Tunneling Nanotubes Provide a Unique Conduit for Intercellular Transfer of Cellular Contents in Human Malignant Pleural Mesothelioma

Abstract

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.

Fascin 1 is an actin filament-bundling protein that regulates ectoplasmic specialization dynamics in the rat testis

“…Fascin 1 was also found to be a component of the TNT (also known as intercellular bridge), which was colocalized with F-actin (Fig. 1D), when Sertoli cells were cultured at lower density, as shown recently in TNT in other mammalian cells (33). The specificity of the antibody used in this report (Table 1) was supported by immunoblotting using lysate of Sertoli and germ cells (Fig.…”

“…Fascin 3 is likely used in the testis for assembling F-actin-rich ultrastructures surrounding the spermatid nucleus (59) and the acrosome-acroplaxome-manchette complex (26,27) during spermiogenesis (57). A recent report also illustrates the involvement of fascin 1 in the organization of intercellular bridges [also known as tunneling nanotubes (TNT)] in epithelial cells in humans (33). Although fascin 1-deficient mice were found to be viable and fertile with no major developmental defects (70), this actin-bundling protein is important for the assembly and functioning of filopodia in mammalian cells such as fibroblasts (70).…”

Mitochondrial DNA in Tumor Initiation, Progression, and Metastasis: Role of Horizontal mtDNA Transfer

“…However, this view was challenged a decade ago when it was shown that membrane connections or cytoplasmic bridges form between cells in culture and that cellular organelles traverse these nanotube connections (1). Since then, considerable in vitro evidence has confirmed organelle transfer, including mitochondria, to and between tumor cells (2)(3)(4)(5)(6)(7)(8) as well as between nontumor cells (9)(10)(11)(12)(13)(14)(15). Additionally, recent phylogenetic evidence suggests that mtDNA can "move" between normal cells and tumor cells in canine venereal transmissible cancer (16,17), while pathophysiological models of lung injury (18,19), lung inflammation (19), and tumor formation by respiration-deficient tumor cells (19) have added weight to intercellular mitochondrial transfer being a new (patho) physiological phenomenon.…”

Histone chaperone APLF regulates induction of pluripotency in murine fibroblasts

“…The amplified Aplf cDNA was cloned into XbaI and BamHI sites in the pUltra lentiviral vector, a gift from Malcolm Moore (Dept. of Cell Biology, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, USA; Addgene; #24129; Lou et al, 2012). Lentiviral particles were generated as described above.…”