Dynamic properties of antigen uptake and communication between dendritic cells

Dendritic Cells: A Bridge between Tolerance Induction and Cancer Development in Transplantation Setting

Dendritic cells (DCs) are a heterogeneous group of antigen-presenting cells crucial for fostering allograft tolerance while simultaneously supporting host defense against infections and cancer. Within the tumor microenvironment, DCs can either mount an immune response against cancer cells or foster immunotolerance, presenting a dual role. In immunocompromised individuals, posttransplant malignancies pose a significant health concern, with DCs serving as vital players in immune responses against cancer cells. Both recipient- and donor-derived DCs play a critical role in the rejection process, infiltrating the transplanted organ and sustaining T-cell responses. The use of immunosuppressive drugs represents the predominant approach to control this immunological barrier in transplanted organs. Evidence has shed light on the immunopharmacology of these drugs and novel strategies for manipulating DCs to promote allograft survival. Therefore, comprehending the mechanisms underlying this intricate microenvironment and the effects of immunosuppressive therapy on DCs is crucial for developing targeted therapies to reduce graft failure rates. This review will delve into the fundamental immunobiology of DCs and provide a detailed exploration of their clinical significance concerning alloimmune responses and posttransplant malignancies.

RalGPS2 Interacts with Akt and PDK1 Promoting Tunneling Nanotubes Formation in Bladder Cancer and Kidney Cells Microenvironment

Simple Summary

Cell-to-cell communication in the tumor microenvironment is a crucial process to orchestrate the different components of the tumoral infrastructure. Among the mechanisms of cellular interplay in cancer cells, tunneling nanotubes (TNTs) are dynamic connections that play an important role. The mechanism of the formation of TNTs among cells and the molecules involved in the process remain to be elucidated. In this study, we analyze several bladder cancer cell lines, representative of tumors at different stages and grades. We demonstrate that TNTs are formed only by mid or high-stage cell lines that show muscle-invasive properties and that they actively transport mitochondria and proteins. The formation of TNTs is triggered by stressful conditions and starts with the assembly of a specific multimolecular complex. In this study, we characterize some of the protein components of the TNTs complex, as they are potential novel molecular targets for future therapies aimed at counteracting tumor progression.

Abstract

RalGPS2 is a Ras-independent Guanine Nucleotide Exchange Factor for RalA GTPase that is involved in several cellular processes, including cytoskeletal organization. Previously, we demonstrated that RalGPS2 also plays a role in the formation of tunneling nanotubes (TNTs) in bladder cancer 5637 cells. In particular, TNTs are a novel mechanism of cell–cell communication in the tumor microenvironment, playing a central role in cancer progression and metastasis formation. However, the molecular mechanisms involved in TNTs formation still need to be fully elucidated. Here we demonstrate that mid and high-stage bladder cancer cell lines have functional TNTs, which can transfer mitochondria. Moreover, using confocal fluorescence time-lapse microscopy, we show in 5637 cells that TNTs mediate the trafficking of RalA protein and transmembrane MHC class III protein leukocyte-specific transcript 1 (LST1). Furthermore, we show that RalGPS2 is essential for nanotubes generation, and stress conditions boost its expression both in 5637 and HEK293 cell lines. Finally, we prove that RalGPS2 interacts with Akt and PDK1, in addition to LST1 and RalA, leading to the formation of a complex that promotes nanotubes formation. In conclusion, our findings suggest that in the tumor microenvironment, RalGPS2 orchestrates the assembly of multimolecular complexes that drive the formation of TNTs.

A Ticket to Ride: The Implications of Direct Intercellular Communication via Tunneling Nanotubes in Peritoneal and Other Invasive Malignancies

