{"gene":"SAMHD1","run_date":"2026-06-10T07:46:29","timeline":{"discoveries":[{"year":2011,"finding":"SAMHD1 is the dendritic- and myeloid-cell-specific HIV-1 restriction factor counteracted by Vpx; Vpx induces proteasomal degradation of SAMHD1, and silencing SAMHD1 in non-permissive cell lines alleviates HIV-1 restriction with accumulation of viral DNA, while overexpression in sensitive cells inhibits HIV-1 infection. The putative phosphohydrolase activity is required for restriction.","method":"siRNA silencing, overexpression, Vpx-mediated degradation, viral DNA quantification","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal loss-of-function and gain-of-function with defined molecular phenotype, widely replicated across labs","pmids":["21613998"],"is_preprint":false},{"year":2012,"finding":"Vpx recruits SAMHD1 to a cullin4A-RING E3 ubiquitin ligase (CRL4) for proteasomal degradation; SAMHD1 contains a conserved nuclear localization sequence (KRPR, residues 11–14) and is targeted by Vpx specifically in the nucleus—cytoplasmic SAMHD1 (NLS-defective) retains antiviral activity but is resistant to Vpx-induced degradation.","method":"Nuclear localization sequence mutagenesis, leptomycin B nuclear export inhibition, subcellular fractionation, co-immunoprecipitation","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 2 / Strong — NLS mutagenesis with functional rescue, nuclear targeting established mechanistically, replicated by independent labs","pmids":["22973040"],"is_preprint":false},{"year":2013,"finding":"SAMHD1 specifically interacts with ssRNA and ssDNA; nucleic acid binding and SAMHD1 complex formation are mutually dependent; interaction requires the HD domain and C-terminal region but not the SAM domain; AGS-associated mutations impair both nucleic acid binding and complex formation.","method":"Fluorescence cross-correlation spectroscopy, domain deletion/mutation analysis, co-immunoprecipitation","journal":"Journal of molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biophysical binding assay with domain mapping and disease mutants, single lab","pmids":["23371319"],"is_preprint":false},{"year":2013,"finding":"Mouse SAMHD1 reduces cellular dNTP concentrations and restricts retroviral replication in lymphocytes, macrophages, and dendritic cells; absence of SAMHD1 triggers IFN-β-dependent transcriptional upregulation of type I IFN-inducible genes, indicating spontaneous IFN production.","method":"Gene-targeted knockout mice, dNTP measurement, retroviral infection assays, interferon gene expression","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse model with defined cellular phenotypes and dNTP measurements, multiple cell types tested","pmids":["23972988"],"is_preprint":false},{"year":2014,"finding":"SAMHD1 possesses RNase activity; the RNase but not the dNTPase function is essential for HIV-1 restriction. RNase-positive/dNTPase-negative mutant D137N restricts HIV-1; RNase-negative/dNTPase-positive mutant Q548A does not. SAMHD1 associates with and degrades HIV-1 RNA during early infection. Phosphorylation at T592 negatively regulates RNase activity.","method":"In vitro RNase assay, point mutagenesis, HIV-1 RNA co-immunoprecipitation, RNA stability assays in macrophages and CD4+ T cells, phosphomimetic mutations","journal":"Nature medicine","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro enzymatic assay plus mutagenesis plus cellular RNA stability; RNase activity disputed by other labs (contradicted by PMID 26667483)","pmids":["25038827"],"is_preprint":false},{"year":2014,"finding":"SAMHD1 deficiency in AGS patient fibroblasts increases dNTP pools, causing genome instability, constitutive DNA damage signaling, cell cycle delay, cellular senescence, and upregulation of IFN-stimulated genes. SAMHD1 is phosphorylated by cyclin A/CDK1 in a cell cycle-dependent manner, with lowest SAMHD1 levels at G1/S phase.","method":"Primary patient fibroblasts, dNTP measurement, cell cycle analysis, DNA damage assays, co-immunoprecipitation with cyclin A, fluorescence cross-correlation spectroscopy, synchronized HeLa cells, siRNA knockdown","journal":"Annals of the rheumatic diseases","confidence":"High","confidence_rationale":"Tier 2 / Strong — patient-derived cells plus multiple orthogonal methods (dNTP measurement, cell cycle, Co-IP, siRNA), functional consequences defined","pmids":["24445253"],"is_preprint":false},{"year":2015,"finding":"CyclinA2-CDK1/2 phosphorylates SAMHD1 at Thr-592 via a bipartite cyclinA2-CDK binding site in the SAMHD1 C-terminus; phosphorylation at T592 down-modulates (but does not abolish) SAMHD1 dNTPase activity in S phase to fine-tune dNTP levels during DNA replication; phosphorylation-defective mutants cause DNA damage checkpoint activation and excessive dNTP depletion.","method":"Cell cycle synchronization, cyclinA2-CDK binding site mutagenesis, dNTP measurement, DNA damage checkpoint assays, phosphomimetic/phosphodead mutations","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — domain mutagenesis with cell cycle synchronization, dNTP measurement, and checkpoint readout; multiple orthogonal methods","pmids":["25847232"],"is_preprint":false},{"year":2015,"finding":"The phosphomimetic T592E mutation reduces SAMHD1 tetramer stability and dNTPase activity; crystal structures of T592E and T592V variants show that the charged T592E induces large conformational changes via electrostatic repulsion, decreasing active tetramer population.","method":"Crystal structure determination, in vitro dNTPase assays, tetramer stability assays, phosphomimetic mutations","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with functional validation and mutagenesis in a single study","pmids":["26294762"],"is_preprint":false},{"year":2015,"finding":"SAMHD1 inhibits LINE-1 retrotransposition by promoting cellular stress granule assembly (associated with increased eIF2α phosphorylation and diminished eIF4A/eIF4G interaction), which sequesters LINE-1 RNP in stress granules; depletion of G3BP1 or TIA1 abrogates stress granule formation and overcomes SAMHD1 inhibition.","method":"Stress granule marker depletion (siRNA), LINE-1 retrotransposition reporter assay, eIF2α phosphorylation assay, co-immunoprecipitation","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with stress granule markers, functional reporter assay; single lab","pmids":["26134849"],"is_preprint":false},{"year":2015,"finding":"Murine SAMHD1 antiviral activity is regulated through phosphorylation at threonine 603 (equivalent to human T592) and is limited to non-dividing cells; murine SAMHD1 blocks retroviral infection at the level of reverse transcription; the proposed RNase activity of mouse SAMHD1 had no detectable effect on incoming viral RNA levels.","method":"SAMHD1 knockout mouse primary myeloid cells, dNTP measurement, retroviral infection with phosphomutant analysis, viral RNA quantification","journal":"Retrovirology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with phosphomutants and dNTP measurement; negative result for RNase activity noted","pmids":["26667483"],"is_preprint":false},{"year":2016,"finding":"SAMHD1 restricts HIV-1 cell-to-cell transmission from infected T lymphocytes to monocyte-derived dendritic cells and prevents type I interferon response and MxA expression in these coculture settings; Vpx-mediated degradation or siRNA silencing of SAMHD1 increases productive cell-to-cell transmission.","method":"Coculture assay with HIV-infected T lymphocytes and MDDCs, siRNA knockdown, Vpx treatment, interferon/MxA measurements","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-to-cell transmission assay with genetic knockdown, defined innate immune readout; single lab","pmids":["23269793"],"is_preprint":false},{"year":2016,"finding":"The spontaneous type I IFN response in SAMHD1-deficient cells and mice requires the cGAS/STING cytosolic DNA-sensing pathway; cell-autonomous lentivirus restriction by SAMHD1 in myeloid cells requires reverse transcription and cGAS/STING signaling, and limits virus-induced IFN production and co-stimulatory marker induction.","method":"Genetic epistasis (cGAS/STING KO combined with SAMHD1 deficiency), reverse transcription inhibitor treatment, in vivo mouse infection","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis in cells and mice with multiple pathway components tested","pmids":["27477283"],"is_preprint":false},{"year":2016,"finding":"Heterozygous cancer-associated SAMHD1 mutations negatively affect dNTPase activity; inactivation of one SAMHD1 allele is sufficient to elevate dNTP pools in mouse embryos; minor dNTP pool changes combined with inactivated mismatch repair dramatically increase mutation rates.","method":"Enzymatic activity assays of mutant proteins, dNTP measurement in mouse embryos, mutation rate analysis in yeast/cell models","journal":"Proceedings of the National Academy of Sciences","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro enzymatic assays plus in vivo dNTP measurement plus mutation rate experiments","pmids":["27071091"],"is_preprint":false},{"year":2017,"finding":"SAMHD1 has a dNTPase-independent function in promoting DNA end resection to facilitate DSB repair by homologous recombination; SAMHD1 is recruited to DSBs; SAMHD1 complexes with CtIP via a conserved C-terminal domain and recruits CtIP to DSBs; a cancer-associated mutant with impaired CtIP interaction (but not a dNTPase-inactive mutant) fails to rescue the end resection impairment.","method":"CRISPR/Cas9 knockout, Vpx-mediated degradation, co-immunoprecipitation (SAMHD1–CtIP complex), recruitment to DSBs by ChIP/imaging, HR reporter assay, domain deletion mutagenesis","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, KO with defined HR phenotype, cancer mutant epistasis; multiple orthogonal methods in single study","pmids":["28834754"],"is_preprint":false},{"year":2017,"finding":"SAMHD1 dNTPase activity is regulated by a redox switch: three cysteine residues form an intrachain disulfide bond that reversibly inhibits protein tetramerization and catalysis; proliferative signals lead to SAMHD1 oxidation in cells, and oxidized SAMHD1 localizes outside the nucleus.","method":"Biochemical identification of disulfide bonds, dNTPase activity assays, cell fractionation, redox manipulation","journal":"Antioxidants & redox signaling","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical assays plus cellular localization; single lab","pmids":["28398823"],"is_preprint":false},{"year":2017,"finding":"SAMHD1 acetylation at lysine 405 by ARD1 acetyltransferase enhances dNTPase activity in vitro; non-acetylated K405R mutant-expressing cancer cells have reduced G1/S transition and slower proliferation; acetylation levels are strongest during G1 phase.","method":"In vitro acetylation assay, dNTPase activity measurement, K405R mutagenesis, cell cycle analysis, co-immunoprecipitation","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro enzymatic assay with mutagenesis and cell cycle phenotype; single lab","pmids":["28978134"],"is_preprint":false},{"year":2018,"finding":"SAMHD1 promotes degradation of nascent DNA at stalled replication forks by stimulating the exonuclease activity of MRE11, which activates the ATR-CHK1 checkpoint and allows fork restart; in SAMHD1-depleted cells, ssDNA fragments accumulate in the cytosol and activate the cGAS-STING pathway to induce type I interferons.","method":"DNA fiber assay (fork restart), MRE11 exonuclease assay, siRNA knockdown, cGAS/STING pathway activation measurement, cytosolic ssDNA detection","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (DNA fiber, exonuclease assay, cGAS/STING genetics) in a single high-quality study, replicated across cell lines","pmids":["29670289"],"is_preprint":false},{"year":2018,"finding":"SAMHD1 dephosphorylation at T592 (activating the protein) is the predominant mechanism of HIV-1 restriction induced by type I, II, and III IFN signaling in macrophages; all IFN types downregulated CDK1 protein expression; pharmacological CDK1 inhibition or siRNA knockdown phenocopied IFN effects on SAMHD1; viral restriction imposed by IFNs or dasatinib was overcome by SAMHD1 depletion.","method":"SAMHD1 phosphorylation state analysis, CDK1 knockdown/inhibition, IFN treatment, HIV-1 infection assay in primary macrophages, SAMHD1 knockdown rescue experiments","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological and genetic epistasis with CDK1, multiple IFN types, SAMHD1 depletion rescue; primary cells used","pmids":["29764952"],"is_preprint":false},{"year":2018,"finding":"SAMHD1 promotes immunoglobulin hypermutation by restricting dNTP supply; CRISPR inactivation of SAMHD1 in germinal center B cells increased transition mutations at C:G base