Cellular and Molecular Networking Within the Ecosystem of Cancer Cell Communication via Tunneling Nanotubes

Mathematical models of intercellular signaling in breast cancer

BACKGROUND AND OBJECTIVES

The development and regulation of healthy and cancerous breast tissue is guided by communication between cells. Diverse signals are exchanged between cancer cells and non-cancerous cells of the tumor microenvironment (TME), influencing all stages of tumor progression. Mathematical models are essential for understanding how this complex network determines cancer progression and the effectiveness of treatment.

METHODOLOGY

We reviewed the current dynamical mathematical models of intercellular signaling in breast cancer, examining models with cancer cells only, fibroblasts, endothelial cells, macrophages and the immune system as whole. We categorized the goals and complexity of these models, to highlight how they can explain many features of cancer emergence and progression.

RESULTS

We found that dynamical models of intercellular signaling can elucidate tissue-level dysregulation in cancer by explaining: i) maintenance of non-heritable intratumor phenotypic heterogeneity, ii) transitions between tumor dormancy and accelerated invasive growth, iii) stromal support of tumor vascularization and growth factor enrichment and iv) suppression of immune infiltration and cancer surveillance. These models also provide a framework to propose novel TME-targeting treatment strategies. However, most models were focused on a highly selected and small set of signaling interactions between a few cell types, and their translational applicability were severely limited by the availability of tumor-specific data for personalized model calibration.

CONCLUSIONS AND IMPLICATIONS

Mathematical models of breast cancer have many challenges and opportunities to incorporate signaling. The four key challenges are: 1) finding ways to treat signaling networks as a context-dependent language that incorporates non-linear and non-additive responses, 2) identifying the key cell phenotypes that signals control and understanding the feedbacks between signals and phenotype that determine the progression of cancer, (3) estimating parameters of specific patient tumors early in treatment, 4) linking models with novel data collection methods that have single cell and spatial resolution. As our approaches advance, it is our hope that dynamical mathematical models of inter-cellular signaling can play a central role in identifying and testing new treatment strategies as well as forecasting impacts of disease treatment.

Extracellular Vesicles and Tunnelling Nanotubes as Mediators of Prostate Cancer Intercellular Communication

Prostate cancer (PCa) pathogenesis relies on intercellular communication, which can involve tunnelling nanotubes (TNTs) and extracellular vesicles (EVs). TNTs and EVs have been reported to transfer critical cargo involved in cellular functions and signalling, prompting us to investigate the extent of organelle and protein transfer in PCa cells and the potential involvement of the androgen receptor. Using live cell imaging microscopy, we observed extensive formation of TNTs and EVs operating between PCa, non-malignant, and immune cells. PCa cells were capable of transferring lysosomes, mitochondria, lipids, and endoplasmic reticulum, as well as syndecan-1, sortilin, Glut1, and Glut4. In mechanistic studies, androgen-sensitive PCa cells exhibited changes in cell morphology when stimulated by R1881 treatment. Overexpression assays of a newly designed androgen receptor (AR) plasmid revealed its novel localization in PCa cellular vesicles, which were also transferred to neighbouring cells. Selected molecular machinery, thought to be involved in intercellular communication, was investigated by knockdown studies and Western blotting/immunofluorescence/scanning electron microscopy (SEM). PCa TNTs and EVs transported proteins and organelles, which may contain specialist signalling, programming, and energy requirements that support cancer growth and progression. This makes these important intercellular communication systems ideal potential targets for therapeutic intervention.

Unveiling the power of mitochondrial transfer in cancer progression: a perspective in ovarian cancer

Mitochondria are dynamic organelles integral to metabolic processes, coordination of essential biological pathways, and oncogenesis and tumor progression. Recent studies have revealed that mitochondria can be transferred between cells via multiple mechanisms, implicating their involvement in the pathogenesis and progression of ovarian cancer. This review provides a comprehensive analysis of intercellular mitochondrial transfer within the context of ovarian cancer and its tumor microenvironment. We also propose targeted pathways and therapeutic strategies that could be utilized to modulate diseases associated with mitochondrial transfer therapy. Finally, we examine recent advancements in this field and identify several unresolved questions.

Targeting mitochondria: a novel approach for treating platinum-resistant ovarian cancer

Ovarian cancer is a prevalent gynecologic malignancy with the second-highest mortality rate among gynecologic malignancies. Platinum-based chemotherapy is the first-line treatment for ovarian cancer; however, a majority of patients with ovarian cancer experience relapse and develop platinum resistance following initial treatment. Despite extensive research on the mechanisms of platinum resistance at the nuclear level, the issue of platinum resistance in ovarian cancer remains largely unresolved. It is noteworthy that mitochondrial DNA (mtDNA) exhibits higher affinity for platinum compared to nuclear DNA (nDNA). Mutations in mtDNA can modulate tumor chemosensitivity through various mechanisms, including DNA damage responses, shifts in energy metabolism, maintenance of Reactive Oxygen Species (ROS) homeostasis, and alterations in mitochondrial dynamics. Concurrently, retrograde signals produced by mtDNA mutations and their subsequent cascades establish communication with the nucleus, leading to the reorganization of the nuclear transcriptome and governing the transcription of genes and signaling pathways associated with chemoresistance. Furthermore, mitochondrial translocation among cells emerges as a crucial factor influencing the effectiveness of chemotherapy in ovarian cancer. This review aims to explore the role and mechanism of mitochondria in platinum resistance, with a specific focus on mtDNA mutations and the resulting metabolic reprogramming, ROS regulation, changes in mitochondrial dynamics, mitochondria-nucleus communication, and mitochondrial transfer.

Potential Mechanisms of Tunneling Nanotube Formation and Their Role in Pathology Spread in Alzheimer's Disease and Other Proteinopathies

Alzheimer's disease (AD) is the most common type of dementia worldwide. The etiopathogenesis of this disease remains unknown. Currently, several hypotheses attempt to explain its cause, with the most well-studied being the cholinergic, beta-amyloid (Aβ), and Tau hypotheses. Lately, there has been increasing interest in the role of immunological factors and other proteins such as alpha-synuclein (α-syn) and transactive response DNA-binding protein of 43 kDa (TDP-43). Recent studies emphasize the role of tunneling nanotubes (TNTs) in the spread of pathological proteins within the brains of AD patients. TNTs are small membrane protrusions composed of F-actin that connect non-adjacent cells. Conditions such as pathogen infections, oxidative stress, inflammation, and misfolded protein accumulation lead to the formation of TNTs. These structures have been shown to transport pathological proteins such as Aβ, Tau, α-syn, and TDP-43 between central nervous system (CNS) cells, as confirmed by in vitro studies. Besides their role in spreading pathology, TNTs may also have protective functions. Neurons burdened with α-syn can transfer protein aggregates to glial cells and receive healthy mitochondria, thereby reducing cellular stress associated with α-syn accumulation. Current AD treatments focus on alleviating symptoms, and clinical trials with Aβ-lowering drugs have proven ineffective. Therefore, intensifying research on TNTs could bring scientists closer to a better understanding of AD and the development of effective therapies.

Macrophage niche imprinting as a determinant of macrophage identity and function

Macrophage niches are the anatomical locations within organs or tissues consisting of various cells, intercellular and extracellular matrix, transcription factors, and signaling molecules that interact to influence macrophage self-maintenance, phenotype, and behavior. The niche, besides physically supporting macrophages, imposes a tissue- and organ-specific identity on the residing and infiltrating monocytes and macrophages. In this review, we give examples of macrophage niches and the modes of communication between macrophages and surrounding cells. We also describe how macrophages, acting against their immune defensive nature, can create a hospitable niche for pathogens and cancer cells.