It is well established that the role of the tumor microenvironment (TME) in cancer progression and therapeutic resistance is crucial, but many of the underlying mechanisms are still being elucidated. Even with better understanding of molecular oncology and identification of genomic drivers of these processes, there has been a relative lag in identifying and appreciating the cellular drivers of both invasion and resistance. Intercellular communication is a vital process that unifies and synchronizes the diverse components of the tumoral infrastructure. Elucidation of the role of extracellular vesicles (EVs) over the past decade has cast a brighter light on this field. And yet even with this advance, in addition to diffusible soluble factor-mediated paracrine and endocrine cell communication as well as EVs, additional niches of intratumoral communication are filled by other modes of intercellular transfer. Tunneling nanotubes (TNTs), tumor microtubes (TMs), and other similar intercellular channels are long filamentous actin-based cellular conduits (in most epithelial cancer cell types, ~15-500 µm in length; 50–1000+ nm in width). They extend and form direct connections between distant cells, serving as conduits for direct intercellular transfer of cell cargo, such as mitochondria, exosomes, and microRNAs; however, many of their functional roles in mediating tumor growth remain unknown. These conduits literally create a physical bridge to create a syncytial network of dispersed cells amidst the intercellular stroma-rich matrix. Emerging evidence suggests that they provide a cellular mechanism for induction and emergence of drug resistance and contribute to increased invasive and metastatic potential. They have been imaged in vitro and also in vivo and ex vivo in tumors from human patients as well as animal models, thus not only proving their existence in the TME, but opening further speculation about their exact role in the dynamic niche of tumor ecosystems. TNT cellular networks are upregulated between cancer and stromal cells under hypoxic and other conditions of physiologic and metabolic stress. Furthermore, they can connect malignant cells to benign cells, including vascular endothelial cells. The field of investigation of TNT-mediated tumor-stromal, and tumor-tumor, cell-cell communication is gaining momentum. The mixture of conditions in the microenvironment exemplified by hypoxia-induced ovarian cancer TNTs playing a crucial role in tumor growth, as just one example, is a potential avenue of investigation that will uncover their role in relation to other known factors, including EVs. If the role of cancer heterocellular signaling via TNTs in the TME is proven to be crucial, then disrupting formation and maintenance of TNTs represents a novel therapeutic approach for ovarian and other similarly invasive peritoneal cancers.

Tunneling Nanotubes and Tumor Microtubes in Cancer

Intercellular communication among cancer cells and their microenvironment is crucial to disease progression. The mechanisms by which communication occurs between distant cells in a tumor matrix remain poorly understood. In the last two decades, experimental evidence from different groups proved the existence of thin membranous tubes that interconnect cells, named tunneling nanotubes, tumor microtubes, cytonemes or membrane bridges. These highly dynamic membrane protrusions are conduits for direct cell-to-cell communication, particularly for intercellular signaling and transport of cellular cargo over long distances. Tunneling nanotubes and tumor microtubes may play an important role in the pathogenesis of cancer. They may contribute to the resistance of tumor cells against treatments such as surgery, radio- and chemotherapy. In this review, we present the current knowledge about the structure and function of tunneling nanotubes and tumor microtubes in cancer and discuss the therapeutic potential of membrane tubes in cancer treatment.

Macrophages enhance 3D invasion in a breast cancer cell line by induction of tumor cell tunneling nanotubes

Background

Metastasis is the cause of most cancer-related deaths. It is known that breast cancer cells in proximity to macrophages become more invasive in an Epidermal Growth Factor (EGF) dependent manner. Tunneling nanotubes (TNTs) are thin, F-actin containing, cellular protrusions that mediate intercellular communication and have been identified in many tumors. The mechanism of TNT formation varies between different cell types. M-Sec (TNFAIP2) has been demonstrated to be involved in TNT formation in some cell types including macrophages. Yet, the requirement of M-Sec in tumor cell TNT formation in response to macrophages has not been explored.

Aim

The aim of this study was to determine whether EGF was required for macrophage induced tumor cell TNTs in an M-Sec dependent manner and what possible roles tumor cell TNTs play in tumor cell migration and invasion.

Methods and Results

Macrophage Conditioned Media (CM) was used to induce an increase in TNTs in a number of breast cancer cell lines as measured by live cell microscopy. Tumor cell TNT formation by CM was dependent on the presence of EGF which was sufficient to induce TNT formation. CM treatment enhanced the level of M-Sec identified using western blot analysis. Reduction of endogenous M-Sec levels via shRNA in MTLn3 mammary adenocarcinoma cells inhibited the formation of TNTs. The role of tumor cell TNTs in cell behavior was tested using in vitro transwell and 3D invasion assays. No effect on chemotaxis was detected but 3D invasion was reduced following the knockdown of M-Sec in tumor cell TNTs.

Conclusions

Our results show that EGF was necessary and sufficient for tumor cell TNT formation which was dependent on cellular M-Sec levels. While tumor cell TNTs may not play a role in individual cell behaviors like chemotaxis, they may be important in more complex tumor cell behaviors such as 3D invasion.

