Inhibition of mTOR complex 1/p70 S6 kinase signaling elevates PD-L1 levels in human cancer cells through enhancing protein stabilization accompanied with enhanced β-TrCP degradation

Regulation of post-translational modification of PD-L1 and associated opportunities for novel small-molecule therapeutics

PD-L1 is overexpressed on the surface of tumor cells and binds to PD-1, resulting in tumor immune escape. Therapeutic strategies to target the PD-1/PD-L1 pathway involve blocking the binding. Immune checkpoint inhibitors have limited efficacy against tumors because PD-L1 is also present in the cytoplasm. PD-L1 of post-translational modifications (PTMs) have uncovered numerous mechanisms contributing to carcinogenesis and have identified potential therapeutic targets. Therefore, small molecule inhibitors can block crucial carcinogenic signaling pathways, making them a potential therapeutic option. To better develop small molecule inhibitors, we have summarized the PTMs of PD-L1. This review discusses the regulatory mechanisms of small molecule inhibitors in carcinogenesis and explore their potential applications, proposing a novel approach for tumor immunotherapy based on PD-L1 PTM.

Casein kinase 1α mediates phosphorylation of the Merkel cell polyomavirus large T antigen for β-TrCP destruction complex interaction and subsequent degradation

Merkel cell polyomavirus (MCPyV) is a double-stranded tumor virus that is the main causative agent of Merkel cell carcinoma (MCC). The MCPyV large T antigen (LT), an essential viral DNA replication protein, maintains viral persistence by interacting with host Skp1-Cullin 1-F-box (SCF) E3 ubiquitin ligase complexes, which subsequently induces LT's proteasomal degradation, restricting MCPyV DNA replication. SCF E3 ubiquitin ligases require their substrates to be phosphorylated to bind them, utilizing phosphorylated serine residues as docking sites. The MCPyV LT unique region (MUR) is highly phosphorylated and plays a role in multiple host protein interactions, including SCF E3 ubiquitin ligases. Therefore, this domain highly governs LT stability. Though much work has been conducted to identify host factors that restrict MCPyV LT protein expression, the kinase(s) that cooperates with the SCF E3 ligase remains unknown. Here, we demonstrate that casein kinase 1 alpha (CK1α) negatively regulates MCPyV LT stability and LT-mediated replication by modulating interactions with the SCF β-TrCP. Specifically, we show that numerous CK1 isoforms (α, δ, ε) localize in close proximity to MCPyV LT through in situ proximity ligation assays (PLA) and CK1α overexpression mainly resulted in decreased MCPyV LT protein expression. Inhibition of CK1α using short hairpin RNA (shRNA) and treatment of a CK1α inhibitor or an mTOR inhibitor, TORKinib, resulted in decreased β-TrCP interaction with LT, increased LT expression, and enhanced MCPyV replication. The expression level of the CSNK1A1 gene transcripts is higher in MCPyV-positive MCC, suggesting a vital role of CK1α in limiting MCPyV replication required for establishing persistent infection.

IMPORTANCE

Merkel cell polyomavirus (MCPyV) large tumor antigen is a polyphosphoprotein and the phosphorylation event is required to modulate various functions of LT, including viral replication. Therefore, cellular kinase pathways are indispensable for governing MCPyV polyomavirus infection and life cycle in coordinating with the immunosuppression environment at disease onset. Understanding the regulation mechanisms of MCPyV replication by viral and cellular factors will guide proper prevention strategies with targeted inhibitors for MCPyV-associated Merkel cell carcinoma (MCC) patients, who currently lack therapies.

A literature review on signaling pathways of cervical cancer cell death-apoptosis induced by Traditional Chinese Medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Cervical cancer (CC) is a potentially lethal disorder that can have serious consequences for a woman's health. Because early symptoms are typically only present in the middle to late stages of the disease, clinical diagnosis and treatment can be challenging. Traditional Chinese medicine (TCM) has been shown to have unique benefits in terms of alleviating cancer clinical symptoms, lowering the risk of recurrence after surgery, and reducing toxic side effects and medication resistance after radiation therapy. It has also been shown to improve the quality of life for patients. Because of its improved anti-tumor effectiveness and biosafety, it could be considered an alternative therapy option. This study examines how TCM causes apoptosis in CC cells via signal transduction, including the active components and medicinal tonics. It also intends to provide a reliable clinical basis and protocol selection for the TCM therapy of CC.

METHODS

The following search terms were employed in PubMed, Web of Science, Embase, CNKI, Wanfang, VIP, SinoMed, and other scientific databases to retrieve pertinent literature on "cervical cancer," "apoptosis," "signaling pathway," "traditional Chinese medicine," "herbal monomers," "herbal components," "herbal extracts," and "herbal formulas."

RESULTS

It has been demonstrated that herbal medicines can induce apoptosis in cells of the cervix, a type of cancer, by influencing the signaling pathways involved.

CONCLUSION

A comprehensive literature search was conducted, and 148 papers from the period between January 2017 and December 2023 were identified as eligible for inclusion. After a meticulous process of screening, elimination and summary, generalization, and analysis, it was found that TCM can regulate multiple intracellular signaling pathways and related molecular targets, such as STAT3, PI3K/AKT, Wnt/β-catenin, MAPK, NF-κB, p53, HIF-1α, Fas/FasL and so forth. This regulatory capacity was observed to induce apoptosis in cervical cancer cells. The study of the mechanism of TCM against cervical cancer and the screening of new drug targets is of great significance for future research in this field. The results of this study will provide ideas and references for the future development of Chinese medicine in the diagnosis and treatment of cervical cancer.

Centipeda minima and 6-O-angeloylplenolin enhance the efficacy of immune checkpoint inhibitors in non-small cell lung cancer

BACKGROUND

Chemotherapeutic agents including cisplatin, gemcitabine, and pemetrexed, significantly enhance the efficacy of immune checkpoint inhibitors (ICIs) in non-small cell lung cancer (NSCLC) by increasing PD-L1 expression and potentiating T cell cytotoxicity. However, the low response rate and adverse effects limit the application of chemotherapy/ICI combinations in patients.

METHODS

We screened for medicinal herbs that could perturb PD-L1 expression and enhance T cell cytotoxicity in the presence of anti-PD-L1 antibody, and investigated the underlying mechanisms.

RESULTS

We found that the aqueous extracts of Centipeda minima (CM) significantly enhanced the cancer cell-killing activity and granzyme B expression level of CD8+ T cells, in the presence of anti-PD-L1 antibody. Both CM and its active component 6-O-angeloylplenolin (6-OAP) upregulated PD-L1 expression by suppressing GSK-3β-β-TRCP-mediated ubiquitination and degradation. CM and 6-OAP significantly enhanced ICI-induced reduction of tumor burden and prolongation of overall survival of mice bearing NSCLC cells, accompanied by upregulation of PD-L1 and increase of CD8+ T cell infiltration. CM also exhibited anti-NSCLC activity in cells and in a patient-derived xenograft mouse model.

CONCLUSIONS

These data demonstrated that the induced expression of PD-L1 and enhancement of CD8+ T cell cytotoxicity underlay the beneficial effects of 6-OAP-rich CM in NSCLCs, providing a clinically available and safe medicinal herb for combined use with ICIs to treat this deadly disease.

Emerging Targets and Therapeutics in Immuno-Oncology: Insights from Landscape Analysis

In the ever-evolving landscape of cancer research, immuno-oncology stands as a beacon of hope, offering novel avenues for treatment. This study capitalizes on the vast repository of immuno-oncology-related scientific documents within the CAS Content Collection, totaling over 350,000, encompassing journals and patents. Through a pioneering approach melding natural language processing with the CAS indexing system, we unveil over 300 emerging concepts, depicted in a comprehensive "Trend Landscape Map". These concepts, spanning therapeutic targets, biomarkers, and types of cancers among others, are hierarchically organized into eight major categories. Delving deeper, our analysis furnishes detailed quantitative metrics showcasing growth trends over the past three years. Our findings not only provide valuable insights for guiding future research endeavors but also underscore the merit of tapping the vast and unparalleled breadth of existing scientific information to derive profound insights.

FAT10 induces immune suppression by upregulating PD-L1 expression in hepatocellular carcinoma

The upregulation of programmed death ligand 1 (PD-L1) plays a crucial role in facilitating cancer cells to evade immune surveillance through immunosuppression. However, the precise regulatory mechanisms of PD-L1 in hepatocellular carcinoma (HCC) remain undefined. The correlation between PD-L1 and ubiquitin-like molecules (UBLs) was studied using sequencing data from 20 HCC patients in our center, combined with TCGA data. Specifically, the association between FAT10 and PD-L1 was further validated at both the protein and mRNA levels in HCC tissues from our center. Subsequently, the effect of FAT10 on tumor progression and immune suppression was examined through both in vivo and in vitro experiments. Utilizing sequencing data, qPCR, and Western blotting assays, we confirmed that FAT10 was highly expressed in HCC tissues and positively correlated with PD-L1 expression. Additionally, in vitro experiments demonstrated that the overexpression of FAT10 fostered the proliferation, migration, and invasion of HCC cells. Furthermore, the overexpression of FAT10 in HCC cells led to an increase in PD-L1 expression, resulting in the inhibition of T cell proliferation and the enhancement of HCC cell resistance to T cell-mediated cytotoxicity. Moreover, in vivo experiments utilizing the C57BL/6 mouse model revealed that overexpression of FAT10 effectively suppressed the infiltration of CD8 + GZMB + and CD8 + Ki67 + T cells, as well as reduced serum levels of TNF-α and IFN-γ. Mechanistically, we further identified that FAT10 upregulates PD-L1 expression via activating the PI3K/AKT/mTOR pathway, but not in a ubiquitin-like modification. In conclusion, our findings indicate that FAT10 promotes immune evasion of HCC via upregulating PD-L1 expression, suggesting its potential as a novel target to enhance the efficiency of immunotherapy in HCC.

