Caspase-8: A key protein of cross-talk signal way in "PANoptosis" in cancer.

Cysteinyl aspartate specific proteinase (Caspase)-8 has long been considered a promoter of apoptosis and part of the mechanism by which cytotoxic drugs kill cancer cells. With the continuous exploration of the types of programmed cell death, an increasing number of studies have confirmed that caspase-8 plays an important role in cancer. Recently, scholars have proposed the term "PANoptosis," which mainly includes three programmed cell death modes, namely pyroptosis, apoptosis and necroptosis. In addition to mediating endogenous apoptotic pathways, caspase-8 can also participate in the cleavage of gasdermin (GSDM) family proteins to induce pyroptosis. Furthermore, the expression of enzymatically inactive caspase-8 (C362S) can cause embryonic lethality and inflammatory tissue destruction in mice by inducing necroptosis and pyroptosis. Therefore, the activation and deletion of caspase-8 enzyme activity, as well as the knockout of the coding gene, are closely related to "PANoptosis." In addition, caspase-8 can also improve the tumor microenvironment and enhance tumor antiimmunity. Studies have shown that caspase-8 is also associated with tumor growth and invasion, angiogenesis and metastasis, therapeutic resistance and poor clinical outcomes. Therefore, it is very important to measure the cancer-promoting and anticancer effects of caspase-8 and find a balance, and to study its role in the effect of "PANoptosis" in depth. This article reviews the role of caspase-8 in "PANoptosis" in cancer to provide new strategies and targets for cancer.

Pyroptosis, a new bridge to tumor immunity.

Pyroptosis refers to the process of gasdermin (GSDM)-mediated programmed cell death (PCD). Our understanding of pyroptosis has expanded beyond cells and is known to involve extracellular responses. Recently, there has been an increasing interest in pyroptosis due to its emerging role in activating the immune system. In the meantime, pyroptosis-mediated therapies, which use the immune response to kill cancer cells, have also achieved notable success in a clinical setting. In this review, we discuss that the immune response induced by pyroptosis activation is a double-edged sword that affects all stages of tumorigenesis. On the one hand, the activation of inflammasome-mediated pyroptosis and the release of pyroptosis-produced cytokines alter the immune microenvironment and promote the development of tumors by evading immune surveillance. On the other hand, pyroptosis-produced cytokines can also collect immune cells and ignite the immune system to improve the efficiency of tumor immunotherapies. Pyroptosis is also related to some immune checkpoints, especially programmed death-1 (PD-1) or programmed death- ligand 1 (PD-L1). In this review, we mainly focus on our current understanding of the interplay between the immune system and tumors that process through pyroptosis, and debate their use as potential therapeutic targets.

Photodynamic therapy induces human esophageal carcinoma cell pyroptosis by targeting the PKM2/caspase-8/caspase-3/GSDME axis.

Photodynamic therapy (PDT) uses a photosensitizer (PS) and visible light to induce cancer cell death. Pyroptosis is a new type of programmed cell death that is associated with the gasdermin protein family. However, the precise mechanism of pyroptosis in PDT-induced suppression of esophageal cancer remains unknown. We demonstrate that PDT can induce gasdermin E (GSDME)-mediated pyroptosis, which is characterized by the formation of pyroptotic blebs in esophageal squamous cell carcinoma (ESCC), which burst and release intracellular contents and pro-inflammatory mediators. Mechanistically, PDT may inhibit pyruvate kinase M2 (PKM2) and consequently, activate caspase-8 and caspase-3, which ultimately releases N-GSDME and triggers pyroptosis in ESCC. Moreover, PDT decreased the efficiency of pyroptosis in the presence of a glycolytic inhibitor. Overall, our results show that PDT induces pyroptosis in ESCC by targeting the PKM2/caspase-8/caspase-3/GSDME axis. This is the first in-depth study of the specific mechanism underlying PKM2-mediated pyroptosis under PDT in ESCC, and potentially has great implications for the clinical application of PDT in ESCC.

eEF2K as a novel metastatic and prognostic biomarker in gastric cancer patients.

BACKGROUND: Although eukaryotic elongation factor 2 kinase (eEF2K) has been reported to be a potential oncogenic factor in many human cancers, its usefulness as a clinical prognostic biomarker for gastric cancer has not been investigated. METHODS: In this study, data about 540 patients with stomach adenocarcinoma (STAD) were analyzed from The Cancer Genome Atlas (TCGA) and the Gene Expression Omnibus (GEO) databases to determine the expression of eEF2K. Immunohistochemistry (IHC), western blots, and real-time polymerase chain reaction (RT-PCR) were also performed to determine the clinical significance of eEF2K expression in 96 postoperative patients with gastric cancer. Among the 96 patients, 36 had low expression of eEF2K and 60 had high expression. RESULTS: Analysis of the TCGA and GEO datasets revealed that eEF2K expression was significantly higher in the STAD tissue samples than in the non-tumorous gastric tissues. IHC, western blots, and RT-PCR confirmed these findings. The high expression level of eEF2K was found to be related to the presence of lymph node metastasis (p = 0.002). Moreover, multivariate analysis showed that eEF2K was an independent indicator of prognosis for overall survival (OS) (hazard ratio [HR] = 1.72, 95% confidence interval [CI] = 1.06-2.79; p = 0.03) and disease-free survival (DFS) (HR = 1.66, 95% CI = 0.997-2.765; p = 0.052) in patients with surgically resected STAD. CONCLUSION: Collectively, our findings suggest that eEF2K is a clinical indicator of metastatic and prognostic significance for STAD survival and could serve as a potential therapeutic target.

