Human APE2 and TREX2 Repair 3'-DNA-Peptide Cross-links Derived from Abasic Sites.

Histones and many other proteins react with abundant endogenous DNA lesions, apurinic/apyrimidinic (abasic, AP) sites and/or 3′-phospho-α,β-unsaturated aldehyde (3′-PUA), to form unstable but long-lived Schiff base DNA–protein cross-links at 3′-DNA termini (3′-PUA–protein DPCs). Poly (ADP-ribose) polymerase 1 (PARP1) cross-links to the AP site in a similar manner but the Schiff base is reduced by PARP1’s intrinsic redox capacity, yielding a stable 3′-PUA–PARP1 DPC. Eradicating these DPCs is critical for maintaining the genome integrity because 3′-hydroxyl is required for DNA synthesis and ligation. But how they are repaired is not well understood. Herein, we chemically synthesized 3′-PUA-aminooxylysine-peptide adducts that closely resemble the proteolytic 3′-PUA–protein DPCs, and found that they can be repaired by human tyrosyl-DNA phosphodiesterase 1 (TDP1), AP endonuclease 1 (APE1) and three-prime repair exonuclease 1 (TREX1). We characterized these novel repair pathways by measuring the kinetic constants and determining the effect of cross-linked peptide length, flanking DNA structure, and the opposite nucleobase. We further found that these nucleases can directly repair 3′-PUA–histone DPCs, but not 3′-PUA–PARP1 DPCs unless proteolysis occurs initially. Collectively, we demonstrated that in vitro 3′-PUA–protein DPCs can be repaired by TDP1, APE1, and TREX1 following proteolysis, but the proteolysis is not absolutely required for smaller DPCs.

Histones catalyze the DNA strand incision at apurinic/apyrimidinic (AP) sites accompanied by formation of reversible but long-lived DNA-protein cross-links (DPCs) at 3'-DNA termini within single-strand breaks. These DPCs need to be removed because 3'-hydroxyl is required for gap-filling DNA repair synthesis but are challenging to study because of their reversible nature. Here we report a chemical approach to synthesize stable and site-specific 3'-histone-DPCs and their repair by three nucleases, human AP endonuclease 1, tyrosyl-DNA phosphodiesterase 1, and three-prime repair exonuclease 1. Our method employs oxime ligation to install an alkyne to 3'-DNA terminus, genetic incorporation of an azidohomoalanine to histone H4 at a defined position, and click reaction to conjugate DNA to H4 site-specifically. Using these model DPC substrates, we demonstrated that the DPC repair efficiency is highly affected by the local protein environment, and prior DPC proteolysis facilitates the repair.

Oxidative stress is a principal cause of DNA damage, and mechanisms to repair this damage are among the most highly conserved of biological processes. Oxidative stress is also used by phagocytes to attack bacterial pathogens in defence of the host. We have identified and characterised two apurinic/apyrimidinic (AP) endonuclease paralogues in the human pathogen Neisseria meningitidis. The presence of multiple versions of DNA repair enzymes in a single organism is usually thought to reflect redundancy in activities that are essential for cellular viability. We demonstrate here that these two AP endonuclease paralogues have distinct activities in DNA repair: one is a typical Neisserial AP endonuclease (NApe), whereas the other is a specialised 3'-phosphodiesterase Neisserial exonuclease (NExo). The lack of AP endonuclease activity of NExo is shown to be attributable to the presence of a histidine side chain, blocking the abasic ribose-binding site. Both enzymes are necessary for survival of N. meningitidis under oxidative stress and during bloodstream infection. The novel functional pairing of NExo and NApe is widespread among bacteria and appears to have evolved independently on several occasions.

Three-prime repair exonuclease 1 (TREX1) is the major DNase in mammalian cells that degrades cytosolic DNA to prevent activation of the cGAS-STING pathway. Genotoxic stress, DNA damage, and radiotherapy induce TREX1 expression in cancer cells, allowing them to evade innate immune activation of type I interferon (IFN-I)-mediated antitumor response. How TREX1 can be targeted for cancer immunotherapy remains elusive. Here, we show that genetic deletion of TREX1 in tumors elicits robust antitumor immunity through tumor-intrinsic cGAS-STING activation, IFN-I signaling, and recruitment of CD8+ T cells. To therapeutically target TREX1, we perform a high-throughput small-molecule inhibitor screen of TREX1 using a cell-free DNase assay. We identify two lead compounds that inhibit TREX1 DNase activity at low micromolar concentrations, induce IFN-I signaling in cancer cells, and inhibit tumor growth in mice in a type I IFN receptor-dependent manner. Additionally, TREX1 inhibitor treatment sensitizes B16-F10 melanoma to anti-PD-1 immunotherapy. We further show that Trex1 knockout cancer cells elicit systemic antitumor immunity and can be used as autologous cancer vaccines to protect against future tumor challenge and metastasis. We also establish an inducible whole-body Trex1 knockout mouse model to simulate “on-demand” systemic TREX1 inactivation in adult mice. Sustained TREX1 loss in adult mice suppresses a broad range of solid tumors and metastatic tumors. Although TREX1 deficiency is associated with severe autoimmune diseases, inducible Trex1 knockout in adult mice does not cause immune toxicity, demonstrating feasibility of an immune-safe therapeutic window. Together, our data present multiple therapeutic modalities for targeting TREX1 using small-molecule inhibitors and as an autologous cancer vaccine, as well as antitumor efficacy and immune safety, which should pave the way for developing TREX1-targeted cancer immunotherapy. Citation Format: Cong Xing, Nan Yan. Targeting the innate immune checkpoint TREX1 elicits antitumor immunity through tumor-intrinsic cGAS-STING signaling [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B022.