Perspective on nanochannels as cellular mediators in different disease conditions

Tunnelling nanotubes (TNTs), also known as membrane nanochannels, are actin-based structures that facilitate cytoplasmic connections for rapid intercellular transfer of signals, organelles and membrane components. These dynamic TNTs can form de novo in animal cells and establish complex intercellular networks between distant cells up to 150 μm apart. Within the last decade, TNTs have been discovered in different cell types including tumor cells, macrophages, monocytes, endothelial cells and T cells. It has also been further elucidated that these nanotubes play a vital role in diseased conditions such as cancer, where TNT formation occurs at a higher pace and is used for rapid intercellular modulation of chemo-resistance. Viruses such as HIV, HSV and prions also hijack the existing TNT connections between host cells for rapid transmission and evasion of the host immune responses. The following review aims to describe the heterogeneity of TNTs, their role in different tissues and disease conditions in order to enhance our understanding on how these nanotubes can be used as a target for therapies.

The Role of Rho-GTPases and actin polymerization during Macrophage Tunneling Nanotube Biogenesis

Macrophage interactions with other cells, either locally or at distances, are imperative in both normal and pathological conditions. While soluble means of communication can transmit signals between different cells, it does not account for all long distance macrophage interactions. Recently described tunneling nanotubes (TNTs) are membranous channels that connect cells together and allow for transfer of signals, vesicles, and organelles. However, very little is known about the mechanism by which these structures are formed. Here we investigated the signaling pathways involved in TNT formation by macrophages using multiple imaging techniques including super-resolution microscopy (3D-SIM) and live-cell imaging including the use of FRET-based Rho GTPase biosensors. We found that formation of TNTs required the activity and differential localization of Cdc42 and Rac1. The downstream Rho GTPase effectors mediating actin polymerization through Arp2/3 nucleation, Wiskott-Aldrich syndrome protein (WASP) and WASP family verprolin-homologous 2 (WAVE2) proteins are also important, and both pathways act together during TNT biogenesis. Finally, TNT function as measured by transfer of cellular material between cells was reduced following depletion of a single factor demonstrating the importance of these factors in TNTs. Given that the characterization of TNT formation is still unclear in the field; this study provides new insights and would enhance the understanding of TNT formation towards investigating new markers.

Lost in translation: applying 2D intercellular communication via tunneling nanotubes in cell culture to physiologically relevant 3D microenvironments

Tunneling nanotubes (TNTs) are membranous conduits for direct cell-to-cell communication. Until the past decade, little had been known about their composite structure, function, and mechanisms of action in both normal physiologic conditions as well as in disease states. Now TNTs are attracting increasing interest for their key role(s) in the pathogenesis of disease, including neurodegenerative disorders, inflammatory and infectious diseases, and cancer. The field of TNT biology is still in its infancy, but inroads have been made in determining potential mechanisms and function of these remarkable structures. For example, TNTs function as critical conduits for cellular exchange of information; thus, in cancer, they may play an important role in critical pathophysiologic features of the disease, including cellular invasion, metastasis, and emergence of chemotherapy drug resistance. Although the TNT field is still in a nascent stage, we propose that TNTs can be investigated as novel targets for drug-based treatment of cancer and other diseases.

Exosomes and nanotubes: Control of immune cell communication

Cell-cell communication is critical to coordinate the activity and behavior of a multicellular organism. The cells of the immune system not only must communicate with similar cells, but also with many other cell types in the body. Therefore, the cells of the immune system have evolved multiple ways to communicate. Exosomes and tunneling nanotubes (TNTs) are two means of communication used by immune cells that contribute to immune functions. Exosomes are small membrane vesicles secreted by most cell types that can mediate intercellular communication and in the immune system they are proposed to play a role in antigen presentation and modulation of gene expression. TNTs are membranous structures that mediate direct cell-cell contact over several cell diameters in length (and possibly longer) and facilitate the interaction and/or the transfer of signals, material and other cellular organelles between connected cells. Recent studies have revealed additional, but sometimes conflicting, structural and functional features of both exosomes and TNTs. Despite the new and exciting information in exosome and TNT composition, origin and in vitro function, biologically significant functions are still being investigated and determined. In this review, we discuss the current field regarding exosomes and TNTs in immune cells providing evaluation and perspectives of the current literature.

