Tumors are not isolated entities, but complex systemic networks involving cell-cell communication between transformed and non-transformed cells. The milieu created by tumor-associated cells may either support or halt tumor progression. In addition to cell-cell contact, cells communicate through secreted factors via a highly complex system involving characteristics such as ligand concentration, receptor expression and integration of diverse signaling pathways. Of these, extracellular vesicles, such as exosomes, are emerging as novel cell-cell communication mediators in physiological and pathological scenarios. Exosomes, membrane vesicles of endocytic origin released by all cells (both healthy and diseased), ranging in size from 30 to 150 nm, transport all the main biomolecules, including lipids, proteins, DNAs, messenger RNAs and microRNA, and perform intercellular transfer of components, locally and systemically. By acting not only in tumor cells, but also in tumor-associated cells such as fibroblasts, endothelium, leukocytes and progenitor cells, tumor- and non-tumor cells-derived exosomes have emerged as new players in tumor growth and invasion, tumor-associated angiogenesis, tissue inflammation and immunologic remodeling. In addition, due to their property of carrying molecules from their cell of origin to the peripheral circulation, exosomes have been increasingly studied as sources of tumor biomarkers in liquid biopsies. Here we review the current literature on the participation of exosomes in the communication between tumor and tumor-associated cells, highlighting the role of this process in the setup of tumor microenvironments that modulate tumor initiation and metastasis.

Translational control mediated by phosphorylation of the alpha subunit of the eukaryotic initiation factor 2 (eIF2␣) is central to stress-induced programs of gene expression. Trypanosomatids, important human pathogens, display differentiation processes elicited by contact with the distinct physiological milieu found in their insect vectors and mammalian hosts, likely representing stress situations. Trypanosoma brucei, the agent of African trypanosomiasis, encodes three potential eIF2␣ kinases (TbeIF2K1 to -K3). We show here that TbeIF2K2 is a transmembrane glycoprotein expressed both in procyclic and in bloodstream forms. The catalytic domain of TbeIF2K2 phosphorylates yeast and mammalian eIF2␣ at Ser51. It also phosphorylates the highly unusual form of eIF2␣ found in trypanosomatids specifically at residue Thr169 that corresponds to Ser51 in other eukaryotes. T. brucei eIF2␣, however, is not a substrate for GCN2 or PKR in vitro. The putative regulatory domain of TbeIF2K2 does not share any sequence similarity with known eIF2␣ kinases. In both procyclic and bloodstream forms TbeIF2K2 is mainly localized in the membrane of the flagellar pocket, an organelle that is the exclusive site of exo-and endocytosis in these parasites. It can also be detected in endocytic compartments but not in lysosomes, suggesting that it is recycled between endosomes and the flagellar pocket. TbeIF2K2 location suggests a relevance in sensing protein or nutrient transport in T. brucei, an organism that relies heavily on posttranscriptional regulatory mechanisms to control gene expression in different environmental conditions. This is the first membrane-associated eIF2␣ kinase described in unicellular eukaryotes.

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Extracellular Vesicles (EVs), membrane vesicles released by all cells, are emerging mediators of cell-cell communication. By carrying biomolecules from tissues to biofluids, EVs have attracted attention as non-invasive sources of clinical biomarkers in liquid biopsies. EVs-based liquid biopsies usually require EVs isolation before content analysis, which frequently increases sample volume requirements. We here present a Flow Cytometry (FC) strategy that does not require isolation or concentration of EVs prior to staining. By doing so, it enables population analysis of EVs in samples characterized by challenging small volumes, while reducing overall sample processing time. To illustrate its application, we performed longitudinal non-lethal population analysis of EVs in mouse plasma and in single-animal collections of murine vitreous humor. By quantifying the proportion of vesicular particles in purified and non-purified biological samples, this method also serves as a precious tool to quality control isolates of EVs purified by different protocols. Our FC strategy has an unexplored clinical potential to analyze EVs in biofluids with intrinsically limited volumes and to multiply the number of different analytes in EVs that can be studied from a single collection of biofluid.

Human cells are constantly exposed to DNA damage. Without repair, damage can result in genetic instability and eventually cancer. The strong association between the lack of DNA damage repair, mutations and cancer is dramatically demonstrated by a number of cancer-prone human syndromes, such as xeroderma pigmentosum (XP), ataxia-telangiectasia (AT) and Fanconi anemia (FA). This review focuses on the historical discoveries related with these three diseases and describes their impact on the understanding of DNA repair mechanisms and the causes of human cancer. As deficiencies in DNA repair are also often related with progeria symptoms, unrepaired damage and aging are somehow related. Several other pathologies associated with DNA repair defects, genetic instability and increased cancer risk are also discussed. In fact, studies with cells from these many syndromes have helped in understanding important levels of protection against cancer and aging, although little help has actually been conferred to the patients in terms of therapy. Finally, the recent advances in combined basic and translational research on DNA repair and chemotherapy are presented.