PhD thesisPancreatic Ductal Adenocarcinoma (PDAC) is characterised by a dense desmoplastic reaction that is attributed to the activation of pancreatic stellate cells (PSCs) in the stroma. This alteration of the tumour microenvironment is thought to contribute to PDAC aggressiveness and resistance to therapy. Recent studies have shown that exosomes (a subgroup of secreted extracellular vesicles) secreted by cancer cells facilitate cross talk between tumour cells and the microenvironment. However, the mechanisms that lead to the secretion of these vesicles remains elusive.
Here, we report for the first time, a novel role for centrosome amplification, a common feature of human tumours, in the secretion of small extracellular vesicles (sEVs). We show that centrosome amplification significantly correlates with and is sufficient to induce the elevated secretion of sEVs in PDAC cell lines. Furthermore, we demonstrate that oxidative stress in cells with supernumerary centrosomes is the driving force behind this altered sEV secretion. An analysis of centrosome amplification-associated increases in cellular reactive oxygen species (ROS) demonstrated an impaired lysosome function and the prevention of MVB/lysosome fusion events. The results indicate that centrosome amplification induced ROS induces sEV secretion by preventing MVB degradation by the lysosome, shifting their fate to fusion with the plasma membrane and subsequent secretion of their intraluminal vesicles (ILVs) as exosomes.
To understand if exosomes secreted from cells with amplified centrosomes could impact the tumour microenvironment, we subsequently investigated the role of these sEVs on the activation of PSCs, as measured by the formation of fibres containing alpha-smooth muscle actin (α-SMA). We found that sEVs isolated from cells with supernumerary centrosomes elicit significantly stronger activation of PSCs compared to sEVs isolated from cells with a normal centrosome number, suggesting a difference in their biological cargo. SILAC based-proteomic analysis revealed the gain or loss of 6 EV protein in sEVs isolated from cells upon the induction of centrosome amplification, that may have a role in the activation of PSCs. We hypothesise, that further understanding the role of centrosome amplification in sEV-mediated PSC activation may help us to identify
innovative ways to block PSC activation and prevent the progression of PDAC, which could have major clinical implications for patients with this devastating disease