Cooperation of Various Cytoskeletal Components Orchestrates Intercellular Spread of Mitochondria between B-Lymphoma Cells through Tunnelling Nanotubes

Membrane nanotubes (NTs) are dynamic communication channels connecting spatially separated cells even over long distances and promoting the transport of different cellular cargos. NTs are also involved in the intercellular spread of different pathogens and the deterioration of some neurological disorders. Transport processes via NTs may be controlled by cytoskeletal elements. NTs are frequently observed membrane projections in numerous mammalian cell lines, including various immune cells, but their functional significance in the 'antibody factory' B cells is poorly elucidated. Here, we report that as active channels, NTs of B-lymphoma cells can mediate bidirectional mitochondrial transport, promoted by the cooperation of two different cytoskeletal motor proteins, kinesin along microtubules and myosin VI along actin, and bidirectional transport processes are also supported by the heterogeneous arrangement of the main cytoskeletal filament systems of the NTs. We revealed that despite NTs and axons being different cell extensions, the mitochondrial transport they mediate may exhibit significant similarities. Furthermore, we found that microtubules may improve the stability and lifespan of B-lymphoma-cell NTs, while F-actin strengthens NTs by providing a structural framework for them. Our results may contribute to a better understanding of the regulation of the major cells of humoral immune response to infections.

HMGB1 promotes mitochondrial transfer between hepatocellular carcinoma cells through RHOT1 and RAC1 under hypoxia

Mitochondrial transfer plays an important role in various diseases, and many mitochondrial biological functions can be regulated by HMGB1. To explore the role of mitochondrial transfer in hepatocellular carcinoma (HCC) and its relationship with HMGB1, field emission scanning electron microscopy, immunofluorescence, and flow cytometry were used to detect the mitochondrial transfer between HCC cells. We found that mitochondrial transfer between HCC cells was confirmed using tunnel nanotubes (TNTs). The transfer of mitochondria from the highly invasive HCC cells to the less invasive HCC cells could enhance the migration and invasion ability of the latter. The hypoxic conditions increased the mitochondrial transfer between HCC cells. Then the mechanism was identified using co-immunoprecipitation, luciferase reporter assay, and chromatin immunoprecipitation. We found that RHOT1, a mitochondrial transport protein, promoted mitochondrial transfer and the migration and metastasis of HCC cells during this process. Under hypoxia, HMGB1 further regulated RHOT1 expression by increasing the expression of NFYA and NFYC subunits of the NF-Y complex. RAC1, a protein associated with TNTs formation, promoted mitochondrial transfer and HCC development. Besides, HMGB1 regulated RAC1 aggregation to the cell membrane under hypoxia. Finally, the changes and significance of related molecules in clinical samples of HCC were analyzed using bioinformatics and tissue microarray analyses. We found that HCC patients with high HMGB1, RHOT1, or RAC1 expression exhibited a relatively shorter overall survival period. In conclusion, under hypoxic conditions, HMGB1 promoted mitochondrial transfer and migration and invasion of HCC cells by increasing the expression of mitochondrial transport protein RHOT1 and TNTs formation-related protein RAC1.

Tumor-Stroma Proportion to Predict Chemoresistance in Patients With Ovarian Cancer

IMPORTANCE

Platinum-based chemotherapy is the backbone of standard-of-care treatment for patients with advanced-stage, high-grade serous carcinoma (HGSC), the most common form of ovarian cancer; however, one-third of patients have or acquire chemoresistance toward platinum-based therapies.

OBJECTIVE

To demonstrate the utility of tumor-stroma proportion (TSP) as a predictive biomarker of chemoresistance of HGSC, progression-free survival (PFS), and overall survival (OS).

DESIGN, SETTING, AND PARTICIPANTS

This prognostic study leveraged tumors from patients with HGSC in The Cancer Genome Atlas (TCGA) cohort (1993-2013) and an independent cohort of resected clinical specimens from patients with HGSC (2004-2014) available in diagnostic and tissue microarray formats from the University of Tübingen in Germany. Data analysis was conducted from January 2021 to January 2024.

EXPOSURE

Diagnosis of HGSC.

MAIN OUTCOMES AND MEASURES

Principal outcome measures were the ability of TSP to predict platinum chemoresistance, PFS, and OS. Using hematoxylin and eosin-stained slides from the Tübingen cohort (used for routine diagnostic assessment from surgical specimens) as well as tissue microarrays, representative sections of tumors for scoring of TSP were identified using previously evaluated cutoffs of 50% stroma or greater (high TSP) and less than 50% stroma (low TSP). Digitized slides from the TCGA Cohort were analyzed and scored in a similar fashion. Kaplan-Meier time-to-event functions were fit to estimate PFS and OS.

RESULTS

The study included 103 patients (mean [SD] age, 61.6 [11.1] years) from the TCGA cohort and 192 patients (mean [SD] age at diagnosis, 63.7 [11.1] years) from the Tübingen cohort. In the TCGA cohort, there was no significant association of TSP levels with chemoresistance, PFS, or OS. However, in the Tübingen cohort, high TSP was associated with significantly shorter PFS (HR, 1.586; 95% CI, 1.093-2.302; P = .02) and OS (hazard ratio [HR], 1.867; 1.249-2.789; P = .002). Patients with chemoresistant tumors were twice as likely to have high TSP as compared to patients with chemosensitive tumors (HR, 2.861; 95% CI, 1.256-6.515; P = .01). In tissue microarrays from 185 patients from the Tübingen cohort, high TSP was again associated with significantly shorter PFS (HR, 1.675; 95% CI, 1.012-2.772 P = .04) and OS (HR, 2.491; 95% CI, 1.585-3.912; P < .001).

CONCLUSIONS AND RELEVANCE

In this prognostic study, TSP was a consistent and reproducible marker of clinical outcome measures of HGSC, including PFS, OS, and platinum chemoresistance. Accurate and cost-effective predictive biomarkers of platinum chemotherapy resistance are needed to identify patients most likely to benefit from standard treatments, and TSP can easily be implemented and integrated into prospective clinical trial design and adapted to identify patients who are least likely to benefit long-term from conventional platinum-based cytotoxic chemotherapy treatment at the time of initial diagnosis.

Treatment with tumor-treating fields (TTFields) suppresses intercellular tunneling nanotube formation in vitro and upregulates immuno-oncologic biomarkers in vivo in malignant mesothelioma

