Extracellular vesicles as mediators of intercellular communication in human breast cancer progression
by Kerstin Menck
Date of Examination:2014-03-31
Date of issue:2014-10-17
Advisor:Prof. Dr. Claudia Binder
Referee:Prof. Dr. Claudia Binder
Referee:Prof. Dr. Uwe-Karsten Hanisch
Persistent Address:
http://dx.doi.org/10.53846/goediss-4743
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Abstract
English
The establishment of a permissive tumor microenvironment is a key step for tumor progression and metastasis formation. Tumor cells are known for their ability to create such a favorable tumor niche by influencing the surrounding benign stroma cells through the secretion of cytokines or growth factors. Recently, there is increasing evidence that also extracellular vesicles (EV) released by the tumor cells are important means of intercellular communication. Therefore, we aimed to investigate their role in tumor-tumor and tumor-stroma crosstalk in human breast cancer. Human breast cancer cells were found to release tumor microvesicles (T-MV) as well as tumor exosomes (T-Exo). Both significantly enhanced invasiveness of the tumor cells in an auto- and heterologous feedback loop, whereas benign MV or the particle-free supernatant had no such effect. In case of T-MV, their pro-invasive function was dependent on a dynamin-dependent uptake into their recipient cells. Moreover, all pro-invasive T-MV carried a highly-glycosylated isoform of the Extracellular Matrix Metalloproteinase Inducer (EMMPRIN) with N-glycosylation at N160 and N268. Anti-EMMPRIN strategies such as knockdown or deglycosylation antagonized the pro-invasive function of T-MV on tumor invasion. Interestingly, EMMPRIN-carrying T-MV increased tumor invasiveness in a matrix metalloproteinase-independent mechanism by activating p38/MAPK signaling. EMMPRIN is not only involved in MV-mediated pro-invasive tumor-tumor crosstalk in vitro, but can also be used as a novel marker to detect T-MV which are circulating at high numbers in peripheral blood of breast cancer patients in vivo. Apart from their autologous influence on tumor invasion, we identified tumor-EV (T-EV) as mediators of a reciprocal tumor-macrophage communication loop. They were able to reprogram macrophages by inducing Wnt5a expression which was not observed for benign MV. Wnt5a induction was mediated by p38/MAPK signaling which could be antagonized by the Wnt-inhibitor DKK-1. Macrophage-Wnt5a was then exported on macrophage-derived EV and transported back to the tumor cells where it increased their invasive potential. Wnt5a expression on EV was shown to depend on the seven-pass transmembrane protein Evenness interrupted (Evi) which had been demonstrated so far only for exosomes and not for non-canonical Wnt ligands like Wnt5a. In conclusion, breast cancer cells were demonstrated to release T-EV into the local environment as well as the bloodstream, where they interact with surrounding tumor as well as stroma cells and support the establishment of a favorable tumor niche.
Keywords: Extracellular vesicles; Breast cancer; Tumor invasion; EMMPRIN; Glycosylation; Tumor-associated macrophages; Wnt5a; Tumor microenvironment