pairs and substantially decreased transversion mutations at A:T and C:G base pairs, indicating that dNTP starvation by SAMHD1 enhances AID mutagenicity.","method":"CRISPR/Cas9 knockout in germinal center B cells, Ig hypermutation sequencing, dNTP measurement","journal":"Proceedings of the National Academy of Sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean CRISPR KO with sequencing of mutation spectra; single lab","pmids":["29669924"],"is_preprint":false},{"year":2019,"finding":"EBV protein kinase BGLF4 phosphorylates SAMHD1 and inhibits its dNTPase activity; this mechanism of phosphorylation-based SAMHD1 inactivation is shared by beta- and gamma-herpesviruses (conserved viral protein kinases).","method":"In vitro kinase assay, dNTPase activity measurement, viral infection assays, phosphorylation site mapping","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus antiviral functional assay; single lab","pmids":["31291580"],"is_preprint":false},{"year":2019,"finding":"SAMHD1 modulates early steps of HCMV infection by suppressing NF-κB activation; SAMHD1 depletion increases HCMV gene expression from the major immediate-early promoter independently of dNTP levels; SAMHD1 inhibits NF-κB, and increased RELA and RNA polymerase II occupy the HCMV MIE promoter in SAMHD1-depleted cells; HCMV viral kinase UL97 phosphorylates SAMHD1 during infection.","method":"SAMHD1 depletion, ChIP (RELA, RNA Pol II), NF-κB reporter assay, viral gene expression measurement, phosphorylation assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP plus genetic depletion with multiple pathway readouts; dNTP-independence established","pmids":["31291579"],"is_preprint":false},{"year":2019,"finding":"HCMV overcomes SAMHD1 restriction in macrophages by using the viral kinase pUL97 (and by hijacking cellular kinases) to phosphorylate SAMHD1 at T592, converting it to its inactive form; HCMV also interferes with SAMHD1 steady-state expression.","method":"SAMHD1 phosphorylation assays in infected cells, viral kinase pUL97 functional analysis, dNTP measurement","journal":"Nature microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — viral kinase phosphorylation assay plus dNTP and infection readouts; single lab","pmids":["31548682"],"is_preprint":false},{"year":2019,"finding":"Murine CMV viral kinase M97 counteracts SAMHD1 restriction in vivo by phosphorylating the regulatory residue T603; phosphorylation correlated with reduced dNTP hydrolase activity and loss of viral restriction; SAMHD1 inhibits MCMV replication in vivo in a SAMHD1 knockout mouse model.","method":"SAMHD1 knockout mice, MCMV infection in vivo and in vitro, viral kinase M97 phosphorylation assay, dNTPase activity measurement","journal":"Nature microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo KO mouse model with viral kinase assay and dNTPase activity measurement","pmids":["31548683"],"is_preprint":false},{"year":2019,"finding":"TRIM21 E3 ubiquitin ligase specifically interacts with SAMHD1 and promotes its proteasomal degradation; ubiquitination occurs at K622 on SAMHD1; phosphorylation of SAMHD1 at T592 also blocks EV71 restriction; TRIM21-mediated SAMHD1 degradation affects HIV-1 restriction and interferon regulation.","method":"Co-immunoprecipitation, ubiquitination assay, proteasome inhibition, domain mutagenesis, EV71 and HIV-1 infection assays","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus ubiquitination site mapping plus functional rescue; single lab","pmids":["31797533"],"is_preprint":false},{"year":2019,"finding":"PIM1 and PIM3 serine/threonine kinases phosphorylate HIV-2 Vpx at Ser13, stabilizing the Vpx–SAMHD1 interaction and promoting ubiquitin-mediated proteolysis of SAMHD1; PIM kinase inhibition promotes SAMHD1 antiviral activity and reduces viral replication.","method":"Integrated proteomics, in vitro kinase assay, co-immunoprecipitation, ubiquitination assay, viral replication assay with PIM inhibitors/knockdown","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus proteomic identification plus functional viral replication readout; single lab","pmids":["31015445"],"is_preprint":false},{"year":2019,"finding":"SAMHD1 is a nucleocytoplasmic shuttling protein; altering subcellular localization by mutating/removing NLS enhances SAMHD1's potency in LINE-1 suppression; cytoplasmic SAMHD1 leads to enhanced depletion of LINE-1 ORF2p.","method":"Digitonin-based cytoplasm/nucleus fractionation, NLS mutagenesis, exportin Xpo1 overexpression, LINE-1 retrotransposition reporter assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — fractionation with functional consequence, mutagenesis; single lab","pmids":["30739781"],"is_preprint":false},{"year":2019,"finding":"SAMHD1 competitively interacts with VP1 of EV71 and EVD68 at the same domain that binds VP2, thereby interfering with VP1–VP2 interaction and viral capsid assembly; this mechanism is independent of dNTPase or RNase activity; T592A mutant maintains this inhibitory effect but T592D mutant does not.","method":"Co-immunoprecipitation, competitive binding assay, viral assembly assay, phosphomutant analysis","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP binding competition plus functional viral assembly readout with phosphomutants; single lab","pmids":["33883225"],"is_preprint":false},{"year":2020,"finding":"Crystal structures reveal that SAMHD1 utilizes a bi-metallic iron-magnesium active-site center that positions a hydroxide nucleophile in-line with the Pα–O5' bond to catalyze phosphoester bond hydrolysis of dNTPs.","method":"X-ray crystallography of SAMHD1 inhibitor complexes, enzymological assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures with functional validation revealing precise catalytic mechanism","pmids":["32576829"],"is_preprint":false},{"year":2020,"finding":"TLR4 activation induces G0 arrest and SAMHD1 antiretroviral activity via an IFN-independent pathway requiring TRIF but not TBK1, IRF3, Myd88, or NF-κB; this involves p21 upregulation and CDK1 depletion, leading to SAMHD1 dephosphorylation at T592; SAMHD1 knockdown confirmed that TLR4-activated HIV-1 block is specifically mediated by SAMHD1.","method":"TLR4 agonist treatment, TRIF/TBK1/IRF3/Myd88 inhibition, SAMHD1 phosphorylation assay, CDK1 level measurement, SAMHD1 knockdown, HIV-1 infection assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic pathway dissection with multiple signaling components plus SAMHD1-specific rescue; primary macrophages used","pmids":["32209460"],"is_preprint":false},{"year":2020,"finding":"HCMV infection induces rapid SAMHD1 phosphorylation at T592 by cellular Cdk2 and viral kinase pUL97, resulting in a significant fraction of phospho-SAMHD1 relocating to the cytoplasm of infected fibroblasts in association with viral particles and dense bodies.","method":"SAMHD1 phosphorylation analysis, subcellular fractionation, co-localization with viral particles by imaging","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphorylation mapping plus localization imaging; single lab","pmids":["32986788"],"is_preprint":false},{"year":2020,"finding":"SAMHD1-mediated dNTP degradation is required for efficient DNA repair during immunoglobulin class switch recombination (CSR); SAMHD1 localizes at the Ig switch region; SAMHD1 depletion impairs CSR and IgH/c-Myc translocation; elevated dNTP pools increase nucleotide insertions at break-point junctions.","method":"ChIP (SAMHD1 at Ig switch region), CSR assay, translocation assay, nucleotide pool manipulation, SAMHD1 siRNA depletion","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — ChIP localization with functional CSR assay and translocation readout plus dNTP pool manipulation","pmids":["32511795"],"is_preprint":false},{"year":2021,"finding":"OGT-mediated O-GlcNAcylation of SAMHD1 at Ser93 stabilizes SAMHD1 and enhances its antiviral activity against HBV; HBP/O-GlcNAcylation positively regulates SAMHD1-dependent antiviral response in vitro and in vivo.","method":"LC-MS identification of O-GlcNAc site, co-immunoprecipitation, OGT overexpression/knockdown, HBV replication assay, S93 mutagenesis","journal":"Theranostics","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — mass spectrometry-identified modification site plus mutagenesis plus functional antiviral assay; single lab","pmids":["33391506"],"is_preprint":false},{"year":2021,"finding":"TRAF6 and TAK1 contribute to SAMHD1-mediated suppression of NF-κB activation; SAMHD1 inhibits TAK1 activation and TRAF6 signaling; TRAF6 knockdown in SAMHD1-deficient cells significantly inhibited HIV-1 infection and NF-κB activation; the NLS is not required for this suppressive function.","method":"SAMHD1 CRISPR KO, TRAF6 siRNA knockdown, TAK1 pharmacological inhibition, IκBα phosphorylation assay, TNF-α mRNA measurement, HIV-1 infection assay, NF-κB reporter","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (KO + KD) with multiple pathway readouts; single lab","pmids":["33177202"],"is_preprint":false},{"year":2021,"finding":"PIAS1 E3 SUMO ligase interacts with SAMHD1 and promotes its SUMOylation at K469, K595, and K622; SUMOylation-deficient SAMHD1 loses anti-EBV activity; SAMHD1 association with EBV genome is PIAS1-dependent.","method":"Co-immunoprecipitation, SUMOylation assay, site mutagenesis (K469R/K595R/K622R), ChIP (SAMHD1 on EBV genome), EBV replication assay","journal":"Cell & bioscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus SUMOylation site mapping plus ChIP with functional antiviral readout; single lab","pmids":["34238351"],"is_preprint":false},{"year":2021,"finding":"SAMHD1 dNTPase activity restrains aberrant nucleotide insertions at DNA break repair junctions during end joining; SAMHD1 expression or low intracellular dNTPs leads to shorter repair joints and impedes insertion of distant DNA regions prior to end repair.","method":"Linear DNA substrate end-joining assay in HEK293 cells, CRISPR/Cas9-induced break monitoring, SAMHD1 dNTPase mutant analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional DNA repair assay with dNTPase mutants; single lab","pmids":["33591315"],"is_preprint":false},{"year":2021,"finding":"R-loops are highly enriched at transcription-replication conflict regions in SAMHD1-deficient cells; SAMHD1 loss leads to R-loop accumulation and activation of DNA damage responses; removal of R-loops in SAMHD1 deficiency reduces cellular responses to genome instability.","method":"R-loop immunofluorescence/ChIP (S9.6 antibody), DNA damage response markers, R-loop removal by RNase H overexpression, SAMHD1 patient fibroblasts","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patient fibroblasts plus R-loop detection plus rescue with RNase H; single lab","pmids":["33857133"],"is_preprint":false},{"year":2022,"finding":"SAMHD1 functions as a single-stranded RNA (ssRNA) 3' exonuclease; loss of SAMHD1 causes cellular RNA accumulation, leading to dissolution of RNA-protein condensates that sequester immunogenic dsRNA; released dsRNA triggers type I IFN activation via RIG-I-like receptors.","method":"ssRNA exonuclease assay, RNA sequencing (RNA accumulation), condensate dissolution imaging, RIG-I-like receptor epistasis, SAMHD1 KO cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro exonuclease assay plus condensate imaging plus RLR epistasis; multiple orthogonal methods in single study","pmids":["36150385"],"is_preprint":false},{"year":2022,"finding":"SIRT1 deacetylase complexes with SAMHD1 and deacetylates it at conserved K354 specifically in response to DSBs; K354 deacetylation promotes SAMHD1 recruitment to DSBs and binding to ssDNA, which facilitates CtIP ssDNA binding and promotes DNA end resection and HR, without affecting tetramerization or dNTPase activity.","method":"Co-immunoprecipitation (SIRT1–SAMHD1), K354 mutagenesis, DSB recruitment assay (ChIP/imaging), ssDNA binding assay, HR reporter assay, CtIP ssDNA binding","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus mutagenesis plus ChIP plus functional HR assay; multiple orthogonal methods","pmids":["36344525"],"is_preprint":false},{"year":2022,"finding":"In SAMHD1-deficient mice, the chronic IFN response is driven by the MDA5/MAVS pathway but requires functional priming through the cGAS/STING pathway; cGAS/STING is positioned upstream of tonic IFN signaling in Samhd1-deficient mice.","method":"Genetic epistasis (Samhd1 KO crossed with cGAS/STING KO and MDA5/MAVS KO), IFN measurement, tumor-free survival analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — double KO genetic epistasis in vivo placing cGAS/STING upstream of MDA5/MAVS in SAMHD1-deficient inflammation","pmids":["36346347"],"is_preprint":false},{"year":2022,"finding":"Phosphorylation at T592 accelerates SAMHD1 tetramer dissociation (~15-fold) and