FBW7-mediated ubiquitination and destruction of PD-1 protein primes sensitivity to anti-PD-1 immunotherapy in non-small cell lung cancer

Targeting PD-1 post-translational modifications for improving cancer immunotherapy

Programmed cell death protein 1 (PD-1) is a critical immune checkpoint receptor that suppresses immune responses largely through its interaction with PD-L1. Tumors exploit this mechanism to evade immune surveillance, positioning immune checkpoint inhibitors targeting the PD-1/PD-L1 axis as groundbreaking advancements in cancer therapy. However, the overall effectiveness of these therapies is often constrained by an incomplete understanding of the underlying mechanisms. Recent research has uncovered the pivotal role of various post-translational modifications (PTMs) of PD-1, including ubiquitination, UFMylation, phosphorylation, palmitoylation, and glycosylation, in regulating its protein stability, localization, and protein-protein interactions. As much, dysregulation of these PTMs can drive PD-1-mediated immune evasion and contribute to therapeutic resistance. Notably, targeting PD-1 PTMs with small-molecule inhibitors or monoclonal antibodies (MAbs) has shown potential to bolster anti-tumor immunity in both pre-clinical mouse models and clinical trials. This review highlights recent findings on PD-1's PTMs and explores emerging therapeutic strategies aimed at modulating these modifications. By integrating these mechanistic insights, the development of combination cancer immunotherapies can be further rationally advanced, offering new avenues for more effective and durable treatments.

Deubiquitinase USP24 activated by IL-6/STAT3 enhances PD-1 protein stability and suppresses T cell antitumor response

Persisting programmed cell death-1 (PD-1) signaling impairs T cell effector function, which is highly associated with T cell exhaustion and immunotherapy failure. However, the mechanism responsible for PD-1 deubiquitination and T cell dysfunction remains unclear. Here, we show that ubiquitin-specific peptidase 24 (USP24) promotes PD-1 protein stability by removing K48-linked polyubiquitin. Increased interleukin-6 level transcriptionally activates the USP24 expression, which leads to PD-1 stabilization. Furthermore, USP24 deficiency reduces PD-1 levels in CD8+ T cells and attenuates EgfrL858R-driven lung tumorigenesis in Usp24C1695A catalytic deficient mice. Targeting PD-1 stability with the USP24-specific inhibitor USP24-i-101 boosts cytotoxic T cell activity, restrains lung tumor growth, and achieves superior therapeutic effects when combined with anti-CTLA4 immunotherapy. Clinically, patients with lung cancer exhibiting high USP24 expression in tumor-infiltrating CD8+ T cells display exhausted features and show unfavorable responses to immunotherapy. Our findings dissect the mechanism for regulating enhanced PD-1 stability in tumor-infiltrating CD8+ T cells and reveal USP24 as a potential target of antitumor immunotherapy.

Programmed cell death protein 1 in cancer cells

Programmed cell death protein 1 (PD-1) is frequently detected in certain subsets of tumor cells, and our understanding of PD-1 signaling consequences has expanded to include control of tumor growth, stemness and drug resistance. Nonetheless, tumor cell-intrinsic PD-1 has been comparatively underexplored in relation to PD-1 expressed on the surface of immune cells as an immune checkpoint, despite the imperative need to comprehensively elucidate the underlying mechanisms of action for achieving optimal responses in tumor immunotherapy. Here, we review the roles of the regulation and function of tumor-intrinsic PD-1 from its expression to degradation processes. Our primary focus is on unraveling its enigmatic influence on tumorigenesis and progression as proposed by recent findings, while navigating the labyrinthine network of regulatory mechanisms governing its expression and intricate functional interplay. We also discuss how the elucidation of the mechanistic underpinnings of tumor-intrinsic PD-1 expression holds the potential to explain the divergent therapeutic outcomes observed with anti-PD-1-based combination therapies, thereby furnishing indispensable insights crucial for synergistic anti-tumor strategies.

Programmed Cell Death Ligand as a Biomarker for Response to Immunotherapy: Contribution of Mass Spectrometry-Based Analysis

Immune checkpoint inhibition is a major component in today's cancer immunotherapy. In recent years, the FDA has approved a number of immune checkpoint inhibitors (ICIs) for the treatment of melanoma, non-small-cell lung, breast and gastrointestinal cancers. These inhibitors, which target cytotoxic T-lymphocyte antigen-4, programmed cell death (PD-1), and programmed cell death ligand (PD-L1) checkpoints have assumed a leading role in immunotherapy. The same inhibitors exert significant antitumor effects by overcoming tumor cell immune evasion and reversing T-cell exhaustion. The initial impact of this therapy in cancer treatment was justly described as revolutionary, however, clinical as well as research data which followed demonstrated that these innovative drugs are costly, are associated with potentially severe adverse effects, and only benefit a small subset of patients. These limitations encouraged enhanced research and clinical efforts to identify predictive biomarkers to stratify patients who are most likely to benefit from this form of therapy. The discovery and characterization of this class of biomarkers is pivotal in guiding individualized treatment against various forms of cancer. Currently, there are three FDA-approved predictive biomarkers, however, none of which on its own can deliver a reliable and precise response to immune therapy. Present literature identifies the absence of precise predictive biomarkers and poor understanding of the mechanisms behind tumor resistance as the main obstacles facing ICIs immunotherapy. In the present text, we discuss the dual role of PD-L1 as a biomarker for response to immunotherapy and as an immune checkpoint. The contribution of mass spectrometry-based analysis, particularly the impact of protein post-translational modifications on the performance of this protein is underlined.

