Suppressing phosphatidylserine externalization overcomes cancer immune evasion and enhances immunotherapy
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ABSTRACT:
ORGANISM(S): Mus musculus Homo sapiens
PROVIDER: GSE342674 | GEO | 2026/08/10
REPOSITORIES: GEO
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Project description:Alterations in lipid metabolism are frequently observed in cancers, playing a pivotal role in tumor cell survival and proliferation. Phosphatidylserine (PS), the most negatively charged glycerophospholipid in eukaryotic membranes, is synthesized in mammals by key enzymes, such as phosphatidylserine synthase 1 (PTDSS1). Here, we identify a PS-dependent metabolic vulnerability in esophageal squamous cell carcinoma (ESCC) and glioblastoma (GBM). Pharmacological inhibition of PTDSS1 potently suppresses tumor growth with nanomolar efficacy. Mechanistically, PS depletion causes a metabolic depletion of PS and phosphatidylethanolamine (PE), triggering endoplasmic reticulum (ER) stress and activating autophagy. These findings reveal an unrecognized PS-dependent metabolic dependency for tumor cell viability, indicating that targeting PS synthesis may offer a promising therapeutic approach for tumor cell suppression.
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Project description:The immunosuppressive tumor microenvironment enables immune evasion through mechanisms beyond canonical immune checkpoints. While phosphatidylserine (PS) externalization coordinates apoptotic clearance under physiological conditions, tumors exploit this pathway by mimicking apoptotic cells through PS exposure to suppress immune responses. Genetic ablation of TMEM16F abolished PS exposure, systemically reprogrammed the tumor microenvironment and primary immune organs toward immune activation, and suppressed tumor growth across cancer models.
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Project description:In cancer and chronic infection CD8 T cell exhaustion is hallmarked by expression of inhibitory surface receptors such as PD-1, TIM-3, CTLA-4, LAG-3, and TIGIT. Thus, inhibitory receptor focus has been limited to surface expressed proteins and an expansion into different classes of inhibitory molecules is needed. In this study we identify the lipid metabolite phosphatidylserine (PS) as a regulator of T cell exhaustion. PS localizes to the inner plasma membrane of live cells but is externalized to the outer membrane of apoptotic cells where it can function as a potent inhibitory ligand. However, the role of PS on live immune cells is less clear4. We show that live, exhausted, antigen specific CD8 T cells externalize PS during chronic lymphocytic choriomeningitis virus (LCMV) infection. PS exposure is initiated upon T cell activation and chronic antigen stimulation led to continued externalization. PD-1+ Tcf1+ stem-like, Tim-3+ transitory, and Tim3+ terminally differentiated/exhausted cells all expose PS. Furthermore, transcriptomic and lipidomic analyses identified increased PS metabolism during exhaustion. To evaluate the inhibitory function of exposed PS in exhaustion we treated chronically infected mice with the PS-targeting antibody (mch1N11)5 and found that monotherapy alone expanded the PD-1+ LCMV-specific CD8 T cell immune response. Most significantly, PD-1+ Tcf1+ stem-like CD8 T cells downregulated quiescence-associated gene modules and increased proliferation and self-renewal after treatment. Mechanistically, we found that exposed PS from exhausted T cells could suppress co-stimulatory molecule expression on neighboring dendritic cells to limit PD-1+ CD8 T cell proliferation. Combination of PS-targeting with aPD-L1 synergized to further increase the CD8 T cell effector response and improve viral control. Lastly, we identify that CD8 tumor infiltrating lymphocytes from human clear cell renal cell carcinoma (ccRCC) and human non-small cell lung cancer (NSCLC) patient tumors similarly expose PS indicating its translational potential. In fact, clinical trials combining PS-targeting antibodies and PD-L1 antibodies have recently been used in combination therapies. Therefore, our work details live PS CD8 T cell biology and provides a potential mechanism of action by which exposed PS facilitates suppressive T cell – DC interactions to function as a ‘non-classical’ inhibitory molecule during exhaustion.
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Project description:In cancer and chronic infection CD8 T cell exhaustion is hallmarked by expression of inhibitory surface receptors such as PD-1, TIM-3, CTLA-4, LAG-3, and TIGIT. Thus, inhibitory receptor focus has been limited to surface expressed proteins and an expansion into different classes of inhibitory molecules is needed. In this study we identify the lipid metabolite phosphatidylserine (PS) as a regulator of T cell exhaustion. PS localizes to the inner plasma membrane of live cells but is externalized to the outer membrane of apoptotic cells where it can function as a potent inhibitory ligand. However, the role of PS on live immune cells is less clear4. We show that live, exhausted, antigen specific CD8 T cells externalize PS during chronic lymphocytic choriomeningitis virus (LCMV) infection. PS exposure is initiated upon T cell activation and chronic antigen stimulation led to continued externalization. PD-1+ Tcf1+ stem-like, Tim-3+ transitory, and Tim3+ terminally differentiated/exhausted cells all expose PS. Furthermore, transcriptomic and lipidomic analyses identified increased PS metabolism during exhaustion. To evaluate the inhibitory function of exposed PS in exhaustion we treated chronically infected mice with the PS-targeting antibody (mch1N11)5 and found that monotherapy alone expanded the PD-1+ LCMV-specific CD8 T cell immune response. Most significantly, PD-1+ Tcf1+ stem-like CD8 T cells downregulated quiescence-associated gene modules and increased proliferation and self-renewal after treatment. Mechanistically, we found that exposed PS from exhausted T cells could suppress co-stimulatory molecule expression on neighboring dendritic cells to limit PD-1+ CD8 T cell proliferation. Combination of PS-targeting with aPD-L1 synergized to further increase the CD8 T cell effector response and improve viral control. Lastly, we identify that CD8 tumor infiltrating lymphocytes from human clear cell renal cell carcinoma (ccRCC) and human non-small cell lung cancer (NSCLC) patient tumors similarly expose PS indicating its translational potential. In fact, clinical trials combining PS-targeting antibodies and PD-L1 antibodies have recently been used in combination therapies. Therefore, our work details live PS CD8 T cell biology and provides a potential mechanism of action by which exposed PS facilitates suppressive T cell – DC interactions to function as a ‘non-classical’ inhibitory molecule during exhaustion.