increases C-terminal domain dynamics; ssDNA binds competitively with GTP to the A1 allosteric site; cryo-EM structure reveals substantial dynamics in the C-terminal domain containing T592.","method":"Cryo-EM structure, tetramer dissociation kinetics, ssDNA binding assay, GTP competition assay, phosphomimetic mutations","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with functional binding assays and kinetics; multiple methods in single study","pmids":["35801923"],"is_preprint":false},{"year":2023,"finding":"SAMHD1 suppresses NF-κB activation by directly interacting (via its HD domain) with IKKα and IKKβ; SAMHD1 suppresses phosphorylation of IKKα/β/γ, inhibiting downstream IκBα phosphorylation; SAMHD1 disrupts the interaction between upstream kinase TAK1 and IKKα or IKKβ; direct in vitro binding between recombinant SAMHD1 and purified IKKα or IKKβ was demonstrated.","method":"Co-immunoprecipitation (endogenous and recombinant), in vitro binding assay with purified proteins, SAMHD1 KO/reconstitution, domain mapping, IKK phosphorylation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro binding with purified proteins plus reciprocal Co-IP plus KO/reconstitution; multiple orthogonal methods","pmids":["37100289"],"is_preprint":false},{"year":2023,"finding":"SAMHD1 inhibits type I IFN induction through the MAVS, IKKε, and IRF7 signaling axis; SAMHD1 interacts with MAVS and suppresses MAVS aggregation upon Sendai virus infection; SAMHD1 prevents IRF7 binding to the kinase domain of IKKε; the SAMHD1 interaction with the inhibitory domain of IRF7 (IRF7-ID) is necessary and sufficient for SAMHD1 suppression of IRF7-mediated IFN-I activation.","method":"Co-immunoprecipitation (SAMHD1–MAVS, SAMHD1–IRF7), MAVS aggregation assay, IRF7-IKKε binding assay, HEK293T reporter assay, IRF7-ID mutagenesis, computational docking/molecular dynamics","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus aggregation assay plus domain mutagenesis plus reporter assay; multiple orthogonal methods in single study","pmids":["37328105"],"is_preprint":false},{"year":2023,"finding":"Deubiquitinase USP7 interacts with SAMHD1 and deubiquitinates it at K421, stabilizing SAMHD1 protein expression; stabilized SAMHD1 interacts with CtIP to promote DNA damage repair; USP7 inhibition sensitizes tumor cells to chemotherapeutic agents by decreasing SAMHD1.","method":"Co-immunoprecipitation (USP7–SAMHD1), ubiquitination site mapping (K421), USP7 inhibitor treatment, DNA damage repair assay, chemosensitivity assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ubiquitination site mapping plus functional repair and sensitivity assays; single lab","pmids":["37081042"],"is_preprint":false},{"year":2023,"finding":"SAMHD1 contributes to cancer cell migration in ccRCC by participating in endocytosis and lamellipodia formation; SAMHD1 binds cortactin to form an endosomal complex, and SAMHD1-stimulated endosomal FAK signaling activates Rac1, promoting lamellipodia formation and cell motility.","method":"Co-immunoprecipitation (SAMHD1–cortactin), FAK signaling assays, Rac1 activation assay, lamellipodia imaging, cell migration assay, patient tissue correlation","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus kinase signaling assay plus functional migration readout; single lab","pmids":["37009792"],"is_preprint":false},{"year":2024,"finding":"SAMHD1 cooperates with MX2 to inhibit HIV-1 at the post-cDNA-synthesis stage by recognizing and binding incoming HIV-1 cores and delivering them to the MX2 molecular trap, blocking nuclear entry; SAMHD1 mutants unable to recognize HIV-1 core showed substantially decreased antiviral activity; this mechanism is distinct from dNTP hydrolysis.","method":"Immunoprecipitation plus mass spectrometry (SAMHD1–MX2), MX2 KO (endogenous disruption), SAMHD1 domain mapping, HIV-1 nuclear import assay, HIV-1 capsid mutant analysis","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP/MS interaction plus nuclear import assay plus genetic KO; single lab, novel mechanism","pmids":["38888311"],"is_preprint":false},{"year":2025,"finding":"SAMHD1 tetramerization alone is insufficient for dNTP hydrolysis; activation requires an inactive tetrameric intermediate with partially occupied allosteric sites; the equilibrium between inactive and active tetrameric states regulates dNTPase activity driven by binding/dissociation of additional allosteric dNTP ligands; catalytic efficiency (but not substrate specificity) is modulated by the identity of dNTPs at allosteric sites; SAMHD1 exhibits facilitated dNTP depletion, whereby increased biosynthesis of certain dNTPs enhances depletion of others.","method":"In vitro dNTPase assays, allosteric site occupancy analysis, tetramerization assays, kinetic modeling","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — rigorous in vitro reconstitution with allosteric analysis; single lab but comprehensive mechanistic dissection","pmids":["39824836"],"is_preprint":false},{"year":2021,"finding":"NONO interacts with SAMHD1 and stabilizes it by inhibiting DCAF1-mediated ubiquitination/degradation; NONO overexpression increases SAMHD1 expression and reduces AML cell sensitivity to Ara-C.","method":"Co-immunoprecipitation (NONO–SAMHD1), ubiquitination assay with DCAF1, NONO overexpression/knockdown, cytarabine sensitivity assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus ubiquitination assay plus functional drug resistance readout; single lab","pmids":["35803902"],"is_preprint":false},{"year":2021,"finding":"Sp-dNTPαS diastereomers (but not Rp-dNTPαS) prevent Mg2+ coordination at allosteric and catalytic sites, rendering SAMHD1 unable to form stable active homotetramers or hydrolyze substrates; Sp-dNTPαS competitively inhibits dNTP hydrolysis; a co-crystal structure of SAMHD1 with Rp-dGTPαS reveals an Fe-Mg-bridging water species poised for nucleophilic attack on Pα.","method":"X-ray crystallography (SAMHD1–Rp-dGTPαS cocrystal), in vitro dNTPase kinetics, tetramerization assay, stereospecific substrate analysis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — cocrystal structure with enzymological validation; reveals stereospecific catalytic mechanism","pmids":["33988981"],"is_preprint":false},{"year":2016,"finding":"Interferon induction of SAMHD1 in primary human monocytes depends on post-transcriptional regulation via 3'-UTR; miR-181a and miR-30a target the SAMHD1 3'-UTR and their down-regulation inversely correlates with SAMHD1 protein up-regulation upon type I and II IFN stimulation in monocytes; this miRNA-dependent regulation does not occur in macrophages or dendritic cells.","method":"Luciferase 3'-UTR reporter assay, miRNA overexpression/inhibition, miRNA-SAMHD1 correlation in primary monocytes, AGO2 co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — 3'-UTR reporter plus AGO2 CLIP plus primary cell correlation; single lab","pmids":["27909056"],"is_preprint":false}],"current_model":"SAMHD1 is a dNTP triphosphohydrolase (active as an allosterically regulated homotetramer using a bi-metallic Fe-Mg catalytic center) that restricts HIV-1 and other viruses primarily by depleting intracellular dNTP pools below levels required for reverse transcription in non-dividing myeloid cells and resting T cells; its activity is regulated post-translationally by phosphorylation at T592 by CyclinA2-CDK1/2 (inactivating the enzyme by destabilizing the tetramer), by a redox-sensitive disulfide switch, by acetylation at K405 (activating), by O-GlcNAcylation at S93 (stabilizing), by TRIM21-mediated ubiquitination at K622 (degrading), and by SIRT1-mediated deacetylation at K354 and USP7-mediated deubiquitination at K421; beyond dNTP depletion, SAMHD1 independently suppresses innate immune signaling by inhibiting NF-κB (through direct interaction with IKKα/β and disruption of TAK1 engagement), suppressing type I IFN induction via the MAVS–IKKε–IRF7 axis, and by functioning as an ssRNA 3' exonuclease to prevent immunogenic dsRNA release from condensates; at stalled replication forks SAMHD1 stimulates MRE11 exonuclease activity to promote fork restart and prevent ssDNA-mediated cGAS-STING activation; SAMHD1 also recruits CtIP (via its C-terminal domain, regulated by SIRT1-mediated K354 deacetylation) to promote DNA end resection and homologous recombination; Vpx from HIV-2/SIV counteracts SAMHD1 by recruiting it via CRL4 E3 ubiquitin ligase for nuclear proteasomal degradation, and multiple herpesvirus kinases phosphorylate T592 to inactivate SAMHD1."},"narrative":{"mechanistic_narrative":"SAMHD1 is an allosterically regulated dNTP triphosphohydrolase that controls intracellular dNTP pools to enforce antiviral restriction and safeguard genome integrity [PMID:21613998, PMID:32576829, PMID:39824836]. As the dendritic- and myeloid-cell HIV-1 restriction factor, it blocks reverse transcription in non-dividing cells and is counteracted by lentiviral Vpx, which recruits it to a CRL4 E3 ligase for nuclear proteasomal degradation [PMID:21613998, PMID:22973040]. Catalysis proceeds through a bi-metallic iron-magnesium active center that positions a hydroxide nucleophile in-line with the Pα–O5' bond, and full hydrolytic activity requires assembly of an allosterically loaded active homotetramer rather than tetramerization alone [PMID:32576829, PMID:33988981, PMID:39824836]. Enzymatic output is tuned by a dense layer of post-translational control: CyclinA2-CDK1/2 phosphorylation at Thr592 destabilizes the tetramer and down-modulates dNTPase activity during S phase, an effect structurally explained by electrostatic disruption of the active tetramer and accelerated subunit dissociation [PMID:25847232, PMID:26294762, PMID:35801923]; a reversible cysteine disulfide switch, ARD1-mediated K405 acetylation, and OGT-mediated S93 O-GlcNAcylation further modulate activity and stability, while TRIM21-, USP7-, and NONO/DCAF1-linked ubiquitination pathways set protein levels [PMID:28398823, PMID:28978134, PMID:33391506, PMID:31797533, PMID:37081042, PMID:35803902]. Beyond nucleotide pool control, SAMHD1 acts directly in genome maintenance, stimulating MRE11 exonuclease activity at stalled forks to enable restart and recruiting CtIP—governed by SIRT1-mediated K354 deacetylation—to drive DNA end resection and homologous recombination, thereby restraining cytosolic nucleic acid release [PMID:29670289, PMID:28834754, PMID:36344525]. It independently suppresses innate immune signaling by binding IKKα/β and disrupting TAK1 engagement to inhibit NF-κB, by interacting with MAVS/IKKε/IRF7 to limit type I IFN induction, and by functioning as an ssRNA 3' exonuclease that prevents immunogenic dsRNA release from condensates [PMID:37100289, PMID:37328105, PMID:36150385]. Loss of SAMHD1 elevates dNTP pools and triggers chronic cGAS/STING- and MDA5/MAVS-dependent type I interferon responses, a pathophysiology underlying Aicardi-Goutières syndrome [PMID:24445253, PMID:29670289, PMID:36346347].","teleology":[{"year":2011,"claim":"Established SAMHD1 as the long-sought myeloid/dendritic-cell HIV-1 restriction factor and the target of lentiviral Vpx, defining its antiviral role.","evidence":"siRNA silencing, overexpression, and Vpx-mediated degradation with viral DNA quantification in non-permissive cells","pmids":["21613998"],"confidence":"High","gaps":["Molecular basis of restriction (dNTPase vs other activities) not yet defined","Did not establish where in the cell restriction occurs"]},{"year":2012,"claim":"Showed Vpx degrades SAMHD1 through a CRL4 E3 ligase acting on nuclear SAMHD1, localizing the counteraction mechanism and identifying its NLS.","evidence":"NLS mutagenesis, leptomycin B export inhibition, fractionation, and co-IP","pmids":["22973040"],"confidence":"High","gaps":["Did not address why nuclear localization is required for Vpx targeting","Antiviral mechanism still unresolved"]},{"year":2013,"claim":"Linked SAMHD1 to dNTP pool depletion as the basis of retroviral restriction and revealed that its loss drives spontaneous type I IFN production in vivo.","evidence":"Gene-targeted knockout mice with dNTP measurement, retroviral infection, and IFN gene expression; parallel nucleic-acid-binding biophysics in human cells","pmids":["23972988","23371319"],"confidence":"High","gaps":["Sensor linking dNTP/SAMHD1 loss to IFN not identified","Relative contribution of nucleic-acid binding vs dNTPase unresolved"]},{"year":2014,"claim":"Connected dNTP pool dysregulation in SAMHD1-deficient patient cells to genome instability and identified cyclin A/CDK1 cell-cycle phosphorylation, tying enzymatic regulation to the cell cycle; a contested report proposed an RNase activity as the restriction determinant.","evidence":"AGS patient fibroblasts with dNTP/DNA-damage assays and cyclin A co-IP; in