Disruption of intercellular communication within tumors is emerging as a novel potential strategy for cancer-directed therapy. Tumor-Treating Fields (TTFields) therapy is a treatment modality that has itself emerged over the past decade in active clinical use for patients with glioblastoma and malignant mesothelioma, based on the principle of using low-intensity alternating electric fields to disrupt microtubules in cancer cells undergoing mitosis. There is a need to identify other cellular and molecular effects of this treatment approach that could explain reported increased overall survival when TTFields are added to standard systemic agents. Tunneling nanotube (TNTs) are cell-contact-dependent filamentous-actin-based cellular protrusions that can connect two or more cells at long-range. They are upregulated in cancer, facilitating cell growth, differentiation, and in the case of invasive cancer phenotypes, a more chemoresistant phenotype. To determine whether TNTs present a potential therapeutic target for TTFields, we applied TTFields to malignant pleural mesothelioma (MPM) cells forming TNTs in vitro. TTFields at 1.0 V/cm significantly suppressed TNT formation in biphasic subtype MPM, but not sarcomatoid MPM, independent of effects on cell number. TTFields did not significantly affect function of TNTs assessed by measuring intercellular transport of mitochondrial cargo via intact TNTs. We further leveraged a spatial transcriptomic approach to characterize TTFields-induced changes to molecular profiles in vivo using an animal model of MPM. We discovered TTFields induced upregulation of immuno-oncologic biomarkers with simultaneous downregulation of pathways associated with cell hyperproliferation, invasion, and other critical regulators of oncogenic growth. Several molecular classes and pathways coincide with markers that we and others have found to be differentially expressed in cancer cell TNTs, including MPM specifically. We visualized short TNTs in the dense stromatous tumor material selected as regions of interest for spatial genomic assessment. Superimposing these regions of interest from spatial genomics over the plane of TNT clusters imaged in intact tissue is a new method that we designate Spatial Profiling of Tunneling nanoTubes (SPOTT). In sum, these results position TNTs as potential therapeutic targets for TTFields-directed cancer treatment strategies. We also identified the ability of TTFields to remodel the tumor microenvironment landscape at the molecular level, thereby presenting a potential novel strategy for converting tumors at the cellular level from 'cold' to 'hot' for potential response to immunotherapeutic drugs.

Tunneling nanotubes: The intercellular conduits contributing to cancer pathogenesis and its therapy

Tunneling nanotubes (TNTs) are intercellular conduits which meet the communication needs of non-adjacent cells situated in the same tissue but at distances up to a few hundred microns. TNTs are unique type of membrane protrusion which contain F-actin and freely hover over substratum in the extracellular space to connect the distant cells. TNTs, known to form through actin remodeling mechanisms, are intercellular bridges that connect cytoplasm of two cells, and facilitate the transfer of organelles, molecules, and pathogens among the cells. In tumor microenvironment, TNTs act as communication channel among cancer, normal, and immune cells to facilitate the transfer of calcium waves, mitochondria, lysosomes, and proteins, which in turn contribute to the survival, metastasis, and chemo-resistance in cancer cells. Recently, TNTs were shown to mediate the transfer of nanoparticles, drugs, and viruses between cells, suggesting that TNTs could be exploited as a potential route for delivery of anti-cancer agents and oncolytic viruses to the target cells. The present review discusses the emerging concepts and role of TNTs in the context of chemo- and radio-resistance with implications in the cancer therapy.

Clinical Significance of the Stromatic Component in Ovarian Cancer: Quantity Over Quality in Outcome Prediction

Background

The tumor stroma is composed of a complex network of non-cancerous cells and extracellular matrix elements that collectively are crucial for cancer progression and treatment response. Within the realm of ovarian cancer, the expression of the stromal gene cluster has been linked to poorer progression-free and overall survival rates. However, in the age of precision medicine and genome sequencing, the notion that the simple measurement of tumor-stroma proportion alone can serve as a biomarker for clinical outcome is a topic that continues to generate controversy and provoke discussion. Our current study reveals that it is the quantity of stroma, rather than its quality, that serves as a clinically significant indicator of patient outcome in ovarian cancer.

Methods

This study leveraged the High-Grade-Serous-Carcinoma (HGSC) cohort of the publicly accessible Cancer Genome Atlas Program (TCGA) along with an independent cohort comprising HGSC clinical specimens in diagnostic and Tissue Microarray formats. Our objective was to investigate the correlation between the Tumor-Stroma-Proportion (TSP) and progression-free survival (PFS), overall survival (OS), and response to chemotherapy. We assessed these associations using H&E-stained slides and tissue microarrays. Our analysis employed semi-parametric models that accounted for age, metastases, and residual disease as controlling factors.

Results

We found that high TSP (>50% stroma) was associated with significantly shorter progression-free survival (PFS) (p=0.016) and overall survival (OS) (p=0.006). Tumors from patients with chemoresistant tumors were twice as likely to have high TSP as compared to tumors from chemosensitive patients (p=0.012). In tissue microarrays, high TSP was again associated with significantly shorter PFS (p=0.044) and OS (p=0.0001), further confirming our findings. The Area Under the ROC curve for the model predicting platinum was estimated at 0.7644.

Conclusions

In HGSC, TSP was a consistent and reproducible marker of clinical outcome measures, including PFS, OS, and platinum chemoresistance. Assessment of TSP as a predictive biomarker that can be easily implemented and integrated into prospective clinical trial design and adapted to identify, at time of initial diagnosis, patients who are least likely to benefit long-term from conventional platinum-based cytotoxic chemotherapy treatment.

Hijacking intercellular trafficking for the spread of protein aggregates in neurodegenerative diseases: a focus on tunneling nanotubes (TNTs)

Over the years, the influence of secretory mechanisms on intercellular communication has been extensively studied. In the central nervous system (CNS), both trans-synaptic (neurotransmitter-based) and long-distance (extracellular vesicles-based) communications regulate activities and homeostasis. In less than a couple of decades, however, there has been a major paradigm shift in our understanding of intercellular communication. Increasing evidence suggests that besides secretory mechanisms (via extracellular vesicles), several cells are capable of establishing long-distance communication routes referred to as Tunneling Nanotubes (TNTs). TNTs are membranous bridges classically supported by F-Actin filaments, allowing for the exchange of different types of intracellular components between the connected cells, ranging from ions and organelles to pathogens and toxic protein aggregates. The roles of TNTs in pathological spreading of several neurodegenerative conditions such as Prion diseases, Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) have been well established. However, the fragile nature of these structures and lack of specific biomarkers raised some skepticism regarding their existence. In this review, we will first place TNTs within the spectrum of intercellular communication mechanisms before discussing their known and hypothesized biological relevance in vitro and in vivo in physiological and neurodegenerative contexts. Finally, we discuss the challenges and promising prospects in the field of TNT studies.

Protective effect of the tunneling nanotube-TNFAIP2/M-sec system on podocyte autophagy in diabetic nephropathy

Podocyte injury leading to albuminuria is a characteristic feature of diabetic nephropathy (DN). Hyperglycemia and advanced glycation end products (AGEs) are major determinants of DN. However, the underlying mechanisms of podocyte injury remain poorly understood. The cytosolic protein TNFAIP2/M-Sec is required for tunneling nanotubes (TNTs) formation, which are membrane channels that transiently connect cells, allowing organelle transfer. Podocytes express TNFAIP2 and form TNTs, but the potential relevance of the TNFAIP2-TNT system in DN is unknown. We studied TNFAIP2 expression in both human and experimental DN and the renal effect of tnfaip2 deletion in streptozotocin-induced DN. Moreover, we explored the role of the TNFAIP2-TNT system in podocytes exposed to diabetes-related insults. TNFAIP2 was overexpressed by podocytes in both human and experimental DN and exposre of podocytes to high glucose and AGEs induced the TNFAIP2-TNT system. In diabetic mice, tnfaip2 deletion exacerbated albuminuria, renal function loss, podocyte injury, and mesangial expansion. Moreover, blockade of the autophagic flux due to lysosomal dysfunction was observed in diabetes-injured podocytes both in vitro and in vivo and exacerbated by tnfaip2 deletion. TNTs allowed autophagosome and lysosome exchange between podocytes, thereby ameliorating AGE-induced lysosomal dysfunction and apoptosis. This protective effect was abolished by tnfaip2 deletion, TNT inhibition, and donor cell lysosome damage. By contrast, Tnfaip2 overexpression enhanced TNT-mediated transfer and prevented AGE-induced autophagy and lysosome dysfunction and apoptosis. In conclusion, TNFAIP2 plays an important protective role in podocytes in the context of DN by allowing TNT-mediated autophagosome and lysosome exchange and may represent a novel druggable target.Abbreviations: AGEs: advanced glycation end products; AKT1: AKT serine/threonine kinase 1; AO: acridine orange; ALs: autolysosomes; APs: autophagosomes; BM: bone marrow; BSA: bovine serum albumin; CTSD: cathepsin D; DIC: differential interference contrast; DN: diabetic nephropathy; FSGS: focal segmental glomerulosclerosis; HG: high glucose; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LMP: lysosomal membrane permeabilization; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; PI3K: phosphoinositide 3-kinase; STZ: streptozotocin; TNF: tumor necrosis factor; TNFAIP2: tumor necrosis factor, alpha-induced protein 2; TNTs: tunneling nanotubes; WT: wild type.