The use of optical trap and microbeam to investigate the mechanical and transport characteristics of tunneling nanotubes in tumor spheroids

The use of optical trap and microbeam for investigating mechanical and transport properties of inter cellular tunneling nanotubes (TnTs) in tumor spheroids has been demonstrated. TnTs in tumor spheroids have been visualized by manipulating TnT connected cells using optical tweezers. Functionality of the TnTs for transferring cytoplasmic vesicles and injected dye molecules by optoporation method has been studied. Further, the TnTs could be longitudinally stretched by manipulating the connected cells and their elastic response was studied. Manipulation of cells at the surface of tumor spheroid using optical tweezers and injection of fluorescent dye into a trapped cell using optoporation technique.

Intercellular communication in malignant pleural mesothelioma: properties of tunneling nanotubes

Malignant pleural mesothelioma is a particularly aggressive and locally invasive malignancy with a poor prognosis despite advances in understanding of cancer cell biology and development of new therapies. At the cellular level, cultured mesothelioma cells present a mesenchymal appearance and a strong capacity for local cellular invasion. One important but underexplored area of mesothelioma cell biology is intercellular communication. Our group has previously characterized in multiple histological subtypes of mesothelioma a unique cellular protrusion known as tunneling nanotubes (TnTs). TnTs are long, actin filament-based, narrow cytoplasmic extensions that are non-adherent when cultured in vitro and are capable of shuttling cellular cargo between connected cells. Our prior work confirmed the presence of nanotube structures in tumors resected from patients with human mesothelioma. In our current study, we quantified the number of TnTs/cell among various mesothelioma subtypes and normal mesothelial cells using confocal microscopic techniques. We also examined changes in TnT length over time in comparison to cell proliferation. We further examined potential approaches to the in vivo study of TnTs in animal models of cancer. We have developed novel approaches to study TnTs in aggressive solid tumor malignancies and define fundamental characteristics of TnTs in malignant mesothelioma. There is mounting evidence that TnTs play an important role in intercellular communication in mesothelioma and thus merit further investigation of their role in vivo.

Tunneling nanotubes provide a unique conduit for intercellular transfer of cellular contents in human malignant pleural mesothelioma

Tunneling nanotubes are long, non-adherent F-actin-based cytoplasmic extensions which connect proximal or distant cells and facilitate intercellular transfer. The identification of nanotubes has been limited to cell lines, and their role in cancer remains unclear. We detected tunneling nanotubes in mesothelioma cell lines and primary human mesothelioma cells. Using a low serum, hyperglycemic, acidic growth medium, we stimulated nanotube formation and bidirectional transfer of vesicles, proteins, and mitochondria between cells. Notably, nanotubes developed between malignant cells or between normal mesothelial cells, but not between malignant and normal cells. Immunofluorescent staining revealed their actin-based assembly and structure. Metformin and an mTor inhibitor, Everolimus, effectively suppressed nanotube formation. Confocal microscopy with 3-dimensional reconstructions of sectioned surgical specimens demonstrated for the first time the presence of nanotubes in human mesothelioma and lung adenocarcinoma tumor specimens. We provide the first evidence of tunneling nanotubes in human primary tumors and cancer cells and propose that these structures play an important role in cancer cell pathogenesis and invasion.

Penetration of antibody-opsonized cells by the membrane attack complex of complement promotes Ca(2+) influx and induces streamers

We have reported that during complement-mediated cytolysis of B cells promoted by the CD20 mAbs rituximab or ofatumumab (OFA), long, thin structures that we call streamers (≥ 3 cell diameters) are rapidly generated and grow out from the cell surface. Streamers appear before cells are killed and contain opsonizing mAbs and membrane lipids. By exploiting the differential Ca(2+) requirements of discrete steps in the complement cascade, we determined that mAb-opsonized cells first tagged with C3b using C5-depleted serum are killed on addition of serum and EDTA, but the cells do not produce streamers. Also, cells first opsonized with OFA are lysed in serum containing Mg-EGTA by the alternative complement pathway but streamers are not produced. These findings indicate that Ca(2+) influx is necessary for streamer formation. Other mAbs that promote complement-mediated cytolysis also induce streamers on target cells. Streamer-like structures called nanotubes have been reported in several cellular systems, and are thought to promote intercellular communication/signaling. We tested whether this signaling could influence the susceptibility of neighboring cells contacted by streamers to complement attack and found that complement-mediated cytolysis of OFA-opsonized cells increases the resistance of unopsonized indicator cell populations to subsequent lysis when these cells are exposed to OFA and complement.

