Chronic myelogenous leukaemia exosomes modulate bone marrow microenvironment through activation of epidermal growth factor receptor

Chronic myelogenous leukaemia (CML) is a clonal myeloproliferative disorder. Recent evidence indicates that altered crosstalk between CML and mesenchymal stromal cells may affect leukaemia survival; moreover, vesicles released by both tumour and non-tumour cells into the microenvironment provide a suitable niche for cancer cell growth and survival. We previously demonstrated that leukaemic and stromal cells establish an exosome-mediated bidirectional crosstalk leading to the production of IL8 in stromal cells, thus sustaining the survival of CML cells. Human cell lines used are LAMA84 (CML cells), HS5 (stromal cells) and bone marrow primary stromal cells; gene expression and protein analysis were performed by real-time PCR and Western blot. IL8 and MMP9 secretions were evaluated by ELISA. Exosomes were isolated from CML cells and blood samples of CML patients. Here, we show that LAMA84 and CML patients' exosomes contain amphiregulin (AREG), thus activating epidermal growth factor receptor (EGFR) signalling in stromal cells. EGFR signalling increases the expression of SNAIL and its targets, MMP9 and IL8. We also demonstrated that pre-treatment of HS5 with LAMA84 exosomes increases the expression of annexin A2 that promotes the adhesion of leukaemic cells to the stromal monolayer, finally supporting the growth and invasiveness of leukaemic cells. Leukaemic and stromal cells establish a bidirectional crosstalk: exosomes promote proliferation and survival of leukaemic cells, both in vitro and in vivo, by inducing IL8 secretion from stromal cells. We propose that this mechanism is activated by a ligand-receptor interaction between AREG, found in CML exosomes, and EGFR in bone marrow stromal cells.