Molecular, morphological and functional properties of tunnelling nanotubes between normal and cancer urothelial cells: New insights from the in vitro model mimicking the situation after surgical removal of the urothelial tumor

Tunnelling nanotubes (TNTs) are membranous connections that represent a unique type of intercellular communication in different cell types. They are associated with cell physiology and cancer pathology. The possible existence of tunnelling nanotubes communication between urothelial cancer and normal cells has not yet been elucidated. Therefore, we analyzed TNTs formed by T24 cells (human invasive cancer urothelial cells) and normal porcine urothelial (NPU) cells, which serve as surrogate models for healthy human urothelial cells. Monocultures and cocultures of NPU and T24 cells were established and analyzed using live-cell imaging, optical tweezers, fluorescence microscopy, and scanning electron microscopy. TNTs of NPU cells differed significantly from tunnelling nanotubes of T24 cells in number, length, diameter, lipid composition, and elastic properties. Membrane domains enriched in cholesterol/sphingomyelin were present in tunnelling nanotubes of T24 cells but not in NPU cells. The tunnelling nanotubes in T24 cells were also easier to bend than the tunnelling nanotubes in NPU cells. The tunnelling nanotubes of both cell types were predominantly tricytoskeletal, and contained actin filaments, intermediate filaments, and microtubules, as well as the motor proteins myosin Va, dynein, and kinesin 5B. Mitochondria were transported within tunnelling nanotubes in living cells, and were colocalized with microtubules and the microtubule-associated protein dynamin 2. In cocultures, heterocellular tunnelling nanotubes were formed between NPU cells and T24 cells and vice versa. The presence of connexin 43 at the end of urothelial tunnelling nanotubes suggests a junctional connection and the involvement of tunnelling nanotube in signal transduction. In this study, we established a novel urothelial cancer-normal coculture model and showed cells in the minority tend to form tunnelling nanotubes with cells in the majority. The condition with cancer cells in the minority is an attractive model to mimic the situation after surgical resection with remaining cancer cells and may help to understand cancer progression and recurrence. Our results shed light on the biological activity of tunnelling nanotubes and have the potential to advance the search for anticancer drugs that target tunnelling nanotubes.

Delineating the dynamic evolution from preneoplasia to invasive lung adenocarcinoma by integrating single-cell RNA sequencing and spatial transcriptomics

The cell ecology and spatial niche implicated in the dynamic and sequential process of lung adenocarcinoma (LUAD) from adenocarcinoma in situ (AIS) to minimally invasive adenocarcinoma (MIA) and subsequent invasive adenocarcinoma (IAC) have not yet been elucidated. Here, we performed an integrative analysis of single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) to characterize the cell atlas of the invasion trajectory of LUAD. We found that the UBE2C + cancer cell subpopulation constantly increased during the invasive process of LUAD with remarkable elevation in IAC, and its spatial distribution was in the peripheral cancer region of the IAC, representing a more malignant phenotype. Furthermore, analysis of the TME cell type subpopulation showed a constant decrease in mast cells, monocytes, and lymphatic endothelial cells, which were implicated in the whole process of invasive LUAD, accompanied by an increase in NK cells and MALT B cells from AIS to MIA and an increase in Tregs and secretory B cells from MIA to IAC. Notably, for AIS, cancer cells, NK cells, and mast cells were colocalized in the cancer region; however, for IAC, Tregs colocalized with cancer cells. Finally, communication and interaction between cancer cells and TME cell-induced constitutive activation of TGF-β signaling were involved in the invasion of IAC. Therefore, our results reveal the specific cellular information and spatial architecture of cancer cells and TME subpopulations, as well as the cellular interaction between them, which will facilitate the identification and development of precision medicine in the invasive process of LUAD from AIS to IAC.

TNTdetect.AI: A Deep Learning Model for Automated Detection and Counting of Tunneling Nanotubes in Microscopy Images

BACKGROUND

Tunneling nanotubes (TNTs) are cellular structures connecting cell membranes and mediating intercellular communication. TNTs are manually identified and counted by a trained investigator; however, this process is time-intensive. We therefore sought to develop an automated approach for quantitative analysis of TNTs.

METHODS

We used a convolutional neural network (U-Net) deep learning model to segment phase contrast microscopy images of both cancer and non-cancer cells. Our method was composed of preprocessing and model development. We developed a new preprocessing method to label TNTs on a pixel-wise basis. Two sequential models were employed to detect TNTs. First, we identified the regions of images with TNTs by implementing a classification algorithm. Second, we fed parts of the image classified as TNT-containing into a modified U-Net model to estimate TNTs on a pixel-wise basis.

RESULTS

The algorithm detected 49.9% of human expert-identified TNTs, counted TNTs, and calculated the number of TNTs per cell, or TNT-to-cell ratio (TCR); it detected TNTs that were not originally detected by the experts. The model had 0.41 precision, 0.26 recall, and 0.32 f-1 score on a test dataset. The predicted and true TCRs were not significantly different across the training and test datasets (p = 0.78).

CONCLUSIONS

Our automated approach labeled and detected TNTs and cells imaged in culture, resulting in comparable TCRs to those determined by human experts. Future studies will aim to improve on the accuracy, precision, and recall of the algorithm.

Tunneling Nanotubes between Cells Migrating in ECM Mimicking Fibrous Environments

Simple Summary

Tumor cells grow, spread, and invade in a three-dimensional manner, but most experimental approaches in cancer cell biology focus on the behavior of cells in two-dimensional spaces. Patterns of cell invasion and spread in 2D may not accurately depict cell behavior in 3D tumors. We cultivated and investigated malignant mesothelioma cells on a 3D scaffold composed of nanofibers positioned in parallel and crosshatched network configurations to overcome this barrier. We focused on studying long extensions called tunneling nanotubes (TNTs) protruding from cells and connecting with other cells, which have been shown to transmit signals from cell to cell and extend into the tumor microenvironments in a 3D manner. This manuscript describes the biophysics of the formation and function of cancer cell TNTs. These findings will impact the research community by accurately assessing how TNTs affect cancer cell invasion and migration in their natural 3D microenvironment using a novel bioengineered platform.

