Truncated CD200 stimulates tumor immunity leading to fewer lung metastases in a novel Wistar rat metastasis model

Emerging Immune Checkpoint Molecules on Cancer Cells: CD24 and CD200

Cancer immunotherapy strategies are based on the utilization of immune checkpoint inhibitors to instigate an antitumor immune response. The efficacy of immune checkpoint blockade, directed at adaptive immune checkpoints, has been demonstrated in select cancer types. However, only a limited subset of patients has exhibited definitive outcomes characterized by a sustained response after discontinuation of therapy. Recent investigations have highlighted the significance of immune checkpoint molecules that are overexpressed in cancer cells and inhibit myeloid lineage immune cells within a tumor microenvironment. These checkpoints are identified as potential targets for anticancer immune responses. Notably, the immune checkpoint molecules CD24 and CD200 have garnered attention owing to their involvement in tumor immune evasion. CD24 and CD200 are overexpressed across diverse cancer types and serve as signaling checkpoints by engaging their respective receptors, Siglec-10 and CD200 receptor, which are expressed on tumor-associated myeloid cells. In this review, we summarized and discussed the latest advancements and insights into CD24 and CD200 as emergent immune checkpoint moieties, further delving into their therapeutic potentials for cancer treatment.

Cell-cycle dependent nuclear gene delivery enhances the effects of E-cadherin against tumor invasion and metastasis

Gene delivery is the process by which foreign DNA is transferred to host cells, released from intracellular vesicles, and transported to the nuclei for transcription. This process is frequently inefficient and difficult to control spatiotemporally. We developed a gene delivery strategy that uses ultrasound to directly deliver plasmid DNA into nuclei via gas vesicles (GVs)-based intracellular cavitation. pDNA-binding GVs can be taken up by cells and cause intracellular cavitation when exposed to acoustic irradiation and delivering their pDNA payloads into nuclei. Importantly, GVs can remain stable in the cytoplasm in the absence of acoustic irradiation, allowing for temporally controlled nuclear gene delivery. We were able to achieve spatiotemporal control of E-cadherin nuclear gene delivery in this manner, demonstrating its efficacy in tumor invasion and metastasis inhibition. Interestingly, we discovered that nuclear gene delivery of E-cadherin during the G2/M phase of the cell cycle in C6 tumor cells inhibited tumor invasion and metastasis more effectively than during the G1 and S phases. The gene delivery of E-cadherin at the G2/M phase resulted in significantly lower expression of Fam50a, which reduced Fam50a/Runx2 interaction and led to reduced transactivation of MMP13, an important factor for epithelial-mesenchymal transition, as observed in a molecular mechanism assay. Thus, using remote acoustic control of intracellular cavitation of pDNA-GVs, we developed a high spatiotemporally controllable gene delivery strategy and achieved stronger tumor invasion and metastasis inhibition effects by delivering the E-cadherin gene at the G2/M phase.

Chloride Intracellular Channel Proteins (CLICs) and Malignant Tumor Progression: A Focus on the Preventive Role of CLIC2 in Invasion and Metastasis

Simple Summary

Although chloride intracellular channel proteins (CLICs) have been identified as ion channel proteins, their true functions are still elusive. Recent in silico analyses show that CLICs may be prognostic markers in cancer. This review focuses on CLIC2 that plays preventive roles in malignant cell invasion and metastasis. CLIC2 is secreted extracellularly and binds to matrix metalloproteinase 14 (MMP14), while inhibiting its activity. As a result, CLIC2 may contribute to the development/maintenance of junctions between blood vessel endothelial cells and the inhibition of invasion and metastasis of tumor cells. CLIC2 may be a novel therapeutic target for malignancies.

Abstract

CLICs are the dimorphic protein present in both soluble and membrane fractions. As an integral membrane protein, CLICs potentially possess ion channel activity. However, it is not fully clarified what kinds of roles CLICs play in physiological and pathological conditions. In vertebrates, CLICs are classified into six classes: CLIC1, 2, 3, 4, 5, and 6. Recently, in silico analyses have revealed that the expression level of CLICs may have prognostic significance in cancer. In this review, we focus on CLIC2, which has received less attention than other CLICs, and discuss its role in the metastasis and invasion of malignant tumor cells. CLIC2 is expressed at higher levels in benign tumors than in malignant ones, most likely preventing tumor cell invasion into surrounding tissues. CLIC2 is also expressed in the vascular endothelial cells of normal tissues and maintains their intercellular adhesive junctions, presumably suppressing the hematogenous metastasis of malignant tumor cells. Surprisingly, CLIC2 is localized in secretory granules and secreted into the extracellular milieu. Secreted CLIC2 binds to MMP14 and inhibits its activity, leading to suppressed MMP2 activity. CLIC4, on the other hand, promotes MMP14 activity. These findings challenge the assumption that CLICs are ion channels, implying that they could be potential new targets for the treatment of malignant tumors.

