ATXN2-Mediated PI3K/AKT Activation Confers Gastric Cancer Chemoresistance and Attenuates CD8+ T Cell Cytotoxicity

Regulation of the CD8⁺ T cell and PDL1/PD1 axis in gastric cancer: Unraveling the molecular landscape

Gastric cancer (GC) remains a significant global health burden, mainly due to immune evasion mechanisms within its complex tumor microenvironment (TME). The interaction between CD8⁺ T cells and the PD1/PDL1 axis is central to these mechanisms. CD8⁺ T cells, key players in antitumor immunity, often exhibit impaired functionality in the GC TME, primarily due to PD1-mediated inhibitory signaling induced by PDL1 expressed on tumor and immune cells. Recent findings have elucidated intricate molecular interactions governing PD1 expression on CD8⁺ T cells and the modulation of PDL1 on tumor cells and immune cells by diverse signals such as cytokines, metabolic factors, and noncoding RNAs. While high PD1 expression typically indicates CD8⁺ T cell exhaustion and poor clinical outcomes, recent studies highlight scenarios where elevated PD1 levels correlate with preserved or enhanced T cell cytotoxic activity, suggesting nuanced regulatory pathways. Therapeutic strategies that disrupt PD1/PDL1 interactions, through checkpoint inhibitors or pharmacological modulation, have demonstrated potential in reactivating antitumor responses. However, resistance mechanisms, including altered antigen presentation, metabolic reprogramming, and immunosuppressive cell infiltration, continue to limit efficacy. Emerging combination therapies, biomarker-driven patient stratification, and novel targets like noncoding RNAs and exosomal PDL1 represent promising avenues to enhance treatment effectiveness. This review synthesizes current insights into the molecular regulation of CD8⁺ T cell functionality and the PD1/PDL1 axis, highlighting potential therapeutic strategies to restore antitumor immunity and improve patient outcomes in gastric cancer.

Overcoming immunotherapy resistance in gastric cancer: insights into mechanisms and emerging strategies

Gastric cancer (GC) remains a leading cause of cancer-related mortality worldwide, with limited treatment options in advanced stages. Immunotherapy, particularly immune checkpoint inhibitors (ICIs) targeting PD1/PD-L1, has emerged as a promising therapeutic approach. However, a significant proportion of patients exhibit primary or acquired resistance, limiting the overall efficacy of immunotherapy. This review provides a comprehensive analysis of the mechanisms underlying immunotherapy resistance in GC, including the role of the tumor immune microenvironment, dynamic PD-L1 expression, compensatory activation of other immune checkpoints, and tumor genomic instability. Furthermore, the review explores GC-specific factors such as molecular subtypes, unique immune evasion mechanisms, and the impact of Helicobacter pylori infection. We also discuss emerging strategies to overcome resistance, including combination therapies, novel immunotherapeutic approaches, and personalized treatment strategies based on tumor genomics and the immune microenvironment. By highlighting these key areas, this review aims to inform future research directions and clinical practice, ultimately improving outcomes for GC patients undergoing immunotherapy.

NNMT suppresses H3K9me3 to facilitate malignant progression and drug resistance in gastric cancer

BACKGROUND AND STUDY AIMS

Nicotinamide N-methyltransferase (NNMT) is aberrantly expressed in tumors and is implicated in the progression and chemoresistance of cancers. This project attempts to explore the specific molecular mechanism by which NNMT enhances 5-fluorouracil (5-FU) resistance in gastric cancer (GC).

MATERIALS AND METHODS

By bioinformatics analysis, the expression of NNMT in GC was analyzed and its relationship with patients' prognoses was examined. The signaling pathway enriched by NNMT was analyzed by the Kyoto Encyclopedia of Genes and Genomes (KEGG). Western blot (WB) and quantitative reverse transcription polymerase chain reaction (qRT-PCR) were employed to measure the mRNA and protein expression of NNMT in normal gastric epithelial cells and GC cells. CCK8 was employed to measure cell viability and the IC50 of 5-FU. The apoptosis rate was assessed by Flow cytometry. WB measured the protein expression of Ki67, epithelial-mesenchymal transition (EMT)-related proteins, PI3K, AKT, p-AKT, NNMT, and H3K9me3. We applied the Transwell assay to measure cell migration and invasion ability. The content of S-adenosylmethionine (SAM) and S-adenosyl-L-homocysteine (SAH) in cells was measured by enzyme-linked immunosorbent assay (ELISA).

RESULT

NNMT was greatly upregulated in GC tissues and cells, exhibiting a negative linkage with patients' prognoses. Knocking down NNMT remarkably repressed the vitality, proliferation, anti-apoptotic ability, migration, and invasion of GC cells but elevated the sensitivity of cancer cells to 5-FU. However, overexpression of NNMT inhibited H3K9 methylation by reducing the universal methyl donor SAM, activated the PI3K/AKT pathway, facilitated GC malignant progression, and triggered resistance to 5-FU.