Abstract

Tunneling nanotubes (TNTs) comprise a unique class of actin-rich nanoscale membranous protrusions. They enable long-distance intercellular communication and may play an integral role in tumor formation, progression, and drug resistance. TNTs are three-dimensional, but nearly all studies have investigated them using two-dimensional cell culture models. Here, we applied a unique 3D culture platform consisting of crosshatched and aligned fibers to fabricate synthetic suspended scaffolds that mimic the native fibrillar architecture of tumoral extracellular matrix (ECM) to characterize TNT formation and function in its native state. TNTs are upregulated in malignant mesothelioma; we used this model to analyze the biophysical properties of TNTs in this 3D setting, including cell migration in relation to TNT dynamics, rate of TNT-mediated intercellular transport of cargo, and conformation of TNT-forming cells. We found that highly migratory elongated cells on aligned fibers formed significantly longer but fewer TNTs than uniformly spread cells on crossing fibers. We developed new quantitative metrics for the classification of TNT morphologies based on shape and cytoskeletal content using confocal microscopy. In sum, our strategy for culturing cells in ECM-mimicking bioengineered scaffolds provides a new approach for accurate biophysical and biologic assessment of TNT formation and structure in native fibrous microenvironments.

Oxidative stress and Rho GTPases in the biogenesis of tunnelling nanotubes: implications in disease and therapy

Tunnelling nanotubes (TNTs) are an emerging route of long-range intercellular communication that mediate cell-to-cell exchange of cargo and organelles and contribute to maintaining cellular homeostasis by balancing diverse cellular stresses. Besides their role in intercellular communication, TNTs are implicated in several ways in health and disease. Transfer of pathogenic molecules or structures via TNTs can promote the progression of neurodegenerative diseases, cancer malignancy, and the spread of viral infection. Additionally, TNTs contribute to acquiring resistance to cancer therapy, probably via their ability to rescue cells by ameliorating various pathological stresses, such as oxidative stress, reactive oxygen species (ROS), mitochondrial dysfunction, and apoptotic stress. Moreover, mesenchymal stem cells play a crucial role in the rejuvenation of targeted cells with mitochondrial heteroplasmy and oxidative stress by transferring healthy mitochondria through TNTs. Recent research has focussed on uncovering the key regulatory molecules involved in the biogenesis of TNTs. However further work will be required to provide detailed understanding of TNT regulation. In this review, we discuss possible associations with Rho GTPases linked to oxidative stress and apoptotic signals in biogenesis pathways of TNTs and summarize how intercellular trafficking of cargo and organelles, including mitochondria, via TNTs plays a crucial role in disease progression and also in rejuvenation/therapy.

Extracellular Vesicles Induce an Aggressive Phenotype in Luminal Breast Cancer Cells Via PKM2 Phosphorylation

BACKGROUND

Aerobic glycolysis is a hallmark of glucose metabolism in cancer. Previous studies have suggested that cancer cell-derived extracellular vesicles (EVs) can modulate glucose metabolism in adjacent cells and promote disease progression. We hypothesized that EVs originating from cancer cells can modulate glucose metabolism in recipient cancer cells to induce cell proliferation and an aggressive cancer phenotype.

METHODS

Two breast cancer cell lines with different levels of glycolytic activity, MDA-MB-231 cells of the claudin-low subtype and MCF7 cells of the luminal type, were selected and cocultured as the originating and recipient cells, respectively, using an indirect coculture system, such as a Transwell system or a microfluidic system. The [18F]fluorodeoxyglucose (FDG) uptake by the recipient MCF7 cells was assessed before and after coculture with MDA-MB-231 cells. Proteomic and transcriptomic analyses were performed to investigate the changes in gene expression patterns in the recipient MCF7 cells and MDA-MB-231 cell-derived EVs.

RESULTS

FDG uptake by the recipient MCF7 cells significantly increased after coculture with MDA-MB-231 cells. In addition, phosphorylation of PKM2 at tyrosine-105 and serine-37, which is necessary for tumorigenesis and aerobic glycolysis, was highly activated in cocultured MCF7 cells. Proteomic profiling revealed the proliferation and dedifferentiation of MCF7 cells following coculture with MDA-MB-231 cells. Transcriptomic analysis demonstrated an increase in glycolysis in cocultured MCF7 cells, and the component analysis of glycolysis-related genes revealed that the second most abundant component after the cytoplasm was extracellular exosomes. In addition, proteomic analysis of EVs showed that the key proteins capable of phosphorylating PKM2 were present as cargo inside MDA-MB-231 cell-derived EVs.

CONCLUSIONS

The phenomena observed in this study suggest that cancer cells can induce a phenotype transition of other subtypes to an aggressive phenotype to consequently activate glucose metabolism via EVs. Therefore, this study could serve as a cornerstone for further research on interactions between cancer cells.

Movement of Mitochondria with Mutant DNA through Extracellular Vesicles Helps Cancer Cells Acquire Chemoresistance

Triple negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer with the worst prognosis after chemo- or radiation therapy. This is mainly due to the development of cancer chemoresistance accompanied by tumor recurrence. In this work, we investigated a new mechanism of acquired chemoresistance of TNBC cells. We showed that extracellular vehicles (EVs) of chemoresistant TNBC cells can transfer mitochondria to sensitive cancer cells, thus increasing their chemoresistance. Such transfer, but with less efficiency, can be carried out over short distances using tunneling nanotubes. In addition, we showed that exosome fractions carrying mitochondria from resistant TNBC cells contribute to acquired chemoresistance by increasing mtDNA levels with mutations in the mtND4 gene responsible for tumorigenesis. Blocking mitochondrial transport by exosome inhibitors, including GW4869, reduced acquired TNBC chemoresistance. These results could lead to the identification of new molecular targets necessary for more effective treatment of this type of cancer.

Membrane nanotubes are ancient machinery for cell-to-cell communication and transport. Their interference with the immune system

Nanotubular connections between mammalian cell types came into the focus only two decades ago, when “live cell super-resolution imaging” was introduced. Observations of these long-time overlooked structures led to understanding mechanisms of their growth/withdrawal and exploring some key genetic and signaling factors behind their formation. Unbelievable level of multiple supportive collaboration between tumor cells undergoing cytotoxic chemotherapy, cross-feeding” between independent bacterial strains or “cross-dressing” collaboration of immune cells promoting cellular immune response, all via nanotubes, have been explored recently. Key factors and "calling signals" determining the spatial directionality of their growth and their overall in vivo significance, however, still remained debated. Interestingly, prokaryotes, including even ancient archaebacteria, also seem to use such NT connections for intercellular communication. Herein, we will give a brief overview of current knowledge of membrane nanotubes and depict a simple model about their possible “historical role”.

Secretome and Tunneling Nanotubes: A Multilevel Network for Long Range Intercellular Communication between Endothelial Cells and Distant Cells

As a cellular interface between the blood and tissues, the endothelial cell (EC) monolayer is involved in the control of key functions including vascular tone, permeability and homeostasis, leucocyte trafficking and hemostasis. EC regulatory functions require long-distance communications between ECs, circulating hematopoietic cells and other vascular cells for efficient adjusting thrombosis, angiogenesis, inflammation, infection and immunity. This intercellular crosstalk operates through the extracellular space and is orchestrated in part by the secretory pathway and the exocytosis of Weibel Palade Bodies (WPBs), secretory granules and extracellular vesicles (EVs). WPBs and secretory granules allow both immediate release and regulated exocytosis of messengers such as cytokines, chemokines, extracellular membrane proteins, coagulation or growth factors. The ectodomain shedding of transmembrane protein further provide the release of both receptor and ligands with key regulatory activities on target cells. Thin tubular membranous channels termed tunneling nanotubes (TNTs) may also connect EC with distant cells. EVs, in particular exosomes, and TNTs may contain and transfer different biomolecules (e.g., signaling mediators, proteins, lipids, and microRNAs) or pathogens and have emerged as a major triggers of horizontal intercellular transfer of information.