Everolimus treatment enhances inhibitory immune checkpoint molecules' expression in monocyte-derived dendritic cells

BACKGROUND

Antigen-specific T-cell immunity is provided by dendritic cells (DCs), which are specialized antigen-presenting cells. Furthermore, they establish a link between innate and adaptive immune responses. Currently, DC modification is a new approach for the therapy of several disorders. During solid organ transplantation, Everolimus, which is a mammalian target of rapamycin (mTOR) inhibitor, was initially utilized to suppress the immune system's functionality. Due to the intervention of Everolimus in various signaling pathways in cells and its modulatory properties on the immune system, this study aims to investigate the effect of treatment with Everolimus on the maturation and expression of immune checkpoint genes in monocyte-derived DCs.

METHODS

To isolate monocytes from PBMCs, the CD14 marker was used via the MACS method. Monocytes were cultured and induced to differentiate into monocyte-derived DCs by utilizing GM-CSF and IL-4 cytokines. On the fifth day, immature DCs were treated with Everolimus and incubated for 24 h. On the sixth day, the flow cytometry technique was used to investigate the effect of Everolimus on the phenotypic characteristics of DCs. In the end, the expression of immune checkpoint genes in both the Everolimus-treated and untreated DCs groups was assessed using the real-time PCR method.

RESULTS

The findings of this research demonstrated that the administration of Everolimus to DCs led to a notable rise in human leukocyte antigen (HLA)-DR expression and a decrease in CD11c expression. Furthermore, there was a significant increase in the expression of immune checkpoint molecules, namely CTLA-4, VISTA, PD-L1, and BTLA, in DCs treated with Everolimus.

CONCLUSION

The findings of this study show that Everolimus can target DCs and affect their phenotype and function in order to shift them toward a partially tolerogenic state. However, additional research is required to gain a comprehensive understanding of the precise impact of Everolimus on the activation status of DCs.

Deciphering Cholesterol's Role in PD-L2 Stability: A Distinct Regulatory Mechanism From PD-L1

Programmed cell death 1 ligand 2 (PD-L2), a member of the B7 immune checkpoint protein family, emerges as a crucial player in immune modulation. Despite its functional overlap with programmed cell death 1 ligand 1 (PD-L1) in binding to the programmed cell death protein 1 (PD-1) on T cells, PD-L2 exhibits a divergent expression pattern and a higher affinity for PD-1. However, the regulatory mechanisms of PD-L2 remain under-explored. Here, our investigations illustrate the pivotal role of cholesterol in modulating PD-L2 stability. Using advanced nuclear magnetic resonance (NMR) and biochemical analyses, we demonstrate a direct and specific binding between cholesterol and PD-L2, mediated by an F-xxx-V-xx-LR motif in its transmembrane domain, distinct from that in PD-L1. This interaction stabilizes PD-L2 and prevents its downstream degradation. Disruption of this binding motif compromises PD-L2's cellular stability, underscoring its potential significance in cancer biology. These findings not only deepen our understanding of PD-L2 regulation in the context of tumors, but also open avenues for potential therapeutic interventions.

Recent advances and mechanisms of action of PD-L1 degraders as potential therapeutic agents

PD-L1 is an important immune checkpoint protein that can bind to T cells' PD-1 receptor, thereby promoting immune escape from tumors. In recent years, many researchers have developed strategies to degrade PD-L1 to improve the effect of immunotherapy. The study of degrading PD-L1 provides new opportunities for immunotherapy. Here, we mainly summarize and review the current active molecules and mechanisms that mediate the degradation of immature and mature PD-L1 during the post-translational modification stages, involving PD-L1 phosphorylation, glycosylation, palmitoylation, ubiquitination, and the autophagy-lysosomal process. This review expects that by degrading PD-L1 protein, we will not only gain a better understanding of oncogenic mechanisms involving tumor PD-L1 protein but also provide a new way to improve immunotherapy.

Deficiency in SLC25A15, a hypoxia-responsive gene, promotes hepatocellular carcinoma by reprogramming glutamine metabolism

BACKGROUND & AIMS

The role of solute carrier family 25 member 15 (SLC25A15), a critical component of the urea cycle, in hepatocellular carcinoma (HCC) progression remains poorly understood. This study investigated the impact of SLC25A15 on HCC progression and its mechanisms.

METHODS

We systematically investigated the function of SLC25A15 in HCC progression using large-scale data mining and cell, animal, and organoid models. Furthermore, we analyzed its involvement in reprogramming glutamine metabolism.

RESULTS

SLC25A15 expression was significantly decreased in HCC tissues, and patients with low SLC25A15 levels had a poorer prognosis. Hypoxia-exposed HCC cells or tissues had lower SLC25A15 expression. A positive correlation between HNF4A, a transcription factor suppressed by hypoxia, and SLC25A15 was observed in both HCC tissues and cells. Modulating HNF4A levels altered SLC25A15 mRNA levels. SLC25A15 upregulated SLC1A5, increasing glutamine uptake. The reactive metabolic pathway of glutamine was increased in SLC25A15-deficient HCC cells, providing energy for HCC progression through additional lipid synthesis. Ammonia accumulation due to low SLC25A15 levels suppressed the expression of OGDHL (oxoglutarate dehydrogenase L), a switch gene that mediates SLC25A15 deficiency-induced reprogramming of glutamine metabolism. SLC25A15-deficient HCC cells were more susceptible to glutamine deprivation and glutaminase inhibitors. Intervening in glutamine metabolism increased SLC25A15-deficient HCC cells' response to anti-PD-L1 treatment.

CONCLUSION

SLC25A15 is hypoxia-responsive in HCC, and low SLC25A15 levels result in glutamine reprogramming through SLC1A5 and OGDHL regulation, promoting HCC progression and regulating cell sensitivity to anti-PD-L1. Interrupting the glutamine-derived energy supply is a potential therapeutic strategy for treating SLC25A15-deficient HCC.

IMPACT AND IMPLICATIONS

We first demonstrated the tumor suppressor role of solute carrier family 25 member 15 (SLC25A15) in hepatocellular carcinoma (HCC) and showed that its deficiency leads to reprogramming of glutamine metabolism to promote HCC development. SLC25A15 can serve as a potential biomarker to guide the development of precision therapeutic strategies aimed at targeting glutamine deprivation. Furthermore, we highlight that the use of an inhibitor of glutamine utilization can enhance the sensitivity of low SLC25A15 HCC to anti-PD-L1 therapy.

Inhibition of CK2/ING4 Pathway Facilitates Non-Small Cell Lung Cancer Immunotherapy

Immune cells can protect against tumor progression by killing cancer cells, while aberrant expression of the immune checkpoint protein PD-L1 (programmed death ligand 1) in cancer cells facilitates tumor immune escape and inhibits anti-tumor immunotherapy. As a serine/threonine kinase, CK2 (casein kinase 2) regulates tumor progression by multiple pathways, while it is still unclear the effect of CK2 on tumor immune escape. Here it is found that ING4 induced PD-L1 autophagic degradation and inhibites non-small cell lung cancer (NSCLC) immune escape by increasing T cell activity. However, clinical analysis suggests that high expression of CK2 correlates with low ING4 protein level in NSCLC. Further analysis shows that CK2 induce ING4-S150 phosphorylation leading to ING4 ubiquitination and degradation by JFK ubiquitin ligase. In contrast, CK2 gene knockout increases ING4 protein stability and T cell activity, subsequently, inhibites NSCLC immune escape. Furthermore, the combined CK2 inhibitor with PD-1 antibody effectively enhances antitumor immunotherapy. These findings provide a novel strategy for cancer immunotherapy.