Background: Three-prime repair exonuclease 1 (TREX1) is a cytosolic DNase that suppresses cGAS–STING–mediated type I interferon (IFN-I) responses by degrading self-DNA. While this function is essential for immune homeostasis—highlighted by the fact that TREX1 loss causes autoimmune disorders such as Aicardi-Goutières syndrome—many cancers exploit TREX1 upregulation to evade immune surveillance, particularly following genotoxic therapies. Therapeutically inhibiting TREX1 offers an opportunity to re-engage IFN-I–driven antitumor immunity, but it also raises concerns about triggering immune-related adverse events. Here, we aimed to define the therapeutic benefit and immune safety of targeting TREX1 in vivo. Methods: We employed a multimodal strategy to assess the therapeutic potential and safety of targeting TREX1. First, we conducted a high-throughput screen to identify small-molecule inhibitors of TREX1 and evaluated lead compound #296 in syngeneic mouse tumor models. Second, we tested TREX1-deficient tumor cells as autologous cancer vaccines. Finally, we generated inducible whole-body Trex1 knockout mice to model systemic TREX1 inhibition and assess its long-term immune safety. Results: Lead compound #296 selectively inhibited TREX1 enzymatic activity, triggered IFN-I signaling in tumor cells, and significantly suppressed tumor growth in multiple syngeneic mouse models. Treatment with #296 enhanced CD8+ T cell infiltration and reversed resistance to anti–PD-1 therapy in poorly immunogenic B16-F10 melanoma, without inducing systemic inflammation or elevated CRP. TREX1-deficient tumor cells activated tumor-intrinsic cGAS–STING signaling and functioned as effective autologous cancer vaccines, eliciting durable systemic antitumor immunity that protects against both tumor rechallenge and metastasis. Importantly, systemic TREX1 deletion in adult mice using an inducible knockout model led to sustained tumor suppression across diverse tumor models, while maintaining immune safety over 6 months with minimal immune toxicity. Conclusions: Our study reveals TREX1 as a druggable target to stimulate IFN-I–driven antitumor immunity. Across three distinct therapeutic approaches—small-molecule inhibitor, cell-based vaccination, and systemic gene knockout—TREX1 targeting elicited durable tumor control with minimal autoimmune toxicity, supporting its translational potential as a safe and effective cancer immunotherapy. Citation Format: Cong Xing, Nan Yan. Therapeutic inhibition of TREX1 elicits type I interferon–mediated antitumor immunity with minimal autoimmune toxicity [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Mechanisms of Cancer Immunity and Cancer-related Autoimmunity; 2025 Sep 24-27; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(9 Suppl):Abstract nr A022.

<div>Abstract<p>Three-prime repair exonuclease 1 (TREX1) is the major DNase in mammalian cells that degrades cytosolic DNA to prevent activation of the cyclic GMP–AMP synthase (cGAS)–stimulator of interferon genes (STING) pathway. Genotoxic stress, DNA damage, and radiotherapy induce TREX1 expression in cancer cells, allowing them to evade innate immune activation of type I IFN–mediated antitumor response. Therefore, targeting TREX1 could represent a potential approach to stimulate antitumor immunity. In this study, we conducted a high-throughput small-molecule inhibitor screen of TREX1 using a cell-free DNase assay. Compound 296 specifically inhibited TREX1 DNase activity at low micromolar concentrations, induced type I IFN signaling in cancer cells, and inhibited tumor growth in mice in an inteferon alpha/beta receptor (IFNAR)–dependent manner. Treatment with compound 296 also stimulated T-cell infiltration into tumors and synergized with immune checkpoint blockade. <i>Trex1</i> knockout cancer cells elicited robust systemic antitumor immunity through tumor-intrinsic cGAS–STING activation and functioned as autologous cancer vaccines that protected against tumor challenge and metastasis. An inducible whole-body <i>Trex1</i> knockout mouse model was established to simulate “on-demand” systemic TREX1 inactivation in adult mice. Sustained TREX1 loss suppressed a broad range of solid and metastatic tumors in adult mice without incurring severe immune toxicity, even when combined with immune checkpoint blockade, demonstrating the feasibility of an immune-safe therapeutic window. Together, these data demonstrate the antitumor efficacy and immune safety of multiple therapeutic modalities targeting TREX1, including targeting small-molecule inhibitors of TREX1 and employing TREX1 knockout tumor cells as an autologous cancer vaccine. These approaches should pave the way for developing TREX1-targeted cancer immunotherapies.</p>Significance:<p>Therapeutic modalities targeting TREX1 can activate cGAS-STING signaling and can be incorporated into autologous cancer vaccine designs to improve cancer treatment, supporting the potential of inactivating TREX1 to harness innate immunity.</p><p><a href="https://aacrjournals.org/cancerres/article-abstract/doi/10.1158/0008-5472.CAN-25-1272" target="_blank"><i>See related commentary by Hanks, p. 2778</i></a></p></div>

Three-prime repair exonuclease 1 (TREX1) is the major DNase in mammalian cells that degrades cytosolic DNA to prevent activation of the cGAS-STING pathway. Genotoxic stress, DNA damage, and radiotherapy induce TREX1 expression in cancer cells, allowing them to evade innate immune activation of type I interferon (IFN-I)-mediated antitumor response. How TREX1 can be targeted for cancer immunotherapy remains elusive. Here, we report a high-throughput small-molecule inhibitor (SMI) screen of TREX1 using a cell-free DNase assay. We identify two lead compounds that inhibit TREX1 DNase activity at low micromolar concentrations, induce IFN-I signaling in cancer cells, and inhibit tumor growth in mice in an IFNAR-dependent manner. We further show that Trex1 knockout cancer cells elicit robust systemic antitumor immunity through tumor-intrinsic cGAS-STING activation and can be used as autologous cancer vaccines to protect against future tumor challenge. We also establish an inducible whole-body Trex1 knockout mouse model to simulate “on-demand” systemic TREX1 inactivation in adult mice. Sustained TREX1 loss in adult mice suppresses a broad range of solid tumors and metastatic tumors without incurring immune toxicity, demonstrating feasibility of an immune-safe therapeutic window. Together, our data present multiple therapeutic modalities for targeting TREX1 using SMIs and as an autologous cancer vaccine, as well as antitumor efficacy and immune safety, which should pave the way for developing TREX1-targeted cancer immunotherapy. Citation Format: Cong Xing, Xintao Tu, Wanwan Huai, Zhen Tang1, Kun Song, Kennady Knox, Nicole Dobbs, Kun Yang, Nan Yan. Therapeutic modality, antitumor efficacy and immune safety for targeting innate immune checkpoint TREX1 as cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A057.