MICAL2PV suppresses the formation of tunneling nanotubes and modulates mitochondrial trafficking

Tunneling nanotubes (TNTs) are actin-rich structures that connect two or more cells and mediate cargo exchange between spatially separated cells. TNTs transport signaling molecules, vesicles, organelles, and even pathogens. However, the molecular mechanisms regulating TNT formation remain unclear and little is known about the endogenous mechanisms suppressing TNT formation in lung cancer cells. Here, we report that MICAL2PV, a splicing isoform of the neuronal guidance gene MICAL2, is a novel TNT regulator that suppresses TNT formation and modulates mitochondrial distribution. MICAL2PV interacts with mitochondrial Rho GTPase Miro2 and regulates subcellular mitochondrial trafficking. Moreover, down-regulation of MICAL2PV enhances survival of cells treated with chemotherapeutical drugs. The monooxygenase (MO) domain of MICAL2PV is required for its activity to inhibit TNT formation by depolymerizing F-actin. Our data demonstrate a previously unrecognized function of MICAL2 in TNT formation and mitochondrial trafficking. Furthermore, our study uncovers a role of the MICAL2PV-Miro2 axis in mitochondrial trafficking, providing a mechanistic explanation for MICAL2PV activity in suppressing TNT formation and in modulating mitochondrial subcellular distribution.

Protective Role of the M-Sec-Tunneling Nanotube System in Podocytes

BACKGROUND

Podocyte dysfunction and loss are major determinants in the development of proteinuria. FSGS is one of the most common causes of proteinuria, but the mechanisms leading to podocyte injury or conferring protection against FSGS remain poorly understood. The cytosolic protein M-Sec has been involved in the formation of tunneling nanotubes (TNTs), membrane channels that transiently connect cells and allow intercellular organelle transfer. Whether podocytes express M-Sec is unknown and the potential relevance of the M-Sec-TNT system in FSGS has not been explored.

METHODS

We studied the role of the M-Sec-TNT system in cultured podocytes exposed to Adriamycin and in BALB/c M-Sec knockout mice. We also assessed M-Sec expression in both kidney biopsies from patients with FSGS and in experimental FSGS (Adriamycin-induced nephropathy).

RESULTS

Podocytes can form TNTs in a M-Sec-dependent manner. Consistent with the notion that the M-Sec-TNT system is cytoprotective, podocytes overexpressed M-Sec in both human and experimental FSGS. Moreover, M-Sec deletion resulted in podocyte injury, with mitochondrial abnormalities and development of progressive FSGS. In vitro, M-Sec deletion abolished TNT-mediated mitochondria transfer between podocytes and altered mitochondrial bioenergetics. Re-expression of M-Sec reestablishes TNT formation and mitochondria exchange, rescued mitochondrial function, and partially reverted podocyte injury.

CONCLUSIONS

These findings indicate that the M-Sec-TNT system plays an important protective role in the glomeruli by rescuing podocytes via mitochondrial horizontal transfer. M-Sec may represent a promising therapeutic target in FSGS, and evidence that podocytes can be rescued via TNT-mediated horizontal transfer may open new avenues of research.

Oxygen gradient and tumor heterogeneity: The chronicle of a toxic relationship

The commencement of cancer is attributed to one or a few cells that become rogue and attain the property of immortality. The inception of distinct cancer cell clones during the hyperplastic and dysplastic stages of cancer progression is the utimate consequence of the dysregulated cellular pathways and the proliferative potential itself. Furthermore, a critical factor that adds a layer of complexity to this pre-existent intra-tumoral heterogeneity (ITH) is the foundation of an oxygen gradient, that is established due to the improper architecture of the tumor vasculature. Therefore, as a resultant effect, the poorly oxygenated regions thus formed and characterized as hypoxic, promote the emergence of aggressive and treatment-resistant cancer cell clones. The extraordinary property of the hypoxic cancer cells to exist harmoniously with cancerous and non-cancerous cells in the tumor microenvironment (TME) further increases the intricacies of ITH. Here in this review, the pivotal influence of differential oxygen concentrations in shaping the ITH is thoroughly discussed. We also emphasize on the vitality of the interacting networks that govern the overall fate of oxygen gradient-dependent origin of tumor heterogeneity. Additionally, the implications of less-appreciated reverse Warburg effect, a symbiotic metabolic coupling, and the associated epigenetic regulation of rewiring of cancer metabolism in response to oxygen gradients, have been highlighted as critical influencers of ITH.

Science-Driven Societal Transformation, Part III: Design

Climate change, biodiversity loss, and other major social and environmental problems pose severe risks. Progress has been inadequate and scientists, global policy experts, and the general public increasingly conclude that transformational change is needed across all sectors of society in order to improve and maintain social and ecological wellbeing. At least two paths to transformation are conceivable: (1) reform of and innovation within existing societal systems (e.g., economic, legal, and governance systems); and (2) the de novo development of and migration to new and improved societal systems. This paper is the final in a three-part series of concept papers that together outline a novel science-driven research and development program aimed at the second path. It summarizes literature to build a narrative on the topic of de novo design of societal systems. The purpose is to raise issues, suggest design possibilities, and highlight directions and questions that could be explored in the context of this or any R&D program aimed at new system design. This paper does not present original research, but rather provides a synthesis of selected ideas from the literature. Following other papers in the series, a society is viewed as a superorganism and its societal systems as a cognitive architecture. Accordingly, a central goal of design is to improve the collective cognitive capacity of a society, rendering it more capable of achieving and sustainably maintaining vitality. Topics of attention, communication, self-identity, power, and influence are discussed in relation to societal cognition and system design. A prototypical societal system is described, and some design considerations are highlighted.

UNC-45A breaks the microtubule lattice independently of its effects on non-muscle myosin II

In invertebrates, UNC-45 regulates myosin stability and functions. Vertebrates have two distinct isoforms of the protein: UNC-45B, expressed in muscle cells only, and UNC-45A, expressed in all cells and implicated in regulating both non-muscle myosin II (NMII)- and microtubule (MT)-associated functions. Here, we show that, in vitro and in human and rat cells, UNC-45A binds to the MT lattice, leading to MT bending, breakage and depolymerization. Furthermore, we show that UNC-45A destabilizes MTs independent of its C-terminal NMII-binding domain and even in the presence of the NMII inhibitor blebbistatin. These findings identified UNC-45A as a novel type of MT-severing protein with a dual non-mutually exclusive role in regulating NMII activity and MT stability. Because many human diseases, from cancer to neurodegenerative diseases, are caused by or associated with deregulation of MT stability, our findings have profound implications in the biology of MTs, as well as the biology of human diseases and possible therapeutic implications for their treatment.This article has an associated First Person interview with the joint first authors of the paper.

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.

Influence of α-Particle Radiation on Intercellular Communication Networks of Tunneling Nanotubes in U87 Glioblastoma Cells

Cellular communication plays a crucial role in the coordination and organization of cancer cells. Especially processes such as uncontrolled cell growth, invasion, and therapy resistance (development), which are features of very malignant tumors like glioblastomas, are supported by an efficient cell-to-cell communication in the tumor environment. One powerful way for cells to communicate are tunneling nanotubes (TNTs). These tiny membrane tunnels interconnect cells over long distances and serve as highways for information exchange between distant cells. Here, we study the response of cellular communication via TNTs in U87 glioblastoma cells to homogeneous irradiation with α-particles as a stress factor. We describe the development of TNT networks in certain time steps after irradiation using confocal live-cell imaging and suggest an evaluation method to characterize these communication networks. Our results show that irradiated cells establish their network faster and have more cell-to-cell connections with high TNT content than sham-irradiated controls within the first 24 h. These findings suggest that there is an additional trigger upon radiation damage which results in fast and intensive network formation by TNTs as a radiation damage response mechanism.