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Project description:PTDSS1 (Phosphatidylserine synthase 1) encodes an enzyme that facilitates production of phosphatidylserine (PS), which mediates a global immunosuppressive signal. Here, based on in vivo CRISPR screen, we identified PTDSS1 as a target to improve anti-PD-1 therapy. Depletion of PTDSS1 in tumor cells increased expression of IFNγ-regulated genes, including B2m, Cxcl9, Cxcl10, and Stat1, even in the absence of IFNγ stimulation in vitro. Loss of PTDSS1 in tumor cells also led to increased expression of MHC-I, which was associated with enhanced cytotoxicity of CD8+ T cells and increased frequency of an iNOS+ myeloid subset. A gene signature derived from the iNOS+ myeloid cell subset correlated with clinical benefit in patients treated with anti-PD-1 therapy. Moreover, genetic and pharmacological inhibition of PTDSS1 in different tumor models improved anti-PD-1 therapy. Together, our results provide insights on a new therapeutic strategy for overcoming immunosuppression by inhibiting PTDSS1 and provide rationale for development of a combination immunotherapy strategy comprised of PTDSS1 inhibition plus PD-1 blockade.
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Project description:PTDSS1 (Phosphatidylserine synthase 1) encodes an enzyme that facilitates production of phosphatidylserine (PS), which mediates a global immunosuppressive signal. Here, based on in vivo CRISPR screen, we identified PTDSS1 as a target to improve anti-PD-1 therapy. Depletion of PTDSS1 in tumor cells increased expression of IFNγ-regulated genes, including B2m, Cxcl9, Cxcl10, and Stat1, even in the absence of IFNγ stimulation in vitro. Loss of PTDSS1 in tumor cells also led to increased expression of MHC-I, which was associated with enhanced cytotoxicity of CD8+ T cells and increased frequency of an iNOS+ myeloid subset. A gene signature derived from the iNOS+ myeloid cell subset correlated with clinical benefit in patients treated with anti-PD-1 therapy. Moreover, genetic and pharmacological inhibition of PTDSS1 in different tumor models improved anti-PD-1 therapy. Together, our results provide insights on a new therapeutic strategy for overcoming immunosuppression by inhibiting PTDSS1 and provide rationale for development of a combination immunotherapy strategy comprised of PTDSS1 inhibition plus PD-1 blockade.
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Project description:PTDSS1 (Phosphatidylserine synthase 1) encodes an enzyme that facilitates production of phosphatidylserine (PS), which mediates a global immunosuppressive signal. Here, based on in vivo CRISPR screen, we identified PTDSS1 as a target to improve anti-PD-1 therapy. Depletion of PTDSS1 in tumor cells increased expression of IFNγ-regulated genes, including B2m, Cxcl9, Cxcl10, and Stat1, even in the absence of IFNγ stimulation in vitro. Loss of PTDSS1 in tumor cells also led to increased expression of MHC-I, which was associated with enhanced cytotoxicity of CD8+ T cells and increased frequency of an iNOS+ myeloid subset. A gene signature derived from the iNOS+ myeloid cell subset correlated with clinical benefit in patients treated with anti-PD-1 therapy. Moreover, genetic and pharmacological inhibition of PTDSS1 in different tumor models improved anti-PD-1 therapy. Together, our results provide insights on a new therapeutic strategy for overcoming immunosuppression by inhibiting PTDSS1 and provide rationale for development of a combination immunotherapy strategy comprised of PTDSS1 inhibition plus PD-1 blockade.
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Project description:Immune checkpoint blockade (ICB) leads to durable and complete tumour regression in some patients but in others gives temporary, partial or no response. Accordingly, significant efforts are underway to identify tumour-intrinsic mechanisms underlying ICB resistance. Results from a published CRISPR screen in a mouse model suggested that targeting STUB1, an E3 ligase involved in protein homeostasis, may overcome ICB resistance but the molecular basis of this effect remains unclear. Herein, we report an under-appreciated role of STUB1 to dampen the interferon gamma (IFNg) response. Genetic deletion of STUB1 increased IFNGR1 abundance on the cell surface and thus enhanced the downstream IFNg response as showed by multiple approaches including Western blotting, flow cytometry, qPCR, phospho-STAT1 assay, immunopeptidomics, proteomics, and gene expression profiling. Human prostate and breast cancer cells with STUB1 deletion were also susceptible to cytokine-induced growth inhibition. Furthermore, blockade of STUB1 protein function recapitulated the STUB1-null phenotypes. Despite these encouraging in vitro data and positive implications from clinical datasets, we did not observe in vivo benefits of inactivating Stub1 in mouse syngeneic tumour models - with or without combination with anti-PD-1 therapy. However, our findings elucidate STUB1 as a barrier to IFNg sensing, prompting further investigations to assess if broader inactivation of human STUB1 in both tumors and immune cells could overcome ICB resistance.
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