Three-prime repair exonuclease 1 (TREX1) is a 3′-5′ exonuclease that plays an important role in clearing cytoplasmic DNA. Additionally, TREX1 is translocated to the nucleus after DNA damage and assists in DNA repair. In this work, we evaluated the activity of TREX1 in the context of the removal of methyl DNA adducts. We observed that TREX1 was less efficient at degrading methyl methanesulfonate (MMS)-treated methylated DNA compared with normal DNA. Two methyl DNA adducts, N1-methyladenine and N3-methylcytosine, were found to block TREX1 exonuclease activity. To understand the mechanism of limited TREX1-mediated degradation of MMS-damaged DNA, stem-loop substrates containing solitary methyl adducts were prepared. We found that when the solitary methyl adducts were present at the 3′-terminal single-stranded overhang, it prevented degradation by TREX1. However, TREX1 could efficiently process internally located duplex DNA methyl adducts when the 3′-terminal of the scissile strand was damage-free. Broadly, these observations suggest that TREX1 may be capable of resecting methyl adducts containing DNA, but it might be less proficient of removing 3′-terminal DNA methyl adducts.

Maintaining genome integrity is important for cells and damaged DNA triggers autoimmunity. Previous studies have reported that Three-prime repair exonuclease 1(TREX1), an endogenous DNA exonuclease, prevents immune activation by depleting damaged DNA, thus preventing the development of certain autoimmune diseases. Consistently, mutations in TREX1 are linked with autoimmune diseases such as systemic lupus erythematosus, Aicardi–Goutières syndrome (AGS) and familial chilblain lupus. However, TREX1 mutants competent for DNA exonuclease activity are also linked to AGS. Here, we report a nuclease-independent involvement of TREX1 in preventing the L1 retrotransposon-induced DNA damage response. TREX1 interacted with ORF1p and altered its intracellular localization. Furthermore, TREX1 triggered ORF1p depletion and reduced the L1-mediated nicking of genomic DNA. TREX1 mutants related to AGS were deficient in inducing ORF1p depletion and could not prevent L1-mediated DNA damage. Therefore, our findings not only reveal a new mechanism for TREX1-mediated L1 suppression and uncover a new function for TREX1 in protein destabilization, but they also suggest a novel mechanism for TREX1-mediated suppression of innate immune activation through maintaining genome integrity.