Research Note: Transcriptome analysis reveals differentially expressed genes regulated muscle development in Pekin ducks during dietary threonine deficiency

To investigate the underlying molecular mechanism of threonine (Thr) regulation on the development of breast muscle in Pekin ducks, 240 male Pekin ducks at 1 d of age were fed a Thr deficiency diet (Thr-D), Thr sufficiency diet (Thr-S), or Thr excess diet (Thr-E) for 21 d. The results showed that Thr-D reduced body weight (BW), average weight gain (ADG), and average feed intake (ADFI), and increased the feed/gain (F/G) in Pekin ducks (P < 0.05), and Thr-E did not affect BW, ADG, ADFI, or F/G (P > 0.05), compared with Thr-S. The diameter and cross-sectional area of the breast muscle fibers in the Thr-S group were larger than those in the Thr-D group (P < 0.05). RNA sequencing revealed 1,300 differential expressed genes (DEGs) between the Thr-D and Thr-S groups, of which 625 were upregulated and 675 were downregulated by Thr-D. KEGG analysis showed that the upregulated genes were enriched in mTOR, FoxO, Wnt, fat digestion and absorption, and other signaling pathways. The downregulated genes were enriched in the MAPK signaling, glycolysis/gluconeogenesis, adipocytokine signaling, and biosynthesis of unsaturated fatty acids signaling pathways. The genes of Wnt family member 3a (Wnt3a), myogenin, myozenin 2, and insulin like growth factor 2 mRNA binding protein were upregulated, and platelet derived growth factor subunit B, PDGF receptor beta and Wnt4 were downregulated by Thr deficiency, which involving in muscle development. Our findings indicated that Thr increased breast fiber size, perhaps because Thr affected the proliferation and differentiation of satellite cells in breast muscle of ducks after hatch. Our results provide novel insights into new understanding of the molecular mechanisms underlying breast muscle development in ducks subjected to dietary Thr.

Hsa-LINC02418/mmu-4930573I07Rik regulated by METTL3 dictates anti-PD-L1 immunotherapeutic efficacy via enhancement of Trim21-mediated PD-L1 ubiquitination

BACKGROUND

Limited response to programmed death ligand-1 (PD-L1)/programmed death 1 (PD-1) immunotherapy is a major hindrance of checkpoint immunotherapy in non-small cell lung cancer (NSCLC). The abundance of PD-L1 on the tumor cell surface is crucial for the responsiveness of PD-1/PD-L1 immunotherapy. However, the negative control of PD-L1 expression and the physiological significance of the PD-L1 inhibition in NSCLC immunotherapy remain obscure.

METHODS

Bioinformatics analysis was performed to profile and investigate the long non-coding RNAs that negatively correlated with PD-L1 expression and positively correlated with CD8+T cell infiltration in NSCLC. Immunofluorescence, in vitro PD-1 binding assay, T cell-induced apoptosis assays and in vivo syngeneic mouse models were used to investigate the functional roles of LINC02418 and mmu-4930573I07Rik in regulating anti-PD-L1 therapeutic efficacy in NSCLC. The molecular mechanism of LINC02418-enhanced PD-L1 downregulation was explored by immunoprecipitation, RNA immunoprecipitation (RIP), and ubiquitination assays. RIP, luciferase reporter, and messenger RNA degradation assays were used to investigate the m6A modification of LINC02418 or mmu-4930573I07Rik expression. Bioinformatics analysis and immunohistochemistry (IHC) verification were performed to determine the significance of LINC02418, PD-L1 expression and CD8+T cell infiltration.

RESULTS

LINC02418 is a negative regulator of PD-L1 expression that positively correlated with CD8+T cell infiltration, predicting favorable clinical outcomes for patients with NSCLC. LINC02418 downregulates PD-L1 expression by enhancing PD-L1 ubiquitination mediated by E3 ligase Trim21. Both hsa-LINC02418 and mmu-4930573I07Rik (its homologous RNA in mice) regulate PD-L1 therapeutic efficacy in NSCLC via Trim21, inducing T cell-induced apoptosis in vitro and in vivo. Furthermore, METTL3 inhibition via N6-methyladenosine (m6A) modification mediated by YTHDF2 reader upregulates hsa-LINC02418 and mmu-4930573I07Rik. In patients with NSCLC, LINC02418 expression is inversely correlated with PD-L1 expression and positively correlated with CD8+T infiltration.

CONCLUSION

LINC02418 functions as a negative regulator of PD-L1 expression in NSCLC cells by promoting the degradation of PD-L1 through the ubiquitin-proteasome pathway. The expression of LINC02418 is regulated by METTL3/YTHDF2-mediated m6A modification. This study illuminates the underlying mechanisms of PD-L1 negative regulation and presents a promising target for improving the effectiveness of anti-PD-L1 therapy in NSCLC.

Integrative multi-omics analysis unveils stemness-associated molecular subtypes in prostate cancer and pan-cancer: prognostic and therapeutic significance

BACKGROUND

Prostate cancer (PCA) is the fifth leading cause of cancer-related deaths worldwide, with limited treatment options in the advanced stages. The immunosuppressive tumor microenvironment (TME) of PCA results in lower sensitivity to immunotherapy. Although molecular subtyping is expected to offer important clues for precision treatment of PCA, there is currently a shortage of dependable and effective molecular typing methods available for clinical practice. Therefore, we aim to propose a novel stemness-based classification approach to guide personalized clinical treatments, including immunotherapy.

METHODS

An integrative multi-omics analysis of PCA was performed to evaluate stemness-level heterogeneities. Unsupervised hierarchical clustering was used to classify PCAs based on stemness signature genes. To make stemness-based patient classification more clinically applicable, a stemness subtype predictor was jointly developed by using four PCA datasets and 76 machine learning algorithms.

RESULTS

We identified stemness signatures of PCA comprising 18 signaling pathways, by which we classified PCA samples into three stemness subtypes via unsupervised hierarchical clustering: low stemness (LS), medium stemness (MS), and high stemness (HS) subtypes. HS patients are sensitive to androgen deprivation therapy, taxanes, and immunotherapy and have the highest stemness, malignancy, tumor mutation load (TMB) levels, worst prognosis, and immunosuppression. LS patients are sensitive to platinum-based chemotherapy but resistant to immunotherapy and have the lowest stemness, malignancy, and TMB levels, best prognosis, and the highest immune infiltration. MS patients represent an intermediate status of stemness, malignancy, and TMB levels with a moderate prognosis. We further demonstrated that these three stemness subtypes are conserved across pan-tumor. Additionally, the 9-gene stemness subtype predictor we developed has a comparable capability to 18 signaling pathways to make tumor diagnosis and to predict tumor recurrence, metastasis, progression, prognosis, and efficacy of different treatments.

CONCLUSIONS

The three stemness subtypes we identified have the potential to be a powerful tool for clinical tumor molecular classification in PCA and pan-cancer, and to guide the selection of immunotherapy or other sensitive treatments for tumor patients.

Autophagy as a Target for Non-Immune Intrinsic Functions of Programmed Cell Death-Ligand 1 in Cancer

Autophagy is a catabolic process that is essential to the maintenance of homeostasis through the cellular recycling of damaged organelles or misfolded proteins, which sustains energy balance. Additionally, autophagy plays a dual role in modulating the development and progression of cancer and inducing a survival strategy in tumoral cells. Programmed cell death-ligand 1 (PD-L1) modulates the immune response and is responsible for maintaining self-tolerance. Because tumor cells exploit the PD-L1-PD-1 interaction to subvert the immune response, immunotherapy has been developed based on the use of PD-L1-blocking antibodies. Recent evidence has suggested a bidirectional regulation between autophagy and PD-L1 molecule expression in tumor cells. Moreover, the research into the intrinsic properties of PD-L1 has highlighted new functions that are advantageous to tumor cells. The relationship between autophagy and PD-L1 is complex and still not fully understood; its effects can be context-dependent and might differ between tumoral cells. This review refines our understanding of the non-immune intrinsic functions of PD-L1 and its potential influence on autophagy, how these could allow the survival of tumor cells, and what this means for the efficacy of anti-PD-L1 therapeutic strategies.

Glutamine regulates the cellular proliferation and cell cycle progression by modulating the mTOR mediated protein levels of β-TrCP

The amino acid glutamine plays an important role in cell growth and proliferation. Reliance on glutamine has long been considered a hallmark of highly proliferating cancer cells. Development of strategies for cancer therapy that primarily target glutamine metabolism has been an active area of research. Glutamine depletion is associated with growth arrest and apoptosis-induced cell death; however, the molecular mechanisms involved in this process are not clearly understood. Here, we show that glutamine depletion activates the energetic stress AMPK pathway and inhibits mTORC1 activity. Furthermore, inhibition of mTORC1 reduces the protein levels of β-TrCP, resulting in aberrant cell cycle progression and reduced proliferation. In agreement with the role of β-TrCP in glutamine metabolism, knockdown of β-TrCP resulted in proliferation and cell cycle defects similar to those observed for glutamine depletion. In summary, our results provide mechanistic insights into the role of glutamine metabolism in regulation of cell growth and proliferation via β-TrCP, uncovering a previously undescribed molecular process involved in glutamine metabolism.

