Dying from within: granzyme B converts entosis to emperitosis

Non-apoptotic regulated cell death mediates reprogramming of the tumour immune microenvironment by macrophages

Tumour immune microenvironment (TIME) plays an indispensable role in tumour progression, and tumour-associated macrophages (TAMs) are the most abundant immune cells in TIME. Non-apoptotic regulated cell death (RCD) can avoid the influence of tumour apoptosis resistance on anti-tumour immune response. Specifically, autophagy, ferroptosis, pyroptosis and necroptosis mediate the crosstalk between TAMs and tumour cells in TIME, thus reprogram TIME and affect the progress of tumour. In addition, although some achievements have been made in immune checkpoint inhibitors (ICIs), there is still defect that ICIs are only effective for some people because non-apoptotic RCD can bypass the apoptosis resistance of tumour. As a result, ICIs combined with targeting non-apoptotic RCD may be a promising solution. In this paper, the basic molecular mechanism of non-apoptotic RCD, the way in which non-apoptotic RCD mediates crosstalk between TAMs and tumour cells to reprogram TIME, and the latest research progress in targeting non-apoptotic RCD and ICIs are reviewed.

The Mechanisms of Regulated Cell Death: Structural and Functional Proteomic Pathways Induced or Inhibited by a Specific Protein-A Narrative Review

Billions of cells die in us every hour, and our tissues do not shrink because there is a natural regulation where Cell Death (CD) is balanced with cell division. The process in which cells eliminate themselves in a controlled manner is called Programmed Cell Death (PCD). The PCD plays an important role during embryonic development, in maintaining homeostasis of the body's tissues, and in the elimination of damaged cells, under a wide range of physiological and developmental stimuli. A multitude of protein mediators of PCD have been identified and signals have been found to utilize common pathways elucidating the proteins involved. This narrative review focuses on caspase-dependent and caspase-independent PCD pathways. Included are studies of caspase-dependent PCD such as Anoikis, Catastrophe Mitotic, Pyroptosis, Emperitosis, Parthanatos and Cornification, and Caspase-Independent PCD as Wallerian Degeneration, Ferroptosis, Paraptosis, Entosis, Methuosis, and Extracellular Trap Abnormal Condition (ETosis), as well as neutrophil extracellular trap abnormal condition (NETosis) and Eosinophil Extracellular Trap Abnormal Condition (EETosis). Understanding PCD from those reported in this review could shed substantial light on the processes of biological homeostasis. In addition, identifying specific proteins involved in these processes is mandatory to identify molecular biomarkers, as well as therapeutic targets. This knowledge could provide the ability to modulate the PCD response and could lead to new therapeutic interventions in a wide range of diseases.

Cell-in-cell structure mediates in-cell killing suppressed by CD44

Penetration of immune cells into tumor cells was believed to be immune-suppressive via cell-in-cell (CIC) mediated death of the internalized immune cells. We unexpectedly found that CIC formation largely led to the death of the host tumor cells, but not the internalized immune cells, manifesting typical features of death executed by NK cells; we named this "in-cell killing" which displays the efficacy superior to the canonical way of "kiss-killing" from outside. By profiling isogenic cells, CD44 on tumor cells was identified as a negative regulator of "in-cell killing" via inhibiting CIC formation. CD44 functions to antagonize NK cell internalization by reducing N-cadherin-mediated intercellular adhesion and by enhancing Rho GTPase-regulated cellular stiffness as well. Remarkably, antibody-mediated blockade of CD44 signaling potentiated the suppressive effects of NK cells on tumor growth associated with increased heterotypic CIC formation. Together, we identified CIC-mediated "in-cell killing" as a promising strategy for cancer immunotherapy.

CD8+ T cells actively penetrate hepatocytes via the CD44/p-ERM/F-actin pathway in autoimmune hepatitis

OBJECTIVE

Emperipolesis is a pathological feature for the diagnosis of autoimmune hepatitis (AIH). We have previously found that CD8⁺ T cells participated in the emperipolesis in AIH. In this study we aimed to clarify the characteristics and molecular mechanisms of emperipolesis in patients with AIH in vitro and in mice with α-Galactosylceramide (α-GalCer)-induced acute hepatitis.

METHODS

The peripheral blood mononuclear cells (PBMC) of patients with various chronic liver diseases and healthy controls were co-cultured with hepatic cell lines to induce emperipolesis in vitro. Confocal staining was performed to illustrate the cellular types and potential mechanisms of emperipolesis in AIH. In addition, a murine model of α-GalCer-induced acute hepatitis that mimics human AIH was used to confirm the role of CD44/p-ERM/F-actin in the emperipolesis process in vivo.