vitro RNase assay with D137N/Q548A mutants","pmids":["24445253","25038827"],"confidence":"High","gaps":["RNase claim disputed by later mouse work (PMID 26667483)","Mechanism converting dNTP excess to DNA damage not defined"]},{"year":2015,"claim":"Defined the CyclinA2-CDK1/2 phosphorylation site (T592) and showed structurally and kinetically that phosphorylation destabilizes the active tetramer to fine-tune dNTP levels.","evidence":"Cell-cycle synchronization with binding-site mutagenesis and dNTP/checkpoint readouts; crystal structures of T592E/T592V with dNTPase assays; mouse T603 phosphomutant analysis","pmids":["25847232","26294762","26667483"],"confidence":"High","gaps":["Phosphatase reversing T592 not identified here","Whether RNase contributes to restriction left contradicted"]},{"year":2016,"claim":"Placed the cGAS/STING DNA-sensing pathway downstream of SAMHD1 loss and established cell-autonomous restriction requiring reverse transcription, unifying antiviral and inflammatory phenotypes.","evidence":"Genetic epistasis (cGAS/STING KO with SAMHD1 deficiency) in cells and mice; cancer-mutation dNTPase and mutation-rate analyses; 3'-UTR/miRNA regulation in monocytes","pmids":["27477283","27071091","27909056"],"confidence":"High","gaps":["Source of the immunostimulatory DNA species not yet defined","Tissue-specificity of miRNA regulation incompletely mapped"]},{"year":2017,"claim":"Revealed dNTPase-independent genome-protective functions: SAMHD1 recruits CtIP to promote DNA end resection and HR, and is regulated by a redox disulfide switch and K405 acetylation.","evidence":"CRISPR KO with HR reporter, reciprocal SAMHD1–CtIP co-IP, cancer-mutant epistasis; disulfide mapping and dNTPase assays; in vitro acetylation by ARD1","pmids":["28834754","28398823","28978134"],"confidence":"High","gaps":["How SAMHD1 is recruited to DSBs not yet defined","Physiological trigger of redox switch in vivo unclear"]},{"year":2018,"claim":"Showed IFN restricts HIV-1 chiefly by dephosphorylating/activating SAMHD1 via CDK1 downregulation, and demonstrated dNTP-control roles in antibody diversification and stalled-fork repair.","evidence":"CDK1 inhibition/knockdown with phospho-SAMHD1 and HIV infection in macrophages; CRISPR KO in germinal-center B cells with mutation spectra; DNA fiber and MRE11 exonuclease assays with cGAS/STING readouts","pmids":["29764952","29669924","29670289"],"confidence":"High","gaps":["Phosphatase mediating IFN-induced dephosphorylation not identified","Mechanism of MRE11 stimulation by SAMHD1 biochemically undefined"]},{"year":2019,"claim":"Demonstrated that diverse herpesviruses inactivate SAMHD1 by viral-kinase phosphorylation of T592, identified TRIM21-mediated degradation and PIM-kinase-enhanced Vpx counteraction, and uncovered NF-κB suppression as a dNTP-independent antiviral mechanism.","evidence":"In vitro/in vivo viral kinase assays (BGLF4, pUL97, M97) with dNTPase readouts and KO mice; TRIM21 co-IP/ubiquitination; PIM1/3 phospho-Vpx proteomics; ChIP of RELA at the HCMV MIE promoter","pmids":["31291580","31291579","31548682","31548683","31797533","31015445","30739781"],"confidence":"High","gaps":["Mechanistic basis of NF-κB inhibition not yet resolved at this stage","Relative in vivo weight of each regulatory PTM unclear"]},{"year":2020,"claim":"Refined the catalytic mechanism (bi-metallic Fe-Mg in-line hydrolysis), defined dNTP-control roles in class switch recombination, and identified an IFN-independent TLR4 pathway activating SAMHD1.","evidence":"X-ray crystallography with enzymology; ChIP/CSR assays with dNTP manipulation; TLR4-agonist pathway dissection (TRIF-dependent, CDK1 depletion)","pmids":["32576829","32511795","32209460","32986788"],"confidence":"High","gaps":["How dNTP levels mechanistically shape repair-junction fidelity not fully resolved","TLR4-to-SAMHD1 signaling intermediates incompletely mapped"]},{"year":2021,"claim":"Expanded the PTM and interactome landscape (O-GlcNAcylation, SUMOylation, NONO stabilization) and uncovered dNTP-control roles at transcription-replication conflicts and end-joining junctions.","evidence":"MS site mapping with mutagenesis and antiviral assays (S93 O-GlcNAc, K469/K595/K622 SUMO); NONO co-IP/ubiquitination; R-loop ChIP with RNase H rescue; end-joining substrate assays","pmids":["33391506","34238351","35803902","33857133","33591315","33988981"],"confidence":"Medium","gaps":["Combinatorial interplay among PTMs not addressed","Most modification studies are single-lab observations"]},{"year":2022,"claim":"Defined SAMHD1 as an ssRNA 3' exonuclease preventing dsRNA-driven IFN, mapped SIRT1-K354 deacetylation as the switch coupling SAMHD1 to CtIP-dependent resection, and ordered cGAS/STING upstream of MDA5/MAVS in SAMHD1-deficient inflammation.","evidence":"In vitro exonuclease assays with condensate imaging and RLR epistasis; SIRT1–SAMHD1 co-IP with K354 mutagenesis and HR assays; double-KO epistasis in mice; cryo-EM with tetramer dissociation kinetics","pmids":["36150385","36344525","36346347","35801923"],"confidence":"High","gaps":["How exonuclease and dNTPase roles are partitioned in vivo unresolved","Switch between sensing pathways across cell types unclear"]},{"year":2023,"claim":"Mechanistically defined SAMHD1's direct innate-immune suppression (IKKα/β binding disrupting TAK1; MAVS/IKKε/IRF7 axis), and revealed USP7-mediated stabilization and a cytoskeletal/migration role via cortactin in cancer.","evidence":"In vitro binding with purified proteins, reciprocal co-IP and KO/reconstitution for IKK and MAVS/IRF7; USP7 co-IP with K421 mapping and chemosensitivity; cortactin co-IP with FAK/Rac1 and migration assays","pmids":["37100289","37328105","37081042","37009792"],"confidence":"High","gaps":["Integration of NF-κB and IFN suppression with dNTPase activity unclear","Migration role is a single-lab observation"]},{"year":2024,"claim":"Identified a dNTPase-independent cooperation with MX2 in which SAMHD1 binds incoming HIV-1 cores and delivers them to an MX2 trap to block nuclear entry.","evidence":"Co-IP/MS, MX2 KO, SAMHD1 domain mapping, and HIV-1 nuclear import/capsid mutant assays","pmids":["38888311"],"confidence":"Medium","gaps":["Single-lab finding awaiting independent confirmation","Structural basis of core recognition undefined"]},{"year":2025,"claim":"Established that allosteric loading of an inactive tetrameric intermediate, not tetramerization per se, governs catalytic efficiency and enables facilitated dNTP depletion.","evidence":"In vitro dNTPase assays with allosteric occupancy analysis, tetramerization assays, and kinetic modeling","pmids":["39824836"],"confidence":"High","gaps":["How cellular ligand fluctuations engage this equilibrium in vivo untested","Single-lab reconstitution"]},{"year":null,"claim":"How SAMHD1's multiple activities (dNTPase, ssRNA exonuclease, MRE11/CtIP regulation, direct innate-immune-kinase inhibition) are spatially and temporally coordinated, and which dominates in a given cell state, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model integrating enzymatic and non-enzymatic functions","Phosphatase reversing T592 not identified in the corpus","Mechanism of recruitment to DSBs incompletely defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,5,6,7,27,45,47]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[36]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[2,36,39]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,37,39]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[40,41,16,13]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1,25,13]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[14,25,29]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[13,16,30,37]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[3,11,36,38,40,41]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[13,16,30,34,37]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,5,12]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[3,6,12,45]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,6,15]}],"complexes":[],"partners":["CTIP","MRE11","IKBKB","CHUK","MAVS","IRF7","TRIM21","USP7"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y3Z3","full_name":"Deoxynucleoside triphosphate triphosphohydrolase SAMHD1","aliases":["Dendritic cell-derived IFNG-induced protein","DCIP","Monocyte protein 5","MOP-5","SAM domain and HD domain-containing protein 1","hSAMHD1"],"length_aa":626,"mass_kda":72.2,"function":"Protein that acts both as a host restriction factor involved in defense response to virus and as a regulator of DNA end resection at stalled replication forks (PubMed:19525956, PubMed:21613998, PubMed:21720370, PubMed:22056990, PubMed:23601106, PubMed:23602554, PubMed:24336198, PubMed:26294762, PubMed:26431200, PubMed:28229507, PubMed:28834754, PubMed:29670289). Has deoxynucleoside triphosphate (dNTPase) activity, which is required to restrict infection by viruses, such as HIV-1: dNTPase activity reduces cellular dNTP levels to levels too low for retroviral reverse transcription to occur, blocking early-stage virus replication in dendritic and other myeloid cells (PubMed:19525956, PubMed:21613998, PubMed:21720370, PubMed:22056990, PubMed:23364794, PubMed:23601106, PubMed:23602554, PubMed:24336198, PubMed:25038827, PubMed:26101257, PubMed:26294762, PubMed:26431200, PubMed:28229507). Likewise, suppresses LINE-1 retrotransposon activity (PubMed:24035396, PubMed:24217394, PubMed:29610582). Not able to restrict infection by HIV-2 virus; because restriction activity is counteracted by HIV-2 viral protein Vpx (PubMed:21613998, PubMed:21720370). In addition to virus restriction, dNTPase activity acts as a regulator of DNA precursor pools by regulating dNTP pools (PubMed:23858451). Phosphorylation at Thr-592 acts as a switch to control dNTPase-dependent and -independent functions: it inhibits dNTPase activity and ability to restrict infection by viruses, while it promotes DNA end resection at stalled replication forks (PubMed:23601106, PubMed:23602554, PubMed:29610582, PubMed:29670289). Functions during S phase at stalled DNA replication forks to promote the resection of gapped or reversed forks: acts by stimulating the exonuclease activity of MRE11, activating the ATR-CHK1 pathway and allowing the forks to restart replication (PubMed:29670289). Its ability to promote degradation of nascent DNA at stalled replication forks is required to prevent induction of type I interferons, thereby preventing chronic inflammation (PubMed:27477283, PubMed:29670289). Ability to promote DNA end resection at stalled replication forks is independent of dNTPase activity (PubMed:29670289). Enhances immunoglobulin hypermutation in B-lymphocytes by promoting transversion mutation (By similarity)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q9Y3Z3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SAMHD1","classification":"Not Classified","n_dependent_lines":53,"n_total_lines":1208,"dependency_fraction":0.043874172185430466},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SAMHD1","total_profiled":1310},"omim":[{"mim_id":"614415","title":"CHILBLAIN LUPUS 2; CHBL2","url":"https://www.omim.org/entry/614415"},{"mim_id":"614257","title":"CHROMOSOME 20q11-q12 DELETION SYNDROME","url":"https://www.omim.org/entry/614257"},{"mim_id":"614216","title":"ACTIVATING SIGNAL COINTEGRATOR 1 COMPLEX, SUBUNIT 2; ASCC2","url":"https://www.omim.org/entry/614216"},{"mim_id":"612952","title":"AICARDI-GOUTIERES SYNDROME 5; AGS5","url":"https://www.omim.org/entry/612952"},{"mim_id":"610448","title":"CHILBLAIN LUPUS 1; CHBL1","url":"https://www.omim.org/entry/610448"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SAMHD1"},"hgnc":{"alias_symbol":["SBBI88","Mg11","HDDC1","MOP-5","AGS5"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y3Z3","domains":[{"cath_id":"1.10.150.50","chopping":"43-115","consensus_level":"high","plddt":84.1859,"start":43,"end":115},{"cath_id":"-","chopping":"381-451","consensus_level":"medium","plddt":98.4227,"start":381,"end":451},{"cath_id":"3.30.70.2760","chopping":"456-509_549-596","consensus_level":"high","plddt":95.234,"start":456,"end":596}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y3Z3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y3Z3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y3Z3-F1-predicted_aligned_error_v6.png","plddt_mean":88.