Post-translational modifications of immune checkpoints: unlocking new potentials in cancer immunotherapy

Immunotherapy targeting immune checkpoints has gained traction across various cancer types in clinical settings due to its notable advantages. Despite this, the overall response rates among patients remain modest, alongside issues of drug resistance and adverse effects. Hence, there is a pressing need to enhance immune checkpoint blockade (ICB) therapies. Post-translational modifications (PTMs) are crucial for protein functionality. Recent research emphasizes their pivotal role in immune checkpoint regulation, directly impacting the expression and function of these key proteins. This review delves into the influence of significant PTMs-ubiquitination, phosphorylation, and glycosylation-on immune checkpoint signaling. By targeting these modifications, novel immunotherapeutic strategies have emerged, paving the way for advancements in optimizing immune checkpoint blockade therapies in the future.

Oxaliplatin induces pyroptosis in hepatoma cells and enhances antitumor immunity against hepatocellular carcinoma

BACKGROUND

Pyroptosis is closely associated with chemotherapeutic drugs and immune response. Here, we investigated whether oxaliplatin, a key drug in FOLFOX-hepatic artery infusion chemotherapy (FOLFOX-HAIC), induces pyroptosis in hepatoma cells and enhances antitumor immunity after tumor cell death.

METHODS

Hepatoma cells were treated with oxaliplatin. Pyroptosis and immunoreactivity were evaluated in vitro and in vivo.

RESULTS

Oxaliplatin activated caspase-3-mediated gasdermin E (GSDME) cleavage and induced pyroptosis in Hep G2 and SK-Hep-1 cells in vitro. Liver cancer cells with high levels of GSDME expression are prone to pyroptosis. Bioinformatic analysis revealed that pyrolysis-related genes are closely related to immunity. In vivo experiments revealed that oxaliplatin exhibited superior antitumor efficacy in mice with normal immune function and more pronounced inhibitory effect on hepatocellular carcinoma with high GSDME levels. Higher levels of cytokines and greater CD8+ T cell infiltration were observed in tumor tissues with better efficacy. Furthermore, an in vitro coculture assay confirmed that oxaliplatin-induced pyroptosis in Hep G2 cells overexpressing GSDME and activated the p38/MAPK signaling pathway to improve the cytotoxicity of CD8+ T cells. Analysis of clinical samples of HCC suggested that the efficacy of FOLFOX-HAIC in patients with high GSDME expression was better than that in patients with low GSDME expression.

CONCLUSIONS

Oxaliplatin induced pyroptosis in hepatoma cells by activating caspase-3-mediated cleavage of GSDME, which enhanced the cytotoxicity of CD8+ T cells by regulating the p38/MAPK signaling pathway. These results suggest that GSDME level may be used as a marker to predict the efficacy of FOLFOX-HAIC.

Progress in understanding the regulatory mechanisms of immune checkpoint proteins PD-1 and PD-L1 expression

Programmed Death Protein-1 (PD-1) is a cell surface receptor that serves as a checkpoint for T cells, playing a pivotal role in regulating T-cell apoptosis. The binding of PD-1 to its ligand, Programmed Death Ligand 1 (PD-L1), inhibits anti-tumor immunity by suppressing T-cell activation signals. Indeed, the PD-1/PD-L1 pathway governs the induction and maintenance of immune tolerance within the tumor microenvironment. Consequently, the regulation of PD-1/PD-L1 immune checkpoint expression is of paramount importance. This review summarizes the mechanisms governing PD1/PD-L1 expression at various stages, including transcription, post-transcription (mRNA processing), and post-translation (protein modifications), as well as immunotherapy targeting PD1/PD-L1, aiming to further explore novel strategies for tumor immunotherapy.

Dysregulation of ubiquitination modification in renal cell carcinoma

Renal cell carcinoma (RCC) is a malignant tumor of the renal tubular epithelial cells with a relatively high incidence rate worldwide. A large number of studies have indicated that dysregulation of the ubiquitination, including ubiquitination and dysregulation, is associated with the occurrence and development of RCC. This review focuses on several abnormal signaling pathways caused by E3 ligases and deubiquitinases. Additionally, we discuss research progress in RCC treatment by targeting key enzymes related to ubiquitination modifications.

CD28 co-stimulation: novel insights and applications in cancer immunotherapy

Substantial progress in understanding T cell signalling, particularly with respect to T cell co-receptors such as the co-stimulatory receptor CD28, has been made in recent years. This knowledge has been instrumental in the development of innovative immunotherapies for patients with cancer, including immune checkpoint blockade antibodies, adoptive cell therapies, tumour-targeted immunostimulatory antibodies, and immunostimulatory small-molecule drugs that regulate T cell activation. Following the failed clinical trial of a CD28 superagonist antibody in 2006, targeted CD28 agonism has re-emerged as a technologically viable and clinically promising strategy for cancer immunotherapy. In this Review, we explore recent insights into the molecular functions and regulation of CD28. We describe how CD28 is central to the success of current cancer immunotherapies and examine how new questions arising from studies of CD28 as a clinical target have enhanced our understanding of its biological role and may guide the development of future therapeutic strategies in oncology.

