Sortilin mediates the release and transfer of exosomes in concert with two tyrosine kinase receptors

Introduction: Cancer cells can influence their cellular microenvironment through intercellular communication. Growing evidence indicates that microenvironment control is supported by the release of extracellular microvesicles, called exosomes. Exosomes have the capacity to transfer their cellular content to neighbouring cells and modify their microenvironment to promote tumour-induced immune suppression, angiogenesis, and pre-metastatic niche formation. Still, the function of proteins found in the exosomal cargo and their mechanisms in membrane transport and the signalling events is not clearly defined. The multifaceted receptor, neurotensin (NT) receptor-3, also called sortilin plays a multitude of roles in the cell as a receptor or a co-receptor, in protein transport to the plasma membrane and to lysosomes, and in the regulated secretion. Numerous studies indicate that sortilin expression is elevated in several human cancers. In this study, we examined closely the secretion mechanism utilized for the extracellular domain of sortilin from human lung cancer cells (A549) and the effect on the microenvironment. Methods: We use a number of experimental approaches in our studies including lentivirus-mediated RNAi, metabolic labelling, immunoprecipitation, immunofluorescence (indirect and confocal), Western blot, exosome purification, EM, FACs analysis, co-culture using AMNIS, microarray, invasion assays, ELISA and the chicken embryo chorioallantoic membrane (CAM) model. Results: Here, we show for the first time that sortilin uses a “canonical pathway” and can be found in exosomes. We demonstrate that sortilin is a key component of exosomes mediating communication between A549 and endothelial cells. Sortilin is already known to play a prime function in cancer cells; however we report herein that it plays new role in both assembly of a tyrosine kinase complex and its exosome release. This novel complex (TES complex) expressed by exosomes results in the linkage of 2 tyrosine kinase receptors, TrkB and EGFR with sortilin. Using in vitro and ex vivo models, we demonstrate that this complex containing sortilin exhibits a control on endothelial cells and angiogenesis activation through exosome transfer. Summary/conclusion: Taken together our data suggest a paracrine function for sortilin and its partners in exosome transfer and the control of the microenvironment. This novel complex containing sortilin could play the role of as a molecular switch in cancer progression by promoting angiogenesis.