Altered expression of the immunoregulatory ligand-receptor pair CD200-CD200R1 in the brain of Parkinson's disease patients

Neuroinflammation, in which activated microglia are involved, appears to contribute to the development of Parkinson’s disease (PD). However, the role of microglial activation and the mechanisms governing this process remain uncertain. We focused on one inhibitory mechanism involved in the control of microglial activation, the microglia inhibitory receptor CD200R1, and its ligand CD200, mainly expressed by neurons. The human CD200R1 gene encodes two membrane-associated and two soluble protein isoforms and the human CD200 gene encodes full-length proteins (CD200full) but also truncated (CD200tr) proteins which act as CD200R1 antagonists. Little is known about their expression in the human brain under pathological conditions. We used human peripheral blood monocytes and monocyte-derived microglia-like cells from control subjects to characterize the expression of the CD200R1 mRNA variants, which showed stimulus-specific responses. We provide evidence of increased CD200R1 (mRNA variants and protein isoforms) and CD200 expression (CD200tr mRNA) in brain tissue of PD patients, mainly in the hippocampus, as well as increased CD200 expression (CD200full and CD200tr mRNAs) in iPSCs-derived dopaminergic neurons generated from skin fibroblasts of PD patients. Our results suggest that CD200-CD200R1 signalling is altered in PD, which may affect the microglial function and constitute a potential target in therapeutic strategies for PD.

Chloride intracellular channel protein 2 is secreted and inhibits MMP14 activity, while preventing tumor cell invasion and metastasis

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CLIC2 is highly expressed in benign, less invasive and less metastatic tumors.

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Forced expression of CLIC2 prevents metastasis and invasion in animal tumor models.

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CLIC2 is associated with decreased vascular permeability in tumor masses.

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CLIC2, a secretable soluble protein, can bind to and inhibit MMP14.

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Extracellular CLIC2 can suppress malignant cell invasion.

The abilities to invade surrounding tissues and metastasize to distant organs are the most outstanding features that distinguish malignant from benign tumors. However, the mechanisms preventing the invasion and metastasis of benign tumor cells remain unclear. By using our own rat distant metastasis model, gene expression of cells in primary tumors was compared with that in metastasized tumors. Among many distinct gene expressions, we have focused on chloride intracellular channel protein 2 (CLIC2), an ion channel protein of as-yet unknown function, which was predominantly expressed in the primary tumors. We created CLIC2 overexpressing rat glioma cell line and utilized benign human meningioma cells with naturally high CLIC2 expression. CLIC2 was expressed at higher levels in benign human brain tumors than in their malignant counterparts. Moreover, its high expression was associated with prolonged survival in the rat metastasis and brain tumor models as well as with progression-free survival in patients with brain tumors. CLIC2 was also correlated with the decreased blood vessel permeability likely by increased contents of cell adhesion molecules. We found that CLIC2 was secreted extracellularly, and bound to matrix metalloproteinase (MMP) 14. Furthermore, CLIC2 prevented the localization of MMP14 in the plasma membrane, and inhibited its enzymatic activity. Indeed, overexpressing CLIC2 and recombinant CLIC2 protein effectively suppressed malignant cell invasion, whereas CLIC2 knockdown reversed these effects. Thus, CLIC2 suppress invasion and metastasis of benign tumors at least partly by inhibiting MMP14 activity.

The Roles of Alternative Splicing in Tumor-immune Cell Interactions

Alternative splicing (AS) plays a significant role in the hallmarks of cancer and can provide neoantigens for immunotherapy. Here, we summarize recent advances in immune system associated tumor specific-antigens (TSAs) produced by AS. We further discuss the regulating mechanisms involved in AS-mediated innate and adaptive immune responses and the anti-tumoral and protumoral roles in different types of cancer. For example, ULBP1_RI, MLL5Δ21spe, NKp44-1Δ5, MHC-IΔ7, CD200SΔ1, 2, PVR α/β/γ/δ and IL-33 variants 1/2/3 act as regulators in solid tumors and IPAK4-L and, FOXP1ΔN100 exhibit functions in hematological cancers.