A patent review of SCF E3 ligases inhibitors for cancer：Structural design, pharmacological activities and structure-activity relationship

Currently, as the largest family of E3 ubiquitin ligases, Skp1-Cullin 1-F-box (SCF) E3 ligase complexes have attracted extensive attention. Among SCF complexes, Skp2, β-TrCP, and FBXW7 have undergone extensive research on their structures and functions. Previous studies suggest Skp2, β-TrCP, and FBXW7 are overexpressed in numerous cancers. Thus, the SCF E3 ligase complex has become a significant target for the development of anti-cancer drugs. Over the past few decades, a variety of anti-tumor inhibitors targeting the SCF E3 ligase complex have been attempted. However, since almost none of the SCF E3 ligase inhibitors passed clinical trials, the design and synthesis of the new inhibitors are needed. Here, we will introduce the structure and function of Skp2, β-TrCP, and FBXW7, their connections with cancer development, the relevant in vitro and in vivo activities, selectivity, structure-activity relationships, and the therapeutic or preventive application of small molecule inhibitors targeting these three F-box proteins reported in the patent (2010-present). This information will help develop drugs targeting the SCF E3 ubiquitin ligase, providing new strategies for future cancer treatments.

PRMT1-mediated methylation of ME2 promotes hepatocellular carcinoma growth by inhibiting ubiquitination

The mitochondrial malic enzyme 2 (ME2), which is frequently elevated during carcinogenesis and may be a target for cancer therapy, catalyzes the conversion of malate to pyruvate. The processes controlling ME2 activity, however, remain largely unclear. In this work, we show that human hepatocellular carcinoma (HCC) tissues contain high levels of ME2 and that the methylation of ME2 stimulates the growth and migration of HCC cells. Furthermore, we observed that ME2 interacts with protein arginine methyltransferase 1 (PRMT1) and that ME2 enzymatic activity is activated by mutation of ME2 at lysine 67. Mitochondrial respiration was markedly increased by activated ME2, which promoted cell division and carcinogenesis. Furthermore, a negative prognosis for patients was strongly linked with the expression levels of PRMT1 and ME2 R67K in HCC tissues. These findings imply that hepatocellular carcinoma growth is aided by PRMT1-mediated ME2 methylation, that is an essential signaling event that cancer cells need to continue mitochondrial respiration.

Molecular insights and clinical implications for the tumor suppressor role of SCFFBXW7 E3 ubiquitin ligase

FBXW7 is one of the most well-characterized F-box proteins, serving as substrate receptor subunit of SKP1-CUL1-F-box (SCF) E3 ligase complexes. SCFFBXW7 is responsible for the degradation of various oncogenic proteins such as cyclin E, c-MYC, c-JUN, NOTCH, and MCL1. Therefore, FBXW7 functions largely as a major tumor suppressor. In keeping with this notion, FBXW7 gene mutations or downregulations have been found and reported in many types of malignant tumors, such as endometrial, colorectal, lung, and breast cancers, which facilitate the proliferation, invasion, migration, and drug resistance of cancer cells. Therefore, it is critical to review newly identified FBXW7 regulation and tumor suppressor function under physiological and pathological conditions to develop effective strategies for the treatment of FBXW7-altered cancers. Since a growing body of evidence has revealed the tumor-suppressive activity and role of FBXW7, here, we updated FBXW7 upstream and downstream signaling including FBXW7 ubiquitin substrates, the multi-level FBXW7 regulatory mechanisms, and dysregulation of FBXW7 in cancer, and discussed promising cancer therapies targeting FBXW7 regulators and downstream effectors, to provide a comprehensive picture of FBXW7 and facilitate the study in this field.

Ubiquitin modification in the regulation of tumor immunotherapy resistance mechanisms and potential therapeutic targets

Although immune checkpoint-based cancer immunotherapy has shown significant efficacy in various cancers, resistance still limits its therapeutic effects. Ubiquitination modification is a mechanism that adds different types of ubiquitin chains to proteins, mediating protein degradation or altering their function, thereby affecting cellular signal transduction. Increasing evidence suggests that ubiquitination modification plays a crucial role in regulating the mechanisms of resistance to cancer immunotherapy. Drugs targeting ubiquitination modification pathways have been shown to inhibit tumor progression or enhance the efficacy of cancer immunotherapy. This review elaborates on the mechanisms by which tumor cells, immune cells, and the tumor microenvironment mediate resistance to cancer immunotherapy and the details of how ubiquitination modification regulates these mechanisms, providing a foundation for enhancing the efficacy of cancer immunotherapy by intervening in ubiquitination modification.