Macrophage activation differentially modulates particle binding, phagocytosis and downstream antimicrobial mechanisms

Phagocytosis provides a critical first line of defense against invading pathogens. Engagement of particles through receptor-mediated binding precedes internalization and induction of cellular antimicrobial responses. Phagocytes have the capacity to differentially regulate binding and internalization processes through changes in their receptor profile and modulation of downstream events. This is necessary for the intricate control of phagocytic antimicrobial responses. Several methods are available for evaluation of phagocytosis. Unfortunately, none allow for accurate quantitation of both binding and internalization events. To overcome these limitations, we have developed a novel phagocytosis assay based on a multi-spectral imaging flow cytometry platform. This assay discriminates between internalized and surface-bound particles in a statistically robust manner and allows multi-parametric analysis of phagocytosis and downstream anti-microbial responses. We also devised a novel approach for examination of phagolysosome fusion, which provides an improved capacity for quantitative assessment of phagolysosome fusion in mixed populations of intact cells. Importantly, our approaches are likely amenable to a broad range of comparative model systems based on our examination of murine RAW 264.7 cells and a goldfish primary kidney macrophage (PKM) model system. The latter allowed us to examine the evolutionary conservation of phagocytic antimicrobial responses in a lower vertebrate model. While it has been previously reported that mixed populations of these macrophage cultures are phagocytic, it remained unclear if sub-populations within them contributed differentially to this activity. In accordance with higher vertebrate models, we found that differentiation along the macrophage pathway leads to an increased capacity for phagocytosis in goldfish PKM. Interestingly, cellular activation differentially regulated particle internalization in PKM monocyte and mature macrophage subsets. We also found differential regulation of phagolysosome fusion and downstream production of reactive oxygen intermediates (ROI). The temporal activation of specific phagocytic antimicrobial responses at distinct stages of PKM differentiation suggests specialization within the macrophage compartment early in evolution, geared to meet specific host immunity requirements within specialized niches.

[When prions use the systems of communication between the immune system and the peripheral nervous system]

Prion disease pathogenesis has been largely studied since the inter-species transmissibility of the infectious protein (PrPSc), the oral uptake as natural route of infection and the exceptional implication in a problem of public health were highlighted. Two sequential preclinical stages are observed before the development of irreversible and fatal lesions in the central nervous system: the lymphoinvasion and the neuroinvasion. The first is characterized by the accumulation of PrPSc within lymphoid tissues and the second by PrPSc scattering the peripheral nervous system towards the central nervous system. The mechanisms involved in the communication between the immune and the peripheral nervous system are still debated. Recent studies even suggest that neuroinvasion can occur through the hematogenous route, independently of the peripheral nervous system. This review analyses (i) the role of immune cells, implicated in prion pathogenesis: dendritic cells as PrPSc vehicle, follicular dendritic cells as PrPSc accumulator and nerve fibres as PrPSc driver and (ii) the respective relations they maintain with peripheral nerve fibres to migrate to the brain.

HIV-1 infection of DC: evidence for the acquisition of virus particles from infected T cells by antigen uptake mechanism

Dendritic cells (DC) play a pivotal role in transmission and dissemination of HIV-1. Earlier studies reported that DC present at the site of infection trap virus particles via DC-SIGN and transfer the virus to the interacting naïve T cells. This prompted us to ask the question whether DC could acquire virus from infected T cells during DC-T cell interaction. To address this, we investigated the likely transfer of virus from HIV-1 infected T cells to DC and the underlying mechanisms involved. Results indicate that DC acquire virus from infected T cells via antigen uptake mechanism and this results in infection of DC with expression of proteins directed by viral DNA. Further studies with HIV-1 lacking the Env protein also resulted in infection of DC. The use of antibodies against DC-SIGN and DC-SIGN-R ruled out a role for receptor in the infection of DC. Additional data show that DC infection is directly correlated with the ability of DC to take up antigen from infected T cells. Overall, these studies provide evidence to suggest that HIV-1, besides infecting immune cells, also utilizes immunological mechanism(s) to acquire and disseminate virus.