trigger of activation-loop autophosphorylation not structurally captured\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified PDIA6 as an inhibitor of HPK1 phosphorylation that dampens JNK/c-Jun signaling and apoptosis in non-hematopoietic NSCLC cells.\",\n      \"evidence\": \"Co-IP, phospho-kinase array, and gain/loss-of-function in NSCLC cells\",\n      \"pmids\": [\"30922965\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect inhibition not distinguished\", \"Single-lab non-hematopoietic context\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Established HPK1 as a therapeutic target for antitumor immunity via an HPK1\\u2013NF-\\u03baB\\u2013Blimp1 axis driving T-cell dysfunction.\",\n      \"evidence\": \"MAP4K1 knockout mice, CAR-T tumor models, pharmacological inhibition, and PROTAC degradation\",\n      \"pmids\": [\"32860752\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct HPK1 substrate in the Blimp1 axis not pinpointed\", \"Catalytic versus scaffolding contribution to T-cell dysfunction unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed an innate-immune negative-regulatory function: HPK1 promotes DTX4-dependent K48-ubiquitination and degradation of TBK1/IKK\\u03b5 to limit interferon responses.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, ubiquitination assays, knockdown/knockout, and IFN-\\u03b2 reporters\",\n      \"pmids\": [\"34908452\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HPK1 kinase activity is required for DTX4 recruitment unclear\", \"Single-lab characterization\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Characterized a druggable allosteric pocket outside the kinase domain and an integrin-induced HPK1 signaling cluster, refining inhibitor strategy and interactome.\",\n      \"evidence\": \"ATP-noncompetitive allosteric inhibitor binding assays; co-IP/MS interactome of HL-60 cells with DAP12/Syk/Rac1\",\n      \"pmids\": [\"34608799\", \"35099066\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Allosteric binding site not structurally resolved\", \"Functional validation of most interactome members lacking\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the citron homology domain structure and its autoinhibitory, substrate-docking, and stabilizing functions, completing the intramolecular regulatory picture.\",\n      \"evidence\": \"CHD crystal structure, HDX-MS, CHD\\u2013KD mutagenesis, kinase assays, co-IP, and stability assays\",\n      \"pmids\": [\"38697971\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How adaptor binding relieves CHD autoinhibition not shown\", \"Conformational coupling between CHD and dimer remodeling unexplored\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended HPK1's immunosuppressive role to NK cells, where aberrant overexpression restrains cytotoxicity and promotes metastasis.\",\n      \"evidence\": \"Conditional NK overexpression and MAP4K1-deficient mice with cytotoxicity and metastasis assays\",\n      \"pmids\": [\"38828677\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"NK-specific substrates not identified\", \"TGF-\\u03b21 linkage mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified HPK1 as a driver of pathological neutrophil hyperactivation and mobilization after ischemic stroke.\",\n      \"evidence\": \"HPK1 loss-of-function mice, pharmacological inhibition, and MCAO stroke model with NF-\\u03baB/STAT3/p38 and gasdermin D readouts\",\n      \"pmids\": [\"40169896\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct HPK1 substrates in neutrophil pyroptosis/NET pathway not defined\", \"Single-lab study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How HPK1 reconciles opposing roles (NF-\\u03baB/CARMA1 activation versus AP-1/adhesion suppression; lymphocyte versus neutrophil adhesion) and how adaptor engagement relieves CHD/dimer autoinhibition to direct catalysis toward specific substrates remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unified model linking conformational state to substrate choice\", \"Catalytic versus scaffolding contributions across contexts not systematically dissected\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 17, 20]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 4, 16, 17, 20]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [22, 26]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [7, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [3, 13]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [7, 13, 24, 25]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 2, 6, 17]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [5, 13, 14, 15]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [20, 25]}\n    ],\n    \"complexes\": [\"IKK complex\"],\n    \"partners\": [\"Grb2\", \"GADS/GRAP2\", \"SLP-76\", \"CRKL\", \"CARMA1\", \"BLNK\", \"TBK1\", \"MEKK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}