Molecular characteristics of early-onset compared with late-onset colorectal cancer: a case controlled study

BACKGROUND

Early-onset colorectal cancer (EOCRC) is associated with a poorer prognosis relative to late-onset colorectal cancer (LOCRC), and its incidence has witnessed a gradual escalation in recent years. This necessitates a comprehensive examination of the underlying pathogenesis and the identification of therapeutic targets specific to EOCRC patients. The present study aimed to delineate the distinct molecular landscape of EOCRC by juxtaposing it with that of LOCRC.

METHODS

A total of 11 344 colorectal cancer patients, diagnosed between 2003 and 2022, were enrolled in this study, comprising 578 EOCRC cases and 10 766 LOCRC cases. Next-generation sequencing technology was employed to assess the tumor-related mutation and tumor mutation burden (TMB) in these patients. PD-L1 expression was quantified using immunohistochemistry. Microsatellite instability (MSI) was determined via capillary electrophoresis (2B3D NCI Panel).

RESULTS

Upon comparing LOCRC with EOCRC patients, the latter group demonstrated a tendency towards advanced TNM stage, lower tumor differentiation, and less favorable histological types. Among LOCRC patients, those with MSI-H status were found to have an earlier TNM stage compared to those with MSI-L/MSS status. Significantly, the incidence of MSI-H was notably higher in EOCRC (10.2%) compared to LOCRC (2.2%). Mutations in the 7-gene panel (ARID1A, FANCI, CASP8, DGFRA, DPYD, TSHR, and PRKCI) were more prevalent in LOCRC. Within the EOCRC cohort, patients with the MSI-H subtype displayed an earlier TNM stage but concurrently exhibited poorer tissue differentiation and a higher frequency of mucinous adenocarcinoma. Among EOCRC patients, FBXW7, FAT1, ATM, ARID1A, and KMT2B mutations were significantly enriched in the MSI-H subgroup. A comparative analysis of MSI-H patients revealed heightened mutation frequencies of FGFBR2, PBRM1, RNF43, LRP1B, FBXW7, ATM, and ARID1A in the EOCRC group. Furthermore, EOCRC patients demonstrated a higher overall TMB, particularly in the MSI-H subtype. PD-L1 expression was elevated in EOCRC and positively associated with MSI status.

CONCLUSIONS

This study revealed a significantly higher MSI-H distribution rate in EOCRC, and EOCRC exhibits a distinct mutational signature coupled with higher PD-L1 expression. These findings hold promise in guiding personalized therapeutic strategies for improved disease management in EOCRC patients.

The HTLV-I oncoprotein Tax inactivates the tumor suppressor FBXW7

Human T-cell leukemia virus type 1 (HTLV-I) is the etiological agent of adult T-cell leukemia (ATL). Mutational analysis has demonstrated that the tumor suppressor, F-box and WD repeat domain containing 7 (FBXW7/FBW7/CDC4), is mutated in primary ATL patients. However, even in the absence of genetic mutations, FBXW7 substrates are stabilized in ATL cells, suggesting additional mechanisms can prevent FBXW7 functions. Here, we report that the viral oncoprotein Tax represses FBXW7 activity, resulting in the stabilization of activated Notch intracellular domain, c-MYC, Cyclin E, and myeloid cell leukemia sequence 1 (BCL2-related) (Mcl-1). Mechanistically, we demonstrate that Tax directly binds to FBXW7 in the nucleus, effectively outcompeting other targets for binding to FBXW7, resulting in decreased ubiquitination and degradation of FBXW7 substrates. In support of the nuclear role of Tax, a non-degradable form of the nuclear factor kappa B subunit 2 (NFκB2/p100) was found to delocalize Tax to the cytoplasm, thereby preventing Tax interactions with FBXW7 and Tax-mediated inhibition of FBXW7. Finally, we characterize a Tax mutant that is unable to interact with FBXW7, unable to block FBXW7 tumor suppressor functions, and unable to effectively transform fibroblasts. These results demonstrate that HTLV-I Tax can inhibit FBXW7 functions without genetic mutations to promote an oncogenic state. These results suggest that Tax-mediated inhibition of FBXW7 is likely critical during the early stages of the cellular transformation process.

IMPORTANCE

F-box and WD repeat domain containing 7 (FBXW7), a critical tumor suppressor of human cancers, is frequently mutated or epigenetically suppressed. Loss of FBXW7 functions is associated with stabilization and increased expression of oncogenic factors such as Cyclin E, c-Myc, Mcl-1, mTOR, Jun, and Notch. In this study, we demonstrate that the human retrovirus human T-cell leukemia virus type 1 oncoprotein Tax directly interacts with FBXW7, effectively outcompeting other targets for binding to FBXW7, resulting in decreased ubiquitination and degradation of FBXW7 cellular substrates. We further demonstrate that a Tax mutant unable to interact with and inactivate FBXW7 loses its ability to transform primary fibroblasts. Collectively, our results describe a novel mechanism used by a human tumor virus to promote cellular transformation.