Investigating Tunneling Nanotubes in Cancer Cells: Guidelines for Structural and Functional Studies through Cell Imaging

By allowing insured communication between cancer cells themselves and with the neighboring stromal cells, tunneling nanotubes (TNTs) are involved in the multistep process of cancer development from tumorigenesis to the treatment resistance. However, despite their critical role in the biology of cancer, the study of the TNTs has been announced challenging due to not only the absence of a specific biomarker but also the fragile and transitory nature of their structure and the fact that they are hovering freely above the substratum. Here, we proposed to review guidelines to follow for studying the structure and functionality of TNTs in tumoral neuroendocrine cells (PC12) and nontumorigenic human bronchial epithelial cells (HBEC-3, H28). In particular, we reported how crucial is it (i) to consider the culture conditions (culture surface, cell density), (ii) to visualize the formation of TNTs in living cells (mechanisms of formation, 3D representation), and (iii) to identify the cytoskeleton components and the associated elements (categories, origin, tip, and formation/transport) in the TNTs. We also focused on the input of high-resolution cell imaging approaches including Stimulated Emission Depletion (STED) nanoscopy, Transmitted and Scanning Electron Microscopies (TEM and SEM). In addition, we underlined the important role of the organelles in the mechanisms of TNT formation and transfer between the cancer cells. Finally, new biological models for the identification of the TNTs between cancer cells and stromal cells (liquid air interface, ex vivo, in vivo) and the clinical considerations will also be discussed.

Tunneling Nanotubes and the Eye: Intercellular Communication and Implications for Ocular Health and Disease

Cellular communication is an essential process for the development and maintenance of all tissues including the eye. Recently, a new method of cellular communication has been described, which relies on formation of tubules, called tunneling nanotubes (TNTs). These structures connect the cytoplasm of adjacent cells and allow the direct transport of cellular cargo between cells without the need for secretion into the extracellular milieu. TNTs may be an important mechanism for signaling between cells that reside long distances from each other or for cells in aqueous environments, where diffusion-based signaling is challenging. Given the wide range of cargoes transported, such as lysosomes, endosomes, mitochondria, viruses, and miRNAs, TNTs may play a role in normal homeostatic processes in the eye as well as function in ocular disease. This review will describe TNT cellular communication in ocular cell cultures and the mammalian eye in vivo, the role of TNTs in mitochondrial transport with an emphasis on mitochondrial eye diseases, and molecules involved in TNT biogenesis and their function in eyes, and finally, we will describe TNT formation in inflammation, cancer, and stem cells, focusing on pathological processes of particular interest to vision scientists.

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.

A Comprehensive Picture of Extracellular Vesicles and Their Contents. Molecular Transfer to Cancer Cells

Critical processes such as growth, invasion, and metastasis of cancer cells are sustained via bidirectional cell-to-cell communication in tissue complex environments. Such communication involves the secretion of soluble factors by stromal cells and/or cancer cells within the tumor microenvironment (TME). Both stromal and cancer cells have been shown to export bilayer nanoparticles: encapsulated regulatory molecules that contribute to cell-to-cell communication. These nanoparticles are known as extracellular vesicles (EVs) being classified into exosomes, microvesicles, and apoptotic bodies. EVs carry a vast repertoire of molecules such as oncoproteins and oncopeptides, DNA fragments from parental to target cells, RNA species (mRNAs, microRNAs, and long non-coding RNA), and lipids, initiating phenotypic changes in TME. According to their specific cargo, EVs have crucial roles in several early and late processes associated with tumor development and metastasis. Emerging evidence suggests that EVs are being investigated for their implication in early cancer detection, monitoring cancer progression and chemotherapeutic response, and more relevant, the development of novel targeted therapeutics. In this study, we provide a comprehensive understanding of the biophysical properties and physiological functions of EVs, their implications in TME, and highlight the applicability of EVs for the development of cancer diagnostics and therapeutics.

Perspectives of cellular communication through tunneling nanotubes in cancer cells and the connection to radiation effects

Direct cell-to-cell communication is crucial for the survival of cells in stressful situations such as during or after radiation exposure. This communication can lead to non-targeted effects, where non-treated or non-infected cells show effects induced by signal transduction from non-healthy cells or vice versa. In the last 15 years, tunneling nanotubes (TNTs) were identified as membrane connections between cells which facilitate the transfer of several cargoes and signals. TNTs were identified in various cell types and serve as promoter of treatment resistance e.g. in chemotherapy treatment of cancer. Here, we discuss our current understanding of how to differentiate tunneling nanotubes from other direct cellular connections and their role in the stress reaction of cellular networks. We also provide a perspective on how the capability of cells to form such networks is related to the ability to surpass stress and how this can be used to study radioresistance of cancer cells.

Comparative Approach to the Temporo-Spatial Organization of the Tumor Microenvironment

The complex ecosystem in which tumor cells reside and interact, termed the tumor microenvironment (TME), encompasses all cells and components associated with a neoplasm that are not transformed cells. Interactions between tumor cells and the TME are complex and fluid, with each facet coercing the other, largely, into promoting tumor progression. While the TME in humans is relatively well-described, a compilation and comparison of the TME in our canine counterparts has not yet been described. As is the case in humans, dog tumors exhibit greater heterogeneity than what is appreciated in laboratory animal models, although the current level of knowledge on similarities and differences in the TME between dogs and humans, and the practical implications of that information, require further investigation. This review summarizes some of the complexities of the human and mouse TME and interjects with what is known in the dog, relaying the information in the context of the temporo-spatial organization of the TME. To the authors' knowledge, the development of the TME over space and time has not been widely discussed, and a comprehensive review of the canine TME has not been done. The specific topics covered in this review include cellular invasion and interactions within the TME, metabolic derangements in the TME and vascular invasion, and the involvement of the TME in tumor spread and metastasis.

Gap junction protein connexin43 and tunneling nanotubes in human trabecular meshwork cells

Intercellular communication via gap junctions and tunneling nanotubes (TNT) play pivotal roles for cell differentiation and proliferation and homeostasis. Intercellular communication has been found in human trabecular meshwork cells, which are key elements for allowing the direct passing aqueous humor and for maintaining the homeostasis of intraocular pressure. Here we showed the expression of gap junction protein connexin43 in human trabecular meshwork cells, and the presence of TNTs in these cells labeled with enhanced GFP generated using highly efficient lentiviral transduction. More importantly, the TNTs in human trabecular meshwork cells were significantly reduced after shRNA or CRISPR Cas9 mediated knockdown of Cx43 in these cells. The results indicated that gap junction protein connexin43 may play an important role in TNTs formation in human trabecular meshwork cells.