Reactive oxygen species (ROS) 1The abbreviations used are: ROS, reactive oxygen species; BER, base excision repair; NER, nucleotide excision repair; AD, Alzheimer's disease; endo, endonuclease; TCR, transcription-coupled repair; 8-oxoG, 8-hydroxyguanine; 8-oxodG, 8-hydroxydeoxyguanine; TG, thymine glycol; AP, apurinic/apyrimidinc; GSR, gene-specific repair assay; XP, xeroderma pigmentosum; CS, Cockayne's syndrome; FapyG, 2,6-diamino-4hydroxyl-5-methylformamidopyrimidine. 1The abbreviations used are: ROS, reactive oxygen species; BER, base excision repair; NER, nucleotide excision repair; AD, Alzheimer's disease; endo, endonuclease; TCR, transcription-coupled repair; 8-oxoG, 8-hydroxyguanine; 8-oxodG, 8-hydroxydeoxyguanine; TG, thymine glycol; AP, apurinic/apyrimidinc; GSR, gene-specific repair assay; XP, xeroderma pigmentosum; CS, Cockayne's syndrome; FapyG, 2,6-diamino-4hydroxyl-5-methylformamidopyrimidine. are generated in cells as a by-product of cellular metabolism. ROS react with proteins, lipids, and DNA. DNA base modifications, abasic sites, deoxyribose damage, and single and double strand breaks are all induced following various forms of oxidative stress. This review will focus on DNA repair of oxidative lesions by base excision repair (BER) and nucleotide excision repair (NER). We will focus on the mammalian BER enzymes that have recently been cloned and characterized. Mitochondrial DNA repair mechanisms for oxidative damage will also be discussed. Although sugar damage and double strand breaks are critical lesions induced by ionizing radiation and bleomycin, repair of these lesions will not be discussed here (see Refs. 1Weaver D.T. Crit. Rev. Eukaryotic Gene Expression. 1996; 6: 345-375Crossref PubMed Scopus (44) Google Scholar, 2Lieber M.R. Grawunder U. Wu X. Yaneva M. Curr. Opin. Genet. Dev. 1997; 7: 99-104Crossref PubMed Scopus (127) Google Scholar, 3Povirk L.F. Mutat. Res. 1996; 355: 71-89Crossref PubMed Scopus (333) Google Scholar for recent reviews).Oxidative DNA Damage and Its ConsequencesThe endogenous attack on DNA by ROS species generates a low steady-state level of DNA adducts that have been detected in the DNA from human cells (4Dizdaroglu M. Halliwell B. Aruoma O.I. DNA and Free Radicals. Ellis Horwood, Ltd., London, United Kingdom1993: 18-39Google Scholar). Some of these base modifications are shown in Fig. 1. There are many more, and it is possible that the full spectrum of oxidative lesions in endogenous mammalian DNA exceeds 100 different types, of which 8-hydroxyguanine (8-oxoG) is one of the most abundant (5Ames B.N. Free Radical Res. Commun. 1989; 7: 121-128Crossref PubMed Scopus (627) Google Scholar).Oxidative DNA damage is thought to contribute to carcinogenesis, aging, and neurological degeneration (for reviews, see Refs. 5Ames B.N. Free Radical Res. Commun. 1989; 7: 121-128Crossref PubMed Scopus (627) Google Scholar and 6Wiseman H. Halliwell B. Biochem. J. 1996; 313: 17-29Crossref PubMed Scopus (1943) Google Scholar). Studies have shown that oxidative DNA damage accumulates in cancerous tissue. For example, higher levels of oxidative base damage were observed in lung cancer tissue compared with surrounding normal tissue (7Olinski R. Zastawny T. Budzbin J. Skokowski J. Zegarski W. Dizdaroglu M. FEBS Lett. 1992; 309: 193-198Crossref PubMed Scopus (243) Google Scholar). Another study reported a 9-fold increase in 8-oxoG, 8-hydroxyadenine, and 2,6-diamino-4-hydroxy-5-formamidopyrimidine in DNA from breast cancer tissue compared with normal tissue (8Malins D.C. Haimanot R. Cancer Res. 1991; 51: 5430-5432PubMed Google Scholar). Further, the cumulative risk of cancer increases dramatically with age in humans (9Ames B.N. Mutat. Res. 1989; 214: 41-46Crossref PubMed Scopus (290) Google Scholar), and cancer can in general terms be regarded as a degenerative disease of old age. There is evidence for the accumulation of oxidative DNA damage with age based on studies mainly measuring the increase in 8-oxoG (10Sohal R.S. Ku H.H. Agarwal S. Forster M.J. Lal H. Mech. Ageing Dev. 1994; 74: 121-133Crossref PubMed Scopus (689) Google Scholar). In Alzheimer's disease (AD), some studies have shown an accumulation of oxidative DNA damage in the brain, and a recent extensive study in cells from familial Alzheimer's disease demonstrated a deficiency in the processing of damage invoked by fluorescent light (11Parshad R.P. Sanford K.K. Price F.M. Melnick L.K. Nee L.E. Schapiro M.B. Tarone R.E. Robbins J.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5146-5150Crossref PubMed Scopus (62) Google Scholar). The effects of fluorescent light exposure were inhibited by the addition of free radical scavengers, and therefore it was proposed that oxidative DNA damage was produced and responsible for the altered response seen in AD cells (11Parshad R.P. Sanford K.K. Price F.M. Melnick L.K. Nee L.E. Schapiro M.B. Tarone R.E. Robbins J.H. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5146-5150Crossref PubMed Scopus (62) Google Scholar). AD cells also respond abnormally to ionizing radiation and simple alkylating agents, and therefore it is possible that lesions introduced by these agents such as oxidative modifications, alkylpurines, or DNA strand breaks are not repaired efficiently in AD cells (12Scudiero D.A. Polinsky R.J. Brumbach R.A. Tarone R.E. Nee L.E. Robbins J.H. Mutat. Res. 1986; 159: 125-131Crossref PubMed Scopus (45) Google Scholar).Many experimental methods have been used to expose cells to oxidative damage, all attempting to mimic endogenous processes (4Dizdaroglu M. Halliwell B. Aruoma O.I. DNA and Free Radicals. Ellis Horwood, Ltd., London, United Kingdom1993: 18-39Google Scholar, 6Wiseman H. Halliwell B. Biochem. J. 1996; 313: 17-29Crossref PubMed Scopus (1943) Google Scholar). Some studies have used hydrogen peroxide, which generates a large spectrum of lesions. Ionizing radiation also generates a wide spectrum of lesions including base damage and single and double strand breaks in DNA. Methylene blue plus visible light exposure primarily generates singlet oxygen damage, and osmium tetroxide generates primarily thymine glycols. For more discussion of this see Refs. 4Dizdaroglu M. Halliwell B. Aruoma O.I. DNA and Free Radicals. Ellis Horwood, Ltd., London, United Kingdom1993: 18-39Google Scholar and6Wiseman H. Halliwell B. Biochem. J. 1996; 313: 17-29Crossref PubMed Scopus (1943) Google Scholar. It is important to distinguish between the different types of oxidative stresses when evaluating experimental results.Technical differences in the methods used for DNA isolation may well result in differences in the analysis of the DNA adducts. A recent review compared the various methods used to detect oxidative damage in DNA (13Beckman K.B. Ames B.N. Methods Enzymol. 1996; 264: 442-453Crossref PubMed Google Scholar). One of the conclusions that emerged from the comparison was that there is a great need for methods to be more standardized and thus to provide more consistent results between different laboratories when comparing different but related techniques.One aspect that is common to many methods used to detect oxidative damage is that the DNA modifications are measured as averages in the total cellular DNA. This is of limited value since advances in recent years have shown that DNA damage processing and the biological consequences of DNA lesions vary considerably depending upon where a lesion is situated in the genome. For example, UV-induced photoproducts are processed differently whether situated in an active gene or in a non-transcribed region, and this may also be the case for oxidative lesions.The gene-specific repair assay (GSR) employs various DNA repair enzymes to detect specific lesions, and this assay has provided new insights about the heterogeneity of DNA repair in the nucleus (14Bohr V.A. Carcinogenesis. 1995; 16: 2885-2892Crossref PubMed Scopus (95) Google Scholar) and more recently about the repair mechanisms for mitochondrial DNA (see below). For example, endonuclease III (endo III) can detect oxidized pyrimidines, and the Fapy DNA glycosylase (Fpg protein) can detect oxidized purines. Endo III-sensitive sites have been assayed in the general genome (15Collins A.R. Duthie S.J. Dobson V.L. Carcinogenesis. 1993; 14: 1733-1735Crossref PubMed Scopus (761) Google Scholar), and more recently, Fpg protein has been used to detect lesions in specific genes (16Driggers W.J. LeDoux S.P. Wilson G.L. J. Biol. Chem. 1993; 268: 22042-22045Abstract Full Text PDF PubMed Google Scholar, 17Taffe B.G. Larminat F. Laval J. Croteau D.L. Anson R.M. Bohr V.A. Mutat. Res. 1996; 364: 183-192Crossref PubMed Scopus (64) Google Scholar).Base Excision Repair of Oxidative DamageBER is initiated by DNA glycosylases, a class of enzymes that recognize a specific set of modified bases such as 8-oxoG or thymine glycol (TG). Glycosylases cleave the N-glycosylic bond between the modified base and the sugar. There are two classifications of glycosylases: simple glycosylases that only cleave the N-glycosylic bond and glycosylase/AP lyase enzymes, which cleave the N-glycosylic bond and the DNA-phosphate backbone. Following the glycosylase step, AP endonucleases are required to remove the 3′-deoxyribose moiety and generate a 3′-hydroxyl group, which can be extended by a DNA polymerase. The process is completed by a DNA ligase rejoining the free DNA ends (for reviews see Refs. 18Seeberg E. Eide L. Bjoras M. Trends Biochem. Sci. 1995; 20: 391-397Abstract Full Text PDF PubMed Scopus (465) Google Scholar and19Friedberg E.C. Walker G.C. Siede W. DNA Repair and Mutagenesis. American Society for Microbiology, Wash., D. C.1995: 135-190Google Scholar).Repair of 8-oxoGThe majority of our knowledge regarding the repair of 8-oxoG has been derived from studies in Escherichia coli. 8-oxoG is considered to be a premutagenic lesion because it can mispair with adenine during DNA replication, and this mispairing results in G → T transversion mutations (20Grollman A.P. Moriya M. Trends Genet. 1993; 9: 246-249Abstract Full Text PDF PubMed Scopus (727) Google Scholar). Bacteria possess an integrated system of BER and error avoidance mechanisms to prevent damage at guanines (for a review see Ref. 20Grollman A.P. Moriya M. Trends Genet. 1993; 9: 246-249Abstract Full Text PDF PubMed Scopus (727) Google Scholar). This system is comprised of three components, an 8-oxoG glycosylase/AP lyase enzyme, called MutM or Fpg protein, an adenine DNA glycosylase, MutY, and a 8-oxodGTPase, MutT. As will be discussed, functional homologs of each of these proteins have now been identified in higher eukaryotes.Two groups have independently cloned an 8-oxoguanine glycosylase/AP lyase from yeast (yOgg1) (21van der Kemp P.A. Thomas D. Barbey R. de Oliveira R. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5197-5202Crossref PubMed Scopus (346) Google Scholar, 22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar). The enzyme is a functional homolog of the Fpg protein because the yeast enzyme shares no amino acid homology with the bacterial protein. The yOgg1 cleaved DNA containing 8-oxoG opposite pyrimidines, abasic sites (21van der Kemp P.A. Thomas D. Barbey R. de Oliveira R. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5197-5202Crossref PubMed Scopus (346) Google Scholar, 22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar), and 2,6-diamino-4-hydroxy-5-methylformamidopyrimidine (FapyG) (21van der Kemp P.A. Thomas D. Barbey R. de Oliveira R. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5197-5202Crossref PubMed Scopus (346) Google Scholar). Cleavage by yOgg1 was consistent with a β-elimination mechanism (21van der Kemp P.A. Thomas D. Barbey R. de Oliveira R. Boiteux S. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 5197-5202Crossref PubMed Scopus (346) Google Scholar,22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar).Recently, the human and the mouse 8-oxoguanine glycosylase/AP lyase (human OGG1 or mouse Ogg1) genes have been cloned by their homology to yeast ogg1 (23Lu R. Nash H.M. Verdine G.L. Curr. Biol. 1997; 7: 397-407Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar, 24Aburatani H. Hippo Y. Ishida T. Takashima R. Matsuba C. Kodama T. Takao M. Yasui A. Yamamoto K. Asano M. Fukasawa K. Yoshinari T. Inoue H. Ohtsuka E. Nishimura S. Cancer Res. 1997; 57: 2151-2156PubMed Google Scholar, 25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar). Human OGG1 gene was localized to the short arm of chromosome 3, 3p26.2 (23Lu R. Nash H.M. Verdine G.L. Curr. Biol. 1997; 7: 397-407Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar, 25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar). Expression of the human gene in E. coli lacking mutM and mutY suppressed the spontaneous mutator phenotype of these cells (24Aburatani H. Hippo Y. Ishida T. Takashima R. Matsuba C. Kodama T. Takao M. Yasui A. Yamamoto K. Asano M. Fukasawa K. Yoshinari T. Inoue H. Ohtsuka E. Nishimura S. Cancer Res. 1997; 57: 2151-2156PubMed Google Scholar, 25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar). Human OGG1 (also called MutM homolog) was shown to cleave the DNA by a β-elimination mechanism preferentially at 8-oxoG:C base pairs (23Lu R. Nash H.M. Verdine G.L. Curr. Biol. 1997; 7: 397-407Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar, 24Aburatani H. Hippo Y. Ishida T. Takashima R. Matsuba C. Kodama T. Takao M. Yasui A. Yamamoto K. Asano M. Fukasawa K. Yoshinari T. Inoue H. Ohtsuka E. Nishimura S. Cancer Res. 1997; 57: 2151-2156PubMed Google Scholar). Several conserved domains have been identified in the yeast, mouse, and human genes including the a helix-hairpin-helix (HhH) and Gly/Pro-rich-Asp motif (GPD motif) (22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar, 23Lu R. Nash H.M. Verdine G.L. Curr. Biol. 1997; 7: 397-407Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar, 25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar). In addition, Arai et al. (25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar) reported that the yeast Ogg1 and human OGG1 contained a putative C2H2 zinc finger-like motif, although in the yeast sequence one of the histidines was an arginine. Alignment of the ogg1 genes with other DNA repair glycosylases suggests that these enzymes may represent a DNA repair superfamily (18Seeberg E. Eide L. Bjoras M. Trends Biochem. Sci. 1995; 20: 391-397Abstract Full Text PDF PubMed Scopus (465) Google Scholar, 22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar, 23Lu R. Nash H.M. Verdine G.L. Curr. Biol. 1997; 7: 397-407Abstract Full Text Full Text PDF PubMed Scopus (309) Google Scholar, 25Arai K. Morishita K. Shinmura K. Kohno T. Kim S. Nohmi T. Taniwaki M. Ohwada S. Yokota J. Oncogene. 1997; 14: 2857-2861Crossref PubMed Scopus (247) Google Scholar).Nash et al. (22Nash H.M. Bruner S.D. Schaerer O.D. Kawate T. Addona T.A. Spooner E. Lane W.S. Verdine G.L. Curr. Biol. 1996; 6: 968-980Abstract Full Text Full Text PDF PubMed Scopus (413) Google Scholar) identified another yeast protein, which preferentially interacted with the substrate 8-oxoG:G; they called the activity Ogg2. This same substrate preference was observed for the yeast Fapy DNA glycosylase previously isolated by de Oliveira et al. (26de Oliveira R. van der Kemp P.A. Thomas D. Geiger A. Nehls P. Boiteux S. Nucleic Acids Res. 1994; 22: 3760-3764Crossref PubMed Scopus (35) Google Scholar). Whether these two proteins are the same or not remains to be determined. In human extracts, an 8-oxoG endonuclease was identified from human polymorphonuclear neutrophils, which cleaved 8-oxoG but not the ring-opened guanine adduct, FapyG (27Chung M.H. Kim H.S. Ohtsuka E. Kasai H. Yamamoto F. Nishimura S. Biochem. Biophys. Res. Commun. 1991; 178: 1472-1478Crossref PubMed Scopus (84) Google Scholar). One distinguishing feature of this enzyme was that it was magnesium-dependent. Another study identified two repair activities, an 8-oxoG glycosylase and an 8-oxoG endonuclease, from HeLa cell nuclear extracts (28Bessho T. Tano K. Kasai H. Ohtsuka E. Nishimura S. J. Biol. Chem. 1993; 268: 19416-19421Abstract Full Text PDF PubMed Google Scholar). The 8-oxoG base pairing preferences for these enzymes were similar to that of yeast Ogg1. Further experiments are required to determine whether these proteins are human OGG1 or novel enzymes.In E. coli, the MutY protein is an adenine DNA glycosylase that removes adenine when base paired with 8-oxoG. Using purified DNA polymerases, it has been demonstrated that the replicative polymerases incorporate adenine opposite 8-oxoG (29Shibutani S. Takeshita M. Grollman A.P. Nature. 1991; 349: 431-434Crossref PubMed Scopus (2024) Google Scholar). A human MutY activity has been purified from calf thymus cells (30McGoldrick J.P. Yeh Y.C. Solomon M. Essigmann J.M. Lu A.L. Mol. Cell. Biol. 1995; 15: 989-996Crossref PubMed Google Scholar). The protein removes adenine mispairs including A:G, A/8-oxoG, and A:C. The glycosylase co-purified with a AP nicking activity, which was inhibited by neutralizing MutY antibodies. Recently, the gene for a human MutY homolog was cloned (31Slupska M.M. Baikalov C. Luther W.M. Chiang J.H. Wei Y.F. Miller J.H. J. Bacteriol. 1996; 178: 3885-3892Crossref PubMed Scopus (327) Google Scholar).In cells, the deoxyribonucleotide pools are also subjected to oxidative damage. dGTP can be converted to 8-oxodGTP and incorporated into nascent DNA strands opposite adenine. To avoid such damage, cells possess an 8-oxodGTPase, which hydrolyzes the triphosphate to the monophosphate so that it can no longer be incorporated into DNA. In bacteria, the MutT gene product is the 8-oxodGTPase enzyme. A human MutT homolog has been cloned from a human cell line (32Sakumi K. Furuichi M. Tsuzuki T. Kakuma T. Kawabata S. Maki H. Sekiguchi M. J. Biol. Chem. 1993; 268: 23524-23530Abstract Full Text PDF PubMed Google Scholar).Repair of Thymine Glycols and Ring-saturated PyrimidinesAnother major adduct generated by oxidative stress is TGs (cf. Fig. 1). Unlike 8-oxoG, TGs block DNA and RNA polymerases and are thought to be lethal (33Ide H. Tedzuka K. Shimzu H. Kimura Y. Purmal A.A. Wallace S.S. Kow Y.W. Biochemistry. 1994; 33: 7842-7847Crossref PubMed Scopus (95) Google Scholar). Endo III is one of the bacterial enzymes responsible for recognition and removal of TGs; however, cells lacking endo III are not hypersensitive to H2O2 or x-rays (34Cunningham R.P. Weiss B. Proc. Natl. Acad. Sci. U. S. A. 1985; 82: 474-478Crossref PubMed Scopus (145) Google Scholar). Subsequently it was shown that bacteria contain another endonuclease that recognizes TG, endonuclease VIII (35Melamede R.J. Hatahet Z. Kow Y.W. Ide H. Wallace S.S. Biochemistry. 1994; 33: 1255-1264Crossref PubMed Scopus (160) Google Scholar). In addition, the Uvr ABC complex was shown to recognize TGs in vitro (36Kow Y.W. Wallace S.S. Van Houten B. Mutat. Res. 1990; 235: 147-156Crossref PubMed Scopus (103) Google Scholar). Recently, a yeast homolog of endo III has been cloned, NTG1 (endonucleasethree-like glycosylase 1) (37Eide L. Bjoras M. Pirovano M. Alseth I. Berdal K.G. Seeberg E. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 10735-10740Crossref PubMed Scopus (146) Google Scholar). NTG1 has a unique substrate specificity; not only does it remove oxidized purines, but it also recognizes and incises the ring-opened guanine adduct, FapyG. However, it does not incise the 8-oxodG adduct (37Eide L. Bjoras M. Pirovano M. Alseth I. Berdal K.G. Seeberg E. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 10735-10740Crossref PubMed Scopus (146) Google Scholar). Deletion of yeast NTG1 renders the cells sensitive to H2O2 and menadione (37Eide L. Bjoras M. Pirovano M. Alseth I. Berdal K.G. Seeberg E. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 10735-10740Crossref PubMed Scopus (146) Google Scholar).A mammalian TG glycosylase activity has been purified from extracts of calf thymus and bovine cells (38Hilbert T.P. Boorstein R.J. Kung H.C. Bolton P.H. Xing D. Cunningham R.P. Teebor G.W. Biochemistry. 1996; 35: 2505-2511Crossref PubMed Scopus (78) Google Scholar). More recently another gene for the human endonuclease III homolog was cloned (39Aspinwall R. Rothwell D.G. Roldan-Arjona T. Anselmino C. J.P. T. Proc. Natl. Acad. Sci. U. S. A. 1997; PubMed Scopus Google Scholar). the bacterial enzyme endo the human enzyme on and TG It also an and a helix-hairpin-helix of and or sites are called abasic are generated as a of normal spontaneous of the N-glycosylic by the of DNA glycosylases or by oxidative damage to the sugar in DNA. AP endonucleases are enzymes that to generate DNA ends for DNA or (for reviews see Refs. Cunningham R.P. Mutat. Res. 1990; PubMed Scopus Google Scholar, B. L. Rev. Biochem. 1994; PubMed Scopus Google Scholar, 1995; PubMed Scopus Google Scholar). One major AP endonuclease has been purified from human cells called (also called and in Ref. 1995; PubMed Scopus Google Scholar). The enzyme to the AP a moiety and a 3′-hydroxyl on the DNA In addition to the AP endonuclease activity, the enzyme other including a and a activity 1995; PubMed Scopus Google Scholar, S. S. S. M. K. K. B. Biophys. 1991; PubMed Scopus Google Scholar, Takeshita M. Grollman A.P. B. J. Biol. Chem. 1995; Full Text Full Text PDF PubMed Scopus Google endonucleases are the major AP sites in DNA are however, nucleotide excision may also 1995; PubMed Scopus Google Scholar). In E. coli, oxidized abasic sites are by various repair endonucleases M. H. B. Boiteux S. B. Nucleic Acids Res. 1994; 22: PubMed Scopus Google Scholar). It be to whether the mammalian also this recognition and of oxidized AP other in the repair of oxidized AP proteins recognize and repair oxidized AP is that repair of oxidative damage by a BER mechanism in mammalian cells is more complex in to the levels of endogenous oxidative damage, mammalian cells may have to repair mechanisms to the it may be to a protein has on the repair of specific types of DNA damage, and of may not be may have to be a phenotype is Excision Repair of Oxidative bacteria and mammalian cells, the repair of oxidative damage is by BER and mechanisms T. Proc. Natl. Acad. Sci. U. S. A. 1993; PubMed Scopus Google Scholar, T. Nature. 1993; PubMed Scopus Google Scholar). employs a complex set of proteins that remove damage from DNA in Rev. Biochem. 1996; PubMed Scopus Google Scholar and A. Rev. Biochem. 1996; PubMed Scopus Google Scholar). There are two of NER, a repair and a active genes are repaired at a genes in active domains of the genome and with a strand the DNA strand E.C. Rev. Biochem. 1996; PubMed Scopus Google Scholar). The between DNA repair and is the which at two DNA repair genes E.C. Rev. Biochem. 1996; PubMed Scopus Google Scholar). have been identified that have NER, xeroderma Cockayne's and with are by their and the of at an age. groups of have been and and groups neurological Studies were to determine whether the oxidative damage repair of the cells with their neurological B. K. J. 1995; Full Text PDF PubMed Scopus Google Scholar, S. Mutat. Res. 1992; PubMed Scopus Google Scholar). A cell assay was used to the of two cell to repair which been by singlet oxygen S. Mutat. Res. 1992; PubMed Scopus Google Scholar). The cells no from normal In another a assay was to the of a blue plus DNA in and cell Using normal cell the a normal response and whether the cell this normal the cell only the of cell repair is in all groups to the repair of singlet oxygen damage is cells the to damage, and most with have neurological However, cells to be normal in their repair of singlet damage. This suggests that there is no between the accumulation of singlet oxygen damage in DNA and the of neurological is possible that an oxidative DNA lesion other generated by singlet oxygen may be critical in the of neurological in This is by a study which whether repair of lesions other the major oxidative adducts was in cell et al. T. Proc. Natl. Acad. Sci. U. S. A. 1993; PubMed Scopus Google Scholar) DNA with or hydrogen plus and the major adducts by the with the Fpg protein and endo III T. Proc. Natl. Acad. Sci. U. S. A. 1993; PubMed Scopus Google Scholar). assayed whether and cell extracts were to DNA repair on such cell DNA repair as compared with normal cell The specific lesion in the which was on for was proposed to be The that although repair of the major oxidative lesions is not in cell extracts, there be some endogenous oxidative lesions that are at low for that in and to neurological are by aging, to and E.C. 1996; PubMed Scopus Google Scholar). with of and have been identified for and E.C. 1996; PubMed Scopus Google Scholar). cells are