The ubiquitin-proteasome system in the regulation of tumor dormancy and recurrence

Tumor recurrence is a mechanism triggered in sparse populations of cancer cells that usually remain in a quiescent state after strict stress and/or therapeutic factors, which is affected by a variety of autocrine and microenvironmental cues. Despite thorough investigations, the biology of dormant and/or cancer stem cells is still not fully elucidated, as for the mechanisms of their reawakening, while only the major molecular patterns driving the relapse process have been identified to date. These molecular patterns profoundly interfere with the elements of cellular proteostasis systems that support the efficiency of the recurrence process. As a major proteostasis machinery, we review the role of the ubiquitin-proteasome system (UPS) in tumor cell dormancy and reawakening, devoting particular attention to the functions of its components, E3 ligases, deubiquitinating enzymes and proteasomes in cancer recurrence. We demonstrate how UPS components functionally or mechanistically interact with the pivotal proteins implicated in the recurrence program and reveal that modulators of the UPS hold promise to become an efficient adjuvant therapy for eradicating refractory tumor cells to impede tumor relapse.

Advances of E3 ligases in lung cancer

Lung cancer is a leading cause of cancer-related death, and the most common type of lung cancer is non-small cell lung cancer, which accounts for approximately 85 % of lung cancer diagnoses. Recent studies have revealed that ubiquitination acts as a crucial part of the development and progression of lung cancer. The E1-E2-E3 three-enzyme cascade has a core function in ubiquitination, so targeted adjustments of E3 ligases could be used in lung cancer treatment. Hence, we elucidate research advances in lung cancer-related E3 ligases by briefly describing the structure and categorization of E3 ligases. Here, we provide a detailed review of the mechanisms by which lung cancer-related E3 ligases modify substrate proteins and regulate signaling pathways to facilitate or suppress cancer progression. We hope to show a new perspective on targeted precision therapy for lung cancer.

ALKBH5 promotes non-small cell lung cancer progression and susceptibility to anti-PD-L1 therapy by modulating interactions between tumor and macrophages

BACKGROUND

Understanding the mechanisms that mediate the interaction between tumor and immune cells may provide therapeutic benefit to patients with cancer. The N6-methyladenosine (m6A) demethylase, ALKBH5 (alkB homolog 5), is overexpressed in non-small cell lung cancer. However, its role in the tumor microenvironment is unknown.

METHODS

Datasets and tissue samples were used to determine the relationship between ALKBH5 expression and immunotherapy efficacy. Bioinformatic analysis, colorimetric assay to determine m6A RNA methylation, dual luciferase reporter assay, RNA/m6A-modified RNA immunoprecipitation, RNA stability assay, and RNA sequencing were used to investigate the regulatory mechanism of ALKBH5 in non-small cell lung cancer. In vitro and in vivo assays were performed to determine the contribution of ALKBH5 to the development of non-small cell lung cancer.

RESULTS

ALKBH5 was upregulated in primary non-small cell lung cancer tissues. ALKBH5 was positively correlated with programmed death-ligand 1 expression and macrophage infiltration and was associated with immunotherapy response. JAK2 was identified as a target of ALKBH5-mediated m6A modification, which activates the JAK2/p-STAT3 pathway to promote non-small cell lung cancer progression. ALKBH5 was found to recruit programmed death-ligand 1-positive tumor-associated macrophages and promote M2 macrophage polarization by inducing the secretion of CCL2 and CXCL10. ALKBH5 and tumor-associated macrophage-secreted IL-6 showed a synergistic effect to activate the JAK2/p-STAT3 pathway in cancer cells.

CONCLUSIONS

ALKBH5 promotes non-small cell lung cancer progression by regulating cancer and tumor-associated macrophage behavior through the JAK2/p-STAT3 pathway and the expression of CCL2 and CXCL10, respectively. These findings suggest that targeting ALKBH5 is a promising strategy of enhancing the anti-tumor immune response in patients with NSCLC and that identifying ALKBH5 status could facilitate prediction of clinical response to anti-PD-L1 immunotherapy.

PD-1 regulation in immune homeostasis and immunotherapy

Harnessing the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis is pivotal in autoimmunity and cancer immunotherapy. PD-1 receptors on immune cells engage with one of its ligands, PD-L1 or PD-L2, expressed on antigen-presenting cells or tumor cells, driving T-cell dysfunction and tumor immune escape. Thus, targeting PD-1/PD-L1 revitalizes cytotoxic T cells for cancer elimination. However, a majority of cancer patients don't respond to PD-1/PD-L1 blockade, and the underlying mechanisms remain partially understood. Recent studies have revealed that PD-1 expression levels or modifications impact the effectiveness of anti-PD-1/PD-L1 treatments. Therefore, understanding the molecular mechanisms governing PD-1 expression and modifications is crucial for innovating therapeutic strategies to enhance the efficacy of PD-1/PD-L1 inhibition. This article presents a comprehensive overview of advancements in PD-1 regulation and highlights their potential in modulating immune homeostasis and cancer immunotherapy, aiming to refine clinical outcomes.