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SAMHD1","jax_strain_url":"https://www.jax.org/strain/search?query=SAMHD1"},"sequence":{"accession":"Q9Y3Z3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y3Z3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y3Z3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y3Z3"}},"corpus_meta":[{"pmid":"21613998","id":"PMC_21613998","title":"SAMHD1 is the dendritic- and myeloid-cell-specific HIV-1 restriction factor counteracted by Vpx.","date":"2011","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/21613998","citation_count":1267,"is_preprint":false},{"pmid":"25604658","id":"PMC_25604658","title":"Characterization of human disease phenotypes associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR, and IFIH1.","date":"2015","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/25604658","citation_count":507,"is_preprint":false},{"pmid":"24183309","id":"PMC_24183309","title":"Assessment of interferon-related biomarkers in Aicardi-Goutières syndrome associated with mutations in TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, and ADAR: a case-control study.","date":"2013","source":"The Lancet. Neurology","url":"https://pubmed.ncbi.nlm.nih.gov/24183309","citation_count":371,"is_preprint":false},{"pmid":"29670289","id":"PMC_29670289","title":"SAMHD1 acts at stalled replication forks to prevent interferon induction.","date":"2018","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/29670289","citation_count":366,"is_preprint":false},{"pmid":"25038827","id":"PMC_25038827","title":"The ribonuclease activity of SAMHD1 is required for HIV-1 restriction.","date":"2014","source":"Nature medicine","url":"https://pubmed.ncbi.nlm.nih.gov/25038827","citation_count":240,"is_preprint":false},{"pmid":"28834754","id":"PMC_28834754","title":"SAMHD1 Promotes DNA End Resection to Facilitate DNA Repair by Homologous Recombination.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/28834754","citation_count":158,"is_preprint":false},{"pmid":"23972988","id":"PMC_23972988","title":"Mouse SAMHD1 has antiretroviral activity and suppresses a spontaneous cell-intrinsic antiviral response.","date":"2013","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/23972988","citation_count":141,"is_preprint":false},{"pmid":"24445253","id":"PMC_24445253","title":"SAMHD1 prevents autoimmunity by maintaining genome stability.","date":"2014","source":"Annals of the rheumatic diseases","url":"https://pubmed.ncbi.nlm.nih.gov/24445253","citation_count":131,"is_preprint":false},{"pmid":"22973040","id":"PMC_22973040","title":"The Vpx lentiviral accessory protein targets SAMHD1 for degradation in the nucleus.","date":"2012","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/22973040","citation_count":117,"is_preprint":false},{"pmid":"26134849","id":"PMC_26134849","title":"SAMHD1 Inhibits LINE-1 Retrotransposition by Promoting Stress Granule Formation.","date":"2015","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/26134849","citation_count":111,"is_preprint":false},{"pmid":"27477283","id":"PMC_27477283","title":"Restriction 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The putative phosphohydrolase activity is required for restriction.\",\n      \"method\": \"siRNA silencing, overexpression, Vpx-mediated degradation, viral DNA quantification\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal loss-of-function and gain-of-function with defined molecular phenotype, widely replicated across labs\",\n      \"pmids\": [\"21613998\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Vpx recruits SAMHD1 to a cullin4A-RING E3 ubiquitin ligase (CRL4) for proteasomal degradation; SAMHD1 contains a conserved nuclear localization sequence (KRPR, residues 11–14) and is targeted by Vpx specifically in the nucleus—cytoplasmic SAMHD1 (NLS-defective) retains antiviral activity but is resistant to Vpx-induced degradation.\",\n      \"method\": \"Nuclear localization sequence mutagenesis, leptomycin B nuclear export inhibition, subcellular fractionation, co-immunoprecipitation\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — NLS mutagenesis with functional rescue, nuclear targeting established mechanistically, replicated by independent labs\",\n      \"pmids\": [\"22973040\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SAMHD1 specifically interacts with ssRNA and ssDNA; nucleic acid binding and SAMHD1 complex formation are mutually dependent; interaction requires the HD domain and C-terminal region but not the SAM domain; AGS-associated mutations impair both nucleic acid binding and complex formation.\",\n      \"method\": \"Fluorescence cross-correlation spectroscopy, domain deletion/mutation analysis, co-immunoprecipitation\",\n      \"journal\": \"Journal of molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biophysical binding assay with domain mapping and disease mutants, single lab\",\n      \"pmids\": [\"23371319\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Mouse SAMHD1 reduces cellular dNTP concentrations and restricts retroviral replication in lymphocytes, macrophages, and dendritic cells; absence of SAMHD1 triggers IFN-β-dependent transcriptional upregulation of type I IFN-inducible genes, indicating spontaneous IFN production.\",\n      \"method\": \"Gene-targeted knockout mice, dNTP measurement, retroviral infection assays, interferon gene expression\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse model with defined cellular phenotypes and dNTP measurements, multiple cell types tested\",\n      \"pmids\": [\"23972988\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SAMHD1 possesses RNase activity; the RNase but not the dNTPase function is essential for HIV-1 restriction. RNase-positive/dNTPase-negative mutant D137N restricts HIV-1; RNase-negative/dNTPase-positive mutant Q548A does not. SAMHD1 associates with and degrades HIV-1 RNA during early infection. Phosphorylation at T592 negatively regulates RNase activity.\",\n      \"method\": \"In vitro RNase assay, point mutagenesis, HIV-1 RNA co-immunoprecipitation, RNA stability assays in macrophages and CD4+ T cells, phosphomimetic mutations\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro enzymatic assay plus mutagenesis plus cellular RNA stability; RNase activity disputed by other labs (contradicted by PMID 26667483)\",\n      \"pmids\": [\"25038827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"SAMHD1 deficiency in AGS patient fibroblasts increases dNTP pools, causing genome instability, constitutive DNA damage signaling, cell cycle delay, cellular senescence, and upregulation of IFN-stimulated genes. SAMHD1 is phosphorylated by cyclin A/CDK1 in a cell cycle-dependent manner, with lowest SAMHD1 levels at G1/S phase.\",\n      \"method\": \"Primary patient fibroblasts, dNTP measurement, cell cycle analysis, DNA damage assays, co-immunoprecipitation with cyclin A, fluorescence cross-correlation spectroscopy, synchronized HeLa cells, siRNA knockdown\",\n      \"journal\": \"Annals of the rheumatic diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — patient-derived cells plus multiple orthogonal methods (dNTP measurement, cell cycle, Co-IP, siRNA), functional consequences defined\",\n      \"pmids\": [\"24445253\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CyclinA2-CDK1/2 phosphorylates SAMHD1 at Thr-592 via a bipartite cyclinA2-CDK binding site in the SAMHD1 C-terminus; phosphorylation at T592 down-modulates (but does not abolish) SAMHD1 dNTPase activity in S phase to fine-tune dNTP levels during DNA replication; phosphorylation-defective mutants cause DNA damage checkpoint activation and excessive dNTP depletion.\",\n      \"method\": \"Cell cycle synchronization, cyclinA2-CDK binding site mutagenesis, dNTP measurement, DNA damage checkpoint assays, phosphomimetic/phosphodead mutations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — domain mutagenesis with cell cycle synchronization, dNTP measurement, and checkpoint readout; multiple orthogonal methods\",\n      \"pmids\": [\"25847232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The phosphomimetic T592E mutation reduces SAMHD1 tetramer stability and dNTPase activity; crystal structures of T592E and T592V variants show that the charged T592E induces large conformational changes via electrostatic repulsion, decreasing active tetramer population.\",\n      \"method\": \"Crystal structure determination, in vitro dNTPase assays, tetramer stability assays, phosphomimetic mutations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with functional validation and mutagenesis in a single study\",\n      \"pmids\": [\"26294762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SAMHD1 inhibits LINE-1 retrotransposition by promoting cellular stress granule assembly (associated with increased eIF2α phosphorylation and diminished eIF4A/eIF4G interaction), which sequesters LINE-1 RNP in stress granules; depletion of G3BP1 or TIA1 abrogates stress granule formation and overcomes SAMHD1 inhibition.\",\n      \"method\": \"Stress granule marker depletion (siRNA), LINE-1 retrotransposition reporter assay, eIF2α phosphorylation assay, co-immunoprecipitation\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with stress granule markers, functional reporter assay; single lab\",\n      \"pmids\": [\"26134849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Murine SAMHD1 antiviral activity is regulated through phosphorylation at threonine 603 (equivalent to human T592) and is limited to non-dividing cells; murine SAMHD1 blocks retroviral infection at the level of reverse transcription; the proposed RNase activity of mouse SAMHD1 had no detectable effect on incoming viral RNA levels.\",\n      \"method\": \"SAMHD1 knockout mouse primary myeloid cells, dNTP measurement, retroviral infection with phosphomutant analysis, viral RNA quantification\",\n      \"journal\": \"Retrovirology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with phosphomutants and dNTP measurement; negative result for RNase activity noted\",\n      \"pmids\": [\"26667483\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SAMHD1 restricts HIV-1 cell-to-cell transmission from infected T lymphocytes to monocyte-derived dendritic cells and prevents type I interferon response and MxA expression in these coculture settings; Vpx-mediated degradation or siRNA silencing of SAMHD1 increases productive cell-to-cell transmission.\",\n      \"method\": \"Coculture assay with HIV-infected T lymphocytes and MDDCs, siRNA knockdown, Vpx treatment, interferon/MxA measurements\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-to-cell transmission assay with genetic knockdown, defined innate immune readout; single lab\",\n      \"pmids\": [\"23269793\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The spontaneous type I IFN response in SAMHD1-deficient cells and mice requires the cGAS/STING cytosolic DNA-sensing pathway; cell-autonomous lentivirus restriction by SAMHD1 in myeloid cells requires reverse transcription and cGAS/STING signaling, and limits virus-induced IFN production and co-stimulatory marker induction.\",\n      \"method\": \"Genetic epistasis (cGAS/STING KO combined with SAMHD1 deficiency), reverse transcription inhibitor treatment, in vivo mouse infection\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis in cells and mice with multiple pathway components tested\",\n      \"pmids\": [\"27477283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Heterozygous cancer-associated SAMHD1 mutations negatively affect dNTPase activity; inactivation of one SAMHD1 allele is sufficient to elevate dNTP pools in mouse embryos; minor dNTP pool changes combined with inactivated mismatch repair dramatically increase mutation rates.\",\n      \"method\": \"Enzymatic activity assays of mutant proteins, dNTP measurement in mouse embryos, mutation rate analysis in yeast/cell models\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro enzymatic assays plus in vivo dNTP measurement plus mutation rate experiments\",\n      \"pmids\": [\"27071091\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SAMHD1 has a dNTPase-independent function in promoting DNA end resection to facilitate DSB repair by homologous recombination; SAMHD1 is recruited to DSBs; SAMHD1 complexes with CtIP via a conserved C-terminal domain and recruits CtIP to DSBs; a cancer-associated mutant with impaired CtIP interaction (but not a dNTPase-inactive mutant) fails to rescue the end resection impairment.\",\n      \"method\": \"CRISPR/Cas9 knockout, Vpx-mediated degradation, co-immunoprecipitation (SAMHD1–CtIP complex), recruitment to DSBs by ChIP/imaging, HR reporter assay, domain deletion mutagenesis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, KO with defined HR phenotype, cancer mutant epistasis; multiple orthogonal methods in single study\",\n      \"pmids\": [\"28834754\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SAMHD1 dNTPase activity is regulated by a redox switch: three cysteine residues form an intrachain disulfide bond that reversibly inhibits protein tetramerization and catalysis; proliferative signals lead to SAMHD1 oxidation in cells, and oxidized SAMHD1 localizes outside the nucleus.