Human three-prime repair exonuclease 1 (TREX1) is the major 3' to 5' exonuclease that functions to deplete the cytosolic DNA to prevent the autoimmune response. TREX1 is upregulated and translocates from cytoplasm to the nucleus in response to genotoxic stress, but the function of nuclear TREX1 is not well understood. Herein, we wish to report our in vitro finding that TREX1 efficiently excises 3'-phospho-α,β-unsaturated aldehyde and 3'-deoxyribose phosphate that are commonly produced as base excision repair intermediates and also from the nonenzymatic strand incision at abasic sites.

BackgroundInflammation significantly contributes to the pathogenesis of osteoarthritis (OA). Recent studies have elucidated the critical role of the three-prime repair exonuclease 1 (TREX1) in regulating inflammatory responses and oxidative stress. The aim of the study was to investigate the regulatory function of TREX1 in maintaining joint homeostasis subsequent to the destabilization of the medial meniscus (DMM) in a murine model.MethodsTrex1-KO mice on a C57BL/6J background were utilized to investigate the role of Trex1 in OA. The DMM-induced OA model demonstrated histological and molecular alterations post-surgery, with immunofluorescence and Western blot analyses employed to assess chondrocyte characteristics and protein expression, respectively. In vitro experiments have been conducted where we established a co-culture system of macrophages and chondrocytes to investigate the regulatory role of Trex1 in macrophage polarization and its subsequent biological effects on chondrocytes, as well as the underlying mechanisms of these regulatory actions.ResultsTREX1 deficiency intensifies OA progression in DMM mice, marked by increased oxidative stress, inflammation, and cartilage damage. TREX1 pretreatment in macrophages mitigates LPS-induced chondrocyte apoptosis and oxidative stress, an effect attenuated by si-c-Fos. AP-1 inhibition counters TREX1’s protective impact on chondrocytes. TREX1 modulates macrophage polarization, influencing chondrocyte differentiation and matrix homeostasis in OA pathogenesis.ConclusionOverall, TREX1’s influence on macrophage polarization affects chondrocyte function and cartilage homeostasis, making it a potential therapeutic target for OA treatment.