Emerging therapeutic frontiers in cancer: insights into posttranslational modifications of PD-1/PD-L1 and regulatory pathways

The interaction between programmed cell death ligand 1 (PD-L1), which is expressed on the surface of tumor cells, and programmed cell death 1 (PD-1), which is expressed on T cells, impedes the effective activation of tumor antigen-specific T cells, resulting in the evasion of tumor cells from immune-mediated killing. Blocking the PD-1/PD-L1 signaling pathway has been shown to be effective in preventing tumor immune evasion. PD-1/PD-L1 blocking antibodies have garnered significant attention in recent years within the field of tumor treatments, given the aforementioned mechanism. Furthermore, clinical research has substantiated the efficacy and safety of this immunotherapy across various tumors, offering renewed optimism for patients. However, challenges persist in anti-PD-1/PD-L1 therapies, marked by limited indications and the emergence of drug resistance. Consequently, identifying additional regulatory pathways and molecules associated with PD-1/PD-L1 and implementing judicious combined treatments are imperative for addressing the intricacies of tumor immune mechanisms. This review briefly outlines the structure of the PD-1/PD-L1 molecule, emphasizing the posttranslational modification regulatory mechanisms and related targets. Additionally, a comprehensive overview on the clinical research landscape concerning PD-1/PD-L1 post-translational modifications combined with PD-1/PD-L1 blocking antibodies to enhance outcomes for a broader spectrum of patients is presented based on foundational research.

PTMs of PD-1/PD-L1 and PROTACs application for improving cancer immunotherapy

Immunotherapy has been developed, which harnesses and enhances the innate powers of the immune system to fight disease, particularly cancer. PD-1 (programmed death-1) and PD-L1 (programmed death ligand-1) are key components in the regulation of the immune system, particularly in the context of cancer immunotherapy. PD-1 and PD-L1 are regulated by PTMs, including phosphorylation, ubiquitination, deubiquitination, acetylation, palmitoylation and glycosylation. PROTACs (Proteolysis Targeting Chimeras) are a type of new drug design technology. They are specifically engineered molecules that target specific proteins within a cell for degradation. PROTACs have been designed and demonstrated their inhibitory activity against the PD-1/PD-L1 pathway, and showed their ability to degrade PD-1/PD-L1 proteins. In this review, we describe how PROTACs target PD-1 and PD-L1 proteins to improve the efficacy of immunotherapy. PROTACs could be a novel strategy to combine with radiotherapy, chemotherapy and immunotherapy for cancer patients.

Post-translational Modification of PD-1: Potential Targets for Cancer Immunotherapy

Activation of effector T cells leads to upregulation of PD-1, which can inhibit T-cell activity following engagement with its ligand PD-L1. Post-translational modifications (PTM), including glycosylation, phosphorylation, ubiquitination, and palmitoylation, play a significant role in regulating PD-1 protein stability, localization, and interprotein interactions. Targeting PTM of PD-1 in T cells has emerged as a potential strategy to overcome PD-1-mediated immunosuppression in cancer and enhances antitumor immunity. The regulatory signaling pathways that induce PTM of PD-1 can be suppressed with small-molecule inhibitors, and mAbs can directly target PD-1 PTMs. Preliminary outcomes from exploratory studies suggest that focusing on the PTM of PD-1 has strong therapeutic potential and can enhance the response to anti-PD-1.

Anti-Tumor Potential of Post-Translational Modifications of PD-1

Programmed cell death protein-1 (PD-1) is a vital immune checkpoint molecule. The location, stability, and protein-protein interaction of PD-1 are significantly influenced by post-translational modification (PTM) of proteins. The biological information of PD-1, including its gene and protein structures and the PD-1/PD-L1 signaling pathway, was briefly reviewed in this review. Additionally, recent research on PD-1 post-translational modification, including the study of ubiquitination, glycosylation, phosphorylation, and palmitoylation, was summarized, and research strategies for PD-1 PTM drugs were concluded. At present, only a part of PD-1/PD-L1 treated patients (35-45%) are benefited from immunotherapies, and novel strategies targeting PTM of PD-1/PD-L1 may be important for anti-PD-1/PD-L1 non-responders (poor responders).

Rab37 mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion in lung cancer

BACKGROUND

Programmed cell death protein 1 (PD-1) is an immune checkpoint receptor expressed on the surface of T cells. High expression of PD-1 leads to T-cell dysfunction in the tumor microenvironment (TME). However, the mechanism of intracellular trafficking and plasma membrane presentation of PD-1 remains unclear.

METHODS

Multiple databases of lung cancer patients were integratively analyzed to screen Rab proteins and potential immune-related signaling pathways. Imaging and various biochemical assays were performed in Jurkat T cells, splenocytes, and human peripheral blood mononuclear cells (PBMCs). Rab37 knockout mice and specimens of lung cancer patients were used to validate the concept.

RESULTS

Here, we identify novel mechanisms of intracellular trafficking and plasma membrane presentation of PD-1 mediated by Rab37 small GTPase to sustain T cell exhaustion, thereby leading to poor patient outcome. PD-1 colocalized with Rab37-specific vesicles of T cells in a GTP-dependent manner whereby Rab37 mediated dynamic trafficking and membrane presentation of PD-1. However, glycosylation mutant PD-1 delayed cargo recruitment to the Rab37 vesicles, thus stalling membrane presentation. Notably, T cell proliferation and activity were upregulated in tumor-infiltrating T cells from the tumor-bearing Rab37 knockout mice compared to those from wild type. Clinically, the multiplex immunofluorescence-immunohistochemical assay indicated that patients with high Rab37+/PD-1+/TIM3+/CD8+ tumor infiltrating T cell profile correlated with advanced tumor stages and poor overall survival. Moreover, human PBMCs from patients demonstrated high expression of Rab37, which positively correlated with elevated levels of PD-1+ and TIM3+ in CD8+ T cells exhibiting reduced tumoricidal activity.