Beta-Transducin Repeats-Containing Proteins as an Anticancer Target

Beta-transducin repeat-containing proteins (β-TrCPs) are E3-ubiquitin-ligase-recognizing substrates and regulate proteasomal degradation. The degradation of β-TrCPs' substrates is tightly controlled by various external and internal signaling and confers diverse cellular processes, including cell cycle progression, apoptosis, and DNA damage response. In addition, β-TrCPs function to regulate transcriptional activity and stabilize a set of substrates by distinct mechanisms. Despite the association of β-TrCPs with tumorigenesis and tumor progression, studies on the mechanisms of the regulation of β-TrCPs' activity have been limited. In this review, we studied publications on the regulation of β-TrCPs themselves and analyzed the knowledge gaps to understand and modulate β-TrCPs' activity in the future.

Unveiling the veil of lactate in tumor-associated macrophages: a successful strategy for immunometabolic therapy

Lactate, traditionally regarded as a metabolic waste product at the terminal of the glycolysis process, has recently been found to have multifaceted functional roles in metabolism and beyond. A metabolic reprogramming phenomenon commonly seen in tumor cells, known as the "Warburg effect," sees high levels of aerobic glycolysis result in an excessive production of lactate. This lactate serves as a substrate that sustains not only the survival of cancer cells but also immune cells. However, it also inhibits the function of tumor-associated macrophages (TAMs), a group of innate immune cells ubiquitously present in solid tumors, thereby facilitating the immune evasion of malignant tumor cells. Characterized by their high plasticity, TAMs are generally divided into the pro-inflammatory M1 phenotype and the pro-tumour M2 phenotype. Through a process of 'education' by lactate, TAMs tend to adopt an immunosuppressive phenotype and collaborate with tumor cells to promote angiogenesis. Additionally, there is growing evidence linking metabolic reprogramming with epigenetic modifications, suggesting the participation of histone modification in diverse cellular events within the tumor microenvironment (TME). In this review, we delve into recent discoveries concerning lactate metabolism in tumors, with a particular focus on the impact of lactate on the function of TAMs. We aim to consolidate the molecular mechanisms underlying lactate-induced TAM polarization and angiogenesis and explore the lactate-mediated crosstalk between TAMs and tumor cells. Finally, we also touch upon the latest progress in immunometabolic therapies and drug delivery strategies targeting glycolysis and lactate production, offering new perspectives for future therapeutic approaches.

Enhanced bypass of PD-L1 translation reduces the therapeutic response to mTOR kinase inhibitors

Increased PD-L1 expression in cancer cells is known to enhance immunosuppression, but the mechanism underlying PD-L1 upregulation is incompletely characterized. We show that PD-L1 expression is upregulated through internal ribosomal entry site (IRES)-mediated translation upon mTORC1 inhibition. We identify an IRES element in the PD-L1 5'-UTR that permits cap-independent translation and promotes continuous production of PD-L1 protein despite effective inhibition of mTORC1. eIF4A is found to be a key PD-L1 IRES-binding protein that enhances PD-L1 IRES activity and protein production in tumor cells treated with mTOR kinase inhibitors (mTORkis). Notably, treatment with mTORkis in vivo elevates PD-L1 levels and reduces the number of tumor-infiltrating lymphocytes in immunogenic tumors, but anti-PD-L1 immunotherapy restores antitumor immunity and enhances the therapeutic efficacy of mTORkis. These findings report a molecular mechanism for regulating PD-L1 expression through bypassing mTORC1-mediated cap-dependent translation and provide a rationale for targeting PD-L1 immune checkpoint to improve mTOR-targeted therapy.

Regulation of post-translational modification of PD-L1 and advances in tumor immunotherapy

The immune checkpoint molecules programmed cell death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are one of the most promising targets for tumor immunotherapy. PD-L1 is overexpressed on the surface of tumor cells and inhibits T cell activation upon binding to PD⁃1 on the surface of T cells, resulting in tumor immune escape. The therapeutic strategy of targeting PD-1/PD-L1 involves blocking this binding and restoring the tumor-killing effect of immune cells. However, in clinical settings, a relatively low proportion of cancer patients have responded well to PD-1/PD-L1 blockade, and clinical outcomes have reached a bottleneck and no substantial progress has been made. In recent years, PD-L1 post-translation modifications (PTMs) have gradually become a hot topic in the field of PD-L1 research, which will provide new insights to improve the efficacy of current anti-PD-1/PD-L1 therapies. Here, we summarized and discussed multiple PTMs of PD-L1, including glycosylation, ubiquitination, phosphorylation, acetylation and palmitoylation, with a major emphasis on mechanism-based therapeutic strategies (including relevant enzymes and targets that are already in clinical use and that may become drugs in the future). We also summarized the latest research progress of PTMs of PD-L1/PD-1 in regulating immunotherapy. The review provided novel strategies and directions for tumor immunotherapy research based on the PTMs of PD-L1/PD-1.

PPARγ inhibited tumor immune escape by inducing PD-L1 autophagic degradation

Blockade of the programmed death 1 (PD-1)/ programmed death ligand 1 (PD-L1) immune checkpoint could increase antitumor immunotherapy for multiple types of cancer, but the response rate of patients is about 10%-40%. Peroxisome proliferator activated receptor γ (PPARγ) plays an important role in regulating cell metabolism, inflammation, immunity, and cancer progression, while the mechanism of PPARγ on cancer cell immune escape is still unclear. Here we found that PPARγ expression exhibits a positive correlation with activation of T cells in non-small-cell lung cancer (NSCLC) by clinical analysis. Deficiency of PPARγ promoted immune escape of NSCLC by inhibiting T-cell activity, which was associated with increased PD-L1 protein level. Further analysis showed that PPARγ reduced PD-L1 expression independent of its transcriptional activity. PPARγ contains the microtubule-associated protein 1A/1B-light chain 3 (LC3) interacting region motif, which acts as an autophagy receptor for PPARγ binding to LC3, leading to degradation of PD-L1 in lysosomes, which in turn suppresses NSCLC tumor growth by increasing T-cell activity. These findings suggest that PPARγ inhibits the tumor immune escape of NSCLC by inducing PD-L1 autophagic degradation.

TSC2 regulates tumor susceptibility to TRAIL-mediated T-cell killing by orchestrating mTOR signaling

Resistance to cancer immunotherapy continues to impair common clinical benefit. Here, we use whole-genome CRISPR-Cas9 knockout data to uncover an important role for Tuberous Sclerosis Complex 2 (TSC2) in determining tumor susceptibility to cytotoxic T lymphocyte (CTL) killing in human melanoma cells. TSC2-depleted tumor cells had disrupted mTOR regulation following CTL attack, which was associated with enhanced cell death. Wild-type tumor cells adapted to CTL attack by shifting their mTOR signaling balance toward increased mTORC2 activity, circumventing apoptosis, and necroptosis. TSC2 ablation strongly augmented tumor cell sensitivity to CTL attack in vitro and in vivo, suggesting one of its functions is to critically protect tumor cells. Mechanistically, TSC2 inactivation caused elevation of TRAIL receptor expression, cooperating with mTORC1-S6 signaling to induce tumor cell death. Clinically, we found a negative correlation between TSC2 expression and TRAIL signaling in TCGA patient cohorts. Moreover, a lower TSC2 immune response signature was observed in melanomas from patients responding to immune checkpoint blockade. Our study uncovers a pivotal role for TSC2 in the cancer immune response by governing crosstalk between TSC2-mTOR and TRAIL signaling, aiding future therapeutic exploration of this pathway in immuno-oncology.

Pharmacological tumor PDL1 depletion with chlorambucil treats ovarian cancer and melanoma: improves antitumor immunity and renders anti-PDL1-resistant tumors anti-PDL1-sensitive through NK cell effects

BACKGROUND

Tumor intracellular programmed cell death ligand-1 (PDL1) mediates pathologic signals that regulate clinical treatment responses distinctly from surface-expressed PDL1 targeted by αPDL1 immune checkpoint blockade antibodies.

METHODS

We performed a drug screen for tumor cell PDL1 depleting drugs that identified Food and Drug Administration (FDA)-approved chlorambucil and also 9-[2-(phosphonomethoxy)ethyl] guanine. We used in vitro and in vivo assays to evaluate treatment and signaling effects of pharmacological tumor PDL1 depletion focused on chlorambucil as FDA approved, alone or plus αPDL1.

RESULTS

PDL1-expressing mouse and human ovarian cancer lines and mouse melanoma were more sensitive to chlorambucil-mediated proliferation inhibition in vitro versus corresponding genetically PDL1-depleted lines. Orthotopic peritoneal PDL1-expressing ID8agg ovarian cancer and subcutaneous B16 melanoma tumors were more chlorambucil-sensitive in vivo versus corresponding genetically PDL1-depleted tumors. Chlorambucil enhanced αPDL1 efficacy in tumors otherwise αPDL1-refractory, and improved antitumor immunity and treatment efficacy in a natural killer cell-dependent manner alone and plus αPDL1. Chlorambucil-mediated PDL1 depletion was relatively tumor-cell selective in vivo, and treatment efficacy was preserved in PDL1KO hosts, demonstrating tumor PDL1-specific treatment effects. Chlorambucil induced PDL1-dependent immunogenic tumor cell death which could help explain immune contributions. Chlorambucil-mediated PDL1 reduction mechanisms were tumor cell-type-specific and involved transcriptional or post-translational mechanisms, including promoting PDL1 ubiquitination through the GSK3β/β-TRCP pathway. Chlorambucil-mediated tumor cell PDL1 depletion also phenocopied genetic PDL1 depletion in reducing tumor cell mTORC1 activation and tumor initiating cell content, and in augmenting autophagy, suggesting additional treatment potential.