<div>Abstract<p>The DNA exonuclease three-prime repair exonuclease 1 (TREX1) is critical for preventing autoimmunity in mice and humans by degrading endogenous cytosolic DNA, which otherwise triggers activation of the innate cGAS/STING pathway leading to the production of type I IFNs. As tumor cells are prone to aberrant cytosolic DNA accumulation, we hypothesized that they are critically dependent on TREX1 activity to limit their immunogenicity. Here, we show that in tumor cells, TREX1 restricts spontaneous activation of the cGAS/STING pathway, and the subsequent induction of a type I IFN response. As a result, TREX1 deficiency compromised <i>in vivo</i> tumor growth in mice. This delay in tumor growth depended on a functional immune system, systemic type I IFN signaling, and tumor-intrinsic cGAS expression. Mechanistically, we show that tumor TREX1 loss drove activation of CD8<sup>+</sup> T cells and NK cells, prevented CD8<sup>+</sup> T-cell exhaustion, and remodeled an immunosuppressive myeloid compartment. Consequently, TREX1 deficiency combined with T-cell–directed immune checkpoint blockade. Collectively, we conclude that TREX1 is essential to limit tumor immunogenicity, and that targeting this innate immune checkpoint remodels the tumor microenvironment and enhances antitumor immunity by itself and in combination with T-cell–targeted therapies.</p><p><i><a href="https://aacrjournals.org/cancerimmunolres/article/doi/10.1158/2326-6066.CIR-23-1093" target="_blank">See related article by Toufektchan et al., p. 673</a></i></p></div>