CONCLUSIONS

Our results provide the first evidence that Rab37 small GTPase mediates trafficking and membrane presentation of PD-1 to sustain T cell exhaustion, and the tumor promoting function of Rab37/PD-1 axis in T cells of TME in lung cancer. The expression profile of Rab37high/PD-1high/TIM3high in tumor-infiltrating CD8+ T cells is a biomarker for poor prognosis in lung cancer patients.

E3 ubiquitin ligases in lung cancer: Emerging insights and therapeutic opportunities

Aim In this review, we have attempted to provide the readers with an updated account of the role of a family of proteins known as E3 ligases in different aspects of lung cancer progression, along with insights into the deregulation of expression of these proteins during lung cancer. A detailed account of the therapeutic strategies involving E3 ligases that have been developed or currently under development has also been provided in this review. MATERIALS AND METHODS: The review article employs extensive literature search, along with differential gene expression analysis of lung cancer associated E3 ligases using the DESeq2 package in R, and the Gene Expression Profiling Interactive Analysis (GEPIA) database (http://gepia.cancer-pku.cn/). Protein expression analysis of CPTAC lung cancer samples was carried out using the UALCAN webtool (https://ualcan.path.uab.edu/index.html). Assessment of patient overall survival (OS) in response to high and low expression of selected E3 ligases was performed using the online Kaplan-Meier plotter (https://kmplot.com/analysis/index.php?p=background). KEY FINDINGS: SIGNIFICANCE: The review provides an in-depth understanding of the role of E3 ligases in lung cancer progression and an up-to-date account of the different therapeutic strategies targeting oncogenic E3 ligases for improved lung cancer management.

Role of F-box proteins in human upper gastrointestinal tumors

Protein ubiquitination and degradation is an essential physiological process in almost all organisms. As the key participants in this process, the E3 ubiquitin ligases have been widely studied and recognized. F-box proteins, a crucial component of E3 ubiquitin ligases that regulates diverse biological functions, including cell differentiation, proliferation, migration, and apoptosis by facilitating the degradation of substrate proteins. Currently, there is an increasing focus on studying the role of F-box proteins in cancer. In this review, we present a comprehensive overview of the significant contributions of F-box proteins to the development of upper gastrointestinal tumors, highlighting their dual roles as both carcinogens and tumor suppressors. We delve into the molecular mechanisms underlying the involvement of F-box proteins in upper gastrointestinal tumors, exploring their interactions with specific substrates and their cross-talks with other key signaling pathways. Furthermore, we discuss the implications of F-box proteins in radiotherapy resistance in the upper gastrointestinal tract, emphasizing their potential as clinical therapeutic and prognostic targets. Overall, this review provides an up-to-date understanding of the intricate involvement of F-box proteins in human upper gastrointestinal tumors, offering valuable insights for the identification of prognostic markers and the development of targeted therapeutic strategies.

FBXW7 and human tumors: mechanisms of drug resistance and potential therapeutic strategies

Drug therapy, including chemotherapy, targeted therapy, immunotherapy, and endocrine therapy, stands as the foremost therapeutic approach for contemporary human malignancies. However, increasing drug resistance during antineoplastic therapy has become a substantial barrier to favorable outcomes in cancer patients. To enhance the effectiveness of different cancer therapies, an in-depth understanding of the unique mechanisms underlying tumor drug resistance and the subsequent surmounting of antitumor drug resistance is required. Recently, F-box and WD Repeat Domain-containing-7 (FBXW7), a recognized tumor suppressor, has been found to be highly associated with tumor therapy resistance. This review provides a comprehensive summary of the underlying mechanisms through which FBXW7 facilitates the development of drug resistance in cancer. Additionally, this review elucidates the role of FBXW7 in therapeutic resistance of various types of human tumors. The strategies and challenges implicated in overcoming tumor therapy resistance by targeting FBXW7 are also discussed.

Targeting the deubiquitinase USP2 for malignant tumor therapy (Review)

The ubiquitin‑proteasome system is a major degradation pathway for >80% of proteins in vivo. Deubiquitylases, which remove ubiquitinated tags to stabilize substrate proteins, are important components involved in regulating the degradation of ubiquitinated proteins. In addition, they serve multiple roles in tumor development by participating in physiological processes such as protein metabolism, cell cycle regulation, DNA damage repair and gene transcription. The present review systematically summarized the role of ubiquitin‑specific protease 2 (USP2) in malignant tumors and the specific molecular mechanisms underlying the involvement of USP2 in tumor‑associated pathways. USP2 reverses ubiquitin‑mediated degradation of proteins and is involved in aberrant proliferation, migration, invasion, apoptosis and drug resistance of tumors. Additionally, the present review summarized studies reporting on the use of USP2 as a therapeutic target for malignancies such as breast, liver, ovarian, colorectal, bladder and prostate cancers and glioblastoma and highlights the current status of pharmacological research on USP2. The clinical significance of USP2 as a therapeutic target for malignant tumors warrants further investigation.

