Understanding the role of extracellular vesicles in the interaction of multiple myeloma with the surrounding microenvironment: the key contribution of the Notch pathway

Introduction Multiple myeloma (MM) is an incurable cancer characterized by a strong tropism to the bone marrow (BM) and an important involvement of the Notch pathway. Recently, extracellular vesicles (EVs) have been reported as novel mediators in creating a supportive milieu for MM. Here we investigate the role of the activated Notch signaling in EVs mediated cross-talk. Materials and methods We established two MM cell lines stably retaining the doxycycline-inducible pTRIPZ vector containing anti-Jagged1 and Jagged2 shRNAs and a BM mesenchymal stromal cell (BMSC) line expressing shRNAs for Notch1 and Notch2. EVs were isolated by ultracentrifugation and used for functional assays and molecular analysis. Results We present evidences that EVs play a crucial role in the dysregulated interactions of MM cells with the BM microenvironment and that Notch regulates their release. Indeed, BMSCs knockdown for Notch1/2 results significantly reduced EVs release and their ability to induce Bortezomib resistance in MM cells and stimulate their migration. On the other side, MM-derived EVs activate Notch signaling in HS5, increasing the production of pro-tumor factors; the effect is lost when EVs are isolated from MM cells knockdown for Jagged1/2. Moreover, EVs released by co-cultures of BMSCs and MM cells silenced for Jagged1/2 display a reduced ability to increase osteoclastogenesis compared with EVs from the control culture. Discussion and Conclusions These new insights in the pathophysiology of the de-arranged BM niche represent the rationale for a therapy aiming to uncouple the crosstalk of MM with the surrounding microenvironment by inhibiting Notch signaling.