CONCLUSIONS

Pharmacological tumor PDL1 depletion with chlorambucil targets tumor-intrinsic PDL1 signaling that mediates treatment resistance, especially in αPDL1-resistant tumors, generates PDL1-dependent tumor immunogenicity and inhibits tumor growth in immune-dependent and independent manners. It could improve treatment efficacy of selected agents in otherwise treatment-refractory, including αPDL1-refractory cancers, and is rapidly clinically translatable.

Docosahexaenoic acid reverses PD-L1-mediated immune suppression by accelerating its ubiquitin-proteasome degradation

PD-L1 interacts with its receptor PD-1 on T cells to negatively regulate T cell function, leading to cancer cell immune escape from the immune surveillance. Therefore, targeting PD-L1 is considered to be an attractive approach for cancer immunotherapy. In this study, we demonstrated for the first time that ω-3 polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) reduced the expression of PD-L1 in cancer cells both in vitro and in vivo. Promotion of PD-L1 ubiquitin-proteasome degradation by DHA resulted in a decrease of PD-L1 expression, leading to reduction of PD-L1 and PD-1 interaction, and reversing PD-L1-mediated immune suppression, which in turn contributed to the inhibitory effect on tumor growth. Furtherly, DHA significantly reduced fatty acid synthase (FASN) expression in cancer cells, which inhibited the palmitoyltransferases DHHC5, promoting the CSN5-dependent PD-L1 degradation. Our present finding uncovered a novel mechanism involved in the anti-cancer activity of DHA, and implicated that DHA holds promising potential to be developed as a novel immune-enhancer for cancer treatment and prevention.

Post-translational regulations of PD-L1 and PD-1: Mechanisms and opportunities for combined immunotherapy

Antibodies targeting programmed cell death protein 1 (PD-1) or its ligand programmed death-ligand 1 (PD-L1) are profoundly changing the methods to treat cancers with long-term clinical benefits. Unlike conventional methods that directly target tumor cells, PD-1/PD-L1 blockade exerts anti-tumor effects largely through reactivating or normalizing cytotoxic T lymphocyte in the tumor microenvironment to combat cancer cells. However, only a small fraction of cancer patients responds well to PD-1/PD-L1 blockade and clinical outcomes have reached a bottleneck without substantial advances. Therefore, better understanding the molecular mechanisms underlying how PD-1/PD-L1 expression is regulated will provide new insights to improve the efficacy of current anti-PD-1/PD-L1 therapy. Here, we provide an update of current progress of PD-L1 and PD-1 post-translational regulations and highlight the mechanism-based combination therapy strategies for a better treatment of human cancer.

An immunotherapy response prediction model derived from proliferative CD4+ T cells and antigen-presenting monocytes in ccRCC

Most patients with clear cell renal cell carcinoma (ccRCC) have an impaired response to immune checkpoint blockade (ICB) therapy. Few biomarkers can predict responsiveness, and there is insufficient evidence to extend them to ccRCC clinical use. To explore subtypes and signatures of immunocytes with good predictive performance for ICB outcomes in the ccRCC context, we reanalyzed two ccRCC single-cell RNA sequencing (scRNA-seq) datasets from patients receiving ICB treatment. A subtype of proliferative CD4⁺ T cells and regulatory T cells and a subtype of antigen-presenting monocytes that have good predictive capability and are correlated with ICB outcomes were identified. These findings were corroborated in independent ccRCC ICB pretreatment bulk RNA-seq datasets. By incorporating the cluster-specific marker genes of these three immunocyte subtypes, we developed a prediction model, which reached an AUC of 93% for the CheckMate cohort (172 samples). Our study shows that the ICB response prediction model can serve as a valuable clinical decision-making tool for guiding ICB treatment of ccRCC patients.

PD-L1/pS6 in Circulating Tumor Cells (CTCs) during Osimertinib Treatment in Patients with Non-Small Cell Lung Cancer (NSCLC)

The PD-1/PD-L1 axis provides CTCs an escape route from the immune system. Phosphorylation of the ribosomal protein S6 is implicated in the same pathway, following mTOR activation. The aim of the study was to investigate the expression of PD-L1 and pS6 in CTCs from NSCLC patients under Osimertinib treatment at a single cell level. CTCs were isolated using ISET from NSCLC patients’ blood [37 at baseline, 25 after the 1st cycle, and 23 at the end of treatment (EOT)]. Staining was performed using immunofluorescence. Cytokeratin-positive (CK+) CTCs were detected in 62% of patients. CK+PD-L1+CD45− and CK+pS6+ phenotypes were detected in 38% and 41% of the patients at baseline, in 28% and 32% after 1st cycle, and in 30% and 35% at EOT, respectively. Spearman’s analysis revealed statistically significant correlations between PD-L1 and pS6 phenotypes at all time points. Survival analysis revealed that CK+pS6+ (p = 0.003) and CKlowpS6+ (p = 0.021) phenotypes after 1st cycle were related to significantly decreased one-year progression-free survival (PFS12m) and PFS, respectively. CK+PD-L1+CD45−phenotype at baseline and after 1st cycle showed a trend for decreased PFS12m. Increased expression of PD-L1/pS6 in CTCs of Osimertinib-treated NSCLC patients implies the activation of the corresponding pathway, which is potentially associated with poor clinical outcomes.

DOCK2 contributes to pulmonary fibrosis by promoting lung fibroblast to myofibroblast transition

Idiopathic pulmonary fibrosis (IPF) is the most common chronic interstitial lung disease and is characterized by progressive scarring of the lung. Transforming growth factor-β (TGF-β) signaling plays an essential role in IPF and drives fibroblast to myofibroblast transition (FMT). Dedicator of cytokinesis 2 (DOCK2) is known to regulate diverse immune functions by activating Rac and has been recently implicated in pleural fibrosis. We now report a novel role of DOCK2 in pulmonary fibrosis development by mediating FMT. In primary normal and IPF human lung fibroblasts (HLFs), TGF-β induced DOCK2 expression concurrent with FMT markers, smooth muscle α-actin (α-SMA), collagen-1, and fibronectin. Knockdown of DOCK2 significantly attenuated TGF-β-induced expression of these FMT markers. In addition, we found that the upregulation of DOCK2 by TGF-β is dependent on both Smad3 and ERK pathways as their respective inhibitors blocked TGF-β-mediated induction. TGF-β also stabilized DOCK2 protein, which contributes to increased DOCK2 expression. In addition, DOCK2 was also dramatically induced in the lungs of patients with IPF and in bleomycin, and TGF-β induced pulmonary fibrosis in C57BL/6 mice. Furthermore, increased lung DOCK2 expression colocalized with the FMT marker α-SMA in the bleomycin-induced pulmonary fibrosis model, implicating DOCK2 in the regulation of lung fibroblast phenotypic changes. Importantly, DOCK2 deficiency also attenuated bleomycin-induced pulmonary fibrosis and α-SMA expression. Taken together, our study demonstrates a novel role of DOCK2 in pulmonary fibrosis by modulating FMT and suggests that targeting DOCK2 may present a potential therapeutic strategy for the prevention or treatment of IPF.

PD-L1 mediates lung fibroblast to myofibroblast transition through Smad3 and β-catenin signaling pathways

Programmed death ligand-1 (PD-L1) is an immune checkpoint protein that has been linked with idiopathic pulmonary fibrosis (IPF) and fibroblast to myofibroblast transition (FMT). However, it remains largely unclear how PD-L1 mediates this process. We found significantly increased PD-L1 in the lungs of idiopathic pulmonary fibrosis patients and mice with pulmonary fibrosis induced by bleomycin and TGF-β. In primary human lung fibroblasts (HLFs), TGF-β induced PD-L1 expression that is dependent on both Smad3 and p38 pathways. PD-L1 knockdown using siRNA significantly attenuated TGF-β-induced expression of myofibroblast markers α-SMA, collagen-1, and fibronectin in normal and IPF HLFs. Further, we found that PD-L1 interacts with Smad3, and TGF-β induces their interaction. Interestingly, PD-L1 knockdown reduced α-SMA reporter activity induced by TGF-β in HLFs, suggesting that PD-L1 might act as a co-factor of Smad3 to promote target gene expression. TGF-β treatment also phosphorylates GSK3β and upregulates β-catenin protein levels. Inhibiting β-catenin signaling with the pharmaceutical inhibitor ICG001 significantly attenuated TGF-β-induced FMT. PD-L1 knockdown also attenuated TGF-β-induced GSK3β phosphorylation/inhibition and β-catenin upregulation, implicating GSK3β/β-catenin signaling in PD-L1-mediated FMT. Collectively, our findings demonstrate that fibroblast PD-L1 may promote pulmonary fibrosis through both Smad3 and β-catenin signaling and may represent a novel interventional target for IPF.