RESULTS

In the co-cultured system of PBMC and hepatic cell line, emperipolesis was observed most commonly in patients with AIH. The main cells participating in emperipolesis were CD8⁺ T cells, and they penetrated hepatic cells actively via the CD44/p-ERM/F-actin pathway. As a result, most CD8⁺ T cells engulfed by hepatic cells underwent apoptosis. In the α-GalCer-induced acute hepatitis model, emperipolesis was observed around the inflammatory foci and was inhibited by the ezrin phosphorylation inhibitor NSC668394. Similarly, activated murine CD8⁺ T cells penetrated primary hepatocytes via the CD44/p-ERM/F-actin pathway in vitro.

CONCLUSIONS

CD8⁺ T cells penetrate hepatic cells actively via the CD44/p-ERM/F-actin signaling pathway and undergo apoptosis. This may be a compensatory mechanism to attenuate the overwhelming immune attack in AIH.

Interaction Networks Converging on Immunosuppressive Roles of Granzyme B: Special Niches Within the Tumor Microenvironment

Granzyme B is a renowned effector molecule primarily utilized by CTLs and NK cells against ill-defined and/or transformed cells during immunosurveillance. The overall expression of granzyme B within tumor microenvironment has been well-established as a prognostic marker indicative of priming immunity for a long time. Until recent years, increasing immunosuppressive effects of granzyme B are unveiled in the setting of different immunological context. The accumulative evidence confounded the roles of granzyme B in immune responses, thereby arousing great interests in characterizing detailed feature of granzyme B-positive niche. In this paper, the granzyme B-related regulatory effects of major suppressor cells as well as the tumor microenvironment that defines such functionalities were longitudinally summarized and discussed. Multiplex networks were built upon the interactions among different transcriptional factors, cytokines, and chemokines that regarded to the initiation and regulation of granzyme B-mediated immunosuppression. The conclusions and prospect may facilitate better interpretations of the clinical significance of granzyme B, guiding the rational development of therapeutic regimen and diagnostic probes for anti-tumor purposes.

Cell-in-cell phenomena in cancer

Cell-in-cell structures are reported in numerous cancers, and their presence is an indicator for poor prognosis. Mechanistic studies have identified how cancer cells manage to ingest whole neighbouring cells to form such structures, and the consequences of cell-in-cell formation on cancer progression have been elucidated. In this Opinion article, we discuss how two related cell-in-cell processes, cell cannibalism and entosis, are regulated and how these mechanisms promote cancer progression. We propose that cannibalistic activity is a hallmark of cancer that results in part from selection by metabolic stress and serves to feed aggressive cancer cells.

A nonmainstream approach against cancer

The discovery of antibiotics as specific and effective drugs against infectious agents has generated the belief that the famous Paul Erlich theory on magic bullet should be applied to cancer as well. However, after around 60 years of failures in finding a magic bullet against cancer, a question appears mandatory: does the magic bullet against cancer really exist? In trying to understand more on the issue, we propose three discoveries are coming from a nonmainstream approach against cancer. Tumor is acidic, and tumor acidity impairs drugs entering within tumor cells and isolates tumors from the rest of the body. Proton pumps are key in allowing tumor cells to live in the acidic microenvironment. A class of antiacidic drugs, proton pump inhibitors (PPIs), were shown to have a potent anti-tumor effect, through inhibition of proton pumps in tumor cells. PPIs are indeed prodrugs needing acidity to be activated into the active molecule. So they use protonation by H+ as an activating mechanism, while the vast majority of drugs are totally neutralized by protonation. An anti-tumor therapy based on PPI showed to be effective both in vitro and in vivo. Differently from normal cells, cancer cells meet their energy needs in great part by fermentation, and it appears conceivable that hypoxia and low nutrient transform tumor cells into fermenting anaerobes. This suggests that cancer cells are more similar to unicellular organisms, aimed at surviving in a continuous fighting, rather than cooperating, with other cells, as it occurs in the normal homeostasis of our body. We have shown that cancer cells take their fuel by "cannibalizing" other cells, either dead or alive, especially when starved and in acidic condition. This finding led to the discovery of a new oncogene TM9SF4 that human malignant cell shares with amoebas. The evidence is accumulating that almost all the cells release extracellular vehicles (EVs), from micro- to nanosize, which shuttle a variety of molecules. Tumor cells, particularly when stressed in their hostile microenvironment, release high levels of EVs, able to interact with target cells in various ways, within an organ or at a distance. They may represent both valuable tumor biomarker and shuttles for drugs with anti-tumor properties. This article wants to burst a real change in future anti-cancer strategies, based on the idea that tumors are much more common features than specific molecular targets.