T-Exo also induced invasion, but to a significantly lesser extent. but by activation of the p38/MAPK signaling pathway in the tumor cells. In conclusion, T-MV stimulate cancer cell invasion via a direct feedback mechanism dependent on highly glycosylated EMMPRIN. Keywords: breast cancer, microvesicles, invasion, EMMPRIN, glycosylation == Introduction == Intercellular communication is an essential aspect of malignant tumors that constitute complex tissues. It serves not only to maintain tissue homeostasis but also to mediate migration and subsequent invasion of tumor cells. While, in the past, soluble factors such as cytokines and growth factors have been considered the main mediators of these processes, the contribution of extracellular vesicles (EV) is now increasingly recognized (Thery et al., 2009; Kucharzewska and Belting, 2013). Tumor cells constitutively produce distinct populations of extracellular vesicles that can be distinguished based on their biogenesis and physical properties. Among the most studied vesicles are exosomes (Exo, diameter: 50100 nm) and microvesicles (MV, 1001000 nm). While Exo are endosomal-derived ITK Inhibitor and can be released upon fusion of multivesicular bodies (MVB) with the cell membrane, MV ITK Inhibitor are actively shed from the plasma membrane (Raposo and Stoorvogel, 2013). Both particle populations carry a plethora of bioactive molecules including lipids, proteins, as well as different types of nucleic acids. Apart from the content of the vesicles, their uptake seems to be an important prerequisite for their function. Although the mechanism of MV uptake is Rabbit polyclonal to ADAMTS8 still poorly understood, it was recently shown that low temperature as well as blocking the GTPase dynamin can reduce MV uptake and even abrogate MV function (Kawamoto et al., 2012), which points to an endocytosis-mediated process. Tumor-derived MV (T-MV) are known to enhance progression of human tumors by modulating the surrounding stroma cells including fibroblasts, endothelial cells, and immune cells (Muralidharan-Chari et al., 2010). However , little is known about the autologous ITK Inhibitor effects of T-MV on the tumor cells themselves. Some studies demonstrate that T-MV can enhance autologous tumor invasion by carrying matrix metalloproteinases (MMPs) or their regulators and thereby mediate degradation of the extracellular matrix (Muralidharan-Chari et al., 2010). The extracellular matrix metalloproteinase inducer (EMMPRIN) is known to stimulate MMP expression in tumor as well as stroma cells (Biswas et al., 1995). Overexpression of EMMPRIN has been described in many cancers and correlates with shortened survival (Nabeshima et al., 2006). EMMPRIN has three N-glycosylation sites, resulting in a highly glycosylated form (HG, 4565 kDa) and a low glycoform (LG, 32 kDa) (Tang et al., 2004a). Among four splice variants, EMMPRIN-2 is the most abundant one (Liao et al., 2011). EMMPRIN can induce its own transcription (Tang et al., 2004b) by homophilic interaction of EMMPRIN on opposing cells (Yu et al., 2008), resulting in activation of p38-/mitogen-activated protein kinase (MAPK) (Lim et al., 1998). Recently, we were able to demonstrate that T-MV induce a proinvasive phenotype in tumor-associated macrophages, which can be partly blocked by inhibition of MV uptake (Menck et al., 2013; Rietkotter et al., 2013). We thus hypothesized that T-MV not only influence the surrounding ITK Inhibitor stroma cells, but also represent an important means of communication between neighboring breast cancer cells to facilitate their spontaneous invasion. Our aim was to specify their mode of action in relation to their uptake and to identify potential MV-related markers that mediate tumor invasion. == Results == == Cancer cell-derived MV but not MV from nonmalignant cells induce invasion == EV from the breast cancer cell lines MCF-7 (T-EVM), SK-BR-3 (T-EVS), and MDA-MB231 (T-EVMDA), as well as the benign, immortalized mammary epithelial cell line hTERT-HME1 (hTERT-EV) were prepared by differential centrifugation without any previous stimulation. Upon transmission electron microscopy (TEM), the MV fraction consisted of ITK Inhibitor a heterogeneous population of membrane-enclosed vesicles with a diameter of 100 up to 1000 nm, which clearly differed from the population of smaller, typically cup-shaped Exo (Figure1A). There was no evidence of apoptotic bodies or cell debris. == Figure 1 . == T-EV induce breast cancer invasion. (A) Electron microscopy (TEM) of T-MV and T-Exo. (B) Microinvasion assay of MCF-7 breast cancer cells stimulated with T-MV, T-Exo, and MV from normal epithelial cells (hTERT-MV) (all at 1 g/ml), as well as the respective particle-free supernatants (sn) (mean SD, n= 3, *P < 0. 001). SuffixM: vesicles/supernatant from MCF-7 cells; S: SK-BR-3; MDA: MDA-MB231; hTERT: hTERT-HME1. (C) Comparative analysis of cell invasion of MCF-7 and benign hTERT-HME1 cells stimulated with MV (10 g/ml) (mean SD, n= 3, *P < 0. 001). Invasion of MCF-7 (Figure1B) as well as SK-BR-3 cells (Supplementary Figure.