The DNA exonuclease TREX1 (Three-prime repair exonuclease 1) is critical for preventing autoimmunity in mice and humans by degrading endogenous cytosolic DNA, which otherwise triggers activation of the innate cGAS/STING pathway leading to the production of type I IFNs. Since tumor cells are prone to aberrant cytosolic DNA accumulation, we hypothesized that they are critically dependent on TREX1 activity to limit their immunogenicity. Here we show, that in tumor cells TREX1 indeed restricts the spontaneous activation of the cGAS/STING pathway and the subsequent induction of a type I IFN response. As a result, TREX1 deficiency compromised in vivo tumor growth in mice. This delay depended on a functional immune system, systemic type I IFN signaling, and tumor-intrinsic cGAS expression. Mechanistically, we show that tumor TREX1 loss drove activation of CD8 T cells and NK cells, prevented CD8 T cell exhaustion and remodeled an immunosuppressive myeloid compartment. Consequently, TREX1 deficiency synergized with T cell directed immune checkpoint blockade. Collectively, we conclude that TREX1 is essential to limit tumor immunogenicity, and that targeting this innate immune checkpoint remodels the tumor microenvironment and enhances anti-tumor immunity by itself and in combination with T cell-targeted therapies. Citation Format: Junghyun Lim, Ryan Rodriguez, Katherine Williams, John Silva, Alan Gutierrez, Paul Tyler, Faezzah Baharom, Tao Sun, Eva Lin, Scott Martin, Brandon Kayser, Robert J. Johnston, Ira Mellman, Lélia Delamarre, Nathaniel West, Sören Müller, Yan Qu, Klaus Heger. The exonuclease TREX1 constitutes an innate immune checkpoint limiting cGAS/STING-mediated anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB361.

<div>Abstract<p>The DNA exonuclease three-prime repair exonuclease 1 (TREX1) is critical for preventing autoimmunity in mice and humans by degrading endogenous cytosolic DNA, which otherwise triggers activation of the innate cGAS/STING pathway leading to the production of type I IFNs. As tumor cells are prone to aberrant cytosolic DNA accumulation, we hypothesized that they are critically dependent on TREX1 activity to limit their immunogenicity. Here, we show that in tumor cells, TREX1 restricts spontaneous activation of the cGAS/STING pathway, and the subsequent induction of a type I IFN response. As a result, TREX1 deficiency compromised <i>in vivo</i> tumor growth in mice. This delay in tumor growth depended on a functional immune system, systemic type I IFN signaling, and tumor-intrinsic cGAS expression. Mechanistically, we show that tumor TREX1 loss drove activation of CD8<sup>+</sup> T cells and NK cells, prevented CD8<sup>+</sup> T-cell exhaustion, and remodeled an immunosuppressive myeloid compartment. Consequently, TREX1 deficiency combined with T-cell–directed immune checkpoint blockade. Collectively, we conclude that TREX1 is essential to limit tumor immunogenicity, and that targeting this innate immune checkpoint remodels the tumor microenvironment and enhances antitumor immunity by itself and in combination with T-cell–targeted therapies.</p><p><i><a href="https://aacrjournals.org/cancerimmunolres/article/doi/10.1158/2326-6066.CIR-23-1093" target="_blank">See related article by Toufektchan et al., p. 673</a></i></p></div>