Dihydroartemisinin mediating PKM2-caspase-8/3-GSDME axis for pyroptosis in esophageal squamous cell carcinoma.

Pyroptosis is a novel type of pro-inflammatory programmed cell death that has been strongly reported to be related to inflammation, immune, and cancer. Dihydroartemisinin (DHA) has good anti-tumor properties. However, the exact mechanism by which DHA induces pyroptosis to inhibit esophageal squamous cell carcinoma (ESCC) remains unclear. After applying DHA treatment to ESCC, we found that some dying cells exhibited the characteristic morphology of pyroptosis, such as blowing large bubbles from the cell membrane, accompanied by downregulation of pyruvate kinase isoform M2 (PKM2), activation of caspase-8/3, and production of GSDME-NT. Meanwhile, it was accompanied by an increased release of LDH and inflammatory factors (IL-18 and IL-1ß). Both knockdown of GSDME and application of caspase-8/3 specific inhibitors (z-ITED-FMK/Ac-DEVD-CHO) significantly inhibited DHA-induced pyroptosis. However, the former did not affect the activation of caspase-3. In contrast, overexpression of PKM2 inhibited caspase-8/3 activation as well as GSDME-N production. Furthermore, both si-GSDME and OE-PKM2 inhibited DHA-induced pyroptosis in vivo and in vitro. Therefore, the results suggest that DHA can induce pyroptosis of ESCC cells via the PKM2-caspase-8/3-GSDME pathway. Implication: In this study, we identified new mechanism of DHA in inhibiting ESCC development and progression, and provide a potential therapeutic agent for the treatment of ESCC.

Antiviral Effect of Epigallocatechin Gallate via Impairing Porcine Circovirus Type 2 Attachment to Host Cell Receptor.

The green tea catechin epigallocatechin gallate (EGCG) exhibits antiviral activity against various viruses. Whether EGCG also inhibits the infectivity of circovirus remains unclear. In this study, we demonstrated the antiviral effect of EGCG on porcine circovirus type 2 (PCV2). EGCG targets PCV2 virions directly and blocks the attachment of virions to host cells. The microscale thermophoresis assay showed EGCG could interact with PCV2 capsid protein in vitro with considerable affinity (Kd = 98.03 ± 4.76 µM), thereby interfering with the binding of the capsid to the cell surface receptor heparan sulfate. The molecular docking analysis of capsid-EGCG interaction identified the key amino acids which formed the binding pocket accommodating EGCG. Amino acids ARG51, ASP70, ARG73 and ASP78 of capsid were found to be critical for maintaining the binding, and the arginine residues were also essential for the electrostatic interaction with heparan sulfate. The rescued mutant viruses also confirm the importance of the key amino acids of the capsid to the antiviral effect of EGCG. Our findings suggest that catechins could act as anti-infective agents against circovirus invasion, as well as provide the basic information for the development and synthesis of structure-based anti-circovirus drugs.

[Porcine transcription factor AP-2δ promotes porcine circovirus type 2 replication through enhancing the activity of the rep gene promoter].

Several putative transcription factor binding sites (TFBSs) exist in the PCV2 rep gene promoter. To explore if porcine circovirus type 2 (PCV2) could regulate the viral replication by using these TFBSs, we conducted electrophoretic mobility shift assay (EMSA), DNA-pull down and liquid chromatography-tandem mass spectrometric (LC-MS/MS) assays. EMSA confirmed the binding activity of the rep gene promoter with nuclear proteins of host cells. DNA-pull down and LC-MS/MS identified the porcine transcription factor AP-2δ (poTFAP2δ) could bind the PCV2 rep gene promoter. Dual-luciferase reporter assay, quantitative real-time PCR, Western blotting and indirect immunofluorescent assay demonstrated that poTFAP2δ could not only promote the activity of the rep gene promoter, but also enhance the transcription/translation activity of the rep/cap gene and the virus titer of PCV2 during the entire life cycle of PCV2 infection. This study revealed the molecular mechanism of PCV2 using host proteins to enhance the viral replication, provided a new perspective for studying the pathogenic mechanism of PCV2 from virus and host interactions, and provided a theoretical basis for developing highly effective PCV2 vaccines.