CD200 mimetic aptamer PEG-M49 markedly increases the therapeutic effects of pegylated liposomal doxorubicin in a mouse model of metastatic breast carcinoma: an effect independent of CD200 receptor 1

We previously reported that CD200 overexpression in the host decreases progression and metastasis of the highly aggressive metastatic 4THM breast carcinoma. We have explored a possible synergistic interaction between the CD200 mimetic PEG-M49 and pegylated liposomal doxorubicin (Peg-Dox) in wild-type CD200 knockout (CD200^-/-) and CD200 Receptor 1 knockout (CD200R1^-/-) mice for the first time. A 4THM breast carcinoma model and three groups of BALB/c mice (wild type, CD200^-/- and CD200R1^-/-) were used. Five days after injection of tumor cells, mice were injected with Peg-Dox (ip, once a week) and PEG-M49 or a control aptamer (iv, every 3 days). Necropsies were performed either 12 (mid-point) or 24 (endpoint) days after injection and the extent of tumor growth, visceral metastasis and changes in the tumor-directed immune response were evaluated. PEG-M49 and Peg-Dox co-treatment induced complete tumor regression and loss of macroscopic lung metastasis in four out of seven WT mice. This synergistic anti-tumoral effect is thought to be due to Peg-M49-induced inhibition of Gr1 + CD11b + cells and Peg-Dox-induced increases in tumor-infiltrating CD8 + and CD8CD4 double-positive cells. Similar changes were observed in CD200R1^-/- mice indicating that the primary effects of Peg-M49 are mediated by non-CD200R1 receptors. We also demonstrated for the first time that tumor growth, metastasis, and tumor infiltrating GR1 + CD11b + cells were markedly increased in CD200R1^-/- mice, indicating an anti-inflammatory and protective role of CD200. CD200 mimetics might be a safe and effective immunomodulatory treatment in conjunction with classical chemotherapeutics for therapy of aggressive metastatic breast carcinoma.

Chloride intracellular channel protein 2 in cancer and non-cancer human tissues: relationship with tight junctions

Chloride intracellular channel protein 2 (CLIC2) belongs to the CLIC family of conserved metazoan proteins. Although CLICs have been identified as chloride channels, they are currently considered multifunctional proteins. CLIC2 is the least studied family member. We investigated CLIC2 expression and localization in human hepatocellular carcinoma, metastatic colorectal cancer in the liver, and colorectal cancer. Significant expression of mRNAs encoding CLIC1, 2, 4, and 5 were found in the human tissues, but only CLIC2 was predominantly expressed in non-cancer tissues surrounding cancer masses. Fibrotic or dysfunctional (aspartate aminotransferase ≥40) non-cancer liver tissues and advanced stage HCC tissues expressed low levels of CLIC2. Endothelial cells lining blood vessels but not lymphatic vessels in non-cancer tissues expressed CLIC2 as well as high levels of the tight junction proteins claudins 1 and 5, occludin, and ZO-1. Most endothelial cells in blood vessels in cancer tissues had very low expressions of CLIC2 and tight junction proteins. CD31⁺/CD45⁻ endothelial cells isolated from non-cancer tissues expressed mRNAs encoding CLIC2, claudin 1, occludin and ZO-1, while similar cell fractions from cancer tissues had very low expressions of these molecules. Knockdown of CLIC2 expression in human umbilical vein endothelial cells (HUVECs) allowed human cancer cells to transmigrate through a HUVEC monolayer. These results suggest that CLIC2 may be involved in the formation and/or maintenance of tight junctions and that cancer tissue vasculature lacks CLIC2 and tight junctions, which allows the intravasation of cancer cells necessary for hematogenous metastasis.

Homing of ICG-loaded liposome inlaid with tumor cellular membrane to the homologous xenografts glioma eradicates the primary focus and prevents lung metastases through phototherapy

Liposomes inlaid with tumor cellular membranes may serve as an excellent nanoplatform for homologous-targeting phototherapy using ICG.