CONCLUSION

Upregulation of NNMT expression in GC cells can induce 5-FU resistance by repressing the activation of PI3K/AKT through the inhibition of histone methylation.

Emerging roles of non-coding RNAs in modulating the PI3K/Akt pathway in cancer

Cancer progression results from the dysregulation of molecular pathways, each with unique features that can either promote or inhibit tumor growth. The complexity of carcinogenesis makes it challenging for researchers to target all pathways in cancer therapy, emphasizing the importance of focusing on specific pathways for targeted treatment. One such pathway is the PI3K/Akt pathway, which is often overexpressed in cancer. As tumor cells progress, the expression of PI3K/Akt increases, further driving cancer advancement. This study aims to explore how ncRNAs regulate the expression of PI3K/Akt. NcRNAs are found in both the cytoplasm and nucleus, and their functions vary depending on their location. They can bind to the promoters of PI3K or Akt, either reducing or increasing their expression, thus influencing tumorigenesis. The ncRNA/PI3K/Akt axis plays a crucial role in determining cell proliferation, metastasis, epithelial-mesenchymal transition (EMT), and even chemoresistance and radioresistance in human cancers. Anti-tumor compounds can target ncRNAs to modulate the PI3K/Akt axis. Moreover, ncRNAs can regulate the PI3K/Akt pathway both directly and indirectly.

Protein Phosphatase 2A Promotes CD8+ T Cell Effector Function through the Augmentation of CD28 Costimulation

Protein phosphatase 2A (PP2A) is one of the most abundant serine/threonine phosphatases and plays critical roles in regulating cell fate and function. We previously showed that PP2A regulates the differentiation of CD4+ T cells and the development of thymocytes. Nevertheless, its role in CD8+ T cells remains elusive. By ablating the catalytic subunit α (Cα) of PP2A in CD8+ T cells, we revealed the essential role of PP2A in promoting the effector functions of CD8+ T cells. Notably, PP2A Cα-deficient CD8+ T cells exhibit reduced proliferation and decreased cytokine production upon stimulation in vitro. In vivo, mice lacking PP2A Cα in T cells displayed defective immune responses against lymphocytic choriomeningitis virus infection, associated with reduced CD8+ T cell expansion and decreased cytokine production. Consistently, the ablation of the PP2A Cα subunit in CD8+ T cells results in attenuated antitumor activity in mice. There is a notable decrease in the infiltration of PP2A Cα-deficient CD8+ T cells within the tumor microenvironment, and the cells that do infiltrate exhibit diminished effector functions. Mechanistically, PP2A Cα deficiency impedes CD28-induced AKT Ser473 phosphorylation, thus impairing CD8+ T cell costimulation signal. Collectively, our findings underscore the critical role of phosphatase PP2A as a propeller for CD28-mediated costimulation signaling in CD8+ T cell effector function by fine-tuning T cell activation.

Sphingosine kinase 1 counteracts chemosensitivity and immune evasion in diffuse large B cell lymphoma cells via the PI3K/AKT/PD-L1 axis

Diffuse large B-cell lymphoma (DLBCL) is a highly aggressive neoplasm of lymphatic system that represent 38-58 % of non-Hodgkin lymphoma. Chemoresistance and immune escape constitute the major obstacles to the treatment of patients. Sphingosine kinase 1 (SphK1) is involved in multiple processes of cancer. Up to now, little research focuses on its function in DLBCL. In the current research, GEPIA and human Protein Atlas databases confirmed high expression of SphK1 in DLBCL tissues. Analogously, increased expression of SphK1 were determined in DLBCL tissues and cells. Intriguingly, knockdown of SphK1 suppressed DLBCL cell viability and increased chemosensitivity to doxorubicin by decreasing cell viability and increasing caspase-3 activity. Reversely, SphK1 elevation facilitated cancer cell resistance to doxorubicin. Furthermore, loss of SphK1 increased the productions of inflammatory cytokine IFN-γ and TNF-α, but reduced IL-10 levels in co-culture model of CD8 + T cells and DLBCL cells. Importantly, SphK1 knockdown enhanced T cell cytotoxicity to DLBCL cells, while its elevation restrained the ability of T cells to kill cancer cells. Concomitantly, targeting SphK1 enhanced the percentage of CD8 + T cells and attenuated co-culture-evoked CD8 + T cell apoptosis, indicating the important roles in T cell escape. Mechanically, SphK1 overexpression enhanced and its knockdown suppressed activation of the PI3K/AKT/PD-L1 pathway. After blockage of this pathway by its antagonist, the beneficial effects of SpHK1 on chemoresistance and immune escape were abrogated. In vivo, targeting SphK1 inhibited tumor growth and enhanced the anti-tumor efficacy of doxorubicin in DLBCL xenograft tumor, concomitant with the inhibition of the PI3K/AKT/PD-L1 signaling. Collectively, SphK1 knockdown counteracted chemoresistance and immune escape from T cell killing by inhibiting the PI3K/AKT/PD-L1 pathway. Therefore, targeting SphK1 may represent a promising therapeutic strategy for overcoming chemoresistance and immune escape in DLBCL.