\",\n      \"method\": \"Biochemical identification of disulfide bonds, dNTPase activity assays, cell fractionation, redox manipulation\",\n      \"journal\": \"Antioxidants & redox signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical assays plus cellular localization; single lab\",\n      \"pmids\": [\"28398823\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SAMHD1 acetylation at lysine 405 by ARD1 acetyltransferase enhances dNTPase activity in vitro; non-acetylated K405R mutant-expressing cancer cells have reduced G1/S transition and slower proliferation; acetylation levels are strongest during G1 phase.\",\n      \"method\": \"In vitro acetylation assay, dNTPase activity measurement, K405R mutagenesis, cell cycle analysis, co-immunoprecipitation\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro enzymatic assay with mutagenesis and cell cycle phenotype; single lab\",\n      \"pmids\": [\"28978134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SAMHD1 promotes degradation of nascent DNA at stalled replication forks by stimulating the exonuclease activity of MRE11, which activates the ATR-CHK1 checkpoint and allows fork restart; in SAMHD1-depleted cells, ssDNA fragments accumulate in the cytosol and activate the cGAS-STING pathway to induce type I interferons.\",\n      \"method\": \"DNA fiber assay (fork restart), MRE11 exonuclease assay, siRNA knockdown, cGAS/STING pathway activation measurement, cytosolic ssDNA detection\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (DNA fiber, exonuclease assay, cGAS/STING genetics) in a single high-quality study, replicated across cell lines\",\n      \"pmids\": [\"29670289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SAMHD1 dephosphorylation at T592 (activating the protein) is the predominant mechanism of HIV-1 restriction induced by type I, II, and III IFN signaling in macrophages; all IFN types downregulated CDK1 protein expression; pharmacological CDK1 inhibition or siRNA knockdown phenocopied IFN effects on SAMHD1; viral restriction imposed by IFNs or dasatinib was overcome by SAMHD1 depletion.\",\n      \"method\": \"SAMHD1 phosphorylation state analysis, CDK1 knockdown/inhibition, IFN treatment, HIV-1 infection assay in primary macrophages, SAMHD1 knockdown rescue experiments\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological and genetic epistasis with CDK1, multiple IFN types, SAMHD1 depletion rescue; primary cells used\",\n      \"pmids\": [\"29764952\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SAMHD1 promotes immunoglobulin hypermutation by restricting dNTP supply; CRISPR inactivation of SAMHD1 in germinal center B cells increased transition mutations at C:G base pairs and substantially decreased transversion mutations at A:T and C:G base pairs, indicating that dNTP starvation by SAMHD1 enhances AID mutagenicity.\",\n      \"method\": \"CRISPR/Cas9 knockout in germinal center B cells, Ig hypermutation sequencing, dNTP measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean CRISPR KO with sequencing of mutation spectra; single lab\",\n      \"pmids\": [\"29669924\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"EBV protein kinase BGLF4 phosphorylates SAMHD1 and inhibits its dNTPase activity; this mechanism of phosphorylation-based SAMHD1 inactivation is shared by beta- and gamma-herpesviruses (conserved viral protein kinases).\",\n      \"method\": \"In vitro kinase assay, dNTPase activity measurement, viral infection assays, phosphorylation site mapping\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus antiviral functional assay; single lab\",\n      \"pmids\": [\"31291580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SAMHD1 modulates early steps of HCMV infection by suppressing NF-κB activation; SAMHD1 depletion increases HCMV gene expression from the major immediate-early promoter independently of dNTP levels; SAMHD1 inhibits NF-κB, and increased RELA and RNA polymerase II occupy the HCMV MIE promoter in SAMHD1-depleted cells; HCMV viral kinase UL97 phosphorylates SAMHD1 during infection.\",\n      \"method\": \"SAMHD1 depletion, ChIP (RELA, RNA Pol II), NF-κB reporter assay, viral gene expression measurement, phosphorylation assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP plus genetic depletion with multiple pathway readouts; dNTP-independence established\",\n      \"pmids\": [\"31291579\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HCMV overcomes SAMHD1 restriction in macrophages by using the viral kinase pUL97 (and by hijacking cellular kinases) to phosphorylate SAMHD1 at T592, converting it to its inactive form; HCMV also interferes with SAMHD1 steady-state expression.\",\n      \"method\": \"SAMHD1 phosphorylation assays in infected cells, viral kinase pUL97 functional analysis, dNTP measurement\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — viral kinase phosphorylation assay plus dNTP and infection readouts; single lab\",\n      \"pmids\": [\"31548682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Murine CMV viral kinase M97 counteracts SAMHD1 restriction in vivo by phosphorylating the regulatory residue T603; phosphorylation correlated with reduced dNTP hydrolase activity and loss of viral restriction; SAMHD1 inhibits MCMV replication in vivo in a SAMHD1 knockout mouse model.\",\n      \"method\": \"SAMHD1 knockout mice, MCMV infection in vivo and in vitro, viral kinase M97 phosphorylation assay, dNTPase activity measurement\",\n      \"journal\": \"Nature microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo KO mouse model with viral kinase assay and dNTPase activity measurement\",\n      \"pmids\": [\"31548683\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TRIM21 E3 ubiquitin ligase specifically interacts with SAMHD1 and promotes its proteasomal degradation; ubiquitination occurs at K622 on SAMHD1; phosphorylation of SAMHD1 at T592 also blocks EV71 restriction; TRIM21-mediated SAMHD1 degradation affects HIV-1 restriction and interferon regulation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, proteasome inhibition, domain mutagenesis, EV71 and HIV-1 infection assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus ubiquitination site mapping plus functional rescue; single lab\",\n      \"pmids\": [\"31797533\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PIM1 and PIM3 serine/threonine kinases phosphorylate HIV-2 Vpx at Ser13, stabilizing the Vpx–SAMHD1 interaction and promoting ubiquitin-mediated proteolysis of SAMHD1; PIM kinase inhibition promotes SAMHD1 antiviral activity and reduces viral replication.\",\n      \"method\": \"Integrated proteomics, in vitro kinase assay, co-immunoprecipitation, ubiquitination assay, viral replication assay with PIM inhibitors/knockdown\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus proteomic identification plus functional viral replication readout; single lab\",\n      \"pmids\": [\"31015445\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SAMHD1 is a nucleocytoplasmic shuttling protein; altering subcellular localization by mutating/removing NLS enhances SAMHD1's potency in LINE-1 suppression; cytoplasmic SAMHD1 leads to enhanced depletion of LINE-1 ORF2p.\",\n      \"method\": \"Digitonin-based cytoplasm/nucleus fractionation, NLS mutagenesis, exportin Xpo1 overexpression, LINE-1 retrotransposition reporter assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — fractionation with functional consequence, mutagenesis; single lab\",\n      \"pmids\": [\"30739781\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SAMHD1 competitively interacts with VP1 of EV71 and EVD68 at the same domain that binds VP2, thereby interfering with VP1–VP2 interaction and viral capsid assembly; this mechanism is independent of dNTPase or RNase activity; T592A mutant maintains this inhibitory effect but T592D mutant does not.\",\n      \"method\": \"Co-immunoprecipitation, competitive binding assay, viral assembly assay, phosphomutant analysis\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP binding competition plus functional viral assembly readout with phosphomutants; single lab\",\n      \"pmids\": [\"33883225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures reveal that SAMHD1 utilizes a bi-metallic iron-magnesium active-site center that positions a hydroxide nucleophile in-line with the Pα–O5' bond to catalyze phosphoester bond hydrolysis of dNTPs.\",\n      \"method\": \"X-ray crystallography of SAMHD1 inhibitor complexes, enzymological assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures with functional validation revealing precise catalytic mechanism\",\n      \"pmids\": [\"32576829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"TLR4 activation induces G0 arrest and SAMHD1 antiretroviral activity via an IFN-independent pathway requiring TRIF but not TBK1, IRF3, Myd88, or NF-κB; this involves p21 upregulation and CDK1 depletion, leading to SAMHD1 dephosphorylation at T592; SAMHD1 knockdown confirmed that TLR4-activated HIV-1 block is specifically mediated by SAMHD1.\",\n      \"method\": \"TLR4 agonist treatment, TRIF/TBK1/IRF3/Myd88 inhibition, SAMHD1 phosphorylation assay, CDK1 level measurement, SAMHD1 knockdown, HIV-1 infection assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic pathway dissection with multiple signaling components plus SAMHD1-specific rescue; primary macrophages used\",\n      \"pmids\": [\"32209460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HCMV infection induces rapid SAMHD1 phosphorylation at T592 by cellular Cdk2 and viral kinase pUL97, resulting in a significant fraction of phospho-SAMHD1 relocating to the cytoplasm of infected fibroblasts in association with viral particles and dense bodies.\",\n      \"method\": \"SAMHD1 phosphorylation analysis, subcellular fractionation, co-localization with viral particles by imaging\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphorylation mapping plus localization imaging; single lab\",\n      \"pmids\": [\"32986788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SAMHD1-mediated dNTP degradation is required for efficient DNA repair during immunoglobulin class switch recombination (CSR); SAMHD1 localizes at the Ig switch region; SAMHD1 depletion impairs CSR and IgH/c-Myc translocation; elevated dNTP pools increase nucleotide insertions at break-point junctions.\",\n      \"method\": \"ChIP (SAMHD1 at Ig switch region), CSR assay, translocation assay, nucleotide pool manipulation, SAMHD1 siRNA depletion\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — ChIP localization with functional CSR assay and translocation readout plus dNTP pool manipulation\",\n      \"pmids\": [\"32511795\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"OGT-mediated O-GlcNAcylation of SAMHD1 at Ser93 stabilizes SAMHD1 and enhances its antiviral activity against HBV; HBP/O-GlcNAcylation positively regulates SAMHD1-dependent antiviral response in vitro and in vivo.\",\n      \"method\": \"LC-MS identification of O-GlcNAc site, co-immunoprecipitation, OGT overexpression/knockdown, HBV replication assay, S93 mutagenesis\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — mass spectrometry-identified modification site plus mutagenesis plus functional antiviral assay; single lab\",\n      \"pmids\": [\"33391506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TRAF6 and TAK1 contribute to SAMHD1-mediated suppression of NF-κB activation; SAMHD1 inhibits TAK1 activation and TRAF6 signaling; TRAF6 knockdown in SAMHD1-deficient cells significantly inhibited HIV-1 infection and NF-κB activation; the NLS is not required for this suppressive function.\",\n      \"method\": \"SAMHD1 CRISPR KO, TRAF6 siRNA knockdown, TAK1 pharmacological inhibition, IκBα phosphorylation assay, TNF-α mRNA measurement, HIV-1 infection assay, NF-κB reporter\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (KO + KD) with multiple pathway readouts; single lab\",\n      \"pmids\": [\"33177202\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PIAS1 E3 SUMO ligase interacts with SAMHD1 and promotes its SUMOylation at K469, K595, and K622; SUMOylation-deficient SAMHD1 loses anti-EBV activity; SAMHD1 association with EBV genome is PIAS1-dependent.\",\n      \"method\": \"Co-immunoprecipitation, SUMOylation assay, site mutagenesis (K469R/K595R/K622R), ChIP (SAMHD1 on EBV genome), EBV replication assay\",\n      \"journal\": \"Cell & bioscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus SUMOylation site mapping plus ChIP with functional antiviral readout; single lab\",\n      \"pmids\": [\"34238351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SAMHD1 dNTPase activity restrains aberrant nucleotide insertions at DNA break repair junctions during end joining; SAMHD1 expression or low intracellular dNTPs leads to shorter repair joints and impedes insertion of distant DNA regions prior to end repair.