Cytoneme-mediated signaling essential for tumorigenesis

Communication between neoplastic cells and cells of their microenvironment is critical to cancer progression. To investigate the role of cytoneme-mediated signaling as a mechanism for distributing growth factor signaling proteins between tumor and tumor-associated cells, we analyzed EGFR and RET Drosophila tumor models and tested several genetic loss-of-function conditions that impair cytoneme-mediated signaling. Neuroglian, capricious, Irk2, SCAR, and diaphanous are genes that cytonemes require during normal development. Neuroglian and Capricious are cell adhesion proteins, Irk2 is a potassium channel, and SCAR and Diaphanous are actin-binding proteins, and the only process to which they are known to contribute jointly is cytoneme-mediated signaling. We observed that diminished function of any one of these genes suppressed tumor growth and increased organism survival. We also noted that EGFR-expressing tumor discs have abnormally extensive tracheation (respiratory tubes) and ectopically express Branchless (Bnl, a FGF) and FGFR. Bnl is a known inducer of tracheation that signals by a cytoneme-mediated process in other contexts, and we determined that exogenous over-expression of dominant negative FGFR suppressed tumor growth. Our results are consistent with the idea that cytonemes move signaling proteins between tumor and stromal cells and that cytoneme-mediated signaling is required for tumor growth and malignancy.

The growth of many types of tumors depend on productive interactions with stromal, non-tumor neighbors, and although there is evidence that tumor and stromal cells exchange signaling proteins and growth factors that they produce, the mechanism by which these proteins move between the signaling cells has not been investigated and is not known. Our previous work has shown that normal cells make transient chemical synapses at sites where specialized filopodia called cytonemes contact signaling partners, and in this work we explore the possibility that tumors use the same mechanism to communicate with stromal cells. We show that cytoneme-mediated signaling is essential for growth of Drosophila tumors that model human EGFR over-expression and RET-driven disease. Remarkably, inhibition of cytonemes cures flies of lethal tumors.

Highly luminescent Zn-Cu-In-S/ZnS core/gradient shell quantum dots prepared from indium sulfide by cation exchange for cell labeling and polymer composites

Gradient core-shell Zn-Cu-In-S/ZnS quantum dots (QDs) of small size and with highly efficient photoluminescence were synthesized via a multi-step high-temperature method involving cation exchange. The procedure starts with the preparation of indium sulfide nanoparticles followed by the addition of Cu and Zn precursors. At this stage, Zn replaces Cu atoms and as a result the concentration of Cu ions in the final QDs is only about 5% of the total In content in a QD. Zn incorporation and the formation of a gradient ZnS shell dramatically increases the photoluminescence quantum yield. Furthermore, the formation of the ZnS shell improves the chemical stability of Cu-In-S QDs, as demonstrated by the preparation of polystyrene-QD composites and labeling of glioma cells. This work provides an effective strategy for obtaining efficient and stable fluorophores free of heavy metals.

Direct Intercellular Communications and Cancer: A Snapshot of the Biological Roles of Connexins in Prostate Cancer

Tissue homeostasis is the result of a complex intercellular network controlling the behavior of every cell for the survival of the whole organism. In mammalian tissues, cells do communicate via diverse long- and short-range communication mechanisms. While long-range communication involves hormones through blood circulation and neural transmission, short-range communication mechanisms include either paracrine diffusible factors or direct interactions (e.g., gap junctions, intercellular bridges and tunneling nanotubes) or a mixture of both (e.g., exosomes). Tumor growth represents an alteration of tissue homeostasis and could be the consequence of intercellular network disruption. In this network, direct short-range intercellular communication seems to be particularly involved. The first type of these intercellular communications thought to be involved in cancer progression were gap junctions and their protein subunits, the connexins. From these studies came the general assumption that global decreased connexin expression is correlated to tumor progression and increased cell proliferation. However, this assumption appeared more complicated by the fact that connexins may act also as pro-tumorigenic. Then, the concept that direct intercellular communication could be involved in cancer has been expanded to include new forms of intercellular communication such as tunneling nanotubes (TNTs) and exosomes. TNTs are intercellular bridges that allow free exchange of small molecules or even mitochondria depending on the presence of gap junctions. The majority of current research shows that such exchanges promote cancer progression by increasing resistance to hypoxia and chemotherapy. If exosomes are also involved in these mechanisms, more studies are needed to understand their precise role. Prostate cancer (PCa) represents a type of malignancy with one of the highest incidence rates worldwide. The precise role of these types of direct short-range intercellular communication has been considered in the progression of PCa. However, even though data are in favor of connexins playing a key role in PCa progression, a clear understanding of the role of TNTs and exosomes is needed to define their precise role in this malignancy. This review article summarizes the current view of the main mechanisms involved in short-range intercellular communication and their implications in cancer and delves into the biological, predictive and therapeutic role of connexins in PCa.

Intercellular transfer of HLA-G: its potential in cancer immunology

Intercellular protein transfer between cancer cells and immune cells is a very common phenomenon that can affect different stages of host antitumor immune responses. HLA-G, a non-classical HLA class I antigen, has been observed to be widely expressed in various malignancies, and its immune-suppressive functions have been well recognised. HLA-G expression in cancer cells can directly mediate immune tolerance by interacting with inhibitory receptors such as ILT2 and ILT4 expressed on immune cells. Moreover, a network of multiple directional intercellular transfers of HLA-G among cancer cells and immune cells through trogocytosis, exosomes and tunnelling nanotubes provides malignant cells with an alternative ploy for antigen sharing and induces more complex heterogeneity, to modulate immune responses, ultimately leading to immune evasion, therapy resistance, disease progression and poor clinical outcome. Herein, we discuss the relative aspects of the intercellular transfer of HLA-G between tumor cells and immune cells and its potential use in tumor immunology research and translational cancer therapy.

Mitophagy in Cancer: A Tale of Adaptation

：In the past years, we have learnt that tumors co-evolve with their microenvironment, and that the active interaction between cancer cells and stromal cells plays a pivotal role in cancer initiation, progression and treatment response. Among the players involved, the pathways regulating mitochondrial functions have been shown to be crucial for both cancer and stromal cells. This is perhaps not surprising, considering that mitochondria in both cancerous and non-cancerous cells are decisive for vital metabolic and bioenergetic functions and to elicit cell death. The central part played by mitochondria also implies the existence of stringent mitochondrial quality control mechanisms, where a specialized autophagy pathway (mitophagy) ensures the selective removal of damaged or dysfunctional mitochondria. Although the molecular underpinnings of mitophagy regulation in mammalian cells remain incomplete, it is becoming clear that mitophagy pathways are intricately linked to the metabolic rewiring of cancer cells to support the high bioenergetic demand of the tumor. In this review, after a brief introduction of the main mitophagy regulators operating in mammalian cells, we discuss emerging cell autonomous roles of mitochondria quality control in cancer onset and progression. We also discuss the relevance of mitophagy in the cellular crosstalk with the tumor microenvironment and in anti-cancer therapy responses.

Tunneling nanotubes, a novel mode of tumor cell-macrophage communication in tumor cell invasion

The interaction between tumor cells and macrophages is crucial in promoting tumor invasion and metastasis. In this study, we examined a novel mechanism of intercellular communication, namely membranous actin-based tunneling nanotubes (TNTs), that occurs between macrophages and tumor cells in the promotion of macrophage-dependent tumor cell invasion. The presence of heterotypic TNTs between macrophages and tumor cells induced invasive tumor cell morphology, which was dependent on EGF-EGFR signaling. Furthermore, reduction of a protein involved in TNT formation, M-Sec (TNFAIP2), in macrophages inhibited tumor cell elongation, blocked the ability of tumor cells to invade in 3D and reduced macrophage-dependent long-distance tumor cell streaming in vitro Using an in vivo zebrafish model that recreates macrophage-mediated tumor cell invasion, we observed TNT-mediated macrophage-dependent tumor cell invasion, distant metastatic foci and areas of metastatic spread. Overall, our studies support a role for TNTs as a novel means of interaction between tumor cells and macrophages that leads to tumor progression and metastasis.