Hydrocortisone Long-term Treatment Effect on Immunomodulatory Properties of Human Adipose-Derived Mesenchymal Stromal/Stem Cells

Cortisol is secreted in prolonged stress and has therapeutic effects in inflammatory diseases. Considering the immunomodulatory effects of mesenchymal stem cells, here we investigated the effect of hydrocortisone (HC) long-term treatment on immunomodulatory properties of human adipose-derived mesenchymal stromal/stem cells (ASCs). Isolated ASCs from healthy subjects were treated with different HC concentrations for 14 days. The effect of HC-treated ASCs on the proliferative response of peripheral blood mononuclear cells (PBMCs) was evaluated in ASCs/2-way mixed leukocyte reaction coculture using 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT)-assay. HC-treated ASCs were further divided into interferon gamma (IFN-γ) stimulated and unstimulated groups. Transforming growth factor beta 1 (TGF-β1) and interleukin (IL)-6 levels were measured in culture supernatants by enzyme-linked immunosorbent assay. Relative expression of cyclooxygenase-2 (COX-2), hepatocyte growth factor, indoleamine dioxygenase, and programmed death-ligand 1 genes was assessed by real-time PCR. Levels of TGF-β1 and COX-2 expression were elevated in unstimulated ASCs, while exposure to high concentration of HC significantly increased TGF-β1 levels and reduced COX-2 expression. Unstimulated HC-5-μM-treated ASCs increased PBMC proliferation ratio on day 2 of coculture compared to the control group (P = 0.05). In IFN-γ stimulated condition, pretreatment with HC-5 μM resulted in a significantly increased IL-6 and significantly decreased COX-2 expression compared to the HC untreated control group. In conclusion, our results showed various alterations of ASC immunomodulatory related features as a result of long-term exposure of different concentrations of HC. It seems that HC at low concentration pushed the balance toward extended immune response in ASCs, while this observation wasn't persistent in ASCs treated with higher concentrations of HC.

p70 S6 kinase as a therapeutic target in cancers: More than just an mTOR effector

p70 S6 kinase (p70^S6K) is best-known for its regulatory roles in protein synthesis and cell growth by phosphorylating its primary substrate, ribosomal protein S6, upon mitogen stimulation. The enhanced expression/activation of p70^S6K has been correlated with poor prognosis in some cancer types, suggesting that it may serve as a biomarker for disease monitoring. p70^S6K is a critical downstream effector of the oncogenic PI3K/Akt/mTOR pathway and its activation is tightly regulated by an ordered cascade of Ser/Thr phosphorylation events. Nonetheless, it should be noted that other upstream mechanisms regulating p70^S6K at both the post-translational and post-transcriptional levels also exist. Activated p70^S6K could promote various aspects of cancer progression such as epithelial-mesenchymal transition, cancer stemness and drug resistance. Importantly, novel evidence showing that p70^S6K may also regulate different cellular components in the tumor microenvironment will be discussed. Therapeutic targeting of p70^S6K alone or in combination with traditional chemotherapies or other microenvironmental-based drugs such as immunotherapy may represent promising approaches against cancers with aberrant p70^S6K signaling. Currently, the only clinically available p70^S6K inhibitors are rapamycin analogs (rapalogs) which target mTOR. However, there are emerging p70^S6K-selective drugs which are going through active preclinical or clinical trial phases. Moreover, various screening strategies have been used for the discovery of novel p70^S6K inhibitors, hence bringing new insights for p70^S6K-targeted therapy.

Dedicator of Cytokinesis 2 (DOCK2) Deficiency Attenuates Lung Injury Associated with Chronic High-Fat and High-Fructose Diet-Induced Obesity

Obesity is a major risk factor for lung disease development. However, little is known about the impact of chronic high-fat and high-fructose (HFHF) diet-induced obesity on lung inflammation and subsequent pulmonary fibrosis. Herein we hypothesized that dedicator of cytokinesis 2 (DOCK2) promotes a proinflammatory phenotype of lung fibroblasts (LFs) to elicit lung injury and fibrosis in chronic HFHF diet-induced obesity. An HFHF diet for 20 weeks induced lung inflammation and profibrotic changes in wild-type C57BL/6 mice. CD68 and monocyte chemoattractant protein-1 (MCP-1) expression were notably increased in the lungs of wild-type mice fed an HFHF diet. An HFHF diet further increased lung DOCK2 expression that co-localized with fibroblast-specific protein 1, suggesting a role of DOCK2 in regulating proinflammatory phenotype of LFs. Importantly, DOCK2 knockout protected mice from lung inflammation and fibrosis induced by a HFHF diet. In primary human LFs, tumor necrosis factor-α (TNF-α) and IL-1β induced DOCK2 expression concurrent with MCP-1, IL-6, and matrix metallopeptidase 2. DOCK2 knockdown suppressed TNF-α-induced expression of these molecules and activation of phosphatidylinositol 3-kinase/AKT and NF-κB signaling pathways, suggesting a mechanism of DOCK2-mediated proinflammatory and profibrotic changes in human LFs. Taken together, these findings reveal a previously unrecognized role of DOCK2 in regulating proinflammatory phenotype of LFs, potentiation of lung inflammation, and pulmonary fibrosis in chronic HFHF diet-caused obesity.

At the Crossroads of Molecular Biology and Immunology: Molecular Pathways for Immunological Targeting of Head and Neck Squamous Cell Carcinoma

Background: Recent advances in immunotherapy for head and neck squamous cell carcinoma (HNSCC) have led to implementation of anti-programmed death receptor 1 (PD-1) immunotherapy to standard of care for recurrent/metastatic HNSCC. However, the majority of tumors do not respond to these therapies, indicating that these tumors are not immunogenic or other immunosuppressive mechanisms might be at play. Aim: Given their role in carcinogenesis as well as in immune modulation, we discuss the relation between the STAT3, PI3K/AKT/mTOR and Wnt signaling pathways to identify potential targets to empower the immune response against HNSCC. Results: We focused on three pathways. First, STAT3 is often overactivated in HNSCC and induces the secretion of immunosuppressive cytokines, thereby promoting recruitment of immune suppressive regulatory T cells and myeloid-derived suppressor cells to the tumor microenvironment (TME) while hampering the development of dendritic cells. Second, PI3K/AKT/mTOR mutational activation results in increased tumor proliferation but could also be important in HNSCC immune evasion due to the downregulation of components in the antigen-processing machinery. Third, canonical Wnt signaling is overactivated in >20% of HNSCC and could be an interesting pleotropic target since it is related to increased tumor cell proliferation and the development of an immunosuppressive HNSCC TME. Conclusion: The molecular pathology of HNSCC is complex and heterogeneous, varying between sites and disease etiology (i.e., HPV). The in HNSCC widely affected signaling pathways STAT3, PI3K/AKT/mTOR and Wnt are implicated in some of the very mechanisms underlying immune evasion of HNSCC, thereby representing promising targets to possibly facilitate immunotherapy response.

Biomarkers of everolimus efficacy in breast cancer therapy

OBJECTIVE

Everolimus is an inhibitor of serine/ threonine kinase mTOR. The drug is approved for the treatment of metastatic ER positive, HER2 negative breast cancers and benefits a subset of patients with these breast cancers in combination with hormonal therapies. Despite extensive efforts, no additional predictive biomarkers to guide therapeutic decisions for everolimus have been introduced in clinical practice.

DATA SOURCES

This paper discusses predictive biomarkers for everolimus efficacy in breast cancer. A search of the medline and web of science databases was performed using the words "everolimus" and "biomarkers". References of retrieved articles were manually scanned for additional relevant articles.

DATA SUMMARY

Everolimus benefits a subset of patients with metastatic ER positive, HER2 negative breast cancers in combination with hormonal therapies. Despite extensive efforts no additional predictive biomarkers to guide therapeutic decisions for everolimus therapy have been confirmed for use in clinical practice. However, promising biomarker leads for everolimus efficacy in breast cancer have been suggested and include expression of proteins in the mTOR pathway in ER positive, HER2 negative breast cancers. In HER2 positive cancers PIK3CA mutations, and PTEN expression loss are prognostic. Other clinical predictive biomarkers with more limited data include characteristics derived from whole genome sequencing, subsets of circulating leukocytes and changes in Standardized Uptake Values (SUV) of Positron Emission Tomography (PET) scans.

CONCLUSIONS

Putative predictive biomarkers for everolimus efficacy in breast cancer patients, both genomic and clinical, deserve further study and could lead to a better selection of responsive patients.

Ribosomal Protein S6: A Potential Therapeutic Target against Cancer?