Ataxin-2: a powerful RNA-binding protein

Ataxin-2 (ATXN2) was originally discovered in the context of spinocerebellar ataxia type 2 (SCA2), but it has become a key player in various neurodegenerative diseases. This review delves into the multifaceted roles of ATXN2 in human diseases, revealing its diverse molecular and cellular pathways. The impact of ATXN2 on diseases extends beyond functional outcomes; it mainly interacts with various RNA-binding proteins (RBPs) to regulate different stages of post-transcriptional gene expression in diseases. With the progress of research, ATXN2 has also been found to play an important role in the development of various cancers, including breast cancer, gastric cancer, pancreatic cancer, colon cancer, and esophageal cancer. This comprehensive exploration underscores the crucial role of ATXN2 in the pathogenesis of diseases and warrants further investigation by the scientific community. By reviewing the latest discoveries on the regulatory functions of ATXN2 in diseases, this article helps us understand the complex molecular mechanisms of a series of human diseases related to this intriguing protein.

Helicobacter pylori infection induces POU5F1 upregulation and SPP1 activation to promote chemoresistance and T cell inactivation in gastric cancer cells

Infection with Helicobacter pylori (H. pylori or Hp) is associated with an increased susceptibility to gastric diseases, notably gastric cancer (GC). This study investigates the impact of Hp infection on chemoresistance and immune activity in GC cells. Hp infection in AGS and MKN-74 cells promoted proliferation, migration and invasion, apoptosis resistance, and tumorigenic activity of cells under cisplatin (DDP) plus gemcitabine (GEM) treatment. Additionally, it dampened activity of the co-cultured CD8+ T cells. Hp infection increased POU class 5 homeobox 1 (POU5F1) level, which further activated secreted phosphoprotein 1 (SPP1) transcription to increase its expression. Silencing of either SPP1 or POU5F1 enhanced the GEM sensitivity in GC cells, and it increased the populations of CD8+ T cells and the secretion of immune-active cytokines both in vitro and in xenograft tumors in immunocompetent mice. However, the effects of POU5F1 silencing were counteracted by SPP1 overexpression. Furthermore, the POU5F1/SPP1 axis activated the PI3K/AKT signaling pathway. This study demonstrates that Hp infection induces POU5F1 upregulation and SPP1 activation, leading to increased DDP/GEM resistance and T cell inactivation in GC cells.

Deciphering drug resistance in gastric cancer: Potential mechanisms and future perspectives

Gastric cancer (GC) is a malignant tumor that originates from the epithelium of the gastric mucosa. The latest global cancer statistics show that GC ranks fifth in incidence and fourth in mortality among all cancers, posing a serious threat to public health. While early-stage GC is primarily treated through surgery, chemotherapy is the frontline option for advanced cases. Currently, commonly used chemotherapy regimens include FOLFOX (oxaliplatin + leucovorin + 5-fluorouracil) and XELOX (oxaliplatin + capecitabine). However, with the widespread use of chemotherapy, an increasing number of cases of drug resistance have emerged. This article primarily explores the potential mechanisms of chemotherapy resistance in GC patients from five perspectives: cell death, tumor microenvironment, non-coding RNA, epigenetics, and epithelial-mesenchymal transition. Additionally, it proposes feasibility strategies to overcome drug resistance from four angles: cancer stem cells, tumor microenvironment, natural products, and combined therapy. The hope is that this article will provide guidance for researchers in the field and bring hope to more GC patients.

miRNA/epithelial-mesenchymal axis (EMT) axis as a key player in cancer progression and metastasis: A focus on gastric and bladder cancers

The metastasis a major hallmark of tumors that its significant is not only related to the basic research, but clinical investigations have revealed that majority of cancer deaths are due to the metastasis. The metastasis of tumor cells is significantly increased due to EMT mechanism and therefore, inhibition of EMT can reduce biological behaviors of tumor cells and improve the survival rate of patients. One of the gaps related to cancer metastasis is lack of specific focus on the EMT regulation in certain types of tumor cells. The gastric and bladder cancers are considered as two main reasons of death among patients in clinical level. Herein, the role of EMT in regulation of their progression is evaluated with a focus on the function of miRNAs. The inhibition/induction of EMT in these cancers and their ability in modulation of EMT-related factors including ZEB1/2 proteins, TGF-β, Snail and cadherin proteins are discussed. Moreover, lncRNAs and circRNAs in crosstalk of miRNA/EMT regulation in these tumors are discussed and final impact on cancer metastasis and response of tumor cells to the chemotherapy is evaluated. Moreover, the impact of miRNAs transferred by exosomes in regulation of EMT in these cancers are discussed.