Tumor exosomes induce tunneling nanotubes in lipid raft-enriched regions of human mesothelioma cells

Abstract

Tunneling nanotubes (TnTs) are long, non-adherent, actin-based cellular extensions that act as conduits for transport of cellular cargo between connected cells. The mechanisms of nanotube formation and the effects of the tumor microenvironment and cellular signals on TnT formation are unknown. In the present study, we explored exosomes as potential mediators of TnT formation in mesothelioma and the potential relationship of lipid rafts to TnT formation. Mesothelioma cells co-cultured with exogenous mesothelioma-derived exosomes formed more TnTs than cells cultured without exosomes within 24-48 hours; and this effect was most prominent in media conditions (low-serum, hyperglycemic medium) that support TnT formation (1.3-1.9-fold difference). Fluorescence and electron microscopy confirmed the purity of isolated exosomes and revealed that they localized predominantly at the base of and within TnTs, in addition to the extracellular environment. Time-lapse microscopic imaging demonstrated uptake of tumor exosomes by TnTs, which facilitated intercellular transfer of these exosomes between connected cells. Mesothelioma cells connected via TnTs were also significantly enriched for lipid rafts at nearly a 2-fold higher number compared with cells not connected by TnTs. Our findings provide supportive evidence of exosomes as potential chemotactic stimuli for TnT formation, and also lipid raft formation as a potential biomarker for TnT-forming cells.

Intercellular Conduits in Tumors: The New Social Network

“…This interrogation of existing datasets identified the role of connexin 43 in tumour microtube formation and activity, providing further evidence that elements of cell-cell communication are not mutually exclusive but rather quite complementary. This is in fact consistent with previous studies demonstrating synergistic effects of exosomes on tunneling nanotubes in cancer [10]. …”

“…Otherwise stated, we should no longer look to examine gap junctions alone, or exosomes, or microtubes/nanotubes, as they may all interact seamlessly to facilitate progression of tumours. This is especially likely considering gap junctions have been found to be localized at the junction of some tunneling nanotubes connecting cells [8], as well as the fact that exosomes and microvesicles can take advantage of nanotube structures as highways for intercellular transport [10]. …”

Tumor-stromal cross talk: direct cell-to-cell transfer of oncogenic microRNAs via tunneling nanotubes

“…A recent study also strongly suggested that the intercellular transfer of miRNAs via contact-dependent mechanisms (gap junction channels) from macrophages to malignant cells significantly affects posttranscriptional gene regulation and thus alters cellular proliferation[8]. We recently demonstrated that exosomes co-localized with TnTs spatially and that they stimulated an increased rate of TnT formation[9]. Our findings of intercellular transfer of miRNAs via TnTs in the current study are also consistent with a prior report in which mRNA-containing organelles were transferred between rat spermatids via what seem to be TnTs (stable cytoplasmic bridges, also called ring canals).…”

Contact-dependent transfer of TiO2nanoparticles between mammalian cells

“…This indicates that NPs for the most part are transferred in a contact-dependent mechanism (Figure 7b). Intercellular exchange of endosomal and other organelles is a constitutive phenomenon that has been demonstrated to be contact dependent in various cell lines, heterocellular cell cultures, as well as anchorage-independent spheroids and explant cultures (Bukoreshtliev et al, 2009;Gousset et al, 2009Gousset et al, , 2013Gurke et al, 2008;Pasquier et al, 2013;Rustom et al, 2004;Thayanithy et al, 2014). This physical transfer is facilitated by several mechanisms including cell-connecting membranous structures called tunnelling nanotubes (Davis & Sowinski, 2008;Rustom et al, 2004), transient local membrane exchange between neighbouring cells (Niu et al, 2009) and partial cell fusion (Driesen et al, 2005).…”