Ribosomal protein S6 (RPS6) is a component of the 40S small ribosomal subunit and participates in the control of mRNA translation. Additionally, phospho (p)-RPS6 has been recognized as a surrogate marker for the activated PI3K/AKT/mTORC1 pathway, which occurs in many cancer types. However, downstream mechanisms regulated by RPS6 or p-RPS remains elusive, and the therapeutic implication of RPS6 is underappreciated despite an approximately half a century history of research on this protein. In addition, substantial evidence from RPS6 knockdown experiments suggests the potential role of RPS6 in maintaining cancer cell proliferation. This motivates us to investigate the current knowledge of RPS6 functions in cancer. In this review article, we reviewed the current information about the transcriptional regulation, upstream regulators, and extra-ribosomal roles of RPS6, with a focus on its involvement in cancer. We also discussed the therapeutic potential of RPS6 in cancer.

Sulforaphane enhances the antitumor response of chimeric antigen receptor T cells by regulating PD-1/PD-L1 pathway

BACKGROUND

Chimeric antigen receptor T (CAR-T) cell therapy has limited effects in the treatment of solid tumors. Sulforaphane (SFN) is known to play an important role in inhibiting tumor growth, but its effect on CAR-T cells remains unclear. The goal of the current study was to determine whether combined CAR-T cells and SFN could provide antitumor efficacy against solid tumors.

METHODS

The effect of combined SFN and CAR-T cells was determined in vitro using a co-culture system and in vivo using a xenograft mouse model. We further validated the effects of combination therapy in patients with cancer.

RESULTS

In vitro, the combination of SFN and CAR-T cells resulted in enhanced cytotoxicity and increased lysis of tumor cells. We found that SFN suppressed programmed cell death 1 (PD-1) expression in CAR-T cells and potentiated antitumor functions in vitro and in vivo. As a ligand of PD-1, programmed cell death ligand 1 (PD-L1) expression was also decreased in tumor cells after SFN treatment. In addition, β-TrCP was increased by SFN, resulting in higher activation of ubiquitination-mediated proteolysis of PD-L1, which induced PD-L1 degradation. The combination of SFN and CAR-T cell therapy acted synergistically to promote better immune responses in vivo compared with monotherapy. In clinical treatments, PD-1 expression was lower, and proinflammatory cytokine levels were higher in patients with various cancers who received CAR-T cells and took SFN orally than that in the control group.

CONCLUSION

SFN improves the cytotoxicity of CAR-T cells by modulating the PD-1/PD-L1 pathway, which may provide a promising strategy for the combination of SFN with CAR-T cells for cancer immunotherapy.

The ubiquitin E3 ligase FBXO22 degrades PD-L1 and sensitizes cancer cells to DNA damage

High expression of programmed death-ligand 1 (PD-L1) in cancer cells drives immune-independent, cell-intrinsic functions, leading to resistance to DNA-damaging therapies. We find that high expression of the ubiquitin E3 ligase FBXO22 sensitizes nonsmall cell lung cancer (NSCLC) cells to ionizing radiation (IR) and cisplatin, and that activation of FBXO22 by phosphorylation is necessary for this function. Importantly, FBXO22 activates PD-L1 ubiquitination and degradation, which in turn increases the sensitivity of NSCLC cells to DNA damage. Cyclin-dependent kinase 5 (CDK5), aberrantly active in cancer cells, plays a crucial role in increasing the expression of PD-L1 in medulloblastoma [R. D. Dorand et al, Science 353, 399-403 (2016)]. We show in NSCLC cells that inhibiting CDK5 or reducing its expression increases the level of FBXO22, decreases that of PD-L1, and increases the sensitivity of the cells to DNA damage. We conclude that FBXO22 is a substrate of CDK5, and that inhibiting CDK5 reduces PD-L1 indirectly by increasing FBXO22. Pairing inhibitors of CDK5 with immune checkpoint inhibitors may increase the efficacy of immune checkpoint blockade alone or in combination with DNA-damaging therapies.

Narrative review of emerging roles for AKT-mTOR signaling in cancer radioimmunotherapy

Objective

To summarize the roles of AKT-mTOR signaling in the regulation of the DNA damage response and PD-L1 expression in cancer cells, and propose a novel strategy of targeting AKT-mTOR signaling in combination with radioimmunotherapy in the era of cancer immunotherapy

Background

Immunotherapy has greatly improved the clinical outcomes of many cancer patients and has changed the landscape of cancer patient management. However, only a small subgroup of cancer patients (~20–30%) benefit from immune checkpoint blockade-based immunotherapy. The current challenge is to find biomarkers to predict the response of patients to immunotherapy and strategies to sensitize patients to immunotherapy.

Methods

Search and review the literature which were published in PUBMED from 2000–2021 with the key words mTOR, AKT, drug resistance, DNA damage response, immunotherapy, PD-L1, DNA repair, radioimmunotherapy.

Conclusions

More than 50% of cancer patients receive radiotherapy during their course of treatment. Radiotherapy has been shown to reduce the growth of locally irradiated tumors as well as metastatic non-irradiated tumors (abscopal effects) by affecting systemic immunity. Consistently, immunotherapy has been demonstrated to enhance radiotherapy with more than one hundred clinical trials of radiation in combination with immunotherapy (radioimmunotherapy) across cancer types. Nevertheless, current available data have shown limited efficacy of trials testing radioimmunotherapy. AKT-mTOR signaling is a major tumor growth-promoting pathway and is upregulated in most cancers. AKT-mTOR signaling is activated by growth factors as well as genotoxic stresses including radiotherapy. Importantly, recent advances have shown that AKT-mTOR is one of the main signaling pathways that regulate DNA damage repair as well as PD-L1 levels in cancers. These recent advances clearly suggest a novel cancer therapy strategy by targeting AKT-mTOR signaling in combination with radioimmunotherapy.

Tubeimoside-1 induces TFEB-dependent lysosomal degradation of PD-L1 and promotes antitumor immunity by targeting mTOR

Programmed cell death ligand 1 (PD-L1)/programmed cell death protein 1 (PD-1) cascade is an effective therapeutic target for immune checkpoint blockade (ICB) therapy. Targeting PD-L1/PD-1 axis by small-molecule drug is an attractive approach to enhance antitumor immunity. Using flow cytometry-based assay, we identify tubeimoside-1 (TBM-1) as a promising antitumor immune modulator that negatively regulates PD-L1 level. TBM-1 disrupts PD-1/PD-L1 interaction and enhances the cytotoxicity of T cells toward cancer cells through decreasing the abundance of PD-L1. Furthermore, TBM-1 exerts its antitumor effect in mice bearing Lewis lung carcinoma (LLC) and B16 melanoma tumor xenograft via activating tumor-infiltrating T-cell immunity. Mechanistically, TBM-1 triggers PD-L1 lysosomal degradation in a TFEB-dependent, autophagy-independent pathway. TBM-1 selectively binds to the mammalian target of rapamycin (mTOR) kinase and suppresses the activation of mTORC1, leading to the nuclear translocation of TFEB and lysosome biogenesis. Moreover, the combination of TBM-1 and anti-CTLA-4 effectively enhances antitumor T-cell immunity and reduces immunosuppressive infiltration of myeloid-derived suppressor cells (MDSCs) and regulatory T (Treg) cells. Our findings reveal a previously unrecognized antitumor mechanism of TBM-1 and represent an alternative ICB therapeutic strategy to enhance the efficacy of cancer immunotherapy.

At the Cutting Edge against Cancer: A Perspective on Immunoproteasome and Immune Checkpoints Modulation as a Potential Therapeutic Intervention

Immunoproteasome is a noncanonical form of proteasome with enzymological properties optimized for the generation of antigenic peptides presented in complex with class I MHC molecules. This enzymatic property makes the modulation of its activity a promising area of research. Nevertheless, immunotherapy has emerged as a front-line treatment of advanced/metastatic tumors providing outstanding improvement of life expectancy, even though not all patients achieve a long-lasting clinical benefit. To enhance the efficacy of the currently available immunotherapies and enable the development of new strategies, a broader knowledge of the dynamics of antigen repertoire processing by cancer cells is needed. Therefore, a better understanding of the role of immunoproteasome in antigen processing and of the therapeutic implication of its modulation is mandatory. Studies on the potential crosstalk between proteasome modulators and immune checkpoint inhibitors could provide novel perspectives and an unexplored treatment option for a variety of cancers.

Helicobacter urease suppresses cytotoxic CD8 + T cell responses through activating Myh9-dependent induction of PD-L1

As a key virulence factor for persistent colonization, Urease B subunit (UreB) is considered to be an ideal vaccine antigen against Helicobacter pylori (H. pylori) infection. However, the role and molecular mechanisms of UreB involved in immune microenvironment dysregulation still remains largely unknown. In the present study, we evaluated the effects of UreB on macrophage activation and found that UreB induced PD-L1 accumulation on Bone marrow-derived macrophages (BMDMs). Co-culture assays further revealed that UreB-induced PD-L1 expression on BMDMs significantly decreased the proliferation and secretion of cytolytic molecules (granzyme B and perforin) of splenic CD8 + T cells isolated from inactivated H. pylori-immunized mice. More importantly, myosin heavy chain 9 (Myh9) was confirmed to be a direct membrane receptor of UreB via using LC-MS/MS and Co-immunoprecipitation and required for PD-L1 upregulation on BMDMs. Molecular studies further demonstrated that the interaction between UreB and Myh9 decreased GCN2 autophosphorylation and enhanced intracellular pool of amino acids, leading to the upregulation of S6K phosphorylation, a commonly used marker for monitoring activation of mTORC1 signaling activity. Furthermore, blocking mTORC1 activation with its inhibitor Temsirolimus reversed UreB-induced PD-L1 upregulation and the subsequently inhibitory effects of BMDMs on activation of cytotoxic CD8 + T cell responses. Overall, our data unveil a novel immunosuppressive mechanism of UreB during H. pylori infection, which may provide valuable clue for the optimization of H. pylori vaccine.