\",\n      \"method\": \"Linear DNA substrate end-joining assay in HEK293 cells, CRISPR/Cas9-induced break monitoring, SAMHD1 dNTPase mutant analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional DNA repair assay with dNTPase mutants; single lab\",\n      \"pmids\": [\"33591315\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"R-loops are highly enriched at transcription-replication conflict regions in SAMHD1-deficient cells; SAMHD1 loss leads to R-loop accumulation and activation of DNA damage responses; removal of R-loops in SAMHD1 deficiency reduces cellular responses to genome instability.\",\n      \"method\": \"R-loop immunofluorescence/ChIP (S9.6 antibody), DNA damage response markers, R-loop removal by RNase H overexpression, SAMHD1 patient fibroblasts\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patient fibroblasts plus R-loop detection plus rescue with RNase H; single lab\",\n      \"pmids\": [\"33857133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SAMHD1 functions as a single-stranded RNA (ssRNA) 3' exonuclease; loss of SAMHD1 causes cellular RNA accumulation, leading to dissolution of RNA-protein condensates that sequester immunogenic dsRNA; released dsRNA triggers type I IFN activation via RIG-I-like receptors.\",\n      \"method\": \"ssRNA exonuclease assay, RNA sequencing (RNA accumulation), condensate dissolution imaging, RIG-I-like receptor epistasis, SAMHD1 KO cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro exonuclease assay plus condensate imaging plus RLR epistasis; multiple orthogonal methods in single study\",\n      \"pmids\": [\"36150385\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SIRT1 deacetylase complexes with SAMHD1 and deacetylates it at conserved K354 specifically in response to DSBs; K354 deacetylation promotes SAMHD1 recruitment to DSBs and binding to ssDNA, which facilitates CtIP ssDNA binding and promotes DNA end resection and HR, without affecting tetramerization or dNTPase activity.\",\n      \"method\": \"Co-immunoprecipitation (SIRT1–SAMHD1), K354 mutagenesis, DSB recruitment assay (ChIP/imaging), ssDNA binding assay, HR reporter assay, CtIP ssDNA binding\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus mutagenesis plus ChIP plus functional HR assay; multiple orthogonal methods\",\n      \"pmids\": [\"36344525\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In SAMHD1-deficient mice, the chronic IFN response is driven by the MDA5/MAVS pathway but requires functional priming through the cGAS/STING pathway; cGAS/STING is positioned upstream of tonic IFN signaling in Samhd1-deficient mice.\",\n      \"method\": \"Genetic epistasis (Samhd1 KO crossed with cGAS/STING KO and MDA5/MAVS KO), IFN measurement, tumor-free survival analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — double KO genetic epistasis in vivo placing cGAS/STING upstream of MDA5/MAVS in SAMHD1-deficient inflammation\",\n      \"pmids\": [\"36346347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Phosphorylation at T592 accelerates SAMHD1 tetramer dissociation (~15-fold) and increases C-terminal domain dynamics; ssDNA binds competitively with GTP to the A1 allosteric site; cryo-EM structure reveals substantial dynamics in the C-terminal domain containing T592.\",\n      \"method\": \"Cryo-EM structure, tetramer dissociation kinetics, ssDNA binding assay, GTP competition assay, phosphomimetic mutations\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with functional binding assays and kinetics; multiple methods in single study\",\n      \"pmids\": [\"35801923\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SAMHD1 suppresses NF-κB activation by directly interacting (via its HD domain) with IKKα and IKKβ; SAMHD1 suppresses phosphorylation of IKKα/β/γ, inhibiting downstream IκBα phosphorylation; SAMHD1 disrupts the interaction between upstream kinase TAK1 and IKKα or IKKβ; direct in vitro binding between recombinant SAMHD1 and purified IKKα or IKKβ was demonstrated.\",\n      \"method\": \"Co-immunoprecipitation (endogenous and recombinant), in vitro binding assay with purified proteins, SAMHD1 KO/reconstitution, domain mapping, IKK phosphorylation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro binding with purified proteins plus reciprocal Co-IP plus KO/reconstitution; multiple orthogonal methods\",\n      \"pmids\": [\"37100289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SAMHD1 inhibits type I IFN induction through the MAVS, IKKε, and IRF7 signaling axis; SAMHD1 interacts with MAVS and suppresses MAVS aggregation upon Sendai virus infection; SAMHD1 prevents IRF7 binding to the kinase domain of IKKε; the SAMHD1 interaction with the inhibitory domain of IRF7 (IRF7-ID) is necessary and sufficient for SAMHD1 suppression of IRF7-mediated IFN-I activation.\",\n      \"method\": \"Co-immunoprecipitation (SAMHD1–MAVS, SAMHD1–IRF7), MAVS aggregation assay, IRF7-IKKε binding assay, HEK293T reporter assay, IRF7-ID mutagenesis, computational docking/molecular dynamics\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus aggregation assay plus domain mutagenesis plus reporter assay; multiple orthogonal methods in single study\",\n      \"pmids\": [\"37328105\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Deubiquitinase USP7 interacts with SAMHD1 and deubiquitinates it at K421, stabilizing SAMHD1 protein expression; stabilized SAMHD1 interacts with CtIP to promote DNA damage repair; USP7 inhibition sensitizes tumor cells to chemotherapeutic agents by decreasing SAMHD1.\",\n      \"method\": \"Co-immunoprecipitation (USP7–SAMHD1), ubiquitination site mapping (K421), USP7 inhibitor treatment, DNA damage repair assay, chemosensitivity assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ubiquitination site mapping plus functional repair and sensitivity assays; single lab\",\n      \"pmids\": [\"37081042\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SAMHD1 contributes to cancer cell migration in ccRCC by participating in endocytosis and lamellipodia formation; SAMHD1 binds cortactin to form an endosomal complex, and SAMHD1-stimulated endosomal FAK signaling activates Rac1, promoting lamellipodia formation and cell motility.\",\n      \"method\": \"Co-immunoprecipitation (SAMHD1–cortactin), FAK signaling assays, Rac1 activation assay, lamellipodia imaging, cell migration assay, patient tissue correlation\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus kinase signaling assay plus functional migration readout; single lab\",\n      \"pmids\": [\"37009792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SAMHD1 cooperates with MX2 to inhibit HIV-1 at the post-cDNA-synthesis stage by recognizing and binding incoming HIV-1 cores and delivering them to the MX2 molecular trap, blocking nuclear entry; SAMHD1 mutants unable to recognize HIV-1 core showed substantially decreased antiviral activity; this mechanism is distinct from dNTP hydrolysis.\",\n      \"method\": \"Immunoprecipitation plus mass spectrometry (SAMHD1–MX2), MX2 KO (endogenous disruption), SAMHD1 domain mapping, HIV-1 nuclear import assay, HIV-1 capsid mutant analysis\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP/MS interaction plus nuclear import assay plus genetic KO; single lab, novel mechanism\",\n      \"pmids\": [\"38888311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SAMHD1 tetramerization alone is insufficient for dNTP hydrolysis; activation requires an inactive tetrameric intermediate with partially occupied allosteric sites; the equilibrium between inactive and active tetrameric states regulates dNTPase activity driven by binding/dissociation of additional allosteric dNTP ligands; catalytic efficiency (but not substrate specificity) is modulated by the identity of dNTPs at allosteric sites; SAMHD1 exhibits facilitated dNTP depletion, whereby increased biosynthesis of certain dNTPs enhances depletion of others.\",\n      \"method\": \"In vitro dNTPase assays, allosteric site occupancy analysis, tetramerization assays, kinetic modeling\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — rigorous in vitro reconstitution with allosteric analysis; single lab but comprehensive mechanistic dissection\",\n      \"pmids\": [\"39824836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"NONO interacts with SAMHD1 and stabilizes it by inhibiting DCAF1-mediated ubiquitination/degradation; NONO overexpression increases SAMHD1 expression and reduces AML cell sensitivity to Ara-C.\",\n      \"method\": \"Co-immunoprecipitation (NONO–SAMHD1), ubiquitination assay with DCAF1, NONO overexpression/knockdown, cytarabine sensitivity assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus ubiquitination assay plus functional drug resistance readout; single lab\",\n      \"pmids\": [\"35803902\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Sp-dNTPαS diastereomers (but not Rp-dNTPαS) prevent Mg2+ coordination at allosteric and catalytic sites, rendering SAMHD1 unable to form stable active homotetramers or hydrolyze substrates; Sp-dNTPαS competitively inhibits dNTP hydrolysis; a co-crystal structure of SAMHD1 with Rp-dGTPαS reveals an Fe-Mg-bridging water species poised for nucleophilic attack on Pα.\",\n      \"method\": \"X-ray crystallography (SAMHD1–Rp-dGTPαS cocrystal), in vitro dNTPase kinetics, tetramerization assay, stereospecific substrate analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cocrystal structure with enzymological validation; reveals stereospecific catalytic mechanism\",\n      \"pmids\": [\"33988981\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Interferon induction of SAMHD1 in primary human monocytes depends on post-transcriptional regulation via 3'-UTR; miR-181a and miR-30a target the SAMHD1 3'-UTR and their down-regulation inversely correlates with SAMHD1 protein up-regulation upon type I and II IFN stimulation in monocytes; this miRNA-dependent regulation does not occur in macrophages or dendritic cells.\",\n      \"method\": \"Luciferase 3'-UTR reporter assay, miRNA overexpression/inhibition, miRNA-SAMHD1 correlation in primary monocytes, AGO2 co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — 3'-UTR reporter plus AGO2 CLIP plus primary cell correlation; single lab\",\n      \"pmids\": [\"27909056\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SAMHD1 is a dNTP triphosphohydrolase (active as an allosterically regulated homotetramer using a bi-metallic Fe-Mg catalytic center) that restricts HIV-1 and other viruses primarily by depleting intracellular dNTP pools below levels required for reverse transcription in non-dividing myeloid cells and resting T cells; its activity is regulated post-translationally by phosphorylation at T592 by CyclinA2-CDK1/2 (inactivating the enzyme by destabilizing the tetramer), by a redox-sensitive disulfide switch, by acetylation at K405 (activating), by O-GlcNAcylation at S93 (stabilizing), by TRIM21-mediated ubiquitination at K622 (degrading), and by SIRT1-mediated deacetylation at K354 and USP7-mediated deubiquitination at K421; beyond dNTP depletion, SAMHD1 independently suppresses innate immune signaling by inhibiting NF-κB (through direct interaction with IKKα/β and disruption of TAK1 engagement), suppressing type I IFN induction via the MAVS–IKKε–IRF7 axis, and by functioning as an ssRNA 3' exonuclease to prevent immunogenic dsRNA release from condensates; at stalled replication forks SAMHD1 stimulates MRE11 exonuclease activity to promote fork restart and prevent ssDNA-mediated cGAS-STING activation; SAMHD1 also recruits CtIP (via its C-terminal domain, regulated by SIRT1-mediated K354 deacetylation) to promote DNA end resection and homologous recombination; Vpx from HIV-2/SIV counteracts SAMHD1 by recruiting it via CRL4 E3 ubiquitin ligase for nuclear proteasomal degradation, and multiple herpesvirus kinases phosphorylate T592 to inactivate SAMHD1.