The roles of protein ubiquitination in tumorigenesis and targeted drug discovery in lung cancer

The malignant lung cancer has a high morbidity rate and very poor 5-year survival rate. About 80% - 90% of protein degradation in human cells is occurred through the ubiquitination enzyme pathway. Ubiquitin ligase (E3) with high specificity plays a crucial role in the ubiquitination process of the target protein, which usually occurs at a lysine residue in a substrate protein. Different ubiquitination forms have different effects on the target proteins. Multiple short chains of ubiquitination residues modify substrate proteins, which are favorable signals for protein degradation. The dynamic balance adapted to physiological needs between ubiquitination and deubiquitination of intracellular proteins is beneficial to the health of the organism. Ubiquitination of proteins has an impact on many biological pathways, and imbalances in these pathways lead to diseases including lung cancer. Ubiquitination of tumor suppressor protein factors or deubiquitination of tumor carcinogen protein factors often lead to the progression of lung cancer. Ubiquitin proteasome system (UPS) is a treasure house for research and development of new cancer drugs for lung cancer, especially targeting proteasome and E3s. The ubiquitination and degradation of oncogene proteins with precise targeting may provide a bright prospect for drug development in lung cancer; Especially proteolytic targeted chimerism (PROTAC)-induced protein degradation technology will offer a new strategy in the discovery and development of new drugs for lung cancer.

Identification of prognosis value and immune microenvironment features of ceRNAs in NSCLC with distinct gene mutation

Non-small cell lung cancer (NSCLC), representing about 85% of all lung cancer (LC) cases, is by far the most common form of LC. High-throughput technology largely expands our ability to analyze the transcriptome data and a plethora of cancer-driving genes has been identified, paving the path to immune therapy, where the effects of cancer-causing mutations are countered with microenvironment complexity. Given that competing endogenous RNAs (ceRNAs) participate in diverse cellular processes by a broad array of mechanisms in cancer, we scrutinized the immune microenvironment and ceRNA signatures in mutation-specific NSCLC by integrating TCGA-NSCLC and NSCLS-associated GEO datasets. The results suggested that RASA1mutation clusters in LUSC had a better prognosis and immunity. Immune cell infiltration analysis indicated that the cluster with RASA1 mutation had a significantly high level of NK T cells and a low level of memory effector T cells. Further analysis of immune-related ceRNAs in LUSC showed that hsa-miR-23a was significantly associated with survival in RASA1-mutation samples, indicating that there may be specific ceRNAs in mutation-specific subgroups in NSCLC. In conclusion, this study verified the presence of complexity and diversity of NSCLC gene mutations and highlighted the intricate links between gene mutation and tumor environment features.

FBXW7 attenuates tumor drug resistance and enhances the efficacy of immunotherapy

FBXW7 (F-box and WD repeat domain containing 7) is a critical subunit of the Skp1-Cullin1-F-box protein (SCF), acting as an E3 ubiquitin ligase by ubiquitinating targeted protein. Through degradation of its substrates, FBXW7 plays a pivotal role in drug resistance in tumor cells and shows the potential to rescue the sensitivity of cancer cells to drug treatment. This explains why patients with higher FBXW7 levels exhibit higher survival times and more favorable prognosis. Furthermore, FBXW7 has been demonstrated to enhance the efficacy of immunotherapy by targeting the degradation of specific proteins, as compared to the inactivated form of FBXW7. Additionally, other F-box proteins have also shown the ability to conquer drug resistance in certain cancers. Overall, this review aims to explore the function of FBXW7 and its specific effects on drug resistance in cancer cells.

The E3 ubiquitin ligases regulate PD-1/PD-L1 protein levels in tumor microenvironment to improve immunotherapy

The tumor microenvironment (TME) is the tumor surrounding environment, which is critical for tumor development and progression. TME is also involved in clinical intervention and treatment outcomes. Modulation of TME is useful for improving therapy strategies. PD-L1 protein on tumor cells interacts with PD-1 protein on T cells, contributing to T cell dysfunction and exhaustion, blockage of the immune response. Evidence has demonstrated that the expression of PD-1/PD-L1 is associated with clinical response to anti-PD-1/PD-L1 therapy in cancer patients. It is important to discuss the regulatory machinery how PD-1/PD-L1 protein is finely regulated in tumor cells. In recent years, studies have demonstrated that PD-1/PD-L1 expression was governed by various E3 ubiquitin ligases in TME, contributing to resistance of anti-PD-1/PD-L1 therapy in human cancers. In this review, we will discuss the role and molecular mechanisms of E3 ligases-mediated regulation of PD-1 and PD-L1 in TME. Moreover, we will describe how E3 ligases-involved PD-1/PD-L1 regulation alters anti-PD-1/PD-L1 efficacy. Altogether, targeting E3 ubiquitin ligases to control the PD-1/PD-L1 protein levels could be a potential strategy to potentiate immunotherapeutic effects in cancer patients.