Membrane-Associated RING-CH 8 Functions as a Novel PD-L1 E3 Ligase to Mediate PD-L1 Degradation Induced by EGFR Inhibitors

Expression of programmed death-ligand 1 (PD-L1) on cancer cells is a critical mechanism contributing to immunosuppression and immune escape. PD-L1 expression may also affect therapeutic outcomes of epidermal growth factor receptor (EGFR)-targeted therapy (e.g., with osimertinib/AZD9291) against EGFR-mutant non-small cell lung cancers (NSCLC) and can even be altered during the treatment albeit with largely undefined mechanisms. This study primarily focuses on elucidating the mechanism by which osimertinib induces PD-L1 degradation in addition to validating osimertinib's effect on decreasing PD-L1 expression in EGFR-mutant NSCLC cells and tumors. Osimertinib and other EGFR inhibitors effectively decreased PD-L1 levels primarily in EGFR-mutant NSCLCs and xenografted tumors. Osimertinib not only decreased PD-L1 mRNA expression, but also prompted proteasomal degradation of PD-L1 protein, indicating both transcriptional and posttranslational mechanisms accounting for osimertinib-induced reduction of PD-L1. Knockdown of β-TrCP or inhibition of GSK3 failed to prevent PD-L1 reduction induced by osimertinib. Rather, knockdown of membrane-associated RING-CH 8 (MARCH8) that encodes a membrane-bound E3 ubiquitin ligase rescued osimertinib-induced PD-L1 reduction. Furthermore, manipulation of MARCH8 expression accordingly altered PD-L1 degradation rate. Critically, MARCH8 interacted with PD-L1 through its N-terminal region and also ubiquitinated PD-L1 in cells. Collectively, these results strongly suggest that MARCH8 is a previously undiscovered E3 ubiquitin ligase responsible for PD-L1 degradation including osimertinib-induced PD-L1 degradation, establishing a novel connection between MARCH8 and PD-L1 regulation. IMPLICATIONS: This study has demonstrated a previously undiscovered function of MARCH8 in mediating PD-L1 degradation induced by EGFR inhibitors in EGFR-mutant NSCLC cells, establishing a novel connection between MARCH8 and PD-L1 regulation.

eEF2K enhances expression of PD-L1 by promoting the translation of its mRNA

Emerging advances in cancer therapy have transformed the landscape towards cancer immunotherapy regimens. Recent discoveries have resulted in the development of clinical immune checkpoint inhibitors that are 'game-changers' for cancer immunotherapy. Here we show that eEF2K, an atypical protein kinase that negatively modulates the elongation stage of protein synthesis, promotes the synthesis of PD-L1, an immune checkpoint protein which helps cancer cells to escape from immunosurveillance. Ablation of eEF2K in prostate and lung cancer cells markedly reduced the expression levels of the PD-L1 protein. We show that eEF2K promotes the association of PD-L1 mRNAs with translationally active polyribosomes and that translation of the PD-L1 mRNA is regulated by a uORF (upstream open reading-frame) within its 5'-UTR (5'-untranslated region) which starts with a non-canonical CUG as the initiation codon. This inhibitory effect is attenuated by eEF2K thereby allowing higher levels of translation of the PD-L1 coding region and enhanced expression of the PD-L1 protein. Moreover, eEF2K-depleted cancer cells are more vulnerable to immune attack by natural killer cells. Therefore, control of translation elongation can modulate the translation of this specific mRNA, one which contains an uORF that starts with CUG, and perhaps others that contain a similar feature. Taken together, our data reveal that eEF2K regulates PD-L1 expression at the level of the translation of its mRNA by virtue of a uORF in its 5'-region. This, and other roles of eEF2K in cancer cell biology (e.g. in cell survival and migration), may be exploited for the design of future therapeutic strategies.

Emerging Role of Ubiquitination in the Regulation of PD-1/PD-L1 in Cancer Immunotherapy

A growing amount of evidence suggests that ubiquitination and deubiquitination of programmed death 1 (PD-1)/programmed death-ligand 1 (PD-L1) play crucial roles in the regulation of PD-1 and PD-L1 protein stabilization and dynamics. PD-1/PD-L1 is a major coinhibitory checkpoint pathway that modulates immune escape in cancer patients, and its engagement and inhibition has significantly reshaped the landscape of tumor clearance. The abnormal ubiquitination and deubiquitination of PD-1/PD-L1 influence PD-1/PD-L1-mediated immunosuppression. In this review, we describe the ubiquitination- and deubiquitination-mediated modulation of PD-1/PD-L1 signaling through a variety of E3 ligases and deubiquitinating enzymes (DUBs). Moreover, we briefly expound on the anticancer potential of some agents that target related E3 ligases, which further modulate the ubiquitination of PD-1/PD-L1 in cancers. Therefore, this review reveals the development of a highly promising therapeutic approach for cancer immunotherapy by targeting PD-1/PD-L1 ubiquitination.

mTOR-targeted cancer therapy: great target but disappointing clinical outcomes, why?

The mammalian target of rapamycin (mTOR) critically regulates several essential biological functions, such as cell growth, metabolism, survival, and immune response by forming two important complexes, namely, mTOR complex 1 (mTORC1) and complex 2 (mTORC2). mTOR signaling is often dysregulated in cancers and has been considered an attractive cancer therapeutic target. Great efforts have been made to develop efficacious mTOR inhibitors, particularly mTOR kinase inhibitors, which suppress mTORC1 and mTORC2; however, major success has not been achieved. With the strong scientific rationale, the intriguing question is why cancers are insensitive or not responsive to mTOR-targeted cancer therapy in clinics. Beyond early findings on induced activation of PI3K/Akt, MEK/ERK, and Mnk/eIF4E survival signaling pathways that compromise the efficacy of rapalog-based cancer therapy, recent findings on the essential role of GSK3 in mediating cancer cell response to mTOR inhibitors and mTORC1 inhibition-induced upregulation of PD-L1 in cancer cells may provide some explanations. These new findings may also offer us the opportunity to rationally utilize mTOR inhibitors in cancer therapy. Further elucidation of the biology of complicated mTOR networks may bring us the hope to develop effective therapeutic strategies with mTOR inhibitors against cancer.

PD-L1 degradation pathway and immunotherapy for cancer

Programmed death ligand 1 (PD-L1, CD274) is an essential immune checkpoint protein that binds to programmed death 1 (PD-1) on T-lymphocytes. T cell plays a critical role in killing cancer cells while the cancer cell exhibits immune escape by the expression of PD-L1. The binding of PD-L1 to PD-1 inhibits T cell proliferation and activity, leading to tumor immunosuppression. Increasing evidence shows that PD-L1 protein undergoes degradation in proteasomes or lysosomes by multiple pathways, leading to enhanced immunotherapy for cancer. Although some specific drugs induce PD-L1 degradation and increase antitumor activity, the combination of these drugs with PD-L1/PD-1 blockade significantly enhances cancer immunotherapy. In this review, we have discussed the interaction of PD-L1 degradation with cancer immunotherapy.

The characteristics and roles of β-TrCP1/2 in carcinogenesis

β-transducin repeat-containing protein (β-TrCP), one of the well-characterized F-box proteins, acts as a substrate receptor and constitutes an active SCF^β-TrCP E3 ligase with a scaffold protein CUL1, a RING protein RBX1, and an adaptor protein SKP1. β-TrCP plays a critical role in the regulation of various physiological and pathological processes, including signal transduction, cell cycle progression, cell migration, DNA damage response, and tumorigenesis, by governing burgeoning amounts of key regulators for ubiquitination and proteasomal degradation. Given that a variety of β-TrCP substrates are well-known oncoproteins and tumor suppressors, and dysregulation of β-TrCP is frequently identified in human cancers, β-TrCP plays a vital role in carcinogenesis. In this review, we first briefly introduce the characteristics of β-TrCP1, β-TrCP2, and SCF^β-TrCP ubiquitin ligase, and then discuss SCF^β-TrCP ubiquitin ligase regulated biological processes by targeting its substrates for degradation. Moreover, we summarize the regulation of β-TrCP1 and β-TrCP2 at multiple layers and further discuss the various roles of β-TrCP1 and β-TrCP2 in human cancer, functioning as either an oncoprotein or a tumor suppressor in a manner dependent of cellular context. Finally, we provide novel insights for future perspectives on the potential of targeting β-TrCP1 and β-TrCP2 for cancer therapy.