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SAMHD1 is an allosterically regulated dNTP triphosphohydrolase that controls intracellular dNTP pools to enforce antiviral restriction and safeguard genome integrity [#0, #27, #45]. As the dendritic- and myeloid-cell HIV-1 restriction factor, it blocks reverse transcription in non-dividing cells and is counteracted by lentiviral Vpx, which recruits it to a CRL4 E3 ligase for nuclear proteasomal degradation [#0, #1]. Catalysis proceeds through a bi-metallic iron-magnesium active center that positions a hydroxide nucleophile in-line with the Pα–O5' bond, and full hydrolytic activity requires assembly of an allosterically loaded active homotetramer rather than tetramerization alone [#27, #47, #45]. Enzymatic output is tuned by a dense layer of post-translational control: CyclinA2-CDK1/2 phosphorylation at Thr592 destabilizes the tetramer and down-modulates dNTPase activity during S phase, an effect structurally explained by electrostatic disruption of the active tetramer and accelerated subunit dissociation [#6, #7, #39]; a reversible cysteine disulfide switch, ARD1-mediated K405 acetylation, and OGT-mediated S93 O-GlcNAcylation further modulate activity and stability, while TRIM21-, USP7-, and NONO/DCAF1-linked ubiquitination pathways set protein levels [#14, #15, #31, #23, #42, #46]. Beyond nucleotide pool control, SAMHD1 acts directly in genome maintenance, stimulating MRE11 exonuclease activity at stalled forks to enable restart and recruiting CtIP—governed by SIRT1-mediated K354 deacetylation—to drive DNA end resection and homologous recombination, thereby restraining cytosolic nucleic acid release [#16, #13, #37]. It independently suppresses innate immune signaling by binding IKKα/β and disrupting TAK1 engagement to inhibit NF-κB, by interacting with MAVS/IKKε/IRF7 to limit type I IFN induction, and by functioning as an ssRNA 3' exonuclease that prevents immunogenic dsRNA release from condensates [#40, #41, #36]. Loss of SAMHD1 elevates dNTP pools and triggers chronic cGAS/STING- and MDA5/MAVS-dependent type I interferon responses, a pathophysiology underlying Aicardi-Goutières syndrome [#5, #16, #38].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Established SAMHD1 as the long-sought myeloid/dendritic-cell HIV-1 restriction factor and the target of lentiviral Vpx, defining its antiviral role.\",\n      \"evidence\": \"siRNA silencing, overexpression, and Vpx-mediated degradation with viral DNA quantification in non-permissive cells\",\n      \"pmids\": [\"21613998\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of restriction (dNTPase vs other activities) not yet defined\", \"Did not establish where in the cell restriction occurs\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed Vpx degrades SAMHD1 through a CRL4 E3 ligase acting on nuclear SAMHD1, localizing the counteraction mechanism and identifying its NLS.\",\n      \"evidence\": \"NLS mutagenesis, leptomycin B export inhibition, fractionation, and co-IP\",\n      \"pmids\": [\"22973040\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address why nuclear localization is required for Vpx targeting\", \"Antiviral mechanism still unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linked SAMHD1 to dNTP pool depletion as the basis of retroviral restriction and revealed that its loss drives spontaneous type I IFN production in vivo.\",\n      \"evidence\": \"Gene-targeted knockout mice with dNTP measurement, retroviral infection, and IFN gene expression; parallel nucleic-acid-binding biophysics in human cells\",\n      \"pmids\": [\"23972988\", \"23371319\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sensor linking dNTP/SAMHD1 loss to IFN not identified\", \"Relative contribution of nucleic-acid binding vs dNTPase unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected dNTP pool dysregulation in SAMHD1-deficient patient cells to genome instability and identified cyclin A/CDK1 cell-cycle phosphorylation, tying enzymatic regulation to the cell cycle; a contested report proposed an RNase activity as the restriction determinant.\",\n      \"evidence\": \"AGS patient fibroblasts with dNTP/DNA-damage assays and cyclin A co-IP; in vitro RNase assay with D137N/Q548A mutants\",\n      \"pmids\": [\"24445253\", \"25038827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"RNase claim disputed by later mouse work (PMID 26667483)\", \"Mechanism converting dNTP excess to DNA damage not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined the CyclinA2-CDK1/2 phosphorylation site (T592) and showed structurally and kinetically that phosphorylation destabilizes the active tetramer to fine-tune dNTP levels.\",\n      \"evidence\": \"Cell-cycle synchronization with binding-site mutagenesis and dNTP/checkpoint readouts; crystal structures of T592E/T592V with dNTPase assays; mouse T603 phosphomutant analysis\",\n      \"pmids\": [\"25847232\", \"26294762\", \"26667483\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase reversing T592 not identified here\", \"Whether RNase contributes to restriction left contradicted\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Placed the cGAS/STING DNA-sensing pathway downstream of SAMHD1 loss and established cell-autonomous restriction requiring reverse transcription, unifying antiviral and inflammatory phenotypes.\",\n      \"evidence\": \"Genetic epistasis (cGAS/STING KO with SAMHD1 deficiency) in cells and mice; cancer-mutation dNTPase and mutation-rate analyses; 3'-UTR/miRNA regulation in monocytes\",\n      \"pmids\": [\"27477283\", \"27071091\", \"27909056\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of the immunostimulatory DNA species not yet defined\", \"Tissue-specificity of miRNA regulation incompletely mapped\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed dNTPase-independent genome-protective functions: SAMHD1 recruits CtIP to promote DNA end resection and HR, and is regulated by a redox disulfide switch and K405 acetylation.\",\n      \"evidence\": \"CRISPR KO with HR reporter, reciprocal SAMHD1–CtIP co-IP, cancer-mutant epistasis; disulfide mapping and dNTPase assays; in vitro acetylation by ARD1\",\n      \"pmids\": [\"28834754\", \"28398823\", \"28978134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How SAMHD1 is recruited to DSBs not yet defined\", \"Physiological trigger of redox switch in vivo unclear\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed IFN restricts HIV-1 chiefly by dephosphorylating/activating SAMHD1 via CDK1 downregulation, and demonstrated dNTP-control roles in antibody diversification and stalled-fork repair.\",\n      \"evidence\": \"CDK1 inhibition/knockdown with phospho-SAMHD1 and HIV infection in macrophages; CRISPR KO in germinal-center B cells with mutation spectra; DNA fiber and MRE11 exonuclease assays with cGAS/STING readouts\",\n      \"pmids\": [\"29764952\", \"29669924\", \"29670289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase mediating IFN-induced dephosphorylation not identified\", \"Mechanism of MRE11 stimulation by SAMHD1 biochemically undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated that diverse herpesviruses inactivate SAMHD1 by viral-kinase phosphorylation of T592, identified TRIM21-mediated degradation and PIM-kinase-enhanced Vpx counteraction, and uncovered NF-κB suppression as a dNTP-independent antiviral mechanism.\",\n      \"evidence\": \"In vitro/in vivo viral kinase assays (BGLF4, pUL97, M97) with dNTPase readouts and KO mice; TRIM21 co-IP/ubiquitination; PIM1/3 phospho-Vpx proteomics; ChIP of RELA at the HCMV MIE promoter\",\n      \"pmids\": [\"31291580\", \"31291579\", \"31548682\", \"31548683\", \"31797533\", \"31015445\", \"30739781\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanistic basis of NF-κB inhibition not yet resolved at this stage\", \"Relative in vivo weight of each regulatory PTM unclear\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Refined the catalytic mechanism (bi-metallic Fe-Mg in-line hydrolysis), defined dNTP-control roles in class switch recombination, and identified an IFN-independent TLR4 pathway activating SAMHD1.\",\n      \"evidence\": \"X-ray crystallography with enzymology; ChIP/CSR assays with dNTP manipulation; TLR4-agonist pathway dissection (TRIF-dependent, CDK1 depletion)\",\n      \"pmids\": [\"32576829\", \"32511795\", \"32209460\", \"32986788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How dNTP levels mechanistically shape repair-junction fidelity not fully resolved\", \"TLR4-to-SAMHD1 signaling intermediates incompletely mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Expanded the PTM and interactome landscape (O-GlcNAcylation, SUMOylation, NONO stabilization) and uncovered dNTP-control roles at transcription-replication conflicts and end-joining junctions.\",\n      \"evidence\": \"MS site mapping with mutagenesis and antiviral assays (S93 O-GlcNAc, K469/K595/K622 SUMO); NONO co-IP/ubiquitination; R-loop ChIP with RNase H rescue; end-joining substrate assays\",\n      \"pmids\": [\"33391506\", \"34238351\", \"35803902\", \"33857133\", \"33591315\", \"33988981\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Combinatorial interplay among PTMs not addressed\", \"Most modification studies are single-lab observations\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined SAMHD1 as an ssRNA 3' exonuclease preventing dsRNA-driven IFN, mapped SIRT1-K354 deacetylation as the switch coupling SAMHD1 to CtIP-dependent resection, and ordered cGAS/STING upstream of MDA5/MAVS in SAMHD1-deficient inflammation.\",\n      \"evidence\": \"In vitro exonuclease assays with condensate imaging and RLR epistasis; SIRT1–SAMHD1 co-IP with K354 mutagenesis and HR assays; double-KO epistasis in mice; cryo-EM with tetramer dissociation kinetics\",\n      \"pmids\": [\"36150385\", \"36344525\", \"36346347\", \"35801923\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How exonuclease and dNTPase roles are partitioned in vivo unresolved\", \"Switch between sensing pathways across cell types unclear\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Mechanistically defined SAMHD1's direct innate-immune suppression (IKKα/β binding disrupting TAK1; MAVS/IKKε/IRF7 axis), and revealed USP7-mediated stabilization and a cytoskeletal/migration role via cortactin in cancer.\",\n      \"evidence\": \"In vitro binding with purified proteins, reciprocal co-IP and KO/reconstitution for IKK and MAVS/IRF7; USP7 co-IP with K421 mapping and chemosensitivity; cortactin co-IP with FAK/Rac1 and migration assays\",\n      \"pmids\": [\"37100289\", \"37328105\", \"37081042\", \"37009792\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Integration of NF-κB and IFN suppression with dNTPase activity unclear\", \"Migration role is a single-lab observation\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified a dNTPase-independent cooperation with MX2 in which SAMHD1 binds incoming HIV-1 cores and delivers them to an MX2 trap to block nuclear entry.\",\n      \"evidence\": \"Co-IP/MS, MX2 KO, SAMHD1 domain mapping, and HIV-1 nuclear import/capsid mutant assays\",\n      \"pmids\": [\"38888311\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding awaiting independent confirmation\", \"Structural basis of core recognition undefined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established that allosteric loading of an inactive tetrameric intermediate, not tetramerization per se, governs catalytic efficiency and enables facilitated dNTP depletion.\",\n      \"evidence\": \"In vitro dNTPase assays with allosteric occupancy analysis, tetramerization assays, and kinetic modeling\",\n      \"pmids\": [\"39824836\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How cellular ligand fluctuations engage this equilibrium in vivo untested\", \"Single-lab reconstitution\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SAMHD1's multiple activities (dNTPase, ssRNA exonuclease, MRE11/CtIP regulation, direct innate-immune-kinase inhibition) are spatially and temporally coordinated, and which dominates in a given cell state, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model integrating enzymatic and non-enzymatic functions\", \"Phosphatase reversing T592 not identified in the corpus\", \"Mechanism of recruitment to DSBs incompletely defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 5, 6, 7, 27, 45, 47]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [36]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [2, 36, 39]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 37, 39]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [40, 41, 16, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 25, 13]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [14, 25, 29]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [13, 16, 30, 37]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [3, 11, 36, 38, 40, 41]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [13, 16, 30, 34, 37]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 5, 12]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 6, 12, 45]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 6, 15]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CtIP\", \"MRE11\", \"IKBKB\", \"CHUK\", \"MAVS\", \"IRF7\", \"TRIM21\", \"USP7\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}